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S E C ® R
<br /> ,yY
<br /> • vicinity of the subject site The well search was conducted within a '/-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 June 23, 2004 is included as Attachment A,
<br /> including Tables 1- 3, Figures 1 - 5, and Graphs 1 - 8 plus field data sheets and groundwater
<br /> analytical reports The site has been monitored and sampled since 2nd quarter, 1990 Between
<br /> 1990 and 1991 the site was monitored/sampled semi-annually From 1992 to the present the Site
<br /> has been monitoredlsampled quarterly Currently MW-1 and MW-3 through MW-13 are monitored
<br /> and sampled quarterly each year Samples are analyzed for TPHg, BTEX, and fuel oxygenates
<br /> During the second 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 second quarter 2004 were 28 ppb
<br /> (MW-11) and 100,000 ppb (MW-7), respectively Concentrations of MtBE, TPHg, and TBA
<br /> continue to decline in site monitoring wells MtBE concentrations in wells MWA, MW-3, MW-4,
<br /> MW-5, MW-6, MW-7, MW-11, and MW-13 continue to decline (from a historical maximum of
<br /> 233,000 ppb to a current maximum of 28 ppb) TBA concentrations in wells MW-1, MW-3, and
<br /> MW-7 continue to decline from a historical maximum of 240,000 ppb to a current maximum of
<br /> 100,000 ppb TBA concentrations in well MW-11 appear relatively stable Based on MtBE and j
<br /> TBA isoconcentration maps (Figures 5 and 6 in Attachment A), these constituents are not
<br /> delineated to the northeast of the site (in the area of Shell well S-2) SECOR recommends that
<br /> during point sampling with Shell, ConocoPhillips' sampling contractor collect split samples from
<br /> Shell wells S-2 and S-5 and analyze for fuel oxygenates to determine the delineation of MtBE and
<br /> TBA
<br /> REMEDATION STATUS
<br /> The ozone infection system consists of a panel mounted KVA C-SpargeT"' System that produces
<br /> 4 grams per hour(0 009 pounds per hour) of ozone The system infects 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 1,309 hours, resulting in 75% runtime
<br /> Ozone infection system operational data is included as Table B-1 in Attachment B
<br /> The performance of the ozone infection 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 April 23, May 19, and June 21, 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 q
<br /> wells MW-3 and MW-4 indicate that ozone sparg+ng continues to be effective in reducing
<br /> concentrations of dissolved petroleum hydrocarbons Results of monthly groundwater sampling .i
<br /> events are summarized in Table B-2 Concentration versus time graphs for dissolved TPHg, s
<br /> benzene, MtBE, and TBA in monitoring wells MW-3 and MW-4 are provided in Figures B-1 and B-
<br /> 2 Remediation field data sheets and certified laboratory analytical reports and chain-of-custody
<br /> documentation are provided in Attachment C
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