Theme: 08. Metals

Topic Area: 8a. Managing Chromium-Contaminated Sites

Formatted Title:

Expedited Implementation of RCRA Corrective Action Process for Hexavalent Chromium: A Case Study

Background/Objectives:

Previous investigations identified the presence of chromium-impacted groundwater in the subsurface at a closed industrial facility in Maryland (site). The site is located within the Atlantic Coastal Plain physiographic province, characterized by wedge-shaped sediments (inter-layered fluvial and deltaic sands, silts, and clays) that thicken to the southeast. Impacts include total and hexavalent chromium related to past pigments-based manufacturing activities. Environmental investigation and mitigation activities began in the mid-1980s. The site was part of a corporate acquisition in 2015. After manufacturing operations ceased in 2019 the new owner prepared the site for sale with expected future industrial/commercial land use. This case study highlights expedited progress through the United States Environmental Protection Agency (USEPA) Resource Conservation and Recovery Act (RCRA) Corrective Action process, from investigation to approval of the Corrective Measures Implementation Plan. It explores a collaborative regulatory approach and will highlight some of the challenges in developing a full-scale remedy to facilitate property sale.

Approach/Activities:

Following transfer of property ownership in 2015, off-site investigations using vertical aquifer profiling were conducted to delineate the extent of off-site groundwater impacts in the 115-acre plume. After active operations ceased in 2019, additional on-site soil and groundwater investigation further characterized impacts within the presumed source area to inform the Corrective Action process. At the suggestion of USEPA, corrective action objectives (CAOs) were negotiated and approved prior to development of remedial alternatives in the Corrective Measures Study. Qualitative and quantitative CAOs were developed by media based on the intended future site use and the improved understanding of impacts. CAOs included residential and non-residential human health, ecological receptors, cross-media transfer, and resource restoration components.

Results/Lessons Learned:

Focused investigation and early regulatory engagement in the project following the change of site ownership facilitated rapid progress through the Corrective Action program within seven years. Onsite direct-push investigation and off-site vertical aquifer profiling completed delineation of chromium impacts in affected media, guiding screening of risk-based remedial options. Regulatory participation and buy-in during the CAO identification process allowed corrective measures selection to focus on a streamlined and targeted set of alternatives. The numerical CAO for groundwater was adjusted from the Regional Screening Level (RSL)-based groundwater cleanup level for hexavalent chromium to 0.35 micrograms per liter using a risk level of 1 in 100,000. The revised groundwater cleanup level provides greater flexibility to meet analytical reporting limits, while remaining protective of human health. Site visits and virtual site visits (using aerial imagery) further allowed development of a common understanding of site physical conditions and constraints on future remedial actions (e.g., existing buildings and site cover). The selected corrective measures focus on future commercial/industrial use and consist of land use controls with targeted soil excavation within building footprints and monitored natural attenuation for groundwater with onsite in-situ treatment. The selected corrective measures include provisions for protection of construction workers and a restrictive covenant for groundwater. Additionally, flexibility was built into the in-situ treatment portion of the selected groundwater alternative to easily permit modifications to the amendment substrate in the future as the remedy progresses. The property has been sold and remedy implementation is anticipated to begin in 2024.

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Matthew McCaughey