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GAVIN NEWSOM Gl)VFRNOR Water Boards ENVIR NME FOA ENVIRONMENTAL PROTECTkON Central Valley Regional Water Quality Control Board 18 December 2023 Mr. Kevin Bertrand Senior Environmental Remediation Manager Nutrien Ag Solutions, Inc. 5296 Harvest Lake Dr. Loveland, CO 80538 REVIEW OF PILOT TEST WORK PLAN, NUTRIEN VERNALIS, 35100 SOUTH HIGHWAY 33, VERNALIS, SAN JOAQUIN COUNTY Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff have reviewed the 28 November 2023 Pilot Test Work Plan (Work Plan) for the Nutrien Vernalis Site Cleanup case located at 35100 South Highway 33 in San Joaquin County (Site). The Work Plan was submitted by Rubik Environmental, Inc. (Rubik) on behalf of Nutrien Ag Solutions, Inc. (Nutrien). In summary, the Work Plan proposes a pilot test to assess the effectiveness of enhanced in-situ bioremediation (EISB) in targeted areas where high concentration of nitrate in groundwater persist and replace monitoring well MW-6RR. The Work Plan highlights the success of similar efforts. In 2002, EISB was used beneath the former evaporation pond, and groundwater monitoring thererafter identified a decrease in concentrations of 1,2,3-trichloropropane (1,2,3-TCP) and nitrate near the treatment area. In 2007, a longer-lasting carbon release compound was used near the former evaporation pond and upgradient of offsite monitoring well MW-5. While the 2007 EISB did not appear to effect nitrate concentrations, the decrease of 1,2,3-TCP observed in downgradient monitorirng wells indicate the pilot test was effective. Since the majority of the effect the 2007 pilot test has been observed, 1,2,3-TCP and nitrate concentrations in groundwater have fluctuated. The Work Plan proposes replacing monitoring well MW-6RR with monitoring well MW-9. MW-9 will be installed to a depth of 70 feet below the ground surface (bgs) and screened below 50 feet bgs — both specifications being 5-feet deeper than MW-6RR. Since 2020 when MW-6RR was installed, the pH has ranged between 10 and 12. The pH in monitoring wells in that portion of the Site prior to the installation of MW-6RR were generally between 6 and 7.5, a range expected under normal conditions. The consistently high pH measurements in MW-6RR suggest that these anomalous observations indicate that an issue with the monitoring well is more likely than an issue with the equipment or procedure used to record the observation. To rule out well MARK BRADFORD, CHAIR I PATRICK PULUPA, Eso„ EXECUTIVE OFFICER 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 � www.waterboards.ca.gov/centralvalley