Review of Public Health Implications of Alternative Removal Actions 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 the remedial action alternatives proposed for the Le Mars Coal Gas Site in Le Mars, Iowa. IDPH has reviewed the draft Engineering Evaluation/Cost Analysis (EE/CA) prepared for the Le Mars site and has provided comments regarding the proposed alternatives with respect to protection of public health. This health consultation applies only to an evaluation of the proposed removal alternatives as presented in the draft EE/CA. The information used in preparation of this health consultation was current at the time of writing. Any data or other site-related information later forthcoming could alter the conclusions and recommendations contained in this health consultation.
The Le Mars Coal Gas site is approximately 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, 2). 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 (3). The nearest residence is about 50 feet south of the site (2).
Contaminants of concern
The contaminants of concern at this site are those associated with former manufactured gas production. Benzo(a)pyrene and other polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs), such as benzene, are present in subsurface soils and in groundwater at the site. A contaminated groundwater plume in a shallow aquifer extends to the west and north of the site. The greatest concentration of PAHs were detected in shallow groundwater directly under the site - up to 160,000 µg/L (micrograms per liter). Benzene has been detected in monitoring wells at concentrations up to 120,000 µg/L. (1,2).
Two municipal wells closest to the site have shown very low concentrations of site-related PAHs; benzo(a)pyrene was detected at 0.0012 µg/L. This is lower than the ATSDR comparison value for benzo(a)pyrene of 0.005 µg/L. Likewise, concentrations of VOCs in the municipal water are all lower than Agency for Toxic Substances and Disease Registry (ATSDR) health-based comparison values. Comparison values serve as a starting point for further evaluation of site-related contaminants. The purpose of conservative (i.e., protective) health-based guidelines, which are used to develop comparison values, is to enable health professionals to eliminate substances from further evaluation of potential health hazards (4).
The two affected municipal wells are now on standby status due to the contamination, even though concentrations of PAHs and VOCs in the wells have not exceeded any health-based standards or comparison values (1, 2). City water officials have indicated that the nearest private well is located approximately 3,000 feet up-gradient of the site. Additionally, six residential wells are located within one mile of the site. There are no private wells in service within the city limits of Le Mars. There have been no reports of site-related contamination of private wells in the area (2).
Indoor air and soil gas samples were tested for PAHs and VOCs at several homes in Le Mars adjacent to the site. The evaluation of soil gas and indoor air did not indicate that the current contamination is affecting the indoor air of the houses that were tested. Public health implications of the soil gas and indoor air results will be addressed in a separate health consultation.
In May 2002, IDPH staff made two visits to the Le Mars Coal Gas site. The first visit coincided with the public availability meeting for the site sponsored by EPA Region 7. The second visit was to observe environmental sampling, both on- and off-site. From these site visits, it has been determined that there are no community health concerns related to the site.
Remedial alternatives presented in the draft EE/CA
EPA Region 7 Superfund Division is now considering options available for contaminant remediation at the Le Mars site. Five options have been identified in the draft EE/CA. However, the preferred alternative has not been identified. The options are listed below:
Alternative 1: No Action.
Alternative 2: On-Site Thermal Desorption and Enhanced Bioremediation
Alternative 3: Containment
Alternative 4: Biosparging and Bioventing
Alternative 5: Heat-Enhanced Vapor Extraction and Enhanced Bioremediation
The proposed removal alternatives for the Le Mars site have been reviewed for effectiveness in protection of human health and the environment.
Alternative 1 - No Action
This alternative will not effectively protect human health now and in the future. It would leave contaminated soils and groundwater in place, and it is likely that without some type of control or containment, the contaminants will continue to migrate off-site. Two Le Mars municipal drinking water wells have been taken out of service, and more wells may be affected in the future if no action is taken.
Alternative 2 - On-Site Thermal Desorption and Enhanced Bioremediation
This alternative uses low temperature thermal desorption of contaminated soils on-site and enhanced bioremediation to treat contaminated on-site groundwater. Bioremediation uses bacteria to break down contaminants and reduce harmful concentrations to safe levels. Additionally, two down-gradient municipal wells which have shown evidence of PAH contamination would be replaced by new wells at an up-gradient location over one mile away from the site. Monitored natural attenuation (MNA) would be implemented to reduce contamination in groundwater off-site. MNA will take approximately 30 years to completion and will require periodic monitoring of its effectiveness in reducing contaminant levels (1).
With proper controls and monitoring systems in place, Alternative 2 would be protective of human health and the environment. If thermal desorption is to be used, it will require development and implementation of an extensive air monitoring plan, which must be effective in preventing or mitigating any releases of airborne contaminants to the surrounding residences. The monitoring plan must be in place and operational before any thermal desorption work has begun.
