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§ 151.20 SUBMITTAL REQUIREMENTS AND PROCEDURES.
   (A)   Application and approval process.
      (1)   Conceptual review. A cursory review of stormwater management and water quality improvements, including verification of an adequate outlet will be completed by the Development Services Department during the plan review period for a zoning map amendment.
      (2)   Preliminary review.
         (a)   Stormwater management features shall be included in the primary plat submittal. Drainage easements shall be included in accordance with § 151.21(J).
         (b)   The primary plat submittal shall be reviewed to ensure that conceptual stormwater management systems have been included and requirements of this chapter are acknowledged by the applicant.
      (3)   Final review.
         (a)   Stormwater management features shall be included in the development plan and final plat submittal. The legal description of the lot or site shall include the appropriate drainage easements in accordance with § 151.21(J).
         (b)   The Development Services Department or their authorized representative shall perform a review of all stormwater, erosion control, and pollution prevention features included in the development plan for compliance with the requirements and intent of this chapter. Final review shall include an engineering/technical plan review.
         (c)   Stormwater management plan approval shall be obtained prior to the initiation of any construction activities. Non-compliance with the terms and conditions of the approved stormwater management plan will be subject to enforcement as described in this chapter. The applicant shall inform all contractors, sub-contractors, construction management firms, and other entities having oversight of construction activities on the site or individual building lots of the terms and conditions of the stormwater management plan approval and schedule for proposed implementation.
      (4)   NOI submittal. Submittal of the NOI to IDEM and the Development Services Department shall be conducted according to § 151.22(A)(7).
   (B)   Minimum requirements of all projects.
      (1)   All projects shall comply with the requirements of this section. The Development Services Department may require projects with one (1) acre or less of land disturbance to comply with § 151.21, § 151.22, and § 151.23 when the project site is located within, near, or along a tributary to an environmentally critical/sensitive area or an area with known erosion or drainage problems.
      (2)   Fueling areas include an existing or proposed land use with fuel tanks or fueling activities. Regulated activities include any fueling area, publicly or privately owned (regardless of the size of land disturbance), that installs or replaces fuel tanks. Refer to § 151.23 for stormwater quality treatment requirements specific to fueling areas. A fueling area may be a part of other land disturbing activities or may be individually permitted.
      (3)   All projects must demonstrate an adequate outlet in accordance with § 151.21(H).
      (4)   Application for approval shall include the following items at a minimum:
         (a)   Completed application.
         (b)   Stormwater application fee (according to an established fee schedule). Inspection fees shall be assessed following the application approval. Fees are to be paid prior to the pre-construction meeting with Town personnel.
         (c)   Statement of financial responsibility form, signed and completed.
         (d)   Affidavit and consent of property owner form, signed and completed.
         (e)   Design plans certified by a professional engineer or land surveyor licensed in the State of Indiana. Each sheet shall be drawn to scale and shall include a scale bar and north arrow. Plans shall include the following sheets and elements at a minimum to show the nature, location, dimensions, and elevations of the area and improvements in question.
            1.   Title sheet:
               a.    Location plan;
               b.    Vicinity map;
               c.   Legal description of property;
               d.   Parcel number or numbers of the site;
               e.    Provide the total impervious surface area for the completed project in square feet. In addition to total area, provide a breakdown of total compacted gravel, building footprint and pavement (asphalt plus concrete) in square feet.
            2.   Overall existing condition site plan:
               a.    Location, elevation, and datum of benchmark placed within the area of the site. If no benchmark is available, the elevation of the nearest road intersection as shown on the U.S. Geological Survey Map shall be indicated;
               b.   Site and the surrounding area one hundred (100) feet in every direction around the site;
               c.    Location, size, and invert elevation of any drainage structures within one hundred (100) feet of the site;
               d.    Existing site grading with contour intervals of one (1) foot;
               e.    General description and nature of the site;
               f.   Soil survey map with the site delineated upon it.
            3.   Existing condition plan sheets (maximum scale of one (1) inch equals fifty (50) feet):
               a.    Contour lines with maximum one (1) foot contour interval;
               b.   One hundred-year (100-yr.) (1% chance/year) floodplain elevation and boundary;
               c.    Existing legal drains and other waterways, detention/retention facilities, roadside ditches and culverts, storm sewer systems, and all other drainage features as applicable;
               d.   Areas potentially impacted by flooding of surface waters including:
                  i.    Designated floodways or floodplains;
                  ii.    Land within seventy-five (75) feet of each bank of any legal drain;
                  iii.    Land within fifty (50) feet of each bank of a natural drainageway; or
                  iv.    Areas above restricted outlets;
               e.    Wetlands;
               f.   Street names, widths, and rights-of-way;
               g.    Existing easements.
            4.   Proposed condition plan sheets (maximum scale of one (1) inch equals fifty (50) feet):
               a.    Contour lines with maximum one (1) foot contour interval;
               b.   One hundred-year (100-yr.) (1% chance/year) floodplain elevation and boundary;
               c.   Pond water surface elevations including one hundred- year (100-yr.) (1% chance/year) and normal pool elevations;
               d.    Proposed grading and areas of cut or fill;
               e.    Elevation of the first floor for all proposed and existing structures;
               f.    Elevation of lowest floor, including basement, for all proposed and existing structures in accordance with § 151.21(K);
               g.    Proposed areas for storage of materials and construction staging;
               h.    Proposed modifications to existing drainage features;
               i.    Proposed discharge location for site;
               j.    Location and size/ dimensions of all existing and proposed detention/retention facilities, roadside ditches and culverts, subsurface drains, legal drains, and all other drainage features, whether permanent or temporary, including those facilities which are crossing or adjacent to the site;
               k.    Location, size/ dimensions, and profile of all existing and proposed storm sewer systems, whether permanent or temporary, including those facilities which are crossing or adjacent to the site;
               l.    Drainage plan including flow arrows for both surface and subsurface water. The drainage plan shall indicate the natural flowage of water to be managed coming into or leaving the site;
               m.   Flood routing plan including path and ponding locations and flow arrows and standards included in § 151.21(I);
               n.   Street names, widths, rights-of-way, and cross sections, including elevation of street centerline;
               o.    Existing and proposed easements.
            5.   Design details, including applicable standard details from the Town of Brownsburg Construction Standards.
            6.   SWPPP, details, and notes in accordance with § 151.22.
         (f)   Drainage report. Engineering design computations and drainage report prepared by a registered professional engineer or land surveyor licensed in the State of Indiana which include the following applicable items at a minimum.
            1.   Written description of the project, including:
               a.    Discussion of the steps taken in the design of the stormwater management system;
               b.    Description of significant drainage problems;
               c.   Soil types, conditions, and limitations;
               d.    Analysis procedure to evaluate problems and propose a solution;
               e.    Hydrologic and hydraulic analysis methodologies and calculations;
               f.    Exhibits showing existing and proposed drainage patterns, drainage areas, flow paths, land uses, etc.;
               g.    Assumptions or special conditions associated with the methods used;
               h.    Proposed design of stormwater management system;
               i.    Results of analysis demonstrating that the proposed system addresses existing drainage problems, accounts for off-site drainage (if applicable), and does not create new drainage problems upstream or downstream of the site;
               j.    Proposal for protecting proposed improvements from loss or damage due to ponding or runoff of surface water;
               k.    Conclusion summarizing the design and explaining how the design satisfies the requirements and intent of this chapter.
            2.   Engineering design computations shall be provided for land drainage practices, erosion control measures, pollution prevention practices, and flood prevention practices, including, but not limited to:
               a.    Runoff coefficients or curve numbers, as appropriate;
               b.    Times-of-concentration;
               c.   Peak runoff rates;
               d.    Detention storage volumes;
               e.   Peak discharge rates;
               f.    Outfall structure and emergency spillway calculations;
               g.   Storm sewer, inlet, open channel, culvert, subsurface drain, and other stormwater conveyance design calculations;
               h.    Low-impact development features design calculations and supporting information;
               i.   Input and output files for computer models and exhibits detailing the setup and relationships within the computer model.
