Active Soil Gas Data Review
CHILLUM PERC SITE
(a/k/a CHILLUM PERCHLOROETHYLENE)
CHILLUM, PRINCE GEORGES COUNTY, MARYLAND
The U.S. Environmental Protection Agency Region III requested the Agency for Toxic Substances and Disease Registry (ATSDR) to review active soil vapor sampling data and to provide recommendations in a public health consultation for the Chillum perc (perchloroethylene or PCE) site. A community member also petitioned ATSDR to evaluate health concerns related to the contamination. The contamination originated in Maryland and expanded into a Washington, D.C., residential community. Several federal and state government agencies have conducted investigation, remediation, and assessment activities at this site since 1990. For this health consultation, ATSDR reviewed active soil gas data collected from January through December 2002. In addition, ATSDR reviewed the initial indoor air data (three air samples and one field duplicate) collected in April 2003.
- Perc soil vapor concentrations ranged from non-detect to 4,600 µg/m3. Five residences had a perc soil vapor concentration above 810 µg/m3, which represents an estimated target indoor air perc concentration of 81 µg/m3 and is based on a conservative attenuation factor of 1/10. These estimated indoor air perc concentrations indicate a low increased risk of cancer;
- Benzene soil vapor concentrations ranged from non-detect to 160 µg/m3. On the basis of the 1/10 attenuation factor, the estimated indoor air benzene concentration is far below its respective comparison value (CV) of 32 µg/m3, and exposure is thus unlikely to be associated with an appreciable risk of adverse health effects;
- Methyl tertiary butyl ether (MTBE) soil vapor concentrations ranged from non-detect to 3,788 µg/m3. The estimated indoor air MTBE concentration, on the basis of the 1/10 attenuation factor, are far below MTBE's respective CV (3,000 µg/m3), and exposure is unlikely to be associated with an appreciable risk of adverse health effects; and
- Volatile organic compound vapors (VOCs) in the initial indoor air samples were detected at very low levels and below their respective CV values.
Because the concentrations for the indoor air pathway are not available and the soil vapor concentrations for perc are above 810 µg/m3, ATSDR has categorized this site as "Indeterminate Public Health Hazard". ATSDR recommends additional indoor air samples in the community to verify the indoor air contamination at the point of exposure.
The U.S. Environmental Protection Agency Region III asked ATSDR to review active soil vapor sampling data and to provide recommendations for the Chillum perc site . The purposes of this public health consultation are 1) to discuss whether, on the basis of available information, a threat to human health via the inhalation pathway exists; and 2) if a data gap exists, to determine actions needed to address the issue.
The contamination at this site consists of a mixed gasoline and perc plume that originated in Maryland and expanded into the Lamond-Riggs Park community in Washington, D.C. (see intro map). The gasoline plume came from a service station located at the intersection of Riggs Road and Eastern Avenue in Chillum, Maryland. EPA is currently investigating the source of the dry cleaning plume.
The service station was constructed in 1954. Since 1989, gasoline has leaked or has been released into the ground from the property as reported to the Maryland Department of the Environment (MDE). In early 2001, the gasoline plume was reported (the actual time when the contamination began affecting the community was not known, the reported time is when the contamination was first documented in the community) to have moved into the Lamond-Riggs Park community, a residential area of approximately 200 homes, a church, and a school located southwest of the service station and immediately adjacent to the Maryland and Washington, D.C. border.
