The General Motors/AC Rochester (GM/AC) site is located at 1805 Zenith Drive in the Tri-View Industrial District of the City of Sioux City. The site occupies 23 acres west of Hamilton Blvd. between a loess bluff to the north and Interstate Highway 29 to the south. Sioux City’s primary water supply well field is located along the Missouri River just southeast the site. In 1965 Zenith Corporation constructed a manufacturing facility for assembling radios on the site. In 1980 General Motors purchased the site and modified the manufacturing facility to assemble and test throttle body injection fuel systems. In March 1993 production at the facility ceased. The site was sold in January 1999 and is currently used for warehousing. In 1993 General Motors conducted an environmental assessment of the site in preparation for sale of the property. The environmental assessment discovered contaminants in groundwater (and small amounts in soil) near the northwestern corner of the manufacturing building. The contaminants that were found are compounds that are typically used as solvents. The source of contamination has not been determined. Only one of the contaminants is known to have been used at the site and it is not one of the major contaminants found. It is speculated that illegal dumping on the north side of the plant parking lot may be the cause of the contamination. Groundwater contamination has been found to extend from the area north of the parking lot to the south and east towards the Missouri River. The edge of groundwater contamination has been found near two city wells in which low levels of contaminants have been detected. The city water works has refrained from using these two wells for the last several years as a precautionary measure. One of the city wells is being pumped to waste as a means of containing contamination so it does not reach other city wells, The amount contamination from the site does not appear to be sufficient to cause a violation of drinking water standards in the city water supply. Since 1994 General Motors has conducted a series of investigations and has evaluated various approaches to address the contamination. The Iowa Department of Natural Resources (DNR) and the U.S. Environmental Protection Agency (EPA) have overseen these efforts. A variety of clean-up measures have been evaluated. The selected method of cleanup near the apparent source of contamination is a biological process called butane biostimulation. It involves injection of gaseous butane and air into the zones of soil and groundwater contamination. Naturally occurring microbes will breakdown the butane and in the process also breakdown the contaminants in soil and groundwater. In addition, in December 2006, GMAC completed installation of a series of shallow wells neat the southeast corner of the site and started pumping these wells to intercept groundwater contamination and prevent it from moving off the site. Pumped water is being discharged to the sanitary sewer. Controls will also be placed on the GM/AC site to prohibit installation of groundwater wells on the site itself.