            3.   Development sites making use of regional or master planned stormwater detention areas must include the following information in the stormwater drainage report:
               a.    Design assumptions, maps, and calculations from the master planned drainage report for the proposed development area;
               b.    Written narrative, maps, and supporting calculations demonstrating that the master planned assumptions will be achieved;
               c.    Current standards and regulations may require additional storage and/or water quality measures if the master planned drainage report does not include those measures.
            4.   Projects disturbing less than one (1) acre of land that are residential uses converting to non-residential commercial and for projects that result in a minor increase in impervious surface projects shall provide the following at a minimum:
               a.   A drainage report including design calculations for onsite stormwater drainage conveyances in accordance with this chapter;
               b.    Demonstrate an adequate outlet is available in accordance with § 151.21(H);
               c.    Demonstrate that the change in peak runoff at all outlets is less than 0.2 cfs for up to the one hundred-year (100-yr.) frequency storm.
         (g)   Operations and Maintenance (O&M) Manual. Prepare an O&M manual in accordance with § 151.29.
         (h)   Performance bonds. As condition of stormwater management plan approval, the applicant shall provide performance assurances in accordance with § 151.26.
      (5)   Where the minimum standards of this chapter cannot be met, additional engineering design calculations and narrative shall be provided to the Development Services Department for consideration.
(Ord. 2017-28, passed 10-12-17; Am. Ord. 2024- 04, passed 4-25-24)
§ 151.21 STANDARDS FOR STORMWATER QUANTITY MANAGEMENT.
   (A)   Watercourse protection.
      (1)   Legal drains within the Town are under the jurisdiction of the Hendricks County Drainage Board. The Indiana Drainage Act has established seventy-five (75) foot easements to either side of legal drain tile lines and seventy-five (75) feet from the top of the bank on each side of open legal drains. Any stormwater discharge or work to be completed within a legal drain easement must obtain approval from the Hendricks County Drainage Board.
      (2)   Waterways within the Town may be under the jurisdiction of the IDEM or the ACOE.
      (3)   Work within a floodway is under the jurisdiction of the IDNR.
      (4)   Any relocation of a watercourse shall require a plan approved by the Development Services Department, and it shall not discharge water onto downstream adjacent property owners in any location different from its existing location.
      (5)   Alterations shall be designed to accommodate all on- and off-site upstream drainage areas. Design capacities shall be determined as described in this chapter.
      (6)   Entities owning property through which a watercourse passes, or such an entity's lessee, shall keep and maintain that part of the watercourse in accordance with this chapter and all applicable state and federal statutes and regulations. In addition, the entity or lessee shall maintain existing privately owned structures within or adjacent to the watercourse so that such structures will not become a hazard to the use, function, or physical integrity of the watercourse. The entity or lessee shall not place or construct a privately-owned structure or other impairment within or adjacent to the watercourse such that is an impairment or a detriment to the flow of water within the channel.
   (B)   Determination of stormwater runoff rates.
      (1)   Stormwater runoff rates shall be calculated in accordance with Chapter 2 of the Hendricks County Stormwater Technical Standards Manual. Composite runoff coefficients shall be calculated and account for connected impervious surfaces such as downspouts connected to stormwater conveyance system; typical composite runoff coefficients shall not be used.
      (2)   Stormwater drainage systems shall be designed to accommodate the following:
         (a)   All upstream off-site drainage.
         (b)   Existing drain tiles from upstream.
         (c)   Diffused water flow from upstream properties.
         (d)   Storm sewers from upstream.
         (e)   The drainage collection system from within the project or property.
   (C)   Detention/retention and pond requirements.
      (1)   General requirements.
         (a)   Storage volume.
            1.   Storage volumes shall be computed using a computer model that can generate hydrographs based on the NRCS TR-55 time of concentration and curve number calculation methodologies.
            2.   Storm durations shall be used that maximize the peak flow for the pre-developed condition and maximize detention storage volume for the post-developed condition. The storm duration shall be equal to or greater than the site time of concentration but shall not be less than thirty (30) minutes.
            3.   When determining curve numbers for post-developed conditions, the initially determined hydrologic soil group for disturbed areas should be changed to the next less infiltrating capacity category (i.e., A to B, B to C and C to D).
         (b)   Detention release rates.
            1.   Detention control devices shall limit the discharge to a rate such that the post developed release rate from the site is no greater than 0.2 cfs per acre of development for the 0-10 year return interval storms and 0.4 cfs per acre of developed area for the 11-100 year return interval storms.
            2.   The two-year (2-yr) (50% chance/year) peak runoff from the post-developed condition shall not exceed the two-year (2-yr) (50% chance/year) peak runoff from the pre-developed condition.
            3.   If the downstream receiving channel or pipe is inadequate to accommodate the post-developed flow, then the release rate must be further reduced.
            4.   The minimum allowable orifice size is four (4) inches.
            5.   For sites where the pre-developed area has more than one (1) outlet, the release rate should be computed based on pre-developed discharge to each outlet point. The computed release rate for each outlet point shall not be exceeded at the respective outlet point even if the post developed condition would involve a different arrangement of outlets.
         (c)   Runoff from upstream tributary areas (off-site areas) may be bypassed around the facility without attenuation. If it is to be routed through the facility, a separate outlet system or channel must accommodate those flows. Unless the pond is being designed as a regional detention facility, the primary outlet structure shall be sized and the invert elevation of the emergency overflow weir determined according to the onsite runoff only. Once the size and location of the primary outlet structure and the invert elevation of the emergency overflow weir are determined by considering on-site runoff, the one hundred-year (100-yr.) (1% chance/year) pond elevation is determined by routing the entire inflow, on-site and off-site, through the pond.
         (d)   The detention facility shall be designed in such a manner that a minimum of ninety percent (90%) of the maximum volume of water stored and subsequently released at the design release rate shall not result in a storage duration in excess of forty-eight (48) hours from the start of the storm unless additional storms occur within the period. In other words, the design shall ensure that a minimum ninety percent (90%) of the original detention capacity is restored within forty-eight (48) hours from the start of the design one hundred-year (100-yr.) (1% chance/ year) event.
         (e)   Refer to the Town of Brownsburg Construction Standards for construction specifications for detention and retention ponds related to the maximum allowable depth of water, maintenance and safety ledges, underdrains in dry ponds and maximum side slopes of ponds.
         (f)   An emergency overflow/spillway shall be designed for the release of exceptional storm runoff or in emergency conditions should the normal discharge devices become totally or partially inoperative. The overflow facility shall be of such design that its operation is automatic and does not require manual attention. At a minimum, emergency spillways shall be capable of handling one hundred twenty-five percent (125%) of the inlet peak discharge resulting from the one hundred-year (100-yr.) (1% chance/year) storm event from the entire contributing watershed in the post-developed condition.
         (g)   All ponds (including both dry and wet ponds, and ponds that are not used for stormwater quality or quantity management) shall incorporate applicable requirements included in the Town's standard detail for "Detention/Retention Ponds."
         (h)   All detention/retention facilities (including underground detention) shall have an upstream BMP designed in accordance with § 151.23 and installed for each inlet pipe, to collect sediments, debris, floatables, and other material prior to entering the detention/retention facility. Forebays are not acceptable. Position BMPs outside right- of-way and not more than fourteen (14) feet from a concrete or paved area for vac-truck and maintenance vehicle access.
         (i)   Underground detention facilities shall have sufficient observation wells or inspection ports, at least ten (10) inches in diameter, to allow access for inspection, maintenance, and regular cleaning operations in each underground chamber.
         (j)   Designers and developers are encouraged to consider methods of runoff reduction such as reducing impervious surface area, disconnecting impervious areas, promoting infiltration, stormwater capture and reuse, and other low-impact development methods to reduce requirements for on-site stormwater detention.
