CIRIA VOC remediation guidance

Transcription

1 CIRIA VOC remediation guidance Joanne Kwan, CIRIA CIRIA Guidance CIRIA C682 The VOC Handbook: Investigating, assessing and managing risks from inhalation of VOCs CIRIA RP938: Remediation and mitigation of risks from VOC vapours 1

2 Presentation Overview Terminology What are VOCs? Sources of VOCs Behaviour of VOCs Vapour Intrusion and the Stack Affect Why Investigate VOCs in Soil Gas? Remediation Strategy t Framework VOC Treatment and/or Management Methods Remediation Completion Terminology Soil gas: Vapour: Vapour intrusion: Vapour emission: Vapour release: used to refer to gases in the subsurface used to describe the VOCs present in an indoor or ambient air space the process by which VOCs migrate into a structure from the subsurface the process by which VOCs migrate from the ground surface or an excavation into atmospheric conditions (often into an outdoor air space) an instantaneous release of VOCs, typically into atmospheric conditions, due to physically disturbing the soil structure 2

3 What are VOCs Organic compounds that are volatile under normal conditions Include: petroleum (non-halogenated hydrocarbons) halogenated hydrocarbons nitrogen, sulphur and oxygen- containing organic compounds VOCs vs other gases? Other gases found in the ground, at higher levels CO 2 and methane asphyxiation, explosion surely worse? So why are VOCs a concern? - Different effects - Effects even at low levels - Behaviour often less predictable Assessment of VOCs is very different from bulk ground gases 3

4 ature of Hazard Hazards from VOCs can be split into three general groups: (1) Health Effects (differing levels of exposure) (2) Odour (3) Flammable/explosive risks Sources of VOCs? Wide-ranging Industry (e.g. leaks, spills) Landfill sites Building, furnishing & consumer household products Vehicle emissions aturally occurring 4

5 Background levels? Important to consider in any assessment for VOCs Source: CIRIA C682 How do VOCs Behave? factors affecting presence in soil gas factors influencing migration in soil gas factors influencing migration into air spaces 5

6 Factors affecting presence in soil gas Physical/chemical properties of the VOC e.g. vapour pressure? Geology e.g. organic matter content? Timescales e.g. continuing source? Chemical/biological e.g. degradation? (e.g. PCE to TCE to DCE to VC) Air pressure gradients Factors affecting migration in soil gas Source: Johnson and Ettinger, 1991 Consider mechanisms diffusion, advection, dispersion Environmental medium? Then wide-ranging: - Physical/chemical - Atmospheric pressure - Rainfall/tidal - Temperature - Wind - Anthropogenic - Other gases Depth considerations 6

7 Movement from subsurface to air Vapour intrusion, emission or release Vapour intrusion building construction and use is key! Vapour emission surface cover, air flow above soil Source: CIRIA C682 Vapour release much more sitespecific, difficult to predict Preferential pathways Stack Affect 7

8 Why investigate VOCs in soil gas? Reduce uncertainty in the assessment Particularly important for petroleum hydrocarbons and chlorinated hydrocarbons Sampling locations 8

9 Is Remediation Required? Robust Conceptual Site Model Robust site evaluation: Use of soil gas sampling Multiple lines of evidence Robust risk assessment: In many cases a Detailed Quantitative Risk Assessment is likely to be required Remediation Strategy Framework.Similar to CLR11 9

10 Aspects covered Pollutant linkages Commercial objectives Health and safety issues Exposure duration Cost benefit analysis Sustainability issues Waste management issues Environmental permitting Geotechnical aspects Why consider geotechnical aspects? Could affect the conceptual understanding of the site. Consider this conceptual site model..is there a vapour intrusion pathway?.how will they construct the building? 10

11 Why consider geotechnical aspects?. Is there a vapour intrusion i pollutant t linkage? Solving the geotechnical problems in some cases could cause an environmental problem! Source Treatment Source destruction In situ Source removal Ex situ Source immobilisation 11

12 Source Treatment Technique Examples Phytoremediation Biopiling Windrow turning In situ chemical oxidation Dual phase extraction In situ soil stabilisation Pathway Management Techniques 12

13 Pathway Management Pathway Management Technique Examples Vertical venting trench Low permeability vapour membranes Virtual curtain TM Geosynthetic venting layers Granular YCLF Meeting: venting Update layers on Challenging Contaminants Tented structures 13

14 Low Permeability Vapour Membranes Various types of membrane available. Commonly used for bulk ground gases. Varying chemical resistance. When to use a specific chemical resistance membrane. How to select a suitable low permeability membrane? Importance of good installation. Verification and validation Multiple Levels of Protection How many levels of protection are required? ot a simple solution therefore no look-up tables Will depend on a number of factors including: Confidence in remediation solution Confidence in the site characterisation Confidence in the DQRA umber of lines of evidence for a risk being presented by the vapour intrusion pathway. 14

