Harwich Water Department Water Quality

Understanding the Monomoy Lens

What threatens Cape Cod's groundwater?
Although Cape Cod's groundwater is of excellent quality and safe for drinking, sandy permeable soils and shallow depth to the water table make it particularly vulnerable to contamination. Some specific sources of contamination include landfills, hazardous waste spills, underground fuel storage tanks, septic systems and stormwater runoff.

Areas of contaminated groundwater are commonly referred to as plumes. A plume can impact significant areas and is often caused by a release of organic or synthetic chemicals into the water. Identified contamination plumes, shown on the map to the left, are also known as a point source of contamination because they can be traced back to a specific spill or discharge point. The toxic chemicals in these plumes do not easily break down or degrade in groundwater and may move a long way without losing concentration.

The greatest threat to water quality on Cape Cod is the widespread use of on-site septic systems that dispose of human waste into the ground. Although the plume associated with each septic system is small, if located too close to a private well, can contaminate the well with virus and bacteria. In addition, when these plumes are too numerous in an area they contaminate groundwater with high levels of nitrogen. Collectively these onsite septic plumes are referred to as non-point sources of contamination.

How are wells protected from contamination?
Wellhead protection efforts over the last two decades have focused mainly on land use regulations. These have been very effective in protecting public water supply wells from identified point sources and in limiting non-point source contamination. Board of health regulations or zoning bylaws may be created to limit the use of hazardous materials within wellhead protection areas, limit septic system density through minimum lot sizes or establish water quality performance standards for new construction. Other regulatory mechanisms include buffers and set back regulations, hazardous material registration and inspection, and storm drain controls

While use of these regulatory mechanisms are a critical way to protect groundwater they are primarily accomplished through town ordinances that can often be appealed, or do not apply because of a pre-existing use. Similarly, without enforcement of these regulations, the goal of water quality protection may not be met.

What are other ways to protect water quality?
Water quality is best protected by outright purchase and preservation of land in the wellhead protection area. It is also important to protect land that may be needed for future water supply sites. The center map shows tracts of land that may be suitable for new public water supplies. These tracts are referred to as potential wellhead protection areas. The tracts are located both in and out of existing wellhead protection areas.

With the advent of the Cape Cod Land Bank in 1998, Cape towns now have a steady stream of revenue with which to buy critical parcels for wellfield protection. However, available funds from this source are often insufficient to pay for the very expensive acreage which Cape Cod has become. The following are some common techniques for protecting these identified potential wellhead protection areas.

Common open space techniques include:

1. Land donation: Landowners can obtain tax incentives in exchange for donating land to wellfield or wellhead protection use.
2. Conservation restriction: Property remains in private hands, but owner agrees not to develop all or part of it in order to protect water quality. Cape towns will lower property taxes on the land under restriction. Also useful for income tax deductions and estate planning.
3. Charitable sale: Seller agrees to take less money than the appraised market price for the land in exchange for tax deductions.
4. Reserved life estate: An owner continues to live on the property, while conveying the title to a water purveyor or other conservation entity. Income tax deductions accrue to owner, depending on how much longer they can be expected to enjoy use of the property.
5. Current use assessment: An owner of five acres or more enrolls each year with town, promising to keep the land in its natural or cultivated condition, rather than develop it. Property taxes are reduced significantly and the town acquires the right to buy the property if sold for other uses.