Required stormwater drainage plans must address both existing and proposed stormwater drainage conditions and drainage channels on the site and the location on the site of excavated soil to be stockpiled during construction. In particular, surface drainage patterns on the site during and after construction must be shown. The following is required at a minimum:
(a) A grading survey which shows the existing stormwater runoff patterns and the location of any special flood hazard areas prior to demolition of any habitable building and before any grading of the site.
(b) An engineered stormwater drainage plan that shows the proposed drainage patterns during and after construction. Site drainage conditions during and after construction may not be any worse than before construction, or impose a greater burden on downstream or upstream property owners than existed before construction. Site runoff volume, rate and direction must be included in the drainage plan for existing and postconstruction conditions. Any increase must be diverted or detained. Easements must be identified. A stormwater drainage plan shall include maintenance provisions.
(c) Sufficient information to substantiate the stormwater drainage patterns proposed, including spot elevations or topographic lines as necessary indicating:
(1) The slope of the property;
(2) The location of any dry wells or storm sewer intakes;
(3) The grades at the top of, and adjacent to, the foundation;
(4) The property lines;
(5) The location of all downspouts (and sump discharges) and their connection to the storm sewer serving the property;
(6) Downspout discharges and overland flow routes as applicable;
(7) Overland flow path(s) and emergency overflow route(s); and
(8) Base flood elevation and floodplain/floodway information (if applicable).
(d) An excavated materials plan showing where the stockpiling will occur, how stormwater runoff will be accommodated and the facilities to be provided to prevent soil erosion or silting of downstream areas.
(e) The plan shall identify and quantify any runoff changes (volume, rate or direction) for existing conditions and postconstruction. Calculations to include a 2-, 10- and 100-year design storm.
(f) Calculate capacity of downstream storm sewers (not necessary if 0 net discharge).
(g) Existing and/or proposed easements for overland flow path(s) and for emergency access.
(h) Maintenance instructions to describe expectations for maintenance of stormwater features including overland flow route(s).
(i) No off site increase in runoff values will be acceptable except as approved by the village engineer.
(j) During construction, spot surveys shall be provided immediately after the foundation pour, including top of foundation (T/F), brick ledge(s) as well as the location of the foundation relative to the building lines.
(k) One set of architectural drawings (with updates as needed) to be provided to the village engineer with the engineering submittal(s). (Ord. 0-09-09, 4-20-2009)