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3.2.2 Sand B Monitoring Wells Historically, in the Sand B monitoring wells (MW-8, MWO-1 x, MW-1413, and MW-15B), depth to water levels have been as shallow as 7.3 feet bgs to as deep as 12.4 feet bgs; the average depth to water over the historic monitoring period is 10.3 feet bgs. Seasonal fluctuations of water table levels beneath the site in the Sand B wells on the order of one to three feet per year are typical (Figure 6). Groundwater flow beneath the site, based on wells screened across the water table in Sand B, has been predominately northeast; however, in early 2006, a shift of the flow direction towards the north and northwest was observed. Water levels and fluctuations in Sand A and Sand B wells appear similar(Figure 6). 3.2.3 Sand C Monitoring Wells Historically, in the Sand C monitoring wells (MW-12C and MW-13C), depth to water levels have been as shallow as 11.4 feet bgs to as deep as 14.1 feet bgs; the average depth to water over the historic monitoring period is 12.9 feet bgs. Seasonal fluctuations of water table levels beneath the site in the Sand C wells of about two feet per year are typical (Figure 6). 3.2.4 Vertical Hydraulic Gradient To evaluate the component of vertical groundwater flow between the intervals of the saturated zone beneath the site in which groundwater monitoring wells have been constructed, �. groundwater elevations from the A/B well pairs MW-2/MWO-1 x, MW-9/MW-8, MW-14A/MW-14B, and MW-15A/MW-15B and B/C well pairs MW-8/MW-12C and MW-13A/B/MW-13C and were compared. During the periods in which the well pairs were gauged (27 quarters for MW-2/MWO-lx, 14 quarters for MW-9/MW-8, and 4 to 7 quarters for the remaining well pairs), differences in piezometric groundwater elevations ranging from—0.67 to +0.22 feet (or about 2.5 to 8 inches) were measured at the A/B well cluster locations indicating relatively small upward and downward components of flow between the A/B intervals. The lack of consistent differences in potentiometric head elevations between wells may suggest no dominant vertical groundwater flow between the A/B portions of the saturated zone. At the B/C cluster well locations, differences in piezometric groundwater elevations ranging from —0.50 to —2.11 feet were measured at the B/C well cluster locations indicating a consistent downward component of flow between the B/C intervals. 3.3 Extent of Petroleum and Fuel-Oxygenate Hydrocarbon Impact 3.3.1 Soil Since the initiation of environmental assessment work at the site in January 1997 through March 2007, more than one hundred soil samples at depths up to 73 feet bgs were collected and analyzed to evaluate the presence and distribution of fuel-related hydrocarbons and oxygenates in soil surrounding the two main source areas (the northern and southern former USTs) (Table 2). Analytical results of these samples indicate that chemicals of concern (COCs) for the site in Page 12 5TKA WO