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' Royal Oak Savings & Loan Page 4 SIO N. Main Street, Manteca, Camornia ' Quarterly Ground Nater Sampling Report October, 1992 -January, 1993 Ground Water Gradient ' Ground water level measurements were camed out monthly during the quarter on October 24, November 24, and December 28, 1992, as well as during the the sampling event on January 27, 1993 The vapor extraction system installed on MW-2 prevented level ' measurements from this well during November and December The ground water elevation measurements are tabulated in Table 1 and gradients for the respective months are contoured on Figures 2, 3, 4 and 5 IThe ground water elevations in the momtonng wells on the Royal Oak site were vi rti ally unchanged for the months of August through December, 1992 (Figures 24) Water ' measurements taken during the monitoring event on January 27, 1993, show that , not only did the water levels all of the wells nse, but also the gradient had reversed with the water table contours forming a southeasterly-trending trough(Figure 5) ' The ground water contours for this pend form a westerly-trending trough, whernt reversed from an easterly-trending trough Incomplete information suggests that the ' westerly-trending trough in the piezometnc surface prevails in the late summer and through most of the winter months The pattern then changes to an easterly-trending trough under the influence of recharge of the aquifer from winter rainfall Summary of Analytical Findings Monitoring wells 7 and 8 were sampled on November 4, 1992, and tested "none detected" for all analytes Well 2 was not tested at that time as a soil vapor extract{on system was installed on I MW-2, and access was temporarily restricted However, all three wells were sampled on January 27, 1993, and were N D for all analytes tested(see Table 2) It is worth noting that au samples tested from the soil vapor system at the start up showed TPH concentrations of greater than 2,500 ppm The levels have declined rapidly and, as of December 25, 1992, the levels are "none detected" We have enclosed a summary of the air testing performed at the site since the soil vapor system was turned on(Table 4) Recommendations WHF recommends that the soil vapor extraction system be removed from the site We also recommend that the site be considered for closure The San Joaquin County Environmental Health Department has condended that the contaminated soils left in place at the comer was the cause of the mternuttent ground water contamination in wells 2 and 7 The soils are now clean, via the soil vapor extraction system, and ground water samples indicate that the ground water is no longer contaminated I