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z • I�j Eo cnnaG. Bnowm JR, •'....1� unv n 0ift MAnHEw RCnRrouez Water Boards Central Valley Regional Water Quality Control Board ApR Q 5 2012 3 April 2012 SPE M�S�Ces CH2M HILL Attn: Daisy Wei, P.E. 1737 N. First Street, Ste. 300 San Jose, CA 95112-4524 SUPPLEMENTAL SOIL AND TREE HEALTH INVESTIGATION, KOPPEL STOCKTON, 2025 WEST HAZELTON AVENUE, SAN JOAQUIN COUNTY The Koppel Stockton Terminal is undergoing phytoremediation to remove nitrogen and ammonium from soil and groundwater. Declining trends in groundwater nitrate concentrations appear to have leveled off in the area of the former Bagging Plant, and Koppel Stockton conducted a detailed soil investigation in 2011. This investigation revealed low pH and high ammonium in specific areas of the former bagging plant. Koppel proposes a supplemental investigation in the February 2012 Former Bagging Plant Root Zone and Soil Investigation Work Plan (Root Zone Work Plan) prepared by CH21M Hill. California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) staff has reviewed the Root Zone Work Plan and discusses it below. Among the objectives of the Root Zone Work Plan is to excavate four short trenches adjacent to trees in the bagging plant area in order to obtain soil samples and assess the general structure and extent of roots of both living and dead trees. The soil properties will be used to create a root zone water balance to assist in identifying how irrigation and/or decaying roots may be influencing nitrogen behavior. Proposed soil analyses include pH, exchangeable aluminum and ammonium, soluble ammonium, nitrate, salinity, micro and macro nutrients. Buffered soil pH was added to the soil analyses by Ms. Daisy Wei of CH2M Hill during a 15 March 2012 telephone conversation with her. Trenching Central Valley Water Board staff concur with the proposed trenches and caution that this could cut through as much as 25% of the root mass of an individual tree. In order to minimize trauma to individual trees affected by a trench, Koppel may wish to consider applying a root hormone solution to cut roots, and generously water the trees when the trenches have been backfilled. The current density of trees is so great that they may be competing for available light. If a tree were to succumb to injuries incurred as part of the trenching operations, the individual loss is unlikely to affect the overall impact of the phytoremediation. Analyses In the Root Zone Work Plan, Koppel proposes to analyze soil for macro and micronutrients, exchangeable aluminum, exchangeable and soluble ammonium, nitrate, salinity, pH, and assess soil properties for field capacity, permanent wilt point and texture classification. In our 15 March telephone conversation, Ms. Wei also proposed to obtain soil buffering pH. KARL E. LONOLEY Sc D, P.E., CHAIR I PAMELA C. CREEDON P.E., BCEE, EXECUTIVE OFFICER 11020 Sun Center Drive#200,Rancho Cordova,CA 85670 1 www.walerboarEs.ca.gov/centralvalleV Li RecvcreR'All.