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Atlantic Richfield Company 5 ARCO 595,6100 North Highway 99,Stockton,Cahfomia September 13,2002 procedures are presented as Attachment D Certified laboratory analytical reports and chain-of-custody documentation for soil samples are presented as Attachment E Groundwater Monitoring Well Development, Sampling, and Surveying After installation, wells MW-8 through MW-10 and DMW-1 through DMW-3 were developed by Cascade on July I I and 12, 2002 by rigorously surging over the length of the screen interval, and by purging approximately ten casing volumes of water from each well Monitoring well development records are included in Attachment F Groundwater samples were collected from the existing and newly installed groundwater monitoring wells on July 16 and 17, 2002, as part of regularly scheduled quarterly monitoring Samples were analyzed for the presence of TPHg, BTEX, and MtBE using the DHS/LUFI' method, and fuel oxygenates (MtBE, DIPE, EtBE, TAME, TBA, 1,2- DCA, EDB, and ethanol) using EPA Method 8260B With the exception of toluene in well MW-8 at 0 81 ppb, TPHg and BTEX constituents were not detected in newly installed wells MW-8 through MW-10 Low concentrations of toluene, ethylbenzene, and xylenes were detected in deep wells DMW-1 through DMW-3 MtBE by EPA Method 8260B was reported in 5 of the 6 groundwater monitoring wells installed (MW-8, MW-9, and DMW-1 through DMW-3) at concentrations ranging from 0 93 ppb (MW-9) to 53 ppb (DMW-3) TBA was detected . in newly installed deep wells DMW-1, DMW-2, and DMW-3 at concentrations of 6 4 ppb, 72 ppb, and 38 ppb, respectively, 1,2-DCA was reported in shallow well MW-8 and in deep wells DMW-1 through DMW-3 at concentrations ranging from 0 89 ppb (DMW- 2) to 4 6 ppb (DMW-3) Other fuel oxygenates were not detected in the newly installed wells It should be noted that the quality control blank contained minor concentrations of BTEX, concentrations of petroleum hydrocarbons in site wells will be confirmed during future groundwater monitoring and sampling events Groundwater analytical data are presented in Tables 2 and 4, and are illustrated on Figure 5 Field and laboratory procedures are presented as Attachment D The certified laboratory,analytical report and chain-of-custody documentation are included in Attachment G Groundwater sampling field sheets are presented in Attachment H The wells were surveyed relative to mean sea level by Morrow Surveying, a California- licensed surveyor A site plan showing well survey locations, elevations, and latitude and longitude coordinates is included in Attachment I Groundwater Flow Direction Based on depth to groundwater data collected on July 16, 2002, groundwater flow within the shallow water-bearing zone on-site was to the northwest-northeast at a gradient of • 0 003 feet per foot (Rift), and groundwater flow within the shallow water-bearing zone off-site was to the north-northeast at a gradient of 0 001 ft/ft (Figure 6) Groundwater flow within the shadow water-bearing zone was to the southeast at a gradient of 0 11 ft/ft dt¢e z 11ARC0105951Reponslwell mstall3 doc