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TABLE OF CONTENTS

1. INTRODUCTION ....................................................................................................... 1

2. LEGAL OBLIGATIONS.............................................................................................. 1

2.1 STATUS QUO ON THE MANDATE OF THE CGS .................................................... 1

2.2. RESPONSIBILITIES OF LOCAL AUTHORITIES AND COMPETENT PERSONS..... 3

3. DOLOMITE STABILITY INVESTIGATIONS............................................................... 5

4. MINIMUM REPORTING REQUIREMENTS ............................................................... 6

5. APPROPRIATE DEVELOPMENT IN RELATION TO RISK CHARACTERISATION 19

5.1 Development principles............................................................................................ 20

5.2 Development Type and Density ............................................................................... 21

6. NEW DEVELOPMENTS IN THE APPROACH BY THE CGS .................................. 25

6.1 Dolomitic Groundwater management, control and influence on development .......... 25

6.2 Submission of report, B4 certificate and CGS comments to the NHBRC................. 26

6.3 Site Development Plans and CGS support for Township Establishment .................. 26

6.4 Change in CBD Cityscape in Centurion ................................................................... 26

6.5 Density Exceedence and Transient Densities .......................................................... 27

6.6 CGS GIS data searches .......................................................................................... 28

6.7 Subdivisions, second dwellings, and land use changes ........................................... 28

6.8 Footprint Investigations............................................................................................ 29

6.9 Investigation Presentation to the CGS ..................................................................... 30

7. PRICING STRUCTURE FOR REVIEW OF SITES ON DOLOMITE FROM JANUARY

2008 ........................................................................................................................ 31

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1. INTRODUCTION

The Council for Geoscience (CGS) last made public its approach to development on

dolomite in October 2004, with the intention of communicating new developments on a

regular basis. Having witnessed various developments and having formulated opinions

on these, the CGS finds it appropriate to present these in a 2007 update. Current

practical considerations at the CGS dictate that its level of involvement in guidance,

assessment and responding to submissions from Competent Persons needs to be

downscaled. In this regard Competent Persons are encouraged to do comprehensive

presentations upon submission of their reports, which should likewise be comprehensive

and complete and address all pertinent issues required by the standards. Progressive

engagement between CGS and Competent Person in a phased approach is no longer

feasible and it is necessary that Competent Persons take greater responsibility in getting

things right the first time. The CGS’ task will be to shortly and succinctly indicate

compliance or non-compliance with the standard. The CGS trusts that the documentation

that follows provides adequate coverage of requirements in this regard.

2. LEGAL OBLIGATIONS

2.1 STATUS QUO ON THE MANDATE OF THE CGS

The CGS recently approached legal council to review its mandate and powers. The

investigation concluded that:

1. The CGS has no regulatory duty.

2. The Geoscience Act requires CGS to advise government institutions and the

general public on the judicious and safe use of land.

3. Specialised geoscientific advice/services must be provided upon request. This

function is obligatory (i.e. non-discretionary).

4. The CGS acts as national custodian of geoscientific information in order to

develop an integrated collection of geological knowledge. As such it may have

geoscientific information that should be made available in the public interest, as

and when required.

5. The CGS is impartial as it derives no benefit from whether a development is

approved or not. The CGS is able to act without any fear or favour and must be

seen to act in the interest of the public.

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6. The CGS cannot be held liable for losses or damages suffered by any party due

to advice given/geoscientific services rendered provided it has acted reasonably

and in the interest of public safety.

7. All geotechnical reports lodged with the CGS in pursuance of Authority approval

becomes available to public scrutiny.

The need for a regulator is particularly apparent to the Department of Public Works’

National Dolomite Risk Management Working Committee (NDRMWC), of which the CGS

forms part. Other stake holders include Local Authorities, Department of Housing,

Department of Planning and Local Government, and the National Home Builders

Registration Council (NHBRC).

The Department of Public Works, together with Standards South Africa, is in the process

of preparing a SANS document which will define how development on dolomite land

must be managed. Standards South Africa (formerly SABS) prepares industry standards

for a range of applications. The bringing into existence of a South African National

Standard for Development of Dolomite Land (SANS 1936) alleviates the problem of

incongruent approaches to the development of dolomite land.

At least until such time as the SANS 1936 becomes applicable, the CGS will continue to

engage with consultants on dolomite sites in accordance with the terms set in this

document.

The NHBRC‘s objectives, are amongst others, to regulate the home building industry and

to improve structural quality in the interest of housing consumers and the home building

industry on a national level. The NHBRC has published a manual in terms of which all

housing developments must conform. According to this manual, in the case of proposed

residential developments on dolomite, a dolomite stability report must be submitted to

the CGS for its confirmation that (a) the investigations concluded on the stability of the

land referred to in the report is in its opinion consistent with sound provisional practice,

and (b) the investigations meet all legal requirements pertaining to such stability

investigations. In the absence of the CGS confirming the aforementioned, the NHBRC is

entitled not to allow the home builder to build his dwelling in terms of the proposed

application, until such time as all requirements or issues that the CGS raise are dealt

with.

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2.2 RESPONSIBILITIES OF LOCAL AUTHORITIES AND COMPETENT PERSONS

2.2.1 Responsibility of Town Council

The Constitution of South Africa and various Acts and Ordinances place a responsibility

on Local Authorities to ensure that the health and safety of inhabitants living within its

area of jurisdiction are ensured. Specific mention is made to geological issues and it can

safely be said that living and developing on dolomite presents challenges to Local

Authorities in this respect.

The matter of whether or not failure by the Local Authority to Act on the issues of safety

in relation to geology constitutes an act of delict is somewhat more involved. Taking into

consideration the new constitutional dispensation and the Bill of Rights, advocates S J

Grobler (SC) and D J Combrink in providing legal opinion to Merafong City Local

Municipality, concludes that any actions of omissions of the Local Authority contrary to its

statutory duties would be regarded as wrongful. Not only do these statutes place a duty

on the Local Authority to ensure the safety of the community, but the Local Authority, in

as much as it may have control over the dangerous situation, has a duty to act to prevent

it.

