Calculating credits for stormwater and rainwater harvest and use/reuse
This page will be developed in Winter, 2016
| Recommended pollutant removal efficiencies, in percent, for infiltration BMPs. Sources. TSS=total suspended solids; TP=total phosphorus; PP=particulate phosphorus; DP=dissolved phosphorus; TN=total nitrogen | |||||||
| TSS | TP | PP | DP | TN | Metals | Bacteria | Hydrocarbons |
| Pollutant removal is 100 percent for the volume that is captured and infiltrated | |||||||
Credit refers to the quantity of stormwater or pollutant reduction achieved either by an individual Best Management Practice (BMP) or cumulatively with multiple BMPs. Stormwater credits are a tool for local stormwater authorities who are interested in
- providing incentives to site developers to encourage the preservation of natural areas and the reduction of the volume of stormwater runoff being conveyed to a best management practice (BMP);
- complying with permit requirements, including antidegradation (see [1]; [2]);
- meeting the MIDS performance goal; or
- meeting or complying with water quality objectives, including Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs).
This page provides a discussion of how infiltration practices can achieve stormwater credits. Infiltration practices include infiltration basins, infiltration trenches (including dry wells), and underground infiltration systems. The discussion does not include bioinfiltration and permeable pavement systems, unless specifically mentioned. To view the credit articles for other BMPs, see the Related pages section.
Contents
Overview
Stormwater and rainwater harvest and use/reuse systems capture and store runoff. This water is typically utilized for irrigation. This water is assumed to infiltrate. Credits for these BMPs are therefore similar to credits for other infiltration practices in that all water applied for irrigation and pollutants in that water are credited. The methodology differs, however, in that the water is captured instantaneously, but use of the water is dependent on the irrigation rate rather than the soil infiltration rate, as is the case with infiltration BMPs. If harvested water is used indoors, it may be discharged to a sewer system, to a septic drainfield, or to another stormwater BMP. Credits for these vary and are discussed below.
Pollutant removal mechanisms
Infiltration practices reduce stormwater volume and pollutant loads through infiltration of the stormwater runoff into the native soil. Infiltration practices also can remove a wide variety of stormwater pollutants through secondary removal mechanisms including filtration, biological uptake, and soil adsorption through plantings and soil media (WEF Design of Urban Stormwater Controls, 2012). See Other Pollutants, for a complete list of other pollutants addressed by infiltration practices.
Location in the treatment train
Stormwater Treatment Trains are comprised of multiple Best Management Practices that work together to minimize the volume of stormwater runoff, remove pollutants, and reduce the rate of stormwater runoff being discharged to Minnesota wetlands, lakes and streams. Because infiltration practices are designed to be off-line, they may either be located at the end of the treatment train, or used as off-line configurations to divert the water quality volume from the on-line system.
Related pages
- Overview for stormwater and rainwater harvest and use/reuse
- Design criteria for stormwater and rainwater harvest and use/reuse
- Construction specifications for stormwater and rainwater harvest and use/reuse
- Operation and maintenance for stormwater and rainwater harvest and use/reuse
- Water quality considerations for stormwater and rainwater harvest and use/reuse
- Environmental concerns for stormwater and rainwater harvest and use/reuse
- Cost-benefit considerations for stormwater and rainwater harvest and use/reuse
- Case studies for stormwater and rainwater harvest and use/reuse
- Calculating credits for stormwater and rainwater harvest and use/reuse
- Definitions for stormwater and rainwater harvest and use/reuse
- Requirements, recommendations and information for using Harvest and re-use/cistern as a BMP in the MIDS calculator
- Links for stormwater and rainwater harvest and use/reuse
- References for stormwater and rainwater harvest and use/reuse
- Technical support for stormwater and rainwater harvest and use/reuse