Monomoy Lens Groundwater Protection

This map shows the Monomoy Lens water table in 10 foot contour levels

Prepared by the
Water Resources Office
Cape Cod Commission
for the Harwich Water Department
January 1998

Cape Cod is fortunate to have an abundant supply of high quality drinking water.  Below please find answers to frequently asked questions about groundwater and further information relative to potential impacts from population growth on drinking water supplies. The information is intended to familiarize residents of the Town of Harwich with local drinking water supply sources and what is being done to ensure they will remain safe for years to come.

Where does the water supply originate?
The Monomoy Lens is the source of fresh water for the town of Harwich. This lens is one of the six groundwater lenses that make up the Cape Cod Sole Source Aquifer. Lenses can be thought of as mounds of groundwater bordered by marine water at the edge, bedrock on the bottom, and separated from each other by tidal waters, such as Bass River, that cut across the Cape peninsula. Groundwater refers to subsurface water in soils and geologic formations that are fully saturated.

Groundwater in the Monomoy Lens is replenished from rain or snow that seeps into the ground. The water percolates through the soil to reach the water table which is the surface of the groundwater lens. Water within the lens slowly moves toward the coast where it discharges into the ocean. Along the way, groundwater flows into the numerous kettlehole lakes and ponds, and into streams feeding marine embayments along the coast.

The map below shows the location of the Harwich public drinking water supplies. The shaded areas represent the land area where the groundwater flows toward the well instead of moving all the way to the shore. These areas are referred to as recharge areas, wellhead protection areas, or, if state approved, Zone II's. Recharge areas for wells located in Dennis, Brewster, and Chatham that cross the Harwich town boundaries are also show.

Harwich Public Supply Wells
Public Supply Wells

How much water does Harwich use?
In 2019, the Harwich Water Department pumped 729,920,258 millon gallons of water and served over 9,989 residential and business accounts.

How can land use impact water supplies?

Open space is beneficial to protect public water supplies from potential contamination sources. One of the greatest threats to water supplies is non-point source pollution from septic systems. Zoning bylaws protect these supplies by setting appropriate setbacks from supply wells and limiting septic system density in areas contributing to water supplies. Water supplies may also be threatened from improper use and disposal of chemical products used in homes or businesses. Steps to educate residents and businesses on proper disposal of these materials is the best defense from pollution. Each year the town holds a household hazardous waste collection to help minimize improper disposal of these materials. Recycling facilities are available at the landfill for batteries, motor oil and filters, antifreeze, and paint.

Groundwater Protection Regulations

Drinking Water Protection District
310 CMR 22.21(2)
Private Well     Board of Health
Individual Sewage Disposal Systems
310 CMR 15:00
DRI review
Board of Health
Wastewater Treatment Plants 310 CMR 5.00 DRI review Zoning/Board of Health
Nutrient Loading 310 CMR 22.21/15:00 RPP/DRI review Zoning
Animal Manures     Zoning
Hazardous Materials
Toxic & Hazardous Materials 310 CMR 22.21 RPP Zoning
Floor Drains 310 CMR 22.21   Board of Health
Underground Storage Tanks 527 CMR 9.00   Board of Health
Herbicides/Pesticides 333 CMR   Board of Health
CMR: Code of Massachusetts Regulation
RPP: Regional Policy Plan (Cape Cod Commission)
Not regulated
DRI: Development of Regional Impact

What actions have been taken to protect water supplies?
The table show above lists the water resource protection controls relating to wastewater and hazardous materials that are enforced at the local, county and state levels. Harwich has many good regulations in place and is in full compliance with state drinking water requirements. Wellhead protection is extended to the surrounding towns of Dennis, Brewster, and Chatham where Zone II's cross into Harwich.

Additionally, groundwater is protected by a variety of Board of Health regulations relating to private wells, commercial floor drains, underground storage tanks, herbicides/pesticides, and on-site septic systems.

What else can be done to safeguard future supplies?
There are several actions that can be taken to strengthen water supply protection efforts in the town. The Board of Health could adopt a townwide hazardous material regulation which includes site inspection, registration, and inventory.

In order to reduce the nitrogen load from septic systems, minimum residential zoning could be increased in zones of contribution to public supply wells. The town should continue to purchase potentially developable residential land located within existing wellhead protection areas and for use as future well sites.

How can I be sure that the water is safe to drink?
Harwich's public water supply is tested at least twice each month for bacteria, and annually for nitrate-nitrogen and other organic and inorganic compounds specified by state and federal standards. If any problems are encountered, law requires public notice to be published in a local paper and the problem corrected. Certified water operators are always available to provide customers with copies of recent water quality results or to answer specific questions.

The water supply is of excellent quality requiring treatment only to control the natural acidity and periodic chlorination when cleaning the tanks.

Private well water quality is the responsibility of individual property owners and should be tested regularly. Private wells may experience aesthetic problems such as staining and odor from high concentrations of iron or manganese. High levels of sodium, from salt water or road salt, are occasionally detected. Wells testing high in bacteria or nitrate-nitrogen may indicate too much fertilizer is being used or a septic system is too close to the well. High levels of nitrate should be monitored, especially if pregnant women or infants are using the supply.

Water testing services are available at the Barnstable County Department of Health and the Environment Water Lab, locate in the Superior Court Building on Route 6A in Barnstable Village. Sterilized containers must be used and are available at the lab and the health department.

For additional information on water supplies:

Harwich Water Department: 508-432-0304

Harwich Health Department: 508-430-7509

Cape Cod Commission: 508-362-3828

Cape Cod Cooperative Extension: 508-362-2511

Barnstable County Dept. of Health and the Environment: 508-362-2511

Dept. of Environmental Protection, Southeast Regional Office: 508-946-2760