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Stormwater Information
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Stormwater Basics
· it runs off into wetlands, rivers, and other water bodies; or
· it can percolate into the soil.
- Increase in volume of runoff. The volume of water available for runoff increases because the impervious area created by roofs, parking lots, streets, and other surfaces reduces the amount of infiltration that can occur. Note that this increase in runoff volume is directly associated with a decrease in recharge of the groundwater.
- Increase in runoff rates. Urban development involves changes in surface cover, and the introduction of channels, curbing, gutters, and storm drainage collection systems. These changes result in hydraulic efficiencies that increase the velocity of runoff as it flows to the watershed outlet. This results in higher peak rates of stormwater discharge as compared to natural watersheds.
Impervious surfaces also have other impacts:
- Impervious surfaces absorb more heat than natural surfaces. When the heat is released it raises the air temperature, contributing to the urban “heat island” effect.
- Because they absorb heat, the runoff that is generated on them tends to have a higher temperature than natural runoff. Even minor temperature differences in runoff can have significant impacts on aquatic life.
- Some impervious surfaces, primarily paved surfaces and particularly roadways, generate more pollution than natural surfaces. Some of these pollutants include: motor oil and grease; heavy metals; nutrients in fertilizers and pet waste; and sediment from sanding operations, erosion, and construction sites.
Listed in the table below are the common heavy metals that are encountered in roadway runoff.
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Residents & Property Owners
Below are a list of simple tips that property owners can follow to help reduce their impact on stormwater quality and reduce the amount of runoff leaving their property.
General Tips
- Never dump or throw anything in a catch basin or the storm drain. Only stormwater runoff should enter these systems.
- Pick up pet waste and dispose of it properly. Throwing pet waste in the trash is the best disposal method. Leaving pet waste on the ground increases public health risks by allowing harmful bacteria and nutrients to wash into storm drains, and ultimately our waterbodies.
- Check your vehicle for leaks and repair quickly. Safely dispose of motor oil at a certified recycling location.
- Use a commercial car washing facility or wash your car on the grass. The soap used to wash cars includes high nutrient loads, which are detrimental to our receiving waterbodies.
Lawn Care and Landscaping
- Use fertilizers sparingly and avoid chemical fertilizers.
- Store all fertilizer and pesticide containers safely to prevent spills, and dispose of the empty containers properly.
- Landscape only with native plants and water lightly and frequently to reduce the potential for disease and insect damage. A 15 to 20 minute watering during dry weather after sunset or before sunrise is usually sufficient.
- Consider replacing pervious surfaces, such as paved driveways and walkways, with more pervious treatments, such as crushed stone or porous pavers.
- Use compost as an alternative to fertilizer. Compost contributes organic matter and gradually releases nutrient to the soil.
- Minimize the use of pesticides in order to keep your lawn safe for earthworms and other “good” insects.
- Whenever soils are disturbed or laid bare, utilize a silt fence or other appropriate methods of erosion control to keep eroded soils from migrating off-site. As soon as possible, re-establish vegetation over the area. Mulch the exposed areas to provide temporary cover and protect the soils from rain.
- If you are re-grading your land, create softer or shorter slopes that have less potential for erosion.
- Maintain wide buffer strips of natural vegetation. Buffer strips help to filter out pollutants and reduce flow velocities.
- Consider planting a rain garden on your property to intercept and infiltrate runoff from grassy or paved surfaces, or from rooftop areas.
- Consider purchasing a rain barrel to intercept clean runoff from your rooftop area that can be reused to water plants and lawns.
Salt & De-Icers
When the snow melts, do you ever wonder where all that salt and de-icer goes? You guessed it! It flows over our driveways, sidewalks, and roads, into the nearest catch basin, and directly (untreated!) into our waterways.
Salt in our fresh water is harmful to plants, wildlife, and people. Birds can mistake salt crystals for food, eating them and getting sick. Salt can be toxic to fish and others in aquatic systems. Salt is not good for our plants, and in many wetlands salt-tolerant invasives are crowding out our native vegetation, which then affects the wildlife that lose their food sources. And of course salt in our water supplies is not good for us -- we all know that salt is linked to high blood pressure and heart disease. Salt includes sodium chloride, as well as calcium and magnesium chloride.
Some use sand, and while it doesn’t carry chemicals into our waterways, it does clog catch basins and cause flooding. It can also carry other pollutants into our waterways. If used, excess sand should be swept up.
De-icer is a preferable alternative to both salt and sand, but it is still not perfect, and should be used smartly and sparingly. De-icers include Sodium or Potassium Acetate and Calcium Magnesium Acetate.
What can YOU do to keep your pavement safe while also keeping your water clean?
- Use de-icer (sodium acetate, potassium acetate, and calcium magnesium acetate) instead of salt (sodium chloride, calcium chloride, and magnesium chloride).
- Shovel early and often. Remove as much snow and ice as you can, and only use de-icer on what you can’t take care of with a shovel.
- Follow product instructions and only use as much de-icer as you need. More is not better.
