INDOT has developed Chapter 204, “Post-Construction Stormwater Best Management Practices” (BMPs), in the Indiana Design Manual (IDM) to help the agency comply with IDEM stormwater and MS4 permit requirements. The BMPs are designed to prevent or reduce non-point source pollution to help achieve water quality goals. This presentation will provide the industry with a project update and an implementation plan for this new chapter

Bowman, Sandra

Eichhorst, Jessica

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      HNTB r.-..n Nextlevel ~INDIANA INDOT DM Chapter 204: Post-ConstructionStormwater BMPs Sandra Bowman, Mgr. Ecology and Waterway Permitting – INDOT Jessica Eichhorst, PE, Project Manager – HNTB  HNTB r.-..n Nextlevel ~INDIANA Outline • Legal Requirements • INDOT as an MS4 • Post-construction structural BMPs • Design Standards • Target Pollutant • BMP Selection • Considerations • Infeasibility Analysis • Inspection and Maintenance • Hydrologic and Hydraulic Design • Best Management Practices • Implementation  HNTB r.-..n Nextlevel ~INDIANA Legal Requirements • Municipal Separate Storm Sewer System (MS4) General Permit • 4.6 SWQMP Post-Construction Stormwater Run-off MCM • New and re-development with land-disturbing activities of one or more acres or less than one acre if part of larger common plan of development with more than one acre disturbance • Establish design criteria to meet or exceed GSGP post-construction requirements • Develop stormwater management measures and standards to improve water quality (structural, non-structural, low impact, green infrastructure) • Address quality and quantity of stormwater run-off • Practices or control for volume reduction, infiltration, filtering, harvesting, evapotranspiration, vegetative practices or alternative treatment systems  HNTB r.-..n Nextlevel ~INDIANA Legal Requirements • Post-Construction Stormwater Run-off Design and EngineeringRequirements 4.6(c)(3) • Control quality and quantity of runoff • Not exceed pre-development discharge based on 2-, 10-, and 100-year peak storm events • Minimize pollutants associated with stormwater run-off from final land use • Size to Water Quality Volume (WQv) or water quality flow rate • Use of one or more measures in tandem or series • Infiltration measures must consider pollutants associated with run-off and potential to contaminate ground water • Use of alternative or pre-treatment if contamination is possible HNTB r.-..n Nextlevel ~INDIANA Legal Requirements • Construction Stormwater General Permit (CSGP) • Section 3.2(a)(9) – Post-construction stormwater management measures • Control quality and quantity of runoff • Not exceed pre-development discharge based on 2-, 10-, and 100-year peak storm events • Minimize pollutants associated with stormwater run-off from final land use • Size to Water Quality Volume (WQv) or water quality flow rate • Use of one or more measures in tandem or series • Use of infiltration measures to minimize discharge pollutants            NTB r.-..n Nextlevel ~INDIANA INDOT as an MS4 • Characteristics • State of Indiana • Linear - 11,000 centerline miles • 4,800 miles within another MS4 • Buildings and grounds (rest areas, district offices, maintenance facilities) • Compliance • “ordinance or other regulatory mechanism” • “local requirements” • Design Manual, Standard Specifications • Develop BMPs for post-construction stormwater run-off control • Total impacted area > 1 acre, or • ??? Under development (ft2 and/or %) West Fork White River, Morgan County, Indiana   NTB r.-..n Nextlevel ~INDIANA Post-Construction Structural BMPs Dry Grass Swale, Hendricks County, Indiana • BMP • Most effective and practical means of preventing or reducing non-point source pollution • Help reach water quality and quantity goals • May be activity based, ex. reducedchloride application for road de-icing • Post-Construction Structural BMPs are permanent designed features • Used alone, tandem, or series    HNTB r.