(A) Generally. Every residential subdivision shall be provided with roadway drainage facilities which can satisfactorily accommodate the storm water surface runoff incident to the 25-year design storm. The roadway drainage facilities in any commercial, institutional or industrial development shall be designed to handle storm water runoff from the 50-year storm. These minimal design requirements shall not be construed to relieve the developer of any legal responsibilities for downstream/upstream storm water damages inflicted or backup from the development.
(B) General design consideration. The plans and specifications shall include provisions to show compliance with the drainage laws of the state and any subdivision thereof in effect at that time. By requiring that the developer evidence compliance with drainage law(s), the village assumes no responsibility to landowners or others for damage caused by noncompliance with such law(s).
(1) Storm sewers. Properly-sized storm sewers shall be provided to carry surface runoff from paved access. The storm sewers shall be of sufficient length that they shall transport the runoff to rear lot lines or existing natural drainageways or swales providing their location does not encroach upon the building site.
(2) Drainage swales. Natural drainage swales may be utilized to accommodate surface runoff providing they are located near lot line and the flows induced therein do not pose health or safety hazards for residents.
(3) Accommodation of upstream drainage areas. Drainage facilities shall be adequate to accommodate potential runoff from the entire drainage area upstream of the proposed subdivision without an increase of water elevation or velocity in the 100-year storm event. Potential runoff shall be determined on the basis of maximum land use upstream of the proposed subdivision. Potential runoff shall be determined on the basis of maximum land use upstream area that is consistent with current zoning or adjacent land use trends.
(4) Sufficient design. All storm sewers, culverts, other drainage structures and/or drainage swales which are proposed in drainageways shall be of sufficient design to pass the 100-year storm event without an increase in either headwater elevation or velocity.
(5) Drainage retention. In order to protect downstream property from potential damages by increased flows or greater velocities, it will be necessary for the developer to provide for drainage detention facilities which should be designed for the excess runoff due to the proposed development for both the ten-year and 100-year storm event.
(C) Technical requirement. Storm drainage facilities shall be designed and constructed in accordance with the criteria set forth herein and the standards contained in Appendix B.
(1) Pipe/storm sewers. All pipe sewers shall be determined by utilization of either the “rational method” or the SCS method, or both, for the design storm(s) previously specified.
(a) The minimum diameter for pipe culverts shall be 15 inches and the minimum diameter for storm sewers shall be 12 inches.
(b) Pipes/storm sewers located under paved surfaces shall be reinforced concrete pipe with rubber-gasket joints and sufficient wall thickness and reinforcement to carry the intended loading with the materials meeting the requirements of ASTM C-76 and ASTM C-443. All concrete storm pipe to be I.D.O.T. inspected and stamped or manufacturers certifications submitted that are satisfactory to the village. Polyvinyl Chloride (PVC) pipe may be considered as an alternate to reinforced concrete pipe with prior approval by the village. All storm sewer pipes must be constructed in accordance with Section 550 of the Illinois Department of Transportation Standard Specifications for Road and Bridge Construction.
(c) Pipes/storm sewers shall be located at least ten feet horizontally and/or 18 inches below any proposed water mains or water service lines. If a pipe/storm sewer must be located within ten feet horizontally and/or within 18 inches below or above water mains or water service lines, the storm sewer shall be constructed to meet water main standards utilizing the following pipe materials:
1. Ductile- iron pipe. Ductile-iron pipe shall conform to ANSI A 21.51 (AWWA C151), with thickness class designed per ANSI A 21.50 (AWWA C150) appropriate to the installation conditions, with tar (seal) coated and cement-lined interior per ANSI A 21.4 (AWWA C104). with rubber ring gasketed push on joints. Joints for ductile-iron pipe shall be according to the following applicable specifications: Push-On Joints - AWWA C111 and C600.
2. Plastic pipe. Polyvinyl Chloride (PVC) and Chlorinated Polyvinyl Chloride (CPVC) shall conform to NSF Standard 14 and ASTM Standard B 1784 or all Standard C 900 or G 905. Piping materials designated Class 12454B (PVC 11201 Class 12454C (PVC 1220) and Class 23447B (CPVC 41201 are acceptable in the following pressure ratings: schedule ratings shall be according to ASTM Standards B 1785 (PVC) and F441 (CPVC): standard dimension ratio pressure rated (SDR-PR) shall be according to ASTM Standards D2241 (PVC) and ASTM F442 (CPVC). Schedule 80 is required for all pipe sizes: pipe to be threaded shall be at least Schedule 120, SDR rating of 26 or less shall be required for PVC 1120, PVC 1220 and CPVC 4120. All pipe and fittings shall bear the National Sanitation Foundation (NSF) seal of approval. The piping shall be visibly marked with specific schedule number of SDR rating.