In order to be liable for any actions of omissions, the actions or omissions must not only

be wrongful, they must also be negligent. Negligence would arise if a defendant a) could

have foreseen the reasonable possibility of his conduct inuring another in his person or

property and causing him patrimonial loss, b) would have been able to take reasonable

steps to guard against such occurrence and c) have failed to have taken such steps.

Expressed in simple terms- the reasonable person standard must be satisfied.

Local Authorities go about their business often allowing them to be approached by

Developers who see commercial opportunity in developing projects on portions of land

under the jurisdiction of the Municipality. In such instances it is the Developer who

appoints and pays the geotechnical practitioner to assess the risk condition of the land

that is to be developed. More often than not the Developer merely seeks to maximize

his return on investment within the rights pertaining to the property. The change to a

higher order development right or development density is very much in the Developer’s

potential favour.

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Whether or not the land is at all suitable for the development or densification proposed is

very much a function of the risk character of the property under consideration. It is here

that the geotechnical consultant (Competent Person) finds himself in the unenviable

position between a profit driven developer who pays for the work that he does and the

norms and acceptance standards that industry and authorities have established in the

past. How this individual is called upon to act is the subject of the remainder of the

document.

2.2.2 Responsibility of the geotechnical practitioner (Competent Person: Geotechnics)

Section 2.1 above demonstrated the responsibility that the Local Authority has towards

the public when geological risk surfaces are occupied or developed. It also showed that

Local Authorities are in most instances not equipped to assess the hazardous nature of

the ground or to develop and maintain the town planning scheme in such a way that safe

utilization from a dolomite risk perspective is achieved. They rely on the geotechnical

consultant appointed by the developer to exercise due care and diligence in bringing to

the table the necessary doctrine of the reasonable dolomite risk professional. The

question would not be whether the diagnoses of the degree of risk was wrong but rather

whether a professional acting under the same circumstances, with the knowledge

available to the field at the time of the assessment, would have concluded that the

assessment was reasonable. Questions about the knowledge of the professional in a

particular discipline in a particular environment would be relevant here. Whether or not

the reasonable professional would be an expert or a general practitioner in this area

would be a further question to answer.

The general state of the science of dolomite stability risk assessment and appropriate

development is summarized in the sections that follow. Clearly the responsibility placed

on the practitioner that accepts an appointment from a developer in this regard is

massive. Not only is it important that he/she practices to current day standards, but must

remain impartial without conflicting interests to influence his/her judgement.

Remuneration other than by way of an agreed professional fee for the service rendered

would cloud the issue.

The CGS submits that the geotechnical practitioner appointed by the Developer has a

duty of care both towards the Local Authority, the NHBRC and the general public as well.

The NHBRC Home Builders Manual requires that the Home Builder appoints the

Competent Person to investigate, to report on the zonation in term of prevailing

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professional practice and to detail any precautionary measures required to reduce the

risk and to formulate any restriction on land use that may be appropriate. These include

layout, erf sizes, density, services etc. The report is then to be submitted to the Council

for Geoscience for their confirmation that the investigations conducted on the stability

and referred to in the report are, in their opinion, consistent with sound professional

practice and that the investigations meet all legal requirements pertaining to such

stability investigations.

In order to raise and set standards the CGS has, in association with SAIEG and SAICE,

produced the Guideline for Engineering Geological Characterization and Development of

Dolomitic Land1 and the October 2004 guideline document. These are supplemented by

GFSH-2, draft SANS 10400 and draft SANS 1936. The attempt has met with some

success and it can safely be said that the past 3 years have seen an education and

guidance process with most Competent Persons having been exposed to the gist of what

is seen as the minimum appropriate standards today.

It is the aim of the SANS standards to promote self regulation within the industry. Once

tied to the National Building Regulations the National Standard will be enforceable and

will become the basis of the development on dolomite and associated administrative,

regulatory and legal procedures.

3. DOLOMITE STABILITY INVESTIGATIONS

The purpose of the investigation is to define the subsurface geology in order to make

appropriate recommendations regarding land usage, layout, density, services, foundation

types and precautionary measures. As dolomite stability assessment is empirical, the

investigator is called to make careful and considered judgments. Thus, an investigator

must:

- Demonstrate a good understanding of the geological model that pertains to the

site

- Have extensive experience in characterising karst terrain

- Have observed instability features and associated ground profile conditions and

have partaken in the rehabilitation of such instability features

- Have a sound knowledge of the engineering geological properties and behaviour

of rock and soil

1 As sold at the CGS Publication Section, Ground Floor, Pretoria Road, Silverton

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- Have an excellent understanding of the applications and limitations of

geophysical methods

- Understand the limitations of engineering design in adapting for dolomite

conditions

It is neither the task nor the intention of the CGS to be the judge of the competency of

the person reporting to be a dolomite specialist. Where greater confidence in the

objectiveness and comprehensiveness of the assessment is evident the CGS is more

likely to support the development.

An investigation may involve the following:

- geophysical surveys (gravity - and other appropriate surveys)

- drilling (typically rotary percussion drilling) and subsurface profiling

- geological and topographical surface mapping (using aerial photographs, site

walkover)

- test pit excavation and augering (and profiling thereof)

This is followed by an evaluation of all the data and culminates in the general delineation

of geotechnical and dolomite stability risk and hazard zones. The first phase evaluation

will, furthermore, enable the consultant to formulate broad recommendations pertaining

to the appropriate development type, density of units, remedial and precautionary

measures and mitigation of risk in the form of a risk management plan.

Additional phases of investigation are likely, during which detailed or additional work is

done to confirm or amend the first attempt at risk zonation. The data gathered during the

soils investigation may also assist in the finalisation of the risk zonation. These phases

of evaluation will assist the consultant in refining the initial recommendations.

The details of the investigation, evaluation and recommendations must be recorded in a

report. The report is to be submitted to the CGS for peer review as and when required by

an Authority.

4. MINIMUM REPORTING REQUIREMENTS

The purpose of a report is to present relevant information, discuss the interpretation

thereof and make recommendations. A report should always be placed in context of

other available information. Irrespective of how brief the report is or how little geological

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information was sourced, the report must contain a discussion on how the investigator

arrived at a certain risk characterization. All crucial elements must exist in letter-reports

undertaken for single stands, all be it briefly.

All dolomite stability reports must include at least the following:

1. Executive Summary

2. Introduction

3. Terms of Reference

Indicate who commissioned the work, when and why.