         (k)   Any regulations of the State Board of Health concerning standing water must be adhered to in the planning and use of temporary ponding facilities or other retention and detention devices.
         (l)   Stormwater detention/retention on roadways or driving lanes is not acceptable.
         (m)   For storm sewer pipes discharging into a pond, the lowest pipe invert at the first upstream storm sewer structure shall not be lower than the normal pool elevation of the pond.
         (n)   The outlet location must be approved by the Town of Brownsburg. The outlet control structure and piping shall be designed to operate simply and effectively with minimal maintenance. The outlet structure shall be positioned in an accessible location for maintenance.
         (o)   A safety ramp and ingress/egress easement from a nearby road must be provided for all ponds. The safety ramp shall be minimum twenty (20) feet wide and have a maximum exit slope of 6H:1V.
         (p)   Detention ponds located within a floodplain must be protected from the base flood elevation and shall not be designed to hold flood waters. Detention ponds may not be used for compensatory flood storage.
      (2)   Pond safety signs.
         (a)   Provide sign with minimum sign area of one (1) square foot and maximum sign area of four (4) square feet.
         (b)   Sign must be constructed of a permanent material, either wood or metal.
         (c)   At a minimum, pond safety signs must have the words "danger", "no swimming", and "stay off ice" and must have "no swimming" and "stay off ice" symbols. Warning may also prohibit trespassing, wading, or other recreational activities that would involve a person entering a pond.
         (d)   The sign color will be determined by the homeowners' association, property owner or developer.
         (e)   Install signs no more than five hundred (500) feet apart. If pond has less than three thousand (3,000) square feet of water surface area, a minimum of two (2) signs are required. If pond has greater than three thousand (3,000) square feet of water surface area, a minimum of four (4) signs are required. A sign must be placed at all public access areas to the pond.
         (f)   Each developer of the construction area and subsequent homeowners' association or property owners shall be responsible for the cost of maintenance and replacement of pond safety signs.
      (3)   Landscaping for ponds.
         (a)   Vegetation planting within drainage easements around ponds must be perennial grasses. Trees and/or shrubs are not allowed.
         (b)   Native grasses may be planted but must be periodically mowed or otherwise maintained to prevent woody vegetation from growing in easements.
   (D)   Storm sewer design standards.
      (1)   Storm sewer requirements.
         (a)   Storm sewers, inlets, and manholes shall accommodate the ten-year (10-yr.) (10% chance/year) peak runoff and maintain the HGL below the crown of the pipe. Flood routing shall be provided in accordance with § 151.21(I). If an overflow route is not available, then the storm sewer system shall be designed for the one hundred-year (100-yr.) (1% chance/year) peak runoff HGL below the ground surface and less than six (6) inches of ponding at inlets.
         (b)   The hydraulic capacity of storm sewers shall be computed using Manning's Equation. Where storm sewers discharge into submerged outfalls, a backwater analysis shall be performed.
         (c)   Minimum pipe size shall be twelve (12) inches.
         (d)   Minimum full-flow velocity of two (2.0) feet per second is desirable to prevent sedimentation in the pipe. Maximum full-flow velocity of ten (10.0) feet per second is recommended. The minimum Manning's n roughness value shall be twelve thousandths (0.012), regardless of material.
         (e)   Storm sewer pipes shall have a minimum of twenty-four (24) inches of cover, measured from the crown of pipe to the ground surface. Shallower depth of cover may be considered by the Town under conditions where engineering design will alleviate concern for surface loadings and frost heave.
         (f)   A minimum vertical separation of eighteen (18) inches shall be provided between storm sewers and other utilities (sanitary sewers, water mains, etc.).
      (2)   Storm structure requirements.
         (a)   Storm sewers shall be straight between storm structures (inlets and manholes).
         (b)   Manholes shall be provided at the following locations:
            1.   Where two (2) or more storm sewers converge;
            2.   Where the pipe size changes;
            3.   Where a change in horizontal alignment occurs;
            4.   Where a change in pipe grade occurs;
            5.   At intervals not to exceed four hundred (400) feet for pipes less than forty-eight (48) inches in diameter and not to exceed five hundred (500) feet for pipes forty-eight (48) inches in diameter and larger.
         (c)   A minimum drop of one-tenth (0.1) foot shall be provided in storm structures.
         (d)   When changing pipe sizes in a storm structure, the crowns of pipe shall be matched unless HGL modeling shows that another arrangement would be as effective.
         (e)   All storm grate castings shall be pre-cast with a pollution prevention message permanently attached. The message shall be included on the site development plans and comply with the Town of Brownsburg Construction Standards.
         (f)   Exposed pipes greater than eighteen (18) inches in diameter shall be equipped with an animal guard or trash rack. Trash racks are typically installed at the inflow end of pipes and animal guards at the outflow end.
      (3)   Inlet sizing and spacing.
         (a)   Inlets shall not be in the path where a pedestrian or bicycle is likely to travel.
         (b)   Inlet grate openings shall be designed to pass the ten-year (10-yr.) (10% chance/ year) peak flow with fifty percent (50%) of the inlet area clogged with a maximum six (6) inches of ponding depth.
         (c)   When underground detention is utilized, inlet grate openings shall be designed to pass the one hundred-year (100-yr.) peak flow with fifty percent (50%) of the inlet area clogged with a maximum six (6) inches of ponding depth.
         (d)   Inlets shall be spaced to prevent water spread over six (6) feet into a travel lane of a street. Bypass flow from upstream inlets shall be incorporated into inlet calculations. Manufacturer's literature should provide the inlet casting's flow-intercept-efficiency coefficient. The United States Department of Transportation Hydraulic Engineering Circular-12 (HEC-12) methods may be used.
         (e)   Stormwater may not be stored on any pavement with pedestrian traffic. Stormwater may be stored on remote areas of pavement with a maximum water depth of six (6) inches.
         (f)   Flood routing shall be provided in accordance with § 151.21(I).
      (4)   Connections to the storm sewer system.
         (a)   Sump pumps which receive and discharge groundwater and other stormwater shall be connected to the storm sewer system where possible, preferably at an inlet or manhole structure. Sump pumps may also be connected to subsurface drains in accordance with § 151.21(F).
         (b)   Footing, perimeter, and other subsurface drains shall be connected to the storm sewer system where possible, preferably at an inlet or manhole structure. Footing and perimeter drains may also be connected to subsurface drains in accordance with § 151.21(F). Footing, perimeter, and other subsurface drain connections to the sanitary sewer are prohibited.
         (c)   Roof downspouts, roof drains, and other roof discharge piping shall be directly connected to a storm sewer system, preferably at an inlet or manhole structure. Downspouts and roof drains connections to the sanitary sewer are prohibited.
         (d)   Floor drains and swimming pool drains shall not be directly connected to the storm sewer system. Discharges must flow over land surface before entering a storm system. Discharge must not impact adjacent properties. Floor drains and swimming pool drains shall be connected to an approved outlet and comply with the requirements of other Town ordinances established for control of illicit discharges and connections.
      (5)   Landscaping for underground infrastructure.
         (a)   Vegetation planting within drainage easements for underground storm systems, sewer pipes, cables, and other underground infrastructure must be perennial grasses. Trees and/or shrubs are not allowed.
         (b)   Native grasses may be planted but must be periodically mowed or otherwise maintained to prevent woody vegetation from growing in easements.
   (E)   Open channel design standards.
      (1)   General requirements.
         (a)   Any relocated open channels shall require stabilization measures to prevent sloughing from layers of seasonally saturated silts and sands.
         (b)   Roadside ditches shall be altered to meet the needs of "strip" housing along that road so that driveway crossings may be installed with adequate cover to prevent frost heave and to be coordinated on grade with each other. They shall be constructed with side slopes flat enough to allow easy mowing and maintenance, even though this may require grading beyond the road right-of-way into the lawns.
      (2)   Open channel requirements.
