GENERAL MOTORS CORPORATION SITE
SIOUX CITY, WOODBURY COUNTY, IOWA
STATEMENT OF ISSUES AND BACKGROUND
The U. S. Environmental Protection Agency (EPA), Region VII Office, provided
the Iowa Department of Public Health (IDPH), Toxic Substances Evaluation Program
(TSEP) with information related to the General Motors Corporation site in Sioux
City, Iowa. The Iowa Department of Natural Resources (IDNR) asked TSEP to review
the data and information provided and determine whether contamination from the
site poses a public health hazard. This Health Consultation only applies to
an evaluation of the data and information provided, as referenced in this document.
This evaluation will provide information about the potential public health and
children's health impact resulting from exposure
to on-site and off-site contaminated media. Any additional information or site
activities could alter the conclusions and recommendations provided in this
The General Motors Corporation (GMC) site is approximately 28 acres. It is located in Sioux City, Woodbury County, Iowa. Approximately 90% of the site is paved or covered by a building. (Figure 1). The surrounding area is a mixture of light industrial, commercial and residential properties. The south side of the site is bordered by Highway 29 and the Missouri River, to the north by a railroad and a steep wooded bluff, to the east by light industry, and to the west by a triangular shaped wooded area (Figure 2).
The site was formerly operated by the AC Rochester facility. It was purchased by the Zenith Corporation in 1965. In 1966, Zenith built a manufacturing facility for the assembling of radios. It was reported that acetone , lacquer thinner, isopropyl alcohol, 1,1,1-trichloroethane and white gas were used. These chemicals were stored in five, 500 gallon underground storage tanks (USTs) near the northwest corner of the manufacturing building. Also, one fuel storage UST was located near the northeast corner of the manufacturing building.
In 1980, GMC's AC Rochester Division, currently known as AC Delco Systems purchased the site. GMC modified the site to assemble and test throttle body injection fuel systems. GMC never used Zenith's five USTs or their contents and removed them in 1984. As part of its operations, GMC used Stoddard solvent and the above-ground Stoddard solvent tank farm located on the north side of the site. In March 1993, production ceased and the site was prepared for sale or transfer. GMC removed the above-ground Stoddard solvent tanks in 1994. The former manufacturing building is currently leased for use as a warehouse.
The GMC site is currently in the Remedial Investigation/Feasibility Study (RI/FS) stage. The RI/FS process is the combination of a technical evaluation of the site, characterization of potential routes of exposure and an assessment of remedial alternatives. The degree of contamination, the level of risk associated with the contamination, and what activities will occur at the site to mitigate exposure and risk will be determined. The RI/FS Work Plan, Field Sampling Plan, and Quality Assurance Plan have been submitted to IDNR for review and comment.
Based on the 1990 U.S. Census Data, 10,209, 3028, and 793 people lived within 1 mile, 0.5 mile and 0.25 mile of the site, respectively. The population in predominantly Caucasian. There were 1334, 361, and 85 children under the age of six living within 1 mile, 0.5 mile and .25 mile respectively (Figure 3).
Phase I Environmental Site Assessment Report (June 1993):
Under contract by GMC, HDR Engineering, Inc. (HDR) conducted a Phase I Environmental Site Assessment (ESA) in April 1993. The Phase I ESA was a nonintrusive process with the purpose of establishing the environmental conditions at the site for sale or other transfer of the site. Basically, the Phase I ESA Report recommended sampling of soil and groundwater at the site. Consequently, it was determined that a Phase II ESA would be conducted at the GMC site.
Phase II Environmental Site Assessment Report (September 1993):
In June 1993, HDR conducted the Phase II ESA to identify environmental conditions of the site in anticipation of the sale or other transfer of the property. Soil and groundwater samples were collected from 15 soil borings and three monitoring wells, respectively. Results of the Phase II ESA indicated that detectable concentrations of volatile organic compounds (VOCs) and total petroleum hydrocarbons (TPH) were found in soil and groundwater from the northwest corner of the manufacturing building. This area was the former location of Zenith's five USTs. Groundwater concentrations of tetrachloroethylene (PCE), 1,1 dichloroethane (DCA), and trichloroethene (TCE) were detected at levels above their respective drinking water maximum contaminant levels (MCLs). Records do not indicate that PCE was ever used or stored at the site by Zenith or GMC.
Also, VOCs (ethylbenzene and xylene) and TPH were detected in the area of the Stoddard solvent tank farm. The groundwater concentrations of ethylbenzene and xylene were not detected at levels above their respective MCLs.
Based on the results, the Phase II ESA recommended that additional field investigation activities be conducted. Per the request of IDNR, a Site Assessment Plan (SAP) was developed in November 1993.
