The History of Water on Martha’s Vineyard
Living on Martha’s Vineyard comes with many wonders and struggles. Water quality can be one of those struggles. The water on the Vineyard varies tremendously based on the different layers of rock and sediment left by the receding ice sheet 10,000 years ago. So levels of iron, manganese, and other minerals as well as acidic or basic water can vary dramatically from property to property. This is why your well water may only be acidic, but your neighbor’s water is full of iron.
While we do not drill wells, we service and replace well pumps, well tanks, and water treatment systems.
Most people have well water on the island. Most well water on the island suffers from two main problems, low pH and iron. Please refer to our What We Test for in your Water page for more information on what issues you may encounter.
Outwash Plain Aquifer: Most of the Island, including all town wells, draws its drinking water from one main aquifer located in the Outwash Plain, where glacial ice deposited layers of sand and gravel as it melted, creating porous deposits that readily absorb rainfall, which percolates down into the water-saturated zone known as an aquifer. The entire Island has been designated by EPA as a Sole-Source Aquifer, since groundwater is the Island’s only source of drinking water. There is a plentiful supply of potable water, provided it is properly protected from contamination. We currently draw about 1.5 billion gallons per year from the main aquifer, of which about 70% finds its way back into the aquifer after wastewater treatment. Rainfall replenishes the aquifer by about 24.5 billion gallons each year, so even if our use went up to 3.9 billion gallons per year (projected by the USGS), it would still be well below the suggested maximum safe withdrawal level of about 16.7 billion gallons (estimated by the MVC).
Chappaquiddick Aquifers: Smaller aquifers lie under Chappaquiddick Island that are not connected to the main aquifer and are replenished only by rainfall. In general, the quantity of water recharged to a 3-acre lot as required by zoning is more than adequate to meet water needs for a home and guest house.
Western Moraine Aquifers: In the hilly Western Moraine, the glacial deposits are very different, displaying a wide range of sediment types ranging from compact, almost impermeable, clay to porous sand. The sandy deposits make good aquifer materials while the clayey deposits may hold some water but do not yield it. As a result, there are numerous aquifers in this area that may or may not be connected with other nearby aquifers. Finding a good source of well water is sometimes difficult.”