Soil Vapor Intrusion Studies, Exposure Assessments and Associated Remedial Actions
Posted on June 12, 2015
- Soil Vapor Sampling
- Indoor Air Sampling
- Data Evaluation and Exposure Assessments
- Remedial Actions to Mitigate Indoor Air Exposures
D&B Engineers and Architects, P.C. has provided soil vapor intrusion study and air contaminant exposure assessment services to numerous private sector clients, authorities, municipalities and federal and state agencies. These services have been completed in conjunction with the investigation of a wide variety of sites, including active and closed landfills, active and abandoned manufacturing facilities, former manufactured gas plant (MGP) sites and petroleum storage facilities, among others. The air monitoring and sampling programs conducted by D&B have ranged from the collection of a single sample from a single on-site building to the collection of numerous samples from multiple structures up to 1 mile from a project site. The characterization of indoor air quality is an essential element in the investigation of contaminated sites due to the fact that contaminants often migrate through subsurface soil and groundwater migration pathways to off-site locations. Site contaminants can then enter buildings and other living spaces where direct exposure to the contaminants can occur.
In recent years, the USEPA and state environmental regulatory agencies have been increasing the emphasis on understanding the fate and transport of volatile chemicals and how they could impact indoor air quality. In the past, the investigation of sites contaminated with volatile organic compounds (VOCs) have focused primarily on the nature and extent of VOCs in soil, sediment, groundwater and surface water. However, due to their fundamental properties, VOCs have the propensity to volatilize from soil and groundwater, and migrate through the subsurface and potentially into indoor air spaces of overlying buildings. Based on the findings of this research and the available guidance documents, it has become standard practice for D&B to include the evaluation of the indoor exposure pathway as part of our investigations of contaminated sites.
D&B closely follows the New York State Department of Health (NYSDOH) document entitled “Final – Guidance for Evaluating Soil Vapor Intrusion in the State of New York,” dated October 2006 when conducting vapor intrusion studies in New York.
Soil Vapor Sampling
An indoor air investigation can be greatly enhanced with soil vapor testing results. This information is often critical in establishing a link between documented groundwater/soil contamination and the contaminants detected in an indoor air sample. Ideally, soil vapor measurements should be obtained in approximately the same timeframe as when the indoor air sample is being collected. The goal of soil vapor testing during an indoor air investigation is to determine if VOCs are present in soil vapor adjacent to the building’s foundation.
The firm utilizes a number of field techniques to obtain soil vapor samples. In most cases, a steel soil vapor probe is driven into the ground using a hand-operated slide hammer or, if depths of greater than 3 feet are required, a Geoprobe direct-push sampling unit is used to drive the steel probe. As a first step, the firm typically utilizes a Photoionization Detector (PID) to determine the relative concentrations of VOCs in soil vapor in parts per million (ppm) concentration ranges. A PID/FID unit is also used to scan typical soil vapor entry points in a foundation, such as cracks, annulus spaces around utility lines and sumps. Flexible tubing is connected from the steel probe to a vacuum pump which then, in turn, can be connected to a PID/FID and/or a Tedlar bag. A Tedlar bag is a container used to collect a soil vapor sample that can be submitted to an analytical laboratory for chemical analysis if the data objectives of the investigation require the identification and quantification of individual VOC species in soil vapor. Since this is often the case, it is important to identify if a particular contaminant present in indoor air is also present in soil vapor, in order to verify that a complete exposure pathway exists from the point of exposure back to the contaminant source.
Indoor Air Sampling
VOCs may accumulate in dwellings or occupied buildings to levels that may pose near-term safety hazards (e.g., explosion), acute health effects or aesthetic problems (e.g., odors). Typically, however, the chemical concentration levels are low. In living spaces with low concentrations, the main concern is whether the VOCs may pose an unacceptable risk of chronic health effects due to long-term exposure to these low levels. A complicating factor in evaluating the potential chronic risk from VOC intrusion is the potential presence of some of the same chemicals, at or above background concentrations, in the living space being tested (e.g., household solvents, gasoline, cleaners).
