Review of Public Health Implications of Soil Gas and Indoor Air Sampling at the Le Mars Coal Gas Site
LE MARS COAL GAS PLANT
LE MARS, PLYMOUTH COUNTY, IOWA
The Iowa Department of Public Health (IDPH) was asked by the U.S. Environmental ProtectionAgency (EPA) Region 7 Superfund Division to review air and soil gas monitoring data collectedat the Le Mars Coal Gas Site in Le Mars, Iowa, during May 2002. Specifically, EPA askedIDPH if the air and soil gas posed as a public health hazard at the site. This health consultation applies only to an evaluation of the May 2002 air and soil gas monitoring data. Information usedin preparation of this health consultation was current at the time of writing. Any new data orother site-related information could alter the conclusion and recommendation contained in this health consultation.
The Le Mars Coal Gas site is 1.6 acres in size. It is located at 331 1st Street Northeast, in the cityof Le Mars, Plymouth County, Iowa. The site is a triangularly shaped lot bordered on the northand west by the Union Pacific and Canadian National Railroads, on the east by 4th AvenueNortheast, and on the south by 1st Street Northeast (1). The area surrounding the site is mostlyresidential with a few commercial properties nearby. The site was formerly the home of amanufactured gas plant, which began operation in 1884 and ceased gas production in or about1939. In the 1950's, the gas plant buildings were demolished. Later a commercial building wasconstructed where the old gas plant had stood. The property has had various owners through theyears; the present owner is the city of Le Mars. The Le Mars city street maintenance departmentis the present occupant of the property (1).
According to 2000 Census records, approximately 9,200 people reside within the city of LeMars. A previous health consultation completed in 1998 reported that approximately 800 peoplereside within 0.25 miles of the site itself; of these, 81 were children under the age of six years (2). The nearest residence is about 50 feet south of the site (1).
Contaminants of concern
The contaminants of concern at this site are those associated with former manufactured gas operations. Chemicals such as benzo(a)pyrene and other polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs), such as benzene, toluene, ethylbenzene and xylene are present throughout the site. Both benzo(a)pyrene and benzene are regarded as carcinogens. PAHs and VOCs are found in the shallow (less than 50 feet depth) groundwater underneath the site. The contaminant plume extends beyond the original site boundaries and now underlies about a 20 square block area of residential land to the west and north of the site. Benzene has been detected in shallow monitoring wells at concentrations up to 120,000 µg/L (micrograms per liter of water) (1).
VOCs such as benzene, toluene, ethylbenzene and xylene are air, soil and water contaminants ofconcern at the site because these compounds can easily become vapors or gases and have thepotential to migrate or move from groundwater into soil and air. They can then be inhaled by theresidents of homes overlying the groundwater contaminant plume (3). Because of the potentialfor VOCs to move through soil and into air, these compounds (primarily benzene, due to itscarcinogenic properties) are of concern in indoor air and soil gas at the site.
The Le Mars coal gas site is scheduled to undergo a removal action in 2003. This action isdesigned to reduce levels of contaminants related to the site. In May 2002, EPA contractorscollected indoor and outdoor air and soil gas samples from several homes in the vicinity of thesite. Twenty-three air samples and 22 soil gas samples were collected from 11 residenceslocated within about a one-half mile radius of the site. Three additional "background" airsamples were collected from outdoor locations in Le Mars. These outdoor samples werecollected for comparison purposes with the indoor samples. Indoor air samples were taken in thebasement and living area of each home. Soil gas samples were taken in the front and back yards of each home.
Samples were collected during May 2002. Air samples were collected over a 24 hour period inthe basement and in a commonly used living area of the home. In addition to the samplescollected from residences in the plume area, two residences southeast of the site, outside of theinfluence of the plume area, were sampled in the same manner. This was done to determinebackground concentrations of VOCs in indoor air. Two outdoor background air samples werecollected about 1,000 feet to the east and northeast of the site. A third background air samplewas collected in the backyard of one of the residences in the plume area. Any containers ofpaints, solvents, gasoline or other similar products found inside the residences were removed atleast 24 hours prior to collection of the indoor air samples (4).