         (a)   Open channels, roadside ditches, swales, and culverts shall accommodate the twenty-five-year (25-yr.) (4% chance/year) peak runoff without overflowing the banks and shall accommodate the one hundred-year (100-yr.) (1% chance/year) peak runoff within the drainage easement, provided however:
            1.   Open channels with a carrying capacity greater than or equal to thirty (30) cubic feet per second at bank-full stage shall be designed in accordance with the National Resources Conservation Service Part 654 Stream Restoration Design National Engineering Handbook, Chapter 10: Two-Stage Channel Design and be capable of accommodating the twenty-four (24) hour, fifty year (50-yr.) (2% chance/year) peak runoff without overflowing the banks;
            2.   Culverts shall be capable of accommodating a fifty-year (50-yr.) (2% chance/year) peak runoff when crossing under a road which:
               a.    Carries a higher volume of traffic than other adjacent routes or has the potential for carrying higher volumes;
               b.   Is part of a pattern of arterial routes for the entire urban area;
               c.   Is oriented primarily to moving traffic rather than to serving abutting land use.
         (b)   Flood routing shall be provided in accordance with § 151.21(I).
         (c)   Any alteration of an existing open outlet channel traversing a property shall be sized as described above or for the capacity of the existing channel, whichever is greater, with provisions made for the one-hundred-year (100-yr.) (1% chance/year) frequency storm so that flooding of adjacent structures, buildings, or properties will not occur. The approval of the IDNR, IDEM, and ACOE must be obtained and their requirements must be followed for all areas within their jurisdiction.
         (d)   The hydraulic capacity of open channel systems shall be computed using Manning's Equation. Backwater analysis shall be performed to determine the one hundred-year (100-yr.) (1% chance/year) water surface elevation along open channel systems.
         (e)   Channel lining shall be designed to accommodate the ten-year (10-yr.) (10% chance/year) peak discharge. The channel lining material shall be selected such that the design shear stress is less than the maximum permissible shear stress for the lining material.
         (f)   For grass-lined channels, the side slope shall be no steeper than three (3) horizontal to one (1) vertical.
         (g)   For armored channels (turf reinforcement mat, riprap, etc.), the side slope shall be no steeper than one and one-half (1½) horizontal to one (1) vertical.
         (h)   Open channels with a bottom width greater than or equal to fifteen (15) feet shall have a riprap or paved invert to convey low flows and prevent meandering.
         (i)   Minor drainage collector swales in rear yards and between homes shall not exceed four hundred (400) feet in length and shall not be used to convey off-site drainage areas.
         (j)   Subsurface drains shall be required if the channel slope is less than one percent (1.0%). The minimum channel slope shall be three-tenths of a percent (0.3%). A minimum channel velocity of two (2) feet per second is desired to prevent deposition within the channel. All rear yard swales shall have subsurface drains.
      (3)   Culvert requirements.
         (a)   Culverts shall be sized in accordance with the Federal Highway Administration's HDS-5 Hydraulic Design of Highway Culverts.
         (b)   Minimum pipe size shall be twelve (12) inches. Minimum full-flow velocity of three (3.0) feet per second is desirable to prevent sedimentation in the pipe. Maximum full-flow velocity of ten (10.0) feet per second is recommended. The minimum Manning's n roughness value shall be twelve thousandths (0.012), regardless of material.
         (c)   Culvert pipes shall have a minimum of twenty-four (24) inches of cover, measured from the crown of pipe to the ground surface, unless shown otherwise in Town of Brownsburg Construction Standards.
         (d)   Outlet protection and energy dissipaters shall be used wherever the velocity of flows leaving a culvert exceed the erosive velocity of the downstream channel.
   (F)   Subsurface drains design standards.
      (1)   Subsurface drains are required for any grass-lined open channel which drains three (3) acres or more.
      (2)   Subsurface drains are required along all streets constructed in the Town to lower the seasonally high-water table in Brookston, Crosby, and Miami soil types.
      (3)   Tees must be provided along the subsurface system to provide an outlet for footing drains and sump pumps from each lot.
      (4)   Subsurface drains shall be a minimum of six (6) inches diameter for areas receiving subsurface flow only. Subsurface drains which may receive surface (roof drains, yard drains, etc.) and subsurface flows shall be a minimum of twelve (12) inches diameter. Underdrain capacity calculations shall be provided to ensure underdrains are properly sized for the subsurface and surface flows.
      (5)   Subsurface drains shall have a minimum of twenty-four (24) inches of cover unless shown otherwise in Town of Brownsburg Construction Standards.
   (G)   Low impact development design standards.
      (1)   Low impact development (LID) is an approach to land planning and engineering design which manages rainfall at the source to reduce stormwater runoff and manage runoff timing, emphasizes conservation and natural features, and protects water quality by controlling pollutants.
      (2)   Designers and developers are encouraged to consider methods of runoff reduction such as reducing impervious surface area, disconnecting impervious areas, promoting infiltration, stormwater capture and reuse, and other LID methods to reduce requirements for on-site stormwater detention.
      (3)   LID features shall conform to current industry guidelines and will be reviewed on a case-by-case basis. Green infrastructure and stormwater BMPs shall be designed in accordance with the Hendricks County Stormwater Technical Standards Manual or the Indiana Stormwater Quality Manual. All design calculations and justification shall be submitted for review.
   (H)   Standards for adequate outlet.
      (1)   Stormwater and drainage from the site must be discharged into an adequate outlet or outlets so as not to adversely affect other landowners. The criteria for outletting is as follows:
         (a)   Open channels shall outlet into an existing open channel, provided that stream bank and channel erosion shall not be aggravated and that the hazard of flooding shall not be increased.
         (b)   All storm sewers shall outlet into an open channel, storm sewer pipe, detention basin, or retention pond.
         (c)   Subsurface drains shall outlet into an open channel, storm sewer pipe, detention basin, retention pond, or existing tile drain, provided that the existing drain has adequate capacity, is not deteriorated, and can be maintained.
         (d)   Detention/retention ponds shall outlet into an open channel or storm sewer pipe.
      (2)   Include calculations demonstrating that the receiving conveyance or pipe has adequate capacity for the total flow, including any additional flow from the development.
   (I)   Flood routing.
      (1)   Stormwater ponding and overflow path routing shall be evaluated for the peak one hundred-year (100-yr.) (1% chance/year) storm event.
      (2)   Peak runoff flows shall be calculated for all contributing drainage areas, on-site and off-site, in their proposed or reasonably anticipated land use.
      (3)   The stormwater collection system (storm sewers, open channels, etc.) shall be assumed full at capacity) from a previous storm event at the beginning of the flood routing analysis.
      (4)   The overflow path/ponding resulting from the flood routing event shall be clearly shown as a hatched area on the plans. Plans shall include cross sections along the flood route path. Cross sections shall include the existing surface, proposed grading, and the maximum water elevation for the peak one hundred-year (100-yr.) (1% chance/year) storm event.
      (5)   The flood routing path and ponding areas shall be placed in a right-of-way or drainage easement in accordance with § 151.21(J). The flood routing path must continue to an adequate conveyance or receiving stream.
      (6)   The overflow path/ponding may be modeled as a successive series of natural ponds and open channel segments. The calculations for determining the one hundred-year (100-yr.) (1% chance/year) flood routing elevations may be based on hand calculation methods utilizing normal depth calculations and storage routing techniques or performed by computer models such as USDA SCS Technical Release 20 (TR-20); ACOE HEC-HMS, and ACOE HEC-1 in combination with ACOE HEC-RAS.
   (J)   Drainage easements.
      (1)   Drainage easements must be provided for maintenance of the stormwater management system of publicly owned systems and privately-owned ponds, detention/retention basins, water quality BMPs, and LID practices. Easements are not required for other private systems.
Area or Situation
Easement Width
Area or Situation
Easement Width
Storm sewer (smaller than 24-in.)