Drawing upon our extensive experience in conducting assessments of indoor air quality, the firm has developed a standardized approach to conducting this work. However, we can modify this standardized approach to ensure we achieve all project-specific data objectives identified by a particular client. The firm’s Indoor Air Sampling Protocol is comprised of two phases, data collection and reporting. The data collection phase includes a pre-sampling assessment of site specific conditions within the area being tested, collection of the air sample(s) and air monitoring during sample collection activities. The reporting phase includes full data validation of the laboratory data and the evaluation of the data with respect to indoor air quality guidance values and standards. This protocol is consistent with the NYSDOH Vapor Intrusion Guidance referenced above.
The first step of the data collection phase is a site visit of the property to be sampled in order to meet and interview the property owner, tenant or manager (“Occupant”). During the site visit, an initial assessment of the property will be conducted to select locations for the collection of both indoor and outdoor air samples. An interview will be conducted with the Occupant utilizing a questionnaire that has been tailored to the project. The questionnaire will be completed in the field based upon information provided by the Occupant, as well as from observations made in the field. In addition, a sketch will be prepared in the field showing the approximate air sampling locations in relation to features of the building/property being sampled.
After selecting appropriate sample locations, the air sampling will be conducted utilizing Summa canisters. A Summa canister is a stainless steel container that has had the internal surfaces specially passivated using a “Summa” process. This process combines an electropolishing step with a chemical deactivation step to produce a surface that is nearly chemically inert. The degree of chemical inertness of a whole air sample container is crucial to minimizing reactions with the sample and maximizing recovery of target compounds from the container. The canisters are typically staged at the selected locations for collection of grab samples.
Typically, 8-hour grab samples will be collected. However, if during the initial scheduling discussions with the Occupant, it is determined that access to the property will not permit collection of 8-hour samples, sample duration will be adjusted according to the conditions of access. The minimum sample duration will be one hour. Generally, indoor air samples will be collected in basement or crawl space locations and at least one first floor living space. In addition, one ambient air sample will be collected outside and adjacent to the structure. Periodic monitoring will be conducted in both the indoor area being sampled and adjacent outdoor areas utilizing a PID. The goal of indoor and ambient air sampling is to evaluate exposure to VOCs by measuring levels low enough to compare to background air levels. Therefore, the samples must be analyzed by methods that can achieve minimum detection limits of 0.25 part per billion for select compounds. The analytical method for VOCs in air that is capable of achieving these detection limits is Environmental Protection Agency (EPA) Method TO-15.
Data Evaluation and Exposure Assessment
Along with the information obtained from the questionnaire discussed above, the firm will evaluate the various data generated as part of the field investigation including soil, groundwater, soil vapor, ambient air and indoor air chemical data to determine if indoor air quality is being adversely impacted as the result of site-related contamination. When making this evaluation, other factors are considered including site hydrogeology, the chemical properties of the contaminants of concern and the construction of the structure or building that was sampled. Other key factors include the use(s) of the building and if similar chemicals are used/stored within or nearby the building. The key components of the data evaluation include:
- Data Representativeness – Data validation should be conducted to assure that the investigation objectives have been met.
- Determination of Possible Data Trends – A review of the data should also be done to identify any increasing or decreasing concentration patterns or trends in contamination (e.g., among various floors or different sections of a building). For example, a data set which indicates that contaminant concentrations are highest in the basement level and progressively decrease within increasing floor level, may point to a basement or groundwater source. A data set which indicates higher in the top levels or uniformity among levels may instead point to an ambient air contaminant source. Thus, in addition to providing information for a quantitative analysis, the data can be reviewed qualitatively to provide additional information on contamination patterns. The contamination trends identified in this step can also be used as one of the criteria for selecting the contaminants of concern (COCs) for the exposure assessment discussed below.
