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' 0 0 ' 2.0 NATURE, SOURCE, AND EXTENT OF CHEMICALS OF CONCERN Potential contaminants onsite are associated with use of the Site as a firing range. Field investigation activities completed September 11 and 14, 2015 by Geocon included: ' ➢ Three direct push soil borings to 20 to 25 feet including collection of soil and grab groundwater samples ➢ Collection of XRF surface lead readings at 152 discrete locations ' ➢ Collection of soil samples at 27 of the 152 discrete locations to confirm XRF readings ➢ Excavation of seven trenches in the primary impact berm and side berms ➢ Metal detecting to determine depth of bullet penetration in the impact berm ' The following laboratory analyses were performed as part of the site investigation: t ➢ Four soil samples for CAM 17 metals by EPA 601013/7471 ➢ 44 soil samples for total lead by EPA 6010B ➢ Six soil samples for WET soluble lead by EPA 7420 ➢ 13 soil samples for TCLP soluble lead by EPA 1311 ' ➢ One groundwater sample for CAM 17 dissolved metals by EPA Test Methods 601013/7470A ' ➢ Two groundwater samples for dissolved lead by EPA 6010B Total lead concentrations in soil samples collected from a depth of one foot or greater ranged ' from<1 to 31 mg/kg. Total lead concentrations in surface soil ranged from 7.9 to 42,000 mg/kg; soluble WET lead concentrations ranged from 3.7 to 1,100 mg/l; and, soluble TCLP lead concentrations ranged from 0.29 to 1,400 mg/l. Other metals were detected in soil including ' antimony, arsenic, barium, copper, vanadium, and zinc. Other metal concentrations were below 2016 Residential USEPA Regional Screening Levels (RSLs) except antimony and arsenic ' (residential RSLs of 31 and 0.68 mg/kg, respectively) detected at maximum concentrations of 300 and 81 mg/kg,respectively (USEPA 2016). It is also noted that the detection limit for cadmium (<20 to <100 mg/kg), cobalt (<20 to <100 mg/kg), and thallium (<20 to <100 mg/kg) ' exceeded the residential RSLs of 71, 23. and 0.78 mg/kg, respectively. Antimony and arsenic concentrations exceeding RSLs were co-located with elevated lead ' concentrations suggesting lead is the metal driving remedial operations. Analysis of a select number of confirmation samples for CAM metals is proposed to a) confirm the observed correlation between antimony, lead, and arsenic concentrations in the site assessment data and b) to confirm that cadmium, cobalt, and thallium concentrations are below their respective RSLs. All dissolved metal concentrations in groundwater were either below laboratory reporting limits ' or were below respective Maximum Contaminant Levels (MCLS). Geocon sample locations and results for the XRF samples and the soil and groundwater samples are included on Geocon's Tables 1 through 4 included in Appendix B. tA statistical analysis was conducted by Geocon to evaluate the correlation between 1) XRF readings and laboratory analytical results for total lead, 2) total and WET lead concentrations, PnciFicEDGE ENcweeawc 4 SREW_Manteca_draft.docx ' (949)470-1937;(949)470-0943(FAX)