CHAPTER 4 - THE TECHNICAL BASIS FOR GROUNDWATER PROTECTION 



Cape Cod Aquifer Management Project Final Report Page 26 



public -supply wells in Barnstable and concluded that both approaches use 

 analytical modelling techniques and yield reasonable delineations of the 

 zones. Please refer to 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," for a discussion of the methods of data 

 reduction for use in such analytical modelling efforts. Appendix F, 

 "CCAMP Aquifer Assessment Committee Report on Evaluation of Approaches to 

 Determine Recharge Areas for Public Supply Wells," provides more 

 information on the group's examination of wellhead-protection area 

 determination methodologies as currently used on Cape Cod. 



A key issue that faced the Committee was the determination of the 

 optimum approach to wellhead-protection area delineation. Determining 

 when the benefits of a more realistic model are outweighed by the expense 

 of collecting the data necessary to adequately define such a model. In 

 order to determine this cost/benefit point, the committee recommended that 

 analytical and numerical modeling techniques be applied and compared in 

 the project area, allowing a controlled demonstration of the shortcomings 

 and benefits of each approach. 



4. 7 Initiation of the Comprehensive Numerical Modeling Project 



An important outcome the Aquifer Assessment Committee recommendations 

 was the initiation of a cooperative project between the DEQE/Division of 

 Water Pollution Control, DEM/Division of Water Resources, the USGS and 

 CCPEDC. The project consists of a demonstration of three-dimensional 

 groundwater modeling to determine wellhead-protection areas. The demon- 

 stration included conditions where the advantages and disadvantages of the 

 modeling approaches can be defined and compared with those of the analyti- 

 cal approaches. Opportunities for model verification with past and future 

 water-level data will be utilized. The models will be applied to areas 

 with complex boundary conditions, multiple aquifer systems, multiple with- 

 drawal points, areally variable recharge, variable aquifer thickness, 

 partial penetration, and changes in aquifer storage. Additional analyses 

 may include comparison of the area of influence with area (zone) of contri- 

 bution and determination of the upgradient boundary of the zone of contri- 

 bution. Data acquisition requirements and costs will be also be 

 described. This will allow the determination of the point at which the 

 benefits of a more realistic model (more accurate wellhead-protection area 

 delineation) are outweighed by the expense of collecting the necessary 

 data to adequately define such a model. The results will be published by 

 the USGS in May, 1990. 



4. 8 Documentation of Modeling 



As an outgrowth of the Committee's examination of models for use in 

 delineating wellhead-protection areas, the group was concerned that many 

 models were not adequately documented; making it difficult to evaluate 



