SITE INFORMATION AND CORRESPONDENCE_CASE 1

Home Browse Search

M. Scott Mansholt - 2 - 16 August 2007 Chevron-US Can-Welty Ro,_ evaluation may be associated with former underground fuel storage tanks at Western Farm Services. The Western Farm Services monitoring well is approximately 200 feet north of the site and US Can-Welty Road well MW-2. According to the fuel fingerprint report, the sample contained 40 pg/L "iso-octane" mono- aromatics (benzene, toluene, ethylbenzene and xylenes-BTEX) compounds, olefins, and other gasoline constituents. The approximate percentages detected were: 19.8 percent C6, 78.4 percent C7 — C10, 1 .7 percent C11 — C14, and zero (0) percent C15+; no diesel range hydrocarbons (C15+) were reported. These results are consistent with the WFSMW-1 groundwater sample results submitted for fuel fingerprint evaluation from the previous quarterly event. TPHd for WFSMW-1 the prior quarter was 390 pg/L. SAIC has proposed the following: • Reduce the frequency for replacement and/or inspection of the oleophilic socks in MW-1 and 2 from quarterly to an annual basis since only 0.34-gallons of separate phase oil has been removed from these wells since 1999; • Discontinue sampling MW-5 since TPHd and/or PAHs have never been reported (for nine consecutive quarterly events starting in 2005) above the Environmental Screening Levels or the Water Quality Objectives for their respective constituents; • Discontinue sampling WFSMW-1 as fuel fingerprint evaluations from the two previous groundwater sampling events indicated the petroleum hydrocarbons reported were within the carbon range expected for gasoline; and, • Prepare a workplan for an additional investigation to further define the extent of petroleum hydrocarbons in soil and groundwater onsite; include a plan for destruction of MW-3 and 4 as the water level has dropped and these wells have not been sampled for approximately two years. Based on our review, we have the following comments: • The inspection and/or oleophilic sock replacement for MW-1 and 2 can be reduced to an annual frequency. Findings of this activity should be provided in the appropriate groundwater monitoring report; • We concur that monitoring wells MW-3 and 4 should be properly destroyed; groundwater samples should be obtained using a temporary well at the approximate locations of MW-3 and 4 since reliable samples have not been collected from these wells for approximately one year; • Regional Water Board staff concurs that two years of consecutive quarterly sampling and analysis for MW-5 is adequate and sampling can be discontinued provided the third quarter 2007 analytical results are consistent with the historical results. Provided the results are comparable to historical reports, MW-5 should be properly destroyed at the