4.08 Stormwater Management

1. General Provisions.
   a. All Applications, regardless of whether the project is subject to the Wetlands Protection Act or not, shall design the stormwater management system in compliance with the goals and objectives of the Massachusetts Department of Environmental Protection Stormwater Management Policy (DEP SMP) to the greatest extent possible given the specific site constraints of each site. These apply to industrial, commercial, institutional, residential subdivision, and roadway projects, including site preparation, construction, redevelopment, and on-going operation. The Applicant shall submit a completed and endorsed Stormwater Management Form (SMF) that indicates compliance to the greatest extent possible, with the SMP's nine (9) Stormwater Management Standards, as most recently amended. The applicant shall also provide calculations indicating compliance with each standard. Refer to the DEP SMP and its referenced sources for specific application of these stormwater management categories.

   There are five general categories of SMPs listed as follows:
   (a) conveyance

   (b) detention

   (c) extended detention

   (d) infiltration

   (e) water harvesting

   b. There shall be no negative impact from drainage on abutting properties, nor any negative impact to any public or private water supply or designated potential future supply.

   c. Whenever possible, irrigation water shall be derived from sources other than the Devens water system, including "gray water," re-used water, detained treated stormwater (stormwater harvesting), roof drainage, or water from on-site wells. "Gray water" is water from sinks, showers, dishwashers, and washing machines. On-site cisterns may be installed to store water for irrigation.

2. Concepts for stormwater management.
   a. The stormwater management objective is to replicate natural conditions of infiltration, evapotranspiration, and runoff whenever possible. In typical natural conditions, approximately 50 percent of stormwater infiltrates, 40 percent leaves land through evapotranspiration, and ten (10) percent as runoff.

   b. For all stormwater improvements, drainage calculations shall be prepared by the applicant's engineer in accordance with the DEP SMP requirements to the greatest extent possible given the specific site constraints of each site, and shall include design criteria, pre- and post-development drainage areas, and other information to verify the size and effectiveness of the proposed stormwater management technique. "Pre-development" drainage areas shall be considered to be "green fields" regardless of any development or improvements on the site at the time of application. Calculations shall be made separately for each drainage facility, showing its location, the total upstream drainage area, the underlying soil types and the flow paths for the times of concentration, the design runoff, facility size, slope, and capacity and velocity of water through all the site drainage system.

3. Design standards and criteria: All designs shall adhere to the following requirements:
   a. The DEC generally encourages stormwater infiltration alternatives which improve groundwater quality (e.g. biofiltration basins, vegetated swales) prior to the stormwater being directly discharged into the basins. The DEC encourages applicants to utilize stormwater management facilities for irrigation purposes.

   b. The post-development peak rate of stormwater discharge off-site shall not be greater than the pre-development peak rate of stormwater discharge for the 2, 10, 25, and 50-year storm events from any point of discharge on the site. No point source discharges within 25 feet of a resource area shall be allowed.

   c. Sideslopes above the design water level shall be provided at a slope of 3:1 (horizontal to vertical) or flatter except as permitted otherwise, conforming to the slope of the existing topography without abrupt or unnatural breaks in slope, unless otherwise permitted within 974 CMR 3.00.

   d. Banks of wet ponds, swales not within maintained landcaped areas (such as lawns or parking lots), and other channels shall be vegetated with woody plant material within ten feet of the high water elevation and with herbaceous plant material at the edge of the pond at the high water elevation.

   e. Shelves below the design water elevation (as described in the Devens Stormwater Pollution Prevention Plan) shall be vegetated with wet area tolerant native plant species at a density needed to establish full coverage by the next growing season. Plant plugs or prevegetated coir-mesh blankets/carpets are recommended methods.

   f. Recommended post-construction erosion control methods include polyethylene geotextile erosion control fabrics staked or anchored to the slope, with loose weave to allow vegetative cover to be established, such as Mirafi 140N, manufactured by Lelanese Fiber Marketing Co., NY, NY or approved equal, or coir fascine logs such as Fiber Rolls, manufactured by King Fiber or approved equal. Vegetative cover shall consist of native woody plant species installed as live brush or nursery stock, or native grasses.