- Comparison of Data with Chemical Background Concentration Distributions – It is important to establish the indoor air background concentrations of the detected target compounds. This information allows for the comparison of indoor air monitoring results to levels of the same compounds that might be expected in the absence of a contaminated site. In the absence of site-specific data (i.e., data collected from the building before it was impacted by the contamination in question), literature data are the next best source of information on typical background concentrations.
After completing the above evaluation, a qualitative risk/exposure assessment will be prepared to determine if the identified COCs pose an unacceptable risk to human health based on current and anticipated use of the building/structure, potential receptors and potential contaminant migration pathways. The COCs will be compared to appropriate federal and/or state air standards and guidelines, and potential exposures will be addressed in consideration of the inhalation of the contaminated air.
Remedial Actions to Mitigate Indoor Air Exposures
Remedial actions are undertaken if the exposure assessment identifies contaminant levels in indoor air above acceptable concentrations. In most cases, indoor air quality is adversely impacted due to contaminant migration from soil vapor located beneath the floor slab of the existing building/structure. Soil vapor can enter the building/structure through cracks or perforations in slabs, basement floors, walls, and/or openings surrounding sump pumps or utility conduit perforations.
The firm has designed and implemented several alternatives to mitigate building occupant exposure to indoor air contaminants on both a time-critical and long-term basis. Time-critical alternatives have involved the installation, operation and maintenance of small-scale air filtration units in affected building/structure, and, if necessary, nearby off-site residential and commercial structures where contaminant migration has occurred or is a potential concern.
Long-term alternatives for mitigating indoor air contaminant exposure have involved sealing potential contaminant infiltration points within the affected structure, as well as, the design, installation and operation of either an active or passive sub-slab depressurization system. Such systems are commonly utilized to create a path of least resistance (lower pressure) for soil vapor to naturally or mechanically migrate outside the structure via engineered pathways rather than permeate to indoor air. During routine operation, soil vapors are drawn from the sub-slab region and exhausted to the exterior of the building. Long-term alternatives have also involved the design, installation and operation of a soil vapor extraction (SVE) systems to remediate contaminated subsurface soils, while simultaneously mitigating potential exposures resulting from sub-slab vapor.
The following is a partial list of representative clients for which the firm has provided air sampling, exposure assessment and design services, as well as a brief description of the services provided:
Kaufman Astoria Studios – Former Levco Metals Finishing Site, Soil Vapor Intrusion Pathway Study, Astoria, New York: In 2011, Kaufman Astoria Studios retained the services of D&B to perform a soil vapor intrusion study at the former Levco Metals Finishing Site, located in Astoria, New York. D&B was in the process of assisting the client with developing the final remedial plan when the NYSDEC notified the Studio that the site was included in their vapor intrusion “legacy site” database. As a result, even though the site was fully characterized in 1995, the NYSDEC required the undertaking of a soil vapor intrusion study to confirm that residual VOCs present in the groundwater did not pose a health risk through the mitigation into nerby buildings. D&B developed an investigation scope of work in accordance with NYSDEC/NYSDOH guidance documents which was quickly approved by the Agencies with no comment. In order to meet the schedule needs of the Client, D&B worked closely with the NYSDEC and undertook the investigation on a fast-track basis. The scope of work included the completion of soil vapor probes in and around a recently constructed stage. In addition, indoor and outdoor ambient air samples were collected for VOC analysis by USEPA Method TO-15. The results indicated no potential for vapor intrusion by VOCs into the nearby stage. Based on D&B’s evaluation of the data presented in our report, the NYSDEC and NYSDOH closed out the project with no further action needed.