Since 1990, several federal and state government agencies and the potentially responsible party (PRP) have conducted investigation, remediation, and assessment activities at this site:
- Initially, MDE, the lead agency, addressed and oversaw the release monitoring and remediation;
- April 2001–The gasoline plume was first suspected to have migrated across the Maryland State line into D.C.;
- September 2001–PRP initiated investigation in the residential area and confirmed the presence of groundwater contamination on the D.C. side;
- October 2001At the request of Councilman Fenty, EPA RCRA program assumed the lead agency role to oversee the PRP's investigation;
- The EPA Superfund became involved when RCRA informed Superfund of the presence of perc;
- October 2002ATSDR Region III representatives visited the Chillum perc site. ATSDR also met with area residents to gather information and listen to community health concerns. At that time, EPA had preliminary soil gas data showing that perc and gasoline constituentsbenzene, toluene, xylene, ethyl benzene, and MTBEwere present. ATSDR concurred with EPA's approach at that time to conduct further characterization of the plume before considering indoor air sampling at the site. Since then, at the direction of EPA, the PRP's contractor (Gannett Fleming Inc.) has sampled and characterized the plume extensively. The sampling results indicate that many of the homes sit directly over the plume [2-4] (see Table 1).
|1954||Service station constructed|
|1984||Service station changed ownership|
|10/1989||Underground storage tank (UST) failed tightness test for the supreme unleaded line|
|11/1989||Five monitoring wells (MW-1 to MW-5) installed; liquid-phase hydrocarbon (LPH) discovered|
|04/1990||Three monitoring wells (MW-6 to MW-8) installed|
|07/1990||Ground water extraction and LPH recovery system installed|
|03/1991||Five monitoring wells (MW-9 to MW-13), two soil vapor extraction wells(VP-1 and VP-2), and a low profile air stripper installed|
|06/1993||Service station changed ownership|
|08/1993||Two monitoring wells (MW-14 and MW-15) and two soil vapor extraction wells (VP-3 and VP-4) installed|
|01/1994||Dual-phase extraction (DPE) system installed for 6 monitoring wells and two vapor extraction wells|
|08/1995||Monitoring well (MW-16) installed|
|05/2001||Recovery well (MW-17) installed|
|08/2001||MW-17 added to the DPE system|
|09/2001||Geoprobe® membrane interface probe (MIP) investigation10 MIP borings, 10 soil samples, 10 groundwater samples, two monitoring wells (MW-18 and MW-19) installed|
|12/2001-06/2002||Groundwater sampling investigation|
|01-06/2002||Active soil vapor samples at 41 properties|
|10-12/2002||Active soil vapor samples at 27 properties|
|01-02/2003||Active six soil vapor samples at four properties|
|12/2002||Twenty-nine passive soil vapor sampling devices were implanted on 26 properties|
|07-09/2003||Thirteen soil vapor implants and six monitoring wells installed; TAGA screened 23 residences; collected 46 indoor air samples, four active soil vapor samples, six groundwater samples, and two tap water samples|
For this health consultation, ATSDR reviewed and evaluated all available active soil gas data as well as a few initial indoor air data for the site. Discussed below are ATSDR's evaluation process, the vapor intrusion pathway, and environmental data evaluation.
ATSDR provides site-specific public health recommendations based on levels of environmental contaminants detected at the site, an evaluation of potential exposure pathways, and duration of exposure.
ATSDR identifies contaminants for their potential to cause adverse health effects using chemical-specific, health-based comparison values derived by various state and federal government agencies. Although concentrations at or below the relevant comparison values for a given contaminant might reasonably be considered safe, concentrations above these values will not necessarily cause harm. ATSDR uses site-specific exposure scenarios and performs in-depth evaluations for substances detected at concentrations above comparison values.
ATSDR used the following comparison values for this health consultation: the environmental media evaluation guides (EMEGs), reference dose media evaluation guides (RMEGs), cancer risk evaluation guides (CREGs), minimal risk levels (MRLs), the EPA draft guidance on indoor vapor intrusion and the American Conference of Government Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs). Appendix A provides a summary of ATSDR Comparison Values and definitions.
At this site, the primary route of potential human exposure is inhalation of potentially contaminated indoor air through vapor intrusion (see Appendix B). Ingestion and dermal contact exposures are not given further consideration because (1) groundwater is not used as a drinking water source, and (2) the absorption of contaminants through dermal exposure is not expected since the contamination is at depths not likely to be encountered during routine activities.
