Ground gas protection

Technical Guidance Document C

Contaminated Land

Radon, CO2, CH4 and VOCs

Presenter

Michael Sweeney MIEI

Contents

• Types and sources of gases

• Current guidance and legislation

• Protection measures – slab types, passive ventilation and gas

barriers

• Installation quality

• Detailed design

• Independent verification

• Q&A

• Radon (Rn)

• Methane (CH4) and Carbon Dioxide (CO2)

• VOCs

– Hydrocarbon vapours

– Hydrocarbon liquids

– Chlorinated solvents

Source Pathway Receptor

Types of gas/vapours

Source, pathway & receptor

What can go wrong?

Newbyres Crescent, Gorebridge, Scotland

• 2013 – 6 people admitted to hospital due to carbon

dioxide poisoning due to a leak from a mothballed

coal mine

• 2014 – Council evacuated street due to

human health concerns

• 2016 – Council demolished 64 homes

with an overall cost approx £12m

• Gas protection measures installed

Crucially inadequate verification carried out

Regulations and guidance

Building Control Regulations 2014

• Introduction of assigned assessors (Chartered architects/engineers/surveyors)

• Certification – Design cert, Ancillary cert and Cert of compliance

• Inspection plan – Sets out frequency and details of verification requirements

• Competent Person Sign Off

– No UKAS accredited body of gas membrane installers

– No Irish qualifications in gas membrane installation

– Conflict of interest and Insurance responsibilities

Regulations and guidance

Irish Regulations and guidance documents

• DOE – Technical guidance document C (2004)

• DOE – Radon in existing buildings (2002)

• DOE – Protection of new buildings and occupants from landfill gas (1994)

• EPA – Guidance on the management of contaminated land and groundwater at EPA

licensed sites (2013)

• EI – Specification and related documents for ground investigation in Ireland (2016)

Regulations and guidance

UK Regulations and guidance

• BRE 211 – 1999 – Radon: Protective measures for new dwellings

• Approved document C – 2004 – Site preparation and resistance to contaminants and moisture

• CIRIA C665 – 2007 – Assessing risks posed by hazardous ground gases to buildings

• BS8485 – 2007 – Revised 2015 – Code of practice for the characterization and remediation from ground gas in affected buildings

• CIEH Ground gas handbook – 2009

• CIRIA C716 – 2012 – Remediating and mitigating risks from VOC vapours from land affected by contamination

• CIRIA C735 – 2014 – Good practice on the testing and verification of protection systems for buildings against hazardous ground gases

• CIRIA C748 – 2014 – Guidance on the use of plastic membranes as VOC vapour barriers

Regulations and guidance

Radon Risk

• WHO estimates between 3-14% of lung cancer in a country is

attributable to radon depending on radon national averages

and smoking prevalence

• Ireland has approx. 2500 diagnosis of lung cancer per year

• 3% - 75 cases / 14% - 350 cases

• HSE states Ireland has an average of 89 Bq/m3

• This is the 8th highest average concentration in the world

• We have approx. 830,000 smokers in Ireland (approx. 22%

of adult population) but thankfully this is declining

Regulations and guidance Technical Guidance Document C - 2004

• National reference level/long term exposure is

200Bq/m3 for dwellings / 300 Bq/m3 for workplaces

• High Radon Areas - >10% above 200Bq/m3

– Membrane and sump

• Other than High Radon Areas

– Stand by sump

• Performance criteria set out for radon barrier (permeability/robustness etc)

• Basically parameters for NSAI IAB certification

– NSAI certify 13 gas barriers / 3 of which conform to BS8485: 2015 for Methane

– 0 of these hold any test data to conform with CIRIA C748 for VOC risk

– Of the waterproofing manufacturers – IAB or BBA – lack of test data

Importance of selecting membrane specific to gas regime on site

• References BS5930: 1999 in relation to site investigation

Regulations and guidance

EPA - Guidance on the management of contaminated land and groundwater at EPA

licensed sites (2013)

• We currently have no specific legislation addressing contaminated land

• Emphasises risk based approach and the conceptual site model

SOURCE PATHWAY RECEPTOR

EI - Specification and related documents for ground investigation in Ireland (2016)

• Provides good practice for SI in Ireland

• References a range of standards inc;

• BS5930 (2015); BS10175 (2011); BS8756 (2013); BS8485( 2015) and CIRIA

guidance

Regulations and guidance

BS5930 / BS10175 and BS8576

• BS5930: Code of practice for ground investigation (2015)

