CHAPTER 4 - THE TECHNICAL BASIS FOR GROUNDWATER PROTECTION 



Cape Cod Aquifer Management Project Final Report Page 28 



and yard chemicals down the drain and into the septic system. The Aquifer 

 Assessment Committee recoiranended that an educational brochure targeted to 

 well owners be developed by CCPEDC and the Barnstable County Health and 

 Environmental Department (BCHED) which has recently developed a model 

 bylaw for private wells. (See Appendix J for Aquifer Assessment Committee 

 recommendations on private wells.) 



4.9.2 Protection of Future Public-Supplv-Well Resources 



The Aquifer Assessment Committee met with Eastham's Water Resources 

 Advisory Committee and reviewed the existing state of knowledge of the 

 town's groundwater resources to enable them to proceed with the develop- 

 ment of a groundwater management strategy. In addition to helping Eastham 

 understand its groundwater resources, the Aquifer Assessment Committee 

 also demonstrated the use of a simple map overlay analysis to locate 

 future public-supply-well sites. With the rapid rate of development on 

 the Cape, it is important to identify such sites and adopt appropriate 

 zoning regulations to protect them before the most suitable siting options 

 are precluded by development. 



The Committee conducted a map overlay analysis at a USGS quadrangle 

 scale to evaluate this issue. The first map was of hydrological data, 

 including water-table contours and brackish areas. Then, only considering 

 hydrological characteristics, areas that would be "good, better, best" for 

 water-supply development were selected. These areas were drawn to: limit 

 the potential for salt water intrusion; avoid lowering pond levels; and 

 have the shortest possible groundwater- flow paths (to limit the potential 

 for contamination from upgradient sources). Areas of conflicting land 

 uses, landfills, commercial businesses and appropriate buffers were then 

 overlayed as another limitation for water-supply development. Parcels of 

 town-owned land were then superimposed, and those that fell in the 

 remaining "best" areas were considered to be the best sites for public 

 supply well development. This process was repeated by computer, using the 

 maps that were digitized for the CCAMP Geographic Information System (GIS) 

 project. The resulting maps and a discussion of the procedure are 

 contained in the separately published GIS report. 



The map overlay methodology is a relatively straightforward procedure 

 that can be performed by any town, either by hand or through the use of 

 sophisticated GIS technology. It is important to begin the analysis by 

 looking at the groundwater resource itself, and not beginning with the 

 available parcels. The overlay analysis provides an initial determination 

 of potential sites that may be suitable for siting water supplies. More 

 specific on-site data may be evaluated in a subsequent overlay analysis to 

 refine the number of suitable sites. At this point, considerable effort 

 and resources will be necessary to evaluate the water -yielding 

 characteristics of each site. 



Once an accurate Zone II (zone of contribution) delineation is 

 completed the delineated area can then be protected through the creation 

 of special zoning districts or other means. 



