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-40 -45 ♦MW-1 ■MW-2 -50 ■ ++ ■ ■ 7 — X M W-3 0 -55 x X ♦ MEX �■ X M W-4 > 1 X ♦ �(C E -60 r ♦ X X ♦MW-5 a •M W-6 _-65 w X X X +MW-7 -70 X • a -MW-8 -75 Y —MW-9 Alt ♦MW- -80 1 10 0 20 40 60 80 100 120 140 Chloride(mg/L) Figure 14: 62H vs. Chloride Based on the above,the First Quarter,2015 Groundwater Monitoring Report recommended that the existing MW-5 be abandoned and destroyed and a new 2-inch monitoring well be constructed in an offset position,with at least a 10 foot annular seal and a minimum of 20 feet of well screen into the existing groundwater.This well has exceeded water quality goals in 34 out of 71 tested quarters with respect to total coliform. The well is also consistently the highest in iron and manganese concentrations. A review of the well log shows that a 6.5 foot well seal was placed in the upper 8 foot sand layer with the well screen beginning at a 7.5 foot depth. Under current California well standards, a minimum 10 foot well seal should be provided except under unusual circumstances. This workplan requests approval of the proposed destruction of MW-5 and the construction of a replacement well,MW-5R,to be located approximately 50 feet west of the existing well to be destroyed. The replacement well is intended to provide for representative sampling of groundwater and prevent any surface or near-surface contaminants from entering the well. The intent of this new well is to validate water quality indicated by MW-5 or confirm groundwater quality generally consistent with other compliance wells at the site.The location of the new well provides close spatial continuity with previous sampling.The well will be located between the perimeter access road and fence,and near the toe of the Pond 6 embankment. July 2015 Contonned with 21 October 2015 Conditional Approval 6 MW-5 Replacement City of Riverbark WWfF Monitoring Well Installation Workplan