dublin city council€¦ · the basement development conserves existing protected and heritage...

Dublin City Council

Basement Development

Guidance Document

Version 1.0

September 2019

DCC Basement Development Guidance Document Version 1.0

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Contents 1. Introduction .................................................................................................................................... 4

1.1 Guidance Overview ................................................................................................................. 4

1.2 Basement Policy Objectives .................................................................................................... 4

1.3 Further DCC planning policies ................................................................................................. 6

1.4 Scope of Basement Guidance ................................................................................................. 7

1.5 Planning context ..................................................................................................................... 7

1.6 Disclaimer ................................................................................................................................ 8

2. Dublin City: Desk Study ................................................................................................................... 8

2.1 General Context ...................................................................................................................... 8

2.2 Dublin City Existing Environment; ........................................................................................... 9

3.0 Potential Impacts of Constructing Basements in Dublin City ....................................................... 11

3.1 Principal concerns relating to basement construction ......................................................... 11

3.2 Groundwater flow impacts ................................................................................................... 11

3.3 Land stability & ground movement impacts ......................................................................... 13

3.4 Surface flow and flooding impacts ........................................................................................ 16

3.5 Cumulative effects of basement construction ...................................................................... 17

3.6 Basement construction related impacts ............................................................................... 17

3.7 Other Potential Factors and Impacts .................................................................................... 18

3.8 Holistic Approach Required to Potential Impacts ................................................................. 19

4.0 Basement Development Specific Considerations ......................................................................... 19

4.1. Size and Extent of Basement Development .......................................................................... 19

4.2 Flood Levels ........................................................................................................................... 21

4.3 Sustainable Urban Drainage Systems (SUDS) ....................................................................... 21

4.4 Archaeological Impact ........................................................................................................... 21

4.5 Conservation areas and listed buildings ............................................................................... 22

4.6 Trees Landscape and Biodiversity ......................................................................................... 22


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4.7 Internal Environment and Appearance of Basement ........................................................... 23

4.8 Lightwells .............................................................................................................................. 23

4.9 Railings, grilles and other lightwell treatment ...................................................................... 24

5.0 Basement Impact Assessment (BIA) Methodology ....................................................................... 24

5.1 Overview of Basement Impact Assessment (BIA Methodology ........................................... 24

5.2 Summary of tasks to be completed as part of BIA ................................................................ 25

5.3 Scoping .................................................................................................................................. 27

5.4 Continuous Site Investigation, Study and Monitoring .......................................................... 29

5.5 Impact Assessment and Mitigation Measures ...................................................................... 30

5.6 Qualifications and accreditation ........................................................................................... 36

6.0 Assessment of Basement Construction Potential Impacts ........................................................... 37

6.1 Introduction .......................................................................................................................... 37

6.2 Site investigation ................................................................................................................... 37

6.3 Extent of Basement and Site Dewatering & Recharge ......................................................... 41

6.4 Calculation Methods and Tools ............................................................................................ 41

6.5 Sources of Information ......................................................................................................... 42

6.6 Standards and Best Practice Guidance ................................................................................. 42

7.0 Planning Authority Assessment of BIA .......................................................................................... 43

7.1 Audit of information supplied ............................................................................................... 43

7.2 Basement Audit Categorisation ............................................................................................ 44

7.6 Updating the baseline ........................................................................................................... 45

7.7 Future Monitoring of Groundwater Levels to verify BIA Assumptions ................................ 45

8.0 Related DCC Corporate Policies .................................................................................................... 45

8.1 DCC Roads Requirement ....................................................................................................... 45

8.2 DCC Ground Anchor Installation Licence (GAIL) ................................................................... 45

8.3 DCC Pollution Control ........................................................................................................... 46

8.4 DCC Traffic Management ...................................................................................................... 46


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8.5 DCC Waste Management ...................................................................................................... 46

8.6 DCC Drainage Planning ......................................................................................................... 47

8.7 Noise, Air Quality and Vibration ........................................................................................... 47

9.0 Glossary of Terms .......................................................................................................................... 48

10. Glossary of Impacts ....................................................................................................................... 51

11. References .................................................................................................................................... 52

Appendix A ............................................................................................................................................ 53

– Items to be submitted and reviewed as part of a Basement Impact Assessment............................. 53

Appendix B ............................................................................................................................................ 58

– Ground Anchor Installation Licence (GAIL) Application Form ........................................................... 58

Appendix C ............................................................................................................................................ 65

– Ground Anchor Installation Licence (GAIL) Guidance Notes ............................................................. 65

Appendix D ............................................................................................................................................ 70

– Cumulative Effects of Basement Construction .................................................................................. 70

Appendix E ............................................................................................................................................ 74

– Noise and Air Quality – “Construction and Demolition Good Practice Guide” ................................. 74


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1. Introduction

1.1 Guidance Overview

1.1.1 The “Basement Development Guidance Document” is intended to complement

both the DCC (Basement Development Policy Document) and the planning

guidance offered in the current Dublin City Development Plan (2016 – 2022). Both

the policy and guidance documents should be understood in the context of all

planning matters outlined in the Development Plan and other related planning

guidance. This guidance document aims to inform both planners and developers

about the potential for a variety of impacts on the city and the environment

arising from basement developments. It also outlines some practices which can

be utilised to identify and mitigate against these impacts at an early stage in the

application and design process.

1.1.2 The Dublin City Planning Authority now requires that all planning applications

containing an underground structure shall need to complete a Basement Impact

Assessment (BIA) as part of the overall planning application. This risk based

impact assessment is to be undertaken with regard to, amongst other potential

impacts, hydrology, hydrogeology and land stability and the consequence of

changes in these areas. Details of and guidance to complete a BIA are contained

herein.

1.1.3 This “Basement Development Guidance Document”, aswell as being of benefit to

Developers, shall also be utilised by the planning authority to ensure all aspects

of a Basement Impact Assessment (BIA) have been thoroughly investigated,

researched and reported upon.

1.1.4 The purpose of the DCC Basement Policy is to identify potential impacts (short-

term and long-term) as a result of basement construction. Owners, users and

developers of lands and property are advised to take account of this Guidance

Document (with reference to the associated “Basement Development Policy

Document”) when assessing the development potential of a particular site. No

assumptions should be made with regard to the development potential, or the

feasibility of constructing a basement, until a full analysis as outlined in this

document has been undertaken and the relevant approvals granted by the

Planning Authority.

1.1.5 DCC wish to acknowledge that the basement policy and guidance, contained

herein, was developed with reference to existing policies and guidance documents

already adopted by the London Borough of Camden.

1.2 Basement Policy Objectives

As is described in the “Basement Guidance Policy Document” a basement or underground

development is considered as being; an accessible area positioned below the existing

https://www.dublincity.ie/sites/default/files/content/Planning/Documents/Basement/BasementDevelopmentPolicyDocument.pdf


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street level or ground level and would include any works that will remain permanently in

the ground, such as embedded wall construction below the base of the accessible area.

The main principles for introducing a basement development policy are summarised in

this section. Each of these requirements should be addressed within the BIA submission.

The DCC basement policy requires Developers to ensure that basement development, as

evidenced in their BIA submission;

Protects and enhances where possible the groundwater quality, quantity

and classification (groundwater environment)

Provides evidence that the construction of basements shall not place the

groundwater at undue risk

Provides evidence that the structural stability of adjoining or neighbouring

buildings are not put at risk. The Developer should also identify the risk to

land stability of the site and adjacent areas and provides appropriate

mitigation, as required.

Provides an in-depth management plan for any demolition works and for the

construction of a basement. The Developer is required to adhere to this plan

(“Construction Management Plan”) if the application is deemed successful

Is in accordance with the proper development of the area with a high quality

design

Does not cause harm or undue nuisance to neighbourhoods and adjoining

buildings where development is to occur, during and after construction.

Ensures adequate consideration is given to traffic planning during

construction and thereafter.

Does not have an adverse effect on existing patterns of surface water

drainage, including infiltration into groundwater and is consistent with DCC’s

Policy on Sustainable Urban Drainage Systems (SUDS).

Does not increase groundwater infiltration into existing sewers and drains

beyond permitted restrictions.

Shall not significantly impact on groundwater or surface water flows to the

extent that this is likely to increase the risk of flooding. This flood risk is to

be evaluated, in accordance with the OPW 2009 Guidelines, during and post

construction with appropriate mitigation provided.

Does not include basement development for residential use, below the

estimated flood levels in flood zone areas Zone A or Zone B (see DCC

Development Plan for Zone locations).

Accounts for the impact of the future planting and mature development of

trees on site. A thickness of at least 1m of soil on the “roof” of a basement

is required to mitigate against and minimise surface water runoff, with

various SUDS measures incorporated.

Ensures that, all basement developments shall account for and

accommodate the existing groundwater contained within and flowing

through their site. As a minimum standard there is to be at least 0.5m wide

of clear space provided between the site/property boundary and the outer


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extent of a basement. This 0.5m wide space and shall extend over the full

height and around the perimeter of the basement and shall be filled with

suitable, highly permeable material (with appropriate wrapping).

Accounts for the characteristic of the site. In the case of a domestic

basement development to the rear of a property (garden) generally should

not exceed the footprint of the original building and be no deeper than one

full storey below ground level. Domestic basement development should

generally not extend to more than 50% of the amenity/garden space.

Provide appropriate evidence for larger schemes, including those consisting

of more than one storey in depth or extending beyond the footprint of the

above ground building, to demonstrate to the Planning Authority`s

satisfaction that the development does not harm the built and natural

environment or local amenity.

Takes account of the content of the “Dublin City Development Plan 2016 –

2022” for construction and development related matters. This policy is to be

read in conjunction with this document and all other current DCC policies.

Conserves and where possible enhances the biodiversity value of the site

Ensures appropriate handling and dealing with waste removal, including

contaminated/hazardous ground arising during construction – details to be

included in the “Construction Management Plan”.

Ensures that the impact of the proposed construction methodologies and

temporary works and ground anchors are fully assessed and any necessary

mitigation measures put in place.

Does not impact negatively on the surrounding areas, both private and

public.

All requirements, as accounted for in this policy document are to be evidenced in detail

within a BIA which is to be submitted as part of the planning application submission for

that particular development.

1.3 Further DCC planning policies

Whilst adhering to the policy requirements as outlined in Section 3.1, each of which are

to be addressed in the BIA submission, it does not preclude the applicant from meeting

other important and relevant DCC policy requirements, many of which are included in

the current “Dublin City Development Plan”. For example, when a basement

development is proposed, the Planning Authority shall also require as a minimum the

following items to be evidenced as part of the overall planning application submission;

The basement development conserves existing protected and heritage

buildings/sites, conservation areas, sites of archaeological interest etc.

The basement development provides an extensive structural stability and

conservation report in the case of listed buildings, or properties adjoining or

adjacent to listed buildings.


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The basement development provides a management plan for demolition

and/or construction where basement works are proposed in conservation

areas or adjacent to a listed building

The basement development does not harm the architectural character of

buildings and surrounding areas e.g. trees and gardens and character in such

areas are not to be harmed.

Ensures that adequate sunlight/daylight penetration is provided

Ensures that adequate ventilation is provided

Ensure that basements are provided with a means of escape allowing access

to a place of safety that provides access to the external ground level

These requirements are to be included within the Planning Application and their

examination is to be referenced accordingly within the BIA submission.

1.4 Scope of Basement Guidance

The scope of this document is to provide guidance on how to comply with the DCC

“Basement Development Policy Document”. In summary this guidance document is

intended to;

present guidance to assist Developers to identify potential impacts of

basement/subterranean infrastructure and other development

assist with the identification of hydrological, hydrogeological and other

geotechnical information that Developers are required to submit as part of

their planning application (and BIA), including a methodology which

Developers should follow to assess the impact of their development

Provide Guidance to Developers in relation to the BIA process.

1.5 Planning context

1.5.1 Principal Issues Concerning the Planning Authority

Specifically relating to basement construction the principal issues which concern

the Planning Authority are summarised in Section 1.2. These potential impacts as

a result of basement construction are described further in Section 3 of this

document.

1.5.2 Temporary Works

1.5.2.1 If temporary works are required to facilitate the construction of the

proposed basement the positioning of such temporary works is not

permitted within public lands/space without a Ground Anchor

Installation Licence (GAIL). The application (Appendix B), if required,

should form part of the development BIA submission and should be

completed in conjunction with the “Ground Anchor Installation (GAIL)

Guidance document” (Appendix C). Under no circumstances are the

temporary installations located within public lands to form part of the

permanent (long-term) structural stability of the development. All

ground anchors shall be temporary and shall not inhibit future


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infrastructure schemes. They shall be of a type which shall permit

effortless excavation, tunnelling etc. through the anchors. The relevant

details are contained in the “Ground Anchor Installation (GAIL) Guidance

document” (Appendix C).

1.5.2.2 Similarly the Developer is required to show that they have the necessary

permissions from the relevant land owner and/or authority for any

temporary works external to the applicant’s site required to assess

existing groundwater conditions or monitor the impact of dewatering

during basement construction.

1.6 Disclaimer

As stated in the DCC “Basement Development Policy Document” it is important to note

that, although prepared in consultation with industry experts this is a work in progress

document and it is based on best available data and guidance at the time of preparation.

Accordingly, all information in relation to basement development and construction is

provided for general policy and guidance only, and may be substantially altered in light

of future data and analysis, or future events etc. As a result, all landowners and

developers are advised that Dublin City Council and their agents can accept no

responsibility for losses or damages arising due to assessments indicating the suitability

of a site for basement construction e.g. vulnerability of their lands to flooding, the impact

of their proposed development on adjoining properties or amenities, cumulative effects

of basement construction, or the design and use of their proposed development.

Owners, users and developers are advised to take all reasonable measures to assess

potential issues (as outlined in this guidance document with reference also to the related

policy document) which may impact upon lands and buildings (including basements) in

which they have an interest, prior to making planning or development assumptions and

decisions.

The BIA Guidance and associated policy will be reviewed on an ongoing basis as is

required.

2. Dublin City: Desk Study

2.1 General Context

Dublin City in its entirety lies within the metropolitan area and the Regional Planning

Guidelines (RPG) give direction to Dublin City as the ‘gateway core’ for high-intensity

clusters, brownfield development, urban renewal and regeneration. The RPG settlement

strategy for the metropolitan area includes a strong policy emphasis on the need to gain

maximum benefit from existing assets, such as public transport and social infrastructure,

through the continuation of consolidation and increasing densities within the existing

built footprint of the city. A further key aspect is that future expansion, whether housing

or mixed uses, occur in tandem with high-quality rail-based public transport and on a

phased basis. The current DCC Development Plan incorporates these principles in a

settlement hierarchy which prioritises the inner city, Key District Centres (KDCs) and


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Strategic Development & Regeneration Areas (SDRA’s). The majority of SDRA’s relate to

a zoning objective which seeks the social, economic physical development or

rejuvenation of

Taking account of the development framework set out in higher level regional and

national plans, the proposed strategy for Dublin promotes the consolidation of the city,

maximising efficient use of land and integrating land use and transport, within the

context of an over-arching philosophy of sustainability and quality of life factors.

Dublin City Developers therefore are now looking to maximise the floor area for each new

development site. With the progress of building technology and available opportunities

the prospect of including a basement is becoming more attractive. This guidance

document aims to compliment the “Basement Development Policy Document” in the

assessment of such proposals on a case-by-case basis. Developers are advised to consult

this document and the DCC basement policy prior to making any development

assumptions or submitting an application for planning.

2.2 Dublin City Existing Environment;

2.2.1 Conservation Culture and Heritage;

As described in the “Dublin City Development Plan 2016-2021” Dublin City`s built

and natural heritage plays a pivotal role in the city`s character. It is a key objective

of the core strategy of Dublin City Council to protect and enhance the special

characteristics of the city`s built and natural heritage. The principle measures

enabling Dublin City Council to do this are the Record of Protected Structures and

the designation of Architectural Conservation Areas. The City Council has

identified priority areas of special historic and architectural interest and within

these areas will review the Record of Protected Structures, consider the

recommendations of the National Inventory of Architectural Heritage and, where

required, designate Architectural Conservation Areas.

In order to work towards such a plan Dublin City Council intends to increase the

sustainability of urban planning, new investment, infrastructure improvement

and regeneration by especially taking into account the existing built environment,

heritage, cultural diversity, socioeconomic and environmental values along with

community values.

Ensuring that new investment, regeneration and intervention acknowledges and

respects the significant archaeological and architectural heritage of the city is an

important issue for DCC. It is best achieved through appropriate objectives for

the protection, enhancement and management of the built heritage, while

encouraging regeneration and change.

2.2.2 Protected Structures;

The Record of Protected Structures presently comprises in excess of 8,500

structures. In respect of the process of managing the Record of Protected


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Structures, during the period from 2011– 2016, there were 51 structures added

and 242 structures deleted and on the basis of ongoing survey and monitoring,

the Record was clarified on a number of occasions.

Dublin City Council endeavours to protect the structures of special interest which

are included on the Record of Protected Structures and continues to review the

Record of Protected Structures within the context of future Architectural

Conservation Area designations and having regard to the recommendations of

the National Inventory of Architectural Heritage. The presence of such structures

shall need to be addressed in the BIA submission for any application in their

vicinity.

2.2.3 Architectural Conservation Areas;

There are presently 21 Architectural Conservation Areas in the city. In the period

2012–2015, Dublin City Council designated 9 Architectural Conservation Areas:

Mountjoy Square, Westmoreland Park, Sandymount, Temple Place, Colliers

Avenue, Elmpark Avenue and Elmwood Avenue, Ranelagh Avenue, Crumlin,

Belmont Avenue/Mount Eden Road, Phibsborough and Great Western Square.

