City of Boston
The City of Boston has enacted Storm Water Ordinances in order to comply with state and federal environmental regulations. The City of Boston is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Boston will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The City of Boston, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Boston has the authority to inspect stormwater facilities and practices in order to ascertain that they properly maintained and functioning.
MASSACHUSETTS STORMWATER STANDARDS
In 1996, the Massachusetts Department of Environmental Protection (the “Department” or “MassDEP”) issued the Stormwater Policy that established Stormwater Management Standards aimed at encouraging recharge and preventing stormwater discharges from causing or contributing to the pollution of the surface waters and ground waters of the Commonwealth. In 1997, MA DEP published the Massachusetts Stormwater Handbook as guidance on the Stormwater Policy. In 2008, MA DEP revised the Stormwater Management Standards and Massachusetts Stormwater Handbook to promote increased stormwater recharge, the treatment of more runoff from polluting land uses, low impact development (LID) techniques, pollution prevention, and the removal of illicit discharges to stormwater management systems, and improved operation and maintenance of stormwater best management practices (BMPs).
The Stormwater Management Standards address water quality (pollutants) and water quantity (flooding, base flow and recharge) by establishing standards that require the implementation of a wide variety of stormwater management strategies. These strategies include environmentally sensitive site design and LID techniques to minimize impervious surface and land disturbance, source control, and the long-term operation and maintenance of stormwater management systems.
There are fewer options for stormwater BMPs for heavily urbanized areas like the City of Boston and the BWSC MS4. The primary barrier to BMP implementation is a lack of physical space. This limitation eliminates many space-intensive options (i.e., extended dry-detention basins, wet ponds) and makes BMPs that could be used on a micro-scale level more feasible. When proposing BMPs for redevelopment BWSC will consider potential engineering concerns such as the redevelopment’s connection to existing storm drain infrastructure, ensure available head, hydraulic grade lines and will review the impacts of possible pipeline bottlenecks that may increase flooding potential. The presence of underground utilities, including gas and water mains, sewer pipes and electric cable conduits in the City of Boston, will also reduce the available space or land suitable for BMPs. Given the many constraints an ultra-urban environment like the City of Boston presents; managing stormwater with redevelopment BMPs is the most feasible option for BWSC.
Stormwater Management Standards and Documenting Compliance
Standard 1: Untreated Discharges
No new stormwater conveyances (e.g. outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth.
This standard allows the direct discharge of stormwater to waters and wetlands provided the discharge is adequately treated. The term “treated” refers to the implementation of stormwater management systems that are specifically designed to achieve sediment and contaminant removal rates that adequately protect ground water, surface waters and wetlands.
To ensure stormwater discharges do not “cause erosion in a wetlands or waters of the
Commonwealth”, BMPs and associated pipes and other conveyances must be properly designed and installed to minimize erosion.
Standard 9: Operation and Maintenance
A Long-Term Operation and Maintenance plan shall be developed and implemented to ensure that stormwater management systems function as designed.
To demonstrate compliance with this Standard the Applicant shall create a Long-Term Operation and Maintenance Plan (O&M Plan), which shall include:
• Stormwater Management Owners;
• Party or parties responsible for operation and maintenance;
• Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks;
• Plan including locations of all stormwater BMPs along with their discharge location;
• Description and delineation of public safety features; and
• An estimated operation and maintenance budget.
Standard 10: Prohibition of Illicit Discharges
All illicit discharges to the stormwater management system are prohibited.
To demonstration compliance with this Standard, the Applicant shall submit a written and signed statement indicating that no illicit discharges to the stormwater management system are being proposed as part of the Project.
BMP Facility Maintenance
Vegetated Filter Strip
Vegetated filter strips are uniformly graded, vegetated, pretreatment practices designed to treat low volume concentrated flows or sheet flow from adjacent roads, highways, small parking lots, and residential driveways. Vegetated filter strips are designed to decrease runoff velocities, capture sediment, and decrease runoff volumes. Filter strips provide effective treatment when combined with bioretention areas and stream buffers.
• Inspect level spreader for sediment buildup and vegetation for signs of erosion
• Mow grass regularly
• Reseed eroded and bare vegetated areas to restore surface permeability, increase sedimentation, and prevent creation of concentrated flow
• Remove trash and debris to prevent creation of concentrated flow
• Remove accumulated sediment at top of filter strip to maintain appropriate slope and prevent formation of berm
Hydrodynamic separator devices are proprietary stormwater BMPs that remove trash, debris, and coarse sediment from incoming flows using screening, gravity settling, and centrifugal forces generated by forcing the influent into a circular motion. By having the water move in a circular fashion, rather than a straight line, it is possible to obtain significant removal of coarse sediments and attached pollutants with less space as compared to other traditional gravity settling devices. Several types of hydrodynamic separation devices are also designed to remove floating oils and grease using sorbent media and baffles and trash racks can be added to reduce trash and debris. Hydrodynamic separators are designed and manufactured by private businesses, and come in different sizes to accommodate different design storms and flow conditions. The effectiveness of proprietary separator varies greatly by design and size, so units must be correctly sized for specific soil conditions and flow profiles.
