WORK PLANS_PRE 2019 - Laserfiche WebLink

Home Browse Search

Phase II Environmental Site Assessment Report 324 East 11 th Street Tracy, CA July 23,2013 SITE ASSESSMENT RESULTS Field Observations As described above, geophysical surveying identified a 20-ft long piping anomaly but did not suggest the presence of USTs. During installation of boring B-1,no USTs were encountered. During field screening of soil and groundwater samples,soil staining and organic vapors were observed in soil and/or groundwater from borings B-1, B4 and B-6. The field observations suggest that petroleum hydrocarbon impact is present in shallow and deeper soil(from l ft to 15 ft depth)in boring B-1. For borings B-4 and B-6, petroleum hydrocarbon impact was encountered only near the soil/groundwater interface at approximately 8 to 11 ft bgs. PID readings and observations are included on the boring logs in Appendix C. Based on soil logging during hand augering and drilling,soil from site borings consisted primarily of silty clay to a depth of approximately 5 to 9 ft bgs,underlain by more permeable sandy clays or clayey sands observed to a depth of approximately 25 ft bgs. Wet soil(possible groundwater)was encountered in the more permeable sandy clay or clayey sand layers encountered at approximately 8 to 1 I ft bgs. Soil Analytical Results Soil analytical results are summarized on Tables 1 and Figure 2.The laboratory analytical reports are included in Appendix D. The maximum TPHg concentration detected during this investigation was 2,400 milligrams per kilograms (mg/Kg) in boring B-1 at a depth of approximately 1 ft. TPHg was also detected at a# concentration of 130 mg/Kg in boring B-1 from 5 ft depth. The only benzene concentration detected in soil was 2.3 mg/kg in boring B-1 at an approximate depth of 10 ft. As shown on Table 1,these TPHg and benzene concentrations in soil exceed Environmental Screening Levels(ESLs)established by the San Francisco Bay- Regional Water Quality Control Board's (RWQCB). Toluene (32 mg/kg), ethylbenzene(9.7 mg/kg), and xylenes(36 mg/kg)concentrations detected in boring B-1 at approximately 1 ft depth also exceeded ESLs.All other detected hydrocarbon concentrations in soil were below applicable ESLs. Grab Groundwater Analytical Results Groundwater analytical results are summarized on Table 2. Key hydrocarbon results for this investigation are summarized on Figures 3 through 5. The laboratory analytical reports are included in Appendix D. The maximum hydrocarbon concentrations in groundwater were detected in onsite boring B-1 in excess of ESLs as follows:6,200 micrograms per liter(µg/L)TPHg,72,000 TPHd pg/L,and 33,000 pg/L TPHmo. TPHg was also detected in concentrations exceeding ESLs in borings B-4(200 pg/L)and B-6(7,300 pg/L).TPHd was 4