-..n Nextlevel ~INDIANA Design Standards • IDEM’s Construction Stormwater General NPDES Permit applies to all qualifying INDOT projects • Qualifying INDOT Projects: proposed land disturbance (in acres), including staging areas for construction, is greater than 1 acre and includes xx,xxx square feet or more of added impervious area • If either of these conditions are not met, post-construction BMPs are notrequired NTB r.-..n Nextlevel ~INDIANA Target Pollutant • Sediment • Most common water pollutant (US EPA) • Primary pollutant in stormwater run-off from pavement • Permanent BMPs target sediment removal • 80 % - sediment removal rate target as Total Suspended Solids (TSS) Sediment-laden run-off in Marsh River (MN) – pca.state.mn.us   Structural BMP Dry Turf Grass Swale Dry Native Grass Swale Filter Strip Dry Detention Pond Wet Swale Wet Retention Pond Infiltration Swale Infiltration Basin Proprietary Device NTB Descri tion A broad and shallow channel planted with grass. Fully drains between rainfall events. A broad and shallow channel planted with dense specialized plants. Fully drains between rainfall events. A vegetated linear section of land. Also often referred to as a buffer strip. An engineered basin planted with grass. Fully drains between rainfall events. Includes an outlet structure to control flow. A broad and shallow channel planted with grass. Designed with a permanent pool and an elevated outlet structure. Engineered basin designed to permanently store run-off. Designed with a permanent pool and an elevated outlet structure. A broad and shallow channel with permeable soil planted with grass. Designed to infiltrate run-off into the underlying soil. Hydrodynamic separators. Pollutant Removal Mechanism Sedimentation, physical filtration, and biofiltration Sedimentation, physical filtration, and biofiltration Physical filtration, sorption, biofiltration Sedimentation, physical filtration, and biofiltration Sedimentation, physical filtration, and biofiltration Sedimentation, physical filtration, and biofiltration Sedimentation, physical filtration, infiltration, sorption, and biofiltration Sedimentation and physical filtration Priori 1 1 1 1 2 2 3 4 r.-..n Nextlevel ~INDIANA Structural BMP Selection 1. Dry turf grass swale 1. Dry native grass swale 1. Filter strip 1. Dry detention pond 2. Wet swale 2. Wet retention pond 3. Infiltration swale 3. Infiltration basin 4. Proprietary device See INDOT guidance documents for references/definitions.   HNTB r.-..n Nextlevel ~INDIANA BMP Selection Flowchart Considerations -• Disturbed area, added pavement • Available ROW • Drainage system type • Soil type • Water table depth • Slope • Wellhead protection area • Peak flow mitigation BMP Selection Water Table Slope Soil Type Drainage System ROW AddedPavement DisturbedArea Wellhead Protection   HNTB r.-..n Nextlevel ~INDIANA Roadway Project Layout/Site-Specific Conditions Site-specific factors that limit post-construction BMP selection • Available right-of-way • Steep slopes and other topographic constraints • Infiltration not allowed in karst areas • High water-table, some BMPs must drain between rainfall events • Bedrock near ground surface – expensive to excavate • Large off-site areas draining to BMPs – require more space – can lead to high velocities • Adjacent land-use draining to INDOT right-of-way • Underlying soil type – affects infiltration and support for needed vegetation  HNTB r.