Jointing shall be pressure slip jointed, solvent welded, heat welded, flanged, or threaded joint. Special precautions shall be taken to insure clean, dry contact surfaces when making solvent or heat welded joints. Adequate setting time shall be allowed for maximum strength. Elastomeric seals (gaskets) used for push-on joints shall comply with ASTM Standard F477. Solvent cement shall be specific for the piping material and shall comply with the ASTM Standard D2564 (PVC) and F493 (CPVC) and be approved by NSF.
(d) Pipes/storm sewers located outside paved surfaces and under nominal fill loadings shall be of any of the following materials:
1. Plastic pipe meeting the requirements of ASTM D-2241, ASTM D-3034, ASTM F-679 and\or AWWA C-900;
2. a. Corrugated aluminum pipe meeting the requirements of AASHTO M-196, minimum plate thickness of 14 ga. for D = 15" to 27": 12 ga. for D 30" and up;
b. For every inlet or catch basin within a proposed project the developer shall install either a placard per village standard or an integral casting indicating “NO DUMPING - FLOWS TO WATERWAYS”;
3. Reinforced concrete pipe with sufficient wall thickness and reinforcement to carry the intended loading and meeting the requirements of ASTM C-76; and
4. Polymer coated corrugated galvanized steel pipe meeting the requirements of AASHTO M-36 and M-180, with gage thickness conforming to the state’s Department of Transportation Standard Specifications for Road and Bridge Construction. Bands are to have the same coating as the pipe. The developer shall be responsible for increasing minimum plate gauges as the final loading dictates. Any storm sewer connecting band shall be a minimum of two feet. One-foot bands will not be permitted.
(e) Installation shall be in accordance with the state’s Standard Specification for Road and Bridge Construction. All trenches for pipes/storm sewers that are located under paved surfaces shall be properly backfilled and compacted in a minimum density of 95% of maximum Standard Lab Dry Density as prescribed by AASHTO T-99. Developer to furnish compaction tests for all trench fills.
(2) Inlets/catch basins. The spacings for inlets/catch basins shall be calculated such that the runoff from the design storm shall not encroach upon the pavement by more than eight feet in the 25-year storm event. Under no circumstances shall water travel more than 500 feet on paved surfaces.
Inlets/catch basins shall be constructed in accordance with the standards in Appendix B. All open-throat inlets shall not have a throat opening greater than six inches with a permitted variance of one-half inch. Streets where the slope exceeds 5% shall utilize vaned inlets within the curb and gutter to prevent by-pass of storm water flows.
(3) Drainage grades. Minimum/maximum gradients of pipes/storm sewers and earth drainageways/swales shall conform to the following criteria.
(a) Pipes/storm sewers.
1. Minimum velocity of storm sewers should be three feet per second to provide a cleansing velocity.
2. Maximum grade: None; Rip-rap and/or energy dissipators shall be utilized as needed at discharge points to minimize erosion.
(b) Drainageways/swa les. All development drainageways/swales meeting the requirements below, except for natural streams and creeks, shall be paved. The paved drainageways shall conform to I.D.O.T. standards. The width of the paved swale shall be determined by the flows involved and conform to I.D.O.T. design standards. In no case shall the paved swale be less than 18 inches with a six-inch bottom and with no steeper than three to one side slopes. This to include all storm sewer and/or culvert outfalls and yard drainage swales.
1. Drainage swales to be paved shall be those with a flow of four cfs or greater in the ten-year storm event except as noted herein.
a. For institutional uses, where the property is to be owned and maintained by the institution and the size of the parcel so owned and maintained exceeds ten acres, paving or lining will only be required if the velocities in the 25-year storm event exceed those allowable for grass surfaces per Table 9 - 503a of the I.D.O.T. Drainage Manual.
b. However, design engineer to evaluate the requirements for lining or paving at any changes in flow direction, at the confluence of two or more swales, ditches or pipes and swales or ditches or areas subject to turbulence, wave action or centrifugal forces. Owner is advised that if the use changes or property is subsequently divided the requirements hereof shall prevail and owner shall pay for all costs to comply with the Code.
2. For drainageways/swales not requiring paving hereunder, the following shall apply:
a. Minimum grade: 1%; and
b. Maximum grade: 3%, with no protection other than sod for those that do not require paving. However, should velocities in the 25-year storm event exceed those allowable per the soil type as shown in Table 9 - 503a in the I.D.O.T. Drainage Manual protective lining shall be required.
3. Twelve percent with paving, rip-rap and/or energy dissipaters or paving and the like.
4. Manholes conforming to the requirements set forth in Appendix B shall be installed at all changes in vertical grade or horizontal alignment of storm sewers if at locations other than inlets/catch basins.
(D) Areas subject to flooding. Whenever a plat is submitted for an area that, in the opinion of the village staff, is subject to flooding, the Board of Trustees will require appropriate protective measures.
(Am. Ord. 2020-03-02A, passed 3-2-2020)
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