4. Investigation Objectives

The purpose of the report must be made clear. The report may be intended to

present the development potential of a site, stand as supportive documentation for

township establishment, NHBRC enrolment, a change in existing development right,

or may document results of trench inspections during construction.

5. Site Location and Description

The site location should be indicated at an appropriate scale with the exact property

boundaries marked on the plan. It is advisable to describe the location relative to

known landmarks and to give information on the present and past use of the land,

vegetation, slope etc.

Include an appropriate locality map with coordinates. Include a scale (bar) and a

north arrow. Include a detailed map, at an appropriate scale, showing the

topography/contour lines on the site and discuss this in the report.

Discuss the site size, topographical aspects and present and past land uses.

As the reports will be lodged in the CGS Dolomite Databank it is essential that the

position of the site be clear. Failure to do so will result in the report not being

considered for review.

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6. Existing Information

All available information must be fully referenced. Relevant data (including that from

adjoining sites) may be used from other reports and sources, provided that the

source is recognized. The data (borehole logs, gravity, instability features etc.) must

be incorporated in the report itself (on plans for instance) and/or be appended as an

addendum. It may be quite useful to indicate the outline of previous sites

investigated relative to the site under consideration and to summarise the outcome of

such investigations.

The investigator should approach the Local Authority and the CGS to establish

whether instability had ever occurred on and in the immediate area of the site.

Instability features must be indicated on plans and discussed as part of the

evaluation.

7. Investigative Procedures

With the introduction of the Housing Consumers Protection Measures Act, the

Occupational Health and Safety Act, the Municipal Systems Act and the Bill of Rights

a paradigm shift came about with respect to dolomite site investigations. Whereas

before the minimum standard for the investigation of dolomite sites included the

undertaking of a gravity survey and a limited number of boreholes, investigative work

currently requires that the following can be ensured:

(a) Not a single house or portion thereof may be located on high risk land

(b) Structures must be designed to withstand ground movement by way of

treated foundation systems and structural design.

(c) Transient densities of towns and cities should be controlled in order to limit

the exposure of the public to ground movement incidences and possible

disasters.

7.1 Field Inspection

Field inspections may present useful information, such as extensiveness of

outcrop, accessibility constraints, old cased boreholes, gravity pegs from

previous investigations, instability features etc. There is sufficient merit in

undertaking field inspections for single stand investigations, particularly in

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cases where it is crucial that the foundation footprint conditions must be

evaluated and/or a proven suitable area found. Misunderstandings regarding

the exact location of the proposed structures may lead to drilling in the wrong

area. Often it is also possible to note potential palaeo-depressions, an

observation that cannot be made unless the site is visited.

7.2 Geophysical Surveys

It is necessary to establish, using some sort of remote sensing technique, how

the geology changes over the site, in particular the bedrock topography. It is of

utmost importance that the geophysicist and engineering geologist

communicate with one another throughout the geophysical survey. Multiple

geophysical techniques may be required, depending on the geology. Normally,

at least a gravity survey is undertaken. It is necessary to indicate which gravity

features were investigated during drilling. ALL borehole positions (from past

and present investigations) should be indicated on the gravity map. Where

further phases of drilling are undertaken, the new positions should be added

and a revised map included in the addendum/additional report.

Discuss the gravity field variations on the site as well as, wherever possible,

how the local gravity pattern fits in with the regional gravity of the area. It is

important to understand the regional/greater gravity setting so that it is possible

to avoid mistakes in interpreting, for example, a gravity gradient at the edge of

the site continuing far beyond the perimeter of the site, as a gravity gradient

going onto a steep narrow low gravity trough. Explain which gravity features

were investigated by drilling, and why. Comment on the correlation between

the gravity and the drilling results.

The gravity report, containing a listing of the gravity elevation and other data,

should be attached to the dolomite stability report. The geophysicist must

comment on the results of the gravity survey. This not only helps the

engineering geological consultant to understand the gravity, but can also guide

the drilling phase on the site. The geophysicist must also comment on the

methods/calculations used to obtain the gravity results. The reduction densities

need to be known if quantitative interpretation is required. The report should

state if the gravity data has been reduced to residual gravity, thereby removing

the effects of the deeper geological units. Gravity surveys must be conducted

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on a grid spacing appropriate for the resolution of data required. As a rule of

thumb the grid spacing should not exceed the thickness of the overburden as

this will result in the loss of useful information. Contour intervals of no more

than 0,1 milliGals should ideally be used. The work should be done with great

care as smaller trends can be indicative of important geological features.

The merit of other geophysical methods, for example, electromagnetics to

establish the contact between conductive material (e.g. Karoo Supergroup

shale and dolomite), must be considered.

7.3 Rotary Percussion Drilling

It is essential to establish what the conditions are of the blanketing layer (from

surface right up to the dolomite interface). It is also necessary to establish the

nature of the interface between the blanketing layer and of the dolomite

bedrock (dolomite bedrock topography). Attention should be given to dolomite

bedrock conditions, i.e. whether it is solid, fractured or cavernous. For this

reason it is advised that boreholes should be drilled at least 6 metres into solid

dolomite bedrock, or at least to a depth of 60 metres. In areas where

uncertainty exists regarding groundwater level depths and control of

groundwater abstraction, boreholes may need to be drilled to 100 metres.

Premature termination of drilling must be explained on the borehole log, e.g.

due to hole collapse, jamming of the drilling equipment etc.

Drilling work must be undertaken using a down-the-hole rotary percussion rig

with a compressor delivering no more than 25,4 m3/min at a pressure of

1800 kPa. Appropriate measures must be taken that the borehole is completed to

the desired depth and that samples be retrieved continuously. Making

assumptions on the materials present in the absence of retrieved sample is

strongly discouraged. Where this happens conservative judgement must be

applied.

X-, Y- and Z-coordinates (values) for each borehole must be placed on the

borehole log. The X- and Y- coordinates may be determined by hand held GPS,

the Z-coordinate must be taken from the gravity survey information. The

coordinate system should preferably conform to the South African Coordinate

System as set in the National Control Survey Network maintained by the Chief

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Directorate: Surveys and Mapping of the Department of Land Affairs. In the

South African coordinate system the X coordinates are measured southwards

from the equator (where x = 0) towards the South Pole which is positive. Y

coordinates are measured from the Central Meridian (CM), increasing from the

CM in a westerly direction so that Y is positive west of the CM and negative

east of the CM.

