What is stormwater and what can we do about it?

WHAT IS STORMWATER AND WHAT CAN WE DO ABOUT IT?

Stormwater and how it is managed can greatly affect your quality of life. If not properly managed, it can be very damaging to our waterways and drinking water. Stormwater runoff can contain higher amounts of pollutants than raw sanitary sewage and can contribute more than 80% of the pollutants affecting our lakes and reservoirs. Often we don't see the damage that improperly managed stormwater runoff has caused, because we don't know what to look for. Other times the damage becomes so great that it cannot be missed.   Protecting our environment and managing stormwater requires everyone's help.

I.         The IMPORTANCE OF STORMWATER RUNOFF

What is stormwater runoff?

When it rains, or when snow melts, only a portion of the water will soak, or infiltrate into the ground. The portion of the water which does not soak into the ground ends up traveling overland until it reaches a body of water. The water that travels overland is called stormwater runoff. There are two principal areas of concern with stormwater runoff: the amount of stormwater runoff that occurs and the quality of that runoff.

A change in the ground cover from forest to lawn, or some type of impervious surface causes an increase in the volume of stormwater runoff. Increasing the volume of stormwater released during a storm event can increase the potential for downstream flooding.  Increasing the volume of stormwater can also cause more water to flow through a stream channel, causing significant changes to the stream channel.  These increases can cause substantial property damage as well as damage to the environment.

These same changes to ground cover can also affect the quality of the stormwater runoff by increasing the concentration of pollutants.  As stormwater runoff travels over land, it picks up and carries many natural and man-made substances such as sediment, nutrients and other pollutants that may impact water quality. In fact, almost anything on the ground can become a source of contamination as stormwater travels over land and is carried into the storm drains and discharges into the surrounding watershed. The faster the stormwater moves the more pollutants it can carry. Because sediment, nutrients and other pollutants found in stormwater runoff come from many poorly defined or indiscreet sources, this type of pollution is often referred to as nonpoint source pollution. Changes in stormwater quality can result in changes to wildlife habitats, increased flooding, a reduction in the populations of fish and other aquatic organisms, and stream bank erosion.

There are a number of characteristics of the natural landscape that help to protect the quantity and quality of stormwater. Trees intercept rainfall and slow its velocity. Trees also provide cooling of stormwater which is important to certain fish habitats. Undisturbed areas of the landscape are generally full of very small natural depressions that temporarily pond stormwater and allow more time for the water to infiltrate into the ground. Similarly, the spongy humus layer of leaves on the forest floor slows the velocity of stormwater and allows more water to infiltrate into the ground.

However, as the land is altered by people, several changes occur.  Trees that had intercepted rainfall are removed, the natural depressions that had temporarily ponded water are graded to a uniform slope, the spongy humus layer of the forest floor that had absorbed rainfall is scraped off, and the underlying soils are eroded or severely compacted.  These changes result in an increase in the quantity of stormwater, and a decrease in its quality, which together affect watershed ecology.  The quantity and quality of stormwater also changes as the land’s surface is changed from forest to lawns to roofs, driveways and parking lots.

One of the primary sources of concentrated amounts of pollutants entering our waterways, and the area of greatest concern are impervious surfaces. Impervious surfaces are areas, including roads, parking lots, driveways and rooftops, which are so dense and hard that they prevent rainfall from entering into the ground. Many different pollutants accumulate on these surfaces from the atmosphere, from vehicles, or are windblown from adjacent areas. During storm events these pollutants quickly wash off, and are rapidly delivered to downstream waters.

The watershed you live in

A watershed is the land where all of the water that is under it or drains off of it goes into the same place. Everywhere you go, you are in a watershed.

The Town of Harrison is in the watershed for the New York City Reservoir System. This means that our streams, the roadside ditches, and even the water that runs over your lawn during and after a rain all end up in one of the reservoirs that make up the Croton Reservoir system. Watersheds can be further divided into individual components or sub-watersheds.

