MS4 Permit Stormwater Retrofit


Purpose/Function:

Stormwater retrofit goals may include, among other things, the correction of prior design or performance deficiencies, flood mitigation, disconnecting impervious areas, improving recharge and infiltration performance, addressing pollutants of concern, demonstrating new technologies and supporting stream restoration activities.

Initiation protocol:

Retrofits include new installations or upgrades to existing BMPs in developed areas where there is a lack of adequate stormwater treatment.

Public acceptance:

The public is likely unaware of the permit requirements to upgrade urban infrastructure and this practice is perceived as maintenance to existing facilities.

Implementation Factors (level of difficulty):

Difficult. Requires engineering and engagement with U.S. Environmental Protection Agency officials to ensure permit compliance. This work is typically carried out within local departments of public works or similar responsible parties.

Funding Sources / Options:

Utility fees are the most common form of funding for these upgrades.

Costs:

Cost Estimates EPA Average
Initial $26,632 $26,632
Annual $290 $290
Lifespan (yrs) 20 20
Annualized $1,621.60 $1,621.60

Load Reduction Efficiency:

Total Nitrogen removed per acre treated per year

Low

1.67 lbs.

Medium

2.73 lbs.

High

4.83 lbs.

Cost per pound removed = between $336 and $970

Total Phosphorous removed per acre treated per year

Low

0.20 lbs.

Medium

0.30 lbs.

High

0.40 lbs.

Cost per pound removed = between $4,053 and $8,159

Total Suspended Solids removed per acre of practice per year

Low

83 lbs.

Medium

388 lbs.

High

573 lbs.

Cost per pound removed = between $2.83 and $19.48

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