Interim Site Assessment Report (October 1994):
The purpose of the investigation was to identify the source and extent of contamination with the goal of developing a remedial action plan, if necessary. The SAP was divided into two phases. The objective of the first phase, Phase I - Initial Investigation, was to identify potential sources of the chlorinated VOCs, and further investigate the potential impact of chlorinated VOCs on the Sioux City drinking water supply. The objective of Phase II - Geoprobe Survey, was to investigate the horizontal and vertical extent of chlorinated VOC groundwater contamination and to identify potential pathways of chlorinated VOC migration. The purpose of the Interim Site Assessment Report is to summarize the results of Phase I and Phase II SAP activities and recommend further action.
The results indicate the presence of detectable concentrations of chlorinated VOCs in soil and groundwater to the west and northwest of the manufacturing building and in the groundwater south of the manufacturing building.
The highest concentrations of chlorinated VOCs in groundwater were located approximately 300 feet west of the manufacturing building along the northern property boundary. The highest concentrations of chlorinated VOCs in groundwater were found approximately 25 feet below ground surface. Groundwater samples at several locations contained chlorinated VOCs (cis-1,2 DCE (dichloroethene), 1,1,1 TCA (trichloroethane), TCE and/or PCE) at levels above their respective MCLs. The presence of cis-1,2 DCE and other metabolites suggests that PCE may be breaking down (undergoing anaerobic microbial transformation).
Concentrations of chlorinated VOCs were detected in groundwater and soil near the northern and southern property boundaries suggesting that contamination appears to be located outside the boundaries of the site.
Headspace results from two sediment samples collected from storm sewers near the area with the highest detected chlorinated VOC groundwater concentrations showed elevated levels of chlorinated VOCs. These results suggest that the storm sewers may have been used for disposal of chlorinated VOCs.
Groundwater samples were collected from the Sioux City Municipal Wells. Only one sample had detectable levels of VOC (1,1-DCA at 9.7 ppb in Municipal Well No. 3). Municipal Well No. 3 is located less than 1000 feet downgradient of the southeast corner of the site (Figure 4). Municipal Well No. 4 is located less than 500 feet down-gradient of the southeast corner of the site, but chlorinated VOCs were not detected in Municipal Well No. 4.
Based on the results, additional horizontal and vertical delineation of chlorinated VOC impacted groundwater and soil was recommended. It was also recommended that groundwater monitoring wells be installed along the downgradient perimeter or the site to confirm the presence and concentration of chlorinated VOCs leaving the site. Additionally, background wells, near the northwest property line, and monitoring wells, near the southern and eastern boundaries between the highest detected concentrations and the city wells, should be installed and screened at varied depths. It was also recommended that two deep monitoring wells be installed.
GMC and IDNR entered into a Consent Order for Remedial Site Inspection, No. 96-01-HC, in May 1996.
Site Inspection Report (May 1996):
The purpose of the Site Inspection (SI) was to collect and analyze samples to quantify levels of previously identified compounds in subsurface soil and groundwater on-site and off-site to the north. Additional goals were to characterize soil, further delineate the presence of contamination in subsurface soil and determine the location of source areas. The scope of the SI included three distinct categories of tasks; soil borings, monitoring well installation, and Geoprobe sampling. The results of the investigation indicate that groundwater concentrations of chlorinated VOCs exceed MCLs northwest, immediately north, immediately northeast, east, south and beneath the manufacturing building. Also, groundwater concentrations of chlorinated VOCs exceed MCLs near or at the northern, eastern and southern property boundaries.
The primary source of chlorinated VOCs appears to be located near the site's northern boundary, in the area that was identified in the 1994 Interim Site Assessment Report as having the highest groundwater concentrations of chlorinated VOCs. Secondary source areas may be located in the northeast portion of the site and south of the manufacturing building.
VOC analysis of soil sample collected from the soil borings indicate the presence of chlorinated VOCs. In general, concentrations of chlorinated VOCs in unsaturated soil increased with increasing depth. The analysis of soil collected in the former Stoddard solvent tank farm area indicates the presence of ethylbenzene, xylenes and TPH.
Based on the results, the SI recommend that further action is warranted and that concentrations of chemicals in soil and groundwater may require corrective action. The SI also stated that, based on the information collected to date, RI/FS activities should begin.
Periodic Monitoring Well Sampling - Summary Report (April 1997 and December 1997):
The April 1997 and December 1997 Periodic Monitoring Well Summary Reports indicate that concentrations of detectable compounds are present in groundwater at varied depths and a clear trend (upward, downward or constant) is not apparent. On-site groundwater continues to show chlorinated VOCs at levels above MCLs.
Site Visit (1998):
On March 4, 1998, TSEP staff members, ATSDR, and IDNR visited the site to observe current conditions at the site and to meet with the Sioux City Water Plant and GMC representatives to discuss current site activities. Community health concerns related to the site were not reported.