Proposed Stormwater Management Regulations: 314 CMR 21.00

Transcription

1 Proposed Stormwater Management Regulations: 314 CMR Stormwater General Permit Requirements Engineering Perspective Craig C. Lizotte, P.E. Manager of Land Development

2 Stormwater General Permit What and When Intended to help improve water quality by treating and infiltrating stormwater Target sites with > 5 Acres Regulated Impervious Area (RIA) State Wide > 2 Acres RIA in TMDL Areas Details for compliance to be in: RIA General Stormwater Permit Workbook Out for public comment, summer 2009 Promulgation late 2009 early 2010 Source: Riverways Website Source: Charles River Watershed Website

3 Stormwater General Permit Requirements All existing sites: baseline performance standards No retrofits required for non TMDL sites New development of RIA Install LID techniques and stormwater BMPs to meet Standards 3-6 of MA Stormwater Management Standards Redevelopment of RIA Install LID BMPs that maintain existing peak rate, recharge and treatment Include infiltration of at least 40% of the redevelopment volume TMDL areas: stormwater discharges from RIA Infiltration BMPs for pollutant reduction required by TMDL

4 Baseline Performance Standards: All Sites All sites: baseline performance standards (Threshold: 5 acres or 2 acres impervious intmdl area) Stormwater Management Plan & Team Operation and Maintenance Plan Snow & deicing practices management plan Pavement sweeping 2X per year Self Certification forms and fees -180 days

5 Stormwater General Permit Requirements Redevelopment of > 5 acres Redevelopment of RIA Redevelopment includes some level roof and pavement repair Install LID BMPs that maintain or enhance existing: Peak discharge rate, recharge volume, water quality treatment Include infiltration of at least 40% of the redevelopment volume Redevelopment volume = recharge volume or the WQV (whichever is greater) Details/clarification on implementation and calculation needed If infiltration not possible, enhanced treatment or reduction of impervious area required Off-site mitigation allowed Variance if cant comply

6 Stormwater General Permit Requirements New Development >5 acres New development of RIAs > 5 acres Development definition is for pavement and/or roof Install LID techniques and stormwater BMPs that can meet Standards 3-6 of the Massachusetts Stormwater Management Standards Standard 3: Recharge. Post development recharge to approximate existing recharge (issue: permeable pavement considered impermeable) Standard 4: TSS Removal. Post development annual removal of 80% TSS loads Standard 5: Land Uses with Higher Potential Pollutant Loads (LUHPPLs) Standard 6: Water Quality Discharge to Critical Areas, ORWS, Drinking Water Supplies, Etc. Requirements generally same as WPA stormwater management standards, but... Will include some upland sites not under WPA Site development is not the trigger but it is the size of roof and/or pavement being developed Off-site mitigation not allowed

7 TMDL Areas: Additional Requirements Existing Sites Existing sites: TMDL areas Stormwater discharge from RIA > 2 acres Retrofits for infiltration BMPs for pollutant reduction required by TMDL Pollutant reduction based on TMDL (65% phosphorous in Charles River) 4.5 years for retrofit design 10 years for construction completion Off-site mitigation allowed

8 TMDL Areas: Additional Performance Standards for Redevelopment/Development Sites Redevelopment/Development of RIAs in TMDL areas > 2 acres In addition to the 65% phosphorous reduction these sites must meet the performance standards for >5 acres sites previously identified.

9 Ssource: Stormwater BMP Manual EPA/Tetratech Pollutant Reduction Calculators Use EPA's "BMP Performance Curve" model to estimate pollution reduction from BMPs 8 BMPs identified: infiltration basin, infiltration trench, gravel wetland, porous pavement, wet pond, dry pond, bioretention, grass swale Removal based on soil type, land use, BMP type and runoff volume directed to BMP BMPs must be designed in accordance with the Stormwater Management Handbook

10 What Does This Mean to You? Regulations still in draft form Non-TMDL areas: more formalized requirements for O&M, new annual compliance efforts New development or redevelopment (Non TMDL): Increased applicability of stormwater management standards. TMDL Areas: retrofits required, must comply with TMDL treatment requirements.

11 Existing Conditions

12 Stormwater Retrofit, Suitable Soils

13 Stormwater Retrofit, Unsuitable Soils