Vapor intrusion is the migration of volatile organic chemicals (VOCs) from the subsurface- contaminated groundwater and soil through the pore spaces of soil into buildings above. The air within the pore spaces of soil is called soil gas or soil vapor [6-7]. Soil vapors can enter residences and other building through foundation cracks and gaps, mechanical ventilation systems, and leakage areas (for example, utility entry points, construction joints, and drainage systems). In recent years, soil vapor sampling data have been used to qualify or quantify indoor air risk through modeling. Soil vapor levels are affected by many factors, such as water and air movements, temperature variations in soil and atmosphere, molecular diffusion, biodegradation, barometric pressure, precipitation, building structures, and pressure differences between the inside and outside of buildings [8-11].
The soil vapor model (e.g., the Johnson and Ettinger Model) is based on a number of simplifying assumptions regarding contaminant distribution and occurrence, subsurface characteristics, transport mechanisms, and building construction. Therefore, the model can be used only as a screening tool to identify conditions that may warrant additional evaluation [13-14]. Soil vapor monitoring and modeling results also do not provide actual measurements of concentrations of contaminants that people may inhale. Subsurface vapors migrating indoors are greatly diluted with outdoor air that enters the home, and by diffusive, advective, or other attenuating mechanisms as the vapor migrates through the soil. Therefore, directly measuring indoor air quality in potentially impacted buildings is the best approach to evaluate air contamination at points of exposure.
Indoor air quality assessment, however, needs to be treated from a multimedia perspective and poses several of its own challenges. First, in addition to soil vapor, a variety of significant sources of VOCs also contribute to the indoor air quality (see Table 2).
|Indoor||Building materials, furnishing, kerosene heaters, gas and wood stoves, carpets, consumer and personal care products ( e.g., air fresheners, cleaners, paints, glues, hair spry, nail polish remover), tobacco smoke, venting of dry-cleaned clothes, molds, and fungi|
|Outdoor||Combustion of fuels, fugitive emissions, manufacturing industries, mobile sources, utilities, solvents coatings, subsurface vapor intrusion|
A second complication is that indoor inhalation risk is often driven by very low VOC concentrations, which may often be near or below even state-of-the art laboratory analytical detection limits. Third, understanding and defining background indoor VOC concentrations is important but difficult because the reported range is large. For example, benzene was found in indoor air from non-detect up to 68 µg/m3 [6, 10-12, 15-22].
For this health consultation, ATSDR reviewed active soil gas data collected by contractors of EPA, PRP, and the community from January to December 2002. In addition, ATSDR reviewed the initial indoor air data (three air samples and one field duplicate) collected in April 2003. Results of the environmental data are discussed below.
The organizations noted collected active soil vapor samples at the site (see also Table 3):
- From January through June 2002 and October through December 2002, Gannett Fleming, Inc. (GF) representatives collected 129 samples from 68 residential properties on behalf of PRP. All samples were collected using direct push Geoprob® soil equipment and post-run tubing soil vapor sampling methods. EPA method 14A (modified) was used for data analysis .
- From January through June 2002, representatives of Quality Environment Solutions, Inc. (QES) collected a second soil vapor sample at each location GF used. Documentations for sampling and analytical methods were not available [23-24].
- From October through December 2002, representatives from U.S. Army Corps of Engineers (USACE) collected split samples from approximately half of the GF samples on behalf of EPA .
- On January and February 2003, representatives of Tetra Tech EM, Inc. (TTEM), under contract with EPA, collected six samples from two properties. TTEM collected the samples in nitrogen-purged Tedlar bags. The samples were analyzed using EPA method TO-15 .
For the 63 VOCs analyzed, sampling detected 18 different VOCs (29%) in shallow soil vapor (samples from depths of < 5 feet below the bottom of the basement slab), and 10 VOCs (16%) were detected in deep soil vapor samples (from a depth of > 5 feet below the bottom of the basement slab). Figure 2 is a summary of all available soil vapor sample locations for the site. All detected VOC concentrations are below levels recommended in the EPA draft guidance on indoor vapor intrusion except for perc, which will be discussed in the next section (see Table 3). Benzene and MTBE will also be discussed and evaluated in response to community concern and EPA request.