Soil gas samples were collected in the front and back yards of the same residences where indoorair samples were taken (11 residences total). Soil gas samples were collected at a depth intervalof 10 - 12 feet below ground surface. Nine residences within the plume area were sampled (twosamples each). Four additional background soil gas samples (two per residence) were taken attwo residences outside the plume area. All soil gas samples were collected within 15 feet of thefoundation of each residence (4).
Air and soil gas sampling results for toluene, ethylbenzene and xylene revealed that these VOCs were present at very low concentrations, both indoors and in soil, but below any health-based comparison values or any levels of health concern. Benzene was found in all indoor samples, and was also present in outdoor ambient air samples. The range of benzene concentrations in indoor air reported was from 0.44-17.0 µg/m3 (micrograms per cubic meter of air) (Table 1).
In several residences, other solvents containing VOCs (e.g., paint thinner, mineral spirits) had been present in the sampled area (although not at the actual time of sampling), and the residue of these solvents may have been the source of benzene in the indoor air samples. Benzene was also found in all soil gas samples. Benzene measured in soil gas ranged from 0.71 - 8.5 µg/m3 (Table 2). Examination of the data revealed no positive relationship between indoor air benzene concentrations and soil gas benzene concentrations. That is, the highest soil gas results did not occur at the same residences with high indoor air concentrations of benzene. Background concentrations of benzene in soil gas were among the highest recorded results (5.4, 5.9, and 7.6 µg/m3). Thus, it is unlikely that benzene is migrating through soil and into the residences.
The benzene concentrations measured were higher (even outdoor air) than the Agency for ToxicSubstances & Disease Registry (ATSDR) inhalation pathway Cancer Risk Evaluation Guideline(CREG) of 0.1 µg/m3. CREGs are values used to identify concentrations of carcinogens that areunlikely to result in an increase of cancer rates in an exposed population (5). CREGs serve asscreening tools only and are not an indication that cancer is expected or predicted.
Air and soil gas samples at the Le Mars coal gas site have shown concentrations of benzenegreater than the ATSDR CREG. Even so, it is unlikely that adverse health effects should occur for the following reasons:
- Health-based evaluation guidelines and comparison values (such as the CREG) are notthresholds of toxicity. Although concentrations at or below relevant comparison values areconsidered to be safe, it does not automatically follow that any environmental concentrationgreater than a comparison value or health evaluation guideline would be expected to produceadverse health effects. These values serve as a starting point for further evaluation of site-relatedcontaminants. The purpose of conservative (i.e., protective) health-based guidelines, which areused to develop comparison values, is to enable health professionals to eliminate substances from further evaluation of potential health hazards (5).
- Measured benzene concentrations in air and soil at the Le Mars site were, in some cases,approximately ten times lower than those measured in other environmental studies of benzeneexposure. The range of benzene concentrations at Le Mars is generally lower than any reportedin nationwide studies of indoor and outdoor air. No adverse health effects have been reportedfrom those prior benzene exposure studies (6). Furthermore, the planned removal action at the site should greatly reduce any likelihood of adverse health effects in the future.
Furthermore, comparison of the benzene concentrations found in indoor air and soil gas at the LeMars site with other studies and measurements shows that Le Mars has relatively low benzeneexposure. The U.S. Environmental Protection Agency's (EPA) Total Exposure AssessmentMethodology (TEAM) study revealed the following:
Benzene was not found, or was found in insignificant amounts in water, food and beverages. More than 99% of the total exposure was through air. Mean personal air exposures exceeded indoor air concentrations, which in turn exceeded outdoor air concentrations. A global average personal exposure was about 15 µg/m3 (range 7-29 µg/m3). This is a higher range of exposure than the Le Mars indoor air measurements reveal (Le Mars range 0.44-17 µg/m3). Indoor concentrations were measured only in the 1987 TEAM studies in Los Angeles, CA, Baltimore, MD, and Bayonne, NJ, and appeared to be on the order of 10 µg/m3. Outdoor concentrations had a global average of 6 µg/m3 (range 2-19 µg/m3). These outdoor concentrations are ten times higher than those at Le Mars. No effect on personal exposure of living close to major fixed sources of benzene (e.g., oil refineries, storage tanks, and chemical plants) could be detected during the TEAM study (6).
