Extended Detention Practices Table 4a Justin Reinhart, PE Division - - PowerPoint PPT Presentation

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Extended Detention Practices Table 4a Justin Reinhart, PE Division - - PowerPoint PPT Presentation

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Extended Detention Practices Table 4a Justin Reinhart, PE Division of Surface Water Northeast Ohio Stormwater Training Council Cleveland, Ohio Richfield, Ohio July 12, 2018 July 25, 2018 Table 4a Extended Detention Post-Construction

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Extended Detention Practices Table 4a

Justin Reinhart, PE Division of Surface Water

Northeast Ohio Stormwater Training Council Cleveland, Ohio Richfield, Ohio July 12, 2018 July 25, 2018

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  • What did the Construction General Permit change ?
  • What may change in the RWLD manual ?
  • Common issues / challenges

Table 4a Extended Detention Post-Construction Practices with Minimum Drain Times Extended Detention Practices Minimum Drain Time of WQv Wet Extended Detention Basin1,2 24 hours Constructed Extended Detention Wetland1,2 24 hours Dry Extended Detention Basin1,3 48 hours Permeable Pavement – Extended Detention1 24 hours Underground Storage – Extended Detention1,4 24 hours Sand & Other Media Filtration – Extended Detention1,5 24 hours

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Dry Extended Detention Basin

What did the permit change ?

– Allows for acceptable pretreatment in place of a forebay and micropool. – Must include a protected outlet.

What will be changing in the RWLD Manual ?

– Standards for acceptable pretreatment practices and protected

  • utlet. (Appendix 10)
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Dry Extended Detention Basin

Acceptable alternatives must be equivalent to a forebay & micropool:

– Remove 50% of annual TSS load. – Require minimal maintenance and oversight for long-term functioning of the extended detention volume. – Prevent scour/erosion at pipe outfalls.

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Pretreatment Alternatives

Grass Swale

  • Vel. ≤1 ft/s @ d ≤ 4 in.

W = 4 ft. to 8 ft. L ≥ 50 ft. S ≤ 4% (< 1% may be an issue)

IMAGE SOURCE: VA DEQ Stormwater Design Specification No. 10

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Pretreatment Alternatives

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Pretreatment Alternatives

Grass Filter Strip Full width of pavement L ≥ 10 ft. Dense turf

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Pretreatment Alternatives

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Pretreatment Alternatives

Still need erosion/scour protection at basin inlet. Manufactured Treatment Device

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SLIDE 10

Pretreatment Alternatives

Deep Sump Trap or Catch Basin Possible for small drainage areas:

parking lot catch basin (6 ft dia.) 4 ft x 28.3 ft2 = 113 ft3 @ 10%, WQv = 1,132 ft3 ~ 1,600 ft2 max. impervious d.a.

IMAGE SOURCE: USEPA

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Dry Forebay… Possibly

  • Not much research
  • Need to develop standards
  • May need test sites
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Dry Forebay… Possibly

Permeable Dike 10% - 20% WQv

Concept based on: UDFCD, Urban Storm Drainage Criteria Manual Vol. 3 (2015)

72-hr Drawdown ?

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SLIDE 13

Dry Forebay… Possibly

IMAGE SOURCE: NJ Stormwater BMP Manual, Chapter 9.5 Infiltration Basins

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Dry Forebay… Possibly

Concrete Impermeable Dike Weep Hole / Pipe

Concept based on: New Jersey Stormwater Manual, Chapter 9.5

72-hr Drawdown ?

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Protected Outlet

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Protected Outlet

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Protected Outlet

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Protected Outlet

Micropool Micropool Micropool

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Protected Outlet

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Protected Outlet

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Protected Outlet

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Protected Outlet

IMAGE SOURCE: www.ads-pipe.com/products/pipes/advanedge-panel/advanedge-site-drain-pipe

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Protected Outlet

“The filter under drain system at Carver County dry detention pond exhibited poor hydraulic performance and failed to keep the pond dry between the storm events.” “Continual maintenance is required to maintain the filter system in an operational condition.”

  • Minnesota DOT. 2006. Water Quality Performance of Dry Detention

Ponds with Under-Drains. Mn/RC-2006-43.

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Protected Outlet

Agricultural “blind inlet” to field tile 24-hr drawdown

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Protected Outlet

“designed to catch sediment and therefore, eventually fail and require maintenance”

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Dry Extended Detention Basin

Pool Volume = WQv + 20% sediment Pool Volume = WQv + 10% forebay + 10% micropool

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Wet Extended Detention Basin

What did the permit change ?

– Permanent pool volume and extended detention volume are now both equal to the WQv (was ¾ WQv).

What will be changing in the RWLD Manual ?

– Not much.

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SLIDE 28

+20% Sediment Storage +20% Sediment Storage ≥ WQv ≥ WQv

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Extended Drawdown

  • Wet & underground: 24-hour minimum
  • Dry: 48-hour minimum
  • Shall not discharge more than the first half of the WQv

in less than one-third of the drain time.

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown

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Extended Drawdown – 2” Min.

  • As designed, the acre basin with a 1⅝ in. diameter orifice.
  • What if the local authority has a minimum 2 in. orifice

diameter requirement ?

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Extended Drawdown – 2” min.

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SLIDE 39

Extended Drawdown – 2” min.

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Underground Stormwater Management Systems

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Underground Stormwater management Systems

What did the permit change ?

– Added infiltrating and extended detention USMS as standard practices pre-approved for general use. – Requires pretreatment at verified efficacy.

What will be changing in the RW&LD Manual ?

– Provisional standard has been posted. – Welcome input.

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USMS – Ext. Det. Pretreatment

  • Verified 50% TSS removal.
  • Can use NJDEP list.
  • Max treatment flow rate/hydraulic loading @ WQf.
  • Size according to each inlet.
  • Can be used in parallel, but does not increase TSS

removal.

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Infiltrating System

Pre-T 80% TSS @ WQF Verified

  • Infl. Rate

Flood Control Outlet

Open System

WQv @ d ≤ IWS No Sediment Storage Flood Control Volume

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Extended Detention System

Pre-T WQ, FC & Overflow Outlets

All Solid Wall

Wet Sump (20% Sediment) WQv Flood Control Volume 50% TSS @ WQF

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Extended Detention System

Pre-T Wet Sump (20% Sediment)

Lined

Contained WQv WQ Outlet Flood Control Volume . Flood Control & Overflow Outlets 50% TSS @ WQF

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Extended Detention System

Pre-T Infiltration

Partially Infiltrating

Flood Control Volume Wet Sump (20% Sediment) Outlets WQv above IWS 50% TSS @ WQF

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Multiple Entry Points

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Multiple Entry Points

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Multiple Entry Points

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WQ Outlet Configuration

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Maintenance Feasibility

  • Access manholes at inlet,
  • utlet and within storage as

necessary for cleaning.

  • Observation wells.
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Maintenance Feasibility

  • Costs ?
  • Depth ?
  • Surface Accessibility ?
  • How Often ?
  • How ?

SOURCE: “Maintaining Stormwater Systems”, Northern Virginia Regional Commission, 2007

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SLIDE 53

Post-Construction O & M Plan

site map w/ stormwater infrastructure

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Storm Water Technical Assistance justin.reinhart@epa.ohio.gov 614-705-1149