Formatted Title
Implementing a Combined Source Remedy for Trichloroethene and Hexavalent Chromium Impacts under a Multi-Party Settlement
Background/Objectives
The site is located in north central Indiana and consists of three parcels totaling a half-acre just west of the Elkhart River. The site has over a 100-year history of various industrial manufacturing operations including metal plating and foundry casting, and is currently vacant following demolition of the former 8,700 square foot main operations building in 2015 by the current municipal owner. The current owner executed a voluntary remediation agreement with the Indiana Department of Environmental Management (IDEM) in 2020, and has pursued cost recovery via pollution liability insurance coverage from multiple past owner/operators at the site. Multiple site investigations were conducted between 2016 through 2023 including the installation of 85 soil borings (on- and off-site); collection of over 188 soil samples for hexavalent chromium analysis and over 157 soil samples for volatile organic compound (VOC) analysis; and completion of 16 permanent monitoring wells, extending 1,250 downgradient of the site. The site hydrogeology consists of a heterogenous unconfined sand and gravel aquifer 50 to greater than 100 feet in thickness with a depth to groundwater of 10 feet below grade. The main constituents of concern (COCs) for groundwater are hexavalent chromium and trichloroethene and the primary COC for soil is hexavalent chromium. The sand-and-gravel aquifer groundwater flow velocity ranges from approximately 3.4 ft/day or 1,241 ft/year with the primary fate of contaminants in groundwater consisting of advective transport toward the Elkhart River, with attenuation through dispersion and volatilization. The groundwater remediation objectives are the Indiana Drinking Water Maximum Contaminant Levels (MCL) found in 327 Indiana Administrative Code (IAC) 8-2-4 (d) for chromium of 0.1 milligrams per liter (mg/L) and 327 IAC 8-2-5.4 for trichloroethene of 0.005 mg/L. The soil remediation objectives proposed for this site are the IDEM published levels for Commercial Soil of 60 milligrams per kilogram (mg/kg) and Excavation Soil level for trichloroethene of 100 mg/kg. The estimated vadose zone soil source area(s) is approximately 1,500 square feet and the vertical depths vary from 2 to 9 feet. The extent of groundwater contamination has been defined to the IDEM Risk Based Closure Guide R2 (July 8, 2022) MCLs.
Approach/Activities
The remediation plan for the Site includes pre-excavation soil confirmation and waste characterization sampling and analysis; source area soil removal via excavation and off-site disposal; source area groundwater treatment via in situ chemical reduction (ISCR) utilizing a ph-buffered, carbon lactate amendment and zero-valent iron (ABC®+) via 50 injection points (10 to 35 feet below grade vertical interval); post remedy groundwater performance monitoring; and institutional controls via an on-site environmental restrictive covenant (ERC) and an enhanced municipal area-specific environmental restrictive ordinance (ERO), if necessary. The ISCR amendment design consists of 100,500 pounds by weight with a ZVI content of 62,000 pounds for a total injection volume of 41,500 gallons. This equates to approximately 5.3 percent (%) of the pore volume assuming 30% aquifer porosity. The ZVI dosing is 0.15 weight percent with respect to soil assuming a soil density of approximately 120 pounds/cubic foot.
Results/Lessons Learned
The remedial construction is scheduled to commence at the end of 1Q2024; with performance monitoring starting in 3Q2024.