SAINTPAUL SUSTAINABLE BUILDING POLICY Saint Paul Sustainable Building Policy Training Module 7 Stormwater Management

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SAINTPAUL SUSTAINABLE BUILDING POLICY Stormwater Management Stormwater Basics Saint Paul Overlay – Stormwater Requirements Interpretation and Calculations for Requirements Verification and Summary of Submissions

SAINTPAUL SUSTAINABLE BUILDING POLICY Stormwater Basics Pavement and other hard surfaces cause excess rainfall to run off the landscape The rate, quality and volume of urban runoff are highly modified from natural conditions Urban runoff delivers pollutants to receiving waters such as lakes or rivers Paved areas prevent replenishment of local groundwater resources

SAINTPAUL SUSTAINABLE BUILDING POLICY Stormwater Basics Urban Impacts Waters are deemed ‘impaired’ when they are not able to support aquatic life or recreation. – Como Lake and the Mississippi River are impaired – Special studies (TMDLs) detail a pollution “diet” – Regulations enforce the pollution “diet” Various best management practices (BMPs) can be used to control urban stormwater runoff Integrated stormwater BMPs focus on rate, quality, and volume of runoff

SAINTPAUL SUSTAINABLE BUILDING POLICY Stormwater Basics Integrated Stormwater Management A complete look at: – Movement of stormwater runoff – Content of stormwater runoff Broad, multi-faceted approach – Rate – Volume – Quality – Groundwater impact

SAINTPAUL SUSTAINABLE BUILDING POLICY Saint Paul Overlay – Stormwater Requirements Stormwater requirements address Rate control Water quality improvement Infiltration rate Stormwater requirements are the same across different sustainable building standards – Developer selected rating system does not affect how stormwater shall be managed on-site

SAINTPAUL SUSTAINABLE BUILDING POLICY Saint Paul Overlay – Stormwater Requirements Site Eligibility: Sites with ¼ acre or more of total land disturbance Rate Control: 1.64 cubic feet per second (cfs) /acres disturbed Water Quality Management: 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) and remove 60% of the average annual post development Total Phosphorus (TP)… Infiltration Rate: Maintain or increase infiltration rates from pre-project site conditions Operation and maintenance: All practices must have an “O and M” plan

SAINTPAUL SUSTAINABLE BUILDING POLICY Interpretations and Calculations Extenuating circumstances at sites may warrant the need for case-by-case interpretation and application Interpretations – Provide guidance on how the stormwater requirements shall be interpreted – Guidance indicates the context and manner in which the stormwater controls shall be applied Calculations – The mechanics of calculating, sizing and demonstrating compliance with requirements

SAINTPAUL SUSTAINABLE BUILDING POLICY Site Eligibility Sites with ¼-acre or more of total land disturbance Land disturbance means: – Disturbance to the land that may result in soil erosion and the movement of sediments into surface waters, drainage systems or onto adjacent properties, including clearing, grading, filling and excavating except for disturbances resulting from the construction or maintenance of public roads and utilities – Same as definition for “construction activity” in City Code Chapter 52.

SAINTPAUL SUSTAINABLE BUILDING POLICY Process Approval is typically handled via the City’s Site Plan Review committee – Public Works Sewer Utility approves rate control – City’s Water Resource Coordinator approves water quality and/or infiltration rate A stormwater management plan for the site must be submitted as part of the approval package

SAINTPAUL SUSTAINABLE BUILDING POLICY Rate Control Interpretation Administered by Department of Public Works – Sewer Utility Requirement is codified – City Code 52.04(c) – City Code (a) – City Code (b) Q = 1.64 x A Q = the maximum acceptable discharge rate in cubic feet per second (cfs) A = the site area in acres All storms up to 100- year critical event

SAINTPAUL SUSTAINABLE BUILDING POLICY Rate Control Calculation Stormwater Management Worksheet – Data for each drainage area – On-site detention – Detention data – Pipe size and elevation HydroCAD used by city to check for conformance with stormwater management requirements

SAINTPAUL SUSTAINABLE BUILDING POLICY Infiltration Rates “Maintain or increase infiltration rates from pre- project site conditions” Options for demonstrating conformance: – Evaluate site imperviousness, or – Abstract rainfall in accordance with Watershed District volume control rule Site imperviousness as surrogate for infiltration rate assessment – Site imperviousness directly influences annual average runoff volume – As imperviousness increases, infiltration rate decreases

SAINTPAUL SUSTAINABLE BUILDING POLICY Infiltration Rate: Interpretation Infiltration at sites may be constrained by factors such as: – Soil contamination – Depth to bedrock – High seasonal groundwater table Constrained sites must – clearly demonstrate limitations – provide increase in infiltration rate by decreasing site imperviousness – include water quality treatment capacity via filtration or other similar mechanism – address rate control

SAINTPAUL SUSTAINABLE BUILDING POLICY Infiltration Rate: Calculation Option A – Site Imperviousness – B3 Minnesota Sustainable Building Guidelines – Appendix S-4 Site Water Infiltration Calculator Option B – Volume Control – Watershed District volume control worksheet – Automatically satisfies water quality management requirement

SAINTPAUL SUSTAINABLE BUILDING POLICY Water Quality Management Requirement NOTE: If project is conforming with Watershed District volume control approach, the water quality management requirement is satisfied. 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) – 60% of the average annual post development Total Phosphorus (TP) By implementing Best Management Practices (BMPs) outlined in – “Urban Small Sites Best Management Practices” handbook (Metropolitan Council), – “Protecting Water Quality in Urban Areas” handbook (Minnesota Pollution Control Agency), – “Minnesota Stormwater Manual” (Minnesota Pollution Control Agency). 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.

SAINTPAUL SUSTAINABLE BUILDING POLICY Water Quality Management Interpretation 2 year, 24-hour rainfall = 2.5 inches Assumes that 80% annual reduction in TSS will provide 60% reduction in TP, and vice-versa Reduction can be met by equivalently treating off-site run-on to the site.

SAINTPAUL SUSTAINABLE BUILDING POLICY Water Quality Management Calculation Pollutant reduction estimates based on Appendix L of Minnesota Stormwater Manual – Five step process – Focuses on phosphorus as key pollutant If treating off-site run-on, must provide separate 5-step evaluation to demonstrate load reductions are met.

SAINTPAUL SUSTAINABLE BUILDING POLICY Operation and Maintenance Plan must provide detailed description Who is responsible for overall operation and maintenance – Name, contact information, – Signature acknowledging responsibility How it will be maintained What is anticipated frequency of inspection and maintenance schedule

SAINTPAUL SUSTAINABLE BUILDING POLICY Verification Compliance with stormwater requirements must be verified Requirements are uniform across rating systems, so verification is uniform Rate Control – Verified using HydroCAD and receipt of as-builts for structural devices Water Quality – Verified by receipt of as-builts Infiltration Rate – Verified by receipt of as-builts and / or post-construction certification by owner of reduced impervious cover

SAINTPAUL SUSTAINABLE BUILDING POLICY Summary of Submittals Stormwater Management Plan – Drainage figures and narrative overview – Rate Control: Public Works calculation sheet – Infiltration Rate: Option A – Site Imperviousness (MSBG Appendix S-4) Option B – Watershed District volume control worksheet – Water Quality: MSM Appendix L Method Operation and Maintenance Plan

SAINTPAUL SUSTAINABLE BUILDING POLICY End of Module 7