• Inspect and clean in accordance with manufacturer requirements, but no less than twice a year following installation, and no less than once a year thereafter.
• Vactor trucks or manual removal of sediment are typical.
Baffle boxes are proprietary concrete or fiberglass structures containing a series of sediment settling chambers separated by bafflers. The stormwater runoff enters the box and begins to fill the first chamber, as the runoff encounters the first baffle, the velocity decreases allowing sediment and pollutants to drop out into internal storage zones. When the first chamber is full, flow is directed to the second chamber where additional settling of sediment occurs. Larger particles typically settle in the first chamber while smaller particles accumulate in the subsequent chambers. To provide additional removal of trash, oil, and grease trash racks, screens, or skimmers may be used. Baffle boxes may be used as pretreatment devices and typically discharge to other treatment or infiltration BMPs.
• Inspect and clean every 2 to 3 months to dispose of accumulated sediment. If not properly maintained, sediment can re-suspend with subsequent storms. Use vactor trucks to remove sediment
• Remove stagnant water every 2 to 3 months to prevent odors and mosquito breeding
• Consult manufacturer for specific maintenance requirements for their product
Bioretention areas (sometimes referred to as rain gardens) use soil, plants, and microbes to treat stormwater, prior to infiltrating or discharging to a stormwater conveyance system or best management practice. Bioretention areas are shallow depressions filled with soil media (referred to as bioretention soil), topped with mulch, and planted with dense native vegetation. These devices, if designed and installed properly, are capable of removing nitrogen, phosphorous, metals, hydrocarbons, and pathogens through filtration, sedimentation, plant uptake, and biological processes.
There are two types of bioretention: Filtering and Exfiltrating. Filtering are designed with an impermeable liner and underdrain to prevent infiltration and recharge. Exfiltrating allow infiltration and recharge to groundwater.
• Inspect pretreatment devices and bioretention areas regularly for sediment build-up, structural damage and standing water
• Inspect for erosion and re-mulch void areas on a monthly basis (or as necessary)
• Remove and replace dead vegetation in spring and fall
• Remove invasive species to prevent from spreading within bioretention area
• Do not store snow in bioretention areas
• Periodically observe function under wet weather conditions
Planter boxes are bioretention treatment control measures that are completely contained within an impermeable structure with an underdrain (they do no infiltrate). The boxes can be comprised of a variety of materials, such as brick or concrete, (usually chosen to be the same material as the adjacent building or sidewalk) and are filled with gravel on the bottom (to house an underdrain system), planting soil media, and vegetation. As stormwater passes down through the planting soil, pollutants are filtered, adsorbed, and biodegraded by the soil and plants.
• Inspect for erosion and repair areas
• Remove accumulated fine sediments, dead leaves and trash to restore surface permeability
• Eradicate weeds and prune back excess plant growth that interferes with facility operation
• Periodically observe function under wet weather condition
Tree Box Filter
Tree box filters are a proprietary biotreatment device that is designed to mimic natural systems such as bioretention areas by incorporating plants, soil, and microbes. Tree box filters are installed at curb level and consist of an open bottom concrete barrel filled with a porous soil media, an underdrain in crushed gravel, and a tree. Tree box filters are highly adaptable solutions that can be used in all types of development and in all types of soils but are especially applicable to ultra-urban areas.
• Annually check tree
• Rake media surface at least twice a year to maintain permeability
• Replace media when tree is replaced (every 5 to 10 years) to restore permeability and pollutant removal efficiency
• Remove accumulated trash and debris to restore permeability
Constructed Stormwater Wetland
A constructed stormwater wetland is a system designed to maximize pollutant removal through vegetative uptake, retention and settling. A typical constructed wetland consists of a sediment forebay to provide pretreatment and dissipate energy, a base with shallow pockets planted with diverse emergent vegetation, deeper areas or micro-pools and a water quality outlet structure. In addition to water quality treatment, constructed wetlands are designed to control peak flow rates from the 2-and 10-year storm through extended detention above the permanent pool elevation. The interactions between the incoming stormwater runoff, aquatic vegetation, wetland soils, and associated physical, chemical, and biological processes are a fundamental part to reducing suspended soils, nutrients, metals, oils and grease, and trash. Site investigations must be conducted prior to design and construction to ensure proper soils, depth to groundwater and suitable land.