Dublin City Council endeavours to protect the special character of the existing

designated Architectural Conservation Areas and Conservation Areas of Dublin

city and shall continue to identify other areas of special historic and architectural

interest and to designate these areas as Architectural Conservation Areas. If a

development is proposed for or close to one of these areas it shall need to be

addressed as part of the development BIA submission.

2.2.4 Importance of Green Infrastructure;

Dublin City Council has traditionally encouraged the utilisation of green

infrastructure systems in all new developments. This policy intends to

complement the existing green spaces of the city squares, historic gardens and

the canals and waterfront promenades. Green infrastructure in cities delivers

health-related benefits such as clean air and better water quality. The utilisation

of green infrastructure and Sustainable Urban Drainage Systems (SUDS) is also an

extremely effective method of managing surface water and provides a “total”

solution to rainwater management while traditional drainage can be considered

as only providing a “collection and disposal” approach. A site wholly covered by

hard impermeable surfaces intercepts all groundwater recharge resulting in

rainwater running off the site and into the surface drainage system.

2.2.5 Flood Risk in Dublin City;

Various projects have been completed in recent years to protect areas known to

be vulnerable to coastal flooding during extreme events. It is a requirement of all

planning applicants to complete a flood risk assessment to assess all forms of

potential flooding, in accordance with statutory flood risk management

guidelines. Such a flood risk assessment shall be referenced in a BIA.


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2.2.6 Construction Stage

Dublin is a vibrant city with considerable areas of mixed land use such as

residential, commercial and office spaces. Whilst the building and upgrade of

structures can be beneficial to a neighbourhood one must be conscious of the

impacts that construction works may have on a community and existing

buildings. The use of piling, deep excavations, change in groundwater levels etc.

and the impact of these on adjacent properties, assets and inhabitants need to

be accounted for. The need for pre and post construction surveys of surrounding

buildings should be considered.

Adequate control of noise, dust, traffic / truck movements, discharge of

groundwater into sewers or watercourses or through ground re-charge are all

elements of a BIA. The design of temporary works needs to be detailed and

investigated such that installation of future infrastructure to an area will be

possible in the future.

3.0 Potential Impacts of Constructing Basements in Dublin City

3.1 Principal concerns relating to basement construction

Some of the principal concerns relating to the excavation of new basements are

presented in this section after being summarised in Section 1.2. The range and variety of

the items illustrate the diverse but interconnected nature of the factors associated with

assessing proposals for basement/subterranean development within Dublin City.

There is a potential for impacts during both the construction phase and the long-

term/steady state phase of the project. Installation of temporary works may also result

in temporary impacts. Each of these impacts should be accounted for in the BIA

submission. Basement constructions impacts can be summarised under the flowing

headings;

Groundwater flow

Land stability and ground movement

Surface water flow and flooding

Cumulative effects

Construction stage impacts (incl. temporary works)

3.2 Groundwater flow impacts

3.2.1 As is referenced in Section 3.1 of the “Basement Development Policy Document”,

the Planning Authority will expect all basement development applications to

provide evidence that the construction of basements shall not place the

groundwater and surrounding environment at undue risk. Potential issues should

be investigated and highlighted in the scoping stage of the Basement Impact

Assessment (see Section 5). All groundwater investigations, assessments and

reports must be carried out by suitably qualified and experienced personnel.

3.2.2 If groundwater was forced to find an alternative flow route past an underground

obstruction such as a basement, it could cause the groundwater level to rise


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locally up gradient or adjacent to the new basement. If there is an existing cellar

that had not been suitably protected (“tanked”) against rising groundwater levels

or ingress, then dampness and/or seepage would likely have a significant impact.

3.2.3 Immediately upstream (up groundwater gradient) of the development the

groundwater level may rise, whilst immediately downstream the groundwater

level may fall. The magnitude of the change in water level will be dependent on

the nature of the natural groundwater flow system and the size and orientation

of the development. A narrow basement parallel to the direction of groundwater

flow will have less of an impact than a wider basement perpendicular to the

direction of flow since there is less blocking or deflection of the groundwater

from its original path. Structures which involve “corralling” shapes, such as an “L”

shaped structure with the convex corner in the line of groundwater flow, may

result in more pronounced effects.

3.2.4 For natural springs (or emergences of groundwater at the surface), the rate of

water flow from the spring might increase or decrease, depending on whether

the alternative route is diverting or increasing the flow to the point of the spring

source. If the flow is diverted from one spring, it may result in the groundwater

flow finding another location to issue from with new springs forming or old

springs being reactivated.

3.2.5 The level of the groundwater in the rock or overburden is commonly called the

“water table”. This level is the level below which all interconnected pores or

spaces in the subsurface are saturated at the particular time that the

measurement was made. The water table varies continuously and is not naturally

static. The level of the ‘water table at any moment in time represents the balance

between the inflows and outflows from the groundwater system. Groundwater

is continually draining under gravity out from the rock and the overburden.

Groundwater levels rise when the input of rainfall recharge exceeds the speed of

drainage from the system. Therefore, in the rise and fall of the water table is

dictated by seasonal changes in rainfall with spikes caused by extreme weather

events.

The level of groundwater and its natural fluctuations can have a significant impact

on the vitality of plants and trees on adjacent land or gardens. A significant and

rapid change in the previous fluctuation in groundwater levels can lead either to

water-logging and asphyxiation of deep plant roots or if the water level falls the

desiccation of shallow plant roots.

The groundwater level is also influenced by man-made drainage or groundwater

pumping and other factors such as pipe bursts and sewer leakage. Any

assessment of changes in ground water level that may be associated with a

specific subterranean development should therefore be viewed in the context of

site specific conditions and conditions under the area around the proposed

development.

3.2.6 Basement development may affect groundwater flows, even if the displaced

water can easily find a new course around the basement obstruction. This may

have other consequences for nearby properties, trees, etc. Given the nature of


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the geology in certain parts of Dublin City, or in locations where streams once

flowed, basement development may have the potential to divert or displace

groundwater which can cause a rise in groundwater and cause flooding of existing

basements or cellars, increased infiltration into sewers or increased pore water

pressure (heave), upstream of the development. Immediately downstream of the

obstructing basement the groundwater level may decline, which in extreme

circumstances, may affect wells, springs and ponds. It is possible that ground

subsidence downstream of the new development could also occur due to a

change in the groundwater levels, drop in pore water pressures (subsidence) and

flow patterns.

3.2.7 A larger basement (or a series of adjacent, contiguous basements) would have a

greater impact (cumulative effect) on the groundwater flow system (discussed in

Section 3.5). The shape of the resulting compound structure in relation to the

groundwater flow direction and soil strata should be considered to assess

whether any damming effect could arise.

3.2.8 The impact of a new basement should not be just assessed in the context of the

completed structure. Groundwater outside the boundary of the site is almost

always affected by dewatering in the site during construction. If there is

continuous dewatering of the excavation then it means that water is coming into

the excavation from below and outside the site. Therefore, the dewatering works

are either draining water underneath any cut off wall from adjacent sediments

outside the cut off wall, or water is flowing up through the floor of the excavation

from sediments or rock below the excavation. Dewatering, in effect, can transmit

an impact outside the boundary of the site. Dewatering could affect the yield and

drawdown in adjacent water supply pumping boreholes. It could lower the level

in ponds or wetlands down gradient of the site. It could draw in water from

adjacent streams. It could also draw in polluted or saline water from under

adjacent sites. Finally it could lower the pore water pressure in compressible

sediments (such as silts and clays) below the foundations of nearby historic

buildings, or below railway lines, canals, roads and sewers.

3.2.9 A simple example of groundwater flow and the relationship with one and more

basements can be seen in Appendix D. It should be noted that Appendix D is a

schematic that assumes a homogeneous aquifer with isotropic hydrogeological

properties. In most real-life scenarios Dublin City such simplified conditions shall

not be present.

3.3 Land stability & ground movement impacts

3.3.1 General

Whatever the ultimate cause of slope instability, one of the triggering factors

which can initiate ground movement is human activity. The act of constructing a

basement may result in instability affecting both that development and the land

surrounding it (Section 3.1 of the “Basement Development Policy Document”), for

example:


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Increases in water content due to alteration of drainage may

increase pore water pressures and decrease the strength of the soil

material.

Dewatering for basement construction may cause settlement.

Removal of vegetation (including tree felling) results in less water

extracted from a slope by plants and more water arriving on the

slope because of reduced interception of rainfall, which may initiate

ground movement through adverse changes in the pressure of water

within the soil pores.

Previous development, including landscaping works, may have also

increased the predisposition to land instability in the area, since the

soil and the surface topography are no longer in their natural state.

For example the presence on maps of areas marked as “worked

ground”, “old pits”, tanneries, “formerly dug”, “brickyard” should be

treated as triggers for further investigation. So too should a site

located near to a railway cutting or close to a cut-and-cover tunnel.

The preferential pathways to groundwater flow are mainly along the

interfaces or boundaries between different soil strata. It should be

noted that these boundaries are not clearly defined, and in an old

urban environment may be greatly influenced by historic building

and drainage works.

Any other local knowledge/guidance offered for slope stability

should be sought at design stage.

3.3.2 Structural damage beyond the site boundary

This section considers the potential effects of subterranean developments on

nearby structures and infrastructure. In the extreme case, an adjacent property

may directly adjoin another and the two buildings may share a common party

wall. In other situations, neighbouring buildings may not share a party wall, but

may still lie within the potential zone of influence of subterranean development

works at that building. Structural damage resulting from activities on a

neighbouring site may be due to changes caused to the geotechnical condition of

the ground but the actual nature and extent of the damage will be specific to the

affected structure.

Basements close to the public road affect both buried services/utilities and the

road/footway foundation and surface. The implications of damage induced by

ground movements, including the potential for legal proceedings arising from

damage to third-party property and structures can be significant.

The Planning Authority will expect all basement development applications to

provide evidence that the structural stability of adjoining or neighbouring

buildings is not put at risk (Section 3.1 of the “Basement Development Policy

Document” and Chapter 11 of “Dublin City Development Plan 2016 – 2022”).

Potential issues should be investigated and highlighted in the scoping stage of the

Basement Impact Assessment (see Section 5). An extensive analysis should occur


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in the case of listed buildings, or properties adjoining or adjacent to listed

buildings for which the Planning Authority shall require a structural stability

report as part of the BIA submission (Section 3.1 of the “Basement Development

Policy Document”). It is the developer’s responsibility to ensure adverse ground

movements and/or instability is guarded against through proper investigation

and design of mitigation measures at planning stage. The developer must then

satisfy the local authority that stability issues have been fully addressed. A pre-

condition survey (undertaken as part of the BIA) of all adjacent properties may

be sought by the Planning Authority. Therefore, DCC are likely to request that for

structures which are likely to be impacted by the proposed works a structural

survey is undertaken by a suitable professional and submitted as part of the BIA.

Issues identified by the survey can then be accounted for as part of the

Development design, temporary works etc. etc. The survey should also identify

whether the relevant buildings are “Protected” as per the current “Dublin City

Development Plan”.

3.3.3 Dewatering and Land Stability;

Where abstraction (dewatering) from an aquifer, as part of the temporary or

permanent works, is necessary to maintain dryness in the basement excavation, there

is the potential for subsidence. Dewatering lowers the groundwater table, reducing

pore water pressures, hence increasing effective stress. This causes the soil layer to

compress, leading to ground settlement. Dewatering can also induce settlement due

to loss of fines, if the groundwater lowering system continually pumps silt and sand

sized particles in the discharge water.

3.3.4 Land Stability key Issues to be assessed;

Instability brought about by basement construction should be guarded against by

ensuring proper investigation and design of mitigation measures is undertaken at

planning stage by the developer. This information should then be conveyed to the

local authority during the planning process to enable the local authority to be satisfied

that any instability has been taken into account.

Typically, through appropriate site investigations and geotechnical appraisal the key

issues for a developer are to determine whether;

the land is capable of supporting the loads to be imposed;

the development will be threatened by unstable slopes on or

adjacent to the site;

the development will initiate slope instability which may threaten

neighbouring structures and adjacent utilities;

the site could be affected by ground movements due to natural

cavities, underground streams/rivers

the site and adjoining structures could be affected by dewatering

processes or a change in groundwater levels over the

short/construction and longer term


16

the site could be affected by ground movements due to past,

present or foreseeable future tunnelling or mining activities

3.4 Surface flow and flooding impacts

3.4.1 As per Section 3.1 of the “Basement Development Policy Document” basement

development shall not significantly impact on groundwater or surface water

flows to the extent that this is likely to increase the risk of flooding.

3.4.2 As with all proposed new development in Dublin City an SFRA (SFRA Dublin City

Development Plan 2016 -2022, Appendix 7) is to be undertaken and prepared in

accordance with The Planning System and Flood Risk Management - Guidelines

for Planning Authorities (Department of the Environment, Heritage and Local

Government and Office of Public Works, 2009) and Department of the

Environment, Community and Local Government Circular PL 2/2014. Flooding

from all sources should be considered (Section 3.1 of the “Basement

Development Policy Document”). In Dublin City some areas are known to be

susceptible to flooding. The guidance seeks to reduce the risk to the development

from flooding, as well as reducing current flood risk in the local area. Where

basement construction is proposed an SFRA is required to be undertaken. This

SFRA should account for the basement and included in the application

submission. The SFRA should be referenced accordingly within the BIA document.

3.4.3 The surface water and flooding elements of the Basement Impact Assessment

should be undertaken by a competent professional specialising in flood risk

management and surface water drainage.

3.4.5 In line with Section 16.10.15 of the Dublin City Development Plan, the Planning

Authority shall not permit “Development of all basements……. or any above

ground buildings for residential use below the estimated flood levels for flood

zone areas Zone A or Zone B…..”. The presence of a basement can provide a route

for flow from inundated sewers and drainage systems to enter into a building,

e.g. through the basement sanitary system. This type of flooding could be

guarded against through the use of non-return valves and anti-flooding devices.

Basements may also be at risk of flooding due to overland flow either from a

surface water course or a roadway and underlying surcharging sewers or from

intense roof run-off on site that exceeds the capacity of an on-site SUDs

infiltration system.

3.4.6 Alterations to the surface water regime are more likely when a basement extends

into areas of a plot which were previously vegetated (e.g. garden areas,

brownfield sites) or to the limits of the plot thus leaving insufficient corridors in

which to manage surface water e.g. constructing a basement under a garden will

reduce the infiltration capacity of the ground surface. As described in Section 3.1

of the “Basement Development Policy Document”, typically a thickness of at least

1m of soil must be placed on the “roof” of a basement to mitigate this. In the case

of a basement built under an existing structure, this situation does not arise, as

the existing building would already preclude rainwater infiltration into the

shallow soil strata.


17

3.4.7 Constructing a basement, either beneath or adjacent to an existing building will

typically remove the permeable shallow ground that previously occupied the site

footprint. This reduces the capacity of the ground to allow rainfall to be stored in

the ground (in essence as a natural SUDS, or sustainable urban drainage system),

potentially leading to greater surface water run-off and greater risk of flooding.

The surface water runoff will flow down-gradient away from the developed

property if measures to manage the runoff have not been taken. Where adjoining

land or properties are at a lower elevation, there is the increased risk of surface

water flooding to that land or property. The reduction in rainfall absorption by

the ground will also reduce recharge to the underlying groundwater system.

3.4.8 If development were to result in an increase in surface runoff (or groundwater

discharge into the river systems) this could lead to an increased frequency of

flooding. The river system has a certain capacity to transport runoff. To assist

overflow areas can provide storage which in extreme rainfall events, when the

capacity of the channel would otherwise be exceeded, can retain a proportion of

the flow, to be released when the peak of the storm has passed i.e. the utilisation

of SUDS to reduce the potential for surface water run-off is an important aspect

to be considered as part of the BIA.

3.5 Cumulative effects of basement construction

A description of the potential for cumulative effects to occur as a result of basement

construction is described in Appendix D.

3.6 Basement construction related impacts

In addition to each of the potential impacts as a result of the basement design and

permanent presence a Developer shall need to be aware of and account for the potential

shorter term impacts as a of the basement construction. The construction of basements

has the potential to cause considerable nuisance to persons living and working close to a

development site.

The likely impacts at Construction Stage impacts include but are not limited to;

Temporary works and use of piling

Impact of deep excavations and piling on adjacent structures and assets and

utilities

Need for a pre and post construction survey

Noise, air quality (including dust) and vibration

o Site working hours

Traffic and heavy vehicular movements

Dewatering and impact on groundwater and adjacent structures

Discharge of groundwater into sewers or watercourses or through groundwater

recharge

Potential for hazardous/contaminated ground

The BIA needs to include an assessment of these impacts together with appropriate

mitigation measures.


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3.6.1 Temporary Works;

If a development requires temporary works e.g. ground anchors, to be installed

to support the basement excavation it should be noted that a Ground Anchor

Installation Licence (GAIL) is required to be completed and submitted as part of

the BIA. A GAIL is required when anchors (or similar) are proposed to be installed

external to the site. These anchors are required to be temporary in nature and

are to be cuttable in design to allow for the installation of future infrastructure.

A detailed survey of existing utilities and infrastructure is required to establish

locations and depths as part of the GAIL. Further details and the necessary

requirements are contained in the GAIL Guidance Document (Appendix C).

