VOC assessment and VOC membranes

Steve Wilson www.epg-ltd.co.uk

The next 25 minutes • Current issues in VOC assessment – where it often goes

wrong ▫ VOC risk assessment process ▫ The CSM and understanding of building construction and

vapour pathways through the floor ▫ VOC membranes ▫ Internal or underfloor void monitoring with PIDs and laboratory

testing ▫ Basement VOC assessments – is it really a vapour issue?

VOC risk assessment – what should happen • Collect the right data • Critically assess the data • Develop a visual CSM • Critically assess CSM and define

what you are going to model • Develop the model or choose an

appropriate off the shelf one (there are several) that fits site and building

• Choose parameters • Do a bit of maths

Time and Effort Required

Note there is

nothing we use that is not in the public

domain

VOC risk assessment – what actually happens in a lot of cases • Collect the right data • Critically assess the data • Develop a visual CSM • Critically assess CSM and define what you are going to

model • Develop the model or choose an appropriate off the shelf one

(there are several) that fits site and building

• Ignore building construction, ground

model and use generic assumptions

• Use GACs or CLEA

Time and Effort

Ground model

• How deep is the contamination • What is the permeability and porosity of

the ground • Depth and nature of buried services –

will these provide a preferential pathway or not? They may not

• Ground improvement – will stone columns provide a preferential pathway? They may not

• Piled foundations – will they provide a preferential pathway – they are not likely to in most cases (paper by Wilson and Mortimer in Environmental Geotechnics (doi.org/10.1680/jenge.17.00009 Paper 17.00009)

Are generic assumptions reasonable?

• Reasonable quality reinforced concrete is often a sufficiently good barrier to vapour (and ground gas) providing pipes are cast in and internally sealed

• Where is the perimeter crack?

• Generic assumptions are over conservative

Are generic assumptions reasonable?

• Block and beam floor - leaky?

• Perimeter crack?

• Vented void - Good barrier? • Odour threshold exceeded in

void?

Remediation using VOC membranes

• Do not assume a membrane will break the pathway • Consultants need to take a stronger role in assessing

membrane suitability and design – signed of by Chartered professionals

• Membrane suppliers are not qualified to make assessments about the suitability of membranes to deal with VOCs – they are not risk assessors

• VOCs permeate through membranes at different rates dependent on: ▫ Concentration gradient ▫ Membrane material ▫ Thickness ▫ Solubility of the contaminant in the polymer ▫ Shape and size of the contaminant molecule

Supplier assessment

• Supplier stated “We have reviewed the attached report and noted there are hydrocarbons on site which would require a Hydrocarbon resistant membrane such as the ACME SUPER DUPER VOC BARRIER”

• Supplier highlighted report • Only contaminants are PAHs that are

not sufficiently volatile to pose a vapour intrusion risk

• Reference to “hazardous” is in relation to waste classification

• In fact there was no need for any VOC or gas membrane

Supplier assessment

• Aluminium foil membranes are often claimed by sales people to be the “Rolls Royce” or “top of the list” of gas or vapour membranes and better than other types

• They are not – many are extremely thin and prone to damage • Supplier of an aluminium foil membrane

▫ “We do not need VOC permeation test data because we have a layer of aluminium”

• Foil can be as thin as 12 microns (0.012mm thick) • It has pinholes through it from manufacture that will allow

vapour to migrate through it • Therefore you need test data as per CIRIA Report C748

Membranes • Check actual properties – sample on site? • Sample of aluminium foil gas membrane

taken from site • Tested at an independent laboratory

Property Claimed on data sheet

Measured values

BS8485: 2015 min

requirements Thickness at reinforcement (mm)

0.4 Not stated where it is measured

0.44 to 0.51 Mean 0.46

(1811 gauge)

--

Thickness in between reinforcement (mm)

Not stated 0.32 to 0.35 Mean 0.33

(1299 gauge)

0.4

Mass per unit area (g/m2)

370 343 to 355 Mean 349

370

Membranes

• It does not meet the minimum requirements from BS8485: 2015

• Ground gas handbook – use minimum 2000g membranes

• Thickness of plastic sheet protecting the critical foil is 0.33mm / 2 = 0.165mm (650 gauge)

• Small nicks and tears in plastic expose aluminium to cement paste if below slabs or screed directly on top – alkaline and corrodes the aluminium

• Membrane needed to prevent cement bleeding and reaching foil membrane!

