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% I Work Plan For Monitoring Well Installation,Tosco(Former BP)Service Station Number 11195,16500 South Interstate-5,Lathrop CA April 19,2002 Six on-site groundwater monitoring wells (MW-1 through MW-6) and five off-site groundwater monitoring wells (MW-8 through MW-12) are present at and around the site. In addition, one 6- inch diameter temporary groundwater extraction conductor casing was installed in the former UST pit prior to backfilling. Current site facilities are shown of Figure 2. PROPOSED SCOPE OF WORK To further evaluate groundwater conditions beneath the site, GR proposes the installation of five groundwater monitoring wells at the locations shown on Figure 2. GR Field Methods and Procedures are included in Appendix A. To complete the proposed scope of work, GR proposes the following tasks: Task 1. Pre-Field Activities GR will update the site-specific safety plan and obtain the necessary well installation permits from the PHS-EHD. A private utility locator will be contracted to locate any underground utilities near the proposed well locations and .Underground Service Alert (USA) will be notified a minimum of 48 hours prior to drilling. a Task 2. Monitoring Well Installation GR will install four off-site groundwater monitoring wells at the locations shown on Figure 2. A California licensed well driller will install the wells. A GR geologist will observe the drilling activities and prepare logs of the well borings. Prior to drilling, the boreholes will be hand excavated to 5 feet bgs to confirm that the locations are clear of underground utilities. The well borings will be advanced to approximately 20 feet bgs with 8-inch-diameter hollow-stem augers. The five wells will be constructed of 2-inch-diameter schedule 40 polyvinyl chloride (PVC) well casing and 0:02-inch machine slotted PVC well screen. The screened interval will extend from approximately 5 feet above to 10 feet below groundwater, which is anticipated to be approximately 10 feet bgs. Proposed groundwater well construction details are shown on Figure 3: Soil samples for description and possible chemical analysis will be obtained from the borings at a minimum of 5 foot intervals and will be collected with a split-spoon sampler fitted with clean brass sample rings. The actual number of samples submitted for chemical analysis will depend on site conditions and field screening data. As a minimum, . it is expected that one unsaturated soil sample from each boring will be submitted for chemical analysis as described in Task 5. 140193.12-1 2 I