Note: Under no circumstances are ground anchors (or similar), installed beneath

public lands, permitted to form part of the proposed permanent structure.

3.7 Other Potential Factors and Impacts

3.7.1 Quality of design and workmanship:

Extending downwards beneath an existing building, especially old, masonry-built

properties that were not designed to contemporary engineering standards and

modern Building Regulations, is a challenging and potentially hazardous

undertaking. The work involved in forming a basement under an existing

structure is not trivial and it merits input from experienced professional

engineers and contractors, including underpinning specialists. A check as to

whether buildings under review are “Protected Structures” should be undertaken

– refer to the current “Dublin City Development Plan” and Section 4.5 of this

document.

3.7.2 Archaeology:

Most basement schemes involve removal of the shallow strata, (e.g. “made

ground”) which, in general, have the highest archaeological potential. Many

archaeological discoveries in Dublin City have been as a result of construction

works: subterranean developments therefore represent a means of increasing

knowledge and understanding of the archaeology in the city. The Developer

should consider this in their application – (Chapter 11 of “Dublin City

Development Plan 2016 - 2022”). A review of Section 16.10.20 of the “Dublin City

Development Plan” is recommended……“New basement development at

medieval sites shall be omitted where it is deemed that undue damage to

archaeology deposits shall occur”.

3.7.3 Uses of created subterranean space:

The principal potential uses of new underground spaces beneath private

residences typically include car parking, leisure (swimming pools and gyms) and

increasing the habitable space of the house, although not usually through

provision of bedrooms or garden flats. New underground spaces could therefore

potentially increase parking facilities within Dublin City, but may also increase car

usage and water consumption, both of which would have adverse effects on


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sustainability and environmental footprint. Depending on the location of the

proposed basement various restrictions may be placed on the basement end use.

3.7.4 Environment – waste to landfill and carbon emissions:

The process of extending a property by digging downwards to form a basement

will produce a considerably greater volume of spoil and require a greater volume

of construction materials (notably concrete, which has a relatively high carbon

dioxide emission rating) than would be typical in an above ground extension to a

residential property, such as a loft conversion or conservatory. The excavated

material taken from the basement space could be “made ground” rather than

natural soil, and it would have to be removed from the site (by lorry) and disposed

of at a suitable landfill site as, typically, non-inert waste. As a rough estimate, a

basement of 150m3 (for example 10m length by 5m width by 3m depth) would

generate in the order of twenty lorry loads, assuming a lorry is carrying one 8

cubic metre per load. The environmental “footprint” of a basement project is

therefore not trivial, and should be viewed with Dublin City Council`s

environmental and sustainability policies in mind. A brief description of DCC

Waste Management Department requirements is outlined in Section 8.5.

3.8 Holistic Approach Required to Potential Impacts

It can be observed in Section 3.3, 3.4 and 3.5 that groundwater, surface water, soil

stability, drainage and SUDs must be assessed by an experienced team. These issues

along with many other potential factors must be analysed and reviewed in an integrated

and holistic manner i.e. each of these potential impacts and factors should not be

assessed in isolation.

4.0 Basement Development Specific Considerations

When considering applications for basement developments, the Planning Authority shall have

regard to the following;

4.1. Size and Extent of Basement Development

4.1.1 Larger basement developments, such as those of more than one storey in depth

or which extend outside of the footprint of the above ground building, are likely

to have a greater impact than smaller schemes. Larger basement developments

require more extensive excavation resulting in longer construction periods, and

greater numbers of vehicle movements to remove the spoil. These extended

construction impacts can have a significant impact on adjoining neighbours

through disturbance through noise, vibration, dust, and traffic and parking issues.

Larger basements also can have a greater impact on the water environment by

reducing the area for water to runoff or soak away and impacting on

groundwater. Basement development that extends below garden space can also

reduce the ability of that garden to support trees and other vegetation leading

to poorer quality gardens and a loss in amenity and the character of the area.


20

4.1.2 The Planning Authority recognises that in the case of larger buildings in Dublin

and on large comprehensively planned sites (for example on large sites that

occupy an urban block) the impacts of basements will differ to basement

schemes in primarily residential neighbourhoods and in such circumstances

larger basements are likely to be more appropriate.

4.1.3 In areas of existing large scale commercial/office development, in certain

instances and if ground conditions allow, a basement may be permitted to cover

a considerable proportion of the site. The feasibility of such proposals shall need

to be validated and highlighted in the submitted BIA with respect to all potential

impact as outlined in this document.

As described in Section 3.1 of the “Basement Development Policy Document” all

basement developments shall account for and accommodate the existing

groundwater contained within and flowing through their site. As a minimum

standard there is to be at least 0.5m wide of clear space provided between the

site/property boundary and the outer extent of a basement. This 0.5m wide

space and shall extend over the full height and around the perimeter of the

basement and shall be filled with suitable, highly permeable material (with

appropriate wrapping).

4.1.4 As per Section 16.10.15 of the “Dublin City Development Plan” and Section 3.1 of

the “Basement Development Policy Document” the permissible size of a

basement development to the rear of a domestic property will be guided by the

characteristic of the site. In the case of large sites a basement development to

the rear of a property generally should not exceed the footprint of the original

building and be no deeper than one full storey below ground level. Domestic

basement development should generally not extend to more than 50% of the

amenity/garden space.

4.1.5 The extent and design of a proposed basement should take account of the

requirements outlined in this document to undertake adequate site investigation

and continuous monitoring (boreholes etc.) before, during and after the

construction phase. Provision for de-watering of the excavation during the

construction phase needs to be accounted for and as such a location for recharge

of groundwater needs to be incorporated within the site boundary. The

location(s) of a groundwater recharge point(s) should be accounted for at the

basement design stage and the location should be included as part of the

construction methodology section of the BIA submission, taking into account and

with reference to the local site geology, hydrogeology, ground conditions etc.

Calculations should be provided as part of the BIA demonstrating the expected

level of groundwater discharge and expected recharge capacity back to the

groundwater (within the site boundary). Where recharge is not possible,

calculations and an analysis of groundwater discharge to sewer should be

included in the BIA for review by the Planning Authority and DCC Pollution

Control department.

4.1.6 The internal environment of the development should be fit for the intended

purpose, and there should be no impact on any trees on or adjoining the site, or


21

to the water environment or land stability (as outlined elsewhere in this

document). As per Section 3.1 of the “Basement Development Policy Document”,

larger schemes, including those consisting of more than one storey in depth or

extending beyond the footprint of the above ground building, will be expected to

provide appropriate evidence within the BIA to demonstrate to the Planning

Authority`s satisfaction that the development does not harm the built and

natural environment or local amenity.

4.1.7 Often with basement development, the only visual features are lightwells and

skylights, with the bulk of the development concealed wholly underground, away

from public view. However, just as overly large extensions above the ground level

can dominate a building, contributing to the over-development of a site, an

extension below ground can be of an inappropriate scale. There may be more

flexibility with the scale of a development when it is proposed underground, but

there are a number of factors that would mean basement development could

result in overdevelopment.

4.2 Flood Levels

As per Appendix 7 of “Dublin City Development Plan 2016 -2022” a Strategic Flood Risk

Assessment (SFRA) will provide an area-wide assessment of all types of significant flood

risk to inform strategic land use planning decisions. A site specific is to be undertaken and

prepared in accordance with The Planning System and Flood Risk Management -

Guidelines for Planning Authorities (Department of the Environment, Heritage and Local

Government and Office of Public Works, 2009) and Department of the Environment,

Community and Local Government Circular PL 2/2014 and is to be referenced within the

BIA submission.

4.3 Sustainable Urban Drainage Systems (SUDS)

The use of SUDS as a requirement for new development has been a feature of DCC

Planning requirements for many years. Taking account of this policy a basement

development should provide an appropriate proportion of soft landscaping and planted

material to compensate for any reduction in the natural storm water infiltration capacity

of the site, in accordance with DCC’s preferences on Sustainable Urban Drainage (refer

to DCC Development Plan for further detail). As detailed in Section 3.4.6 the basement

“roof” should be covered with an adequate depth of soil (not less than 1m) and an

associated drainage membrane to allow the soft landscaping extend over the basement

area. The impact of SUDs proposal should be assessed in the context of groundwater flow

and levels and consequential impacts (see section 3.4.8).

When designing SUDS systems account should also be taken of Section 3.4 (Surface flow

and flooding) and Section 4.1.3 and 4.1.4.

4.4 Archaeological Impact

As described in Section 3.7.2 Archaeology discoveries are deemed to be extremely

important to the city as a whole. Chapter 11 and Section 16.10.10 of the Dublin City


22

Development Plan outlines DCC policy requirements and guidance with respect to

development on archaeological sites in zones of archaeological interest.

4.5 Conservation areas and listed buildings

4.5.1 As described in Section 3.1 of the “Basement Development Policy Document” and

Chapter 11 of the “Dublin City Council Development Plan 2016 - 2022” an

extensive structural stability and conservation report is required in the case of

listed buildings, or properties adjoining or adjacent to listed buildings. A record

of protected structures is contained in Volume 4 of the “Dublin City Council

Development Plan 2016 – 2022”.

4.5.2 As with all development schemes, the Planning Authority shall need to be

satisfied that effective measures will be taken during demolition and construction

works to ensure that damage is not caused to the listed building and any buildings

it directly adjoins (e.g. Chapter 11 of Dublin City Development Plan 2016 – 2022).

Poor demolition and construction methods can put neighbouring properties at

risk and so can have considerable effects on the character and appearance of

heritage buildings and conservation areas.

4.5.3 As per Section 3.1 of the “Basement Development Policy Document”, the Planning

Authority (as part of the BIA) requires the submission of a management plan for

demolition and/or construction where basement works are proposed particularly

in conservation areas or adjacent to a listed building. All relevant details and

references should be contained in the overall “Construction Management Plan”

(see Section 5.5) to be submitted as part of the BIA.

4.5.4 Each of the reports mention in this section should be referenced accordingly

within the BIA.

4.6 Trees Landscape and Biodiversity

4.6.1 As per Section 16.10.15 of the “Dublin City Development Plan 2016 - 2022” the

basement development should provide an appropriate proportion of planted

material to allow for rain water to be absorbed and/or to compensate for the loss

of biodiversity caused by the development. This will usually consist of a green

roof or detention pond on the top of the underground structure. As per Section

3.1 of the “Basement Development Policy Document” it will be expected that a

minimum of 1 metre of soil be provided above basement development that

extends beyond the footprint of the building, to enable garden planting and to

mitigate the effect on infiltration capacity. The use of SUDS is sought in all

basement developments that extend beyond the footprint of the original

building.

4.6.2 Again as per Section 16.10.15 of the “Dublin City Development Plan 2016 - 2022”

consideration should be given to the existence of trees on or adjacent to the site,

including street trees and the required root protection zone of these trees.

Existing trees and shrubs shall be surveyed by qualified professionals and

retained or replaced to maintain the street environmental character. Any plants

or animals of scientific interest shall be reported to the appropriate authority and


23

any guidance from this authority followed. Restrictions on tree cutting periods

shall be followed.

ROOT PROTECTION ZONE The area around the base or roots of the tree that

needs to be protected from development and compaction during construction to

ensure the survival of the tree.

4.7 Internal Environment and Appearance of Basement

Where basement accommodation is to provide living space, the Planning Authority in line

with Section 16.10.15 of the “Dublin City Development Plan 2016 – 2022” will take

cognisance of the development standards relating to (but not limited to);

space,

amenity and

natural light

Ventilation

Means of escape

4.8 Lightwells

4.8.1 Adequate sunlight/daylight penetration will be required which will be influenced

by site orientation and the size of site and any lightwell/courtyard; the planning

authority may require a daylight analysis to be submitted as part of a planning

application.

4.8.2 The building stock in Dublin is varied. Some areas contain basements

developments that include front lightwells taking up part, or all, of the front

garden. Other areas do not have basements or lightwells that are visible from the

street. The presence or absence of lightwells helps define and reinforce the

prevailing character of a neighbourhood.

4.8.3 Where basements and visible lightwells are not part of the prevailing character

of a street, new lightwells should be discreet and not harm the architectural

character of the building, or the character and appearance of the surrounding

area, or the relationship between the building and the street. In situations where

lightwells are not part of the established street character, the characteristics of

the front garden or forecourt will help to determine the suitability of lightwells.

4.8.4 In plots where the depth of a front garden is quite long, basement lightwells are

more easily concealed by landscaping and boundary treatments and a substantial

garden area can be retained providing a visual buffer from the street. In these

situations new lightwells that are sensitively designed to maintain the integrity of

the existing building may be acceptable, subject to other design requirements

and environmental considerations.

4.8.5 In plots where the front garden is quite shallow, a lightwell is likely to consume

much, or all, of the garden area. This may not be unacceptable in streets where

lightwells are not part of the established character and where the front gardens

have an important role in the local townscape.

4.8.6 Excessively large lightwells may not be permitted in any garden space.


24

4.8.7 A lightwell to the side or rear of a property is often the most appropriate way to

provide a means of providing light to a new or extended basement development,

and can often provide a link to the rear garden. Lightwells to the side or rear of a

property should be set away from the boundary to a neighbouring property.

4.9 Railings, grilles and other lightwell treatment

4.9.1 Light wells should be secured by either a railing (1.1m high) or a grille. In gardens

that front a street, railings can cause a cluttered appearance to the front of the

property and can compete with the appearance of the front boundary wall, or

obscure front windows. This is particularly the case in shallow gardens. Where

front light wells are proposed, they should be secured by a grille which sits flush

with the natural ground level, rather than railings. In certain publicly accessible

locations grilles should be lockable.

4.9.2 Railings will be considered acceptable where they form part of the established

street scene, or would not cause harm to the appearance of the building.

4.9.3 The lowering of the natural ground level to the rear of the property should be

minimised as much as is practicable. It is recommended that the rear garden

should be graded rather than secured by railings.

4.9.4 Where a basement extension under part of the front or rear garden is considered

acceptable, the inclusion of skylights designed within the landscaping of a garden

will not usually be acceptable, as illumination and light spill from a skylight can

harm the appearance of a garden setting and cause light pollution.

5.0 Basement Impact Assessment (BIA) Methodology

5.1 Overview of Basement Impact Assessment (BIA Methodology

5.1.1 A BIA is intended to provide sufficient and accurate information which the

Planning Authority can utilise to determine whether or not to grant planning

consent. This information is also used by affected parties to evaluate the

acceptability of the development and its impacts.

5.1.2 It should be noted that other factors relating to Planning Policy may have equal

or overriding importance than the content of a BIA when it comes to the Planning

Authority reaching a decision on the application.

5.1.3 The proposed BIA methodology is derived from the Environmental Impact

Assessment (EIA) model which is a well-established and widely-utilised process

of identifying, predicting, evaluating and mitigating relevant environmental

effects of development proposals prior to decisions being taken.

5.1.4 The Dublin City Council Basement Policy states that the Planning Authority will

only permit basements and other underground development that does not cause

harm to the built and natural environment and local amenity and does not result

in an increased risk of flooding both above ground or of basements and cellars in

nearby properties or ground instability. Developers are required to demonstrate

by methodologies which are appropriate to the particular site ensuring that;


25

The structural stability of the building and neighbouring properties are

maintained

The water environment shall not be adversely affected and

groundwater flow, drainage and/or run-off shall also not be negatively

impacted

Avoid cumulative impacts upon structural stability or the water

environment

Take account of overland surface and underground water flows

5.1.5 The information which is to submitted to the Planning Authority to support a

planning application for a basement development will need to address, amongst

others, the issues above in order to enable the Planning Officer to determine an

application.

Unless agreed differently with DCC Planning Department the methodology used

to assess the impact of a proposed basement with regard to the matters

described above, takes the form of an impact assessment. The Basement Impact

Assessment (BIA) process takes the form of the well-established EIA process.

5.1.6 A BIA is critically dependent on the expertise, experience, independence and

objectivity of water, soils, environmental and structural specialists. It is the

responsibility of the Developer`s Specialists to understand the proposed

development sufficiently so that likely significant adverse impacts can be

anticipated and mitigated where possible. The Specialists are required to

characterise the existing environment and then predict how the receiving

environment will interact with the proposed environment (physical and

ecological). If the Specialist anticipates significant adverse impacts they will need

to work with the Developer and Design Team to devise measures to eliminate or

mitigate such impacts. The suitably qualified Specialist who prepares each section

should be identified in the report.

5.1.7 The BIA process requires disclosure of information and commitments to

mitigation. These are the responsibilities of the Developer. Prior to

commencement of a BIA a Developer should be aware of the requirements

arising from the BIA planning assessment (Section 1.2).

5.1.8 The BIA shall identify potential impacts during the construction of the

development (incl. temporary works) and in the longer term (steady state) when

the building is constructed. Reference to the baseline condition (pre-

development) should be referenced throughout the BIA.

5.2 Summary of tasks to be completed as part of BIA

5.2.1 The tasks which are to be incorporated and detailed within a BIA to be submitted

to the Planning Authority are summarised as;

Scoping

o Scoping is the process of identifying significant issues which should

be addressed as part of the BIA.

o Informal review with Planning Authority utilising pre-planning queries

during the BIA compilation and drafting process


26

Continuous Site Investigation, Study and Monitoring

o Site Investigation works and analysis will be required as part of the

scoping stages of a BIA and in order to establish the baseline site

conditions. Additional and continuous site investigation and/or

monitoring, specific to the particular site and particular development

is likely to be required pre-planning, pre-construction, during

construction and post construction.

