APPENDIX E 



HYDROGEOLOGIC CONSIDERATIONS OF ZONE OF CONTRIBUTION METHODS 



USED BY CAPE COD PLANNING AND ECONOMIC DEVELOPMENT COMMISSION 



AND SEA CONSULTANTS, INC. 



FOR PUBLIC-SUPPLY WELLS IN BARNSTABLE, MASSACHUSETTS 



Douglas L. Heath 

 U.S. Environmental Protection Agency, Region 1 

 Boston, MA 



December, 1985 



Introduction 



Successful determination of a public-supply well's zone of contribu- 

 tion requires accurate information about the following factors: well dis- 

 charge, aquifer recharge, local hydraulic gradient of the water table, 

 horizontal and vertical hydraulic conductivity, and the saturated thick- 

 ness of the aquifer from which a well draws its water. Additional factors 

 such as a well's proximity to sources of pollution, fresh/salt-water bod- 

 ies and urban areas are also important considerations in protecting 

 ground-water quality. 



Previous attempts to determine protection areas for public-supply 

 wells on Cape Cod were made in 1982-1983 by the Cape Cod Planning and 

 Economic Development Commission (CCPEDC) and for Barnstable in 1985 by SEA 

 Consultants, Inc. (SEA). Both attempts combined analytical and numerical 

 methods which differed in both assumptions and data, resulting in limited 

 agreement about a particular zone's size or orientation. 



Refinement of these methods consists in tailoring each zone of contri- 

 bution to individual site conditions, which entails understanding the 

 natural flow system and assessing basic assumptions. The purpose of this 

 paper is to describe the necessary factors, to outline sources of informa- 

 tion, and to provide a comparison of recent attempts to delineate recharge 

 areas for public-supply wells in Barnstable, Massachusetts. 



Barnstable Public-Supply Well Discharge Records 



Barnstable township is currently served by 31 public water supply 

 wells operated by three municipal fire districts and one private company. 

 These wells have pumps which operate independently from one another in 

 response to distribution head changes in their respective water-supply 

 systems which connect the source of supply to both commercial and private 

 residents. Each supplier maintains records of daily well pumpage at indi- 

 vidual wells measured in gallons per day. According to company superinten- 

 dents, historical accounts of daily discharge extend back at least to 1975 

 at both the Barnstable Water Company and the Centerville-Osterville Fire 

 District, to 1972 at the Barnstable Fire District, and at least to 1950 at 

 the Cotuit Fire District. Pumping records indicate that because of sea- 

 sonal fluctuations in demand, a public-supply well may operate for 24 

 hours a day over many weeks during the summer, yet remain idle for several 

 months during the winter. In addition, wells are occasionally taken 

 off-line" for pump maintenance, screen cleaning or the installation of 



