Challenge. Determine nature and extent of contamination and design and implement remedial technology to mitigate human health and environmental impacts from nitrate in soils and groundwater.

Solution. INTERA performed a remedial investigation (RI) to characterize the site and enable the selection and design of an effective remedial action strategy. Work included the installation of soil borings, analysis of soil samples, and installation of permanent monitoring wells. Water quality sampling and pneumatic slug testing were completed to characterize the aquifer and a variably saturated flow model was used to evaluate nitrate and water movement through the vadose zone and calculate a dilution attenuation factor and site-specific clean-up level for total nitrogen in soil. To address the contamination, we have designed and installed an enhanced in-situ biodenitrification treatment system to remove some 450,000 pounds of nitrate from the groundwater hotspots, and allow the remainder of the groundwater to naturally attenuate. After negotiating property access and performing a pilot test of the emulsified oil substrate injection process, INTERA installed and is operating and maintaining the Phase 1 portion of the full-scale system. Treatment results show that nitrate (as nitrogen) concentrations in groundwater are being reduced to less than 40 milligrams per liter—the remediation target concentration. Contaminant fate and transport modeling indicates that groundwater with this target concentration of nitrate will naturally attenuate to levels below groundwater standards within a reasonable, and regulatory agency-approved, timeframe.