Prevention rather than remediation

The reservoir system which supplies New York City's drinking water is rated as one of the cleanest and safest water supply systems. However, right now - today - the water supply system is being threatened. Even if no additional development were to occur within the watershed, the problem would still exist. Excessive nutrients are affecting the overall health of our reservoirs. As per NUSDEC guidelines, they are receiving too much phosphorous. In order to maintain a healthy watershed and reservoir system, the amount of phosphorous entering reservoirs must be reduced. This can only be accomplished by a cooperative effort by everyone who lives, and works within the watershed.  There are a number of practices, described here and elsewhere, that you can be used to help reduce the quantity of stormwater runoff, and improve its quality.

Next: Water Quality and Phosphorous

II. Water Quality and Phosphorous

Phosphorous and where it comes from

Although several pollutants are a concern to our water quality and NYC reservoirs, phosphorus is of particular concern. Both phosphorous and nitrogen are naturally occurring nutrients essential for plant growth. Nitrogen is in much greater supply in the environment and therefore much more difficult to control.  Phosphorus is less abundant and the easier to control and is considered the limiting nutrient in algae and plant growth. Phosphorous comes from many sources. Soils, weathered minerals and rock, decomposing organic material, car exhaust, failed septic systems and atmospheric deposition all contribute to the amount of phosphorus in the watershed.

Croton Reservoir System

The New York City Water Supply System includes a watershed of 1,969 square miles across eight counties north and west of the City: Westchester, Putnam and Dutchess on the east side of the Hudson River and Delaware, Greene, Schoharie, Sullivan and Ulster in the Catskill Mountains, west of the Hudson. The watershed provides approximately 10% of the cities average daily water demand.  In addition to the water provided by the reservoir system, there are also thousands of private and public wells within the City's watershed.

Best Management Practices

Best Management Practices (BMPs) are methods, measures or practices employed to prevent or reduce water pollution. They can be divided into two types: structural BMPs, which are constructed practices such as the installation and catch basins, grass swales or detention ponds, and cultural BMPs, which are methods, measures or practices that affect or change an individual's behavior, such as proper usage and disposal of household products and good housekeeping.

Next: Your Home and Stormwater: Things You Can Do

III. Your Home and Stormwater: Things You Can Do

Low Impact Development Design

Most practices currently used to manage stormwater tend to move the stormwater off site as quickly and efficiently as possible, and deal with managing the quantity or quality of the stormwater at the end of the pipe. This method has a number of disadvantages to our environment. Most importantly, by moving the stormwater off site, it is no longer available to replenish the groundwater. A different technique for managing stormwater, called low impact development (LID), seeks to preserve the natural, pre-development conditions of a development by using one or more small stormwater BMPs on each individual site, rather than one large BMP at the end of the pipe.

Managing Household Hazardous Products

Proper disposal of materials

When you pour something down your sink's drain, it eventually will end up in your drinking water.  That's because you are in a watershed and what you dispose in it ends up in groundwater, waterways and reservoirs. The proper disposal of household cleaners and other products is vitally important to maintaining water quality. Many products found in the home contain chemicals which are potentially harmful to people, and need to be disposed of properly.

Harrison Recycling Center

The Town of Harrison offers aggressive recycling programs. Information on the curbside pickup and drop-off programs is available on the Town of Harrison website at http:/www.harrison-ny.gov, or by calling the Department of Public Works at 914-670-3100.

Westchester County Household Material Recovery Days

Westchester County sponsors Household Material Recovery Days at various times and locations throughout the year.  Materials that can be disposed of at HMRD include any household product used for cleaning, gardening, home hobby supplies, pesticides, automotive products, and cosmetics such as nail polish remover and hair dyes, which if improperly disposed of, may result in pollution of the environment or injury to the public.

A full calendar of events can be found on the Westchester County website at http:/www.westchestergov.com/recycling or by calling the Recycling Help Line at 914-813-5425.

Managing your Septic System

A properly designed, constructed and maintained septic system can provide long-term effective treatment of household wastewater. However, if not maintained, your septic system may eventually fail, and release improperly treated wastewater to the surface. Repairing a failed septic system is costly.  Proper system maintenance will ensure a properly functioning system and will help protect water quality.

A typical septic system has two main components: a septic tank and a drainfield. Wastewater from your home travels through a pipe into the septic tank where solids settle out and oils and grease float to the surface. Wastewater exits the septic tank and is discharged into the drain fields. As the wastewater infiltrates through the soil microbes digest or remove most contaminants from the wastewater.

