ARCHIVED REPORTS XR0011263 - Laserfiche WebLink

Home Browse Search

Groundwater Flow Direction/Gradient(upper zone) Radial flow outward from MW-5/0 005 to 0 006 ft/ft Groundwater Flow Direction/Gradient (lower zone) Southeast/0 006 ft/ft DISCUSSION As discussed In the Site Conceptual Model (SCM), review of the subsurface geology and groundwater well elevation data indicate that although different transmissive (i a sandy) zones have been identified at various depths at this site, these zones are hydraulically connected and form one continuous water- bearing zone The monitoring well network, as currently installed, was intended to target these sandy, more transmissive zones and potential migration pathways Groundwater monitoring wells have been screened at two distinct intervals Upper zone wells, MW-1 through MW-7, are screened in sandy zones between 46 5 and 70 feet below ground surface (bgs), to monitor petroleum hydrocarbon impact to the uppermost 15 to 20 feet of the water-bearing zone Lower zone wells, MW-8 through MW-12, are screened between 94 and 115 feet bgs, within the laterally continuous sandy unit first encountered at approximately 95 to 105 feet bgs At the time of the third quarter 2003 monitoring event, groundwater was encountered in the monitoring wells screened within the upper zone at depths ranging from 49 10 to 51 04 feet bgs. Well MW-3 is obstructed Groundwater was encountered in the monitoring wells screened within the lower zone at depths ranging from 50 23 to 51 94 feet bgs Groundwater elevations decreased approximately 1 64 to 2 74 feet in upper zone wells since the May 28, 2003, monitoring event except for well MW-4 where groundwater elevation increased by 0 78 feet In the lower zone wells, groundwater elevations decreased 1 08 to 2 63 feet in wells MW-9 and MW-11 and increased 0 04 to 0 37 feet In wells MW-10 and MW-12 Groundwater monitoring data were normalized to mean sea level (MSL) and used to prepare groundwater elevation contour maps A groundwater elevation contour map for the upper zone is shown on Figure 2 In the upper zone, the groundwater flow direction on August 11, 2003, was calculated to be radial outward from well MW-5 at gradients ranging from 0 005 to 0 006 ft/ft Since 1995, groundwater flow in the upper zone has consistently been toward the east and southeast A groundwater elevation contour map for the lower zone is shown on Figure 3 In the lower zone, groundwater flow during the second quarter 2003 was toward the southeast at an average gradient of 0 006 ft/ft Groundwater flow in the lower zone has historically been toward the south and east In the upper zone wells, THPG and BTEX were reported in wells VEW-1 and VEW-2 The highest TPHG concentration (120,000 µg/L) was reported in VEW-2, and the highest benzene concentration (3,100µg/L) was reported in well VEW-1 1,2-DCA was reported in wells MW-2 (6 1 µg/L) and MW-5 (2 7 µg/L) TPHG or benzene were not reported in the samples collected from upper zone wells MW-2, and MW-4 through MW-7 MTBE was not reported in any of the upper or lower zone wells In the lower zone wells, TPHG and benzene were reported in well MW-9 at concentrations of 5,200 µg/L and 610 jag/L, respectively 1,2-DCA was reported in wells MW-8, MW-9, and MW-11, with the highest concentration (17 jtg/L) reported in well MW-9 TPHG, benzene, and MTBE concentrations for samples collected and analyzed during the third quarter 2003 are included on Figure 4 SJCEHD has requested that all peaks detected in the analyses be reported A copy of the laboratory tentatively identified compounds (TIC) report is attached Tentatively identified compounds were reported for wells MW-9, VEW-1, and VEW-2 Results of the TIC analysis are summarized in Table 3 An access agreement for the proposed work on the adjacent parcel to the east has been received Stratus will continue efforts to obtain an encroachment permit from the City of Stockton for the proposed work in the public right-of-way immediately north of the site Once the encroachment permit has been procured, a drilling and well installation package will be submitted to SJCEHD and a well drilling contractor • will be scheduled We anticipate the proposed drilling and well installation activities will be completed during the fourth quarter 2003 P 1Apache PlasticslQuarterly reports120031Apache_3Q03 DOC 5rRA rus