– Referenced in TGD C (1999) Landfill Doe (1981) and EI (2015)

– States in foreword it doesn’t provide guidance on contaminated sites

• BS10175: Investigation of potentially contaminated sites (2011) +A1(2013)

– Sets out SI process and CSM development

– References onto further guidance for intrusive monitoring and sampling

• BS8576: Guidance on investigations for ground gas and VOCs (2013)

– Provides sampling techniques and strategies and frequency for data collection

• All three provide site characterisation technique in line with CSM

• Our guidance references BS8485 through these documents and others (BS8102)

Regulations and guidance

BS8485: 2015 + A1: 2019

• Site characterisation of specific contamination risk

– Characteristic Situation 1 to 6

• Looks at conceptual site model and building type in risk assessment

• Uses a point scoring system for each protection element

• Detailed design required providing assumptions, risk assessment,

methodology and calculations

• Independent verification strategy and how to risk assess this element

• Includes annex’s on Radon and VOCs

Regulations and guidance

BS8485: 2015 + A1: 2019 - Table 4 – Gas protection score by CS and type of building

A) Residential should not be built on CS4 or higher unless additional levels of protection can be incorporated e.g. High-performance ventilation or pathway intervention

B) The gas hazard is too high for this empirical method used to define gas protection measures

CS Minimum gas protection score (points) High Risk Medium Risk Low Risk Type A Type B Type C Type D

1 0 0 0 0

2 3.5 3.5 2.5 1.5

3 4.5 4 3 2.5

4 6.5 A) 5.5 A) 4.5 3.5

5 - B) 6.0 A) 5.5 4.5

6 - B) - B) - B) 6.0

Slab design

BS8485: 2015 + A1: 2019 – Table 5 – Gas protection scores for the structural barrier

A) Scores and conditional on breaches of floor slabs, etc., being effectively sealed

B) To achieve 1.5 the slab should be well reinforced to control cracking and have minimal penetrations

C) Score conditional on waterproofing design of Type B: Structural concrete design

D) If Type A: Membrane employed points can be achieved if it meets criteria in Table 7

Floor and substructure design Score A)

Precast suspended segmental subfloor (i.e. Beam and block) 0

Cast in situ ground bearing floor slab (with only min mesh reinforcement) 0.5

Cast in situ monolithic reinforced ground bearing raft or suspended floor slab with minimal penetrations

1 or 1.5 B)

Basement floor and walls conforming to BS8102:2009 Grade 2 C) + D) 2

Basement floor and walls conforming to BS8102:2009 Grade 3 C) + D) 2.5

Slab design

Venting design

BS8485: 2015 + A1: 2019 – Table 6 – Gas protection scores for ventilation measures

Protection element Score Comments

Pressure relief pathway 0.5 Minimum protection

Passive sub floor dispersal layer 1.5 or 2.5 Dependent on ‘very good’ or ‘good’ performance

Active dispersal layer 1.5-2.5 Normally fans providing active abstraction

Active positive pressurization 1.5-2.5 Creation of a blanket of external fresh air beneath the slab

Ventilated car park 4 Ventilation to deal with exhaust fumes to Approved Doc F

Venting design

Protection Systems

Venting Systems

• Block and beam floor (clear void)

• Geocomposite venting mats

• Polystyrene vent systems

• Gravel and pipe design

• Radon sump layouts

Gas membranes

BS8485: 2015 + A1: 2019 – Table 7 – Gas protection scores for the gas resistant

membrane

Protection element Score Comments

• CH4 transmission rate <40 ml/day/m2/atm. Tested to BS ISO 15105-1 • Durable to remain serviceable for anticipated life of building • Robust to withstand stresses (settlement if below slab?) • Robust to withstand installation process (puncture from steel etc) •Provide a complete barrier to relevant gas •Verified in line with CIRIA C735 •If VOCs are present consult CIRIA C748

2

Performance is heavily dependent on quality of design, installation and resistance to damage after installation and integrity of joints If a membrane is installed that doesn’t meet criteria in column 1 then the score is Zero! A reinforced LDPE (virgin polymer) membrane having a min mass per unit area of 370 g/m2 and not significantly less than 0.4mm thick.