Impact Assessment and Mitigation Measures

o Impact assessment is completed in order to establish the impact of

the proposed basement on the baseline conditions (during

construction and longer term post construction). Any proposed

mitigation measures are to be accounted for and the residual impacts

reviewed

Review and Decision making

o This step is to be undertaken by the DCC Planning Department. An

audit of the suitability and content of the BIA is undertaken. The

significance of each of the impacts and proposed mitigation measures

for a particular development is then analysed and a decision taken.

5.2.2 The BIA process will be developer-led, with Dublin City Council providing

guidance in the initial scoping stages, followed by review of the resulting impact

assessment by the Planning Authority. The BIA process should be undertaken for

all proposed basement developments that are subject to planning, regardless of

size, location or proposed use. The scale and content of the BIA will, however,

differ for each proposal and should be appropriate to the proposed development

and the scale of the potential impacts identified during the scoping and site

investigation stages. Further details with regard to the categorisation of

basement development is outlined in Section 7.2.

5.2.3 The following sections outline the methodology that has been devised for

specifying and undertaking a BIA in the Dublin City administrative area.

5.2.4 Developers need to ensure that they allocate a realistic period to allow for the

research, investigation and the compilation of data such that a BIA can be

adequately prepared. The length of time involved very much depends on the

objective of the work being undertaken or the sensitivity of the receiving

environment. For example, groundwater and/or ecological baselines may require

observations and monitoring on either a seasonal basis or over a hydrological

year, from October through to the following September.

5.2.5 A non-technical summary of the evidence that applicants shall have gathered at

each stage of the BIA is required to be submitted in a format which can be fully

understood by those with limited technical knowledge.

5.2.6 Forms and checklists to be completed by the Planning Applicant and included

within the BIA submission are included in Appendix A (Section 1 and Section 2).

Submitted BIA review sheets, to be utilised by the Planning Authority, are also

included for reference in Appendix A, Section 3.


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5.3 Scoping

5.3.1 A BIA is required for all developments which include the construction of a

Basement (as per Section 3.2 of “Basement Development Guidance Document”).

Scoping is the activity of defining in further detail the matters to be investigated

as part of the BIA process.

5.3.2 Scoping must be focused on issues and impacts which are;

Scientifically based

Likely to occur

Significant and adverse

5.3.3 The BIA scoping stage aims to define the scope of investigation required in order

to provide the information necessary to make an assessment of the impact of the

issues identified. The defined scope should be specific to the site and proposed

development.

5.3.4 A conceptual ground model is often a useful tool to assist in the carrying out the

scoping stage as it can include the known and suspected features on, below and

adjacent to a proposed site (see Section 5.3.11).

Scoping process

5.3.5 For a BIA, it is proposed that the scoping stage requires the developer to identify

the potential impacts for each of the matters of concern. Some of the main

potential impacts of basement development in Dublin City are described in

Section 3 of this document.

5.3.6 In practice, identifying the potential impacts is facilitated if a conceptual ground

model is developed for the proposed site. A conceptual ground model includes

the flow of groundwater through the site and the known and suspected features

on, below and adjacent to a proposed site, including geotechnical details. Such a

model will assist in identifying the likely implications of the ground, groundwater

or surface water for a proposed basement development. It is helpful to portray

the conceptual ground model as a three-dimensional block model showing

adjacent buildings, trees, gardens, and buried infrastructure that allows the scale

of the features, in relation to the size of the development, to be appreciated.

5.3.7 To undertake the scoping stage of the BIA process, a developer would need to

have some information on the specific project as well as the site. This may involve

some preliminary data collection and field work. It is the applicant’s responsibility

to obtain appropriate information proportionate to the potential impacts of the

proposed basement. Information likely to be required for scoping for a BIA

includes, but not limited to:

Characteristics of the Project

o Brief description of the proposed development.

o A plan showing the boundary of the development including any

land required temporarily during construction.


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o An assessment and description of the ground conditions

groundwater levels and as history of previous built infrastructure

on the site of the proposed excavation.

o The physical form of the development (layout, dimensions,

construction materials, etc.).

o A work programme for construction, operation and

commissioning phases, and restoration and after-use where

appropriate.

o Construction methods – incl. any temporary/permanent works

o Information about mitigation measures being considered.

o Details of any other permits required for the project (T2, GAIL,

waste, discharge, etc.).

Location of the Project

o Maps and photographs showing the location of the project

relative to surrounding buildings, topography, protected

structures, natural and man-made features.

Characteristics of the Potential Impact

Impacts on soils, land use, water quality and hydrology.

Nature and scale of the impacts (i.e. short, medium and long-term,

permanent and temporary, positive and negative).

Extent of the impacted area.

Mitigation incorporated into the project design to reduce, avoid or offset

significant adverse impacts.

5.3.8 The potential impacts identified at this stage will be used by a developer to devise

a study and an investigation to obtain information which will answer the

questions posed. The aim should be to ensure as far as possible that the scope of

the BIA includes such considerations as the incremental effect of the proposed

basement upon the cumulative impact of basements in the area. The maps

included in this report should assist the Planning Authority in recognizing where

potential impacts beyond those which a developer might, unbidden, take into

account in his assessment.

5.3.9 The scoping should identify the matters which should be covered in the technical

information submitted by the developer to the Planning Authority in the BIA, in

particular, to identify the matters which are of most importance so that these can

be addressed in most detail. It is not necessary for the scoping activity to produce

a detailed schedule or specification for the study, but it should define the nature

of the matters to be investigated in sufficient terms that a specification can be

produced at the next stage of the BIA process.

5.3.10 Consultation with local residents; Parallel to the scoping stage of the BIA, a

developer may wish to enter pre-consultation and/or set-up a working group

with local residents who may be impacted by a proposed basement. The purpose

of community involvement would be to understand and address in the BIA

process local residents concerns with regard to the proposed development.


29

This is not a formal stage or requirement within the BIA methodology and should

be viewed solely as a recommendation for developers to assist in identifying

potential matters of concern. It should supplement the scoping stages of the BIA

methodology. Local residents may also have some knowledge of the flooding

history.

5.3.11 The Conceptual Ground Model; This is an integrated subsurface and surface

conceptual model. The translation of an identified possible impact into the scope

for an investigation involves deciding what should be measured, where, and at

what scale. In order to do that, an understanding is needed of the relevant

physical processes in operation, including the scale and speed at which they

operate. This requires a conceptual ground model to be developed.

A ground model contains all the known geological (in the broadest sense

encompassing hydrological and hydrogeological and geotechnical as well as

stratigraphic) information about the site and the physical processes which affect

it. In other words, the ground model should be an explanation of how the site

works. The ground model may initially be quite generalised, and would be revised

as new information is obtained.

5.4 Continuous Site Investigation, Study and Monitoring

5.4.1 Site investigation, study and monitoring will be required to adequately complete

all stages of a BIA, pre-planning, pre-construction, during construction and post

construction. Site investigation is to be designed and undertaken such that it is

specifically appropriate and relevant to the proposed development.

5.4.2 The site investigation required for a BIA should identify the conditions which may

affect a particular development and to arrive at an understanding of the site and

immediate surroundings which will allow safe and economic development. The

“conditions” are understood to include the ground conditions (i.e. the soil and

rocks) and also the surface water and groundwater regime, any contamination

and the effects of previous uses of the site and its environs. The degree of

investigation will vary depending upon the matters of concern identified in the

scoping stage, and therefore will be dependent on the location of the proposed

basement within the city, it`s size and setting in relation to the existing

development on the site and its relationship to adjacent properties and nearby

features of importance.

5.4.3 The BIA site investigation comprises several stages including:

desk study, including site walkover

field investigation, including intrusive investigation

establishment of a baseline condition

monitoring (before, during and post construction phase)

reporting

interpretation

comparison to baseline condition post-construction (seasonal

monitoring required)


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5.4.4 The field investigation stage is likely to include intrusive investigation within the

boundary of the site. The field investigation might, however, also include surveys,

intrusive investigations and measurements which extend beyond the site

boundary. Monitoring for both a short and an extended period is required both

within and beyond the site boundary.

5.4.5 The data and information collected in the site investigation will be analysed and

interpreted by the developer or his specialist adviser/consultant, to provide

baseline data which, in the next stage of the BIA, can be used in order to make

an assessment of the potential impacts identified through the scoping exercise.

5.4.6 It should be noted that variations in groundwater level can be caused by seasonal,

tidal, fluvial changes as well as storm events. Site investigation measures/stages,

as per Section 6.2.3 shall need to be undertaken to observe and record these

changes and fluctuations such that a comprehensive baseline reference and

understanding is available as part of the BIA submission for the specific site.

Dependent on the location and nature of the development this may require

extensive monitoring over a hydrological cycle (hydrological year) before, during

and post construction such that a reasonable comparison to the baseline post-

construction can be assessed and fluctuation limits established for the

construction and post-construction phases. Such details are to included in the

BIA.

5.4.7 Specific site investigation should account for and report upon the suitability of

the temporary works required to construct the proposed basement. The site

investigation works should reference the proposed temporary works design and

be sufficiently adequate to inform the Ground Anchor Installation Licence (GAIL)

process, where Developers wish to apply for permission to install ground anchors

or similar in a public space e.g. location of existing utilities and infrastructure,

suitability of ground conditions etc. (Appendix B and Appendix C).

5.4.8 As further issues may arise during investigations these too should be scoped and

addressed as part of the BIA submission.

5.5 Impact Assessment and Mitigation Measures

Impact Assessment for a basement development may be defined as the process of

evaluating the direct and indirect geo-environmental implications of the proposed

project. It should be a flexible process and can make use of a number of evaluation

methods and techniques. Guidance in undertaking an impact assessment is provided in

the following section.

5.5.1 In simple terms, a BIA describes the impacts of the project on the environment

by comparing the present situation (the baseline) with the situation as it would

be with the basement in place i.e. constructed. The approach is similar to an

economic analysis or an EIA.

5.5.2 A systematic approach is required, and the BIA should describe, quantify, and

then aggregate the effects of the development on those attributes or features of

the hydrogeological and hydrological environment which have been identified (in

the scoping stage) as being potentially affected.


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5.5.3 Whenever possible, impacts should be described by reference to an existing

acknowledged standard or criteria for the topic. The criteria on which the

terminology is based should be clearly defined for each discipline. Where this is

not possible then it is recommended that impacts should be described by

reference to the “glossary of impacts” (Section 10).

5.5.4 The generic review of attributes is summarised as below (but is not limited to):

Surface (hydrological) flow

Rate of runoff

Direction of overland flow

Stream hydrograph

Soil moisture

Frequency of surface flooding

Sediment transport (erosion and siltation)

Subsurface (groundwater) flow

Groundwater levels and existing natural fluctuations

Groundwater chemistry and bacteriology

Spring hydrographs

Soil moisture

Water quality

Slope stability

Slope angle

Moisture content

Porewater pressure

Stiffness

Compressibility

Bearing capacity (strength)

Atterberg limits

5.5.5 The BIA should evaluate the attributes with and without the development and

consider the possibility of alternatives. For example, what are the groundwater

levels (including range of seasonal fluctuation) by hydrogeological calculation,

beneath the site, before development and the predicted levels, post

development? The impacts should be measured in terms of the “nett” changes

in the attribute at a given point in time. For example the nett change may be the

rise upstream and the lowering downstream of groundwater levels due to a

basement.

5.5.6 As part of the BIA an assessment should be taken of the potential impacts during

construction if/when dewatering is required to facilitate construction. There may

be a risk to adjoining structures etc. Similarly, when dewatering ceases and the

water-table is allowed return to the natural levels there is again a potential for

land and structure stability issues. This scenario shall also need to be assessed by

a suitably competent person(s) and accounted for in the BIA.


32

5.5.7 Monitoring of groundwater levels and other applicable parameters should be

undertaken during and post development to permit a comparison with the

baseline levels and to establish threshold limits for dewatering etc.

5.5.8 The consequences of changes in attributes determine the amount of change from

baseline conditions which may be accepted. Thus, a predicted rise in

groundwater level upstream of a proposed basement may have consequences in

terms of an increased likelihood of groundwater flooding, or a risk of damage to

the foundations of a neighbouring building, both of which would be

unacceptable.

5.5.9 The baseline would incorporate the presence of existing basements, so that the

additive effect of another basement would be the assessed change. Nearby and

adjacent basements should be accounted for and highlighted within the report.

5.5.10 If the consequences are not acceptable, mitigation should be incorporated into

the proposed scheme and the changes in attributes re-evaluated and the new

nett consequences determined. Any mitigation measures incorporated into the

proposed scheme should be described in the BIA report with details of how they

reduce and/or alter the impact of the proposed basement on the surrounding

environment.

5.5.11 Mitigation measures which may be included in basement development proposals

include (but are not limited to):

Controlled or adequate drainage

High permeability corridors

Underpinning of neighbouring structures

Setting the basement in from property boundaries

Etc.

5.5.12 The baseline conditions (pre-construction) should be established and the

relevant mitigation measures and residual impacts should be accounted for and

demonstrated separately for the subsequent two stages of the development;

i. Construction stage

ii. Steady state (long-term post construction)

It is imperative that these mitigation measures and residual impacts are

accounted for and highlighted in the BIA. The construction stage impacts and

mitigation measures should be included within the “Construction Management

Plan” (Section 5.5). The steady state scenario (impacts and mitigation measures)

are to be recorded and should form part of the as-built drawings of the structure

and included as part of the scheme Safety File, to be made available at future

request for interested parties.

5.5.13 Alternative options should be examined and considered during design and

consultation to ensure that options that are of interest to all parties are

evaluated.

5.5.14 Consequences will differ from one location to another, but their assessment

should be based on the concept of identified targets. The susceptibility of the

targets, which might be watercourses, utilities, existing buildings, roads or


33

structures in close proximity to the proposed basement, possibly even trees,

should be evaluated using appropriate methods.

5.5.15 In the case of susceptibility of buildings to damage resulting from ground

subsidence, there are established methods in geotechnics. Where the target is a

groundwater supported feature such as a spring or wetland the methods may be

more subjective even when the impact of the development on the relevant

attribute (groundwater seepage) can be reasonably quantified.

5.5.16 The Geotechnical Design Report for the project, as required in IS EN 1997, should

address the issues relevant to the BIA.

5.5.17 Special attention is to be given to protected and heritage structures. These

structures and measures are to be highlighted with the BIA with the relevant

planning guidelines followed.

5.5.18 All design measures are the responsibility of the Applicant`s design/specialist

team.

Cumulative impacts of basement development

5.5.18 The cumulative effect of the incremental development of basements in close

proximity, particularly when these are large, can potentially create a significant

impact. Therefore, Basement Impact Assessments must identify neighbouring

basements (both existing and those with planning approval or already in the

planning process) and make the assessment considering all such nearby

basements. Basement Impact Assessments must respond to the issues of

cumulative impacts and account for/undertake appropriate mitigation measures.

5.5.19 In order to avoid cumulative effects and in an effort to be as fair and equitable as

possible to all development proposals, all basement developments shall account

for and accommodate the existing groundwater contained within and flowing

through their site. Any scheme with a proposed basement shall ensure that the

ability of groundwater to exit and/or to pass through the site shall remain

unchanged post construction. Groundwater levels upstream or downstream of

the development are not to be altered as a result of the development i.e. each

basement development shall implement measures to ensure that the volume of

groundwater, within and passing through the site pre-development shall be

unchanged post-development and there should be no impact upon groundwater

levels up-stream or down-stream of the groundwater gradient.

5.5.21 Further to the point made above, in an effort to be as fair and as equitable as

possible, as a minimum standard, all basement development is required to

provide at least 0.5m wide of clear space between the site/property boundary

and the outer extent of a basement. This 0.5m wide space shall extend over the

full height and around the perimeter of the basement and shall be filled with a

suitable, highly permeable material (with appropriate wrapping), thus reducing

the potential for cumulative effects if further basements are to be constructed

nearby.


34

In providing the highly permeable 0.5m wide space between the site boundary

and the basement structure the design team should ensure that erosion and

undermining beneath the adjoining site/property would not be possible.

5.5.22 If the required 0.5m wide high permeable space is regarded by the developer`s

design team as being inadequate to account for the volume of groundwater

observed within a particular site the Developer is required to identify more

robust measures in order to meet the requirements described in Section 5.5.19.

Construction Management Plans

5.5.23 The Planning Authority shall require a construction management plan for all

underground basement developments to manage and mitigate the construction

impacts of these schemes. Construction management shall be particularly

important on constrained sites, in conservation areas, for listed buildings and at

sites located adjacent to listed buildings amongst others. The level of content of

the Construction Management Plan should be proportional to the scale and

complexity of the proposed development. The Developer is required to adhere

to this “Construction Management Plan” if the application is deemed successful.

5.5.24 A basement construction plan sets out detailed information to demonstrate how

the design and construction of the basement has been prepared in order to

minimise the impacts on neighbouring properties, public lands and the water

environment. The basement construction plan should provide a programme of

measures to be undertaken whereby the Developer shall minimise and mitigate

against any potential impact on the structural integrity of neighbouring

properties and sensitive structures e.g. the public road infrastructure.

5.5.20 A basement “Construction Management Plan” should plan should contain (as a

minimum);

Provision for phasing of the works

Provision for site management, safety and supervision

A method statement detailing the proposed method of ensuring the

safety and stability of neighbouring properties and land throughout

the construction phase, including temporary works sequence

drawings

Provision to monitor movement of structures and land (details to be

provided)

Provision to monitor groundwater levels and alerts to be raised as

required (details to be provided). Appropriate limits of groundwater

fluctuation to be accounted for and detailed. Critical groundwater

threshold levels are to be identified such that alarm set-points can be

established. Appropriate mitigation measures to be detailed if these

limits are reached or exceeded e.g. to prevent occurrence of ground

movement

Proposed site working hours

Management of noise, vibration and dust


35

Construction & Demolition Waste Management Plan – reference to

soil conditions, contaminants, hazardous waste etc.

