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The Denton site is located at a previous Commodity Credit Corporation/U.S. Department of Agriculture (CCC/USDA) grain bin storage facility. Carbon tetrachloride and ethylene dibromide were used as fumigants until 1986. KDHE conducted a Site Reconnaissance and Evaluation (SRE) of groundwater at the site in 1998. Carbon tetrachloride was detected in private wells at concentrations below the Environmental Protection Agency (EPA) maximum contaminant limit (MCL); ethylene dibromide was detected above the MCL of 0.05 micrograms per liter (?g/L); and nitrate was detected above the MCL of 10 milligrams per liter (mg/L) as nitrogen. However the source of the contamination was not identified at that time.

A Comprehensive Investigation (CI) was done by Tetra Tech in 1999-2000. Carbon tetrachloride detections were below KDHE?s Tier 2 Levels for both soil and groundwater underlying the former CCC/USDA site. However, nitrate, carbon tetrachloride and ethylene dibromide were detected at levels above the regulatory limits in groundwater and soil underlying, and downgradient of, the Denton Co-op.

The site was transferred to the State Cooperative Program in June 2001. KDHE did a Preliminary Assessment/Site Remediation Study in 2001. A request for information was sent to the Ag Partners Cooperative Association (Ag Partners) Denton Co-op in June 2001. Ag Partners signed a Consent Order with KDHE on May 8, 2002, to conduct additional investigation, followed by corrective action.

A soil and groundwater investigation conducted in the spring of 2003 identified soil contaminated with ethylene dibromide at a level exceeding the KDHE Tier 2 Level. Carbon tetrachloride, chloroform, and ethylene dibromide were present in groundwater at levels exceeding MCLs. Nitrate and ammonia were detected in both soil and groundwater at levels exceeding KDHE's Tier 2 Levels for groundwater and the soil to groundwater pathway.

The Denton Co-op completed an additional soil and groundwater investigation in 2006 to fully characterize the nitrate/ammonia soil-contamination in preparation for an Interim Remedial Measure (IM) involving excavation and land application of the contaminated soil. Denton Co-op retained the services of Enviro Tech Services, Inc. for remedial work at the Site. Nitrate in soil near the fertilizer storage area occurred at a maximum level of 3300 milligrams per kilogram (mg/kg). The maximum nitrate concentration in groundwater was 468 mg/L at a shallow monitoring well near the fertilizer storage area.

In June 2008, KDHE conducted a domestic well survey in Denton. No wells identified as domestic water supply. Denton receives its water from Rural Water District #3 which blends the local groundwater with purchased water from the City of Atchison.

Additional direct push surveys of nitrate concentration in groundwater in Denton area performed in March 2008 and August 2010 defined the southern-most limit of the plume for nitrate but not for carbon tetrachloride and ethylene dibromide.

In 2009 a work plan was developed for a vapor intrusion assessment (VI). The work plan was implemented in 2011.

Indoor air in living areas and basements at three homes was tested using summa canisters. A sub-slab sample was collected in the basement of one of the homes. Results from the VI survey indicated that human exposure to vapor intrusion from contaminants in groundwater was not occurring at this time.

Enviro-Co consulting firm was retained in 2013 to continue work at the Site. A path-forward meeting with Ag-Partners in April 2014 resulted in implementation of the excavation and monitoring program. Monitoring wells for pre-excavation sampled in February 2015. Excavation occurred late April through May 13, 2015. 4500 cubic yards of dirt were removed for beneficial reuse on cropland. Post excavation monitoring plan completed and approved. Site sampled Work Plan from new contractor approved in October 2020.