Dry Detention-Recharge Basin

General Information

Applicable DEP Stormwater Management Policy Performance Standards

Standards #3 and #4. If sufficient additional storage and appropriate outlet structures are provided, recharge basins may also be used to meet Standard #2.

TSS Removal

DEP Credit:          

80%

Estimated Range from Literature:

>90%

Relative Cost

Construction:        Moderate to high; varies depending on types soils of contributing drainage area, soils at site of system, storage depth, and type of outlet structure

Maintenance:       Moderate to high

Potential Constraints to Use

• Depth to groundwater
• Depth to bedrock or other impermeable stratum
• Suitability of site soils for infiltration

Other Considerations

• May be combined with detention or extended detention
• Pre-treatment must be provided, to prevent clogging of soils surface by sediments in the influent storm water.
• Frequent maintenance may be required, to remove accumulated sediment and restore infiltrative capacity.
• Recharge systems can provide high levels of treatment of other pollutants, in addition to TSS removal.

Maintenance Requirements

• Inspect a minimum of twice annually.
• Periodic mowing of embankments
• Removal of woody vegetation from embankments
• Removal of debris from outlet structures
• Clean forebay as required.
• Clean basin of accumulated sediment as required.
• Clean flow control structures at least once annually, or as indicated by inspection.
• Maintain vegetation in healthy condition.

Primary Design References

MA DEP Technical Bulletin, (pending)

Schueler, 1987

Schueler, et. al., 1992

Young, et. al., 1996

Contributing Drainage Area

No specific upper or lower limits on drainage area

Storm frequency for design flow

Varies with system. Recharge systems are sized for recharging an annual volume, not an event storm.

Annual Recharge Volume

Compute annual recharge volume using methodology specified in DEP Technical Bulletin (see Primary Design References), or use an alternative method conforming to accepted engineering practice.

Required Storage Volume

Compute storage volume using methodology specified in DEP Technical Bulletin.

Design Recharge Rate

Determine recharge rate based on soil texture/hydrologic group as specified in Technical Bulletin, confirmed by on-site field testing; or use an alternative method conforming to accepted engineering practice.

Design Safety Factor

Surface systems shall be sized with a safety factor of 1.0 times the design recharge rate.

Maximum Draw-down Time

The basin should be designed to drain the design storage volume in 48 hours or less, using the design recharge rate times the applicable safety factor.

Maximum Depth of System

Depth of system shall be equal to or less than the depth permitting draw-down in the required time.

Depth to Bedrock or Impermeable Stratum

Minimum 0.6 meters (2 feet) below bottom of system, unless engineering analysis demonstrates that lesser separation is feasible.

Depth to seasonal high groundwater

Small systems: Minimum 0.6 meters (2 feet) below bottom of system.

Large systems: Groundwater mounding analysis may be required.

Pretreatment

Pre-treatment system required; provide 25% TSS removal prior to discharge to a surface recharge system. Use forebay or equivalent measure.

Velocity Dissipation at Inlet

Provide measures to dissipate velocity of flows into the recharge basin, to prevent erosion of basin interior.

Setback from slab foundation

3.0 meters (10 feet)

Setback from cellar foundation

6.1 meters (20 feet)

Setback from slope >15%

4.6 meters (15 feet) (top edge of system to top of slope), or as required for impoundment stability. Distance may need to be greater where potential for “break-out” and resulting slope instability may be a problem.

Setback from on-site sewage disposal system

15.2 meters (50 feet) (or greater, if required under 310 CMR 15.000 [Title 5])

Setback from private well

30.5 meters (100 feet)

Setback from groundwater supply

Zone I radius; additional setback may be required depending on hydro-geologic conditions

Setback from surface water supply

Zone A, and 30.5 meters (100 feet) from tributaries

Performance under frozen conditions.

Recharge basins should be designed to either:

• Provide for capture and recharge of required annual volume during the period April to December; or
• Provide for capture and recharge during the entire year, with provisions for introduction of recharged storm water into the ground under frozen conditions (e.g., through use of wick drains, leaching galleries, or chambers, or other measures).

Construction of infiltration surface

The infiltration surface shall be constructed to preserve and enhance the capability of the soil to pass flows from the basin into the groundwater.   Consider measures such as:

• Minimizing trafficking by heavy construction equipment
• Use of a minimum thickness of topsoil required to establish plantings
• Using a planted surface, rather than crushed stone or sand surface

Protection During Construction

Runoff from disturbed areas shall not be discharged to the recharge basin. The contributing site shall be completely stabilized, prior to placing the recharge basin in service.

Access for maintenance, repair, and rehabilitation

Design shall consider accessibility to system, and capability to replace system components, to provide for eventual repair and rehabilitation of the system.

Other

• Provide maintenance access, including access to basin interior
• Stabilize slopes as indicated for other impoundment-type BMPs
• Design embankment to meet applicable safety standards
• Provide emergency spillway as indicated for other impoundment-type BMPs
• Consider providing method to drain lowest stage in the event of clogging of infiltration surface, so that surface can be rehabilitated.