Village of Cold Spring – Site Characterization Study of former MGP Site, Cold Spring, New York: Under the NYSDEC Environmental Restoration Program (ERP), D&B was retained by the Village of Cold Spring to perform a Site Characterization Study of a former manufactured gas plant site (MGP) located in the Village, adjacent to the Hudson River. The site operated as an MGP from approximately 1868 to 1897 and as a result, soil and groundwater contamination by MGP tar which contains VOCs was spread throughout the site. Given the proximity of several buildings to the identified contamination, D&B performed a soil vapor pathway intrusion study in accordance with NYSDEC/NYSDOH protocols including sub-slab soil vapor samples, indoor air samples and outdoor ambient air samples. All samples were analyzed for VOCs by USEPA Method TO-15. Based on the generated analytical data and D&B’s exposure pathway assessment, it was determined that vapor intrusion by VOCs was not a significant concern. The NYSDEC and NYSDOH concurred with this finding and approved the overall Site Characterization Report with only minor comments.
KeySpan Corporation – Former Manufactured Gas Plant Remedial Investigation Program: The firm was retained by KeySpan Corporation (KeySpan) under a multi-year contract to undertake and complete remedial site investigations at a number of its former manufactured gas plant (MGP) and gas holder sites located throughout Suffolk, Nassau, Queens and Kings Counties, New York. As part of this program, the firm conducted soil vapor, ambient air and indoor air sampling and analysis. This investigation program included a site inspection and the interview of the property owners prior to the collection of samples. A total of 85 soil vapor, 25 ambient air samples and 52 indoor air samples were collected for analysis as part of this program. The generated data was used to determine if there existed a potential indoor air exposure pathway for on-site and off-site receptors.
NYSDEC – AVM Gowanda Site Remedial Design Investigation, Gowanda, NY: The firm was retained by the New York State Department of Environmental Conservation (NYSDEC) under the New York State Superfund program to undertake and complete remedial design activities at an Inactive Hazardous Waste site located in Cattaraugus County, New York. As part of this investigation, the firm conducted ambient air, subslab and indoor air sampling and analysis in accordance with NYSDOH protocols. This investigation program included a site inspection and interview of the property owners prior to the collection of samples. A total of three ambient air samples, eight subslab and 12 indoor air samples were collected for analysis as part of this program. The generated data was used to determine if nearby residential properties were impacted by site-related VOCs.
NYSDEC – Franklin Cleaners Remedial Investigation/Feasibility Study, Hempstead, NY: The firm was retained by the NYSDEC to perform a remedial investigation, feasibility study and remedial design for the soil and groundwater contamination at the Franklin Cleaners Site in Hempstead, New York. During the remedial investigation, elevated concentrations of tetrachloroethene (PCE), above the NYSDOH action level of 1000 ug/m3, were detected in the basement of the building and adjacent commercial establishments. As a result, D&B provided technical services in connection with implementation of an interim remedial measure (IRM) in two phases in the basement. The initial remediation program consisted of the installation of several self-contained air purifying units. Periodic sampling was performed by D&B using passive sampling devices during implementation of the IRMs, and improvements in air quality were observed in the commercial establishments. Ultimately, a soil vapor extraction (SVE) and air sparging (AS) system was installed to remediate soil and groundwater contamination at the site. Groundwater contaminant levels have decreased to below NYSDEC standards, and PCE concentrations inside the building have decreased below the NYSDOH action level. Upon achieving site specific remedial objectives, both the SVE and the AS systems were decommissioned and a “radon type” sub-slab depressurization system was installed as a protective measure to mitigate residual soil vapors in the sub-slab region of the structure.
NYSDEC – Farrand Controls Remedial Design Investigation, Valhalla, NY: The firm was retained by NYSDEC to perform remedial design services associated with the remediation of groundwater contaminated by Freon 113 and other chlorinated volatile organic compounds. Potential human health exposure routes included the migration of subsurface vapors from shallow groundwater into facility buildings and nearby residences. Therefore, soil vapor and indoor air sampling was conducted. Sub-slab soil vapor samples were collected from the concrete floors of the main facility building and an indoor tennis court building. Nine sub-slab soil vapor samples were collected from the facility. The samples were analyzed for the site-specific VOCs and Freon 113 breakdown products. Concurrent with the subslab soil vapor sampling, indoor air sampling was conducted. For the indoor air samples, two samples were collected from the building’s basement (one in the vicinity of the basement sump and one in the office room to the west) and two samples were collected from the building’s first floor (centrally located in the areas of the first floor subslab soil vapor sampling). Additionally, one background ambient outdoor air sample was collected. An evaluation of the analytical results of the soil vapor and air sampling program determined that indoor air in the main facility building contained elevated chlorinated volatile organic compounds not associated with the site groundwater contamination, but apparently associated with materials in the building. The off-site soil vapor and indoor air sample results did not identify any impacts of site chemicals of concern at nearby properties.
