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wetlands/ponds were established prior to 1991 is required to qualify for the exemption. Proof can include (a) engineering plans for the ponds, (b) documents that show the ponds were originally designed and constructed as stormwater treatment ponds, (c) a sediment lneasurementlanalysis that demonstrates where natural soils exist that are covered by recent sedimentation, (d) outlet information which provides evidence confirming that a wetland fonned as a result of the construction of the stormwater treatment pond, or (e) permits obtained for pond construction. Under the exemption, the wetland stormwater treatment ponds can be excavated to regain their original design characteristics. However, excavation which increases the wetland/pond's surface area or depth beyond its original design will likely require wetland replacement. Wetland replacement may also be required if [lie wetland ecosystem has been stabilized and the excavation will significantly disturb the stabilized system. Excavation (other than the removal of sediment deposition deltas) in any ponds that were wetlands, partial wetlands, or lacustrine wetlands prior to their original construction is generally not recommended because wetland mitigation would likely be required, and such mitigation can be very expensive. This requirement could greatly increase the cost of the pond upgrade. Therefore. in those instances, the city may wish to consider meeting its water quality treatment goals or requirements by modifying the pond's outlet structure to make the pond operate as an extended detention basin. This has the potential to delay sediment removal by many years. possibly a decade or more. Also extended detention structures can significantly reduce (if not remove) a short-circuiting problem for basins where their inlets are in close proximity to the outlet. Since some of Silver View Pond's inlets are close to the pond's outlet, short-circuiting is likely occurring in the pond. Since Silver View Pond has the potential to be a highly efficient basin, no increase in pond depth is recommended beyond sediment removal necessary to recreate the pond's original configuration. MPCA guidelines suggest that treatment ponds should be 4 to 10 feet in depth. Most of Silver View Pond would fall within this guideline if its accumulated sediment is removed. The shallowest areas of the pond are at sediment deltas at the inlets to the pond. These deltas alone could be removed, as opposed to widespread sediment removal, to improve localized efficiencies and delay future maintenance issues in the pond. 3.3 Stormwater Pond Wetland Evaluation Silver View Pond was evaluated for (lie likelihood of having been constructed out of historic wetlands as opposed to constructed wholly out of uplands. Available data used in the assessment included aerial photos ranging froin 1991 to the present, National Wetland Inventory data, USDA 1' MpK 21 MIN ti':1621002 SiIivF View Pond Assesmiew W'orAriIt: ti Roport Sivtr V iew fond Assessmul-nu t.doex 14