APPENDIX F: EVALUATION OF APPROACHES TO DETERMINE RECHARGE AREAS 



Cape Cod Aqifer Management Project Final Report Page F-2 



"Different models require different amounts and types of data. Associ- 

 ated with each level of model sophistication is a data base requirement. 

 Generally, as the model becomes more sophisticated in order to more close- 

 ly conform to reality, the associated data requirements increase. The 

 modeler is faced with the decision of when the benefits of a more realis- 

 tic model are outweighed by the difficulty and expense of collecting the 

 data necessary to adequately define such a model." 



Groundwater flow models can be separated into two broad categories: 

 analytical models and numerical models. Analytical models are appropriate 

 for the analysis of aquifer test data, simplified aquifer system analysis, 

 and the design of numerical models. They generally include a greater 

 number of simplifying assumptions. They represent the less sophisticated 

 end of the modeling spectrum described above. Numerical models are more 

 adaptable than analytical models. They allow for a more discrete and 

 therefore representative description of the aquifer system. They are 

 appropriate for the analysis of complex aquifer systems. They generally 

 include a lesser number of simplifying assumptions and represent the more 

 sophisticated end of the modeling spectrum. 



The ability of a modeling effort (Zone II delineation) to optimize the 

 cost/benefit (model accuracy) relationship, described earlier, is a princi- 

 pal consideration in the choice of the modeling approach. This decision 

 is directly dependent upon the complexity of the hydrogeologic system 

 under consideration (hydrogeologic data availability) . The choice of an 

 analytical modeling approach, and the greater number of simplifying assump- 

 tions associated with the technique, will generally result in an overesti- 

 mate of the extent of the Zone II area. This is generally a result of the 

 modeler utilizing more conservative parameter input to compensate for the 

 model's inability to account for complex aquifer interrelationships. The 

 choice of a numerical modeling approach, and the lesser number of simplify- 

 ing assumptions associated with that technique, will generally result in a 

 more realistic delineation of the Zone II area. This is a result of the 

 model's ability to account for complex aquifer interrelationships such as 

 multiple withdrawal and recharge points, boundary conditions, spatial and 

 directional variation of aquifer properties and recharge, militarily aqui- 

 fer systems, and partially penetrating wells. This is significant in the 

 Cape Cop pilot area, because in most cases these complex conditions are 

 present. 



The importance of a realistic delineation of Zone II becomes apparent 

 when you consider the ramifications of the land use controls that must be 

 placed in this area. 



The significance of the relationships described above can best be 

 evaluated by comparing an actual application of both analytical and numeri- 

 cal modeling techniques in the pilot area. 