20 feet, centered over sewer
Storm sewer (24-in. and larger)
25 feet, centered over sewer
Grassed waterways (including equivalent sized-lined channels)
Width of channel plus 15 feet, centered over waterway
Subsurface drain
20 feet, centered over drain
Open outlet channel (including equivalent sized-lined channels)
20 feet from top of each bank
Retention pond, detention basin, and/or permanent sediment basin
Elevation of the emergency spillway design flow, plus 20 feet (horizontally)
Underground detention facility
Detention facility footprint plus 15 feet in every direction (horizontally)
Stormwater BMP (above or below grade)
BMP footprint plus 15 feet in every direction (horizontally)
Flood routing path/ponding area
Width of flood path/ponding area
 
      (2)   Access easements must be provided from a public roadway to the drainage easement, for access to stormwater management facilities.
      (3)   Structures, fences, or landscaping may not be placed in an easement in a way that will impede the free flow of stormwater.
      (4)   Drainage easements shall be maintained by the property owner.
   (K)   Grading and building pad elevation policy.
      (1)   No construction of buildings within the Town shall be permitted within twenty-five (25) feet of a stormwater conveyance or within twenty-five (25) feet of the side slopes of open channels without plans prepared by registered engineers, land surveyors or architects, certifying that there is adequate room for maintenance of the drainage facility.
      (2)   No building or structure shall be separated by the one hundred-year (100-yr.) (1% chance/year) elevation of stormwater detention facilities by less than twenty-five (25) feet.
      (3)   The lowest adjacent grade (including walkout basement floor elevation) of all residential, commercial, or industrial buildings must be located a minimum of two (2) feet above the one hundred-year (100-yr) (1% chance/year) flood elevation, the one hundred-year (100-yr.) (1% chance/year) pond elevation, or the emergency overflow weir elevation, whichever is higher. The lowest adjacent grade for all residential, commercial, and industrial buildings shall be set a minimum of one (1) foot above the noted overflow path/ponding elevation resulting from flood routing as described in § 151.21(I) and included on the final plat.
      (4)   Positive drainage shall be provided over the entire lot. Protective slopes shall slope away from building foundations and water supply wells for a minimum of six (6) inches of fall per ten (10) feet horizontal, except where restricted by property lines. Maximum gradient of protective slopes shall be two and one-half (2½) inches per foot or twenty-one percent (21%) for a minimum of four (4) feet away from all building walls, except where restricted by property lines.
   (L)   Adjoining property impacts policy.
      (1)   Land disturbance, and alterations to the site shall provide for the discharge of all stormwater runoff from upstream off-site areas as well as the stormwater runoff from the areas being developed or altered to one or more acceptable outlets having capacity to receive upstream on-site and off-site drainage (as determined by the Development Services Department).
      (2)   No activities conducted as part of the land disturbance shall be allowed to obstruct the free flow of flood waters from an upstream property. Any existing field tile or other stormwater facility encountered during the construction shall be incorporated into the proposed stormwater collection system or otherwise tied to an acceptable outlet. Design calculations shall be provided to demonstrate that the downstream system has sufficient capacity to accommodate flows from existing facility. Calculations shall be certified by a professional engineer or land surveyor licensed in the State of Indiana.
      (3)   Where an adequate outlet is not located on the site or the outfall from a site's stormwater system flows onto or through property not owned by the developer prior to reaching a regulated drain or natural waterway, off-site drainage improvements may be required and the flow path must be contained with a right-of-way or easement. Off-site improvements may include, but are not limited to, extending or replacing storm sewers; clearing, dredging, and removing obstructions to open channels or natural waterways; and replacement of undersized culvert pipes.
(Ord. 2017-28, passed 10-12-17; Am. Ord. 2024- 04, passed 4-25-24)
§ 151.22 STANDARDS FOR STORMWATER POLLUTION PREVENTION PLANS FOR LAND DISTURBANCES.
   (A)   Applicability and exemptions.
      (1)   The Town will require a SWPPP, which includes erosion and sediment control measures, pollution prevention practices and materials handling procedures, to be submitted as part of the construction plans and specifications. Any project located within the Town that involves land disturbance (with exception of divisions (A)(2) and (A)(3) below) shall comply with this section. Calculation of land disturbance should follow the guidelines contained in division (C) of this section. Land disturbance falls into one (1) of two (2) categories with differing requirements as follows:
         (a)   Land disturbances which are one (1) or more acres shall obtain coverage under IDEM's CSGP for construction activities and are subject to the requirement of this section. This section also applies to disturbances of less than one (1) acre of land that are part of a larger common plan of development or sale if the larger common plan will ultimately disturb one (1) or more acres of land.
         (b)   Land disturbances which are less than one (1) acre shall submit a SWPPP that at a minimum includes the following:
            1.   Installation and maintenance of appropriate perimeter control measures. These measures are to be installed prior to land disturbance and maintained until bare soils are permanently stabilized to at least seventy percent (70%) density of permanent perennial vegetated cover. Maintain existing vegetation when possible.
            2.   Installation of a temporary construction entrance/drive. Minimize sediment and soil discharge and tracking from the disturbed area. Clean-up sediment that is either tracked or washed on to roads or into stormwater conveyances (sewers, ditches, waterways, storm inlets, and the like). Cleaning surfaces shall not include flushing the area with water. Cleared sediment and soil must be collected and redistributed or disposed of in a manner that is compliant with all applicable statutes and rules.
            3.   Establish a concrete washout area to contain residual concrete and washout waters. Water collected from washout that does not harden or evaporate must be handled as wastewater.
            4.   Bare soils are to be stabilized in areas where work is complete, or where bare soils are to be inactive for more than seven (7) days. Utilize soil stabilization measures that are appropriate for the season.
            5.   Adjacent areas disturbed by an individual lot operator must be repaired and stabilized with temporary or permanent surface stabilization.
            6.   Install inlet protection at all stormwater inlets that receive runoff from disturbed areas. For inlets within a road or driving lane, inlet protection must be installed below the grate with an overflow or bypass so that ponding water does not cause unsafe driving conditions.
            7.   Where construction disturbs surfaces greater than 3H:1V slope or in areas of concentrated flow, establish permanent vegetation with erosion control blanket and seeding.
      (2)   The requirements under this chapter do not apply to the following activities:
         (a)   Agricultural land-disturbing activities, including tillage, planting, cultivation, or harvesting operations for the production of agricultural or nursery and vegetative crops, pasture renovation and establishment, the construction of agricultural conservation practices, and the installation and maintenance of agricultural drainage tile.
         (b)   Silvicultural activities associated with nonpoint discharges (40 CFR 122.27).
         (c)   Stormwater discharges associated with oil and gas exploration, production, processing or treatment operations, or transmission facilities (40 CFR 122.26).
         (d)   Ditch maintenance for activities performed on a regulated drain by a county drainage board as defined in I.C. 36-9-27.
         (e)   Single family residential with disturbance of less than five hundred (500) square feet.
      (3)   The requirements under this section do not apply to the following activities, provided other applicable state permits contain provisions requiring immediate implementation of soil erosion control and pollution prevention measures:
         (a)   Landfills that have been issued a certification of closure under 329 IAC 10.
         (b)   Coal mining activities permitted under I.C. 14-34.
         (c)   Municipal solid waste landfills that are accepting waste pursuant to a permit issued by IDEM under 329 IAC 10 that contains equivalent stormwater requirements, including the expansion of landfill boundaries and construction of new cells either within or outside the original solid waste permit boundary.
      (4)   For an individual lot where land disturbance is expected to be one (1) acre or more, the individual lot owner must complete their own notice of intent (NOI) letter, obtain stormwater management plan approval, and ensure that a SWPPP is completed in accordance with the requirements of this chapter and other relevant ordinances.