-..n Nextlevel ~INDIANA Infeasibility Analysis • Economically infeasible • Limited right-of-way, utility relocations, topographic constraints, and amount of added flow from offsite • Option to treat existing pavement instead of new added pavement in a different location within the same watershed • TMDLs • Must consider receiving streams on the current 202(d) list of impaired waters • Pollutants not from INDOT ROW may be infeasible to remove in post-construction BMPs • Documentation • Prior coordination with INDOT is required and the documentation listed in Chapter 204 must be submitted   NTB INDIANA DEPARTMENT OF TRANSPORTATION POST-CONSTRUCTION BMP MAINTENANCE PLAN -COOrdlnattls;, DrMnlJDlr«llons This s·wale w.a.s designed to remove Total Suspen ded Solids {TS S} from ·stonnwater runoff. Turf gTa-ss height should be at least 6 inches for adequate TS S removal. This swa.le was des tgned to be dry between rainfaU e-ve.nts . Twice per year du-ri:ng first year after construction~ then one time per year. • Vegetation - cover should be app1oximately 90% • Erosion and scou r • Trash a.nd debr i.s bu~ldup • Exce,ss ive pondi:ng - s-tag:nated water • l.nftow and outflow points andlor struchl.res are not blocked or damaged • Sediment buildup - should be~ 25% of original design volume • Vegetation - re-estabfish turf grass as needed so that cover is approximately '90% • Erosion and ·scou:r- re-grade a-s needed, install erosion protection if re-quired • Trash a.nd debris buEldup - remove trash and debris as needed • Excessive pondi:ng - regrade as needed to drain excessive ponded or stagnated water • Inflow and outflow points and!or struchl res - repair s tructures and remove debris or blockage as ne-eded • Sediment buildup - should bes" 25%-of original design volume- remove sediment as needed -1 of2 r.-..n Nextlevel ~INDIANA Inspection and Maintenance • BMP given an asset ID number and added to inspection schedule • Designer provide BMP inspection and maintenance plan • Quarterly checks • Maintenance as needed • Editable maintenance plan templates     HNTB r.-..n Nextlevel ~INDIANA Hydrologic and Hydraulic Design • Water Quality Event: A rainfall event of one inch, assumed to remove a significant percentage of pollutant from the roadway • Also known as the “first flush” • Water Quality Volume: The volume ofrun-off generated by the Water Quality Event for treatment in BMPs • Water Quality Treatment Rate: The peak flow rate of stormwater run-off generated by the Water Quality Event Rain on grass – edu.rsc.org 15   HNTB r.-..n Nextlevel ~INDIANA Water Quality Volume WQv = (P * Rv * A) ÷ 12 Where: WQv = water quality volume, acre-feet P = rainfall, inches (use 1.0 inches) Rv = volumetric run-off coefficient A = total proposed onsite drainage area, acres And: Rv = 0.05 + (0.009 * I) Where: I = percent new impervious cover, % And: I = [(Pia – Eia) ÷ A] * 100 Where: Pia = Proposed Onsite Impervious Area Eia = Existing Onsite Impervious Area 16  100 I 98 96 94 ,::; 92 ::: z 90 ~ ... QI .Cl 88 E :::, z 86 QI > :i 84 0 >, :t: 82 "iij :::, a 80 ... $ ~ 78 76 ~ 1.,,... ~ ,-, / 'ti" ~ ~ ,_ l.-- ~v ~ I ~ ,_ - -,_ 1' ~1 I ---r , I 74 72 70 I 0 10 20 30 NTB Water Quality Curve Number I I ----~.-----,,,,. ,,,,. -- I ~ ,,,,. ~t ,, I I ,- - - ,_ ,~ ,_ - ,~ ,_ - - I ~ ~ - l.-- I ~ I I I r 40 50 60 Percent Added Imperviousness --------·~ ' I ~ -,_ ,_ ,~ 70 80 I ,_ ,_ ,~ ,_ 90 --- '--100 r.-..n Nextlevel ~INDIANA Water Quality Treatment Rate • Qwq • Calculate Tc using TR-55 methodology • Calculate CNwq using provided graph • Compute Qwq in cfs following hydrograph-oriented procedures approved in IDM Chapter 202 • Use NRCS Type II rainfall distribution and depth of 1 inches 17     NTB 3:1 Maximum Side Slope t il::'. Roadway Optional Filter Strip Side Slope (3 :1 Max) Swale Bottom Side Slope t Plan View Seasonal High Water Table Cross Section View r.-..n Nextlevel ~INDIANA Dry Swales • Designed to fully drain between rainfall events • Planted with turf grass or native grasses • Trapezoidal, V-shaped, or natural cross section • No underdrain • Water depth during Water Quality Event at or below grass height (6 inches for turf, 2.5 feet for native) • Sized using Water Quality Treatment Rate and Hydraulic Residence Time Tahr = (Lswale ÷ vwq) ÷ 60 Where: Tahr = hydraulic residence time, minutes Lswale = length of swale, feet vwq = peak flow velocity at water quality event, ft/s Tahr of 9 minutes = 80% TSS removal 18      NTB r.