Additionally, it is difficult to determine if benzene in indoor air is coming from contaminatedgroundwater and soil, or from some commercial product (such as solvents or paints) present inthe home. Containers of these and similar products were removed from each residence 24 hoursprior to air sampling, but residue from these containers could have been detected in the airsamples. Also, the two highest indoor air benzene readings in Le Mars were found in homes thathad many of these products removed (4).
Soil gas samples do not show that benzene is migrating through the soil. No relationship existsbetween high soil gas benzene concentrations and high indoor air benzene concentrations in theresidences sampled. Moreover, the low levels of benzene found in the residences should notpresent a health hazard. Furthermore, the proposed removal action will prevent any futuremigration.
IDPH recognizes that children have unique vulnerabilities to some environmental contaminants. IDPH has not identified any existing exposure scenarios that may lead to the occurrence ofadverse health effects among children living near the Le Mars site. Concentrations of benzeneand other contaminants in air are lower than those reported to cause health effects, even among children.
Benzene exposure through air and soil gas at the Le Mars coal gas site currently poses no apparent public health hazard. This health hazard category is used when exposure tocontaminants might be occurring or might have occurred in the past, but at levels below any known health hazard.
IDPH recommends that the contaminant removal action at the Le Mars site proceed as planned to reduce the potential for future exposures. No additional public health actions are required at this time.
- Agency for Toxic Substances and Disease Registry. Health Consultation. Le Mars CoalGas Plant. Le Mars, Plymouth County, Iowa. CERCLIS No. IA0001032556. June 26, 1998.
- State of Iowa Data Center. Profile of General Demographic Characteristics: 2000. LeMars city, Iowa. 2002.
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Benzene. Prepared by Research Triangle Institute, Research Triangle Park, NC. Prepared for U.S.Department of Health and Human Services. Public Health Service. Agency for Toxic Substances and Disease Registry. Atlanta, GA. September 1997.
- Data supplied to U.S. Environmental Protection Agency Region 7 Superfund Division byTetra Tech EM, Inc. Lenexa, KS. July 2002.
- Agency for Toxic Substances and Disease Registry. Public Health Assessment GuidanceManual (Update). Public Comment Draft. U.S. Department of Health and Human Services.Public Health Service. Atlanta, GA. May 2002.
- Wallace, L. Environmental Exposure to Benzene: An Update. Environmental HealthPerspectives. 104 (Suppl. 6): 1129-1136, 1996.
|Sample Location||Benzene Concentration (µg/m3)|
|1. Basement |
Basement (duplicate sample)
|2. Basement |
|3. Basement |
|4. Basement |
|5. Basement |
|6. Basement |
|7. Basement |
|8. Basement (background residence) |
|9. Basement (background residence) |
|10. Basement |
|11. County Fairgrounds (outdoor ambient air)||0.69|
|12. Cemetery (approximately 1000 feet east of site; outdoor ambient air)||0.52|
|13. Basement |
Back Yard (outdoor ambient air)
|Field trip/blank||0.25 U (essentially not detected)|
*Leaking can of mineral spirits found in the basement of this residence. Was removed 24 hours prior to sampling, along with other containers of solvents and paints.
**Numerous containers of solvents and paints were removed from this basement 24 hours prior to air sampling.
|Sample Location||Benzene Concentration (µg/m3)|
|1. Front yard||1.1|
|2. Front yard |
|3. Front yard |
|4. Front yard |
|5. Front yard |
|6. Front yard |
|7. Front yard |
|8. Front yard (background residence) |
|9. Front yard (background residence) |
|10. Front yard |
|11. Front yard |
Dr. Charles Barton, Dr. John Johnson, and Dr. Swana Toney
Hazardous Waste Site Health Assessment Program
Iowa Department of Public Health
Alan Parham, LCDR
ATSDR Technical Project Officer
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
LTJG Shawn Blackshear
ATSDR Regional Representative
Office of Regional Operations, Region VII
The Iowa Department of Public Health, Hazardous Waste Site Health Assessment Program, hasprepared this health consultation for the Le Mars, Iowa, coal gas site under a cooperativeagreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is inaccordance with approved methodology and procedures existing at the time the healthconsultation was begun.
Alan G. Parham
Technical Project Officer, SPS, SSAB, DHAC, ATSDR
The Division of Health Assessment and Consultation, ATSDR, has reviewed this healthconsultation, and concurs with its findings.
Chief, SPS, SSAB, DHAC, ATSDR