It is important that when borehole information from other reports is used to

supplement the investigation. All relevant information, such as borehole profile

and driller’s log sheets (where the information is not duplicated on the borehole

profile), should be included in the investigator’s report.

The borehole logs should indicate penetration rates (in minutes and seconds) at

1-metre intervals in the case of stopwatch recording. Where electronic logging

is done the data should be reduced to sensible intervals that allow relevant

features of importance to be highlighted. Report on any air and sample losses

encountered during the drilling process.

Report whether water is encountered or added. Also report on the rest water

level, which should ideally be measured at least 24 hours after the borehole

was drilled. If water level monitoring did not take place, a reason should be

given.

The boreholes must be suitably backfilled. The minimum standard is to backfill

the borehole to 5 metres depth below ground with drill spoil, then tremiefill the

remainder with high slump 15 MPa concrete, place a 800x800x250 mm wood

floated 20 MPa concrete cap with borehole number. It is recommended that the

driller and consultant’s names be inscribed on a metal tag and imbedded in the

cap. Where cavernous ground conditions are encountered the boreholes should

be tremie grouted from the bottom up.

The investigator must as a minimum have a responsible supervisor present on

site to verify the positions and depths of boreholes drilled and ensure that water

rest level measurements are taken when necessary. Drillers must have skilled

staff present who are able to record sample and air loss, hole collapse, water

strikes etc. on a drillers log.

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Density of borehole information for GFSH-2 type Phase 1 investigations should

at least comply with the following:

1a: Minimum frequency of percussion boreholes in

Dolomitic Areas for study areas not greater than

10ha

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 12

Study Area (ha)

Exploratory Holes per Hectare

Note:

For intermediate hole numbers,

round values upwards,

e.g. 4.1 holes = 5 holes

6.8 holes = 7 holes

1b: Minimum frequency of percussion boreholes in

Dolomitic Areas for study areas greater than 10ha

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600

Study Area (ha)

Exploratory Holes per Hectare

Note:

For intermediate hole numbers, round values upwards,

e.g. 4.1 holes = 5 holes

6.8 holes = 7 holes

For study areas greater than 500ha - frequency of

boreholes should be 0.15 x study area

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Particularly in the case of residential development, confirmation of conditions

within a zone should ideally be contemplated at the following borehole

densities, particularly in cases where concern exist over the uniformity of

ground conditions and therefore inherent risk zonation. Due to the fact that the

NHBRC requires confirmation of Inherent Risk conditions per individual stand,

the following minimum borehole densities should be attained before a township

establishment application is lodged:

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Table 1: Minimum Required Borehole Densities

INHERENT RISK CLASS

APPROXIMATE BOREHOLE DENSITY

COMMENT

1 1 borehole per 7000 m2

Applies to homogenous conditions over larger areas


Applies to homogenous conditions over larger areas

3a 1 borehole per 2200 m2 -

3b 1 borehole per 2000 m2 -

4a/b 1 borehole per 3300 m2 -


Prove suitability for proposed structure

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7

8

Not applicable Housing not considered

8. Geology

Include a map of the regional geology. The regional geology map may be an extract

from the 1: 50 000 or even 1: 250 000 Geology Map Series. A legend must be

included.

It is important to understand/investigate the bedrock topography. In addition to this,

the overlying horizons need to be identified and their continuity established. Where

transition between dolomite and intrusive sills/dykes cannot be delineated accurately,

broad zone boundaries should be introduced.

9. Geohydrology

Indicate and discuss the nature of the groundwater level fluctuations,

compartmentalization, original groundwater level, etc, and how these affect the

stability on and in the vicinity of the site. If the stability of the site is dependent on the

groundwater level being kept at a constant level, discuss how groundwater level

drawdown will impact on any development. The investigator must indicate how the

groundwater level is going to be monitored and name the person/body/institution

responsible for monitoring and/or maintaining the groundwater level. Identify the

authority that can control the extraction of ground water in the area. If there is any

uncertainty regarding any of the above mentioned aspects, the investigators must not

only state this but also factor it into the stability assessment.

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10. Stability Evaluation

The method utilised to assess the stability and to zone this site is outlined in the paper:

"Proposed method for dolomite land hazard and risk assessment in South Africa." by

Buttrick, Van Schalkwyk, Kleywegt and Watermeyer 2001, Journal of the South African

Institution of Civil Engineering, Volume 43, Number 2.

The predominant mobilising agencies considered in this investigation are major

groundwater level fluctuations (>6m), ingress water, ground vibrations and gravity. Use

is made of a generalised list of evaluation factors to evaluate the risk of sinkhole and

doline formation. These factors are as follows:

- Receptacle development;

- Mobilising agencies, particularly ingress water from leaking services;

- Potential sinkhole development space;

- Nature of the blanketing layer;

- Mobilisation potential of the blanketing layer;

- Bedrock morphology.

Sites are characterised primarily in terms of eight standard Inherent Risk Classes

defined as follows:

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Table 2: Inherent Risk Class Characterisation

RISK CLASS CHARACTERISATION OF AREA

Class 1 Areas characterised as reflecting a low Inherent Risk of sinkhole and doline formation (all sizes) with respect to ingress of water.

Class 2 Areas characterised as reflecting a medium Inherent Risk of small sinkhole and doline formation with respect to ingress of water.

Class 3 Areas characterised as reflecting a medium Inherent Risk of medium sinkhole and doline formation with respect to ingress of water.

Class 4 Areas characterised as reflecting a medium Inherent Risk of large size sinkhole and doline formation with respect to ingress of water.

Class 5 Areas characterised as reflecting a high Inherent Risk of small sinkhole and doline formation (all sizes) with respect to ingress of water.

Class 6 Areas characterised as reflecting a high Inherent Risk of medium size sinkhole and doline formation with respect to ingress of water.

Class 7 Areas characterised as reflecting a high Inherent Risk of large sinkhole and doline formation with respect to ingress of water.

Class 8 Areas characterised as reflecting a high Inherent Risk of very large size sinkhole and doline formation with respect to ingress of water.

