Ground-Gas Monitoring, Guidance, Protection and Best

Practice

Day 1 – 3rd April 2013 - Southampton

Ground-Gas Monitoring and Guidance

Arrangements for the Day

• Fire alarm and assembly area

• Toilets

• Tea/Coffee and lunch

• Feedback forms & CPD Certificates

Arrangements for the Day 1 • 9:30 – Introduction

• 9:45 – Unit 1 – New guidance

• 11:00 – break

• 11:30 – Unit 2 – Radon

• 12:30 – Lunch

• 13:30– Unit 3 – Best practice in collecting data

• 14:30 - break

• 15:00 – Unit 4 – Risk assessment with continuous data

• 16:00 – Q & A

• 16:30 - Ends

The Deal:

• You fill in the feedback form and hand it in,

• We’ll send you electronic copies of the presentations!

Ground-Gas Monitoring, Guidance, Protection and Best Practice

Unit 1- New guidance on Ground Gas

1.1 - New BS 8576 (in draft) - Guidance on the investigation of ground gas – permanent gases and volatile compounds.

1.2 - CIRIA C716 (2012) – Remediating and mitigating risks from VOC from land affected by contamination

1.3 - CIRIA Validation & Verification.

1.4 - BS 8485 - Review.

Objectives of Ground-Gas Assessment

• Determine the true subsurface gas regime

• Predict how this may change in the future

• Assess the ground-gas risks, and

• Manage those risks

History of Ground-Gas Hazard

1913 Senghenydd Colliery Disaster

14th October 1913

439 miners died

• Believed a methane (firedamp) explosion was caused by an electrical

spark. The force of the explosion disturbed coal dust from the floor which then ignited and raced through the mine.

• Those that survived the explosion and fire probably died from afterdamp (carbon monoxide, carbon dioxide, very low oxygen)

Abbeystead Valve House Disaster

• 23rd May 1984

• 28 people injured

• 16 people died

History of Ground-Gas Hazard

• Dissolved methane within natural groundwaters entered the concrete lined Wyresdale Tunnel through cracks and porosity

• No investigation boreholes were drilled along the length of the tunnel – “Designers’ extensive experience of work on other tunnels”

• Degassing of methane in a confined space – design issue?

• Operator departure from Operational Manual

• Possible ignition source from smoking?

History of Ground-Gas Hazard

Loscoe Landfill Gas Explosion

• 6:30am,

24th March 1986

• 3 people injured

• Migration of landfill gas which accumulated in a subfloor void to within the explosive range of methane

CIRIA 130, 1995

Loscoe Public Inquiry

Previously Published Guidance •1987 BRE 100: Measurement of Gas Emissions from Contaminated Land

•1991 BRE 212: Construction of New Buildings on Gas Contaminated Land

•1991 DOE Approved Document C (Building Regulations)

•1991 DOE WMP 27: Landfill Gas (2nd Edition)

•1993 CIRIA 130: Methane: its occurrence and Hazards in construction

•1993 CIRIA 131: The Measurement of Methane and Other Gasses from the Ground

•1995 CIRIA 149: Protecting Development from Methane

•1995 CIRIA 150: Methane Investigation Strategies

•1995 CIRIA 152: Risk Assessment for Methane and Other Gasses from the Ground

Previously Published Guidance

•1997 DETR/PiT Passive Venting of Soil Gases Beneath Buildings

•1998 IWM The Monitoring of Landfill Gas (2nd Edition)

•1998 OWEN & PAUL Methodology for the quantitative design of gas dispersal layers paper, published in Polluted and Marginal Land 1998

•1999 WILSON &CARD Reliability and risk in gas protection design paper, published in Ground Engineering

•2001 BRE 414: Protective Measures for Housing on Gas Contaminated Land

•2003 EA Consultation: Building Development on or within 250m of a Landfill Site (consultation closed Oct 2003 )

•2004 ODPM Approved Document C (Building Regulations 2000)

Recently Published Guidance •NHBC - Guidance on evaluation of development proposals on sites where methane and carbon Dioxide are present Report No 10627-RO1 (04) January 2007

•CIRIA - C665 Assessing Risks posed by hazardous ground gases to buildings 2007

•BS8485 – Code of Practice for the characterisation and remediation from ground gas in affected developments Dec 2007

