Congressional District # 06
U.S. AVIEXEPA ID# MID980794556
Last Updated: March, 2011
The U.S. Aviex site is a six-acre facility, located in Cass County, Michigan, just south of the city of Niles. The site is in a residential neighborhood that primarily includes single family homes. The nearest home is within 100 feet of the facility. Minor agricultural and horticultural activities were performed in the general vicinity of the site.
Historically, the U.S. Aviex Company produced non-lubricating automotive fluids from the early 1960s until late 1978. The products were blends of diethyl ether (DEE) and volatile organic chemicals (VOCs). Large quantities of these chemicals were stored onsite in tanks and the chemicals were piped to the process area. During operations in the 1960s and 1970s, releases of chlorinated hydrocarbons, such as benzene, trichloroethylene (TCE), tetrachloroethylene (PCE) and DEE occurred. These compounds contaminated the private residential wells near the site. In 1972, an underground pipeline containing DEE ruptured during excavation at the plant. In 1978, a large but unknown quantity of chemicals, including TCE, was also released during a fire at the plant. These releases impacted the drinking water aquifer in the area. Contaminants were detected in downgradient private residential wells southwest of the plant as far as one-half mile away. Consequently, the U.S. Aviex site was added to the National Priorities List on September 8, 1983.
Site ResponsibilityThis site is a fund-financed, state lead Superfund Site.
Threats and ContaminantsPrior to remedial activities the groundwater and soil were contaminated with volatile organic compounds (VOCs). There are no current human health or environmental threats associated with contamination from the site.
In 1983, Michigan Department of Natural Resources (MDNR) investigations resulted in U.S. Aviex installing a 200 gallon-per-minute groundwater extraction and treatment system to contain and treat the on-site groundwater contamination. U.S. Aviex operated the system for about 10 years. In 1985 an Administrative Order by Consent (AOC) was signed between U.S. Aviex and U.S. EPA (EPA) to conduct a Remedial Investigation (RI) to determine the nature and extent of site contamination, and a Feasibility Study (FS) to examine site cleanup alternatives. The RI was completed in 1986. After U.S. Aviex subsequently declared bankruptcy, EPA completed the FS.
The RI delineated two areas in need of cleanup: (1) about 13,000 cubic yards of VOCs contaminated soils; and (2) the contaminated groundwater plume extending to Almagus Road, approximately one-third mile from the facility.
In 1987 MDNR finished constructing a municipal water supply for about 220 homes affected by the contaminated groundwater plume. In 1988 a Record of Decision (ROD) documenting EPA's cleanup plan was signed. The remedy included:
* A five-well extraction system;
* Modifying and rehabilitating the existing air stripper to remove the VOCs;
* Monitoring to ensure effective treatment; and
* Soil flushing by extraction and treatment.
The groundwater extraction and treatment ("pump-and-treat") remedy was operated briefly by EPA. In 1993 MDNR assumed the long-term response action (LTRA) at the facility. In 1993, study results showed significant contaminant reduction in the 13,000 cubic yards of soil. A 1993 Explanation of Significant Differences (ESD) was signed, documenting the decision to eliminate the soil flushing treatment. In 1993, contamination was found beyond the capture zone of the installed pump-and-treat system. An additional purge well was installed in 2000 to prevent further migration of contaminants, also documented in an ESD.
The pump-and-treat system effectively in reduced the VOC contaminants to very low concentrations. The 2003 quarterly monitoring data showed that only 1,2-dichorloethane (1,2-DCA) remained above its maximum contaminant level (MCL) of 5 ppb for drinking water. An MCL is the highest level of a contaminant in drinking water that will not adversely affect health over a lifetime of exposure. Additional studies conducted by Michigan Department of Environmental Quality (MDEQ), formerly the MDNR, indicated that no contamination was detected in the city of Niles well protection zones. The studies conducted by MDEQ identified two additional small areas of contamination on the U.S. Aviex property. A 100 square-foot "perched" water table located north of the warehouse contained benzene, TCE, 1,2-DCA, and other chemicals at concentrations above the MCLs. In addition, an area was found south of the groundwater treatment system that contained PCE, TCE, trichloroethane (TCA), and 1,2-DCA.
MDEQ conducted a pilot study using a new injection treatment method, which decreased the contamination above the perched water table. The pilot study also suggested that in-situ air/ozone treatment would effectively reduce the contamination south of the groundwater treatment system. EPA decided to change the pump-and-treat remedy to monitored natural attenuation (MNA), augmented by the injection method for the area near the warehouse. In addition, EPA began in-situ ozone/air treatment of the area south of the groundwater treatment system. This decision resulted in a change to the 1988 selected remedy, and was documented in a 2004 ROD Amendment. The Amendment included the following six actions:
* Shut down the pump-and-treat system and rely on MNA to further reduce contaminant levels in the groundwater beyond the Aviex facility property line;
* Monitor the attenuation of the downgradient contaminants;
* Install and operate an in-situ ozone/oxygen treatment system to assist MNA;
* Update the groundwater clean-up standards to the current MCLs;
* Use the ozone air sparging treatment for the southern area to prevent further off-site migration of contaminated groundwater;
* Provide contingency plan(s) that may include the operation of the existing extraction system with a new air stripper system and/or the installation of a down gradient pump-and-treat system.
EPA conducted the first five-year review in December 2004. Five-year reviews are required whenever waste is left on site above levels that allow for unrestricted use and unlimited exposure. The review found that the remedy was functioning as intended by the ROD, ESD and ROD Amendment. The pump-and-treat remedy reduced all contaminants of concern (COC), except for 1,2-DCA, to very low concentrations. The review also indicated that 1,2-DCA was present in the groundwater plume primarily north of the capture zone at concentrations ranging from 6 to 35 ppb, slightly above its MCL of 5 ppb. This suggested that the chemical treatment of the perched water table north of the warehouse had eliminated the source of 1,2-DCA. All current residual 1,2-DCA is expected to naturally attenuate to below 5 ppb over the next several years.
The ongoing operation and maintenance (O&M) activities at the site include groundwater monitoring, site maintenance, and enhancements to the MNA, including the ozone sparge and treat system. The MDEQ will maintain the site until the groundwater meets the MCL cleanup criteria.
The 2004 review also found that the exposure assumptions, toxicity data, clean up levels and remedial action objectives used at the time of the remedy are still valid. MDEQ Part 201 Residential Health-Based Ground Water Criteria reflect concentrations in drinking water which are safe for both long-term and daily consumption. The remedy was determined to be protective of human health and the environment, but in order to be protective in the long term, an assessment of the MNA activity must be continued.
In November 2009, EPA issued the third five-year review. The review stated that the remedy remains protective of human health and the environment in the short term and is functioning as intended by the ROD, ESD and ROD Amendment. Excavation and treatment of the source area soil prevents further contamination of the groundwater. Groundwater COC concentrations have declined significantly over the last five years. The plume does not appear to pose a threat to the Niles municipal water supply. Although some institutional controls (ICs) are in place such as municipal zoning ordinances to prevent the installation and/or use of private wells, further evaluation of ICs should be conducted. In order for the remedy to be protective in the long term, ICs to restrict the use of the site property need to be implemented. A restrictive covenant for the site property is planned for 2011.
ContactsRemedial Project Manager, U.S. EPA
sheila sullivan (firstname.lastname@example.org)
Community Involvement Coordinator, U.S. EPA