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2 October 31.2002 DISCUSSION (CHEVRON): On September 24, 2002, Gettler-Ryan (G-R) conducted groundwater monitoring and sampling for the 3rd quarter 2002 Chevron station 9-4275 in conjunction with Arco station No 2133 (2908 West Benjatntn Holt Drive) Nine Chevron wells were sampled during this event Groundwater samples were analyzed for total petroleum hydrocarbons quantified as gasoline(TPHg),benzene, toluene,ethylbenzene, and xylenes(BTEX), and the fuel oxygenates including methyl-tertiary-butyl-ether(MtBE), ethyl-tertiary-butyl-ether(EtBE),di-isopropyl ether(DIPE),tertiary-amyl-methyl-ether(TAME), tertiary- butanol/tertiary-butyl-alcohol(TBA), 1,2 dichloroethane(1,2 DCA) and 1,2 dibromoethane(EDB) DIPE,ETBE, toluene,and EDB were not detected in samples from any of the wells TPHg was detected in samples collected from five wells at concentrations ranging from 50 micrograms per liter(µg/L) (MW-4)to 170µg/1.(MW-2) MtBE was detected in samples from five wells at concentrations ranging from 4µg/L(MW-4) to 2,500gg/L(MW- 1) Ethylbenzene was detected in one well at a concentration of 4 gg/l (MW-5) Xylene was detected in one well at a concentration of lµg/l(MW-5) TAME was detected in samples collected from three wells at concentrations of 3 µg/L(MW-3)to 31 µg/L(MW-1) DISCUSSION (ARCO): !q Total petroleum hydrocarbons as gasoline(TPHg)were reported in 4 of theiffwells sampled this quarter at concentrations ranging from 72 gg/L(PR-2)to 570µg/L(E-10) Benzene was reported in 4 of the 19 wells at concentrations ranging from 0 64µg/L(E-4)to 5 8 µg/L(E-10) Methyl tert-butyl ether(MtBE) was reported m7 of the 19 wells(E-4,E-6,E-10,PR-2,MW-1,MW-2,and BHD-1) at concentrations ranging from 3 0µg/L(MW- I 2)to 780µglL(E-10) MtBE was reportedJo.Lihe first time in wells MW-2 Chemical concentrations were generally consistent with historical data,except for a decrease in TPHg,benzene, and MtBE in E-4 and E-10 Groundwater elevations across the site decreased by an average of 1 84 ft Groundwater flow was to the north-northeast at an approximately gradient of 0 002—0 003 ft/ft,which is generally consistent with historical data Arco's groundwater elevation and analytical data are summarized in Table 1 Chevron's groundwater monitoring and analytical data are summarized in Tables 2 and 3 Table 4 presents historical groundwater gradient data A groundwater elevation contour map is presented as Figure 2 Groundwater concentrations are summarized for TPHg,benzene,and MtBE in Figure 3 Attachment A contains ARCO's historical SVE and recent AS system operational data Attachment B contains field and laboratory procedures Attachment C contains ARCO certified laboratory analytical results,chain of custody documentation,and field data sheets Attachment D contains Chevron certified laboratory analytical results,chain of custody documentation,and field data sheets This report presents our understanding of existing conditions at the subject site The conclusions contained herein are based on the analytical results,and professional judgment in accordance with current standards of professional • practice,no other warranty is expressed or implied SECOR assumes no responsibility for exploratory borings or data reported by other consultants or contractors