Site Narrative:
The Commodity Credit Corporation/U.S. Department of Agriculture (CCC/USDA) operated a grain storage facility from 1950 to 1976, consisting of 223 grain bins. Commercial grain fumigants containing carbon tetrachloride were in common use by the grain storage industry. In 1973, the CCC/USDA grain bins were sold at auction to local farmers. By 2006, nine residences were located on or adjacent to the former CCC/USDA property.
Contamination at the Site was identified in Feb. 1998 when low levels of carbon tetrachloride and chloroform were detected in samples collected from 2 private wells. In a follow-up sampling event in April 1998, carbon tetrachloride and chloroform were detected but below the respective Maximum Contaminant Levels (MCLs) established by the U.S. Environmental Protection Agency for public water systems. In July 1998, KDHE conducted a Site Reconnaissance and Evaluation to determine whether the former facility was a source of the contamination in the private wells. Carbon tetrachloride was detected in soil samples below the Tier 2 Risk-based Standards for Kansas (RSK) screening level for the soil-to-groundwater pathway and in 3 private wells below the MCL. Carbon tetrachloride was detected in one private well sample at 5.9 micrograms per Liter (µg/L), above the MCL of 5.0 µg/L. KDHE concluded that the CCC/USDA facility was the source area for residual carbon tetrachloride. Based on the low contaminant concentrations, additional sampling was not conducted until 2006, when two private wells were resampled.
In 2007, at the request of a Hanover resident, CCC/USDA conducted soil sampling at the former facility at 61 locations and indoor air samples at 9 residences. Carbon tetrachloride was detected below Tier 2 RSK levels. In 4 of the 9 air samples, carbon tetrachloride was detected at concentrations ranging from 1.4 micrograms per cubic meter (µg/m3) to 4.8 µg/m3. KDHE requested CCC/USDA to fully characterize the extent and magnitude of contamination in groundwater, soil, and indoor air at the Site.
Field work was initiated in winter 2008 and continued through spring 2009, focusing on determining potential vapor intrusion and groundwater contamination. By May 2009, 45 groundwater monitoring wells were installed to track contaminant migration.
Indoor air and sub-slab samples were collected from 60 homes within the area in 2009. Carbon tetrachloride above the Tier 2 level of 4.055 µg/m3 was detected in several samples. In 2009-2010, indoor air mitigation systems were installed in 5 homes. Indoor air samples were collected from the 2 schools in Hanover in late Feb. 2010 with no detection of carbon tetrachloride.
The Environmental Site Investigation Report was submitted and approved by KDHE in June 2011. A revised Corrective Action Study was submitted and approved by KDHE in January 2014.
A draft Corrective Action Decision identifying the preferred remedial alternative was released for public comment March 18 - April 17, 2015. KHDE held a public meeting on Tuesday, March 31, 2015, in Hanover, where KDHE, CCC/USDA, and Argonne presented information and invited public participation. The selected corrective action includes: groundwater extraction and treatment with a horizontal extraction well piped to an air stripper treatment system, groundwater monitoring, inspection and maintenance of vapor intrusion mitigation systems, abandonment of lawn and garden wells with well owner approval, municipal land use control program, and five-year reviews to evaluate the remedy.
CCC/USDA submitted the Remedial Design Plan and KDHE subsequently requested revisions in June 2016. Baseline groundwater sampling was conducted in June 2017. The horizonal well was installed in August 2017. Active remediation of groundwater throught the use of the horizonal well is ongoing. Remediation Monitoring Results for (2017-2020) submitted in Oct. 2020 |