The Le Mars Coal Gas Plant Site (Site), in Le Mars, Plymouth County, Iowa, is a non-time critical former manufactured gas plant (FMGP) site. The Environmental Protection Agency (EPA) is removing coal tar waste containing benzene, toluene, ethylbenzene, xylenes (BTEX) and polycyclic aromatic hydrocarbons (PAHs) from the site area. The Action Memorandum for the site was signed on September 26, 2003. The complete Administrative Record for the site can be found at the site record repository located at the Le Mars Public Library.
Approximately 14 feet of contaminated soil requires excavation down to the water table. Some de-watering may be necessary. In addition, Gas Holders A and B, the tar well, the 12,000-gallon underground storage tank (UST) and one 2,000-gallon UST will also be removed.
The site is located at 331 1st Street Northeast, Le Mars, Plymouth County, Iowa, and is a 1.6-acre, right-triangle-shaped property, which is bordered on the northwest by the Union Pacific and Canadian National railroads, on the east by 4th Avenue Northeast and on the south by 1st Street Northeast. The area surrounding the site is occupied by residential and commercial properties. The site is in Section 9, Township 92 North, Range 45 West (U. S. Geological Survey [USGS] 1985). The geographic coordinates of the Site are latitude 42°47'40" north and longitude 96°09'37" west.
The Le Mars Coal Gas plant was constructed by the Le Mars Gas Light Company in 1884. Initially the plant included a single production building housing the retort room, coal room, lime and meter room, purifying room, one gas holder (Gas Holder A), a tar well, and a main office building. The Le Mars Gas Company acquired the facility in 1898 and expanded operations to include the conversion from coal gas to water and oil gas, the addition of an oil tank, and a 100,000 cubic-foot gas holder.
Sometime before 1920, the Le Mars Gas Company discontinued production of oil gas and by 1930 converted from water gas to carbureted water gas. In 1929, the Le Mars Gas Company produced 23 million cubic-feet of gas. In 1939, the Le Mars Gas Company ceased operation when the facility converted from manufactured gas to natural gas. This conversion was completed on December 14, 1939, while the Le Mars Gas Company was a subsidiary of Great Lakes Utilities Corporation.
The Iowa Public Service (IPS) Company purchased the natural gas distribution system in 1942. The site was included in this purchase. On March 19, 1953, IPS entered into a contractual agreement with C.W. Miller of Le Mars for the sale of the Le Mars site property. A service building was constructed and the building was leased to IPS for 20 years. On September 14, 1967, Miller sold the property to the City of Le Mars which is the current property owner. The site is currently occupied by the Le Mars Street Department, which uses it for office, maintenance, and storage facilities. The Street Department vehicles are parked and maintained on the Site property.
In 1985, during the city of Le Mars’ ownership of the site, the city installed a UST. During the installation, the city noted and observed potential contamination at the site. In 1990, a city contractor collected subsurface samples from a soil boring near the USTs at the site. The analytical results associated with the samples indicated the presence of total organic hydrocarbons in concentrations as high as 2,300 ug/kg. In November 1990, the city of Le Mars collected subsurface soil samples from two 20-foot-deep soil borings in the area of the fuel USTs to satisfy Iowa UST liability insurance requirements. The total organic hydrocarbons detected in some samples exceeded the Iowa Department of Natural Resources (IDNR) guideline of 100 micrograms per gram. On the basis of those sample results, IDNR requested that the city of Le Mars conduct a pressure test of the USTs during December 1990. The pressure test results indicated that no leaks had occurred from the USTs.
The contaminants of concern identified for the site are BTEXs and PAHs in the soil and groundwater. Sources of contaminants of concern at FMGP sites typically are associated with gas holders, tar wells, and oil tanks. The likely sources of contaminants of concern at the site include Gas Holders A and B, a tar well, and two oil tanks. Three USTs installed after the site ceased operations could also be sources of contaminants of concern. Although the U.S. Environmental Protection Agency (EPA) typically does not have the authority to address releases of petroleum from USTs, potential releases from the USTs would have commingled with contaminants of concern released at the site, and could act as a co-solvent of contaminants of concern which could contribute to and exacerbate migration of the coal tar contamination.
The EPA conducted Site Inspection (SI) sampling activities on February 24-27, 1997. The results of groundwater, near-surface and subsurface soil, and sediment samples indicated volatile and semi-volatile organic compounds (VOCs and SVOCs) throughout the site. Soils on the eastern portion of the site contained up to 2,273 milligrams per kilogram (mg/kg) carcinogenic PAHs and 8,506 mg/kg total PAHs. VOC and PAH levels were found in soil samples taken as deep as 16 feet below ground surface (bgs) in the area of the former gas holder. VOCs, SVOCs, and cyanide levels were detected in samples taken from the Le Mars municipal well #8, the drainage ditch, Willow Creek, and nearby residential surface and subsurface soils, although not above the Maximum Contaminant Levels (MCLs).