Gas membranes

Protection Systems

Barriers

• 1200g (0.3mm) DPM

• 2000g (0.5mm) DPM

• 1600g (0.4mm) LDPE reinforced proprietary

gas barrier

• 1600g (0.4mm) LDPE reinforced proprietary

gas barrier including aluminium foil layer

• 2000g (0.5mm) HDPE reinforced barrier

including EVOH layer

• 4000g (1mm) HDPE

• 4000g (1mm) PP

Installation quality

• Difference between ground worker/flooring

contractor and specialist gas membrane

installer?

• A membrane manufacturers training course

is not a qualification to be a specialist

• Cskills NVQ L2 in gas protection installation

TWI CSWIP welding qualifications

• Large variance in design, installation and

verification techniques

Installation quality

Examples of installations

Installation quality

Examples of installations

Detailed design

Detailed design – Regardless of contamination type e.g. Rn/CO2/CH4/VOCs

• Design and specification should be clearly defined and justified

• Referencing solution scores and tables in recommendations

• Pre-construction drawings and notes

• Detail critical assumptions made during assessment

• Justify any venting design including calculations to show specified vent performance

• Membrane specification including justification for use:

– Inc site specific constraints (any protection required)

– Where is the membrane installed? Above or below slab? Differential Settlement

– Performance requirements of gas membrane

Independent verification

Verification Strategy

• Plan for independent verification put in place at design stage.

• How, when and by whom?

• Provides a plan setting out the strategy of:

– Installation of protection measures

– Inspections and integrity testing

– Reporting remediation highlighted and to be carried out

– Compiled into a verification report at the end of the installation

• All to be carried out in line with CIRIA C735

• This should be a key element and assessment in Building Control Regulations

What can go wrong?

Newtongrange, Midlothian - 2018

• Project manager forged validation reports

detailing integrity testing of gas protection membranes

• Court ruled his actions put 11 families potentially

at risk

• Project manager was convicted and jailed for

7 months

Conflict of interest

“The Environment Agency recommends that conflicts of interest in

verification should be avoided. A contractor or gas membrane

supplier certifying

their own work or product is considered to be a conflict of interest

and is not good practice. If verification is carried out by the same

company (or related company) that carried out the installation then

the process, the results

and report should be audited by an independent consultant”

CIRIA C735

Certificate of compliance

• Quality of assigned assessment?

• Qualification of who is inspecting and signing

the work off?

• Clear conflict of interest in contractor or

sales rep signing Bcar certificates

• Lack of insurance

• Crucially against best practice

Verification strategy

Risks to Design Team and Contractors

• Currently see Manufacturers confusing matters by addition to NBS specification

• Manufacturer ‘validation reports’

• ‘Specialist Contractors’ holding no qualifications setting up separate validation companies to

validate their own work –

• ‘Specialist Contractors’ providing design’s with little or no methodology, risk assessment or

detailing

Verification strategy

Risks to Design Team and Contractors

• Assess the suitability of the verification plan and crucially who is providing inspections.

• Check limitations

• Ask for proof that the inspection company is separate to the installer if they are providing

this

Verification strategy

Elements to consider (Matrix – CIRIA C735 – Mallett et al.)

• Gas regime

Low/Intermediate/High risk

• Design complexity

Simple (few service penetrations and

subfloor void)

Complex (variety or protection

measures, numerous columns,

penetrations and corners)

• Number of buildings/plots

Small <5/Medium 3-15/Large >10

• Installation workforce

Non specialist (general builder/ground

worker)

Specialist (NVQ L2 qualification)

Integrity testing

• This is not the same as Independent validation

• It involves the integrity testing of the

gas protection system

• Seam Joint Testing

– Air lancing seam joints – ASTM D4437

• Leak Detection or Pinhole Testing

– Tracer gas testing

– Smoke testing

– Dielectric porosity testing – ASTM D4787

Summary

• Design standards

– Design report

– Where is the membrane to be installed?

– How likely will it last the construction process?

– Complexity of detailing?

• Specification of membrane

– Less reliance solely on certification

– More emphasis on membrane test data and robustness

Summary

• Venting options

– Pressure relief/Passive/Active ventilation?

– Calculations proving venting performance

– Inspection of venting layouts

• Independent verification

– Risk based approach

– Verification plans outlining integrity testing requirements at design stage

– More cost effective than remediation post construction

– Photographic report covered by relative insurance

– Importantly carried out by someone suitably qualified and independent of the

installation contractor and not a manufacturers sales person

Ground gas protection

Michael Sweeney

michael@gqa.ie

+353 86 241 8683

+353 74 974 2481

http://www.engineersjournal.ie/2019/05/20/assigned-assessment-of-contaminated-land-risks/