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REVISED WORK PLAN FOR ADDITIONAL SITE INVESTIGATION Former Helena Chemical Facility 2245 West Charter Way Stockton, California February 27, 2018 1.0 INTRODUCTION This revised work plan was prepared by Condor Earth (Condor) to describe proposed additional Site investigation activities at the location of the former Helena Chemical facility at 2245 West Charter Way (Site) in Stockton, California (Figures 1 and 2, Appendix A). Condor prepared this revised work plan at the request of Ms. Beverly Garcia of Raymond Investment Corporation (property owner) and as directed by Ms. Aimee Phiri of the Central Valley Regional Water Quality Control Board (Central Valley Water Board) in a letter dated December 15, 2017. As stated in Condor's SITE INVESTIGATION REPORT, dated July 22, 2016, the purpose of the work is to further evaluate the extent of pollutants associated with historical pesticide storage area in the northern portion of the Site, near boring B39/GW12 (Figure 3, Appendix A). In a letter dated October 26, 2016, the Central Valley Water Board concurred with the report's recommendation. Condor submitted a work plan dated October 19, 2017 that outlined the proposed scope of work, which would have included drilling five soil borings and sampling soil and groundwater for the presence of Nitrate as Nitrogen (Nitrate-N), 1,2,3-Trichloropropane (1,2,3-TCP), and triazines (atrazine and simazine). However, in the December 15, 2017 letter, the Central Valley Water Board requested additions to the proposed work plan as indicated below: Drill and sample step-out borings near well MW-3 to collect soil and groundwater samples for analysis of 1,2,3-TCP, and at least one boring in the area between B39/G12 and MW-3 to verify whether or not a 1,2,3-TCP plume exists in the area; Install at least three additional groundwater monitoring wells to fully defme the extent of the nitrate plume and monitor potential migration of the plume a) south of previously drilled boring B32/GW10, b) east/southeast of previously drilled boring B39/GW12, and c) northwest of well MW-1; Include quality assurance/quality control (QA/QC) procedures to ensure that data obtained by the proposed sampling and analytical techniques is reliable, repeatable, and representative of conditions at the Site; and Describe how the proposed soil borings will be backfilled. 2.0 SITE SETTING The Site is located in the Great Valley Geomorphic Province in the northern San Joaquin Valley. The San Joaquin Valley is a northwest-trending, structural depression, filled with up to six vertical miles of lithified non-marine and marine sediments and unlithified non-marine sediments. Regionally, the lithology of the upper 3,000 feet of sediments is indicative of uplift and erosion of the Sierra Nevada to the east and, to lesser degree, the Coast Range Mountains to the west. The Sierra Nevada Province is an asymmetric range, with a steep fault-bounded eastern front and gentle western slope that dips under the sediments of the Great Valley to the west. The bedrock complex of the Sierra Nevada Mountains generally consists of C, CONDOR