Management of construction traffic and parking incl. traffic

movements/routes to and from site

Details demonstrating that the basement has been designed using

evidence of local factors including ground conditions, the local water

environment and the structural condition of neighbouring properties,

in order to minimise the impact on them.

The Construction Management Plan should contain the

structural/geotechnical design submissions (as required in IS EN

1997).

Appropriate monitoring including details of risk assessment

thresholds and contingency measures e.g. for ground movement,

groundwater levels, surface water flooding etc.

The location(s) of a groundwater recharge point(s) should be

accounted, taking into account and with reference to the local site

geology, hydrogeology, ground conditions, development extent and

site boundary etc.

If discharge is proposed to a local sewer details related to the

anticipated pumped volumes and discharge quality is to be detailed

The locations of a minimum of 4no. groundwater monitoring points

facilitating monitoring during pre-planning, pre-construction phase,

construction phase and post construction phase, taking into account

and with reference to the local site geology, hydrogeology, ground

conditions, development extent and site boundary etc. (coordinates

provided and to be accessible and maintained post-construction

where possible).

Details as to whether temporary or permanent works are to extend

outside the site boundary, e.g.

o Boreholes required to monitor groundwater? – permissions

required

o Ground anchors/soil nails for which a Ground Anchor

Installation Licence (GAIL) shall be required (Appendix B) –

see also Ground Anchor Installation Licence guidance

document (Appendix C).

Provision to retain at the property throughout the construction phase

a suitably qualified engineer and supported as required by a

hydrogeologist from a recognised relevant professional body

(including dewatering phase) to monitor impacts, adjust pumping

rates, inspect dewatering arrangement, review and apply the

threshold groundwater levels (pumping controls) and approve the

permanent and temporary basement construction works.


36

Measures to ensure the ongoing maintenance and upkeep of the

basement.

5.5.21 The “Construction Management Plan” should ensure that:

Suitably qualified and experienced engineers and hydrogeologists

have agreed the design, construction process and monitoring and

mitigation protocols.

The modelling of ground conditions and water environment is

appropriately conservative; and

Permission has been sought from the Local Authority or third parties

if temporary/permanent works are to extend beyond the site

boundary e.g. GAIL application to be submitted.

Best endeavours are undertaken to prevent any impact on the

structural integrity of the neighbouring properties

The construction methodologies and proposals are in accordance with

the Design Team proposals and requirements and that each design

element has been accounted for. All requirements to construct the

building as per design is required to be included in the “Construction

Management Plan” and scoped accordingly e.g. structural stability of

adjoining building requirements has been incorporated, sequencing

of works as per design requirements etc. etc.

5.5.22 Prior to final submission to the Planning Authority for approval, Basement

Construction Management plans will need to be certified by a suitably qualified

and experienced engineer and/or a hydrogeologist who is independent of the

design team. The certification will need to be funded by the applicant.

5.5.23 Construction Management Plans should take into consideration other

developments taking place in the local area with a view to minimising the

combined effects of these construction works. The Planning Authority

encourages applicants to inform and engage with affected neighbours at an early

stage.

5.5.24 If successful the Construction Management Plan submitted in the BIA shall form

a material consideration in the conditioning of a planning application

5.6 Qualifications and accreditation

5.6.1 At each stage in the process, the person/s undertaking to complete the BIA

process on behalf of the developer should hold qualifications relevant to the

matters being considered. Details of these qualifications/accreditation should be

submitted as part of the BIA.


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6.0 Assessment of Basement Construction Potential Impacts

6.1 Introduction

The BIA toolkit gives further guidance with regard to the site investigation stage of the

BIA. This section comprises the following set of methods and techniques to be used for

the site investigation and study;

calculation methods and tools,

reference literature

information sources

applicable standards and best practice guidance

A competent consultant or site investigation contractor should be well aware of these as

well as being experienced and knowledgeable in their use. The following sections draw

attention to particular issues which should be borne in mind by a developer when

specifying an investigation and by DCC when reviewing the output from an investigation.

6.2 Site investigation

Site investigation required for a BIA may include several parts, including desk study,

intrusive investigation, monitoring, reporting and interpretation. This section outlines

further guidance to Section 5.4 with regard to completing the different parts of a site

investigation.

6.2.1 Desk Study;

Phase 1 of a site investigation is usually a desk study, which is the collation and

review of information already available about the site. The desk study need not

be restricted to the site boundary; indeed the desk study is the right place to

present information on the wider interaction between the development and its

environs.

The desk study does not involve site works, but will usually include a visual

inspection or walkover of the site and its surrounding area. Some sources of

hydrogeological information for a desk study are listed in Section 6.5. Some of

the desk study information may have already been gathered at the screening and

scoping stage.

6.2.2 Intrusive testing (boreholes and trial pits);

The next phase(s) of site investigation involves subsurface inspection of the

ground to determine the soil types and soil properties at the site and entails

drilling boreholes and/or excavation of trial pits. The driver for carrying out an

intrusive investigation is usually the developer’s or client’s civil or structural

engineer, and the information collected may be no more than what the engineer

needs for the structural design of the building in accordance with the relevant

Building Regulations. In recent years the scope of a standard site investigation

has been enlarged to include inspection for contamination and also the

acquisition of information to support drainage design, but it remains substantially

focused on the needs of the building designer. This section is intended to provide


38

guidance on expanding the extent of an intrusive investigation to ensure that the

data collected will be appropriate to later allow the impacts of the basement to

be determined with respect to the matters of concern identified in this study.

The intrusive part of a site investigation is usually carried out only within the

boundaries of the proposed development, because that is all the developer or his

client has access to. However, groundwater conditions and environmental factors

outside the site boundaries can have a significant effect on conditions inside the

boundaries. Also, a development can have a potentially significant effect beyond

the site boundary. A standard investigation carried out for geotechnical and

structural design purposes does not necessarily address these collateral factors.

Intrusive testing beyond the site boundary is only possible with the consent of

adjacent landowners. Where permission is given to investigate beyond the site

boundary, the investigation should be extended accordingly and appropriate

testing of the ground should be undertaken to address the identified relevant

matters of concern. Where permission is not given to investigate beyond the site

boundary, the undetermined ground conditions beyond the site boundary should

be identified as a risk in the impact assessment and mitigated against accordingly.

Any site investigation works, and any subsequent basement construction, should

undertake a duty of care to prevent any damage to neighbouring properties,

infrastructure, ponds etc.

The detailed scope of the intrusive testing phase(s) (the “ground investigation”)

of a site investigation will depend upon the nature of the proposed development

and the particular site conditions. Guidance can be found in many readily-

accessed publications. Many of the problems which may be encountered in

attempting to interpret the results of a site investigation have quite simple and

avoidable causes; advice on some of the most common is given below:

For basements beneath existing houses and those in gardens, intrusive

investigation may be required.

Boreholes or trial pits should extend to a depth at least 3 metres below

that of the proposed basement and foundation excavations and typically

further into the rock if possible, to assess the underlying soil that may

affect or be affected by, for example, the loads from the building.

Construction design and methods for boreholes and trial pits should be

specified to ensure that information can be obtained to assess the

matters of concern described in the scoping stage of the BIA. All borehole

drilling and trial pits will be supervised, directed and logged by suitably

qualified professionals to obtain the best relevant information. These

professionals on site can adjust the drilling methodology and focus of

attention in the light of the findings as they emerge, in order to obtain

the appropriate samples and information with detail extent to reflect the

scale of the development.

For proposed basements beneath an existing house, it may be necessary

to position boreholes / trial pits beyond the footprint of the proposed

basement.


39

The location of site investigation boreholes adopted for groundwater

monitoring, groundwater dewatering boreholes and groundwater

recharge boreholes should be such that monitoring can continue both

during and after construction works have taken place. Groundwater

monitoring shall be required before, during and after construction for a

duration determined by the findings of the BIA and the conditions of a

planning permission.

A minimum of four boreholes or trial pits (converted to groundwater

monitoring boreholes) is usually required in order to determine the

groundwater flow direction. For larger plots more locations will be

needed.

The direction of flow of groundwater can be determined from

measurement of the elevation of the water surface at four points;

The water table rises and falls seasonally. Broadly speaking, it will be

highest (closest to the surface) from December to April, and lowest at the

end of September to middle of October.

All data should be referenced to a common geographic coordinate

system, and the reference given to an appropriate level of resolution. A

six-digit OS grid reference is only accurate to 100m which is not sufficient

when an individual dwelling plot is being considered, and in that case the

location of features should be quoted to eight digits or better. Maps at

scales of larger than 1:10,000 are of little use for site assessment and

1:1,250 plans should be used.

Elevation data (including water levels, the observed increased inflows of

water during drilling and soil and lithological changes in boreholes and

trial pits) should be quoted with reference to Malin Head Ordnance

Datum. This allows sub-surface data to be correlated with topographic

data, which is related to OD.

Borehole numbering can be a source of confusion. A unique numbering

scheme should allow the inclusion of extra boreholes; it should be as

informative as reasonably possible. Most importantly, the numbering

scheme should not be changed or boreholes re-numbered.

6.2.3 Monitoring;

Hydrogeological processes are subject to seasonal and longer-term cyclical

influences. Measurements taken at one particular time may not indicate how

conditions might be in a month or six months from that time. The effect of a

change in conditions, such as the construction of a basement, may be marked at

first but reduce with time as the effect of the disturbance dissipates – or the

reverse might occur, with a gradual increase in cumulative effects. Monitoring of

groundwater levels over a period of time is therefore necessary. The frequency

of measurement and duration of monitoring must be chosen with reference to

the specific effect which is being investigated. For example, if the matter of

concern is the potential for groundwater flooding, measurement is best taken

during the period of the year when groundwater levels are naturally at their


40

highest (March or April). If the impact being considered is related to increased

disposal of rainfall to the ground, a measurement should be taken frequently, e.g.

daily, during periods of contrasting rainfall intensity.

Rainfall and tide fluctuations should be monitored for comparison with

groundwater levels. This may be through on-site monitoring and/or acquisition

of external third-party weather station data (if a nearby weather station

representative of the site conditions is available). Further information on data

sources is included in Section 6.5.

It may take some time, hours or several days, for water levels in newly installed

boreholes to stabilise and reach equilibrium with the surrounding groundwater

system. Appropriate efforts to accurately record groundwater levels and

groundwater movement should be undertaken, recorded in the BIA and

incorporated into the building design and the “Construction Management Plan”.

Dependent on the location, extent and nature of the proposed development,

recording and monitoring of groundwater flow/level for a full “hydrological year”,

in order to establish an accurate seasonal baseline, may be required.

If the applicant is successful and construction works commence, groundwater

monitoring is required to continue throughout the construction phase of a

project and for a minimum of one full hydrological year following completion or

such time as approved by DCC and/or as specified in the planning decision. This

is to be undertaken by the Developer to demonstrate and quantify the impacts

associated with a proposed development. All associated costs with groundwater

monitoring throughout the different phases are to be covered by the

Applicant/Developer.

6.2.4 Site investigation report

The Site Investigation Report will consist of a factual description of the work

carried out and an interpretation of this information.

Intrusive site investigation techniques are used to characterise the

hydrogeological and engineering properties of the subsurface below the site for

the purposes of engineering design. The results of the site investigation are

compiled into the first part of the site investigation report, by suitably qualified

personnel.

Details of the ground conditions, driller’s logs, geology and groundwater

conditions will be provided in the factual report. The report will contain details

and results of tests undertaken during the work and the results of laboratory

analyses of soil, rock and water.

A factual report will contain no interpretation and as such will generally

necessitate specialist knowledge to interpret the data contained in the report.

6.2.5 Interpretative report;

The interpretative part of the Site Investigation report will comprise three parts:

an interpretation of the detailed site soils and geology

an interpretation of the geotechnical properties of the ground


41

an engineering and hydrogeological interpretation of the

implications of the ground conditions for the development project.

The interpretative part of the report will bring together the data from the desk

study and the findings of the site investigation. Production of a conceptual

ground model at the site along with expected geotechnical and hydrogeological

properties for each layer, lens or zone will be included with the interpretative

report.

The interpretations will assess the significance of the interpreted ground

conditions and any geological or other hazards identified in relation to the

proposed development. The level of interpretation will be related to the type and

size of the development however it may include a discussion on the type of

foundations, the need for ground treatment or piling, likely settlements,

groundwater control and expedients necessary to deal with the site problems.

For large construction projects additional reports may be necessary including

detailed geotechnical design based on the interpretive report however these

reports would normally form part of the design process as part of the project.

6.3 Extent of Basement and Site Dewatering & Recharge

The extent and design of a proposed basement should take account of the DCC Basement

Policy requirements to undertake adequate site investigation and continuous monitoring

(boreholes etc.) throughout construction and post the construction phase. Provision for

de-watering of the excavation during the construction phase is likely to be required and

as such a location for recharge of groundwater needs to be incorporated within the site

boundary. The location(s) of a groundwater recharge point(s) should be accounted for at

the basement design stage and the location should be included as part of the construction

methodology section of the BIA submission, taking into account and with reference to

the local site geology, hydrogeology, ground conditions, development extent and site

boundary etc. Calculations should be provided as part of the BIA demonstrating the

expected level of groundwater discharge and expected recharge capacity to back to the

groundwater (within the site boundary) if this is necessary or possible.

As outlined in Section 5.5.6 an impact assessment of the effect of dewatering and then

ceasing dewatering and the water-table returning to its natural level needs to be

assessed, understood and included as part of the BIA. Such water-table fluctuations may

have a negative impact on the stability of adjacent lands or structures.

6.4 Calculation Methods and Tools

It may be necessary to perform calculations on the data collected during intrusive

investigation and monitoring phases of site investigation in order to derive parameters,

for example hydraulic conductivity, or to estimate ground responses to certain effects,

for example groundwater level response to dewatering.

Appropriate methods should be used in the derivation of technical parameters. Any

method used should be referenced, and a source given. Calculations should be checked

and approved.


42

Standard calculation methods should be used where possible. Some methods of

calculation are given in Construction Industry Research and Information Association

(CIRIA) guides and in BS and EN standards. However, when using these guides and

standards, account should be taken should of fracture controlled groundwater flow found

in the limestone bedrock below Dublin City.

6.5 Sources of Information

In addition to published literature available from libraries and via the internet, statutory

authorities and agencies hold information which is relevant to the hydrogeology and

hydrology of the Dublin area. Some of the principal sources are listed below. Developers

and their consultants should consult these sources when preparing their BIA`s;

Irish Geological Survey

o Bedrock Geology map Sheet 16

o Geotechnical database site and borehole Records

o Previous site investigation reports

o Groundwater Well records

The Ordnance Survey Map

Water Framework Directive (2000/60/EC). The Water Framework

Directive (WFD) establishes a framework for the protection,

improvement and sustainable use of all water environments;

The Construction Industry Research and Information Association

(CIRIA) Environmental Good Practice on Site (C502) (1999). C502

provides guidance on how to avoid causing environmental damage

when on a construction site

CIRIA Control of Water Pollution from Construction Sites (C532)

(2001). C532 provides guidance on how to plan and manage

construction projects to control water pollution.

• The Environment Protection Agency (EPA)

o Licensed abstractions

o River flow data

o Statutorily protected sites of ecological interest

o Surface water quality data

• Meteorological Office (Met Office) & Dublin City Council

o Rainfall data

o River/Estuary Levels

6.6 Standards and Best Practice Guidance

Site investigation consultants, specialists and contractors are expected to operate quality

management systems, preferably integrating health, safety, quality and environment

systems which are accredited to recognised European or Irish Standards. It is particularly

important that soil and water testing laboratories are INAB accredited to provide

assurance of the validity of test results.


43

The site investigation should be specified and supervised by suitable qualified person/s

(see Section and 5.6 and Section 6.2). The person/s (the contractor) undertaking the site

investigation should be experienced and competent in the works being undertaken.

Intrusive ground testing (e.g. boreholes and trial pits) should be specified in accordance

with Site Investigation best practice. Guidance on geotechnical desk studies is available

from the Geotechnical Society of Ireland. Guidance on groundwater and borehole design

and construction can be found in the Institute of Geologists of Ireland Water Well

Guidelines (2007).

Specific advice can also be found in publications from British Standards (BS5930 and

BS10175), AGS (2000), Eurocode 7 [50], Ciria C515, and in geotechnical texts (such as

Simons et al, 2002). Guidance on good practice and procedures in Environmental Impact

Assessment are also relevant to the planning and execution of a BIA.

7.0 Planning Authority Assessment of BIA

7.1 Audit of information supplied

The BIA should be submitted with the planning application so that the Planning Authority

has all the information necessary to support decision making.

The assessment by DCC Planning Authority of the information submitted in a BIA is

essentially a process of auditing the submission against the criteria given in Section 6 to

ensure the Development achieves the policy requirements as outlined in Section1.2. The

objective of the process should be that the developer will have been required, under the

powers enshrined in DCC Basement Policy, to consider such factors as the incremental

contribution of the proposed scheme to the cumulative impact of all basement

developments in the relevant locality. The adequacy of the information provided and

assessed within BIA should be assured through proper scoping and the professional

competence of the contractor/consultant.