•LA Guide to Ground Gas (Ground gas handbook) (Sept 2008) – Wilson, Card and Haines

New guidance

•BS8576 Guidance on investigations for ground gas – permanent gases and volatile

organic compounds (VOCs)

•CIRIA C716 remediating and mitigating risks from Volatile organic

compound (VOC) vapours from land affected by contamination

•CIRIA validation and verification title to be confirmed

•BS8485 review

BS 8576: 2013 (Draft)

• Guidance on investigations for

ground gas – Permanent gases

and Volatile Organic Compounds

(VOCs)

• In final draft now

• Links together key recent

documents into a full British

Standard

• Monitoring and sampling of

ground gases

• Does not cover Radon

Permanent Gas and VOC definitions

Permanent Gas

“Element or compound that is a gas at all ambient temperatures likely

to be encountered on the surface of the earth” – except Radon!

Volatile Organic Compound

“a) organic compound that is volatile under normal

environmental/atmospheric conditions, although it can be found in the

ground in the solid, liquid and dissolved phase form as well as in

gaseous phase. (from CIRIA Report 682)

b) organic compound which is liquid at 20 °C and which generally has

a boiling point below 180 °C (after ISO CD 11074:2011)”

Preliminary Investigation • Desk study and site reconnaissance (site walkover) in line

with BS 10175 and establishes the site investigations to

follow based on the objectives set

• For sites in which migration of permanent ground gases is to

be investigated, a conceptual model cross section ‘should’ be

included

Investigation & Monitoring • Permanent ground gas monitoring done

with standard borehole installation and

also small diameter sampling probes

• Twin gas taps with internal

tube to allow gas recirculation

(depth to around 0.5m above

SWL)

Investigation & Monitoring • Volatile sampling done with probes and have small

restricted response zone (0.15 to 0.5m)

• Leak tests

• Variable methods of

monitoring and many types of

sampling media

• Laboratory discussions

important

Includes Continuous Monitoring • Where a more comprehensive characterization of a ground

gas regime is required, for example, to improve a risk

assessment, the collection of data at a higher frequency may

be considered. This type of monitoring is not necessary on all

sites. It can be achieved in a number of ways using either well

head or in-hole monitors programmed to sample at regular

intervals. This can enable valuable information to be recorded

for later downloading and analysis or for the information to be

sent by telemetry for real-time assessment. The benefit of

higher frequency data should be considered against the

period of time over which it is collected.

NOTE 3

How Much?

• Decision Table in Figure 5

CIRIA C682 – VOC Handbook

• Lead authors:

• Arcadis

• Nottingham County

Council

“Investigating, assessing

and managing risks from

inhalation of VOCs at

land affected by

contamination.”

CIRIA C682 - 2009

• The investigation VOC’s document was already out of date when it was published.

• Included sorbant tubes, low flow pumps and PIDs.

• Didn’t include:

– Continuous monitoring

– Vacuum cannisters (e.g. Silco)

• Very good guidance on VOC risk assessment

CIRIA C682 - 2009

CIRIA C682 – VOC Handbook

CIRIA C716 – Remediating VOC Risks

• Lead authors Arcadis

• Funders included:

– PAG & GGS

• Covers:

– Petroleum

hydrocarbons

– Halogenated

hydrocarbons

– N, S & O containing

organic compounds

CIRIA C682 - 2009 CIRIA C716 - 2012

CIRIA C716

The guidance leads the reader through the three stages of remediation risk mitigation as outlined by DEFRA and the Environment Agency of England and Wales (2004) namely :

1 Development of the remediation strategy

2 Design and implementation of the remediation strategy

3 verification of the remediation strategy (including long term monitoring and maintenance)

CIRIA C716

1.0 Introduction

2.0 Assessment of Risk from VOC Vapours

3.0 Development of remediation Strategy

4.0 Source treatment / management

5.0 Pathway management

6.0 Receptor management

7.0 Remediation completion

A1 Findings of the electronic survey

A2 Good practice case study

A3 UK Building construction and the stack effect

A4 Source treatment / management – techniques overview

A5 Pathway management – techniques overview

A6 Low permeability vapour membranes

A7 Modelling the efficiency of a pathway management technoque

A8 Checklist to aid remediation verification

CIRIA C716

Assessment ( 6 pages)

Strategy development (19 pages)

Source Treatment / management (21 pages)

Pathway Management (23 pages)

Receptor management (5 pages)

Remediation completion (10 pages)

Appendices (65 pages)

Gas Protection Guidance

CIRIA Validation and verification

• Peter Atchison

Validation & Verification

New document not yet published

Approaching “final draft” stage

Likely to be published in 12-18 months time!!!!!

