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1 .0 Introduction ' 1.1 Purpose This report provides a plan for the implementation for the selected remedial alternative to address excess nitrogen in soil and groundwater at the Koppel Stockton Terminal in Stockton,California. The selected alternative includes two components,phytoremediation and natural attenuation and monitoring groundwater and soil. The purpose of this report is to provide the following information: • A conceptual design for tree planting and maintenance to support the phytoremediation ' A description and schedule for monitoring soil and groundwater • A description and schedule for reporting • Criteria for evaluating the success of the remedial action • A contingency plan to address potential deficiencies in this remedial action • A schedule for implementation 1 .2 Background The Koppel Stockton Terminal is a warehouse with associated facilities located adjacent to the Port of Stockton. A site map is shown on Figure 1. The site has been the subject of numerous investigations since the early 1990s to identify the extent of nitrogen ' contamination in the soil and groundwater. Soil types encountered onsite include discon- tinuous beds of sand,gravel,clay,and silt deposited in a continental alluvial fan environ- ment. It is possible that some or all of the site has been covered with fill. The water table is approximately 3 to 10 feet below the ground surface(bgs) (0 to-7 feet mean sea level [msl]). Groundwater flow direction is generally southerly but can vary across the site in possible response to rainfall,nearby pumping, tidal fluctuations, and recharge of ponded runoff. ' Nitrogen(in the form of nitrate and ammonium)has been detected at elevated levels in five areas of the site identified in the Feasibility Study Report Koppel Stockton Terminal (FS) (CH2M HILL,20O0a).The total affected area comprises approximately 5.5 acres. ' A test grove of 267 poplar trees was planted in May 1998 to evaluate the effectiveness of phytoremediation to remove nitrogen from soil and groundwater. The test grove is shown on Figure 1.The remedial action described in this plan includes planting an additional 1,535 trees at select site locations and the subsequent monitoring of groundwater and soil. 1.3 Cleanup Goals Cleanup goals targeted for the Koppel Stockton Terminal for both groundwater and soil are presented in Table 1. Because the Regional Water Quality Control Board (RWQCB) and the ' RDD/003670317.DOC(CAH710.DOC) 1