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NNW Underground Storage Tank Dehnu n Sampling Using Cone Penetration Testing With An Ultra-Violet Optical Screening Tool Report 216 N.California Street Page 2 of 7 on the north end and 6,300 mg/kg on the south end of the UST excavation. The UST removal activities were described by SJCEHD and Thorpe Oil in the notes made during the UST removal. In a letter dated December 22, 2004, Margaret Lagorio of the SJCEHD directed the Property Owner to submit a work plan to investigate the lateral and vertical extent of contamination at the Site. Condor prepared the Underground Storage Tank Closure Sampling Work Plan dated January 15, 2008. The work plan was approved on January 26, 2008 by SJCEHD. Condor completed one boring (SB-1) on February 19, 2008. The direct-push drilling equipment did not make efficient progress from a depth of 25 feet and deeper using direct-push drilling/continuous core methods in the former tank pit area due to saturated conditions. A groundwater sample was collected using a push-type groundwater sampler. Soil exhibiting excavation backfill characteristics (medium brown silty sand and clayey sand) was encountered from surface to approximately 18 feet below ground surface (bgs). Soil staining was visible as greenish-gray discoloration from 11.5 feet bgs to the total drilling depth of 50 feet bgs. Noticeable petroleum hydrocarbon odors were coincident with stained soil. Silty clay was encountered from approximately 16 feet bgs to 26 feet bgs. From 26 feet bgs to 36 feet bgs, a downward-coarsening lithology was encountered (sandy silt to silty sand). Groundwater was encountered at approximately 30 feet bgs and sampled at 34 feet bgs, although groundwater depths in nearby monitoring wells had recently been reported at approximately 24 feet bgs. Silty sand was encountered from 36 feet bgs to 42 feet bgs, followed by coarse sand with gravel from 42 feet bgs to 44 feet bgs. Sand with silt was encountered from 44 feet bgs to 48 feet bgs, followed by finer-grained silty sand with clay to 50 feet bgs. Laboratory analytical results indicated that concentrations of total petroleum hydrocarbons quantified as _ diesel (TPH-D) in soil were 2,400 mg/kg and 4,500 mg/kg at depths of 20 and 29.5 feet, respectively. Laboratory analytical results of soil samples collected below encountered groundwater indicated that concentrations of TPH-D in soil of 850 mg/kg and 40 mg/kg were present at depths of 36 and 48 feet, _ respectively. TPH-D was detected in the groundwater sample at a concentration of 590,000 micrograms per liter(µg/L) at 34 feet bgs. The petroleum hydrocarbon impacted soil is present from the former tank excavation to the present depth of groundwater at approximately 30 feet. Petroleum hydrocarbon concentrations in soil decrease from a depth of 30 feet to a depth of 48 feet. The Site was historically in the channel of Miner Slough which flowed from east toward the west with tidal influences (see Figure 6,Appendix A). The soils encountered indicated that stream channel deposits are present to a depth of 48 feet. Present day groundwater gradient directions in the vicinity of the Site as reported by the SJCEHD are generally toward the east-northeast. 2.0 BORING INSTALLATION FIELD PROCEDURES 2.1 SITE PREPARATION Condor obtained an encroachment permit, including street and sidewalk closure, and a traffic control plan, from City of Stockton, Public Works Department. Condor obtained the soil boring installation permit from SJCEHD. The proposed boring locations were marked with white paint and Underground Service Alert (USA) was notified five days in advance of the fieldwork to locate and identify underground utilities in and near the work area. However, Pacific Gas and Electric Company did not mark their electrical or gas 'Condor Earth Technologies, Inc. Subsurface Investigation, 216 N. California St., Stockton, San Joaquin County, California. Letter report to Ms. Ava Langston-Kenney, Program Manager, City of Stockton Redevelopment Department. i� CONDOR