Properly operating septic systems will effectively reduce or eliminate most human or environmental threats posed by pollutants in household wastewater. However, septic systems do require periodic maintenance to ensure that they continue to function properly.

Landscaping

Stormwater can become contaminated from excessive or improper use of pesticides, herbicides and fertilizers. Maintaining landscaped areas properly can help prevent fertilizers, pesticides, and soil and grass clippings from polluting the watershed. Improper landscape practices can allow excess amounts of nitrogen, phosphorous, other nutrients, pesticides, and herbicides, to discharge to the watershed.

One of the most important landscape features which minimize the impacts of stormwater are trees. Trees intercept rainfall, slowing its velocity, which in turn reduces soil erosion. Trees also retain a small amount of the rainfall on their leaves. The leaf litter on the forest floor promotes better infiltration of rainfall into the ground.

Underground Storage Tanks

Underground storage tanks, used for the storage of home heating oil or other petroleum products, pose a very serious concern for both groundwater and surface water. These storage tanks corrode over time and ultimately begin leaking petroleum into the ground. A leaking storage tank may go unnoticed for years until contaminants appear within a drinking water source (well), or when a breakout to surface water is observed. When a leak occurs the clean-up costs could potentially run into tens of thousands of dollars.

Next: Streams and Riparian Buffers

IV. Streams and Riparian Buffers

Stream Classification and Order

Streams carry concentrated stormwater runoff and discharged groundwater across the length of the watershed until it reaches its final destination; a waterway.

Stormwater runoff begins its journey as a thin sheet of water flowing across the surface of the land. As it flows down through the watershed, the flow becomes more and more concentrated until finally a small stream is formed. This beginning of a stream is called the stream's headwater. Each headwater stream is designated as a first order stream. When two first order streams combine together they produce a second order stream, two second order streams combine to produce a third order stream and so on. Only when two streams of the same order are combined does the stream order increase. Numerous lower order streams may enter a main stream without changing the stream order.

Riparian Buffers

Immediately adjacent to and extending away from a stream channel is an area that is critically important for protecting and maintaining the integrity and health of a stream. Called the stream's riparian buffer, this area needs to be maintained in a natural state, and be of sufficient width to ensure that activities occurring in the general vicinity of the stream, wetland or water body do not affect the health or integrity of the aquatic system. Buffers, maintained in their natural state, provide several benefits crucial to maintaining a healthy stream or wetland.

Streambank Erosion

Urban development dramatically affects the frequency and magnitude of storm flows As a result of this development, urban stream channels experience more bankfull and sub-bankfull flow events each year than they had prior to development (Center for Watershed Protection).  Both the bed and bank of a stream are exposed to highly erosive flows more frequently and for longer intervals. Streams typically respond to this change by becoming wider and/or deeper. This is a highly unstable condition for the steam and results in severe streambank erosion and habitat degradation.

Next: Soil and Erosion Control in Harrison

V. Soil and Erosion Control in Harrison

What is soil erosion and why is it so important? Soil erosion begins with rainfall. We become so accustomed to the rain we don't realize how much force is in a single raindrop. When a rain drop hits soil, it does so with enough force to dislodge it and begin breaking the soil particles into much smaller pieces, making it much easier to move. When a sufficient amount of rainfall has accumulated on the ground's surface it begins to move downhill. The more rainfall, and the steeper the hill, the faster the rainfall will flow over the surface. The rainfall or stormwater moving over the surface of the land picks up tiny particles of soil and nutrients and carries them down the hill. The faster the stormwater is flowing (its velocity), the more energy it has to carry particles of soil and nutrients. Stormwater runoff will continue to carry these particles of soil until its velocity is slowed, at which time most of the particles fall out of the stormwater and are left behind. This is called soil erosion. Unfortunately, the soil particles are usually left behind in the most inappropriate places like stream bottoms or lakes.

To help prevent soil erosion, in February of 2002 the Town of Harrison adopted a Soil Erosion Control Law aimed at protecting property owners from uncontrolled erosion. The law requires that an individual obtain a permit prior to commencing any of a number of activities.

There are certain practices which you as a homeowner can do to help reduce the potential for soil erosion.

