PSA - Erskine Drainage Improvements Study - McCormick Engineering, LLC.

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Exhibit A- Engineer's Services Erskine Municipal Golf Course. Note that the Miami Basin outfall does not currently direct runoff to the Chippewa Basin. This hydrologic analysis shall be based upon the predicted watershed response to the following precipitation events: • December 2015 Storm Event, Depending on available stage -discharge records available from EmNet for the Miami Basin for this notable extreme event. • 2-year, 6 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 2-year, 12 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 2-year, 24 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 2-year, 96 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) 10-year, 6 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 10-year, 12 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 10-year, 24 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 10-year, 96 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) Events up to the 10-year event are assumed to be conveyed primarily in the combined sewer system, as well as the portions of the surface watershed that have been separated, such as the Kensington Farms area. The hydrologic model will focus on the estimated response of the Chippewa Basin watershed for the purpose of sizing drainage improvements at the Erskine Municipal Golf Course. For the purposes of this Work, MCCORMICK will not be explicitly considering the smart sensor response in the Kensington Farm or Fairfax basins. The current modeling might consider a simplification of this existing control logic such as static orifice representation. Proposed hydrologic analysis will focus on open channel conveyance needed through the Erskine Municipal Golf Course for storm events up to and including the 10-year event, to accommodate discharges from the three noted sources from above. Proposed features might also include compensatory storage elements so as to not increase basin levels at the Chippewa Basin as a result of potential increased discharge release rates from the Miami Basin. Task SR4 — Alternative Solution Analysis At a minimum, the following conceptual alternative components will be considered in the report will include: Conceptual infrastructure, including open channel and cart crossings, needed to convey Design storm discharges from Ireland Road through the Erskine Municipal Golf Course to the Chippewa Basin Facility (primary focus) Miami Basin design discharges needed to convey 10-year peak discharge without overtopping the existing berm to the south onto private property Erskine Drainage Improvement Study - Scope of Services Page 2 of 3 (Exhibit A- Engineer's Services)