There are five types of Constructed Stormwater Wetlands: shallow marsh, basin/wetland, extended detention, pocket, and gravel
• Inspect wetland during both the growing and non-growing season during first 3 years after construction to determine dominant wetland plants, presence of invasive wetland species, accumulation of sediment in forebays and micro-pools, and stability of original depth zones
• Inspect wetland at least once a year to evaluate health and prevent monocultures of plant species
• Clean out sediment forebay annually to restore storage volume capacity
• Clean out sediment in basin/wetland system at least once every 10 years to restore storage volume
Sand filters are engineered sand filled depressions that treat stormwater runoff from small tributary areas. Sand filters allow for the percolation of runoff through the void space within the sand before it is eventually released through an underdrain at the bottom of the filter. Stormwater runoff enters the filter from a pretreatment system (sediment forebay or vegetated filter strip) and spreads evenly over the surface. As flows increase, water backs up on the surface of the filter where it is held until it can percolate through the sand. As stormwater passes through the sand, pollutants are trapped in the small pore spaces between sand grains or are adsorbed to the sand surface. The effectiveness and efficiency of a sand filter depends heavily on the pretreatment BMPs performance to settle out sand, clay, and silt particles, which prevent clogging of the sand filter.
• Inspect filter and remove debris after every major storm for first few months to ensure proper function. Inspect every 6 months thereafter to prevent clogging.
• Rake sand to restore infiltration rates
• Remove sediment and trash that have accumulated on top of sand
• Remove top several inches of discolored media (presence of fine sediments) and replace with clean media to restore filtration removal mechanisms
Gravel trenches are long, narrow, gravel-filled trenches, which treat stormwater runoff from small drainage areas. Gravel trenches remove stormwater pollutants through infiltration, sedimentation and filtration. Reactive media (e.g., zeolite, activated carbon, oxide-coated sand, etc.) may be incorporated into the design to increase sorption capacity and target specific pollutants. Pretreatment may be provided to prevent clogging of the gravel bed and sub-grade.
• Remove trash and debris to prevent clogging and restore permeability
• Remove minor sediment accumulations near inlet structure to prevent clogging
• If clogging is observed, remove top layer of pea gravel and sediment capture layer. If slow conditions persist, entire trench may need to be excavated and replaced
• Periodically observe under wet weather conditions to ensure all components are working properly
• Pollutant Removal Efficiencies
Dry wells, or seepage pits, are excavated areas filled with gravel and very similar to infiltration trenches. They are designed to receive and treat stormwater runoff from non-metal roofs or metal roofs outside Zone II, Interim Wellhead Protection Area (IWPA) of a public water supply, or an industrial site. Dry wells are constructed to reduce stormwater runoff volumes through increased groundwater recharge and can be used as retrofits of highly urbanized areas. Dry wells are not recommended to treat parking lot runoff or areas with potentially high pollutant loadings.
• Inspect well at least 4 times a year and after major storm events to ensure that maximum draw down time (72 hours) is not being exceeded
• Clean roof gutters to prevent clogging of dry well
• Replace filter screen as necessary
Subsurface Infiltration Systems
Subsurface infiltration structures are underground systems that capture and infiltrate runoff into the groundwater through highly permeable rock and gravel. It is usually not practical to infiltrate runoff at the same rate that is generated; therefore, these facilities generally include both a storage component and a drainage component. Typical subsurface infiltration systems that can be installed to enhance groundwater recharge include pre-cast concrete or plastic pits, chambers (manufactured pipes), and perforated pipes.
• Inspect inlets at least twice a year.
• Remove any debris that may be clogging the device
Dry Water Quality Swale
Water quality swales are shallow, open conveyance channels with low-lying vegetation designed to settle out suspended pollutants due to shallow flow depths and slow velocities. Additional pollutant removal mechanisms include volume reduction through infiltration and evapotranspiration and biochemical processes that provide treatment of dissolved constituents. It is generally accepted that water quality swales have higher pollutant removal efficiencies than grass channels. An effective vegetated swale achieves uniform sheet flow through a vegetated area for at least 10 minutes.
