Town of Easton, MA Chapter 200 Stormwater Management

[HISTORY: Adopted by the Annual Town Meeting of the Town of Easton 5-17-2021 ATM by Art. 13. Amendments noted where applicable.]

§ 200-1 Standards.

All development and redevelopment that results in a minimum of 40,000 square feet of land disturbance shall address any stormwater runoff during and after construction in accordance with the Town of Easton 2016 Municipal Small Separate Sewer System Permit (Easton MS4 Permit), as outlined in part 2.3.6 of the Easton MS4 Permit, and the MassDEP Stormwater Handbook as either may be amended. The following standards shall be met to protect the stormwater infrastructure in public ways and wetland resource areas. (All terms are defined in the MassDEP Stormwater Handbook.) Failure to comply with these standards may result in enforcement action and fines up to $300 per violation per day.

A. The area of land disturbance shall include sites less than 40,000 square feet if the site is part of a larger common plan of development or redevelopment which disturbs 40,000 square feet or greater.

B. Low Impact Development (LID) site planning and design strategies must be implemented unless infeasible in order to reduce the discharge of stormwater from development sites.

C. Stormwater management systems design shall be consistent with, or more stringent than, the requirements of the 2008 Massachusetts Stormwater Handbook.

D. Stormwater management systems on new development shall be designed to meet an average annual pollutant removal equivalent to 90% of the average annual load of Total Suspended Solids (TSS) related to the total post-construction impervious area on the site and 60% of the average annual load of Total Phosphorus (TP) related to the total post-construction impervious surface area on the site. Average annual pollutant removal requirements in the Easton MS4 Permit, section 2.3.6.a.ii.3, are achieved through one of the following methods:

(1) Installing Best Management Practices (BMPs) that meet the pollutant removal percentages based on calculations developed consistent with EPA Region 1's BMP Accounting and Tracking Tool (2016) or other BMP performance evaluation tool provided by EPA Region 1, where available. If EPA Region 1 tools do not address the planned or installed BMP performance, then any federally or State-approved BMP design guidance or performance standards (e.g., the MassDEP Stormwater Handbooks and design guidance manuals) may be used to calculate BMP performance; or

(2) Retaining the volume of runoff equivalent to, or greater than, one inch multiplied by the total post-construction impervious surface area on the new development site; or

(3) Meeting a combination of retention and treatment that achieves the above standards; or

(4) Utilizing off-site mitigation that meets the above standards within the same USGS HUC12 (watershed area) as the new development site.

E. Stormwater management systems on redevelopment sites shall be designed to meet an average annual pollutant removal equivalent to 80% of the average annual post-construction load of Total Suspended Solids (TSS) related to the total post-construction impervious area on the site and 50% of the average annual load of Total Phosphorus (TP) related to the total post-construction impervious surface area on the site. Average annual pollutant removal requirements in Easton MS4 Permit section 2.3.6.a.ii.4 are achieved through one of the following methods:

(1) Installing BMPs that meet the pollutant removal percentages based on calculations developed consistent with EPA Region 1's BMP Accounting and Tracking Tool (2016) or other BMP performance evaluation tool provided by EPA Region 1, where available. If EPA Region 1 tools do not address the planned or installed BMP performance, then any federally or State-approved BMP design guidance or performance standards (e.g., State stormwater handbooks and design guidance manuals) may be used to calculate BMP performance; or

(2) Retaining the volume of runoff equivalent to, or greater than, 0.8 inch multiplied by the total post-construction impervious surface area on the redeveloped site; or

(3) Meeting a combination of retention and treatment that achieves the above standards; or

(4) Utilizing off-site mitigation that meets the above standards within the same USGS HUC12 (watershed area) as the redevelopment site.

F. Redevelopment activities that are exclusively limited to maintenance and improvement of existing roadways (including widening less than a single lane, adding shoulders, correcting substandard intersections, improving existing drainage systems, and repaving projects) shall improve existing conditions unless infeasible and are exempt from Easton MS4 permit part 2.3.6.a.ii.4. Roadway widening or improvements that increase the amount of impervious area on the redevelopment site by greater than or equal to a single lane width shall meet the requirements of Easton MS4 Permit part 2.3.6.a.ii.4.