The EPA conducted an Expanded Site Inspection (ESI) in 2000 to: (1) delineate soil contamination detected at the site; (2) evaluate the threat posed by contaminated soil at the site to groundwater in the surficial, buried channel and Dakota Aquifers; (3) identify the effect of on-site contamination on local surface water features; and (4) evaluate the threat posed to both human health and the environment. The ESI included the installation of 12 groundwater monitoring wells, and the sampling of soil, sediment, and surface water. Analysis of samples from the monitoring wells indicated that VOCs, including benzene and toluene, PAHs and cyanide have migrated off-site in the shallow aquifer. Sediment samples taken from the drainage ditch indicated elevated PAH levels, including benzo(a)pyrene, and indeno(1,2,2-cd)pyrene; VOC levels, including benzene, toluene, ethyl benzene, and xylene; and cyanide levels were detected in surface and subsurface soils on-site as well as at an adjacent residence. The most highly contaminated soil samples were collected from locations where FMGP structures, such as the gasometer, gas holder and tar well, were located.
A potential exposure risk exists for on-site workers and nearby residents. Elevated levels of PAHs and cyanide were identified in soils at levels above health-based benchmarks and/or background concentrations. Based on analytical data, contamination has migrated off-site in the shallow aquifer approximately 2,700 feet northwest with the potential to travel through the marginal aquitards to the Le Mars municipal water supply. A human health risk may also exist for individuals that fish Willow Creek.
Water in the vicinity of Le Mars is derived from three aquifers: a surficial aquifer, the buried channel aquifer, and the Dakota formation sandstone aquifer. None of the samples from the buried channel or Dakota aquifers exceeded preliminary remediation goals (PRGs) for the contaminants of concern.
A benzene plume in the surficial aquifer emanates from the site and is about 1,600 feet long by 650 feet wide. The direction of flow is toward the west-northwest, which is about the same direction as the groundwater flow. The highest benzene concentration detected in the plume is 160,000 micrograms per liter (µg/L) at monitoring well 2, which is near the eastern end. The western (or down gradient) end of the plume terminates just beyond monitoring well 3I, where the benzene concentration is 3,600 µg/L. The monitoring well 3I is about 1,000 feet west-northwest of the site.
Municipal Wells (Mun. Well) 4 and 8 are about 1,800 feet northwest of the site. These wells were sampled on five separate occasions between 1997 and 2000. Site-related contaminants were detected in Mun. Well 4 during the January 2000, sampling event. Contaminants detected in Mun. Well 4 included acenapthlyene (0.010 µg/L), naphthalene (0.084 µg/L) and phenanthrene (0.013 µg/L). Site-related contaminants were detected in Mun. Well 8 during the February 1997, August 1997, and January 2000, sampling events. Contaminants detected in Mun. Well 8 in February 1997, included benzo(a)pyrene (B(a)P) (0.012 µg/L) cyanide (26 µg/L), ethylbenzene (0.5 µg/L) and total xylenes (4.0 µg/L). Contaminants detected in Mun. Well 8 in August 1997, included B(a)P (0.0018 µg/L), ethylbenzene (5.0 µg/L) and total xylenes (34 µg/L). Contaminants detected in Mun. Well 8 in January 2000, included acenapthlyene (0.22 µg/L), naphthalene (0.14 µg/L), and phenanthrene (0.018 µg/L). None of the contaminants detected in the municipal wells exceeded an MCL.
Site-related contaminants have been detected in groundwater from the surficial aquifer. All of these MCL exceedances occurred at sampling locations within the benzene plume described above. Cyanide was detected above its MCL of 200 µg/L at four sampling locations. Sampling Location 111 is the only off-site location where the cyanide MCL was exceeded and that location is about 80 feet north of the site. Other contaminants that were detected off-site in groundwater above their respective MCLs included toluene, styrene, and B(a)P.
Four sampling intervals (0-2, 6-14, 14-20, and deeper than 20 feet bgs) were used to depict the extent of contaminants of concern in soil. All samples collected from the 0-2 bgs interval are considered to be surface soil samples. The PRGs for benzene and total B(a)P equivalents in surface soil are 15,000 micrograms per kilogram (µg/kg) and 2,900 µg/kg, respectively.