Aimed at clients and engineers / specifiers in order to assist them in setting appropriate levels of validation according to what system has been used and by whom installed.

Uses all state of the art validation techniques from visual inspection to integrity testing

Validation and Verification

Presumptions:

ALL installations should be subject to some form of validation

Validation should be proportionate to the risks from the site AND the experience of the installation operatives

Validation should be conducted by suitably qualified INDEPENDENT practitioners.

In the event of appropriate self validation this should be AUDITED by a suitably qualified independent auditor

Validation & Verification

Validation and verification is the single most important aspect of barrier installation and has been implied for many years. Only with the development of this document will designers, clients, practitioners and the like be able to substantiate the presumptions of the past 20 years.

NOS’s VR 612 and 613 describe the process

NVQ level 2 qualification in gas membrane installation has been developed and offered by NSAC

Up-skilling course for installation operatives available via the British Geomembrane Association

Gas Protection BS8485 an introduction

Start with the site

• Information is key, quality and quantity should be in line with expectations

• Analysis is based on “Gas Screening Values” • Professional judgement should be used. • CIRIA C665 gives excellent guidance • Consider the receptor. • Use Risk analysis techniques. • BS8576 recently published

• Ground bearing concrete slab

• The slab is poured directly on to the gas barrier, below which is a venting layer. Ventilation paths must be provided from the venting layer to atmosphere

• Suspended beam and block floors.

• Gas barrier is laid over the structural floor and covered with a screed. The sub floor can be ventilated by air bricks

Housing

Apply the guidance

BS8485 code of practice

Is a framework for managing ground gas risk and solutions.

Builds on the work in C665 and the NHBC document.

Uses “points based” system to identify levels of protection required and provided.

Splits the protection into ventilation, slab, barrier and monitoring / validation sections.

Is designed to offer a common approach for designers, regulators and construction professionals.

Confirm requirements

Table 2 in BS8485 identifies recommended levels of gas protection for characteristic gas situations and various construction types.

Characteristic

Gas situation

NHBC Traffic

light

Non Managed

property

E.g. private

housing

Public

Buildings

Commercial

Buildings

Industrial

Buildings

1 Green 0 0 0 0

2 Amber 1 3 3 2 1

3 Amber 2 4 3 2 2

4 Red 6 5 4 3

5 6 5 4

6 7 6

BS8485 application

Refer to Table 3 to select a range of measures which contribute to the required gas protection score

Only one element from each sub section

– Ventilation

– Floor slabs

– Membranes (including installation)

– Monitoring and detection

– Pathway intervention

– VALIDATION / VERIFICATION?

NHBC Traffic Lights

• Green site – Ground gas protection measures not required

• Amber “1” site – Low to Moderate measures required may consist of barrier installed by ground worker to good standards and involve validation

towards the upper end. Ventilation should offer 1 change in 24hrs

• Amber “2” Site – Moderate to high measures required

membranes should be installed by specialist contractor, involve appropriate CQA measures

and should be validated, Integrity testing should be considered at the upper end.Ventilation should offer 1 change in 24 hrs as with amber “1”

• Red site – Residential housebuilding not allowed unless the site characteristic situation can be demonstrably lowered.

Housing

• Ground bearing concrete slab

• The slab (0.5-1.5pts) is poured directly on to the gas barrier, (0.5-2.0pts) below which is a venting layer. Ventilation paths must be provided from the venting layer to atmosphere (0-2.5pts)

• Suspended beam and block floors.

• Gas barrier (0.5-2.0pts) is laid over the beam & Block floor (0pts) and covered with a screed. The sub floor is ventilated by air bricks (2.5pts)