      (5)   An individual lot with land disturbance less than one (1) acre, located within a larger permitted project site, is considered part of the larger permitted project site, and the individual lot operator must comply with the terms and conditions of the stormwater management plan approved for the larger project site. The stormwater management plan for the larger project site must include detailed erosion and sediment control measures for individual lots. The following general requirements apply to all individual building lots, where the individual lot operator/owner is working within a permitted project.
         (a)   All stormwater measures, including erosion and sediment control measures, necessary to comply with this permit must be implemented in accordance with the overall project construction plan
         (b)   Provisions for erosion and sediment control and project management on individual building lots regulated under the overall project site permit must ensure:
            1.   The individual lot operator (contractor/subcontractor), whether owning the property or acting as the agent of the individual lot owner, is responsible for erosion and sediment control requirements associated with activities on individual lots.
            2.   Installation and maintenance of a stable construction site access unless the site is to be accessed solely from impervious or similar non-erosive areas.
            3.   Installation and maintenance of appropriate erosion and sediment control measures prior to land disturbance.
            4.   Temporary stabilization is utilized on the building site, but not required during periods when accessibility to the building site is a necessity.
            5.   Sediment discharges and tracking from each lot is minimized until permanent stabilization has been achieved.
            6.   Sediment that is either tracked or discharged onto internal project site roads is removed by the end the same day. Clearing of sediment must not include flushing the area with water, unless authorized by the permittee of the overall project site and the sediment is directed to an appropriate on-site sediment control measure. Cleared sediment must be redistributed or disposed of in a manner that is compliant with all applicable statutes and rules.
            7.   Adjacent lots disturbed by an individual lot operator are required to be repaired and stabilized with permanent surface stabilization.
            8.   Construction and domestic waste must be managed to prevent the discharge of pollutants and windblown debris. When disposed of in waste containers (trash receptacles) the receptacle must be covered when not in use and at the end of the day. Waste that is not disposed of in trash receptacles must be removed at the end of the day from the site and disposed of properly.
            9.   Demolition waste must be managed to prevent windblown debris and to protect water quality.
            10.   Concrete washout areas provided by the permittee of the overall project site are utilized unless a leak-proof containment system is operated on the building lot, or special arrangements are made to properly dispose of the wash water. Concrete washout systems on individual lots must be properly installed and maintained. Wash water must be disposed of by the individual lot operator and is not allowed to discharge.
         (c)   For an individual residential lot to be considered stabilized according to the criteria in § 151.28, the individual lot operator must:
            1.   Complete final stabilization taking into account weather and season;
            2.   Initiate permanent seeding with appropriately crimped or tackified mulch cover, erosion control blanket, sod; or
            3.   Install appropriate and/or ensure functional erosion and sediment control measures are in place on the individual lot. Upon issuance of the certificate of occupancy and concurrence of the homeowner, the homeowner is responsible to maintain the sediment control measures until final stabilization has occurred.
      (6)   It will be the responsibility of the project site owner to obtain stormwater management plan approval and ensure that a sufficient construction plan is completed and submitted to the Town in accordance with the requirements of this section and other relevant ordinances. It will be the responsibility of the project site owner to ensure compliance with this section during the construction activity and implementation of the construction plan, and to notify the Town with a sufficient NOT letter upon completion of the project and stabilization of the site. However, all persons engaging in construction and land disturbing activities must comply with the requirements of this section.
      (7)   For land disturbing projects owned or operated by the Town, construction plans must be submitted to the Development Services Department and County SWCD for review and approval.
   (B)   Policy on stormwater pollution prevention. Effective stormwater pollution prevention on construction sites is dependent on a combination of preventing movement of soil from its original position (erosion control), intercepting displaced soil prior to entering a waterbody (sediment control), and proper on-site materials handling and pollution prevention practices. The developer must submit to the Town a SWPPP with detailed erosion and sediment control plans as well as a narrative describing materials handling and storage, and construction sequencing. The following principles apply to all land-disturbing activities and should be considered in the preparation of a stormwater pollution prevention plan within the Town.
      (1)   Minimize the potential for erosion by designing a development that fits the topography and soils of the site. Deep cuts and fills in areas with steep slopes should be avoided whenever possible, and natural contours should be followed as closely as possible.
      (2)   Existing natural buffers that are adjacent to waters of the state to promote infiltration and provide protection of the water resource shall be preserved, unless infeasible. Activities performed by a county drainage board under I.C. 36-9-27 are excluded.
      (3)   Natural buffers must be preserved, including the entire buffer bordering and/or surrounding the water resource. Buffers:
         (a)   Fifty (50) feet or more in width must be preserved to a minimum of fifty (50) feet.
         (b)   Less than fifty (50) feet in width must be preserved in their entirety.
         (c)   May be enhanced with vegetation that is native and promotes ecological improvement and sustainability.
         (d)   Runoff directed to the natural buffer must be:
            1.   Treated with appropriate erosion and sediment control measures prior to discharging to the buffer.
            2.   Managed with appropriate runoff control measures to prevent erosion from occurring within the buffer area.
         (e)   Further information regarding buffer requirements is contained in IDEM's "Implementation of Buffers" guidance document.
      (4)   Unvegetated or vegetated areas with less than seventy percent (70%) cover that are scheduled or likely to be left inactive for seven (7) days or more must be temporarily or permanently stabilized with measures appropriate for the season to reduce erosion potential. Alternative measures to site stabilization may be acceptable if the project site owner or their representative can demonstrate they have implemented and maintained erosion and sediment control measures adequate to prevent sediment discharge from the inactive area. Vegetated areas with a density of less than seventy percent (70%) shall be restabilized using appropriate methods to minimize the erosion potential.
      (5)   All practices on a site should be conducted in a logical sequence so that the smallest practical area of land will be exposed for the shortest practical period during land disturbing activities.
      (6)   The length and steepness of designed slopes should be minimized to reduce erosion potential. Drainage channels and swales must be designed and adequately protected so that their final gradients and resultant velocities will not cause erosion in the receiving channel or at the outlet. Guidance for determining acceptable velocities and energy dissipation is provided in HEC-14.
      (7)   Sediment basins, where feasible, must withdraw water from the surface of the water column.
      (8)   Basin slopes must be stabilized upon achieving design grades to eliminate sediment inflow from the measure itself.
      (9)   The outfall of a basin must be stabilized and non-erosive within twenty-four (24) hours of installation of the basin outlet.
      (10)   Pipe outlets discharging from the project site must be provided with temporary or permanent energy dissipation within twenty-four (24) hours of discharging runoff.
      (11)   Sediment-laden water which otherwise would flow from the project site shall be treated by erosion and sediment control measures appropriate to minimize sedimentation.
      (12)   A stable construction site access shall be provided at all points of construction traffic ingress and egress to the project site.
      (13)   Stormwater runoff leaving a project site must be discharged in a manner that is consistent with applicable state or federal law.
      (14)   Appropriate measures shall be implemented to prevent wastes or unused building materials, including garbage, debris, packaging material, fuels and petroleum products, hazardous materials or wastes, cleaning wastes, wastewater, concrete truck washout, port-a-let waste, and other substances from being carried from a project site by runoff or wind. Identification of areas where concrete truck washout is permissible must be clearly posted at appropriate areas of the site. Wastes and unused building materials shall be managed and disposed of in accordance with all applicable state statutes and regulations. Proper storage and handling of materials such as fuels or hazardous wastes, and spill prevention and cleanup measures shall be implemented to minimize the potential for pollutants to contaminate surface or groundwater or degrade soil quality.
      (15)   Public or private roadways shall be kept cleared of accumulated sediment that is a result of runoff or tracking. Bulk clearing of accumulated sediment shall not include flushing the area with water. Cleared sediment shall be redistributed or disposed of in a manner that is in accordance with all applicable statutes and regulations.
      (16)   Natural features, including wetlands and sinkholes, shall be protected from pollutants associated with stormwater runoff.