Perchloroethylene (PCE or "perc") is a chemical used for dry cleaning of fabrics and for metal-degreasing. It is also known by other names, including perc, tetrachloroethene, perclene, and perchlor. A nonflammable liquid at room temperature, perc evaporates easily into the air with a sharp, sweet odor . The major sources of perc emissions are dry cleaning businesses, which contribute about 60 % of total perc emissions. Many studies have reported that indoor air concentrations of perc are generally higher than outdoor air concentrations, and most human exposures (about 7078%) are the result of wearing and storing newly dry-cleaned clothes containing perc residues  (see Table 4).
|Source||Date||Sample size (Sample number/homes)||Concentration (mean/maximum) (µg/m3)|
|Kurtz et al||2002||282/NA||1.12 /440|
|Foster et al||2002||427/NA||1.62/42|
|Davis et al||1996||757/757||2.7/313|
|Shah et al||1988||2195/NA||20.58/NA*|
|Stolwijk||1990||1170/1170||5 (at 50th percentile)|
NA = not available.
* = Value may be skewed high because of the inclusion of a few high values.
Human studies showed that exposures to very high concentrations (49,494 to 135,600 µg/m3) of perc in air cause adverse health effects of the nervous system. However, the health effects of breathing in air with low levels of perc are not known completely. Animal study results indicated that animals exposed to high perc concentrations (678,000 to 1,356,000 µg/m3) might develop liver and kidney damage and cancers .
For this site, about 180 total soil vapor samples were analyzed for perc. The concentrations ranged from non-detect to 4,600 µg/m3 (see Table 5). The average concentrations for shallow- and deep-soil vapor samples were 313 and 457 µg/m3, respectively. As noted earlier, soil vapor concentrations migrating into indoor air spaces become highly diluted, so estimated indoor air concentrations can be 10-100 times less than the soil vapor concentrations.
ATSDR's chronic EMEG/MRL for perc is 271 µg/m3, the concentration of perc in air that is unlikely to be associated with any appreciable risk of adverse, non-cancer effects for more than one year of exposure. On the basis of detected soil vapor concentrations, all estimated perc indoor air concentrations are below the CV and are therefore unlikely to cause adverse, non-cancer health effects. For cancer effects, using a conservative soil vapor to indoor air attenuation factor of 1/10, EPA's draft subsurface vapor intrusion guidance suggests that the perc soil vapor concentration of 810 µg/m3, denotes an estimated target indoor air perc concentration of 81 µg/m3. This estimate indicates a low, theoretical increased risk of cancer (i.e., no more than one excess cancer in 10,000 exposed persons). Five residences have perc soil vapor concentrations above 810 µg/m3. However, because many factors can attenuate soil vapor levels by the time they move indoors, and because they do not represent actual concentrations of perc inhaled, indoor air sampling was necessary to verify the perc concentrations at the point of exposure. EPA took additional indoor air samples at selected residences during the summer of 2003. ATSDR will evaluate this data when it becomes available.
Benzene found in the environment comes from natural processes as well as human activities. Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke. Used widely, benzene ranks in the top 20 in production volume for chemicals produced in the United States. It is a colorless and highly flammable gas that evaporates into air quickly .
The major sources of benzene exposure are tobacco smoke (45%), automobile exhaust and industry (20%), and other home sources (16%). Home sources include paints and gasoline stored in the home (i.e., in basements or attached garages). On average, smokers have 6-10 times as much benzene in their blood as non-smokers [27-28].
Benzene has been identified in indoor and outdoor samples of both rural and urban environments. In Maryland, the ambient air levels of benzene range from 0.06 to 4.4 µg/m3 . Outdoor concentrations of benzene from 300 cities in 42 states have an average of 9.1 µg/m3. Indoor concentrations of benzene from 30 cities in 16 states have an average of 16.7 µg/m3 .