The CGS acknowledges that drilling often cannot simply render a zone as a single

numbered Inherent Risk Class. Studies of the overburden conditions sometimes

present uncertainty regarding the mobilization potential thereof. The CGS therefore

accepts that allowance must be made on certain occasions for a range of mobilization

potential, e.g. a low to medium- or medium to high mobilization potential:

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Table 3: CGS Inherent Risk Class Adjustments to Allow for a Difference in

Mobilization Potential

RISK CLASS CHARACTERISATION OF AREA

Class 3a Areas characterised as reflecting a low to medium Inherent Risk of medium sinkhole and doline formation with respect to ingress of water.

Class 3b Areas characterised as reflecting a medium to high Inherent Risk of medium sinkhole and doline formation with respect to ingress of water.

Class 4 a Areas characterised as reflecting a low to medium Inherent Risk of large size sinkhole and doline formation with respect to ingress of water.

Class 4b Areas characterised as reflecting a medium to high Inherent Risk of large size sinkhole and doline formation with respect to ingress of water.

Zones delineated on a site may be combinations of the above. In some instances, the

Inherent Risk Classes are indicated with the primary zone description given first,

followed by a suffix in brackets. The primary Inherent Risk Class describes the

predominant characterisation of the zone and the suffix describes the characterisation

of anticipated pockets or small sub-areas within the zone. As an example a

designation of 8(4) indicates that the zone predominantly displays a high Inherent Risk

for very large sinkhole and doline formation with anticipated pockets or small sub-areas

of Class 4 i.e. displaying a medium risk for medium size sinkhole and doline formation.

Inherent Risk is defined in terms of ingress water and groundwater level drawdown

reflected by two Inherent Risk Class designations separated by a double forward slash

i.e. Inherent Risk Class (Ingress water)//Inherent Risk Class (ground water level draw

down). As an example a designation of 5//1 indicated that the zone displays a high

Inherent Risk with respect to water ingress but a low Inherent Risk with respect to

ground water level draw down.

The evaluative procedures must be set out in the report as well as a discussion on

what the investigator expected to find (‘predicted geological model’) at the onset and

as the work progressed. Special attention should be given where data is shown to

be at variance to these expectations (e.g. shallow dolomite is revealed not to contain

deep slots).

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Include a zonation map with the gravity contour lines and all the borehole positions

depicted there on: It is important to discuss/indicate how the investigator used the

gravity (as well as other remote sensing techniques) and the borehole results to

delineate the stability zones. Always indicate when information is lacking or not

reliable. Care should be taken in the definition of zone boundaries and their accurate

positions on plans and in the field.

Investigators should be mindful of the implication of statements such as “conditions

between boreholes may be found to be at variance with those described/predicted”

as this may effectively imply that the risk zonation as presented is as a whole or in

places incorrect. Possible variances must be considered as part of the evaluation

and ‘built’ in to the risk evaluation. Minor anticipated variances may be acceptable

but need to be dealt with in the construction/completion report. Clearly such

variances must be possible to be resolved by trench inspection only. Boreholes are

not normally drilled during the construction stage, but circumstances may dictate

otherwise.

11. Conclusions

The dolomite stability risk classification and the NHBRC ‘D’ designation is given. The

investigator must be mindful of the fact that ‘D’ designation is a function of inherent

risk in combination with proposed development types.

12. Recommendations

The recommendations regarding appropriate development, derived from the risk

classification and ‘D’ designation, are given here. This section should include water

precautionary measures, a risk management plan and any other appropriate

recommendations deemed necessary to maintain sustainable development for the

lifetime of the structures. A construction report should be called for.

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The following serves as a list of items which should as a minimum be tabled in this

section:

• Present suitable development types and densities for each Inherent Risk zone.

• Assign D designations for each Inherent Risk zone.

• Specify whether special design requirements are necessary, for example D3,

and motivate why. Where it is required, determine the minimum loss of support

which must be catered for in the foundation design in each relevant zone.

• In the case where development proposal already exists discuss the details

thereof and indicate whether these are commensurate with the risk

assessment. Where certain aspects are not found to be commensurate,

highlight these.

• Ensure that a recommendation is made which requires the certification of site

development plans (SDP) from a dolomite perspective.

• Indicate any land restrictions required, for example no second dwellings or

subdivisions.

• Recommend appropriate water precautionary measures. Highlight the

importance of storm water control and wet service systems that can be tested.

• Recommend implementation of a site specific dolomite risk management

strategy.

5. APPROPRIATE DEVELOPMENT IN RELATION TO RISK CHARACTERISATION

Once the risk zonation has been completed, an appropriate development type can be

selected for each zone taking cognisance of the development risk. The broad

development types recommended for the various risk classes are detailed by the most

recent technical paper on the subject:"Proposed Method for Dolomite Land Hazard and

Risk Assessment In South Africa" by DB Buttrick, A Van Schalkwyk, R J Kleywegt, and

RB Watermeyer published in Journal of the South African Institution of Civil Engineering,

No 44, Number 3, 2002.

The NHBRC dolomitic area designation, in addition to the risk class number allocation,

should be given for each geologically defined zone. Whereas the risk class allocations

are obtained from stability assessment, and are therefore geologically related, dolomitic

area designation is arrived at by considering the type of development in the context of

the stability assessment. It is therefore both geology and design-related.

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5.1 Development principles

(a) As a result of the complexities of dolomitic land evaluation, the procedure for

development on such land will vary according to the circumstances which prevail at

individual developments.

(b) Residential development should be restricted to the lower-numbered risk class

areas.

(c) The density of developments should decrease as the risk class number increases.

(d) Higher-numbered risk class areas should be reserved for commercial and light

industrial development or for open space and park land in the case of the highest-

numbered risk class areas.

(e) The lower the density of information, the greater the uncertainty.

(f) No low cost, high density housing should be placed on land of risk class 5, 6 or 7.

Where such housing is considered for risk class 2, 3 or 4 land, a designation of D3

must be assigned.

(g) A low confidence in the characterisation of the land must translate into a

conservative approach on the part of the consultant.