      (17)   Ground water from the dewatering of excavations, trenches, foundations, etc. must not be discharged when:
         (a)   Sediment and ground water is not first directed to an appropriate stormwater quality measure or a series of control measures that minimize the discharge of the sediment.
         (b)   A visible sheen and/or pollutants are present at a level that requires additional treatment and/or an individual permit from IDEM.
      (18)   Fertilizer applications associated with the stabilization plan for the project must meet the following requirements:
         (a)   Apply fertilizer at a rate and amount as determined by a soil analysis or in accordance with the Indiana Stormwater Quality Manual or similar guidance documents.
         (b)   Apply fertilizer at an appropriate time of year for the project location, taking into consideration proximity to a waterbody, and preferably timed to coincide with the period of maximum vegetative uptake and growth.
         (c)   Avoid applying fertilizer before rainfall events that could result in the discharge of nutrients.
      (19)   Soil compaction is to be minimized, especially in areas where permanent vegetation will be re-established and/or areas that are designated to infiltrate stormwater for the post-construction phase.
      (20)   Topsoil is to be preserved, unless infeasible.
      (21)   Generation of dust shall be minimized through dust suppression techniques to prevent deposition into waters of the state.
      (22)   The use of anionic polymers (cationic polymers are not authorized for use) on the project site are authorized for sediment control provided their use is in conformance with current State of Indiana standards and specifications. The use of the polymers requires notification to IDEM and the Town.
      (23)   Required postings.
         (a)   The project site owner shall post a notice near the main entrance of the project site. For linear projects sites, such as a pipeline or highway, the notice must be placed in a publicly accessible location near the project field office. The notice must be maintained in a legible condition and contain the following information:
            1.   Copy of the completed IDEM NOI and the CSGP number issued by IDEM, where applicable.
            2.   Name, company name, telephone number, e-mail address (if available), and address of the project site owner or a local contact person.
            3.   Location of the construction plan.
         (b)   This permit and posting of the notice does not provide the public with any right to trespass on a project site for any reason, nor does it require that the project site owner allow members of the public access to the project site.
      (24)   All stormwater quality measures must be designed and installed under the guidance of a trained individual (refer to definitions section or according to the requirements of the CSGP).
      (25)   Certified professionals shall be utilized for activities associated with the development and design of the SWPPP, stormwater measure implementation, and stormwater project management.
      (26)   Personnel associated with the project must be informed of the terms and conditions of this permit and the requirements within the SWPPP. The permittee is required to document this process. Information must be provided through training, preconstruction meetings, written notification, contracts, or other means that effectively communicates the provisions and requirements of the permit and SWPPP. Personnel include, but are not limited to:
         (a)   General contractors, construction management firms, grading or excavating contractors, trade industry representatives (i.e., concrete industry), and utility contractors associated with the overall project.
         (b)   Contractors or individual lot operators that have primary oversight on individual building lots.
         (c)   Those responsible for the implementation of the SWPPP, and the installation, repair, and maintenance of stormwater measures.
         (d)   Those responsible for the application and storage of treatment chemicals.
         (e)   Those responsible for administering inspections.
   (C)   Calculations and design standards and specifications.
      (1)   In calculating the total area of land disturbance, for the purposes of determining applicability of this section to the project, the following guidelines should be used:
         (a)   Off-site construction activities that provide services (for example, road extensions, sewer, water, and other utilities) to a land disturbing project site, must be considered as a part of the total land disturbance calculation for the project site, when the activity is under the control of the project site owner.
         (b)   Strip developments will be considered as one (1) project site and must comply with this chapter unless the total combined disturbance on all individual lots is less than one (1) acre and is not part of a larger common plan of development or sale.
         (c)   To determine if multi-lot project sites are regulated by this chapter, the area of land disturbance shall be calculated by adding the total area of land disturbance for improvements, such as, roads, utilities, or common areas, and the expected total disturbance on each individual lot, as determined by the following:
            1.   A single-family residential project site where the lot(s) is one-half (0.5) acre or more in total size, as one-half (0.5) acre of land disturbance.
            2.   A single-family residential project site where the lot(s) is less than one-half (0.5) acre in size, as the actual lot size.
            3.   All other types of project sites, such as industrial and commercial project sites, as a minimum of one (1) acre for all lots regardless of size.
      (2)   The calculation methods as well as the type, sizing, and placement of all stormwater pollution prevention measures for construction sites shall meet the design criteria, standards, and specifications outlined in the Indiana Stormwater Quality Manual and the Town of Brownsburg Construction Standards.
   (D)   Submittal requirements. For those projects meeting the requirements of this section, a construction stormwater pollution prevention plan is required in addition to the submittal requirements listed in § 151.20. This plan must include the following information:
      (1)   IDEM NOI form along with the information required by the NOI form.
      (2)   Proof of publication in a newspaper of general circulation, in the affected area, that notified the public that a construction activity is to commence. The publication must include language required by the CSGP.
      (3)   Construction plans and SWPPP shall contain the information required by the CSGP. SWPPP figures shall also contain the following:
         (a)   Contour lines with maximum one (1) foot contour interval.
         (b)   Stormwater infrastructure and facilities.
         (c)   Open conveyances.
         (d)   Flood routing path and ponding locations in accordance with § 151.21(I).
      (4)   SWPPP sequencing shall consider various phases of construction activities and may require more than one (1) SWPPP plan sheet. Possible phases of construction include initial clearing, earth moving activities, hauling of borrow or fill soils, current site conditions, installation of infrastructure, final stabilization, off-site work associated with the project, etc.
(Ord. 2017-28, passed 10-12-17; Am. Ord. 2024- 04, passed 4-25-24)
§ 151.23 STORMWATER QUALITY MANAGEMENT FOR POST-CONSTRUCTION.
   (A)   Applicability and exemptions.
      (1)   The stormwater application must include post-construction stormwater quality measures. These measures are incorporated as a permanent feature into the site plan and are left in place following completion of construction activities to continuously treat stormwater runoff from the stabilized site. Any project located within the Town that includes clearing, grading, excavation, and other land disturbing activities, resulting in the disturbance of one (1) acre or more of total land area, is subject to the requirements of this section. This includes land disturbances of less than one (1) acre of land that are part of a larger common plan of development or sale if the larger common plan will ultimately disturb one (1) or more acres of land.
      (2)   The requirements under this section do not apply to the following activities:
         (a)   Land-disturbing activities where there will be no additional impervious surfaces associated with the final completed project, including but not limited to, ditch construction/reconstruction and utility installation/maintenance activities.
         (b)   Single-family residential strip development offered for sale or lease without land improvements and the project is not part of a larger common plan of development or sale.
         (c)   Residential developments consisting of four (4) or fewer lots where the proposed impervious surfaces are ten percent (10%) or less of the project acreage. Impervious is determined by the sum of all infrastructure (roads, paths, parking, etc.) and the average projects hard surfaces associated with all building lots within the project.
         (d)   Single-family residential strip development offered for sale or lease without land improvements, and the project is not part of a larger common plan of development or sale.
      (3)   It will be the responsibility of the project site owner to ensure proper construction and installation of all stormwater BMPs in compliance with this chapter and with the approved stormwater management plan, and to notify the Town with a sufficient NOT letter upon completion of the project and stabilization of the site. However, all eventual property owners of stormwater quality facilities meeting the applicability requirements must comply with the requirements of this chapter and this section.
   (B)   Policy on stormwater quality management.
      (1)   BMPs must be implemented for the management of total suspended solids (TSS) including floatables. BMP systems or treatment trains shall have at least one (1) component of the system providing floatable control. Position BMPs outside right-of-way and not more than fourteen (14) feet from a concrete or paved area for vac-truck and maintenance vehicle access.
      (2)   The project site owner must submit to the Town a SWPPP that would show placement of appropriate BMPs designed, constructed, and maintained.
      (3)   For ease of maintenance and to reduce the frequency of pond dredging, all detention/retention facilities (including underground detention) shall have an upstream BMP installed for each inlet pipe, to collect sediments, debris, floatables, and other material prior to entering the detention/retention facility. Forebays are not acceptable.