Next: Phase II Stormwater Regulations

VI. Phase II Stormwater Regulations

The 1972 Clean Water Act, enacted by Congress, established a policy to protect and improve the waters of the United States. In 1987, Congress amended the Clean Water Act to require implementation of a program to address stormwater discharges. Rules were promulgated by EPA to establish a phased approach to implementation of the program which went into effect in 1992. Phase I required NPDES permits for a number of categories of stormwater discharges including industrial activities, construction-related disturbances greater than 5 acres, and large and medium size municipal separate storm sewer (MS4) operators.

Phase II of the program requires NPDES permits for construction disturbances of one acre or greater and small MS4 operators located in an Urbanized Area. Urbanized Areas are established by the US Census Bureau as:

"An urbanized area is a land area comprising one or more places- central place(s) - and the adjacent densely settled surrounding area- urban fringe - that together have a residential population of at least 50,000 and an overall population density of at least 1,000 persons per square mile."

Those portions of a municipality located in urbanized areas are automatically designated and must comply with the Phase II requirements. In addition, the EPA and/or a delegated authority can identify special areas which are considered additionally designated areas, and which must also comply with the Phase II Stormwater Regulations.

The authority to administer the Clean Water Act and stormwater regulations can be delegated to an individual State, as is the case in New York. In New York, administration of the program is the responsibility of the Department of Environmental Conservation. In implementing Phase II, the Department of Environmental Conservation has determined that the East of Hudson reservoir watershed, which includes all of Harrison, should be considered an additionally designated area and subject to the Phase II requirements.

As required by the NYS DEC, on March 10, 2003 the Town submitted an application to obtain coverage under the NYS DEC General Permit for MS4 operators. By submitting an application (termed an NOI) the Town is agreeing to develop, implement and enforce a stormwater management program (SWMP) designed to reduce the discharge of pollutants to the maximum extent practicable. In addition, where stormwater discharges are to a receiving waterbody for which a total maximum daily load has been developed for any particular pollutant, such as the East Branch Reservoir, the MS4 Operator must also seek to attain a reduction in any pollutant of concern.

The six minimum measures that the Town of Harrison must address in their stormwater program are:

1. Public Education and Outreach on Stormwater Impacts: An MS4 must, at a minimum plan and conduct an ongoing public education and outreach program designed to describe the impacts of stormwater discharges on waterbodies, and how the pollutants found in stormwater can be reduced.
2. Public Involvement/Participation: An MS4 must, design and conduct a public involvement program. In addition, the MS4 must conduct a public hearing on the annual report that is submitted to the NYS DEC. And finally, the MS4 must identify a local point of contact for public concerns regarding stormwater management and compliance with the permit.
3. Illicit Discharge Detection and Elimination: An MS4 must develop, implement and enforce a program to detect and eliminate illicit discharges into the storm sewer system. An illicit discharge is any discharge to a storm sewer system, such as a catch basin or grass swale, which is not composed entirely of stormwater and which is a significant contributor of pollutants.
4. Construction Site Stormwater Runoff Control: An MS4 must implement and enforce a program to reduce pollutants in any stormwater runoff from construction activities that result in a land disturbance of greater than or equal to one acre.
5. Post-Construction Stormwater Management: An MS4 must develop and implement a program that includes a combination of structural and/or non-structural management practices appropriate for the community that will reduce the discharge of pollutants to the maximum extent practicable In addition, the MS4 must adopt an ordinance or other regulatory mechanism to address post-construction runoff from new development and re-development projects to the extent allowable under State or local law.
6. Pollution Prevention/Good Housekeeping For Municipal Operations: An MS4 must develop and implement an operation and maintenance program that is designed to reduce and prevent the discharge of pollutants to the maximum extent practicable from municipal activities, including but not limited to park and open space maintenance, fleet and building maintenance, new construction and land disturbances, stormwater system maintenance, roadway and right-of-way maintenance, marine operations, and hydrologic habitat modification.

Documents relating to the Town of Harrison's Phase II Stormwater Management program can be found on the Harrison Engineering page.

Next: For More Information

VII. More Information

Local Contact

For more information contact the Harrison Engineering Department by email at http:/www.engineering-harrison-ny.gov or at 914-670-3102.