(h) Investigation of dolomitic land should be undertaken in a phased manner. Such a

process may need to be iterative and involve investigation, evaluation, further

investigation and re-evaluation until the site has been adequately investigated for

the said purpose. An advantage of such an approach is that the developer can cut

losses at any stage if it has become evident that parts of, or the entire site is not

suited for the requirements. Current investigative techniques are not necessarily

fully reliable and it is important that all assessment is done conservatively in order

to promote safe and sustainable development. Re-assessment at various stages

of the investigation also allows for optimal planning.

(i) A developer should contemplate undertaking preliminary investigations prior to

purchasing a property to establish its suitability for the proposed development.

Should the outcome of the investigation be unfavourable, in other words, the land

seems to be unsuitable for the developer’s intended purpose, the developer can

still withdraw from the project and seek more suitable land. In cases where

investigations have already been done on sites, the developers should familiarise

themselves with the information or appoint an experienced consultant in this regard

so that duplication of data acquisition is prevented and so that it is ensured that

previous investigations covering the area are updated in accordance with current

requirements and standards.

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5.2 Development Type and Density

The CGS encourages residential development on risk class 1 and 2 land only. Where

development is considered on higher risk class numbers, every effort is required to fully

understand the geological setting and apply conservative judgement throughout.

Development density is one area where conservative judgement is applied in particular.

To consider development density on its own is not satisfactory. It is obvious that the

number of people exposed, layout of wet services, footprint configuration etc. all

contribute to development risk. The interactive effects and the exact extent to which

these affect development risk are not yet adequately addressed. Hence, the CGS will

continue to apply conservative development densities until new research shows that

change is warranted. The CGS will also continue to apply conservative judgement until it

is entirely satisfied that every Local Authority affected by dolomitic land has a functioning

Risk Management System.

The CGS aligns itself with the pending SANS 10400, which indicates the building types

suitable for the 8 inherent risk classes:

Table 4: Building classes associated with inherent risk classes

BUILDING CLASSES1) INHERENT RISK CLASS

All classes 1

A, B (light only), C, D (light (dry) only), E, F, G, H, J 2

A, B (light only), C, D, (light (dry) only), E, F, G, H, J 3

A, B (light only), C, D (light (dry) only), E, F, G, H, J 4

A, B (light only), C, D (light (dry) only), E (if no safer alternative available), F,G,H (depending upon densities and mitigation measures that are adopted.), J

5

A5, B (light only), D (light (dry) only), G1 (with appropriate remedial measures), J

6

J3, J4 7

No classes 8

1) Refer to table 1 of Part A of the National Building Regulations

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Table 5: Occupancy on Building Classification

CLASS OF OCCUPANCY OR

BUILDING OCCUPANCY

A1 Entertainment and public assembly Occupancy where persons gather to eat drink, dance or participate in other recreation.

A2 Theatrical and indoor sport : Occupancy where persons gather for the viewing of theatrical, operatic, orchestral, choral, cinematographical or sport performances.

A3

Places of instruction : Occupancy where school children, students or other personas assemble for the purpose of tuition or learning.

A4 Worship : Occupancy where persons assemble for the purpose of worshipping.

A5 Outdoor sport : Occupancy where persons view outdoor sports events.

B1

High risk commercial service. : Occupancy where non-industrial process is carried out and where either the material handled or the process carried out is liable in the event of fire, to cause combustion with extreme rapidity or give rise to poisonous fumes, or cause explosions.

B2

Moderate risk commercial service: Occupancy where a non-industrial process is carried out and where either the material handled or the process carried out is liable, in the event of fire to cause combustion with moderate rapidity but is not likely to give rise to poisonous fumes or cause explosions.

B3

Low risk commercial service : Occupancy where a non-industrial process is carried out and where either the material handled nor the process carried out falls into the high or moderate risk category.

C1 Exhibition hall : Occupancy where goods are displayed primarily for viewing by the public.

C2 Museum : Occupancy comprising a museum , art gallery or library.

D1

High risk industrial : Occupancy where an industrial process is carried out and where either the handled or the process carried out is liable, in the event of fire to cause combustion with extreme rapidity or give rise to poisonous fumes, or cause explosions.

D2

Moderate risk industrial : Occupancy where an industrial process is carried out and where either the material handled or the process carried out is liable, in the event of fire to cause combustion with moderate rapidity but is not likely to give rise to poisonous fumes, or cause explosions.

D3

Low risk industrial : Occupancy where an industrial process is carried out and where neither the material handled nor the process carried out falls into the high or moderate risk category.

D4 Plant room : Occupancy comprising usually unattended mechanical or electrical services necessary for the running of a building.

E1 Place of detention : Occupancy where people are detained for punitive or corrective reasons or because of their mental condition.

E2 Hospital : Occupancy where people are cared for or treated because of physical or mental disabilities and where they are generally bed-ridden.

23

E3

Other institutional (residential) : Occupancy where groups of people who either are not fully fit or who are restricted in their movements or their ability to make decisions, reside and are cared for.

F1 Large shop : Occupancy where merchandise is displayed and offered for sale to the public and the floor area exceeds 250m².

F2 Small shop : Occupancy where merchandise is displayed and offered for sale to the public and the floor area does not exceed 250m²

F3 Wholesalers store : Occupancy where goods are displayed and stored and where only a limited selected group of persons is present at any one time.

G1 Offices : Occupancy comprising offices, banks, consulting rooms and other similar usage.

H1 Hotel : Occupancy where persons rent furnished rooms, not being dwelling units.

H2 Dormitory : Occupancy where groups of people are accommodated in one room.

H3 Domestic residence : Occupancy consisting of two or more dwelling units on a single site.

H4 Dwelling houses : Occupancy consisting of a dwelling unit on its own site, including a garage and other domestic outbuildings, if any.

J1

High risk storage : Occupancy where material is stored and where the stored materials is liable, in the event of fire to cause combustion with extreme rapidity or give rise to poisonous fumes, or cause explosions.

J2

Moderate risk storage : Occupancy where material is stored and where the stored material is liable, in the event of fire, to cause combustion with moderate rapidity but is not likely to give rise to poisonous fumes or cause explosions.

J3 Low risk storage : Occupancy where the material stored does not fall into the high or moderate risk category.

J4 Parking garage : Occupancy used for storing or parking more than 10 motor vehicles.

