HEALTH CONSULTATION
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 Protection Agency (EPA) Region 7 Superfund Division to review air and soil gas monitoring data collected at the Le Mars Coal Gas Site in Le Mars, Iowa, during May 2002. Specifically, EPA asked IDPH 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 used in preparation of this health consultation was current at the time of writing. Any new data or other 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 city of Le Mars, Plymouth County, Iowa. The site is a triangularly shaped lot bordered on the north and west by the Union Pacific and Canadian National Railroads, on the east by 4th Avenue Northeast, and on the south by 1st Street Northeast (1). The area surrounding the site is mostly residential with a few commercial properties nearby. The site was formerly the home of a manufactured gas plant, which began operation in 1884 and ceased gas production in or about 1939. In the 1950's, the gas plant buildings were demolished. Later a commercial building was constructed where the old gas plant had stood. The property has had various owners through the years; the present owner is the city of Le Mars. The Le Mars city street maintenance department is the present occupant of the property (1).
According to 2000 Census records, approximately 9,200 people reside within the city of Le Mars. A previous health consultation completed in 1998 reported that approximately 800 people reside 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 of concern at the site because these compounds can easily become vapors or gases and have the potential to migrate or move from groundwater into soil and air. They can then be inhaled by the residents of homes overlying the groundwater contaminant plume (3). Because of the potential for VOCs to move through soil and into air, these compounds (primarily benzene, due to its carcinogenic 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 is designed to reduce levels of contaminants related to the site. In May 2002, EPA contractors collected indoor and outdoor air and soil gas samples from several homes in the vicinity of the site. Twenty-three air samples and 22 soil gas samples were collected from 11 residences located within about a one-half mile radius of the site. Three additional "background" air samples were collected from outdoor locations in Le Mars. These outdoor samples were collected for comparison purposes with the indoor samples. Indoor air samples were taken in the basement and living area of each home. Soil gas samples were taken in the front and back yards of each home.
Methods
Samples were collected during May 2002. Air samples were collected over a 24 hour period in the basement and in a commonly used living area of the home. In addition to the samples collected from residences in the plume area, two residences southeast of the site, outside of the influence of the plume area, were sampled in the same manner. This was done to determine background concentrations of VOCs in indoor air. Two outdoor background air samples were collected about 1,000 feet to the east and northeast of the site. A third background air sample was collected in the backyard of one of the residences in the plume area. Any containers of paints, solvents, gasoline or other similar products found inside the residences were removed at least 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 indoor air samples were taken (11 residences total). Soil gas samples were collected at a depth interval of 10 - 12 feet below ground surface. Nine residences within the plume area were sampled (two samples each). Four additional background soil gas samples (two per residence) were taken at two residences outside the plume area. All soil gas samples were collected within 15 feet of the foundation of each residence (4).
Results
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 Toxic Substances & 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 are unlikely to result in an increase of cancer rates in an exposed population (5). CREGs serve as screening 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 benzene greater than the ATSDR CREG. Even so, it is unlikely that adverse health effects should occur for the following reasons:
Furthermore, comparison of the benzene concentrations found in indoor air and soil gas at the Le Mars site with other studies and measurements shows that Le Mars has relatively low benzene exposure. The U.S. Environmental Protection Agency's (EPA) Total Exposure Assessment Methodology (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 contaminated groundwater and soil, or from some commercial product (such as solvents or paints) present in the home. Containers of these and similar products were removed from each residence 24 hours prior to air sampling, but residue from these containers could have been detected in the air samples. Also, the two highest indoor air benzene readings in Le Mars were found in homes that had many of these products removed (4).
Soil gas samples do not show that benzene is migrating through the soil. No relationship exists between high soil gas benzene concentrations and high indoor air benzene concentrations in the residences sampled. Moreover, the low levels of benzene found in the residences should not present a health hazard. Furthermore, the proposed removal action will prevent any future migration.
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 of adverse health effects among children living near the Le Mars site. Concentrations of benzene and 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 to contaminants might be occurring or might have occurred in the past, but at levels below any known health hazard.
RECOMMENDATION & PUBLIC HEALTH ACTION PLAN
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.
Table 1. Benzene Concentrations in Indoor Air Samples
| Sample Location | Benzene Concentration (µg/m3) |
| 1. Basement Basement (duplicate sample) Living Room |
0.69 0.51 0.76 |
| 2. Basement Living Room |
0.52 0.57 |
| 3. Basement Living Room |
0.99 1.0 |
| 4. Basement Living Room |
0.67 0.89 |
| 5. Basement Living Room |
0.71 1.1 |
| 6. Basement Living Room |
0.44 0.82 |
| 7. Basement Living Room |
0.94 1.0 |
| 8. Basement (background residence) Living Room |
0.72 0.77 |
| 9. Basement (background residence) Living Room |
0.87 1.1 |
| 10. Basement Living Room |
17.0* 11.0* |
| 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) |
3.8** 0.48 |
| 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.
Table 2. Soil Gas Benzene Concentrations
| Sample Location | Benzene Concentration (µg/m3) |
| 1. Front yard | 1.1 |
| 2. Front yard Back yard |
1.6 1.4 |
| 3. Front yard Back yard |
7.8 2.0 |
| 4. Front yard Back yard |
1.3 0.89 |
| 5. Front yard Back yard |
4.2 3.2 |
| 6. Front yard Back yard |
2.8 4.5 |
| 7. Front yard Back yard |
8.5 1.6 |
| 8. Front yard (background residence) Back yard |
0.82 7.6 |
| 9. Front yard (background residence) Back yard |
5.9 5.4 |
| 10. Front yard Back yard |
0.79 0.92 |
| 11. Front yard Back yard |
1.9 1.6 |
Dr. Charles Barton, Dr. John Johnson, and Dr. Swana Toney
Hazardous Waste Site Health Assessment Program
Iowa Department of Public Health
Reviewed by
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, has prepared this health consultation for the Le Mars, Iowa, coal gas site under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was begun.
Alan G. Parham
Technical Project Officer, SPS, SSAB, DHAC, ATSDR
The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation, and concurs with its findings.
Roberta Erlwein
Chief, SPS, SSAB, DHAC, ATSDR
