2006 Annual Water Quality Report

Harwich Water System and Source

The Town of Harwich is supplied by groundwater from fourteen( 14) gravel packed wells. Our wellfields are located in South, East and North Harwich, which draw water from the Monomoy Lens Aquifer. The Main Station tubular wellfield and Stations One (1) through Four (4) are located off of Chatham Road, behind the Water Department's main office and garages. Station Five (5), Six (6) and Seven (7) are located off of Depot Road in South Harwich, next to the bike path. Stations Eight (8) and Nine (9) are off of Bay Road in East Harwich, Station Ten (10) is in North Harwich off of North Westgate Road on the Brewster Town line and Station number Eleven (11) is located off of Pleasant Bay Road in East Harwich.

Well Four (4), which can produce up to 500,000 gallons a day, has been restored to service. This particular well has elevated levels of iron and manganese. Although iron and manganese are not considered a health risk they can cause staining of laundry and household fixtures. Therefore, the Department will blend water from this well with that from several other wells, which do not have elevated iron or manganese to neutralize the iron and manganese levels in Well Four (4).

Momonomy Lens--Groundwater Source

Protecting the Monomoy Lens starts with understanding how it works - its hydrogeology. 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 rivers, such as Bass River, that cut across the Cape peninsula. Groundwater refers to subsurface water located beneath the water table, in soils and geologic formations that are fully saturated. The entire layer of fresh groundwater beneath the Cape is referred to as the Cape Cod Sole Source Aquifer. Recharge to this lens comes from precipitation and snow fall.

The Monomoy Lens is approximately 300 feet thick and serves 49 municipal public water supply wells and an estimated 1,000 private wells. In the 1999 off-season, Cape municipal water suppliers pumped an average of five million gallons per day. Inseason this figure almost triples.

The Monomoy Lens supplies generally excellent drinking water from its porous sand and gravel deposits. The water is considered "soft" due to the lack of calcium and magnesium. The pH of the water is naturally low, which can cause blue staining on plumbing fixtures from copper piping. Municipal water supplies are treated to neutralize the pH. Naturally occurring iron and manganese can cause staining, odor and taste problems. Sodium chloride can be elevated in coastal areas due to salt spray or saltwater intrusion.

Momonoy Lens' Interconnection with Surface Waters

The Monomoy Lens also boasts over 200 freshwater lakes and ponds, 20 streams, and 150 miles of coastal shoreline. The inland surface water bodies are windows on the aquifer that reflect the intersection of low areas in the ground surface with the water table. Groundwater typically discharges into a pond on one side and then pond water recharges the lens on the other side. Streams and rivers act as drains that skim groundwater off the surface of the water table. The large Monomoy ponds (Long, Seymour and Hinkleys) receive groundwater discharge from the lens, which in turn, feeds the Herring River so that groundwater ultimately discharges as the stream flows into Nantucket Sound. Where there is only coastal shoreline, groundwater discharges directly into marine water as fresh water seepage. Because of this interconnection, all uses of water- whether for drinking, swimming, boating, clamming, cranberry farming, or wetland habitat - are dependent upon maintaining the quantity and quality of the lens.