Table 6: Design Population

CLASS OF OCCUPANCY OF ROOM OR STOREY OR PORTION THEREOF

POPULATION

A1, A2, A4, A5 Number of fixed seats or 1 person per m² if there are no fixed seats.

E1, E3, H1, H3 2 persons per bedroom.

G1 1 person per 15m².

J1, J2, J3, J4 1 person per 50m².

C1, E2, F1, F2 1 person per 10m².

B1, B2, B3, D1, D2, D3 1 person per 15m².

C2, F3 1 person per 20m².

A3, H2 1 person per 5m².

Notes: (1) The population of any room or storey or portion thereof shall be taken as the actual population of such room,

storey or portion thereof where such population is known. (2) In the case of any occupancy classified as F1, where the total floor area is more than 500 m² shall, for the

purposes of calculation of the population, be reduced to an amount of 20%.

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In the absence of a defined and rigorous assessment of how to appropriately reduce the

development risk, the following CGS guidelines with respect to density of residential

development on dolomite should prevail:

Table 7: CGS Guidelines with Respect to Density of Residential Development

INHERENT RISK CLASS RESIDENTIAL TYPE AND (DENSITY)**

1 All types of residential limited to 60 u/ha

2 All types of residential limited to 40 u/ha

2(5)

Selected residential: Gentleman’s estates Residential 1 type stands (≥1000 m2) Group housing in new towns (30 to 35 u/ha)

3a

Low to medium inherent risk of medium size sinkholes and dolines

Selected residential: Gentleman’s estates Residential 1 type stands (≥500 m2) Residential 2 and 3 type (up to 18 u/ha)

3b

Medium inherent risk of medium size sinkholes and dolines

Selected residential: Gentleman’s estates Residential 1 type stands (≥1000 m2)

4a

Low to medium inherent risk of up to very large size sinkholes and dolines


4b

Medium inherent risk of up to very large sinkholes and dolines


1/2/4a Affordable housing (≥300m2)

5 (3) or 3 (5) Selected residential: Gentleman’s estates Residential 1 type stands (≥1000 m2)

5 (6)

No residential development. However in case of very large stands (Gentleman’s estates) identify a suitable footprint area (risk class 4 or better OR 5(3))

6 or 6 (5)

7

8

4/5/6/7

Transition zones Steep gravity gradients

No residential development

** Conditional to the following, to bring development to acceptable development risk: (a) Implementation of a specific risk management plan for the development (b) Existence of a working Regional Risk Management Plan (Local Authority) (c) Confirmation of stability zones by Competent Person during construction (d) Proper project management and supervision of construction work by a Competent Person

(including laying of wet-services) (e) Implementation and supervision of appropriate founding solution

25

Guidance on appropriate engineering design, such as wet service systems. can be

obtained from the Department of Public Works’ Manual for Consultants (PW344),

available on their web site.

6. NEW DEVELOPMENTS IN THE APPROACH BY THE CGS

The following important aspects have been considered by the CGS which has an

influence on practitioners and the industry:

6.1 Dolomitic Groundwater management, control and influence on development

Regional groundwater information (depths, elevations, extent of compartments,

groundwater barriers etc.) is only available for certain areas. Areas such as Delmas, for

example, have not been investigated regionally. Similarly no information is available for

the dolomite areas in the Southern District Municipality Area. Although the Department

of Water Affairs and Forestry (DWAF) has a groundwater database, the information

supplied to users is unprocessed and does not allow rapid extraction of the regional

dolomite groundwater levels. This implies that investigators must approach a

geohydrologist or evaluate the data him/herself.

DWAF is charged with control and management of dolomite groundwater. DWAF largely

relies on the Water User Associations to police their own groundwater use. The CGS

continues to engage with role players to ensure adequate investigation of all dolomite

groundwater aquifers and appropriate monitoring and control of abstraction.

In the interim the CGS will consider supporting areas for development where historic

dolomite groundwater information exists and an Authority is monitoring its fluctuations on

a regular and continual basis. Even so, areas which represent a high Inherent Risk in the

event of groundwater level drawdown (IRC6-8) will not be supported. Areas of which

regional groundwater data is lacking and control of the groundwater level cannot be

established shall not be supported for development, where dolomite bedrock is below

site specifically reported rest water levels.

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6.2 Submission of report, B4 certificate and CGS comments to the NHBRC

The NHBRC have requested the CGS to assist them in ensuring that the dolomite

stability report reviewed by it is the same report which reaches the NHBRC offices for

technical review, as delivered by the developer/enrolment applicant.

We have endeavored to assist by requesting the consultant to submit an additional

report copy upon collection of our letter of comment in support of NHBRC enrolment.

The B4 certificate will be copied and forwarded together with the second report copy to

the NHBRC and will bear a CGS stamp which verifies the report to be the final report

considered.

Please assist us in this process by ensuring that the second copy does reach this office,

as the technical reviewers at the NHBRC will not process and review applications without

the CGS certification.

6.3 Site Development Plans and CGS support for Township Establishment

The CGS can only consider support for a site for township establishment having

considered a Site Development Plan (SDP), which indicates land usage, development

type and density and stand sizes. The CGS requires the superimposition of the dolomite

risk zones on such a plan. The plan should include a legend showing the primary

inherent risk zonation and D designation. The SDP should be signed by the consultant to

indicate that the layout is commensurate with the identified risk and the development risk

is acceptable. If satisfied the CGS will co-sign the plan.

6.4 Change in CBD Cityscape in Centurion

The CGS, in discussions with the City of Tshwane Metropolitan Municipality, has come

to appreciate the pressure to change the Centurion CBD Cityscape to a compact mega

city, envisaged to consist of a number of skyscrapers, intensive and mixed

developments, concentrated around the Gautrain Station. The CGS has taken the

viewpoint that in the interim development proposals can only be considered to the extent

that the proposal is in keeping with the cityscape as it is at present. Development

proposals beyond this will not be contemplated. The Local Authority may elect to engage

with the CGS on sites where inherent rights exist which developers wish to exercise, in

which case the CGS may be able to advise the CTMM on risk management principles.

