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The Centralia USDA Site was identified during a Commodity Credit Corporation/United States Department of Agriculture (CCC/USDA) sponsored private well sampling program conducted by KDHE in 1998, during which carbon tetrachloride contamination was detected in a nearby private well in Centralia, Kansas at a concentration of 19.3 micrograms per liter (?g/L). CCC/USDA promptly connected the residence to the Nemaha County Rural Water District #3 in 1998. KDHE conducted a Site Reconnaissance and Evaluation (SRE) of the site in August 1998, which identified carbon tetrachloride in both soil and groundwater samples collected at the former CCC/USDA grain storage facility.

Argonne National Laboratory (ANL), on behalf of CCC/USDA, conducted Phase I of an investigation to characterize the contamination at the site from 2002-2003, and a Phase II investigation was completed in April 2004. During the Phase II investigation, carbon tetrachloride was detected at a concentration of 219 micrograms per kilogram (?g/kg) in subsurface soils, and groundwater samples collected revealed a maximum concentration of 176 ?g/L of carbon tetrachloride. Based on the results, KDHE requested that monitoring wells be added to the well network to further characterize the groundwater contamination at this site. In 2004, CCC/USDA installed and sampled six monitoring wells at the site.

In late 2004, KDHE approved semi-annual sampling at the site to observe changes in plume dynamics and geochemistry, and to determine whether natural attenuation is a viable remedial option for the site. Preliminary results indicated that concentrations of carbon tetrachloride were increasing at the site. In 2006, additional monitoring wells were installed and sampled, and in November 2007, an Interim Measure (IM) pilot test work plan was approved and implemented at the site, using in situ chemical reduction to remove the carbon tetrachloride. Pilot test results indicated that the IM is affecting contamination levels in the treatment area.

Monitoring is ongoing at both the injection area and the monitoring wells situated at the site.