APPENDIX F 



EVALUATION OF APPROACHES TO DETERMINE RECHARGE AREA 

 FOR PUBLIC- SUPPLY WELLS 



Aquifer Assessment Committee 

 Cape Cod Aquifer Management Project 



April 3, 1986 



Introduction 



The Aquifer Assessment Committee has been charged with the evaluation 

 of existing Zone II delineations (zones of contribution around public- 

 supply wells) and the determination of alternative approaches to delineate 

 the Zone II that would be appropriate for the pilot area. The purpose of 

 this report is to outline the salient considerations surrounding these 

 issues, to summarize our evaluation of existing Zone II delineations in 

 the project area, and to recommend future courses of action to meet our 

 charge. The Aquifer Assessment Committee has reviewed the methods used by 

 SEA Consultants and the CCPEDC to estimate Zone II (zone of contribution) 

 about the public-supply wells in Barnstable. It should be noted that 

 Eastham has no community public-water-supply wells and accordingly no 

 existing Zone II delineations. 



Background Information 



The Zone of Contribution (ZOC) or Zone II as defined in 310 CMR 24.00 

 is that area of an aquifer which contributes water to a well under the 

 most severe recharge and pumping conditions that can be realistically 

 anticipated. It is bounded by the groundwater divides which result from 

 pumping the well and by the contact of the edge of the aquifer with less 

 permeable materials such as till and bedrock. At some locations, streams 

 and lakes may form recharge boundaries. The delineation of this area is 

 analogous to the delineation of the watershed to a reservoir and it pro- 

 vides the foundation for most quality related groundwater resource plan- 

 ning decisions. It is the area in which the implementation of land-use 

 restrictions should be applied to prevent the contamination of well wa- 

 ter. Accordingly the importance of an accurate delineation of Zone II is 

 apparent . 



The Zone II delineations performed to date and the alternative methods 

 the Committee will be considering both involve groundwater flow modeling. 

 As described by Walton, 1984: "Modeling is concerned with the dynamic 

 behavior of groundwater systems. Models simulate and are simplified repre- 

 sentations of groundwater systems. Modeling is an exercise in systems 

 analysis whereby data and theories concerning the behavior of groundwater 

 systems are organized into models." 



"An important aspect of modeling is the proper acknowledgment of the 

 approximate nature of modeling through the clear description of model 

 assumptions and limitations. Adequate documentation and appreciation of 

 assumptions greatly assist the modeler and model user in keeping model 

 result expectations within a realistic perspective." 