27

Figure 1: The Centurion CBD

6.5 Density Exceedence and Transient Densities

The CGS wishes to pursue sensible geoplanning principles in order to ensure long term

sustainability, limit undue financial and injury exposure and promote sensible use of

resources. The CGS is however confronted with various development proposals in the

Centurion CBD, for example, which it believes may not be in harmony with the dolomite

stability conditions prevalent in the area.

Increased densities of people (even more so in the case where development densities

have been exceeded) require additional resources to be made available by the Local

Authority to implement Dolomite Risk Management on a regional scale as well as to

strengthen capacity to deal with dolomite related incidents, in particular sinkholes which

may cause damage to infrastructure as well as cause harm to life and limb.

The CGS perceives exposure to dolomite related instability to be an issue which not only

affects individual properties and developments, but also open areas and areas of high

human and vehicular traffic. These areas are rarely if ever treated to lower the risk of

sinkhole formation. In the past the CGS has sought to control this traffic or transient

28

density by controlling the development density and type on individual properties. In the

Centurion CBD this is fast becoming impossible. The CGS is in the process of

researching the impact that changing the cityscape to a mega city has on the transient

population. Having contemplated such it should be possible to investigate the risk the

population has of exposure to sinkhole events.

6.6 CGS GIS data searches

The CGS is in the process of incorporating all dolomite stability investigations housed in

the Geotechnical Databank in a Global Information System. A list is available to the

public of all the sites previously investigated and lodged in the databank. Practically all

site boundaries have been transferred into a Global Information System and are linked to

file numbers which relate to files which contain the report and correspondence relating to

the site. Should a consultant wish to determine the existence of information near or on a

site of interest, Ms Judith Grobler at 012 841-1152.

Figure 2: Dolomite Report Boundaries and Boreholes Plotted on GIS

29

6.7 Subdivisions, second dwellings, and land use changes

Subdivisions, second dwellings and land use changes can only be contemplated to the

extent that the development type and density conforms to those recommended in this

document (Section 5.2). Concomitant with this, the entire property must undergo a wet-

service audit (testing of wet-services) and upgrading to current standards where wet

services are found not to comply.

No subdivision or second dwellings should be contemplated in townships established

after 1 January 2004.

6.8 Footprint Investigations

In the event that poor conditions are encountered on a stand, and a suitable footprint is

then investigated, the following information is important:

The investigator must certify that the structure and associated patios and highly

trafficked areas (pedestrian) immediately around the structure are within the proven

footprint area and adequately treated to prevent sinkhole formation and allow for safe

evacuation in the event of a sinkhole occurring. Such certification must be required

before enrolment is finalized.

No structures may be placed or contemplated on the remainder of the property nor

should water features or ponded water be permitted. Very small structures should not be

entertained due to the risk of the structure failing/collapsing into a sinkhole.

Stringent water precautionary measures must be applied. The appointed engineers must

prepare a detailed set of water precautionary measures based on the specific structure

proposed. The specifics of measures must be audited by the Local Authority. All open

areas of high risk, particularly highly trafficked areas (vehicles) must be appropriately

sealed. All wet services must be easily accessible for inspection and testing. Wet

services should be thus preferably be placed in sleeves and upon entry to building be

fully accessible to inspect and repair. Implementation of these measures must be audited

by the Local Authority in the course of their inspection of the property.

The owner appointed competent persons must prepare a detailed monitoring

programme. The specifics of the system must be audited by the Local Authority.

30

The owner appointed competent persons must recommend guttering and/or adequate

paving around the structure, which should always be functional. All stormwater must be

discharged in the municipal stormwater system. Roof water may thus not cascade off

the apron and directly into the soil. The stand should be landscaped in a way that the

stormwater is channeled around the structures. The site must be assessed after a heavy

rainstorm to check that this water flows off the site properly.

6.9 Investigation Presentation to the CGS

The CGS is compelled to change the peer review process as it has transpired since

October 2004. The CGS recognises the value in giving the investigator an opportunity to

present details regarding an investigation in person in a presentation. This practice is

continued, although the format of the presentations needs to be adapted and informal

discussion sessions are abolished.

All sites should be presented to the CGS Peer Review Committee as an Executive

Presentation which must cover ALL of the following topics:

• Site Locality and size (figure to be presented)

• Site Layout (figure to be presented)

• Available information

• Regional Geology (figure to be presented)

• Regional Geohydrology (compartment, depth to dolomite groundwater, elevation of

regional groundwater level, groundwater levels struck and rest water levels

encountered in boreholes drilled on site)

• Gravity survey/remote sensing results (drawing with gravity survey and borehole

positions to be presented)

• Inherent Risk Zonation (drawing with zonation to be presented)

Inherent Risk Characterisation of each Zone, examples of borehole logs in each

zone (borehole logs to be presented) from an ingress- and a groundwater level

drawdown perspective

• Borehole information density per zone (report zone area, borehole numbers and

compliance with CGS borehole densities)

• Recommendations: suitable development type and density

The purpose of the presentation is for the consultant to convey his/her findings and

recommendations, not to serve as deliberations. The CGS will peer review the report and

31

present its findings in writing to the appropriate Authority and will be copied to the

investigator.

32

7. PRICING STRUCTURE FOR REVIEW OF SITES ON DOLOMITE FROM JANUARY 2008

Ad hoc matters R700/hour

Single Stands Fees

Subdivision/rezonation/second dwelling applications R800

Includes: 1 submission peer review -

1 letter of comment -

NHBRC enrolment application R1000

Enrolment application submitted within 12 months of submission of a

subdivision/ resonation/second dwelling application to the CGS R400

Fees to paid upon collection of letter of comment

Additional submissions R500 each

Fees to paid upon conclusion of each

Greenfield/Brownfield sites Fees

Sites < 10 Hectares R4000

Township establishment / NHBRC enrolment (which includes a development proposal and/or

layout)

Includes: 1 presentation audience R1000

1 submission peer review

1 letter of comment R3000

Development planning (i.e. excludes development proposal and/or layout) R3500

Fees for intended study discussion may be paid together with fees for submission of data,

provisional zonation and assessment upon conclusion of discussion

Sites 11 - 50 Hectares R6000

Township establishment/NHBRC enrolment (which include as development proposal and

layout)







Sites > 50 Hectares R8000

Township establishment/NHBRC enrolment (which include as development

proposal and layout)







consultants guide: approach to sites on dolomite...

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