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A site plan depicting a geologic cross section path is presented as Figure 4 and the geologic cross section is presented as Figure 5. 3.2 Hydrogeology In February 2017, the average depth to water (DTW) in the A-zone wells was 45 feet below the ground surface(bgs). Between 2012 and 2016, groundwater elevations in all three zones declined approximately 18 feet. The A-zone wells near the former north evaporation pond went dry in August 2015, contained approximately 2 feet of water in March 2016, and went dry again in August 2016. In February 2017, there was 10 to 15 feet of water in the A-zone wells following the rainy season. The well construction details are presented in Table 1. Historical groundwater elevations are summarized on Table 2. Prior to 2012, groundwater in the A- and B-zones generally flowed west/southwest and west/northwest, respectively. The pre-2012 groundwater flow directions and gradients may have been influenced by surface water infiltration from the unlined Stockton Diverting Canal, located approximately 600 feet northeast of the site. During the drought from 2012 to 2017, the Canal contained little to no water and groundwater in both zones flowed predominantly to the northeast. Due to heavy precipitation during the 2016-17 winter, water returned to the canal and in February 2017 groundwater in the A- and B-zones flowed to the southwest. Rose diagrams depicting the historical groundwater flow directions are included on Figure 6. In 2014, pumping and slug tests were performed on A-zone wells. Except for well MW-23A, all the tested A-zone wells dewatered and the tests could not be completed. The hydraulic conductivity (K) measured in well MW-23A, located near the south tank farm, was 70 feet/day (Rubik, 2014). Based on the pump test data and historical groundwater gradients, the groundwater velocity of the A-zone is approximately 40 feet per year, regardless of the flow direction. 4.0 CHEMICALS OF CONCERN The primary chemicals of concern (COCs) in groundwater are nitrate (reported as total oxidized nitrogen [TON]; the sum of nitrate as nitrogen [-N] + nitrite-N), total ammonia-N (ammonia-N + ammonium-N), 1,2-dichloropropane (1,2-DCP), and 1,2,3-trichloropropane (1,2,3-TCP). Other COCs include 1,2-Dibromo-3-chloropropane (DBCP) and ethylene dibromide (EDB). The highest COC concentrations in the groundwater have been detected in the A-zone wells located adjacent to the former north pond and the existing south tank farm. The February 2017 COC concentrations detected in the A-zone wells are depicted on Figure 7. Historical groundwater analytical data is summarized in Table 2. 5.0 PREVIOUS REMEDIATION 5.1 Cap and Liner System Installation In October 1996, the former north and south evaporation ponds were excavated to approximately 4 feet bgs. Following the excavation, a Gundseal® geosynthetic clay liner consisting of HDPE sheeting affixed to a layer of granulated bentonite was installed in each location to prevent the CPS Stockton, California 2 7^'� Pilot Test Work Plan hC