15 B Receptor Management The different receptor management techniques include: Evacuation of the land and/or building Restricted access to land and/or building Modification or change to the land usage Receptor monitoring and protection Techniques Look Up Tables Mitigation method Technique also used for Source management Receptor management Applicable media Applicable compounds Halogenated hydrocarbons on-halogenated hydrocarbons, S and O2- containing compounds Bulk ground gases Advantages Disadvantages Comments / challenges Other factors Cost Implementation timescale (years) Environmental sustainability Horizontal atural or engineered clay barrier SG Y Y Y Y - well understood technology - potential for on-site source of clay Barriers - can be breached by unplanned excavations and services - may be a conflict between obtaining low permeability properties and geotechnical improvement as different mixes and moisture contents would ideally be used for each aspect - drainage layer will require ventilation at edges of barrier to allow dispersion of gas to atmosphere. <1 Soil-bentonite admixture barrier SG Y Y Y Y - no special jointing required - swelling properties can result in punctures self-sealing - geotechnical properties of soil can also be increased (for example, via addition of cement) - not suitable for coarse materials such as gravel - treatability study recommended to assess suitable mixes and affects inground chemicals may have on mixture - placement generally restricted to flat surfaces or gentle gradients where sufficient compaction can be achieved. - may be a conflict between obtaining low permeability properties and - not normally suitable for vertical trenches geotechnical improvement as different mixes and moisture contents - vulnerable to shrinkage and cracking if allowed to dry out. would ideally be used for each aspect - certain chemicals can impair the swelling properties of - drainage layer will require ventilation at edges of barrier to allow bentonite dispersion of gas to atmosphere <1 Synthetic low permeability vapour membrane SG Y Y Y Y - well understood technology - relatively cost effective - can be breached by unplanned excavations and services - may not be suitable in isolation - durability of membrane - resistance of membrane to chemical and/or biological attack - resistance of membrane to physical damage (puncturing and tearing) - potential future ground movement tearing membrane - detailing of joints requires design and consideration - drainage layer will require ventilation at edges of barrier to allow dispersion of gas to atmosphere. <0.5 Vertical Soil bentonite admixture barrier SG, G, APL Y Y Y Y - only limited disposal of contaminated soil. - can be breached by unplanned excavations - treatability study recommended to assess suitable mixes and affects inground chemicals may have on mixture <0.5 Synthetic low permeability vapour membrane (in-trench) SG, G, APL Y Y Y Y - well understood technology - only suitable to depths of about 5m - many membranes can resist a wide range of contaminants - potential disposal of contaminated soil - excavation sides may require support or battering back - can be breached by unplanned excavations - membrane can be damaged during backfilling if it is not adequately specified and protected - durability of membrane - resistance of membrane to chemical and/or biological attack - resistance of membrane to physical damage (puncturing and tearing) - potential future ground movement tearing membrane - detailing of joints requires design and consideration <0.5 Grout injection and slurry wall SG, G, APL Y Y Y Y - well understood technology - can be constructed to depths in excess of 20m - potential disposal of contaminated soils - disposal of bentonite slurry - can be breached by unplanned excavations - ensuring appropriate design to match geological and hydrogeological setting <0.5 Clay filled trench SG, G, APL Y Y Y Y - well understood technology - easily installed by groundworkers - only suitable to about 5m depth - potential disposal of contaminated soil - excavation sides may require support or battering back - can be breached by unplanned excavations - particle size, moisture content, method of compaction and placement all need consideration if barrier is to perform satisfactorily - potential for cracking if allowed to dry out - testing recommended to ascertain compaction and permeability characteristics of clay prior to use <0.5 Barriers formed by piling - sealed sheet pile wall SG, G, APL Y Y Y Y - can be installed to depths of about 15m - limited space required - no excavation of contaminated soil - can act as retaining wall YCLF Meeting: - vibration Update can be an issue on (but push Challenging systems are Contaminants available) piles and problem with sealing - obstructions can prevent design depth being reached - very dense granular deposits or rock can result in buckling of sheet - quality of sealing can be difficult to control. <0.5 Barriers formed by piling - secant pile wall SG, G, APL Y Y Y Y - can be constructed to depths in excess of 20m - can act as retaining wall - expensive - unlikely to be suitable as gas barrier in isolation. - quality of sealing between piles can be difficult to control <0.5 15

16 Remediation Completion Importance of good verification and validation Verification plan Engineering-based and outcomebased criteria Multiple lines of evidence Common problems and potential solutions Verification report Refinement of CSM Long-term monitoring and maintenance Summary Many different options available for remediating / mitigating against the risks presented by VOCs Development of a successful remediation strategy relies on a good site investigation, conceptual site model and DQRA Multiple levels of protection may be required Validation and verification is of fundamental importance in delivering a successful YCLF Meeting: Update remediation Challenging Contaminants solution 16

17 Thank you for listening Tel: ii 17