ARCHIVED REPORTS_XR0006084 - Laserfiche WebLink

Home Browse Search

07 May 2004 AGE-NC Project No 98-0534 ' Page 9 of 14 below the tops of the well casings(within the screened interval), ground water was inferred ' to be flowing to the southwest across the former UST area to 0 002 ft/ft The ground water r, elevation of monitoring well MW-4 appeared anomalously low, out of the range of the surrounding wells by 1 foot and therefore the data from that well was not used to map the s ground water elevation TPH-d was not detected in the ground water samples collected from the wells TPH-g was detected in the ground water samples collected from wells MW-4 and MW-6 at concentrations of 90 gg/1 and 120 µg/l, respectively BTEX compounds were not detected in the ground water samples MTBE was detected by EPA Method 8260 in the samples from wells MW-4 and MW-6 at concentrations of 10 gg/1 and 72 µg/1,respectively ' No other fuel oxygenates were detected in any of the samples Ground water elevations are summarized in Table 1, analytical results of ground water samples are summarized in Table 2 Results of the October 2003 ground water monitoring event were reported in Quarterly ' Report- 4th Quarter 2003, dated 29 January 2004, prepared by AGE • 06 February 2004 - ground water levels measured at MW-1 through MW-6 and MW-8 ' averaged 9 33 feet below the tops ofthe well casings(near the screened interval) MW-7 was not accessible during the monitoring event, ground water was inferred to be flowing to the northwest across the former UST area at a gradient of 0 02 ft/ft No petroleum hydrocarbons ' or fuel oxygenates were detected in any of the analyzed samples Ground water elevations are summarized in Table 1, analytical results of ground water samples are summarized in Table 2 24 REGIONAL GEOLOGIC ETTING S The site is located within the northern San Joaquin Valley which comprises part of the Great Valley geomorphic province of California The San Joaquin Valley is formed by the Great Valley ' geosyncline,which is a large, elongate, northwest-trending asymmetrical structural trough (basin) It is bordered by the Coast Ranges to the west, the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east This trough has been filled with sediments derived from - ' both marine and continental sources Thickness of the sedimentary fill ranges from thin veneers along the valley edges to greater than 20,000 feet in the south central portion of the valley ,The - sedimentary formations`range in age with the older deposits being primarily marine in origin and the - - ' younger deposits being primarily continental Contmental-denved sediments were primarily deposited in lacustnne, fluvial, and alluvial environments with sources being the mountain ranges surrounding the valley(Olmsted and Davis,'1961) The site is located on unconsolidated and semi- consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977) The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San ' Joaquin Valley Ground Water Basin (Basin 5-22) Advanced GeoEnvironmental,Inc l