Benzene is classified as a known human carcinogen. It has been associated with leukemia in workers exposed to very high concentrations (3190 µg/m3 for 40 years) . The current ATSDR guidance states that exposures where the maximum concentration is < 32 µg/m3 pose no apparent public health hazard . The EPA draft vapor intrusion guidance suggested that a benzene soil vapor concentration of 310 µg/m3 represents an estimated target indoor air concentration of 31 µg/m3, using a conservative soil vapor to indoor air attenuation factor of 1/10. This estimated indoor air benzene concentration represents a low, theoretical increased risk of cancer. For the Chillum site, benzene soil vapor concentrations ranged from non-detect to 160 µg/m3 in the 224 samples analyzed (see Table 6). The average concentrations for shallow- and deep-soil vapor samples were 21 and 53 µg/m3, respectively. Therefore, the estimated indoor air benzene concentrations are far below benzene's CV and are thus unlikely to be associated with appreciable risk of adverse health effects.
MTBE is a flammable liquid that can evaporate quickly into air. It has a distinctive odor and is used as an additive for gasoline to make the fuel burn more cleanly. MTBE is found in the environment at low levels, and most MTBE (about 74%) migrates to water because of its high water solubility and resistance to biodegradation [33-34]. For example, MTBE is commonly detected in water samples collected in urban areas throughout the United States. The United States Geological Service National Water-Quality Assessment Program found that MTBE was the second most frequently detected chemical after chloroform .
Most people are exposed to MTBE from automobile exhaust while driving or adding gasoline to automobile tanks. Some people have reported symptoms such as headaches, nausea, dizziness, and irritation of the nose or throat. ATSDR has established a chronic EMEG/MRL of 3,000 µg/m3 for long-term MTBE exposures.
Some 180 soil vapor samples were analyzed for MTBE from all sampling events at this site (see Table 7). Concentrations ranged from non-detect to 3,788 µg/m3. The average concentrations for shallow and deep soil vapor samples were 37 and 148 µg/m3, respectively. The estimated indoor air MTBE concentrations are far below its respective CVs and it is unlikely to be associated with any appreciable risk of adverse health effects from the subsurface vapor intrusion to indoor air pathway. It should be noted that (1) the highest concentration of 3,788 µg/m3 was the single extreme value in the data set, (2) this value was an estimated value which may not be accurate or precise as defined by the laboratory performing the analysis, and (3) the sampling depth for this sample was relatively high (18.7 feet), therefore, the attenuation factor of 100 should be appropriate to use for estimating the targeted indoor air concentration.
Human epidemiological studies of the carcinogenic effects of MTBE are not available. Animal studies provide evidence that MTBE causes cancer in laboratory animals (rats and mice) at very high concentrations (1,444,000 to 28,880,000 µg/m3). The Department of Health and Human Services, the International Agency for Research on Cancer, and the EPA have not classified MTBE for its ability to cause cancer in human. . A recent report indicated that MTBE is an animal carcinogen with the potential to cause cancer in humans because it must be assumed that MTBE poses some human cancer risk unless definitive data of animal cancer types are shown to have negligible predictive value for humans .
EPA contractor collected three air samples and one field duplicate in April 2003 at the site. All samples were collected in Summa canisters and analyzed for VOCs using EPA Method TO-15. Of the 63 VOCs analyzed, six were detected at very low levels. These VOCs were propene (1 µg/m3), 2-propanol (2 and 130 µg/m3), acetone (6 µg/m3), hexane (3 µg/m3), benzene (1 µg/m3), and toluene (1 µg/m3). All detected VOC concentrations fell below their respective CV values. However, limited samples at one location may not be representative for the entire affected area. Additional indoor air sampling more representative of site conditions is needed to fill the data gap and to support sound public health decisions (see Table 8).
ATSDR considers children in the evaluation of all exposures, and the agency uses health guidelines that are protective for children. In general, ATSDR assumes that children are more susceptible to chemical exposures.
