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TECHNICAL WORKPLAN MODIFIED WORKPLAN CALIFORNIA WATER SERVICE COMPANY 1602 E. Lafayette Street Stockton, CA 95205 This workplan (WP), prepared by Chow Engineering, Inc. (CE), for submittal to the San Joaquin County Environmental Health Department (County) on behalf of California Water Service Company (Cal Water), presents the modified Scope of Work for the final closure of the two Underground Storage Tank (UST) system at the Cal Water site at 1602 E. Lafayette Street, Stockton, CA (site). The location of the site is presented on Figure 1. A map of the site is presented as Figure 2. This work plan proposes 1) backfilling of the excavation and 2) disposition of the pipelines associated with the former USTs. Two (2) USTs, approximately 8,500 gallons in capacity, were discovered at the site in October 2011. The USTs were apparently installed during the 1930s. The USTs were taken out of service sometime ago and one was filled with sand while the other was partially filled with water. Both tanks were used as fuel oil tanks for heavy fuel oil supply to the boiler house nearby. When removed from service the tanks were partially filled with inert material (sand in Tank #1 and water in Tank #2) on top of the heel (3 to 4 inches) of fuel oil in the bottom of each tank. In the current closure, the sand and oily water were removed from the tanks and the tanks rinsed with water. The residual products were disposed of as hazardous waste by Veolia Environmental Services. The USTs were inerted and excavated on December 13, 2011 under County permit SR0063739 and the City of Stockton Fire Department permit 11/12-093. The tanks were transported and disposed of as hazardous waste at Ecology Control Industries (ECI) of Richmond, CA under manifest numbers 002135911 JJK and 002135912 JJK. Four (4) confirmation soil samples were collected from the bottom of the tank excavation on December 13, 2011. In addition, three (3) soil samples were collected from the bottom of the adjoining main pipeline trench. A total of five (5) soil samples were also collected from the two soil stockpiles onsite. On December 15, 2011, five (5) additional confirmation soil samples were collected from approximately two feet deep in the floor of another trench with pipelines in the vicinity. On December 19, 2011, five (5) confirmation soil samples were collected from pot -holes along the main pipeline trench (see Figure 3). All samples were collected under chain of custody and delivered to McCampbell Analytical, a state certified laboratory for analysis, on the day they were sampled. Analytical results are presented in Section 2.0 of this Plan. CE Project No. 11 R-120 Work Plan — Cal Water Stockton