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i i Site Background Information - Guardino and Crawford Page 2 of 6 f iA letter from the San Joaquin County Environmental Health Department (EHD), dated 07 March 1996, indicated that further investigation related to the former UST would be required before site closure could be issued. SITE ASSESSMENT ACTIVITIES On 19 September 1995, three soil probe borings (P 1 through P3) were advanced at the site to a depth of 25 feetbsg; boring P was advanced north of the former UST area, boring P2 was advanced near the center of the former UST excavation, and boring P3 was advanced near the former dispenser location. Five additional soil borings (P4 through P8) were advance on 21 April 1997; four borings (P5 through P8) were advanced in the vicinity the former UST, and one boring (P4) was advanced i in the City of Stockton right-of--way on Fremont Street. Total petroleum hydrocarbons quantified as gasoline (TPH-g) was detected in soil samples from probe borings P2, P3 , and P7 at concentrations as high as 230 mg/kg (P3- 10). Volatile aromatic compounds benzene, toluene, ethylbenzene, and total xylenes (BTEX) were detected in soil samples collected from P3 at concentrations ranging from 0.010 mg/kg (ethylbenzene, P3-25) to 19 mg/kg (xylenes, P3 - 10). Petroleum hydrocarbons were not detected in soil samples analyzed from any other probe borings advanced during this investigation. • Analytical results of soil samples submitted for physicochemical analysis and microbiological enumeration indicated that there is microbial activity at the site, however it is segregated from the area of the hydrocarbon release. The lack of biodegrading bacteria in the area of the dispenser may be due to the presence of biotoxic compounds in the subsurface at the site, such as metals or pesticides. However, adequate concentrations of necessary nutrients for microbe growth and sustenance were present in the soil at the site. • TPH-g was detected in four of six grab ground water samples collected from the site at concentrations ranging from 510 micrograms per liter (µg/1) to 94,000 µg/1. BTEX compounds were detected in five of six samples analyzed at concentrations ranging from 1 .3 µg/1 benzene in boring PI to 19,000 µg/l toluene in boring P6. MTBE was detected at concentrations as high as 290 µg/1. No petroleum hydrocarbons were detected in the grab ground water sample collected from the City of Stockton right-of-way in Fremont Street, located in the apparent up-gradient direction from the former UST area. On 15 and 16 June 1999, AGE advanced four pilot soil borings for the construction of ground water monitoring wells and collected and procured laboratory analysis of soil samples . The four soil borings (MW- 1 through MW4) were advanced utilizing hollow-stem auger drilling techniques and were subsequently completed as monitoring wells of the same designations. Advanced GeoEnvironmental, Inc.