4. Design standards and criteria for detention/retention/recharge basins: Stormwater basins and associated fixtures shall be designed to meet the following criteria:

   a. The design shall minimize basin sizes by creating smaller basins using smaller catchment areas contributing to each basin. The Applicant shall make all reasonable efforts to minimize the extent of disturbance to natural or reestablished vegetated treed areas. The Applicant shall demonstrate to the DEC why alternative areas or alternative stormwater management design methods are not appropriate if disturbed areas for stormwater management detention/retention basins exceed 5,000 square feet per basin.

   b. In parcels with undulating topography consisting of medium to high relief, basins shall be located in naturally occurring low spots on the site. Plan configuration of the basins shall complement the major natural topographic movement of the site (see 974 CMR 3.06(4) Figure D). Rigid plan geometries (see 974 CMR 3.06(5) Figure E) for the basins shall be avoided unless the basin's geometry complements the overall design concept of the Site Plan.

   c. In parcels with low topographic relief, the configuration of the basins shall be designed to avoid rigid geometries unless the layout complements the overall design concept of the Site Plan.

   d. Banks steeper than 3:1 (horizontal to vertical) shall be used only to tie into headwall/outfall structures. The applicant shall specify post-construction erosion control methods for slopes steeper than 3:1. Rip-rap/trap rock solutions shall not be acceptable, except as water dissipaters below storm water outfalls or as channel liners for steep swales.

   e. Steep slopes shall transition to slopes of less than 3:1 as quickly as possible to minimize areas of potential erosion problems.

   f. All basins shall have an emergency outlet to accommodate storm flows in excess of the 100-year storm event.

   g. Basins/infiltration structures shall be designed using the Natural Resources Conservation Service (NRCS, formerly Soil Conservation Service) TR-20 methodology in accordance with the DEP SMP.

   h. The floor of all basins/infiltration structure/swales shall be designed a minimum of two feet above the spring high groundwater elevation. Spring high groundwater testing shall be conducted before the basin design at the proposed location of each basin in compliance with Title V (310 CMR Section 15.103), as most recently amended or reliable data pursuant thereto shall be provided.

   i. A falling head soil permeability test shall be conducted in retention/infiltration basins before the basin design in all basins and infiltration structures. Percolation tests are permitted where soil allows a percolation rate of 2 minutes per inch or faster.

   j. Percolation tests shall be conducted in detention basins before the basin design and shall be conducted in compliance with Title V (310 CMR Section 15.105), as most recently amended.

   k. The DEC may require stormwater detention/retention basins to be fenced and/or screened if it determines that safety or appearance require such measures.

5. Closed Drainage Systems.
   a. Open-drainage swale systems are encouraged in smaller parking lots not subject to truck traffic, truck and container storage, and other railroad related vehicles.

   b. When utilized, Closed Drainage Systems (CDS) and swales shall be designed to accommodate the 25-year storm event based on the Rational Method without surcharging. The CDS shall be designed in accordance with the DEP SMP. Intensity/duration/frequency curves for the area, as presented in Technical Paper 40 of the National Weather Service, shall be used in the drainage design calculations. The minimum time of concentration shall be five minutes.

   1. All drainage structures shall be constructed of pre-cast concrete.
   2. Catch basins shall have oil traps and provide a four-foot sump.
   3. Details for all drainage structures shall be provided.
   4. Flow capacities shall be calculated, using two feet per second (fps) minimum velocity and 10 fps maximum velocity under a 2-to-25 year design storm event. The designer shall account for partial pipe flow capacities, if applicable to the design.
   5. Catch basin to catch basin connections are prohibited in paved areas.

6. Monitoring and Maintenance of Stormwater Facilities. All Applicants shall agree to comply with a monitoring and maintenance schedule for stormwater management systems.

