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Ajb 2019 ddd presentation 16 sep19 100319

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Vapor Migration in the Phase I ESA: Lessons Learned from Recent Case Studies

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Ajb 2019 ddd presentation 16 sep19 100319

  1. 1. Vapor Migration in the Phase I ESA: Lessons Learned From Recent Case Studies Anthony J. Buonicore, P.E., BCEE, QEP Principal, The Buonicore Group Chairman, ASTM Vapor Intrusion Task Group
  2. 2. OVERVIEW • ASTM E2600 Standard: Migration Criteria • Case Studies • Lessons Learned • Q&A
  3. 3. AOC consists of the target property (TP) and the surrounding area, within which, if sources of volatile/semi-volatile chemicals of concern (COC) are present, such contamination may produce vapors that can encroach upon the TP. E2600: Area of Concern (AOC)
  4. 4. • 1/3rd mile (1,760 ft.) for known or suspect contaminated sites with COCs • 1/10th mile (528 ft.) for known or suspect contaminated sites with Petroleum Hydrocarbons (PHCs) – a subset of COCs that can rapidly biodegrade in soil • Default AOC is established conservatively based upon 90th Percentile plume lengths (and plume widths) • Default AOC is typically adjusted based upon the EP’s professional judgment and experience with respect to local area conditions E2600: Default AOC
  5. 5. • Use knowledge of groundwater flow direction • Use knowledge of subsurface characteristics such as: ‒ the presence of relatively impermeable soil or soil layers, such as wet, fine-grained or highly organic soils – clay, silty-clay soils that retard vapor migration ‒ the presence of a perched water table (clean water above contaminated groundwater) – that can reduce vapor intrusion (VI) potential ‒ fractured bedrock – that can increase vapor migration Common Ways to Adjust the AOC
  6. 6. • Use knowledge of surface natural features such as: ‒ major water tributaries (rivers, etc.) that can intercept migrating vapors ‒ wetlands that can impede vapor migration • Use knowledge of man-made features such as: ‒ utility corridors/piping on a gravel or sand base that can act as preferential pathways and intercept migrating vapors, potentially re-directing vapors away from TP or toward TP ‒ nearby buildings with structural characteristics that may act as barriers to vapor migration, e.g., below grade structures with relatively impermeable walls/foundations, underground parking, etc. Common Ways to Adjust the AOC
  7. 7. CD represents a best estimate of the lineal distance COC vapors volatilized from contaminated groundwater or contaminated soil might migrate in the vadose zone * 100’ for COCs in moderately permeable soils * 30’ for PHC subset in moderately permeable soils (as PHCs will undergo relatively rapid biodegradation) The distance is measured from the nearest edge of the contaminated plume (soil or groundwater) and the nearest TP boundary. E2600: Critical Distance (CD)
  8. 8. Adjusting the AOC when groundwater flow direction is known or can be inferred
  9. 9. Adjusting the AOC when groundwater flow direction is known or can be inferred
  10. 10. Adjusting the AOC when groundwater flow direction is known or can be inferred
  11. 11. • Assume a COC source located in the cross-gradient quadrant would be located at a point where the plume width from the COC source would be widest (conservative); and • Assume plume width (Pw) can reasonably be estimated as 1/3rd of the 90th percentile plume length (conservative) (per Domenico’s and Gelhar’s et. al. work; Newell et. al. work; State LUST data; actual dry cleaner plume data and actual SHWS plume data) * Buonicore, A.J., “Methodology for Identifying the Area of Concern Around a Property Potentially Impacted by Vapor Migration from Nearby Contaminated Sources,” Paper #2011-A-301, Proc. AWMA 104th Annual Conference, Orlando, FL, June 20-24, 2011 (copies available upon request) Accounting for plume width for a cross-gradient source under a conservative scenario with no actual plume data*
  12. 12. Source Location Up-gradient Down-gradient Cross-gradient Adjusted AOC for COC Sources when groundwater flow direction is known or can be inferred E 2600-15 Default 1,760’ 1,760’ 1,760’ Adjusted Based on GW Flow 1,760’ 100’ 365’
  13. 13. Source Location Up-gradient Down-gradient Cross-gradient Adjusted AOC for PHC sources when groundwater flow direction is known or can be inferred E 2600-15 Default 528’ 528’ 528’ Adjusted Based on GW Flow 528’ 100’ (LNAPL) 30’ (Dissolved) 165’ (LNAPL) 95’ (Dissolved)
  14. 14. Soil Type(s) Permeability Notes Clay/Silty Clay Very Slow Silty Clay Loam/ Moderately Slow Silt Loam Loam/Sandy Loam Moderate Sandy Moderately Rapid Gravel Very Rapid Adjustment considerations in upgradient/cross-gradient distance for subsurface soil conditions Many EPs reduce search distance around TP to 100’ or less for soils with slow permeability
  15. 15. • Present and former gas station sites • Present and former dry cleaner sites • Present and former industrial sites, particularly those using chlorinated solvents for degreasing and parts cleaning • Former manufactured gas plant sites • Former hazardous waste disposal sites • Present and former garbage landfills Most prevalent sources of concern
  16. 16. CASE STUDIES AND LESSONS LEARNED
  17. 17. • TP is multifamily property located across the street from a retail strip plaza constructed in 1969. • Based upon groundwater flow experience in the area, the Consultant established that groundwater flow in the area identifies the retail strip plaza as being hydraulically cross- gradient from the TP. • The strip plaza property line is 120’ from the TP property line and the actual buildings in the strip plaza are located 475’ from the TP property line. • The Phase I ESA (city directory search) identifies a former dry cleaner in the strip plaza from 1969 – 1988 as the only environmental concern. • Government records did not identify any releases from the dry cleaner. • Soil throughout the area is moderately permeable - sandy loam. Case Study #1