In evaluating health effects from the site-specific environmental exposures at the site, children were considered as a special population because
- Children weigh less than adults, resulting in higher doses of chemical exposures relative to body weight;
- Children have higher rates of respiration;
- Metabolism and detoxification mechanisms differ in both the very young and very old and may increase or decrease susceptibility; and
- A child's developing body systems can sustain permanent damage if toxic exposures occur during critical growth stages.
ATSDR has considered these factors in the development of conclusions and recommendations for this site. CVs used for this health consultation are intended to represent exposures that may be continued for a lifetime for the general population, including potentially susceptible subgroups such as children, without appreciable health risks. To account for human variability, ATSDR derived comparison-value MRLs by using an uncertainty factor of 10. ATSDR considers this uncertainty factor to include the variability related to age (children and elderly) when no data indicate a need for special metabolic or sensitivity considerations. Therefore, ATSDR considers the MRLs to include age-related variability and thus to be protective of children.
Although the soil vapor data do not suggest adverse health effects, prudent public health practice suggests that more indoor air samples be collected to verify exposures on site. In addition, the Bethlehem Church of God Holiness is located near the site, and very limited sampling data were available to evaluate the extent of contamination in these buildings. Therefore, a more complete characterization of exposure and the extent of vapor intrusion will require further investigation.
ATSDR categorizes this site as an "Indeterminate Public Health Hazard" (see definition, Appendix C) because of limited indoor air data and a lack of environmental data for potentially affected locations, such as the church in the area.
The perc soil vapor concentrations ranged from non-detect to 4,600 µg/m3. The average concentrations for shallow- and deep-soil vapor samples were 313 and 457 µg/m3, respectively. Five residences have perc soil vapor concentrations above 810 µg/m3 that represent an estimated target indoor air concentration of 81 µg/m3. This concentration represents a low, theoretical increased risk of cancer.
Benzene soil vapor concentrations ranged from non-detect to 160 µg/m3. The average concentrations for shallow- and deep-soil vapor samples were 21 and 53 µg/m3, respectively. The estimated indoor air benzene concentrations are far below benzene's CV, and it is unlikely to be associated with any appreciable risk of adverse health effects from subsurface vapor intrusion indoors.
The MTBE soil vapor concentrations ranged from non-detect to 3,788 µg/m3. The average concentrations for shallow- and deep-soil vapor samples were 37 and 148 µg/m3, respectively. The estimated indoor air MTBE concentrations are far below MTBE's CV, and it is unlikely to be associated with any appreciable risk of adverse health effects from the subsurface vapor intrusion indoors.
Six VOCs were detected at very low levels and below their respective CV values in the initial indoor air samples. Additional indoor air sampling is needed to better characterize the exposure and the extent of vapor intrusion.
- Collect additional representative indoor air samples at the community to verify estimated indoor air contamination at the points of exposure.
- Investigate potentially impacted locations in the area, such as the church.
- EPA collected additional indoor air samples at selected residences in the community during summer 2003.
- ATSDR released a site-specific fact sheet and a community health concern sheet in early December 2003.
- EPA and PRP continue to investigate potentially impacted areas, such as the church.
- ATSDR will assist, as needed, in further evaluations of additional environmental data to better characterize the exposure and the extent of vapor intrusion.
- ATSDR will continue to work with EPA, the District of Columbia Department of Health, and MDE to respond to public health questions and concerns.
- ATSDR will compile results of the community health concern sheets in early 2004 and determine appropriate responses.
Environmental Health Scientist
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry (ATSDR)
FFIMS Data Manager
Information Resources Management Branch
Office of Program Operations and Management
Brian M. Kaplan
Environmental Health Scientist
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Joseph Sigalas, PhD
Office of Communication
John E. Abraham, PhD, MPH
Chief, Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Chief, Consultation Section
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Lora Siegmann Werner, MPH
Office of Regional Operations
LaFreta A. Dalton
Health Communication Specialist
Community Involvement Branch
Division of Health Assessment and Consultation
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