- For heavy snowfalls, shovel early and often to avoid the snow compacting and forming ice.
- For wet snow or sleet and freezing rain, apply de-icer product early on to prevent snow from bonding or ice from building up.
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Development & Construction
The term “Best Management Practices” or BMPs describe control measures that are taken to mitigate the effects of runoff, such as increased peak runoff rates and volumes, and impaired water quality. They can be “structural,” such as something that is constructed or installed, or they can be “non-structural,” such as how a site is managed during construction.
There are many types of BMPs Developers and Contractors can implement during all phases of their project. Below is a framework which provides guidance through the construction process. There are three (3) major phases with respect to Development & Construction and Stormwater Management. Within each phase there are aspects which may or may not pertain to your project. Knowing that all projects are different, the Town of Winchester will work with Developers and Contractors to make sure the appropriate aspects for each phase are considered.
Pre-Application Consultation
Applicants should consult with Town staff from the Engineering Department, DPW, Building Department, Planning Department, and the Conservation Commission early in the design phase to discuss the required permits and to determine which Town standards and regulations will apply to the proposed project. These include:
- Rules and Regulations Regarding the Use of Public Sewers and Storm Drains in the Town of Winchester, Massachusetts.
- Winchester’s Zoning Bylaw;
- Rules and Regulations Governing the Subdivision of Land in the Town of Winchester, Massachusetts;
- Winchester’s Wetlands Bylaw and the Massachusetts Wetlands Protection Act.
Sediment and Erosion Control Measures
Sediment and erosion control measures are installed temporarily during construction to prevent or reduce the movement of sediment from the site through the implementation of man-made structures and perimeter controls, site management techniques, and natural processes.
Sites disturbing one or more acres of land through clearing, grading, excavating, or stockpiling of fill are required to apply for a National Pollutant Discharge Elimination System (NPDES) stormwater permit with USEPA. The permit requires the development of a stormwater pollution prevention plan (SWPP) to document how the site “operator” plans to control stormwater runoff from your construction site.
Perimeter Controls
Examples of perimeter controls include haybales, silt fencing and compost filter tubes. These types of BMPs are installed prior to the start of construction and remain in place until the site is fully stabilized.
Site Management
Controlling the potential for pollution to leave the site via stormwater runoff is an effective method to reducing impacts to downstream receptors. Managing workflow and materials are effective tools at a Developer’s disposal to control pollution at the source. Effective site Management techniques/controls include:
- Construction phasing
- Sequence activities so soil is not exposed for long periods of time
- Limiting grading to small areas
- Schedule site stabilization actives to be completed when the phase of work is complete
- Installation of temporary sedimentation basins
- Temporary Site Stabilization, such as hydroseeding and mulching.
Structural BMPs
There are many examples of structural BMPs that have been successfully implemented within the Town of Winchester to mitigate stormwater runoff volumes and rates in accordance with local, state, and federal regulations. A few examples are discussed below:
Deep Sump Catch Basins
Deep sump catch basins are devices that improves water quality, though they do not reduce the peak flow or volume of runoff. As illustrated below, a catch basin contains a sump, which is a pit below the outlet pipe, and the outlet pipe has a hood over it. When runoff flows into the catch basin, instead of immediately going out the outlet, it first sits in the sump, which allows sediments to settle out. The hood prevents floatable materials, such as trash and oil, from flowing down the drain. They need to be maintained by routinely cleaning out the sump.
Porous Pavement
Porous pavement is a permeable pavement surface with a stone reservoir underneath. The reservoir temporarily stores surface runoff before infiltrating it into the subsoil. Runoff is infiltrated directly into the soil and receives some water quality treatment. Porous pavement often appears the same as traditional asphalt or concrete but is manufactured without "fine" materials, and instead incorporates void spaces that allow for infiltration.
Bioretention areas and Rain gardens
Bioretention areas use soils, plants, and microbes to treat stormwater before it is infiltrated or discharged. They are typically shallow depressions that are filled with sandy soils and covered with mulch and dense native vegetation. When stormwater enters the bioretention area, the soil acts as a filter that removes pollutants.
A bioretention area captures runoff from an impervious surface and allows that water to infiltrate through the soil media. As the water infiltrates, pollutants are removed from the stormwater runoff through a variety of mechanisms including adsorption, microbial activity, plant uptake, sedimentation, and filtration. Some of the incoming runoff is temporarily held by the soil of the bioretention area and later "leaves" the system by way of evapotranspiration or exfiltration to the groundwater.
Infiltration Systems
Infiltration systems are one of the best BMPs available as they reduce peak runoff rates and volumes, and also improve water quality.
Infiltration BMPs can consist of above-ground excavated basins or perforated underground units that store stormwater and allow it to slowly infiltrate into the ground. In Winchester, most of the municipally-owned infiltration systems are subsurface, such as at Manchester Field and Davidson Park.
Infiltration systems and basins recharge groundwater and better mimic natural hydrologic conditions. Pre-treatment of runoff is often required to prevent pollutants from entering the groundwater or clogging the infiltration systems.
