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<br /> vicinity of the subject site The well search was conducted within a '/Z-mile radius around the site
<br /> Based on the available data supplied by the California Department of Water Resources (DWR),
<br /> three municipal wells were identified within the '/-mile radius of the study area, the closest well is
<br /> located approximately 1,000 feet north-northwest of the site The depths of all three municipal
<br /> wells were reported to exceed 550 feet bgs and contain screened intervals beginning at a
<br /> minimum of 350 feet bgs The SRS was conducted within a 500-foot radius centered around the
<br /> subject site The SRS involved distributing questionnaires to all residences and businesses
<br /> within the study area, requesting information about potential groundwater receptors GR
<br /> distributed 141 questionnaires via the U S Post Office and a total of 49 questionnaires (35%)
<br /> were returned to GR None of the returned questionnaires identified the presence of a well within
<br /> the SRS study area (GR, 2001)
<br /> MONITORING AND SAMPLING
<br /> TRC's Groundwater Monitoring Report dated November 10, 2004 is included as Attachment A,
<br /> including Tables 1- 3, Figures 1 - 6, plus field data sheets and groundwater analytical reports
<br /> The site has been monitored and sampled since 2nd quarter, 1990 Between 1990 and 1991 the
<br /> site was mon itoredlsampled semi-annually From 1992 to the present the Site has been
<br /> monitored/sampled quarterly Currently MW-1 and MW-3 through MW-13 are monitored and
<br /> sampled quarterly each year Samples are analyzed for TPHg, BTEX, and fuel oxygenates
<br /> During the third quarter 2004 groundwater flow was toward the north at a gradient of 0 002 ft/ft
<br /> Maximum reported concentrations of MtBE and TBA during the third quarter 2004 were 12 ppb
<br /> (MW-4) and 83,000 ppb (MW-7), respectively Concentrations of MtBE, TPPH, and TBA continue
<br /> to decline in site monitoring wells MtBE concentrations in wells MW-1, MW-3, MW-4, MW-5,
<br /> MW-6, MW-7, MW-11, and MW-13 continue to decline (from a historical maximum of 233,000
<br /> • ppb to a current maximum of 12 ppb) TBA concentrations in wells MW-1, MW-3, and MW-7
<br /> continue to decline from a historical maximum of 240,000 ppb to a current maximum of 83,000
<br /> ppb TBA concentrations in well MW-11 have increase to a historical high during the third
<br /> quarter Based on MtBE and TBA isoconcentration maps (Figures 5 and 6 in Attachment A),
<br /> these constituents are not delineated to the northeast of the site (in the area of Shell well S-2)
<br /> SECOR recommends that during joint sampling with Shell, ConocoPhdlfps' sampling contractor
<br /> collect split samples from Shell wells S-2 and S-5 and analyze for fuel oxygenates to determine
<br /> the delineation of MtBE and TSA
<br /> REMEDATION STATUS
<br /> The ozone injection system consists of a panel mounted KVA C-SpargeTM System that produces
<br /> 4 grams per hour (0 009 pounds per hour) of ozone The system injects ozone to ten ozone wells
<br /> SP-A through SP-H, SP-J, and SP-K The system was placed into operation on December 20,
<br /> 2001 During the current quarter the system operated for 754 hours, resulting in 41% runtime
<br /> The system was found to be non-operational on July 29 and August 18, 2004, due to the GFI
<br /> being tripped It was restarted both times On September 20, 2004, the compressor piston was
<br /> replaced, as it was fading Ozone injection system operational data is included as Table B-1 in
<br /> Attachment B
<br /> The performance of the ozone injection system is evaluated based on the results of regular
<br /> groundwater sampling Monthly groundwater samples were collected from monitoring wells MW-3
<br /> and MW-4 on July 29, August 19, and September 16, 2004, and analyzed for total petroleum
<br /> hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX
<br /> compounds), methyl tert-butyl ether (MtBE), and tert-butyl alcohol (TBA) Monthly sampling of
<br /> wells MW-3 and MW-4 indicate that ozone sparging continues to be effective in reducing
<br /> concentrations of dissolved petroleum hydrocarbons Results of monthly groundwater sampling
<br /> events are summarized in Table B-2 Concentration versus time graphs for dissolved TPHg,
<br /> benzene, MtBE, and TBA in monitoring wells MW-3 and MW-4 are provided in Figures B-1 and B-
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