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0 0 Work Plan for Groundwater Investigation and Groundwater Monitoring Well Installation Field Maintenance Shop #24, Stockton, California northeast, but had not extended to the facility boundary (URS, 2007). The report further concluded that the lateral extent of contamination at the former UST site had been determined. 2.5. MARCH 2010 SITE INVESTIGATION (OTIE) The site investigation conducted by OTIE in March 2010 included advancing five soil borings that were subsequently converted to groundwater monitoring wells (FMS-MW1 to -MW5). The borings were advanced using HSA and soil samples were collected at approximately five foot intervals from each boring. Soil samples were analyzed for TPH-g, TPH-d, VOCs including BTEX and fuel oxygenates, and total lead. Groundwater samples collected from the monitoring wells after installation and development were analyzed for TPH-g, TPH-d, and VOCs including BTEX and fuel oxygenates. The locations of each boring and subsequent monitoring well are depicted on Figure 3. The key findings associated with implementation of the 2010 soil and groundwater investigation are summarized below: • Physical soil conditions were shown to be generally consistent with the findings from previous site investigations, as documented in the 2004 Versar and 2007 URS reports, and indicate that the shallow first water bearing zone (35-40 feet bgs) is dominated by interbedded sand units within fat clays and silty/sandy clays. • Lead was detected at generally low (below any potentially applicable regulatory standard) and consistent concentrations in all soil samples collected during the investigation. • Although trace concentrations of petroleum hydrocarbon constituents and/or select VOCs were detected intermittently in samples from soil borings for each of the groundwater monitoring wells, only soil samples from the boring for well FMS-MW5 (within the immediate vicinity of the former USTs) indicated marked impacts from petroleum hydrocarbons. • The most significant impacts from petroleum hydrocarbon constituents documented in soil samples from the boring for well MW -5, as indicated above, were generally in samples at or near the occurrence of first groundwater (35-45 feet bgs), and included exceedances of potentially applicable regulatory standards for TPH-d, TPH-g, benzene, and/or ethylbenzene. • Groundwater elevations resulting from surveyed well datum elevations indicate that the generally east/northeast direction of groundwater flow presumed in the 2007 URS report is correct, that the gradient is relatively low (0.0015), and that no evidence of separate phase hydrocarbons (SPH) exists on the groundwater. • With the exception of upgradient well FMS-MW1, groundwater samples collected in association with groundwater monitoring well installation activities during the First Quarter 2010 monitoring event indicate that groundwater has been impacted with petroleum hydrocarbon constituents and related VOCs at concentrations that exceed potentially applicable regulatory standards. 2.6. 2010-2011 QUARTERLY GROUNDWATER MONITORING (OTIE) Subsequent to monitoring well installation in March 2010, OTIE performed four quarters of groundwater gauging and sampling at the site between April 2010 and February 2011. During OTIE 7