The audit stage of the process, as with the earlier stages, has much in common with the

corresponding step in the EIA process.

The process will be based on reviewing the BIA approach undertaken by the Developer.

It shall follow the approach recommended in this report and should include the following:

Check qualifications / credentials of author

Thorough review of scoping undertaken in the BIA

Does the description of the proposed development include all aspects

of temporary and permanent works which might impact upon

geology, hydrogeology and hydrology?

Have the appropriate issues been investigated? This includes

assessment of impacts with respect to the DCC Basement Policy

including land stability, hydrology, hydrogeology etc.?

Is the scale of any included maps appropriate? That is, does the map

show the whole of the relevant area of study and does it show

sufficient detail inside and outside the site?


44

Have the issues been investigated using EIA methodology? (Section 5)

Has the need for mitigation been considered and are appropriate

mitigation methods incorporated in the scheme? (Section 5)

Has the need for monitoring been addressed and is the proposed

monitoring and analysis of data before, during and after construction

sufficient and adequate? (Section 6.2.3)

Have the residual (after mitigation) impacts been clearly identified?

Is there a proposal for continuous monitoring of impacts been

included?

Where the information listed above, and any other pertinent details relating to the

development, is not provided to an adequate standard within an application, the Planning

Authority may not validate the application, or may refuse applications due to lack of

information, or may require further information to finalise its assessment.

The Planning Applicant is required to review and submit all items required in the BIA

Policy and Guidance Documents which are briefly summarised as per the BIA checklist,

included in Appendix A.

7.2 Basement Audit Categorisation

The size, scale and nature of basement development are to be split into three categories,

A, B and C. The level of detail contained within a BIA for a particular development shall

be dependent on which category the development fits into. The assigned/referenced

category for a development should be appropriate to the proposed development and the

scale of the potential impacts identified during the scoping and site investigation stages.

Category A

Residential or commercial development with single storey basement where the Scoping

Stage of the Basement Impact Assessment indicates no matters of concern which need

further investigation.

Submitted BIA anticipates no significant impact relating to:

land stability or impacts, buildings or infrastructure;

groundwater flow or surface water flooding and underground tunnels

Category B

Residential single basement or commercial development with single or double basement

where the Scoping Stage of the Basement Impact Assessment identifies matters of

concern which need further investigation.

Submitted BIA anticipates potential impact:

to a listed building;

on land stability;

on groundwater flow;

on potential for surface water flooding ;

on underground tunnels or infrastructure; and

cumulative impact on ground stability and the water environment


45

Category C

Exceptional development (in terms of geometry, area, depth, location/position or

complexity) which may be a single or double basement with potential complications.

Submitted BIA anticipates potential for significant impact:

to a listed building;

on other buildings and or with land stability issues;

to groundwater flow and potential for surface water flooding ;

underground tunnels or infrastructure; cumulative basement

impacts;

relating to significant technical issues raised by third parties.

7.6 Updating the baseline

If the scheme is granted planning consent, and if it proceeds to construction, the baseline

will have changed for potential future applications. The Developer is required to submit

a copy of their basement as-built drawings to DCC for future reference.

7.7 Future Monitoring of Groundwater Levels to verify BIA Assumptions

It is imperative that the Developer continues to monitor groundwater levels and other

environmental parameters to ensure that the as-constructed development reflects the

residual impacts identified in the BIA.

8.0 Related DCC Corporate Policies

In addition to the requirements outlined earlier in this document Developers of basement

structures are required to take account of other existing DCC policies where appropriate.

Some of the existing polices which are likely to be applicable to basement construction are

briefly referenced in this Section. It shall be the responsibility of the Developer to identify and

comply with these and any other relevant DCC/statutory policies.

8.1 DCC Roads Requirement

The Planning Applicant should take account of the existing DCC Roadworks Control and

DCC Road Maintenance requirements where works in public spaces (roads, footpath etc.)

are required.

8.2 DCC Ground Anchor Installation Licence (GAIL)

If as part of the proposed development it is intended to install ground anchors (or similar)

beneath a public space the applicant is required to complete a Ground Anchor Installation

Licence (GAIL) application. This application is required to be submitted as part of the BIA.


46

8.3 DCC Pollution Control

No discharge of trade effluent (groundwater discharged during construction) shall take

place unless under and in accordance with a licence to be issued by the relevant

Sanitary Authority.

8.4 DCC Traffic Management

As part of a BIA submission the Planning Authority shall require a “Transport

Assessment”. A “Transport Assessment” is a comprehensive review of all the potential

transport impacts of a proposed development. In the case of developments with

significant vehicular trip generation potential and attraction rates, applicants will be

required to submit a detailed assessment of the transportation systems provided and the

impact of the proposed development on the surrounding environment and

transportation network through the submission of a Transport Assessment. Details of the

requirements for a Traffic Assessment can be seen in the Dublin City Development Plan.

Details relating to the construction phase of the proposed development is an extremely

important element of the “Traffic Assessment” and should be included as part of the BIA

submission.”

8.5 DCC Waste Management

The following conditions will be considered by DCC Waste Regulations Section for

inclusion into a Construction & Demolition Waste Management Plan when a submission

is requested by the Planning Office. The conditions to be inserted in individual planning

permissions may vary for each. A developer should make themselves aware of all

potential conditions and plan for the environmental sound management of any wastes

that may be generated by the proposed development.

8.5.1 Provide a detailed account of potential wastes arising on site including waste

description, quantities and corresponding List of Waste (LoW) code, previously

known as the EWC code.

8.5.2 A full list of authorised waste collection permit holders and their NWCPO

numbers, including any sub-contractors to be used to transport waste off site.

8.5.3 A full list of destination waste facilities that the authorised waste collection

holders intend to use.

8.5.4 Provide letters on headed paper signed by a relevant competent person from

the destination waste facilities confirming acceptance of material and agreed

tonnages to be received.

8.5.5 Contact details for the site manager (email and mobile phone number).

8.5.6 Ensure, and confirm, that the waste dockets used are specific to

the authorised waste collector collecting each waste load, subcontractors cannot

move waste under another waste carries documentation.

8.5.7 Please be aware that crushing concrete onsite is classified as a waste activity

requiring authorisation under the Waste Management (Facility Permit and

Registration) Regulations 2007 as amended. Any mobile plant brought onto the

site for any waste activity must be covered by a valid Waste Facility Permit

(WFP)/Certificate of Registration (COR). The developer and/or site owner is liable


47

to ensure the necessary WFP/COR authorisations are in place. Where an

application for a WFP/COR will be required, a minimum of 6 weeks should be

allowed. In addition, the waste activity must be outlined in the planning decision.

8.5.8 Laboratory testing of any soil to be removed off site will be required prior to its

removal. A waste characterisation report and laboratory results will be required

in advance of a planning decision.

8.5.9 An Invasive Species survey will be required, if any invasive plant species are

identified on the site, an Invasive Species Management plan will be required.

8.5.10 An Asbestos Survey must be carried out prior to demolition works taking place. If

asbestos is identified, an Asbestos Management Plan will be required.

8.5.11 A live log of all waste movements must be available in digital format for

inspection by Dublin City Council personnel upon request.

8.5.10 Where it is intended to reuse material on another site, a notification must be

submitted to the Environmental Protection Agency (EPA) in accordance with

Article 27 of the European Communities (Waste Directive) Regulations 2011. The

EPA determination should be obtained prior to the commencement of any works.

8.5.11 Each site owner is responsible for identifying their environmental liabilities in

accordance with the Environmental Liabilities Regulations 2008. The developer

and site owner will remain liable throughout the storage, transport and

disposal/recovery for the environmentally sound management of any wastes

produced during the development works.

8.6 DCC Drainage Planning

The DCC Drainage Department shall review each application bearing in mind proposals

for some important surface water drainage design aspects in relation to (amongst

others);

Sustainable Urban Drainage Systems (SUDS)

Reference to Greater Dublin Strategic Drainage Study (GDSDS)

Greater Dublin Regional Code of Practice for Drainage Works

DCC Strategic Flood Risk Assessment (SFRA)

8.7 Noise, Air Quality and Vibration

In order to regulate noise, air quality and vibration DCC have developed a “Construction

and Demolition Good Practice Guide” (Appendix E). The developer is requested to adhere

to these guidelines with proposals reflected in the project Construction Management

Plan, to be submitted as part of the BIA.

Although it is conceivable for ground-borne vibration from construction projects to

cause building damage, the vibration from construction activities is almost never of

sufficient amplitude to cause even minor cosmetic damage to buildings. The primary

concern is that the vibration can be intrusive and annoying to building occupants. Most

construction vibration is in the mid- to upper- frequency range, and therefore has a

lower potential for structural damage.


48

DCC has guidelines for vibration levels from construction related to their activities, and

recommends that the maximum peak-particle-velocity levels remain below 1 mm per

second at the nearest structures.

9.0 Glossary of Terms

Aquifer

A body of permeable rock or overburden, or impermeable rock with open interconnected

fractures or conduits, that is capable of storing and transmitting water.

Archaeology

The study of past societies of any period through the material remains left by those societies

and the evidence of their environment. The material things (objects, monuments, sites,

features, deposits) which archaeology uses to study past societies are referred to as

‘archaeological heritage’.

Baseline Survey

A description of the existing environment against which future changes can be measured.

Ecology

The study of the relationships between living organisms and between organisms and their

environment (especially animal and plant communities), their energy flows and their

interactions with their surroundings.

Effluent

Any liquid discharged from a source into the environment.

Environmental Impact Assessment – EIA

The process of examining the environmental effects of development - from consideration of

environmental aspects at design stage through to preparation of an Environmental Impact

Statement, evaluation of the EIS by a competent authority and the subsequent decision as to

whether the development should be permitted to proceed, also encompassing public response

to that decision.

Emission

a) An emission into the atmosphere of a pollutant within the meaning of the Air

Pollution Act 1987.

b) A discharge of polluting matter, sewage effluent or trade effluent within the

meaning of the Local Government (Water Pollution) Act 1977 to waters or sewers

within the meaning of that Act.

c) Disposal of waste, or

d) Noise.

EPA (see section EPA)

The Environmental Protection Agency.


49

Geology

The science of the earth, including the composition, structure and origin of its rocks.

Habitat

The area in which an organism or group of organisms live.

Hydrology and Hydrogeology

These applied sciences are concerned with the occurrence and circulation of water in all its

phases and modes, and the relationship of these to man. Hydrology particularly relates to

surface water, and Hydrogeology particularly relates to subsurface water.

Impact

The degree of change in an environment resulting from a development.

Impact Anticipation

Using knowledge of both the development and the receiving environment to predict the likely

effects and consequences.

Impact Avoidance

The modification of project decisions (about site location or design for example) having regard

to predictions about potentially adverse environmental effects.

Infrastructure

The basic structure, framework or system which supports the operation of a development

project for example, installations such as roads and sewers which are necessary to support

development projects.

Land-use

The activities which take place within a given area of space.

"Likely Effects / Impacts"

The effects that are proposed to take place - based on an understanding of the interaction of

the proposed development and the receiving environment".

Methodology

The specific approach or techniques used to analyse impacts or describe environments.

Mitigation

Measures designed to avoid, reduce, remedy or compensate for impacts.

Mitigation by Remedy

Impact Avoidance When no change is caused.

Impact Reduction

Where the significance of adverse impacts is lessened.

Impact Remedy

When an adverse effect is replaced with a more acceptable effect.


50

Mitigation Measures

The means by which decisions about a proposed development are modified to avoid, reduce or

remedy the adverse environmental effects that are identified.

Monitoring

The repetitive and continued observation, measurement, analysis and evaluation of

environmental data to follow changes over a period of time, to assess natural conditions, the

impact of activities and the efficiency of control measures.

Pollution

Any release to the environment which has a subsequent adverse effect on the environment or

man.

Precautionary Principle

The theory that the absence of complete information should not preclude precautionary action

to mitigate the risk of significant harm to the environment.

Reasonably Foreseen

A working assumption about the future that assumes that a project will be developed as

planned and used within a receiving environment that will change in accordance with currently

evident trends. It will include a consideration of the likelihood and consequences of abnormal

occurrences - such as accidents.

Receptor

Any element in the environment which is subject to impacts.

Residual impacts

Those impacts that remain following the implementation of the mitigation measures proposed

Risk Assessment

An analytical study of the probabilities and magnitude of harm to human health or the

environment associated with a physical or chemical agent, activity or occurrence.

Scoping

The process of identifying the significant issues which should be addressed by a particular

Environmental Impact Assessment.

Screening

The process of assessing the requirement of a project to be subject to Environmental Impact

Assessment based on project type and scale and on the significance or environmental sensitivity

of the receiving environment.

Sensitivity

The potential of a receptor to be significantly changed.

Significance

The sensitivity of a receiving environment to change or the consequence of change for the

receiving environment.


51

Sustainable Development

Defined by the Brundtland Commission 1987 "Development that meets the needs of the

present without comprising the ability of the future generation to meet their own needs".

Threshold

The magnitude of a project which, if exceeded, will trigger the requirement for an

Environmental Impact Assessment to be carried out.

10. Glossary of Impacts

Quality of Impacts

Positive Impact

A change which improves the quality of the environment (for example, by increasing species

diversity; or the improving reproductive capacity of an ecosystem, or removing nuisances or

improving amenities).

Neutral Impact

A change which does not affect the quality of the environment.

Negative Impact

A change which reduces the quality of the environment (for example, lessening species diversity

or diminishing the reproductive capacity of an ecosystem; or damaging health or property or by

causing nuisance).

Significance of Impacts

Imperceptible Impact

An impact capable of measurement but without noticeable consequences.

Slight Impact

An impact which causes noticeable changes in the character of the environment without

affecting its sensitivities.

Moderate Impact

An impact that alters the character of the environment in a manner that is consistent with

existing and emerging trends.

Significant Impact

An impact which, by its character, magnitude, duration or intensity alters a sensitive aspect of

the environment.

Profound Impact

An impact which obliterates sensitive characteristics.

Duration of Impacts

Short-term Impact

Impact lasting one to seven years.


52

Medium-term Impact

Impact lasting seven to fifteen years.

Long-term Impact

Impact lasting fifteen to sixty years.

Permanent Impact

Impact lasting over sixty years.

Temporary Impact

Impact lasting for one year or less.

Types of Impacts

Cumulative Impact

The addition of many small impacts to create one larger, more significant, impact.

‘Do Nothing Impact’

The environment as it would be in the future should no development of any kind be carried out.

Indeterminable Impact

When the full consequences of a change in the environment cannot be described.

Irreversible Impact

When the character, distinctiveness, diversity or reproductive capacity of an environment is

permanently lost.

Residual Impact

The degree of environmental change that will occur after the proposed mitigation measures

have taken effect.

Synergistic Impact

Where the resultant impact is of greater significance than the sum of its constituents.

`Worst case’ Impact

The impacts arising from a development in the case where mitigation measures substantially

fail.

11. References

Environmental Protection Agency, Guidelines on the information to be contained in

environmental impact statements, 2002.

London Borough of Camden, Camden Planning Guidance, Basements and Lightwells, July 2015

London Borough of Camden (Ove Arup & Partners Ltd), Camden geological, hydrogeological and

hydrological study, Guidance for subterranean development, November 2010


53

Appendix A

– Items to be submitted and reviewed as part of a Basement Impact Assessment


54

SECTION 1 – Basement Impact Assessment (BIA) Applicant and BIA Author Details – completed by Applicant

Before completing this form, please read the accompanying documents, “DCC Basement Development

Policy document" and the “DCC Basement Development Guidance document”.

This form is to be completed in BLOCK LETTERS:

Planning Ref. for Development: _____________________________________________

Development Address: _____________________________________________

Development Description: _____________________________________________

_____________________________________________

Applicant Name: _________________________________________________

Applicant Address: _________________________________________________

Applicant Contact Name: _________________________________________________

Applicant Contact Phone Number: Mobile; ________________________________

Office; _________________________________

Applicant Contact E-Mail: _________________________________________________

BIA Author Company: _______________________________________________

BIA Author Contact Name: _________________________________________________

BIA Author Contact Ph. No: Mobile; ________________________________

Office; _________________________________

BIA Author E-Mail: _________________________________________________

Note: Basement Impact Assessments are required to adhere to the “DCC Basement Development

Policy document” and are to be undertaken in accordance with the “DCC Basement Development

Guidance document”.


55

SECTION 2 – Basement Impact Assessment (BIA) Submission Check Sheet - completed by Applicant:

Items provided for Basement Impact Assessment (BIA)1

Item provided Yes, No or N/A2

Name of BIA document/appendix in which information is contained and/or comment

1 Description of proposed development. Choose an item.

2

Plan showing boundary of development

including any land required temporarily

during construction.

Choose an item.

3

Plans, maps and or photographs to show

location of basement relative to

surrounding structures.

Choose an item.

4

Plans, maps and or photographs to show

topography of surrounding area with any

nearby watercourses/waterbodies

including consideration of the relevant

maps in the FRA

Choose an item.

5 Plans and sections to show foundation

details of adjacent structures.

Choose an item.

6 Plans and sections to show layout and

dimensions of proposed basement.

Choose an item.

7 Programme for enabling works,

construction and restoration.

Choose an item.

8

Identification of potential risks to land

stability (including surrounding structures

and infrastructure), and surface and

groundwater flooding.

Choose an item.


56

9

Assessment of impact of potential risks on

neighbouring properties and surface and

groundwater.

Choose an item.

10 Identification of significant adverse

impacts.

Choose an item.

