Watershed Evaluations and Stormwater Management Plans

Watershed Evaluations and Stormwater Management Plans

Stormwater Runoff

A lake is a passive collector that sits at a low point in the landscape and accumulates water and materials that flow into it. The water and materials are retained in the lake until they are discharged to a point lower in the landscape. As a result, waterbodies are heavily affected by runoff from their watershed. Stormwater runoff carries pollutants such as sediments, roadway grease, fertilizers and excess nutrients into bodies of water with little to no filtration. Stormwater runoff is one of the leading causes of poor water quality in lakes, rivers, streams, and ponds.

In an undisturbed world, rainwater would fall to the ground and be mostly absorbed by the native vegetation and natural soils. Yet when rainwater falls onto impervious surfaces such as paved roads, parking lots, and houses, the rain cannot sink into these materials and instead “runs off.” The runoff then flows downhill into an area where the water is either able to infiltrate into the ground, or to where it meets a roadway storm drain and is then carried through an underground culvert system.

IMG_4393A watershed evaluation consists of identifying every single inlet to the lake, big and small, during a rain event. At each inlet, we record its size and flow rate and collect a water sample to test for nutrient concentrations. Looking at the amount of water each inlet carries, together with the nutrient concentrations of each inlet, we determine which inlets carry the highest nutrient loads. We then recommend actions for reducing nutrients in these problem inlets and oversee the rectification process.

Under U.S. Environmental Protection Agency regulation, some towns and cities are required to produce Stormwater Management Plans to reduce discharge pollution.

What is an MS4?
An MS4 is a conveyance or system of conveyances that are used to collect stormwater runoff and direct water, untreated, into local water bodies. MS4 stands for Municipal Separate Storm Sewer Systems. The “separate” component indicates that the underground pipes are for stormwater only, and do NOT connect to the sanitary sewage pipes or water treatment plants. In some older cities and rural environments, there are still “combined” sewers, where the pipes of residential sewage and stormwater all lead to the treatment plant. However, in periods of intense rainfall combined sewer systems have an overflow feature that prevents the treatment plant from being inundating with water over its capacity. This “overflow” results in untreated wastewater – a combination of raw sewage and stormwater – to escape into waterbodies completely untreated, which is an environmental disaster and a human health concern. For this reason, most cities and towns have progressed towards the “separate” systems, or MS4.

MS4 systems are owned by either the state, city, or town, but they serve large areas and it is extremely difficult to regulate what “goes down the drain.” This type of pollution is called “nonpoint source pollution,” because the pollution is extremely widespread and the sources are difficult to track down through the net of MS4 conveyances that transport runoff from streets, driveways, roof drains, lawns, gardens, sidewalks, parking lots, etc.

Nonpoint source pollution is different than “point source” pollution, which is discharge from single entities such as industrial factories, animal farms, and wastewater treatment plants. These types of discharges require permits and water quality monitoring through the State Environmental Protection Organization and the U.S. Environmental Protection Agency. The permitting system is called NPDES, or the National Pollutant Discharge Elimination System.

Now, cities and towns all across the US are required to develop Stormwater Management Plans and to take steps towards achieving discharge pollution compliance. Much of this has already happened, but states continue to update their list of permitted MS4 areas.