b'From Glaciers to Kettle PondsSome 10,000 years ago, as the last glacier receded from this, its southernmost reach, the Cape was formed by the deposit of sand and debris over an ancient clay base.Colder, denser blocks of ice remained embedded in the substrate, and when these fi nally melted, the terrain collapsed, producinghollows. These then fi lled with groundwater, formingthe freshwater ponds and lakes of Chatham. Later, as the sea rose, forming what are now Pleasant Bay and Chathams South Coast embayments,some of these pondsCrows Pond, Ryders Cove, Oyster Pond and Mill Pond are examplesbecame connected to the ocean and Nantucket Sound.Cape Cod AquifersAll of our drinking water, whether from municipal water supplies or from private wells, comes from the rain and snow that falls on Cape Cod and soaks into the sandy soils left by the glacier.The entire layer of groundwater beneath the Cape is re-ferred to as the Cape Cod Sole Source Aquifer and is made up of six separate freshwater lenses.Lenses can be thought of as mounds of groundwater bordered by marine water at the edges, bedrock on the bottom, and separated from each other by tidal rivers or inlets that cut across the Cape penin-sula. Groundwater is the subsurface water located beneath the water table, in soils and geologic forma-tions that are fully satu-rated.The drinking water forChatham and adjacent towns to the north and west is drawn from one large aquifer that lies beneath these towns.This large aquifer is called the Monomoy Lens. This lens is approximately 300 feet thick. deeper than the height of the Provincetown Monument, and is the sole source of drink-ing water for over 40,000 homes and businesses in six towns. More than fi ve million gallons are pumped out each day in the off -season.When our population triples in the summer, so does the water consumption.The soil types and geologic deposits are relatively continuous and allow water to move through them at a speed averaging one foot per day.Flow from the middle of the Monomoy Lens to the shorea distance of more than 3.5 milestakes over 18,000 days, or nearly 50 years.Contami-nants that are introduced into the lens and degrade water quality can ruin our drinking water for more than a generation.In 1982, the Environmental Protection Agency designated the Capes water supplyas a Sole Source Aquifer. This designation recognizes that the Capes groundwateris our only source of drinking water.About 40% of the annual rainfall seeps into the ground to replenish our aquifer.Page 10 bluepages.indd 10 8/26/2009 1:49:19 PM'