11 Evidence of consultation with neighbours. Choose an item.

12

Ground Investigation Report and

Conceptual Site Model including

- Desktop study

- exploratory hole records

- results from monitoring the local groundwater regime

- confirmation of baseline conditions

- factual site investigation report

Choose an item.

13 Ground Movement Assessment (GMA). Choose an item.

14 Plans, drawings, reports to show extent of

affected area.

Choose an item.

15

Specific mitigation measures to reduce,

avoid or offset significant adverse

impacts.

Choose an item.

16

Construction Sequence Methodology

(CSM) referring to site investigation and

containing basement, floor and roof

plans, sections (all views), sequence of

construction and temporary works.

Choose an item.

17 Proposals for monitoring during

construction.

Choose an item.

18

Confirmatory and reasoned statement

identifying likely damage to nearby

properties according to Burland Scale

Choose an item.

19


with supporting evidence that the

structural stability of the building and

neighbouring properties will be

Choose an item.


57

maintained (by reference to BIA, Ground

Movement Assessment and Construction

Sequence Methodology), including

consideration of cumulative effects.

20


with supporting evidence that there will

be no adverse effects on drainage or run-

off and no damage to the water

environment (by reference to ground

investigation, BIA and CSM), including

consideration of cumulative effects.

Choose an item.

21 Identification of areas that require further

investigation.

Choose an item.

22 Non-technical summary for each stage of

BIA.

Choose an item.

Additional BIA components (added during

Review/Audit)

Item

provided

Yes , No or N/A2 Comment

Notes:

1 It is assumed that consideration of architectural character, impacts on archaeology, amenity and

other matters which are not covered by this checklist shall be incorporated elsewhere within the

applicant`s submission.

2 Where response is ‘no’ or ‘N/A’, an explanation is required in the Comment section.


58

Appendix B

– Ground Anchor Installation Licence (GAIL) Application Form

Roads Maintenance Services,

Floor 4, Block 2,

Civic Offices,

Wood Quay, Dublin 8.

Ph. (01) 222 2255

59

SECTION 1 – Ground Anchor Installation Licence Application Form Applicant Details

Before completing this form, please read the accompanying document "Ground Anchor Installation

Licence – Guidance Document"

This form is to be completed in BLOCK LETTERS:

Applicant Name: Click or tap here to enter text.

Applicant Address: Click or tap here to enter text.

Applicant Contact Name: Click or tap here to enter text.

Applicant Contact Phone Number: Mobile; Click or tap here to enter text.

Office; Click or tap here to enter text.

Applicant Contact E-Mail: Click or tap here to enter text.

Location of Anchor Installation: Click or tap here to enter text.

(Road / Street & Building Number)

Planning Ref. for Development: Click or tap here to enter text.

Ground Anchor/Structural Designer: Click or tap here to enter text.

Ground Anchor Designer Contact: Click or tap here to enter text.

Ground Anchor Designer Contact Ph. No: Click or tap here to enter text.

Ground Anchor Designer E-Mail: Click or tap here to enter text.

Number of Anchors to be installed: Click or tap here to enter text.

Period for which Licence is required: Click or tap here to enter text.

Public Liability Insurer & Policy No.: Click or tap here to enter text.

Minimum cover of €6.5 million, with specific indemnity to Dublin City Council

Note: The installation of a ground anchor into/beneath a public road/path without a Ground Anchor

Installation Licence is not permitted. Under Section 13 of the Roads Act (1993), any person to do so

shall be guilty of an offence.


Floor 4, Block 2,

Civic Offices,


Ph. (01) 222 2255

60

SECTION 2 – Ground Anchor Installation Licence Application Form Application Check Sheet

What must be submitted with a Ground Anchor Installation Licence Application Form?

The following items are required to be included as part of the GAIL application. An incomplete

application will result in delays. Please include and tick as appropriate. The Applicant is referred

throughout to a more detailed list of requirements as included in the "Ground Anchor Installation

Licence – Guidance Document".

Application Procedure for Installation of Ground Anchors: Submitted by

Applicant

Completed GAIL Application form (Section 1 & 2), with fee included and signed DECLARATION (as

per para. 3.1 & 3.2 of GAIL Guidance Document)

Choose an

item.

Details of anchor type, materials proposed, length of time required, detailed anchor drawings in plan

and section etc. (as per para. 3.3 & 3.4 of GAIL Guidance Document)

Choose an

item.

Detailed Section & Plan with location of anchors and existing utilities identified (as per para. 3.5 of

GAIL Guidance Document)

Choose an

item.

Anchor designer’s Risk Assessment Choose an

item.

Certification provided by Anchor Designer identifying available utility corridor (as per para. 3.6 of

GAIL Guidance Document)

Choose an

item.

Baseline survey and proposed monitoring system throughout “anchor support period” (as per para.

3.7 of GAIL Guidance Document)

Choose an

item.

Utilities have been contacted by the Applicant in advance (as per para. 3.8 of GAIL Guidance

Document)

Choose an

item.

Safety Statement and MS submitted, which incorporates the proposed anchor installation works and

which complies with all relevant Health & Safety Legislation (as per para. 3.10 & 3.11 of GAIL

Guidance Document)

Choose an

item.

Bond enclosed (rate per anchor, as per para. 3.13 of GAIL Guidance Document) Choose an

item.

Application only relates to installation of anchors in public domain only (as per para. 3.14 of GAIL

Guidance Document)

Choose an

item.


Floor 4, Block 2,

Civic Offices,


Ph. (01) 222 2255

61

All relevant statutory utilities to be advised 7 days in advance of any anchor installation taking place

(as per para. 4.1 of GAIL Guidance Document)

Choose an

item.

Proof of DCC indemnity submitted by Applicant (period from start of works through until one year

after end of “anchor support period” (as per para. 4.2 of GAIL Guidance Document)

Choose an

item.


Floor 4, Block 2,

Civic Offices,


Ph. (01) 222 2255

62

SECTION 3 – Ground Anchor Installation Licence Application Form End of Anchor Support Period – Check Sheet

What Must be Submitted at Expiry of “Anchor Support” Period?

At the end of the licensed “anchor support” period (decommissioning of anchors) the following

documentation and submission confirmation is to be submitted to the DCC Road Maintenance

Department. The Applicant is referred to a more detailed list of requirements as included in the

"Ground Anchor Installation Licence – Guidance Document".

Expiry of GAIL Licence (end of “Anchor Support Period): Submitted by

Applicant

Confirmation that DCC Roads Maintenance have been informed of date for

decommissioning of anchors (as per para. 5.2 of GAIL Guidance Document)

Choose an item.

Design Certificate submitted by anchor Designer and signed by Chartered Engineer

confirming that for all anchors installed the entire anchor length is no longer

structurally required and has been de-commissioned and de-stressed (if applicable).

The anchor headblock securely capped or buried

Choose an item.

As constructed detailed drawings are to be provided to DCC Roads Maintenance

Department showing the location and details of installed anchors in plan and in section

with additional information provided for all materials used (as per para. 5.4 of GAIL

Guidance Document)

Choose an item.

Final monitoring survey submitted (as per para. 5.5 of GAIL Guidance Document) Choose an item.

Signature of Applicant: __________________________________ Date: ___________

Print Name of Applicant: ___________________________________

Signature of Anchor Designer: __________________________________ Date: ___________

Print Name of Anchor Designer: ___________________________________


Floor 4, Block 2,

Civic Offices,


Ph. (01) 222 2255

63

SECTION 4 – Declaration

I hereby apply for approval for a Ground Anchor Installation Licence (GAIL) and agree to be bound by

the conditions as listed in the "Ground Anchor Installation Licence – Guidance Document", the “GAIL

Application Form” and any specific conditions imposed by Dublin City Council.

I agree to comply with the provisions of the submitted, anchor design, installation methodology and

proposed materials, end of “anchor support period” requirements and submit all documentation, as

per Section 1, 2 & 3 of this application, to the satisfaction of DCC.

This licence pertains only to the installation of ground anchors. Separate discussions requiring the

opening and reinstatement of the public road / footpath / Park Area etc. must be held with and

permissions obtained from the relevant departments of Dublin City Council.

For clarity Section 1, 2 and 4 of this application along with the relevant documentation are to be

submitted 8 weeks prior to the issuing of the Commencement Notice or the commencement of

construction, whichever is the earlier. Section 3 of this form is to be submitted along with the relevant

documentation at the end of the “anchor support period”.

In addition to complying with the requirements of the DCC published “Ground Anchor Installation

Licence – Guidance Document” I also hereby agree to:

Liaise with Dublin City Council’s Roadworks Control Unit in the planning and execution of the

works and to fully comply with the "Directions for the Control and Management of Roadworks

in Dublin City" as issued by them.

Maintain the roadway and/or footpath to the specification of Dublin City Council’s Roads

Maintenance Services all of which is included in the Directions for the Control and

Management of Roadworks in Dublin City.

Lodge the required Licence Fee payable to Dublin City Council with Roads Maintenance

Services, Floor 4, Block 2, Civic Offices, Dublin 8, with the licence application. The licence fee

incorporates both the cost of inspection of anchor installation, removal and associated

administration costs.

Apply for a Road Opening Licence if excavation in the public domain if required.

The GAIL only becomes effective when approved by a representative from DCC Roads

Maintenance Services.

Indemnify and save harmless the Council (with minimum indemnity of €6,500,000.00 for any

one claim in respect of all claims, proceedings, liabilities, losses or expenses of whatever

nature, howsoever arriving in connection with the activities covered by this application.) The

period of cover shall be from the start of the works through until taking back in charge by DCC.


Floor 4, Block 2,

Civic Offices,


Ph. (01) 222 2255

64

Take charge of the defence of any proceedings as aforesaid at the request of the Council.

The applicant must give written notification to the Area Engineer on completion of the works,

at which point an inspection of the works will be carried out and items as per Section 3 of the

GAIL Application are submitted.

Signature of Applicant: __________________________________ Date: ___________

Print Name of Applicant: ___________________________________

Signature of Anchor Designer: __________________________________ Date: ___________

Print Name of Anchor Designer: ___________________________________

For Office Use Only

Total Fee Received: ______________________

Approved: _____________________________ Date: _______________________________

65

Appendix C

– Ground Anchor Installation Licence (GAIL) Guidance Notes

66

Ground Anchor Installation Licence (GAIL) – Guidance Notes:

1. Introduction

Dublin City Council acting in its statutory role as the Roads Authority has decided to establish

standards, protocols and procedures to cover the issuing of licences to third parties who wish to install

ground anchors or similar structural support devices under or within areas, lands, roads, public domain

etc. under the ownership or control of DCC.

These standards, protocols and procedures have been adopted by Order of the City Engineer and are

available to view in full on the Dublin City Council website, together with details of how to apply for

the requisite licence.

2. Standards Specified by Roads Authority

In order to preserve the availability of space under roads for maintenance or installation of existing or

future services the DCC Environment & Transportation (E & T) Department will only consider

applications for the installation of temporary ground anchors (referred to as ‘ground anchors’ in this

guidance document) under areas/lands in its charge. The anchors shall be designed and constructed

as a temporary structural support and only be required to have a structural role for a clearly defined

period (the “anchor support period”). This “anchor support period” is limited to a point in time where

the permanent works are constructed and the structural support provided by ground anchors is no

longer required.

Ground anchors must be capable of being easily broken/cut if required in the future e.g. a Glass Fibre

Reinforced Plastic (GFRP) anchor.

Ground anchors shall be constructed and such measures taken following construction as are required

so that, immediately following the conclusion of the “anchor support period”, normal excavations,

whether by open cut trenches, tunnelling or directional drilling or any other method of excavation can

be carried out safely and without any obstruction or additional risk or cost arising from the presence

of the ground anchors.

3. Application Procedure for Installation of Ground Anchors:

3.1 All applications for a Ground Anchor Installation Licence (GAIL) must be made by the Developer

of the site in whose name the Planning Permission has been granted or their Agent (the

Applicant).

3.2 All Applicants must complete a GAIL Application Form. A minimum fee of €500 is payable with

each application. A separate application must be made for each road affected. If it is proposed

to excavate the road surface a Road Opening Licence Application must be submitted to DCC.

The GAIL application form must be submitted to DCC Roads Maintenance Department 8 weeks

67

prior to the issuing by the Developer of the Commencement Notice or the commencement of

construction, whichever is the earlier.

3.3 Full details of the type of anchor proposed, materials to be used etc., and the length of time the

anchors are required as a structural support are to be submitted as part of the application. If

steel couplers are required to be installed within the anchor bond length the coupler location

should be staggered.

3.4 Accurate and detailed drawings are to be provided showing location of proposed anchors in

plan and in section with XYZ Coordinates of the anchor head, toe, coupling location, top and

base of bonded length and type of bonded length provided.

3.5 Detailed cross section and plan, showing proposed anchors and clearances to existing services

are to be submitted showing:

Location, levels and diameter of all existing services (when required these cross-

sections should be verified on site by trial holes and witnessed by relevant

statutory utility staff. A Road Opening Licence is required for excavation of trial

holes.)

Location and angle of installation of proposed ground anchors and clearances

horizontal and vertical relative to existing services.

Cross sectional area and longitudinal extent, with XYZ coordinates, indicating an

available corridor within the road-space which may be excavated/tunnelled

through if necessary during the period when the anchors are structurally required.

3.6 The Application shall be accompanied by a Certificate, signed by a Chartered Structural Engineer

or Chartered Geotechnical Engineer or appropriately qualified person, stating that the corridor

identified in para. 3.5, above, is available for use by a third party for excavation/tunnelling

purposes during the anchor support period. The Certificate shall confirm that excavation within

this corridor can take place without any impact on the required performance of the anchor.

Contact details of the anchor designer should be provided as part of the application for which

any correspondence relating to a proposed excavation of a public area where anchors are

installed and still structurally required can be directed.

3.7 The applicant is to develop a baseline topographic survey encompassing the public area where

the anchors are proposed to be installed. Subsequent and in addition to the approved baseline

survey the applicant is required to establish a suitable monitoring system which is to be

maintained throughout the course of the “anchor support period”. The survey and monitoring

proposals are required to be submitted to DCC in advance as part of the application process.

3.8 Confirmation by the Applicant that all the relevant Utilities have been contacted and agreement

reached regarding the proposal in advance of license application. Please note that Utility

Providers may have detailed requirements in this regard including submission of a bond and/or

indemnities, supervision of works, etc.

68

3.9 DCC does not accept any responsibility for establishing/verifying the ground conditions in the

public domain. All design information relating to ground conditions located in the public domain

are the responsibility of the Applicant.

3.10 The Applicant is to confirm that that there is a valid Safety Statement in place, which

incorporates the proposed anchor installation works and which complies with all relevant

Health & Safety Legislation. The Safety Statement should identify the relevant parties, their

registered offices and it should be signed by an authorised person, with their name and position

within the company identified.

3.11 A detailed method statement should be submitted demonstrating that an appropriate system

is proposed for installation of the anchors which ensures that there is no negative impact or

disturbance to existing infrastructure / structures / property etc.

3.12 Notwithstanding the submission of details as requested, an application for a Ground Anchor

Installation Licence (GAIL) may be refused, where, in the view of the E&T Department the

installation of ground anchors may have an adverse impact in terms of safety and /or cost on

the maintenance or installation of existing or future services in the road.

3.13 A fee of €1,000 per anchor must be lodged with the DCC Road Maintenance Services as part of

the GAIL application prior to works commencing.

3.14 The Ground Anchor Installation Licence relates only to the public domain and lands/areas under

the ownership or control of DCC. The GAIL does not provide or imply permission to install

ground anchors in any other property.

4. Applicant Requirements during GAIL Period (“anchor support period”):

4.1 All relevant statutory utilities (i.e. services which have been identified as per para. 3.5) are to

be advised 7 days in advance of any anchor installation taking place.

4.2 The Applicant shall Indemnify and save harmless the Roads Authority (with minimum

indemnity of €6,500,000 for any one claim in respect of all claims, proceedings, liabilities, loses

or expenses of whatever nature, howsoever arriving in connection with the activities covered

by this application). The period of cover shall be from the start of the ground anchor installation

works through until one year after Applicant has fully completed installation and

decommissioning of all ground anchors (i.e. one year after expiry of “anchor support period”).

4.3 Any persons wishing to excavate a road where anchors have already been installed and remain

structurally required (as per approved GAIL details) shall be referred by DCC Road Maintenance

Services to the anchor Design Engineer (whose details are submitted as part of the GAIL

application). The anchor Design Engineer is required to assess the risk in undertaking the

proposed excavation works and provide guidance and direction to the relevant party, with no

fee required. This assessment should also be provided to DCC Road Maintenance Services so

that they are aware of the anchor designer`s review of the proposed works.

69

4.4 Drilling logs and anchor design drawings shall be made available to the DCC Road Maintenance

Services upon request. These logs are to include full details in respect of anchors installed

including, installation time, date, location, length, volume of grout used etc. (as per relevant

guidance documents and standards).

4.5 The applicant is required to monitor, record and report to DCC Roads Maintenance Services (or

other relevant DCC department) any ground movement and /or disturbances to the public road

where anchors have been installed. A baseline grid survey should be established in advance of

works taking place, as outlined in para. 3.7. Routine and regular checks of the grid should be

undertaken thereafter, particularly during and directly after drilling has taken place, as per para.

3.7. The installation of an inclinometer may be applicable in certain cases (as advised with

guidance from the anchor Design Engineer or to be installed as required on instruction by Road

Maintenance Services).

5. Expiry of GAIL (end of “anchor support period”):

5.1 Any extension of the Licence is at the discretion of the Roads Authority and will be subject to

an additional application process.