      (4)   Fueling areas must install appropriate practices to reduce lead, copper, zinc, and polyaromatic hydrocarbons in stormwater runoff. These requirements will apply to all new facilities and existing facilities that replace their fuel tanks.
      (5)   Infiltration practices will not be allowed in wellhead protection areas. Discharges will not be allowed directly into sinkholes or fractured bedrock, without treatment that results in the discharge meeting Indiana groundwater quality standards as referenced in 327 IAC 2-11.
      (6)   Any stormwater practice that is a Class V injection well must ensure that the discharge from such practices meets Indiana groundwater quality standards as referenced in 327 IAC 2-11.
   (C)   Calculations and design standards and specifications.
      (1)   Calculation of land disturbance should follow the guidelines contained in § 151.22(C).
      (2)   The target TSS removal rate is eighty percent (80%). For the purposes of this requirement, TSS is defined as particles smaller than one hundred twenty-five (125) microns in diameter.
      (3)   There are two (2) methods for calculating the required size of a BMP. The first method calculates the water quality volume to be treated, which applies to detention-based BMPs. The second method calculates the water quality peak flow rate to be treated, which applies to filtration processes and mechanical-type BMPs such as hydrodynamic devices.
      (4)   The appropriate stormwater quality volume (WQv) and/or stormwater quality flow rate (Qwq) generated from a qualifying site shall be adequately treated before discharge. Traditional structural BMPs are presumed to comply with the eighty percent (80%) TSS removal rate if BMPs are:
         (a)   Sized to capture the prescribed water quality volume or flow rate, as applicable;
         (b)   Designed according to the specific performance criteria outlined in Appendix D of the Hendricks County Stormwater Technical Standard Manual or the Indiana Stormwater Quality Manual;
         (c)   Constructed properly; and
         (d)   Maintained regularly.
      (5)   Mechanical-type BMPs must be approved by the Town and meet ASTM standard methods for verifying performance and must be certified by a professional engineer. The BMP must meet the eighty percent (80%) TSS removal rate and floatable control without resuspension of particles at the design water quality flow rate resulting from a one inch (1-inch) rainfall depth. Testing of the TSS removal rate must be conducted by an independent testing facility rather than by the manufacturer.
      (6)   Water quality volume (WQv) - The WQv is the storage needed to capture and treat the runoff from the first one inch (1-inch) of rainfall. A twenty-four (24) to forty (40) hour emptying time must be used for the release of the WQv, with no more than fifty percent (50%) of the water quality volume being released in the first twelve (12) hours. The WQv is equivalent to one inch (1-inch) of rainfall multiplied by the volumetric runoff coefficient (Rv) and the site area. The volume of runoff is directly related to the amount of impervious cover at the site and is calculated using the following equation.
 
WQv =    PRVA  
       12
 
where:
WQv = water quality volume (acre-feet, ac-ft)
P = rainfall depth (inches, in) = 1 inch
Rv = volumetric runoff coefficient — see the following equation
A = site area (acres)
 
Rv = 0.05 + 0.009 I
 
where:
Rv = volumetric runoff coefficient
I =percentage of impervious cover (%)
      (7)   Water quality flow rate (Qwq) - The Qwq is needed to size BMP devices designed to treat runoff at a peak design flow rate through the system. The rational method in conjunction with a rainfall intensity will be used to calculate the Qwq in cfs. This method relies on an intensity that is one-half (0.5) of the two-year (2-yr) (50% chance/year) storm intensity from the intensity-duration-frequency curve along with the percent of impervious cover to identify the appropriate runoff coefficient for the proposed land use.
Step 1 – Using the percent of impervious cover, calculate the corresponding runoff coefficient for land use using the following equation:
 
C = 0.858 ic3 - 0.78 ic2 + 0.774 ic + 0.04
 
where:
C = Runoff Coefficient for Land Use
ic = Percent of Impervious Cover (%/100)
Step 2 – Calculate the site time of concentration in minutes (Tc) and area in acres (A).
Step 3 – Using the time of concentration (Tc), define the peak intensity (in inches/hour) of the two-year (2-yr.) (50% chance/year) storm event utilizing the intensity-duration-frequency curve (shown in table form) from the NOAA Point Precipitation Frequency Estimates which can be found at https:// hdsc.nws.noaa.gov/pfds/pfds_map_cont.html?bkmrk=in. Interpolation may be necessary for times of concentration between given values.
Step 4 – To meet the design specification, divide the intensity determined in Step 3 by two (2) to identify one-half (0.5) of the two-year (2-yr) (50% chance/year) storm intensity.
Step 5 – Use the Rational Method equation shown utilizing the previously calculated values to calculate Qwq.
 
Qwq = C x p x A
 
where:
Qwq = Water Quality Flow Rate (cfs)
C = Runoff Coefficient for Land Use
p = one-half (0.5) of the two-year (2-yr) (50% chance/year) storm intensity (inches/hour)
A = Area (acres)
   (D)   Easement requirements. All stormwater quality management systems, including detention or retention basins, filter strips, pocket wetlands, in-line filters, infiltration systems, conveyance systems, structures and appurtenances are to be located outside of the right-of-way and shall be incorporated into permanent easements as listed in § 151.21(J).
   (E)   Submittal requirements. A post-construction stormwater pollution prevention plan is required in addition to the submittal requirements listed in § 151.20. This plan must include the following information:
      (1)   A description of potential pollutant generating sources and a list of pollutants from the proposed land use that may reasonably be expected to contribute pollutants to stormwater discharges.
      (2)   A description of stormwater quality and stormwater management measures that will be installed to address post-construction sources that are expected to generate pollutants in stormwater discharges after construction activities have been completed. The measures selected should achieve, at a minimum, the following objectives:
         (a)   Stormwater quality measures that target pollutants of concern and are designed to remove or minimize pollutants from stormwater runoff that is associated with the final land use.
         (b)   Stormwater quality measures that will be implemented to prevent or minimize adverse impacts to aquatic resources including, but not limited to, wetlands, streams, karst features, and riparian habitats.
         (c)   Stormwater management measures that will address the potential impacts of increased runoff from the project. Measures must be designed and approved according to this permit or where applicable local requirements and drainage ordinances. A certified professional must approve that the design meets the applicable requirement(s).
         (d)   Measures, including structural and those based on low impact development principles, selected to address the pollutant(s) of concern, reduction of peak flows, and ability to infiltrate.
         (e)   Protective measures that will be implemented during active construction when the type of post-construction measure(s) planned are susceptible to pollutants, specifically sediment that may be generated during land-disturbing activities.
         (f)   Measures that will prevent or minimize adverse impacts to stream and riparian habitat.
      (3)   The location, dimensions, detailed specifications, and construction details of all post-construction stormwater quality and stormwater management measures.
      (4)   A sequence describing when each post-construction stormwater measure will be installed in relation to project construction.
      (5)   An O&M manual shall be provided in accordance with § 151.29. This O&M manual must be signed and provided to future parties who will assume responsibility for the operation and long-term maintenance of the post-construction stormwater measures.
      (6)   Calculations demonstrating the required water quality treatment volume or water quality treatment rate for post-construction stormwater quality measures.
      (7)   A sequence describing when each post-construction stormwater quality measure will be installed.
(Ord. 2017-28, passed 10-12-17; Am. Ord. 2024- 04, passed 4-25-24)
§ 151.24 RESERVED.
§ 151.25 STORAGE OF POLLUTANTS.
   Storage or stockpiling of pollutants within any floodplain is strictly prohibited. Storage or stockpiling of pollutants on active construction sites must include adequate protection and/or containment to prevent any such materials from entering any temporary or permanent stormwater conveyance or watercourse.
(Ord. 2017-28, passed 10-12-17; Am. Ord. 2024- 04, passed 4-25-24) Penalty, see § 151.99
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