• Inspect during first few months to ensure adequate vegetation growth
• Inspect slopes, soil moisture, vegetative health, soil stability, soil compaction, soil erosion, ponding, and sedimentation of swale at least twice a year to maintain overall integrity and efficiency
• Reseed eroded areas to maintain flow reduction and pollutant removal efficiencies
Porous pavement is a permeable alternative to conventional asphalt and concrete and constructed in pedestrian, highly urbanized, or residential settings with low traffic speeds and volumes. A high surface void ratio allows precipitation to pass through the pavement and a stone base, where runoff is retained and sediments and metals are treated to some degree. Porous pavement is designed to achieve peak flow attenuation of small intensity storms and groundwater recharge through infiltration into underlying soils. Porous pavement includes porous asphalt and pervious concrete, which are poured in place, and paving stones and grass pavers, which are typically precast and installed in an interlocking array to create a surface.
• Power wash and vacuum sweep area to prevent clogging
• Do not sand or salt during the winter
• Use snowplows with rollers on bottom to prevent damage to porous pavement
• Periodically observe function under wet weather conditions to determine decrease in performance and clogging
Disconnect Impervious Areas
Disconnecting impervious surfaces from the public stormwater conveyance system and directing runoff to pervious surfaces can reduce stormwater volumes, flow rates, pollutant loadings, and increase groundwater recharge. This practice can be applied in both, residential and commercial, locations. By incorporating small depressions into site grading and routing impervious surface runoff to these locations where permissible, small storm volumes can be retained and the site’s rainfall-runoff response time and peak flows can be reduced.
The impervious surface must discharge into a suitable receiving area for the practices to be effective. Typical receiving pervious surfaces include landscaped areas and/or other BMPs (i.e., planter boxes, filter strips, bioretention).
• Compacted soil must be amended, tilled, and re-vegetated to restore infiltration capacity
• Clean gutters annually to prevent clogging or downspouts and pervious areas
Cisterns and rain barrels are structural tanks designed to capture stormwater runoff from impermeable surfaces for non-potable use. For uses other than irrigation, a filter system must be implemented. Rain barrels are 50 to 100 gallon covered plastic tanks usually installed above ground to store runoff from residential rooftops. Rain barrels must be disconnected and completely drained before winter to prevent cracking of the barrel. Cisterns are partially or fully buried 100 to 10,000 gallon tanks with a cover and a discharge pump. They may receive runoff from multiple residential roofs, commercial or industrial roofs, and parking decks. Cisterns usually contain a pump to distribute water for intended use.
• Inspect seal of rain barrel to prevent mosquito breeding and leaks
• Clean gutters and roof catchment to prevent clogging of downspouts
• Inspect overflow pipe to provide proper draining of system during large events
• If above ground, drain system before winter to prevent cracking of tank
Green roofs are vegetated roof covers designed to reduce stormwater volumes through storage of precipitation in a soil media layer and increased evapotranspiration. Green roofs decrease the impervious footprint of buildings and help mimic pre-development hydrology. They are applicable in highly urbanized locations where land is limited and expensive. Due to an observed increase in nitrogen and phosphorous discharged from green roofs, they should not be used in nutrient sensitive waters, or locations where groundwater recharge is a priority due to low baseflows. There are two types of green roofs: intensive green roofs and extensive green roofs. Extensive green roofs are lightweight systems requiring minimal maintenance and a shallow soil media, while intensive green roofs are larger and deeper systems requiring regular maintenance (irrigation, fertilizing, mowing) throughout the year.
• Add additional mulch, irrigate, weed, and prune plants as necessary to preserve life of roof and established plants
• Remove wooded plants that may become established to preserve roof integrity
• Fertilize intensive green roofs to support growth of plants
Infiltration basins are stormwater impoundments, over permeable soils with vegetated bottoms and side slopes. Infiltration basins are designed to reduce stormwater volumes through exfiltration and groundwater recharge. Pretreatment is vital to ensuring successful performance. There are 2 types of infiltration basins: full exfiltration and partial or off-line exfiltration. Full exfiltration basins are designed to store, treat, and exfiltrate the full required water quality volume and attenuate peak flows. Partial or off-line exfiltration basins are designed to exfiltrate a portion of the runoff (usually the “first flush” or runoff from first 0.5 inches of precipitation), while diverting the remaining runoff to another BMP through flow splitters or weirs. The type of infiltration basin is chosen based upon site conditions and limitations.
• Develop and implement an aggressive maintenance and operations plan
• Inspect basin and pretreatment device after major storms to ensure it is functioning properly, for the first few months post construction
• Inspect, at a minimum, twice a year for cracking, erosion, leakage in embankments, tree growth, condition of riprap, sediment accumulation, health of turf and signs of differential settlement
• Mow buffer area, side slopes, and basin bottom at least twice a year
• Remove trash and debris to prevent clogging
• Remove sediment from basin as necessary to prevent clogging