5.2 At the end of the “anchor support period” (strands and/or bars) are to be decommissioned and

de-stressed (if applicable). The DCC Roads Maintenance Department shall be informed 1 week

in advance so that they can attend and witness the process. A Design Certificate is to be

submitted by the Applicant’s anchor Designer confirming that, for all anchors installed, the

entire anchor length is no longer structurally required and has been fully decommissioned and

de-stressed (if applicable). This certificate must be signed by a Chartered Structural Engineer

or Chartered Geotechnical Engineer and submitted to DCC Roads Maintenance.

5.3 Once the cuttable anchor has been decommissioned and any remaining steel strand removed,

the headblock shall be immediately securely capped or buried within the completed structure.

This is to ensure that the redundant anchor pre-stressed free length cannot remove itself in the

event the anchor is cut at a later date. The presence of the headblock is to be confirmed by the

Anchor Designer as part of the Design Certificate.

5.4 As constructed detailed drawings are to be provided to the DCC Roads Maintenance

Department (or other relevant DCC department) showing the location and details of installed

anchors in plan and in section with additional information provided for all materials used.

5.5 Once the anchors have been decommissioned and removed from service a final survey is to be

undertaken (similar to that as detailed in para. 3.7) and submitted to DCC Road Maintenance

Services. This survey is to be submitted within 2 months of the end of the anchor support

period.

5.6 The deposit fee of €1,000 per anchor will only be refunded when all items outlined in this

document have been submitted and are deemed satisfactory to DCC Road Maintenance

Services.

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Appendix D

– Cumulative Effects of Basement Construction

71

Cumulative Effects of Basement Construction;

The cumulative effect - if any - of several underground developments in a given street could potentially

differ from the impact of the initial single basement. It is therefore appropriate for the Planning

Authority to consider the layout and proximity of existing basements and/or where multiple

basements are proposed. It should again be noted that Appendix D1 is a schematic that assumes a

homogeneous aquifer with isotropic hydrogeological properties;

The shape of the structure in relation to the groundwater flow direction and soil strata

should be considered to assess whether any damming effect could potentially arise.

If the basement is to be constructed perpendicular to the flow of groundwater it shall

have the greatest impact.

Appendix D1 (Scenario B1, B2 and B3) illustrates the principle of groundwater flow

around a single basement structure. The diversion of flow paths around the basement

structure leads to an increase in groundwater levels upstream, and a similar reduction

in groundwater levels downstream.

Appendix D1 (Scenario C1, C2 and C3) demonstrates the effect of several basements

acting cumulatively. Scenario C provides a notional example where a one house width

gap is always present between adjacent basements. Groundwater flows through the

gaps between basement structures and is prevented from passing beneath the houses

with new basements. The effect is an increase in groundwater levels upstream of the

structures, and a decrease downstream.

For hydraulic cut-off structures such as sheet piles, the purpose of which is to form a

barrier to groundwater flow. In the notional case shown in Appendix D1 (Scenario C1,

C2 and C3) the space remaining open between buildings, as a proportion of the

original flow channel, is approximately 40%. The flow velocity through the narrowed

channel will be higher than before, which might conceivably result in piping and

subsurface erosion of loose sandy material if this is present, but the greater impact

will be to the groundwater levels. The higher flow velocity is due to the increased

hydraulic gradient resulting from the rise in water levels upstream, and lowering

downstream of the row of basements.

The change in water levels could be assumed to be in proportion to the increase in

the length of the flow path. In the case of a site measuring 10m in the direction of

groundwater flow, the natural difference in groundwater level might be one or two

centimetres. Introducing a basement of dimension 10m by 10m will increase the flow

path from 10m before to approximately 20m.

Where several basements effectively act as a single barrier to groundwater flow such

as in Appendix D1 (Scenario D1,D2 and D3) the impact will be larger. In this case the

water will be forced to follow a longer flow path, with greater energy loss as a

consequence, and therefore the changes in groundwater levels upstream and

downstream will be greater.

The extent to which the cumulative effects of basements may impact groundwater

flow and levels is likely to depend on the properties of the aquifer materials. In highly

permeable formations groundwater flow can easily be diverted around basements,

and will not ultimately lead to a groundwater level rise upstream of the basement.

72

Therefore, a single basement in extensive sand and gravel deposits is unlikely to have

a significant impact, whereas a single basement blocking a narrow linear gravel

deposit with clay in either side, will have a very significant impact.

Detail of groundwater flows due to cumulative effects shall need to be accounted for

in the basement design. In order to make basement construction fair and equitable

for all parties the Planning Authority shall require a Hydrogeological Assessment of

the site to determine the extent of existing groundwater passing through the site pre-

development (relative to depths etc.). Each development shall then be required to

account for the groundwater flows and volumes of groundwater below and through

their own site ensuring that there shall be minimal change to the groundwater flows,

levels and volumes post-completion of the works when compared to the pre-

development scenario. These proposals should be described in detail within the BIA.

Details of the required seasonal monitoring and site investigation required to record

the required relevant data is detailed further later in this document.

73

Appendix D1 – Cumulative effects of basement construction

74

Appendix E

– Noise and Air Quality – “Construction and Demolition Good Practice Guide”

75

Air Quality Monitoring and Noise

Control Unit’s Good Practice Guide

for Construction and Demolition

Prior to the commencement of work on the site a construction and demolition plan must be

developed. When developing the construction and demolition plan reference must be made

to the requirements of the Air Quality Monitoring and Noise Control Unit’s Good

Practice Guide for Construction and Demolition.

This Guide has been produced with reference to the London Good Practice Guide:

Noise and Vibration Control for Demolition and Construction produced by the London

Authorities Noise Action Forum, July 2016.

76

In order to ensure that demolition and construction work does not have an adverse impact

on those living and working nearby, the following best practice guidance has been

developed. All construction and demolition work has the potential to have adverse

environmental impacts no matter what the scale. The following best practice guide sets out

the measures which all developers should consider prior to commencement of work and

provides further recommendations for the control of noise, vibration and air pollution.

A risk based approached is to be used taking into account the locality, nature of the work

and the expected duration of the work.

Risk Assessment A – Locality/Site Information

The site should be assessed in relation to the duration of the work, distance to sensitive

receptors, ambient noise levels and working hours. Tick the field most likely to apply and add

up the number of ticks in each column.

Risk Assessment B - Work Information

Tick the field that is most likely to represent the works in each category, add up the total

number of ticks in each column.

Total Risk Assessment

The table ‘total risk assessment’ contains the sub-total numbers from ‘Risk Assessment A

and B. The column in total risk assessment with the most ticks indicates the risk category

that should be employed for the site.

If two risk categories have an equal number of ticks, the higher category of the two shall

apply. Once the risk category is known the ‘good practice measures’ outlined in this code of

practice shall be employed.

77

1. Locality

Identify those who may be affected by noise, including particularly sensitive locations

(hospitals/schools) and determine ambient noise levels (noise maps or noise

monitoring)

Low Medium High

Expected duration of work

Less than 6 months

6 months to 12 months

Over 12 months

Proximity of nearest sensitive receptors

Greater than 50 metres from site

Between 25m and 50m

Less than 25 metres

Hospital or school within 100 metres

Day time ambient noise levels

High ambient noise levels (>65dB(A))

Medium ambient noise levels (55-65dB(A)

Low ambient noise levels (<55dB(A)

Working Hours

7am – 6pm Mon-Fri; 8am-1pm Sat

Some extended evening or weekend work

Some night time working, including likelihood of concrete power floating at night

SUBTOTAL A

78

2. Work information

Low Medium High

Location of works

Majority within existing building

Majority External

External Demolition

Limited to two weeks

Between 2 weeks and 3 months

Over three months

Ground Works

Basement level planned

Non-percussive methods only

Percussive methods for less than 3 months

Percussive methods for more than 3

months

Piling

Limited to one week

Bored Piling Only

Impact or vibratory piling

Vibration generating activities

Limited to less than 1 week

Between 1 week and 1 month

Greater than 1 month

SUBTOTAL B

79

Low Medium High

Risk Assessment A

Risk Assessment B

Total

The column in total risk assessment with the most ticks indicates the risk category that

should be employed for the site.

80

1. General Considerations

All site staff shall be briefed on noise mitigation

measures and the application of best

practicable means to be employed to control

noise.

All sites

Good Quality site hoarding should be erected to

maximise the reduction in noise levels

Medium and High risk sites

The contact details of the contractor and site

manager shall be displayed to the public,

together with the permitted operating hours,

including any special permissions given for out

of hours work


The site entrance shall be located to minimise

disturbance to noise sensitive receptors


Internal haul routes shall be maintained and

steep gradients shall be avoided


Material and plant loading and unloading shall

only take place during normal working hours

unless the requirement for extended hours is for

traffic management(i.e road closure) or health

and reasons(application must be made to DCC

a minimum of 4 days prior to proposed works)

All sites

Use rubber linings in chutes, dumpers and

hoppers to reduce impact noise

High risk sites

Minimise opening and shutting of gates through

good coordination of deliveries and vehicle

movements


No materials shall be burned on site All sites

Adequate dust/debris screening should be in

place at the site boundary to contain and

minimise the amount of windblown dust. This

must be maintained in good condition at all

times.

Medium and High Risk sites

All consignments containing material with the

potential to cause air pollution being transported

by skips, lorries, trucks or tippers must be

covered during transit on and off site.

All sites

81

The site shall be dampened down as necessary

to minimise windblown dust when necessary or

during periods of dry weather.

All sites

Dust suppression equipment must be used

when point source emissions are likely.

All sites

The entry and exit points to the site should be

constructed of hard standing which is regularly

dampened to minimise dust emissions.

Medium and High Risk Sites

2. Plant

Ensure that each item of plant and equipment

complies with the noise limits quoted in the

relevant European Commission Directive

2000/14/EC

All sites

Fit all plant and equipment with appropriate

mufflers or silencers of the type recommended

by the manufacturer

All sites

Use all plant and equipment only for the tasks

for which it has been designed

All Sites

Shut down all plant and equipment in

intermittent use in the intervening periods

between work or throttle down to a minimum

All sites

Power all plant by mains electricity where

possible rather than generators


Maximise screening from existing features or

structures and employ the use of partial or full

enclosures for fixed plant


Locate movable plant away from noise sensitive

receptors

All sites

3. Vehicle activity

Ensure all vehicle movements (on site) occur

within normal working hours. (other than where

extension of work requiring such movements has

All sites

82

been granted in cases of required road closures

or for health and safety reasons )

Plan deliveries and vehicle movements so that

vehicles are not waiting or queuing on the public

roads. If unavoidable engines should be turned

off.


Minimise the opening and closing of the site

access through good coordination of deliveries

and vehicle movements


Plan the site layout to ensure that reversing is

kept to a minimum


Where reversing is required use broadband

reverse sirens or where it is safe to do so

disengage all sirens and use banks-men


Rubber/neoprene or similar non-metal lining

material matting to line the inside of material

transportation vehicles to avoid first drop high

noise levels.


Wheel washing of vehicles prior to exiting the site

shall take place to ensure that adjoining roads

are kept clean of dirt and debris. Regular

washing of adjoining streets should also be

carried out by the developer, as required by

mechanical road sweepers


4. Demolition Phase

Employ the use of acoustic screening; this can

include planning the demolition sequence to

utilise screening afforded by buildings to be

demolished.


If working out of hours for Health and Safety

reasons (following approval by DCC) limit

demolition activities to low level noise activity

unless absolutely unavoidable)

All sites

83

Use low impact demolition methods such as

non-percussive plant where practicable


Use rotary drills and ‘bursters’ activated by

hydraulic or electrical power or chemically

based expansion compounds to facilitate

fragmentation and excavation of hard material.

High Risk sites

Avoid the transfer of noise and vibration from

demolition activities to adjoining occupied

buildings through cutting any vibration

transmission path or by structural separation of

buildings


Consider the removal of larger sections by lifting

them out and breaking them down either in an

area away from sensitive receptors or off site.

High Risk Sites

5. Ground Works and Piling Phase

The following hierarchy of groundwork/piling

methods should be used if ground conditions,

design and safety allows:

pressed in methods, e.g., hydraulic jacking

Auger/bored piling

Diaphragm walling

Vibratory piling or vibro-replacement

Driven Piling or dynamic consolidation


The location and layout of the piling plant should

be designed to minimise potential noise impact of

generators and motors


Where impact piling is the only option utilise a non-

metallic dolly between the hammer and driving

helmet or enclose the hammer and helmet with an

acoustic shroud


Consider concrete pour sizes and pump locations.

Plan the start of concrete pours as early as

possible to avoid overruns


Where obstructions are encountered, work should

be stopped and a review undertaken to ensure that

work methods that minimise noise are used.


84

When using an auger piling rig do not dislodge

material from the auger by rotating it back and

forth. Use alternate methods where safe to do so.


Prepare pile caps using methods which minimise

the use of breakers, e.g., use hydraulic splitters to

crack the top of the pile.


6. Monitoring

Establish pre-existing levels of ambient noise by

baseline monitoring or use of the noise maps.


Carry out regular on site observation monitoring

and checks/audits to ensure that BPM is being

used at all times. Such checks shall include;

Hours of work

Presence of mitigation measures

Number and type of plant

Construction methods

Site reviews must be recorded and made available

for inspection

High Risk Sites

Monitor noise and vibration continuously during

demolition, piling, excavation and sub and

superstructure works at agreed locations and

report to DCC at agreed intervals and in an agreed

format.

To comply with this the following must take place.

The monitoring locations for existing sites as

agreed with officers of Dublin City Council must

remain in situ. If additional monitoring is required

this will be provided and the new locations will be

agreed with Dublin City Council. For all new sites

the monitoring locations must be agreed with

Dublin City Council.

High Risk Sites

85

The results of the monitoring must be forwarded to

officers of the Air Quality Monitoring and Noise

Control Unit every two weeks in the following

format:

Provide the construction noise level as defined in British Standard 5228 and the peak particle velocity readings for the hours of operation of the site. This will include the construction noise level for any overtime period worked outside of normal working hours. Provide a report detailing and discussing the noise and vibration levels over the reporting period. If a breach is recorded the follow up action that took place to prevent any further breaches must be included in the report.

This information must be provided in electronic format If results are required owing to complaints the results will be provided as soon as possible by the contractor to Dublin City Council.

Appraise and review working methods, processes

and procedures on a regular basis to ensure

continuous development of BPM


The ‘ABC’ Method detailed in Paragraph E.3.2 of

BS 5228-1:2009 shall be used to determine

acceptable noise levels for day, evening and night

time work.


Vibration levels must be kept below 1.0 mm/sec

(PPV) where possible. Where levels are expected

to exceed this value residents must be warned and

an explanation given.


Appropriate dust suppression must be employed to

prevent fugitive emissions affecting those

occupying neighbouring properties or pathways

All sites

Street and footpath cleaning must be undertaken

during the demolition and ground works phase to

minimise dust emissions


Continuous dust monitoring along the site

boundary should be undertaken during any

demolition or ground works

High Risk Sites

7. Communication and Liaison

86

A Community Liaison Plan should be developed by

the developer in consultation with local

residents/businesses and a single point of contact

nominated to engage with Dublin City Council and

the residents/businesses and to handle complaints

and communication of site information. A copy of

this plan must be sent to Dublin City Council

Planning Department as a matter of urgency in the

case of sites where development has already

commenced and 14 days in advance of

commencement of works for any other site


Contact details for the site manager and liaison

officer should be displayed prominently on the site

hoarding


All staff should be briefed on the complaints

procedure and the mitigation requirement and their

responsibilities to register and escalate complaints

received.


Send regular updates at appropriate intervals to all

indentified affected neighbours/ businesses via a

newsletter and post relevant information on the site

hoarding. Also make the information available via

email/website including weekly noise monitoring

reports


Arrange regular community liaison meetings at

appropriate intervals including prior to

commencement of the project.

High Risk Sites

Meet regularly with neighbouring construction sites

to ensure activities are coordinated to minimise

any potential cumulative issues.

High Risk Sites

Extensions of Working Hours in exceptional circumstances

Ensure at least 4 days notice is given to Dublin

City Council Planning Department when applying

for extensions to normal working hours. Do not

undertake out of hours work unless permission to

do so has been granted.

All sites

87

The applicant must demonstrate in writing that

the works required cannot be carried out during

normal working hours. The documentation sent

in must be accompanied by a detailed

engineering or/and traffic management or/and

safety case as to why the works are required

outside normal hours.

Power floating after 6pm is the only activity that

will be permitted during the extensions where

they relate to required large concrete pours. All

reasonable and appropriate measures to

minimise noise associated with these works must

be put in place and no works other than those

approved may be carried out during extended

working hours.

The Developer/his agent must give the times and

dates of the proposed work, and the mitigation

measures that are to be used to minimise

noise/disturbance

All sites

Advise neighbours about requirement for and

duration of any permitted works outside of

normal working hours, and associated

environmental mitigation measures being put in

place during the course of the extended works,

following receipt of approval from DCC

All sites

All complaints will be referred directly to the site

liaison person and a reply must issue to the

complaint within 3 hours of receipt of the

complaint.

All sites

A log of all complaints and a summary of how

they were dealt with should be kept and be made

available to DCC, as required

All sites

Any breaches of permitted working hours or

permitted extended working hours or developers

or subcontractors not carrying out their

requirements under this protocol may lead to

enforcement action and may also result in the

withdrawal of any extension of hours of works for

a period that will be at the discretion of Dublin

City Council.

All sites