The State of Minnesota
Sustainable Building Guidelines (MSBG) Version 2.0

S.2 Stormwater Management

Intent
Minimize negative impacts on the natural site hydrologic cycle as much as possible by treating stormwater close to where it falls, reducing downstream impacts thereby improving the overall water quality and clarity, and recharging groundwater through infiltration as local soils and subsurface conditions allow and re-using stormwater wherever possible.

Required Performance Criteria
Runoff Rate:

A. 1. Control the quantity of runoff from the site to pre-settlement conditions for the 100 year 24 hour precipitation event (Note: Minneapolis 100 yr/24 hr = 5.9 inches [Source: NRCS TR-55]) and
2. There shall be no discharge from the site for a 1.25" rainfall based on the Rational Method (Source: MPCA Stormwater Manual, Chapter 1, Sections 1.1-5 and 6). Methods to achieve this shall be consistent with those found in the Minnesota Pollution Control Agency's "Minnesota Stormwater Manual".

B. Create micro catchments less than 1 acre and treat storm water at these 1 acre source points for a 2 year 1 hour storm event.

Runoff Quality:
C. For a 2 year, 24-hour rainfall event, provide treatment systems designed to remove 80% of the average annual post development Total Suspended Solids (TSS), by implementing Best Management Practices (BMPs) outlined in the handbook "Urban Small Sites Best Management Practices" (Metropolitan Council), "Protecting Water Quality in Urban Areas" handbook (Minnesota Pollution Control Agency), the "Minnesota Stormwater Manual" (Minnesota Pollution Control Agency), or the Local Governing Unit (LGU). All BMP treatment systems for subject site need to include safety factors, maintenance, and a back-up plan in case of failure. All manufactured devices require independent laboratory testing to confirm product claims.

D. For a 2 year, 24-hour rainfall event, provide treatment systems designed to remove 60% of the average annual post development Total Phosphorus (TP), by implementing Best Management Practices (BMPs) outlined in the handbook "Urban Small Sites Best Management Practices" (Metropolitan Council), "Protecting Water Quality in Urban Areas" handbook (Minnesota Pollution Control Agency), the "Minnesota Stormwater Manual" (Minnesota Pollution Control Agency), or the Local Governing Unit (LGU). All BMP treatment systems for subject site need to include safety factors, maintenance, and a back-up plan in case of failure.

E. NOT USED

F. NOT USED

G NOT USED

H. NOT USED

I. For Type D soils, abstract the difference in volume between the pre-settlement conditions and the proposed site conditions using the Rational Method for a 1.25" rainfall, which may be stored for irrigation, non potable uses, or other alternative purposes and/or transpired using proposed vegetation (e.g. trees, shrubs, herbaceous vegetation, green roofs, and green walls) with supporting calculations.

J. Sites' included within or adjacent to significant municipal or Local Governing Unit(LGU) potable well head protection areas may follow rules laid out in Section I.

K. All stormwater BMPs must have an Operations and Maintenance manual created which addresses all potential maintenance issues. Basins, ponds, and reservoirs must be cleaned of deposited materials two times per year minimum.

Infiltration Rate and Quality:
L. Maintain or increase infiltration rates from pre-project site conditions.

M. Provide treatment systems designed to remove solids and pollutants for on-site water quality to comply with "Urban Small Sites Best Management Practices" (Metropolitan Council).

Overall:
N. Implement a stormwater management plan that reduces impervious cover, promotes infiltration, and captures and treats the stormwater runoff from 90% of average annual rainfall using acceptable Best Management Practices (BMPs).

Note: Portions of this guideline are adapted from LEED Version 2.0.

Compliance Tools and Resources

• "Urban Small Sites Best Management Practices" (Metropolitan Council)
• "Protecting Water Quality in Urban Areas" handbook (Minnesota Pollution Control Agency)
• Minnesota Stormwater Manual" (Minnesota Pollution Control Agency)
• Local Governing Unit (LGU) BMPs for stormwater treatment systems
• MPCA Standards performance thresholds. www.pca.state.mn.us/water/standards
• Local Governing Unit (LGU) Water Quality Standards