Although infiltration BMPs can be highly effective, they are not suitable everywhere and require careful design by a professional engineer. Some soils are simply not capable of infiltrating large amounts of water, due to poor soil composition (such as high clay or silt content) or presence of ledge. They also require a minimum two-foot separation between the bottom of the system and the estimated high groundwater elevation so that that the system doesn’t back up.
Sedimentation Tanks
Sedimentation tanks are underground storage tanks with multiple chambers designed to separate heavy particulates, floating debris and oil from stormwater.
In a typical system; stormwater enters the first chamber where heavy sediments and solids drop out. The flow moves into the second chamber where oils and greases are removed. Oil and grease are stored in the second chamber for future removal. After moving into the third outlet chamber, the clarified stormwater runoff is then discharged to a pipe and another BMP.
Sedimentation tanks provide water quality treatment but do not control runoff peak rates or volumes. They require routine maintenance to remain effective. There are several publicly-owned sedimentation tanks located throughout Town, including on Mystic Valley Parkway, Washington Street, and in the parking lot at Town Hall.
Waste Management
Construction debris needs to be securely stored in a waste container. Hazardous construction waste must be stored in a separate sealed container.
Project Close-out/Operation & Maintenance
At the completion of construction, developers and future property owners are responsible for the following:
- Final site stabilization;
- Removal of sediment and erosion control measures (when approved by the Town);
- Close-out of all administrative and permit requirements for the project, including Certificate of Compliance, as-builts, and engineering certifications; and
- Implementation of an approved long-term Operation and Maintenance (O&M) Plan.
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Business
Parking Lot Maintenance
Regular sweeping of your parking lot improves the appearance for clients and customers, while also keeping pollution out of our waterways. During a storm, rain can carry trash, oil, grease, and even heavy metals across the parking lot, into the catch basin, through our pipes, and into our rivers and lakes. Remember, anything that goes into our storm sewer system will flow untreated into the water we use for swimming, boating, fishing, and drinking.
Regular sweeping also reduces the need for and cost of catch basin cleaning and prolongs the life of your asphalt.
Some tips to keep in mind:
- Use dry cleaning methods (e.g., sweeping, vacuuming) to keep pollutants out of our catch basins and eventually our waterways. Sweeping is the most efficient method for removing coarse particles, leaves, and trash.
- Determine the frequency of sweeping based on usage of space.
- Dispose of parking lot sweeping debris in a landfill.
- Provide plenty of trash cans. Empty trash on a regular basis to prevent spillage. Consider signs to discourage littering.
- Clean out catch basins on a regular basis. Improperly maintained catch basins not only allow debris to reach our streams, rivers, and oceans, but clogged catch basins can result in the ponding of water in your parking lot after storms, negatively impacting your customers.
- Repair cracks and potholes right away.
Remember, your parking lot is the first thing your clients and potential customers see. Keep it clean, and keep our waterways clean, too!
Dumpster & Trash Maintenance
Protect our streams and rivers and comply with health codes by following these simple maintenance tips:
- Cover: Keep dumpsters and compactors under cover to keep rain out.
- Close : Close and dumpster lids every day and repair them right away to prevent wildlife and rainfall from entering.
- Clean: Inspect dumpsters regularly to ensure they are clean and don’t leak. Keep them away from storm drains!
- Contain: Fix leaks and use a spill kit to immediately clean up spills.
Salt & De-Icers
When the snow melts, do you ever wonder where all that salt and de-icer goes? You guessed it! It flows over our driveways, sidewalks, and roads, into the nearest catch basin, and directly (untreated!) into our waterways.
Salt in our fresh water is harmful to plants, wildlife, and people. Birds can mistake salt crystals for food, eating them and getting sick. Salt can be toxic to fish and others in aquatic systems. Salt is not good for our plants, and in many wetlands salt-tolerant invasives are crowding out our native vegetation, which then affects the wildlife that lose their food sources. And of course salt in our water supplies is not good for us -- we all know that salt is linked to high blood pressure and heart disease. Salt includes sodium chloride, as well as calcium and magnesium chloride.
Some use sand, and while it doesn’t carry chemicals into our waterways, it does clog catch basins and cause flooding. It can also carry other pollutants into our waterways. If used, excess sand should be swept up.
De-icer is a preferable alternative to both salt and sand, but it is still not perfect, and should be used smartly and sparingly. De-icers include Sodium or Potassium Acetate and Calcium Magnesium Acetate.
What can YOU do to keep your pavement safe while also keeping your water clean?
- Use de-icer (sodium acetate, potassium acetate, and calcium magnesium acetate) instead of salt (sodium chloride, calcium chloride, and magnesium chloride).
- Shovel early and often. Remove as much snow and ice as you can, and only use de-icer on what you can’t take care of with a shovel.
- Follow product instructions and only use as much de-icer as you need. More is not better.
- For heavy snowfalls, shovel early and often to avoid the snow compacting and forming ice.
- For wet snow or sleet and freezing rain, apply de-icer product early on to prevent snow from bonding or ice from building up.