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California Department of Transportation September 6, 2001 Shop 10 Maintenance Station, Stockton, California Protect No 400296001 s 2. INTRODUCTION AND SCOPE OF SERVICES This report summarizes the results of the Second Quarter 2001 groundwater monitoring activities conducted June 4-5, 2001 at the Shop 10 Maintenance Station, located in Stockton, California (Figure 1) The work conducted by Ninyo & Moore was in accordance with Task Order No 10- 987901-NP and Caltrans Contract No 43AO012 Our scope of services include 1) attendance of a prework site visit, 2) preparation of a site safety plan, 3) measurement of the depth to static groundwater at selected wells, 4) purging of a minimum of three well volumes to labeled recon- ditioned 55-gallon drums, 5) collection and chemical analysis of groundwater samples, and 6) preparation of this report documenting our field activities and findings 3 SITE BACKGROUND According to a report entitled, Revised Report, Third Quarter 1998 Groundwater Monitoring Re- port by Professional Service Industries (PSI), dated March 19, 1999, four underground storage tanks (USTs) were removed from the site in August 1986 Subsequent to the removal, fourteen soil borings were drilled on-site and four were drilled off-site between 1987 and 1991 to deter- mine the extent of soil contamination Analytical results of soil samples collected indicated maximum concentrations of total petroleum hydrocarbons as gasoline (TPH-G) to be 3,800 mil- ligrams per kilogram (mg/kg) and total petroleum hydrocarbons as diesel (TPH-D) to be 4,500 mg/kg Groundwater monitoring wells currently in use and sampled during quarterly groundwater monitoring for the site include MW-9, MW-11, MW-12, MW-13, MW-16, MW-19, MW-20, MW-24, MW-25 and VM-1 Monitoring wells MW-14 and VM-2 were not accessible because they have been paved over Since 1988 several wells were installed and subsequently abandoned including MW-1, MW-2, MW-3, MW-4, MW-5, MW-7, MW-8, MW-10, MW-26 and VW-1 The approximate locations of the monitoring wells sampled are shown in Figure 2 Quarterly groundwater monitoring has been conducted at the site in the wells since 1990 Historically, con- centrations of TPH-G, TPH-D, benzene, toluene, ethylbenzene, and total xylenes (BTEX) and methyl tertiary butyl ether(MTBE) have been detected in the on-site monitoring wells z0off"&prRm%T G 0296 01 r shop 10 2Q01 doc 2