-..n Nextlevel ~INDIANA Dry Grass Swale Grass Swale in I-70 Median – Maryland DOT State Highway Administration 19   NTB 75 z, 65 (I) ~ ......, .L: tn 55 C ~ 0. ·;:: 45 01 ,._ ~ iI: 35 ,,/ / ./ v,.... / / / v 2 Vegetated Filter Strip Length Drainage Area Soil: Sand HSG: A ,....v V V V v:7 / V 17 vv ~v / V v '-"'" / / v ,....v / / 1 Turf Grass I / /,, I 60% TSS Removal v v I/ ~ v I./ I/ I Nat ive Grasses ,I 170% TSS Removal v v v I Native Woods 1~ v 180% TSS Removal / v _ i..--~ 1...-- i..-----~ 3 4 5 Filter Strip Slope (Percent) 6 7 r.-..n Nextlevel ~INDIANA Filter Strips • Vegetated, uniformly graded area • Planted with turf grass or native grasses • Can utilize existing native woods • Typically located between roadway and another BMP or waterbody • Effectiveness for TSS removal controlled by underlaying soil, type ofvegetation, and cross-sectional slope • Run-off sheet flows through the vegetation 20 NTB Roadway --------------------------------'-V '-V 1 'V ~ 'V '-V '-V Runoff '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V Vegetated Filter Strip '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V '-V Plan View Roadway -- Vegetative Filter ... . .. . . . . Waterway Profile View r.-..n Nextlevel ~INDIANA Filter Strip Examples Vegetated Filter Strip – dot.state.oh.us 21     HNTB r.-..n Nextlevel ~INDIANA Dry Detention Ponds • Capture and temporarily detain stormwater run-off • Can be a peak flow mitigation BMP as well as water quality BMP • 2 design options for TSS removal • First option – model as a basin • Detain Water Quality Volume for 24hours • If outlet pipe D is 10 inches or less, 50 feet of perforated pipe installed in stone trench and connected to outlet structure • Second option – model as a swale • Construct a meandering pilot channel • Design using Water Quality Treatment Rate • Depth of flow in channel during water quality event at or below the grassheight • Follow design process in dry swale section 22 imum Pool Elevation \ PIiot Channel \ \ ~Width* I I I I I Swale Block outlet Structure *Length~-----==-------= -------~ ---~-­Offset Spillway if Channelized Channel Inlet, Type F-7 for Design Storm Trash Rack I ' I / ! I I *3:l Min. Length to Width Ratio Plan View Not to Scale Spillway Elevation, . ** 1 Ft. Above 100-Year Storm Elevation Riprap on Geotextile Along Spillway Ditch Low Flow Pipe for Water Quality Volume Storage overflow Outlet Pipe **Spillway May be Channelized if Desired I. 10 Ft ... I Detention Berm Cross Section dean Washed Stone Perforated Pipe Geotextile Filter Stone Trench Cross Section Not to Scale Perforated Pipe Clean washed Stone Orifice for Release of Storms Greater than Water Quality Event Perforated Pipe Ground Surface Clean washed Stone wrap Stone Trench in Geotextile Filter Reducer if Outlet Pipe Diameter is less than 6" 50' Min Berm and Trench Plan View Not to Scale Inlet, Type F-7 for 100-year storm 5' Min -----Spillway Elevation, . 1 Ft. Above Design Storm Elevation Outlet Pipe for Extended Detention, Minimum Diameter 4" Riprap on Geotextil1 Along Spillway Detention Berm Cross Section Detention Pond Detail 23  NTB Permanent Pool Elevation Swale Bottom ---11.___ 3 3:1 Maximum Side Slope Spillway Elevation, 1 Ft. Above Permanent Pool Elevation* 5 Ft. Min, Profile View Riprap on Geotextile Along Spillway *Spillway May be Recessed into Berm Seasonal High Water Table Varies Cross Section View \n Nextlevel ~INDIANA Wet Swales • Natural or engineered • High water table or poorly drained soils • Permanently retain the Water Quality Volume • Advantages – provide aquatic wildlife habitat, can require less linear space than a dry swale, can treat for other pollutants • Disadvantages – water can be come stagnant, attract nuisance insects, vegetation requires proper pH levels 24      NTB r.-..n Nextlevel ~INDIANA Wet Swale Wet Swale along US 113 – Maryland DOT State Highway Administration 25  HNTB r.