  18. 18. • Since the buildings in the strip center are located 475’ from the TP property line, this distance exceeds 365’ (90th percentile) and the Consultant determined that a VEC was not likely. • Since the TP was multifamily, the prospective purchaser requested that the consultant perform confirmatory soil gas sampling at the TP property boundary. • Soil gas sampling revealed the presence of PCE, cis-DCE and 1,1-DCE. • Phase II investigation underway at strip plaza. • Phase II consultant believes the contamination may have resulted from dry cleaner spent filter cartridge disposal in the dumpster located at the property line (120’ from the TP property line and well within the 365’ distance). • Property transaction on hold. Case Study #1 (cont’d)
  19. 19. • Unless other information is available, assume former dry cleaners with on-site cleaning used PERC (which has been used since the 1930s). • Assume dry cleaners using PERC had releases – even if there were no records of releases (experience has shown that almost all have had releases). • Likely releases result from: accidental spills, e.g., during solvent transfer, equipment and piping leaks and malfunction, separator or filter rinse water releases to landscaping or storm water drains, leaking sanitary sewer lines, improper handling of spent filter cartridges (e.g., disposal in dumpsters) and still bottoms residue. • Contaminants that might be found in dry cleaner releases include: PERC, TCE, cis-1,2- DCE, trans-1,2-DCE, 1,1-DCE and vinyl chloride. Case Study #1: Lessons Learned
  20. 20. • Historic dry cleaner tenant space in a strip center may be different from its current location. • When former dry cleaner location is not known, assume the worst case location (i.e., closest to the TP). • Assuming the location of a dumpster on the site is unknown, and since spent filters loaded with solvent may have been disposed of in the dumpster, it is best to evaluate vapor migration potential from the TP property line to the nearest property line associated with the property having the former dry cleaner. • City directories are an excellent historical resource to identify former dry cleaners, and historical aerial photographs may be able to identify dumpster locations. Case Study #1: Lessons Learned
  21. 21. • TP is multifamily property located approximately 90’ from an existing gas station (USTs) constructed approximately 40 years ago. • Based upon groundwater flow experience in the area, the Consultant established that groundwater flow is away from the TP towards the gas station (i.e., the gas station is hydraulically down-gradient from the TP). • The gas station replaced its underground tanks in 1991 and contaminated soil removed and disposed; groundwater sampling was not performed. • The multifamily property is on municipal water. • Since the gas station USTs are located 90’ from the TP property line, this distance does not exceed 100’ and the Consultant determined that a VEC was likely. • Soil throughout the area is moderately permeable – sandy loam. Case Study #2
  22. 22. • The consultant recommended conducting soil gas sampling at the TP boundary for both BETEX and chemicals often associated cleaning and washing (brakes, carburetor and parts) and repairs. • Soil Gas sampling indicated the presence of BTEX above state screening levels. Case Study #2 (cont’d)
  23. 23. • According to the API, old bare steel USTs (pre-RCRA) that have been in the ground at gas stations for more than 17 years are highly likely to have had releases (with the probability of releases increasing with tank age due principally to corrosion). • Vapors do not necessarily follow the direction of groundwater flow; rather, they follow the path of least resistance (which may be opposite the groundwater flow direction). • The AOC distances are based upon 90th percentile plume lengths and widths meaning that they will be reasonable 90% of the time which is quite conservative (but understand that this is NOT 100% of the time). • Gasoline releases are in the form of LNAPL (free product) and dissolved phase – even if free product has been recovered, recovery is never 100% effective – as such it is best to assume that some LNAPL exists. Case Study #2: Lessons Learned
  24. 24. • Appropriate search distances for different soil conditions in the TP area should be established by the firm’s geologists/geotechs. • Consider developing and standardizing a “cheat sheet” with the appropriate AOC distances for the various conditions, e.g., when groundwater flow is known or can be inferred, different soil types, etc. • If you are making assumptions, be sure these are clearly identified; assumptions such as:  groundwater flow follows surface topography  surface soil type found in soil survey maps (SSURGO/STATSGO2) is representative of soil in the entire vadose zone  no preferential pathways, man-made (such as underground conduits) or natural (such as fractured bedrock) Some Final Comments on Lessons Learned
  25. 25. • Check to see if the state has developed vapor intrusion guidance that might address the AOC, e.g.,  MI EGLE Guidance: 100’ preliminary screening  NJ DEP Guidance: 100’ / 30’ for PHCs - Vapor Migration Distance  NC DWM Guidance: 100’ (or 500’ for landfills producing methane)  PA DEP Guidance: 100’ / 30’ for PHCs – Vapor Migration Distance • If there is a situation deserving of a most conservative analysis, it would be when the TP is a residential property (this is where most of the litigation has taken place). Some Final Comments on Lessons Learned
  26. 26. Comment on the Challenge presented by Underground Utility Corridors
  27. 27. • The existence of underground structures such as utility corridors or piping networks can intercept vapor releases and redirect them in the path of these structures. • Underground structures particularly for piping associated with utilities is often in a bed of stone or sand with very high (rapid) permeability, representing a path of least resistance for migrating vapors. • If the existence of underground corridors that might intercept vapor releases is not evident or is unknown, the professional opinion in the Phase I ESA should be conditioned on the assumption that these do not exist. One Final Comment on Underground Utility Corridors
  28. 28. QUESTIONS?

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