Benzene contamination detected in the 0-2 bgs interval did not exceed the PRG at any of the sampling locations. The highest benzene concentration (262 µg/kg) was detected at Sampling Location 6, which was at the northwestern corner of the 12,000-gallon UST and inside of the footprint of Gas Holder A. In the 6-14 bgs interval, the highest benzene concentrations were detected in and around Gas Holder A and the 12,000-gallon UST. The contamination plume above the PRG is mostly within the site boundary. Benzene concentrations ranged between 120,000 and 307,000 µg/kg at Sampling Locations 5, 7, BH-1, and BH-5. Those samples were collected about 10 feet bgs or deeper. Benzene concentrations at most of the other sampling locations within the plume were about 3 to 4 orders of magnitude below those levels.
In the 14-20 bgs interval, the highest benzene concentrations were again detected near Gas Holder A. The contamination plume above the PRG covers most of the central portion of the site and extends off-site to the northwest, about 200 feet from the site boundary. Benzene was detected at Sampling Location 3 and BH-3 at concentrations of 152,000 and 160,000 µg/kg, respectively. Benzene was also detected at concentrations an order of magnitude below those levels from the sampling location near the 12,000-gallon UST, the tar well, and Gas Holder B. Most of the samples in this interval were collected at 18 - 20 feet bgs.
In the sampling interval under 20 feet bgs, the highest benzene concentration (31,000 µg/kg) was detected about 100 feet south of the site at Sampling Location 25, which was about 38 feet bgs. The highest on-site benzene concentration (9,730 µg/kg) was detected at Sampling Location 6, which was about 28 feet bgs. This sampling location was below Gas Holder A. The data is not sufficient to develop a reasonable plume to show benzene concentrations above the PRG.
There has been a release of hazardous substances into the environment from the site. Both groundwater and soil have been affected by the release of the coal tar wastes over an extended period of time. The compounds PAH and BTEX have been confirmed and documented as posing a human health risk to the citizens of Le Mars, Iowa.
Indoor Air Sampling: The EPA evaluated the potential impacts of contaminants in groundwater as a potential source of indoor air contamination. The EPA reviewed groundwater sampling locations and analytical data to identify a location that was in a residential area and showed elevated concentrations of a VOC such as benzene, toluene, ethylbenzene or xylene. The location was northwest of the site in an area that is a mix of residential and commercial buildings. It was decided to use benzene as the contaminants of concern because it is carcinogenic and would be expected to be the risk driver, if an unacceptable risk was identified. The Johnson and Ettinger Model (EPA 2000c) was used to assess potential impacts of groundwater concentrations on indoor air. This model has a screening module that is based on a series of default assumptions and estimates indoor air concentrations based on groundwater concentrations.
The results of the model noted is that the excess lifetime cancer risk from benzene in groundwater was 2 E-06. This cancer risk is within the acceptable risk range used by the EPA to evaluate potential risks at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites. Indoor air and soil gas sampling data from the removal assessment sampling effort indicate an incomplete vapor intrusion exposure pathway from contaminants of concern-contaminated groundwater in the surficial aquifer to indoor air in overlying structures.
In 2003, the EPA completed an Engineering Evaluation/Cost Analysis (EE/CA) to identify proposed removal action alternatives for benzene and total B(a)P equivalents-contaminated soil and groundwater at the site. See the Engineering Evaluation/Cost Analysis dated June 30, 2003, for a detailed description of the alternatives evaluated and the EPA’s proposed removal alternative. A 30-day public comment period was held, and on August 18, 2003, the EPA held an availability session at the Le Mars Public Library to discuss the EE/CA and the EPA’s proposed removal alternative. Several city officials and local residents attended the session to discuss the cleanup alternatives. No comments were received during the public comment period.
The Action Memorandum has been signed and funding has been approved for this non-time critical removal action. The removal activities planned for this site include:
a. Air monitoring of removal action construction
b. UST and product removal
c. Excavation of the on-site soil source area
d. Off-site thermal treatment of highly contaminated soil
e. Off-site disposal of nonhazardous soil and debris
f. Backfilling with off-site soil and site restoration
On Wednesday, May 12, 2004, an Action Memorandum Amendment was signed allowing all of the contaminated soil to be thermally treated.
This amendment was needed due to the denial of three Iowa Subtitle D landfills in accepting the coal tar contaminated waste. There is one Nebraska Subtitle D landfill located in Jackson that is willing to accept the waste. However, the Nebraska Department of Environmental Quality (NDEQ) requires a public notification period that would result in Site personnel de-mobilizing at a significant cost to the EPA and present a hardship to the city of Le Mars Street Department personnel who have re-located during the removal action. Also, due to seasonal fluctuations, the EPA is not encountering the water table at 14 feet below ground surface (bgs).
