City of Quincy
The City of Quincy has enacted a Stormwater Management Ordinance in order to comply with state and federal regulations and to manage stormwater in a responsible and sustainable manner. The objectives of the ordinance are:
- Protect groundwater and surface water from degradation;
- Require practices that eliminate soil erosion and sedimentation and control the volume and rate of stormwater runoff resulting from land disturbances;
- Promote infiltration and the recharge of groundwater;
- Ensure that soil erosion and sedimentation control measures and stormwater runoff control practices are incorporated into the site planning and design process and are implemented and maintained;
- Require practices to control waste such as discarded building materials, concrete truck washout, chemicals, litter, and sanitary waste at the construction site that may cause adverse impacts to water quality;
- Comply with state and federal statutes and regulations relating to stormwater discharges; and
- Establish the City of Quincy’s legal authority to ensure compliance with the provisions of the ordinance through inspection, monitoring, and enforcement.
Examples of Structural and Non-Structural Stormwater BMPs
Water Quality Unit
Proprietary water quality units provide efficient removal of free oils, debris and total suspended solids (TSS) and are ideal for use within ultra-urban and constrained sites. Numerous products are available to achieve the required TSS removal efficiencies and can operate in an online or offline configuration. These manufacturers have followed rigorous testing as required by some local and state agencies. Although the Massachusetts Strategic Envirotechnology Partnership (STEP) recalled the Technology Fact Sheets that instructed local and state government officials regarding the technology used by various proprietary units last year, the Technology Acceptance and Reciprocity Partnership (TARP) Tier 2 Protocol and the New Jersey DEP Total Suspended Solids Laboratory Testing Procedure have become accepted sources of testing verification. Although not the main objective of a water quality unit some removal of other pollutants such as heavy metals, pathogens, and other nutrients may be achieved.
Subsurface Infiltration Basin (Subsurface Structure)
A subsurface infiltration basin is an underground stormwater LID feature that provides both water quality and quantity control by capturing, detaining, filtering and infiltrating stormwater runoff to the groundwater. The subsurface infiltration basin is designed to infiltrate the required water quality volume. The water quality volume is considered the volume stored within the basin below the lowest outletted invert elevation (elevation below the lowest pipe invert). The water quality volume is infiltrated or “recharged” into the ground, providing final treatment prior to entering the groundwater. If necessary, the basin can also be sized to provide water quantity control by attenuating the runoff and discharging through an outlet control structure at a controlled rate to reduce peak runoff rates. The use of subsurface infiltration basins are often limited by high ground water tables and/or poor subsurface soils. Pretreatment of the stormwater runoff entering the subsurface infiltration basin is required if the runoff originated from a paved surface that generates more than 1,000 vehicle trips per day (LUHPPL).
A bioretention basin is an LID site feature that provides water quality benefits prior to discharging to receiving waters. The bioretention basin treats stormwater using a specific planting soil bed mixture to naturally filter out pollutants. The bioretention basin has been designed to collect surface runoff from proposed pavement area. Pretreatment and energy dissipation can be provided prior to collecting in the bioretention basin by a gravel filter strip or a sediment forebay. The bioretention basin is designed to infiltrate the required water quality volume (i.e. typical average small storm events are infiltrated). In larger storm events where runoff volume is increased, runoff will flow into the bioretention basin and an overflow outlet will collect excess flows and convey them into the drainage system.
A sediment forebay is a BMP consisting of an excavated pit or bermed area designed to slow incoming stormwater runoff and facilitating the gravity separation of suspended solids. Sediment forebays can be used as a pretreatment device prior to infiltration. The sediment forebay volume is designed to hold 0.1-inch per impervious acre to pretreat the water quality volume.
A green roof is a permanent rooftop planting system containing live plants in a lightweight engineered soil medium designed to retain precipitation where the water is taken up by plants and transpired into the air. As a result, less water runs off the roof compared to conventional rooftops. Green roofs can range from extensive to intensive. Extensive roofs typically have shallow soil depths with low lying plants species and are not open to public access because they are installed to achieve an environmental benefit. Intensive roofs are installed to primarily achieve an aesthetic benefit and have deeper soil depths with taller plants species. Buildings that benefit from a green roof will incur energy savings, higher roof durability, reduction of stormwater runoff, reduction of heat island effects, and more appealing aesthetics.
Tree Box Filters
Tree box filters are mini bioretention areas installed beneath trees that can be very effective at controlling and filtering runoff and are well suited for urban environments. Runoff is directed to the tree box, where it is filtered by combination of vegetation and an engineering soil mixture (typically enclosed in precast concrete) before entering the stormwater conveyance system. The runoff collected in the boxes helps irrigate the tree. Tree box filters with an open bottom will also infiltrate stormwater runoff during smaller storm events and will bypass higher flows to the stormwater conveyance system.
Massachusetts Stormwater Management Standards Compliance
The MassDEP has developed ten stormwater performance standards for properties within Massachusetts.
1. No new stormwater conveyances may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth.
2. Stormwater management systems must be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates.
3. Loss of annual recharge to groundwater shall be eliminated or minimized through the use of infiltration measures including environmentally sensitive site design, low impact development techniques, storm water best management practices, and good operation and maintenance. At a minimum, the annual recharge from the post-development site shall approximate the annual recharge from pre-development conditions based on soil type. This standard is met when the stormwater management system is designed to infiltrate the required recharge volume as determined in accordance with the Massachusetts Stormwater handbook. .
4. Stormwater Management systems shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids (TSS). This standard is met when:
- Suitable practices for source control and pollution prevention are identified in a long-term pollution prevention plan, and thereafter are implemented and maintained;
- Structural storm water best management practices are sized to capture the required water quality volume determined in accordance with the Massachusetts Stormwater Handbook.
- Pretreatment is provided in accordance with the Massachusetts Stormwater Handbook.
5. For land uses with higher potential pollutant loads (LUHPPL), source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable. If, through source control and/ or pollution prevention, all land uses with higher potential pollutant loads cannot be completely protected from exposure to rain, snow, snow melt and storm water runoff, the proponent shall use the specific structural storm water BMPs determined by the Department to be suitable for such uses as provided in the Massachusetts Stormwater handbook. Stormwater discharges from land uses with higher potential pollutant loads shall also comply with the requirements of the Massachusetts Clean Waters Act.
6. Stormwater discharges within the Zone II or Interim Wellhead Protection Area of a public water supply and storm water discharges near any other critical area require the use of the specific source control and pollution prevention measures and the specific structural storm water best management practices determined by the Department to be suitable for managing discharges to such areas as provided in the Massachusetts Stormwater Handbook.
7. A redevelopment project is required to meet the following Stormwater Management Standards only to the maximum extent practicable: Standard 2, Standard 3, and the pretreatment and structural storm water best management practice requirements of Standards 4, 5 and 6. Existing Stormwater discharges shall comply with Standard I only to the maximum extent practicable. A redevelopment project shall also comply with all other requirements of the Stormwater management Standards and improve existing conditions.
8. A plan to control construction related impacts including erosion, sedimentation and other pollutant sources during construction and land disturbance activities (construction period erosion, sedimentation, and pollution prevention plan) shall be developed and implemented.
9. A long-term operation and maintenance plan shall be developed and implemented to ensure that stormwater management systems function as designed.
10. All illicit discharges to the storm water management system are prohibited.