-..n Nextlevel ~INDIANA Wet Retention Ponds • Can serve as peak flow mitigation BMP along with water quality BMP • Promotes settling of TSS and biological uptake of suspended pollutants • Design to permanently store the Water Quality Volume • Outlet structure and emergency spillway are required • Advantages – • Provide aquatic wildlife habitat • Can reduce velocities in downstream receiving water body • Can treat for other pollutants • Disadvantages • Water can be come stagnant • Attract nuisance insects • Vegetation requires proper pH levels • Require more maintenance compared to some BMPs • Larger footprint required 26    NTB r.-..n Nextlevel ~INDIANA Wet Retention Pond Example Wet Pond along MD 291– Maryland DOT State Highway Administration 27       HNTB r.-..n Nextlevel ~INDIANA Infiltration • Can be a swale or a basin • Collect run-off and allow it to drain through the underlying soil • Dependent on the existing underlying soil – soil testing required perguidelines provided in IDM Chapter 203 • Can be used to meet water quantity and water quality goals • Designed to infiltrate the Water Quality Volume • If used for peak flow mitigation, a computer model will be submitted per requirements in IDM Chapter 203 • If used for Water Quality only, equations can be used to calculate volume infiltrated and time to drain (provided in IDM Chapter 204) • Demonstrate the Water Quality Volume is infiltrated 28 >­"' J it~ 100-Year Water .... .S _ Surface Elevation _ y _ Water Quality Volume Water Surface Ele NTB Basin Banks w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w w Plan View Spillway Elevation* Outlet Pipe Basin Berm Cross Section Basin Berm Overflow Structure Offset Spillway if Channelized Riprap on Geotextile Along Spillway 10 Ft. *Spillway May be Channelized if Desired >­"' J .'c. u:'.Vl 100-Year Water .... .S _ Surface Elevation _ y __ Water Quality Volume Water Surface Ele 3 Inlet, Type F-7 for Design Storm 3:1 Maximum Side Slope Profile View Seasonal High Water Table Cross Section View Riprap on Geotextile Along Spillway Ditch I . 10 Ft •• I *Spillway May be Channelized if Desired r.-..n Nextlevel ~INDIANA Infiltration Basin and Swale Details 29        HNTB r.-..n Nextlevel ~INDIANA Hydrodynamic Separators • Proprietary post-construction BMP device • Many  other types available, Hydrodynamic Separators preferred for INDOT projects • Flow-through device • Use a swirl or vortex to remove solids and trash via gravity from run-off • Relatively small footprint • Maintenance is critical – frequent inspection and cleanout required • Design Criteria • TSS removal rates for INDOT projectswill come from the most current Certified TSS Removal Rates for each hydrodynamic separator from NJ DEP • Treatment train may be required to achieve desired pollutant removal • Other manufactured stormwater devices with TSS removal rates certified by NJ DEP will be considered for use 30   HNTB r.-..n Nextlevel ~INDIANA Implementation (under development) • DM Chapter 204 reference to Post-Construction BMP Guidance Document • Allow for modifications• Development of related modifications – standard specifications, pay items, other design manual chapters, standard specifications • Effective date/project development stage (TBD) • Evaluation to determine whether Post-construction BMPs are required is a legal requirement now • Infeasible to apply to projects beyond – ROW, Stage 2/3 design, ….? • Include in all projects currently being scoped • Include in all future scoping HNTB r.-..n Nextlevel ~INDIANA Questions Jessica Eichhorst, PE PM/Water Resources Engineer HNTB Corporation jeichhorst@hntb.com Sandra Bowman Mgr. Ecology and Waterway Permitting INDOT SBowman@indot.IN.gov 

INDOT DM Chapter 204: “Post- Construction Stormwater BMPs”

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INDOT DM Chapter 204: “Post- Construction Stormwater BMPs”

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