Agenda - Public Works Committee - 02/21/2012

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new outlet would be constructed at an elevation of 857.8, two feet lower than the existing outlet. The following table summarizes the 100-year HWL's for Depression 1, assuming the pond construction shown on Exhibit 14, and Depression 2: Location 100-year HWL Depression 1 — Existing 864.7 Depression 1 — Proposed 864.6 Depression 2 — Existing 866.0 Depression 2 — Proposed 865.9 The following table summarizes the 100-year HWL's for Depression 1, assuming the pond construction shown on Exhibit 15, and Depression 2: Location 100-year HWL Depression 1 -- Existing 864.7 Depression 1 — Proposed 864.0 Depression 2 — Existing 866.0 Depression 2 — Proposed 865.8 As shown, adding this additional outlet pipe has very little effect on the high water levels of the two depressions. One reason for this is that the storm sewer system downstream of Depression 2 is at or above capacity and is flowing back into Depression 2 prior to draining downstream. The estimated cost to construct this additional outlet pipe is $158,609. Table 24 includes the individual costs for this alternative. Alternative 4 Alternative 4 includes constructing an additional 18" outlet pipe from Depression 1. As shown on Exhibit 16, the new outlet pipe would run east from Depression 1 to Depression 2. The new outlet would be constructed at an elevation of 8 5 8.2; 1.6-feet lower than the existing outlet. This alternative assumes that the new outlet from Depression 2, as discussed in Alternative 3, would also be constructed. The following table summarizes the 100-year HWL's for Depression 1, assuming the pond construction shown on Exhibit 14, and Depression 2: Location 100-year HWL Depression 1 — Existing 864.7 Depression 1 — Proposed 864.6 Depression 2 — Existing 866.0 Depression 2 — Proposed 865.5