*** NEW *** Hummock Pond Water Quality Report (Click Here.)

*** NEW *** Miacomet Pond Water Quality Report (Click Here.)

To read the NLC's brochure "Our Gardens, Our Water" Click here or on the brochure image to the left.

An Introduction

As Nantucket moves into the 21st century and continues to grow, it is essential that every islander be aware of the need to protect the island's clean water supply. By understanding how what we do affects the quality and quantity of our water, we can take steps to insure that future generations will have drinking water and clean, healthy ponds and harbors.

Ground water is the single source of drinking water on the island. It is also the principal source of fresh water for domestic, commercial and agricultural use. There is no nearby alternative drinking water supply if our aquifer becomes contaminated. Because of this, Nantucket has been designated a sole source aquifer by the U.S. Environmental Protection Agency.

Nantucket Islands Watersheds

Every resident lives in a watershed. A watershed is an area of land where water flows from high elevations to low elevations, eventually making its way to a pond or harbor. Water may flow as surface runoff, streams, or seep into the soil and flow as ground water. Since ground water eventually discharges to a pond or harbor, it has tremendous influence on water level in ponds and water quality in ponds and harbors.

Nantucket has an average annual precipitation of 44 inches. Of that total approximately 25 inches quickly cycle back to the atmosphere through surface evaporation and plant transpiration, 1 inch travels to lower elevations as surface runoff, and 18 inches recharge the ground water and travel to ponds or harbors, and the ocean. This water movement perpetually cycles between atmosphere and land.

Ten watersheds were delineated for Nantucket in 1990 and appear on the watershed map.

The island's sandy soils allow water to infiltrate rapidly to the water table and to store large amounts of ground water in the aquifer. Course-grained soils also allow rapid downward movement of nutrients and chemicals to the ground water and waterways. The flow rate through this permeable soil is a few feet per day. Clay and other fine-grained soils are less permeable. Water runs over the surface or infiltrates slowly at a rate of 1-3 feet per year. Ground water is the island's only source of drinking water.

Nantucket taps into the ground water aquifer from public wellfields and from private on-site wells. A private well draws a small amount of water, sufficient to meet the needs of the individual property owner, and the drawdown area is localized. Residential areas and farms lying outside of town and Siasconset village are serviced by private wells.

Wannacomet and Siasconset Water Companies draw large quantities of ground water from two public wellfields to supply residential and commercial drinking water needs. The drawdown areas for each of these wellfields extends far beyond where the actual pumping occurs. Areas of land that potentially contribute and replenish ground water to these public wellfields are called Zone II's. Some land uses such as underground fuel storage, animal manure storage or junkyards may deleteriously affect public drinking water supplies. Such land uses are not allowed within Zone II's.

Providing public freshwater systems and sewer systems for expanding development reduces the amount of fresh water flow into individual coastal ponds.

For instance, Wannacomet's expanded public water supply system, which draws from the Miacomet Pond watershed and exports ground water to customers in town, reduces the amount of natural flow that would recharge Miacomet Pond. This can have profound effects on plants and animals living in the ponds or in hydrologically connected wetlands.

The water transferred from Miacomet Pond watershed to town is used by households and businesses, then shunted through the town's sewer system to the Surfside wastewater treatment facility and discharged to the ocean.

While certain health benefits are associated with public water and sewer supplies, health of ponds are in part reliant on natural flows of ground water recharge.

Watersheds as Natural Areas

Watersheds include a variety of natural ecosystems such as woodlands, grasslands, and wetlands. Each watershed's upland ecosystems are connected to Nantucket ponds and harbors by streams, surface runoff, and ground water recharge. Changes to upland ecosystems in turn change pond and harbor ecosystems.

An increase of high demand land use activities such as paved roads, buildings, and lawns has resulted in a decrease of natural landscapes that once buffered ponds and harbors from excessive pollutant loads.

Buildings, patios, paved driveways, streets, and parking lots now consume land that once was available to recharge the ground water, ponds, and harbors. This increase in impervious surface area has reduced the amount of recharge to the aquifer and increased the volume of surface runoff. As a consequence storm water runoff carries more sediment and pollutants directly into ponds and harbors, contributing to the deterioration of water quality and aquatic ecosystems.

Polluted drainage within watersheds is the result of unsustainable practices including a)bulldozing that strips away naturally evolved vegetation leaving bare soil exposed, b) paving that covers pervious soils reducing areas of recharge and increasing polluted runoff, and c) landscaping that is maintained with excessive fertilizers and irrigation.

Nutrient Loading and Eutrophication

Eutrophication is the over stimulation of plant growth caused when nutrients, primarily nitrogen and phosphorus, exceed the buffering capacity of the pond or harbor. This may cause oxygen levels to fall below the minimum required by most fish and shellfish to survive. Reduced oxygen levels may also generate toxic levels of hydrogen sulfide and excessive plant growth which results in dense mats of algae. These are indicators of poor water quality. Nutrient overloading is primarily due to human practices and these practices can be changed. Nitrogen typically limits plant growth in marine systems, while phosphorus typically limits plant growth in freshwater systems. Sources of nitrogen and phosphorus include sewage and laundry detergent generated through septic systems, boat dishcarges, pet and waterfowl wastes, and excessively fertilized home landscape and agricultural practices. For more information on organic lawn care, read our brochure: Healthy Lawns and Landscapes

Bacterial Contamination

Bacterial contamination is assessed by the amount of fecal coliform bacteria present in water, and is an indicator of the presence of sewage. State standards set maximum limits for determining whether water is safe for drinking, shellfish harvesting, and/or swimming.

Sources of contamination include leachate from failed septic systems, leaking sewers, improper boat discharge, fecal matter from pets and livestock, waterfow, and sanitary landfills.

Nantucket and Madaket Harbors and Miacomet Pond have experienced periodic beach and shellfish bed closures due to excessive levels of coliform. Each of these water bodies are shallow, enclosed or semi-enclosed systems which hold the pollutant for an extended time. Redirecting portions of storm drain discharge from public beaches in Nantucket Harbor has reduced the frequency of closures, but heavy rainstorms still cause pulses of unfiltered storm water to discharge directly into the harbor water and cause contamination. The sources of bacteria causing shellfish bed closures in Madaket Harbor and beach closure in Miacomet Pond have not yet been determined.

Other contaminants such as vehicle and boat oil, grease and gas drippings, metals and volatile organic compounds are from everyday conveniences such as cars and trucks, underground storage tanks, landfills, dry cleaning, printing and photograph development agents. Even small amounts of these pollutants lower the reproductive success of fish and shellfish.

Protecting Your Watershed

Nantucket homeowners can help protect the health of our ponds, harbors and ground water by making some of the following choices...

• Have your septic system pumped every three years to keep it in working order.

• Leave wide buffers of undisturbed natural vegetation along the perimeters of ponds and harbors to minimize the adverse impacts of surface runoff from adjacent developed land.

• Minimize lawn size and/or consider using newer lawn seed mixtures formulated for drought resistance and lower nitrogen requirements. If fertilizing the lawn, choose fertilizer containing slow-release, water-insoluble forms of nitrogen and limit the frequency of fertilization.

• If watering your lawn or garden do so early in the morning to minimize evaporation.

• Use non-toxic cleaners. For example, instead of toxic drain cleaners, try using boiling water, a plunger, or a metal snake to clean drains. Baking soda or vinegar mixed with warm water and elbow grease are useful ingredients for oven and general household cleaning.

• Dispose of paint and oil cans at Nantucket's household hazardous waste days.