DASNY – Bronx Psychiatric Center/PCB Monitoring, Bronx, New York: The firm was retained by the Dormitory Authority – State of New York (DASNY) to monitor PCB contamination discovered during transformer upgrades in 1993. As part of a Consent Order with the NYSDEC, periodic monitoring is conducted of groundwater and indoor air to assess PCB concentrations in two transformer rooms. Specific to air monitoring, the air in each room is sampled annually using portable pumps and Florisil sorbent tubes for an 8-hour period. The samples are analyzed for PCBs using NYSDOH Method 311-1 and EPA Method 8082. No PCBs have ever been detected in the transformer rooms and, as a result, DASNY was not required to perform any further testing or remedial measures.
NYSDEC – Jimmy’s Dry Cleaner Remedial Design, Roosevelt, New York: The firm was retained by NYSDEC to perform remedial design services associated with the remediation of soil and groundwater contaminated by PCE. The site has an existing interim remedial measure soil vapor extraction system that was utilized to mitigate contaminated soil vapor migration from the site to nearby residences. D&B conducted indoor air sampling at four nearby residences as part of a quarterly sampling program. Two background ambient air samples were also collected during each sampling event. The sampling was conducted using 6-liter Summa canisters to collect air samples over a 24-hour period. The samples collected were analyzed for the presence of VOCs according to USEPA Method TO-15. D&B completed the NYSDOH Indoor Air Quality Questionnaire and Building Inventory forms for each property. An evaluation of the analytical results were presented in a quarterly report and provided information on the effectiveness of the soil vapor extraction system at mitigating migration of contaminated soil vapor to nearby residences. In addition, as part of the pre-design investigation activities, D&B performed soil vapor monitoring on-site to determine if the proposed groundwater remedy, in-situ chemical oxidation, would impact soil vapor quality on-site. Soil vapor samples were collected from four soil vapor wells surrounding the injection point for the chemical oxidant prior to the injection of the oxidant and 24 hours after the injection of the oxidant. Each sample was analyzed for VOCs in accordance with Method TO-15. One ambient air sample was also collected during each sampling event. Based on the results of the analysis, concentrations of VOCs in the soil vapor did not increase as a result of the injection of the chemical oxidant into the aquifer.
Confidential New York City Client: As part of a standby contract with a private client D&B has conducted over 20 Soil Vapor Intrusion and Indoor Air Quality Surveys throughout the five boroughs of New York City. The surveys were conducted for a wide range of building types and businesses including but not limited to educational facilities, commercial/industrial establishments, gasoline stations and residential buildings. D&B was responsible for preparing a sampling program which included conducting the pre-sampling inspection of the Site in order to inventory/identify any potential contaminants, collection of sub-slab vapor samples, collection of indoor air samples and background outdoor ambient air samples. Samples were collected utilizing certified 6-Liter SUMMA canisters and analyzed for volatile organic compounds via USEPA Method TO-15. Utilizing the sample results, the regulatory levels and decision matrices provided in the New York State Department of Health Final Guidance for Evaluating Soil Vapor Intrusion in the State of New York dated October 2006. D&B evaluated the potential for vapor intrusion at the Site and determined what action was required at the site, no action, monitoring or mitigation. Based on these results D&B has designed numerous sub-slab depressurization systems (SSDS) and soil vapor barrier systems.
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