Alternative 3 - Containment
Alternative 3 is protective of public health. This alternative will utilize a slurry wall (underground barrier) and asphalt cap (on the site surface) to contain both groundwater and soil contaminants. Two municipal wells will be relocated up-gradient, and MNA will be used in treating off-site contaminated media. Contaminant concentrations in on-site groundwater and soils will be decreased by removal of the contamination source (i.e., product removal). The slurry wall will physically impede groundwater movement off-site, and the asphalt cap over the site will reduce contaminant migration from soil to groundwater. Replacement of the two municipal wells will help ensure that no residents are exposed to contaminated water (5). The nearest private well is located approximately 3,000 feet up-gradient of the site. Additionally, six residential wells are located within one mile of the site. There are no private wells in service within the city limits of Le Mars (2).
Currently Le Mars residents are not being exposed to contaminants in drinking water at levels of health concern, and there seems to be no indication that vapor intrusion into homes is occurring at the present time. Future exposure to contaminants through the municipal water supply is unlikely, as the two wells containing PAHs and VOCs at concentrations below any health-based exposure guidelines have been put on stand-by status. No private wells are in use within the Le Mars city limits, and there have been no reports of PAH- or VOC-contaminated private wells in the vicinity (2).
Alternative 4 - Biosparging and Bioventing
Biosparging and bioventing use microorganisms to decrease contaminant concentrations to acceptable levels; microorganisms utilize the contaminants as a food source, thus over time reducing the amount of contaminant from a particular source. These techniques are most effective at reducing concentrations of benzene and lighter (lower molecular weight) PAHs. Because of decreased water solubility, heavier PAHs are less available for microorganisms and are not effectively reduced by biosparging or bioventing. These heavier PAHs found at the site include several carcinogens (e.g., benzo(a)anthracene, benzo(a)pyrene, and dibenzo(a,h)anthracene (5).
This alternative also includes removal of source product, installation of an asphalt cap over the site, replacement of two contaminated municipal wells, and use of MNA to decrease concentrations of contaminants off-site. Alternative 4 will be fully protective of public health only if the carcinogenic PAHs are effectively removed from soils and groundwater by the biosparging and bioventing processes.
Alternative 5 - Heat-Enhanced Vapor Extraction and Enhanced Bioremediation.
Activities associated with this alternative include: product removal, treatment of on-site subsurface soils by heat-enhanced vapor extraction (HEVE), remediation of on-site groundwater through enhanced bioremediation, the installation of an asphalt cap over the site, and the relocation of two municipal wells to an uncontaminated place.
Alternative 5 is protective of public health, since contamination will be reduced to levels considered safe. Due to the venting of gases from the vapor extraction process, this alternative will require the implementation of an air monitoring system similar in scope to that used for the thermal desorption system, as described under Alternative 2.
IDPH has not identified any current exposure scenarios for children at the Le Mars coal gas site. The greatest potential for exposure is from the public drinking water supply via the Le Mars municipal well system. Two city wells down-gradient of the site have been found to contain site-related PAH contaminants. The concentrations were below health-based comparison values. The most likely future scenario whereby children could be exposed would be from the public drinking water wells. If municipal wells are adversely impacted by site contaminants, exposure to unacceptable levels of contamination may occur. The planned removal action should greatly reduce any likelihood of adverse health effects.
With the exception of Alternative 1 - No Action, the contaminant removal alternatives suggested for the Le Mars site in the draft EE/CA would be protective of public health. Each method has inherent strengths and limitations which have been reviewed in the context of protecting and preserving the health of all Le Mars residents.
IDPH recommends that actions be implemented to prevent future exposures. Alternatives 2, 3, 4 and 5 will prevent future exposures if appropriate safety and control measures are implemented.
- U.S. Environmental Protection Agency Region 7. Engineering Evaluation/Cost Analysis. Response Action under the Comprehensive Environmental Response Compensation and Liability Act. Prepared by Tetra Tech EM, Inc. Lenexa, KS. July 5, 2002.
- Agency for Toxic Substances and Disease Registry. Health Consultation. Le Mars Coal Gas Plant. Le Mars, Plymouth County, Iowa. CERCLIS No. IA0001032556 . June 26, 1998.
- State of Iowa Data Center. 2002. Profile of General Demographic Characteristics: 2000. Le Mars city, Iowa.
- Agency for Toxic Substances and Disease Registry. Public Health Assessment Guidance Manual (Update). Public Comment Draft. U.S. Department of Health and Human Services. Public Health Service. Atlanta, GA. May, 2002.
- Memorandum from IDPH to Dan Garvey, EPA Region 7 Superfund Division. July 29, 2002.
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, 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.
Chief, SPS, SSAB, DHAC, ATSDR