Exposure to concrete

• Slight tear that is commonly seen on site (actually not as bad as some damage seen just from foot traffic let alone steel fixing)

Practical implications

• C748 places emphasis on robustness, chemical resistance as well as testing of permeation rates

• Thin foil membranes are not robust or durable enough to act as VOC membranes

BBA certificates

Which one would you have most confidence in?

1. VOC membrane with a BBA certificate

2. VOC membrane without a BBA certificate

BBA Certificate membrane

• Certificate states “the product is chemically resistant when exposed to, and limits the transmission of, volatile organic compounds (VOCs)”

• “Buildings in areas at risk of VOCs should follow the guidance detailed in CIRIA C748”

• BUT • Permeation test data is not in accordance with ISO 15105-02 as

recommended in C748 • Permeation test data limited to toluene and xylene (also diesel and petrol) • Permeation test is a liquid permeation test • Durability testing is not in accordance with C748 • Indicates joints can be taped but then states: • “The butyl tape has limited resistance to diesel and similar materials.

Welded joints must be used where there is any doubt over the compatibility of butyl tape”

Non BBA membrane

• Permeation test data in accordance with C748 with laboratory test results available

• Permeation coefficients provided

• Durability test data in accordance with C748

• Welded joints not affected by VOCs

• Resistant to puncture and tear • JUTA GP Titan • Proctor VOC Flex

Comparison of permeation rates

Can membranes solve everything?

• VOC membranes are not the solution to all problems

• NAPL at 0.65m – allowable concentrations exceeded even with a membrane and void with standard ventilation

• Could increase ventilation ? • But should we really be

leaving NAPL at shallow depth below housing sites?

• Consider concentrations in the void – odour issues at air bricks?

Permeation rates

• Ask to see laboratory test results • If nothing to hide a supplier will provide the test certificates and

graphs • Has testing continued to breakthrough?

Continuous internal monitoring - VOCs

• Often the primary contaminants of concern in VOC assessments are BTEX and chlorinated solvents PCE, TCE, DCE and vinyl chloride.

• Extremely low residential indoor air quality targets for these contaminants (particularly the chlorinated solvents)

• Requires ppb level instrument (can also change lamp voltage to target more specific range of VOCs)

• Sampling and analysis also requires very low MDLs - using a lab from the USA who are able to achieve lower MDLs than the UK labs.

• ppm monitor is unlikely to measure VOCs at a site where the risk is borderline. It may however provide useful information at a high risk site for in ground monitoring

• Understanding internal sources is critical with lower limits of detection

RfCs for various VOCs

Compound Mol Wt. RfC

(ug/m3) Concentration

(ppb) Concentration

(ppm)

Benzene 78.11 5 1.5 0.0015

Toluene 92.14 5000 1302.4 1.3024

Ethylbenzene 106.16 260 58.8 0.0588

Xylene 106.16 200 45.2 0.0452

Naphthalene 128.17 30 5.6 0.0056

Tetrachloroethylene (PCE) 165.83 40 5.8 0.0058

Trichloroethylene (TCE) 131.39 2 0.4 0.0004

Cis 1,2-dichloroethylene 96.94 0.27 0.1 0.0001

Vinyl chloride 62.5 1 0.4 0.0004

1,1,1-trichloroethane (TCA) 133.41 380 68.4 0.0684

1,1-dichloroethane 98.96 5 1.2 0.0012

1,2-dichloroethane 98.96 0.4 0.1 0.0001

1,1-dichloroethylene (DCE) 96.94 5 1.2 0.0012

Groundwater or vapour assessment?

• Consider the CSM (again!)

Final thoughts • The key to successful VOC risk assessment is choosing the most

appropriate ground model and building parameters • VOC membranes need to be critically assessed to make sure the risk

is mitigated to an acceptable level • Critically assess VOC membrane properties especially those relating to

durability • Use ppb level instruments for internal or underfloor void VOC

monitoring • For basements consider whether the VOC hazard is from vapour or

groundwater ingress

Thank You

Contact: stevewilson@epg-ltd.co.uk