7. Water Resources Protection Districts.
   (a) All Applications shall comply with the By-Laws, the DEP Stormwater Management Policy, March 1997 (as it may be revised), and the Devens Water Resources Protection Report, November 1994. The By-Laws (Article XI) and the Devens Water Resources Protection Report state the requirements for Water Conservation Measures, Storage and Application of Deicing Materials, Transportation of Hazardous Materials and Waste, Hazardous Waste and Materials, Storage Tanks, Radioactive Materials and Medical/Research Wastes, Floor Drains, and Pesticides and Herbicides. All development shall utilize current Best Management Practices (BMPs) as most appropriate to the site conditions and in keeping with the DEP SMP and the BMPs in the Devens Water Resources Protection Report. Provision of appropriate BMPs will further the goals of pollutant reduction of total suspended solids, petroleum hydrocarbons, lead, zinc, copper, and total nitrogen as outlined. Appropriate BMPs shall be selected dependent on site specific conditions and consideration of the level of protection needed in the Watershed, Aquifer, Zone II and Zone I Districts. The BMP's and protective measures for the three overlay districts created in the By-Laws (Article X, Section C) increase progressively from the Watershed, to the Aquifer, to the Zone II districts (with the Zone II having the most extensive requirements). The Zone II requirements are therefore inclusive of those for the Watershed and Aquifer districts, while the Aquifer includes the Watershed requirements.

   (b) All Applications shall also comply with the following:

   1. All Districts/Zones. Best Management Practices (BMP) selection(s) shall be used that are considered acceptable per the DEP Stormwater Management Policies, as most recently amended. All proposed BMPs shall comply with the restrictions (prohibition, setbacks, etc.) for each districts/zones as recommended in the Stormwater Management Policies.

   2. Aquifer District. The following requirements also apply in addition to the requirements previously stated:
      a. The applicant shall prepare a Hazardous Material Spill Response Plan to indicate methods for the interception and isolation of potential spills of hazardous materials. Clean-up of spills shall be completed in accordance with the Hazardous Material Spill Response Plan or as specified in the Devens Spill Prevention Control and Countermeasure Plan.

      b. Proposed developments within the Aquifer District shall be designed to maintain the high level of water quality at Devens and within the District. A Groundwater Quality Monitoring Plan (GWQMP) shall be developed for Site Plans involving a use of an industrial nature and/or use involving the handling, treatment, storage, or generation of hazardous waste defined under State Regulations in excess of those quantities allowed as a Very Small Quantity Generator.

      The GWQMP shall include the following information as a minimum:

      i. Determination of the overall hydrogeological profile of the site and the area in general;

      ii. Determination of groundwater flow direction and elevations through the impacted area of the site;

      iii. Determination of up-gradient monitoring well locations;

      iv. Determination of down-gradient monitoring well locations;

      v. Sampling objectives;

      vi. Sampling collection and analysis summary;

      vii. Chain of custody, and quality control/quality assurance procedures for testing;

      viii. Sampling frequency; and

      ix. Pollutant-testing parameters and methods of testing. Pollutant-testing parameters shall include as a minimum, EPA Priority Pollutants, total petroleum hydrocarbons (as required by ASTM D3328-78), metals (lead, zinc, copper), oil and grease, pH, and other pollutants consistent with the activities associated with the proposed use required to ensure that the development will not degrade water quality as determined by State and Federal drinking water quality standards.

   3. Per the DEP SMP, post-development volume of discharge shall not exceed the pre-development volume of discharge for the two and ten year storm events. Stormwater recharge must be provided to maintain or exceed pre-developed levels of recharge for the two year storm event. In the absence of hydrogeologic analysis, stormwater systems that have been designed to recharge the increased volume of a two-year storm event will be presumed to have met this criterion. If the site geology is unsuitable (for example, glacial till), the applicant shall consider other stormwater BMP's to meet this requirement. If none others prove feasible, this requirement may be waived by the DEC, based on provision of sufficient data by the applicant.

   4. Zone II. The following requirements also apply in addition to the requirements previously stated:
      a. The applicant shall utilize BMP's for the predicted stormwater removal guidelines for total suspended solids (TSS), petroleum hydrocarbons, lead, zinc, copper and nitrogen from runoff prior to ground water recharging and/or stormwater discharging from the site. Water quality evaluations shall be based on a two year storm event. Biofiltration systems should be considered as part of the strategy for pollution mitigation.