In-situ Chemical Oxidation Remediation Program

Former Beechcraft Corporation – Herington, KS

In-situ Chemical Oxidation Remediation Program implemented concurrently with Soil Vapor Extraction System to expedite Remediation of Chlorinated Solvents to meet Kansas Department of Health & Environment (KDHE) Remedial Action Objectives.

Weaver Consultants Group’s (WCG) Remediation Services team provides environmental consulting services to continue implementation of remedial measure activities at the Tri-County Public Airport (TCPA) project approved by the KDHE in a September 26, 2013, letter and completing activities required in the Consent Agreement and Final Order (CAFO) executed on September 15, 2015. The TCPA covers 1,724-acres approximately eight miles east of Herington, Kansas, and is located in a rural agricultural farming and ranching area.

The TCPA (Site) was constructed during World War II, where it primarily served as a processing center for bombardment crews and heavy equipment. Specific processes employed included chromium conversion coating, wastewater treatment, degreasing operations, painting, and paint stripping. In 1989, KDHE completed a Buried Tank Leak Assessment and detected Carbon Tetrachloride, Chloroform, 1,2-Dichloroethene, 1,2-Dichloroethane, and Trichloroethene (TCE) in a groundwater sample from an AgriServices well on-Site. The United States Army Corp of Engineers (ACOE) conducted a follow-up investigation at the TCPA from 1994 to 1997 to determine the extent of groundwater and soil contamination resulting from Department of Defense (DOD) activities and identified TCE in the soil and groundwater. Hawker Beechcraft Corporation (HBC) subsequently entered into a Consent Agreement with KDHE to complete a Remedial Investigation (RI) and Feasibility Study (FS) for TCE and related biological degradation products detected at the Site.

Findings from the RI and additional characterizations identified TCE impacts and TCE degradation products in the overburden soil and shallow bedrock at five primary locations at the Site, including 1) Hangar 1 (H1); 2) former Spark Plug Cleaning Building; 3) Potential Burial Area (PBA); 4) Air Corps Bulk Storage Building; and 5) Hangar 4 (H4). These five areas were also identified as potential source areas for Chlorinated Volatile Organic Compounds (CVOCs), including TCE and related biological degradation products (primarily cis-1,2-Dichloroethylene [DCE] and Vinyl Chloride [VC]). 

During these investigations, groundwater in underlying Water-Bearing Zones (WBZs), including challenging fractured limestone geological formations of the Cresswell, Stovall, and Towanda, were determined to be impacted by TCE and related biological degradation products. The impacted groundwater was determined to originate from source areas identified on the TCPA property and to have migrated off-Site. The TCE impacts in groundwater extend from the Site to the northwest to and past the town of Latimer. Natural attenuation and degradation of TCE have been observed in groundwater in the Cresswell, Stovall, and Towanda WBZs. 

During the previous RI investigation, area residential water supply wells surrounding the TCPA and spring, seep, and surface water locations along the intermittent tributaries of Clarks Creek and the main branches of Clarks Creek northwest of the Site were sampled. Select locations were discovered to contain CVOCs at concentrations above the Environmental Protection Agency (EPA) maximum contaminant level (MCL). Interim remedial actions were implemented to mitigate potential exposure to surrounding residents with water supply wells affected by CVOCs. Residential properties determined to have water supply wells impacted by CVOCs were initially provided bottled water, followed by the installation of whole-house water treatment systems.

Interim Measures (IMs) implemented by WCG at the Site include Hanger 4 Chemical Oxidation, Hanger 4 Soil Vapor Extraction (SVE), Hanger 1 In-Situ Chemical Oxidation, and a Hanger 1 Tracer Study Program. In addition, quarterly and semi-annual groundwater monitoring is performed to facilitate an evaluation of natural attenuation occurring at the Site. Ongoing IMs in the H4 area with SVE and sodium permanganate (NaMnO₄)injections within the Cresswell and Stovall formations continue to decrease TCE concentrations significantly. The H1 IMs have exhibited positive influences, particularly in the Stovall formation since the October 2014 NaMnO₄ injection. Vapor extraction in the H4 area has effectively removed an appreciable amount of CVOCs in both the shallow bedrock and unsaturated portion of the Cresswell unit. Although the results of the monitored natural attenuation (MNA) monitoring do not indicate the prevalence of strong natural biodegradation at the Site, an analysis of the data indicates stable and primarily decreasing trends over the long term in the off-Site areas and supports the occurrence of long-term attenuation mechanisms. The recent data reflect more consistent and pronounced attenuation of the CVOCs as defined by decreasing trends in MNA monitoring wells along the plume axis across the Site. These CVOC reductions are interpreted to reflect the cumulative effects from the physical processes of volatilization, dispersion, dilution, adsorption, and the IM remediation activities conducted in the H1 and H4 former source areas.