CHAPTER 2 - CCAMP STUDY AREA: TOWNS OF BARNSTABLE AND EASTHAM 



Cape Cod Aquifer Management Project Page 9 



aquifer is among the most permeable in New England, yielding large 

 quantities of naturally high quality water. The term aquifer, therefore, 

 is used to define those underground formations that contains sufficient 

 saturated permeable material to yield significant quantitites of water to 

 wells. Yet the same highly permeable sands and gravels which provide an 

 excellent medium for withdrawing large quantities of water, create an 

 aquifer that is extremely susceptible to contamination. Sandy soils are 

 low in organic content and have a poor capacity for attenuating 

 contaminants by sorption and ion exchange. In addition, the depth to the 

 water table for a major portion of the Cape is generally quite shallow so 

 contaminants do not have far to travel before they reach groundwater. 



The aquifers of Barnstable and Eastham are generally unconfined; their 

 upper boundary is the water table , except in local areas in which clay and 

 silt confine the sand and gravel. The lower boundary of the aquifer under- 

 lying Barnstable consists of fine grained lake deposits and bedrock forma- 

 tions (Figure 2.1, 2.2). The lower boundary of the Eastham fresh-water 

 aquifer is the fresh-water/salt-water interface, which lies at a depth of 

 about 450 feet below land surface at the center of the aquifer as revealed 

 by uses test drilling in October, 1987. Groundwater in Eastham and 

 Barnstable is found in two of six fresh-water lenses which together 

 comprise the Cape Cod aquifer (LeBlanc et al. , 1986) (Figure 2.3). 



In Barnstable, glacial lake sediment is thought to underlie most of 

 the outwash plain, and may have been deposited in a lake which extended 

 from the retreating edge of the glacier to Martha's Vineyard and Nantucket 

 (Oldale, 1974a). These glacial sediments are underlain by much older 

 consolidated rocks (Oldale, 1974a, 1974b). 



Eastham is underlain by about 200 feet of sand and gravel outwash 

 deposits that were formed by meltwater streams from the retreating conti- 

 nental glacier, which was located to the east of Cape Cod. The Eastham 

 outwash plain deposits are underlain by approximately 300 feet of 

 fine-grained lake deposits of silt and clay which rest on crystalline 

 granite as revealed by USGS test drilling completed in October of 1987 

 (Barlow, 1988 personal communication). The shores of Eastham and 

 Barnstable are bordered in most locations by beach, dune, salt marsh and 

 swamp deposits of post-glacial age. 



The general direction of groundwater flow in the aquifers of Eastham 

 and Barnstable, as shown in Figure 2.3, is from the central areas of the 

 peninsula to bays, marshes, Nantucket Sound, Cape Cod Bay and the Atlantic 

 Ocean, which surround Cape Cod. Many of Cape Cod's ponds are in hydraulic 

 contact with the surrounding aquifers, with their water-level elevations 

 being similar to those of the regional water table. The ponds can be 

 areas of both groundwater discharge and groundwater recharge, depending 

 upon the direction of groundwater flow in the area. 



Precipitation is the sole source of recharge on Cape Cod. Average 



annual precipitation on the peninsula ranges from 40 inches per year on 



the Outer Cape to 47 inches per year on the Inner Cape. The amount of 



precipitation which does not run off or is not returned to the atmosphere 



