APPENDIX D 



DRASTIC MAPPING OF AQUIFER VULNERABILITY 



IN EASTERN BARNSTABLE AND WESTERN YARMOUTH, 



CAPE COD, MASSACHUSETTS 



Douglas L. Heath 



U.S. Environmental Protection Agency, Region 1 



Boston, MA 



July 1987 



The permeable glacial deposits of Cape Cod are highly vulnerable to contam- 

 ination from improper storage, handling and spillage of hazardous chemi- 

 cals. The towns of Barnstable and Yarmouth -- like all communities on the 

 Cape -- rely on ground water to supply the needs of their citizens. The 

 risk of contamination of ground water resources will increase unless 

 preventive measures are taken. 



In 1985 , the Cape Cod Aquifer Management Program began a study of land 

 uses within Zone I, an area of recharge to nine public supply wells in 

 eastern Barnstable, which has experienced rapid development over the last 

 thirty years. With an area of 3,650 acres, Zone I is the largest zone of 

 contribution in Barnstable. The study included a detailed inventory of 

 common land uses, such as an airport and industrial park, service sta- 

 tions, dry cleaners and septic systems that might contain sources of pollu- 

 tion that threaten the quality of ground water (Gallagher and Steppacher, 

 1987; SEA Consultants, 1985). The study also included an analysis of the 

 relative vulnerability of soils and ground water to chemicals generated by 

 such activities. Using the methods and criteria in DRASTIC (Aller and 

 others, 1985), the pollution potential for contamination in Zone I was 

 evaluated, mapped and incorporated into a geographical information system 

 developed by the U. S. Geological Survey. The purpose of this paper is to 

 describe how DRASTIC was applied as a mapping tool for ground-water manage- 

 ment in this hydrogeological setting. 



DRASTIC 



As a standardized system developed jointly by the U.S. Environmental Pro- 

 tection Agency and the national Water Well Association, DRASTIC is de- 

 signed to provide numerical rating of relative vulnerability to contamina- 

 tion in most hydrogeological settings found in the United States. The 

 name is an acronym for seven factors that influence how quickly chemicals 

 may move through unsaturated and saturated soils and rock. These are 

 Depth to water, net Recharge, Aquifer media, Soil media, general Topogra- 

 phy, impact of the vadose zone and the hydraulic Conductivity of the aqui- 

 fer. These seven factors are assigned numerical weights and ratings that, 

 when added together, provide a vulnerability in a wide variety of set- 

 tings, DRASTIC is not designed for use in areas small than 100 acres. 



In eastern Barnstable and western Yarmouth, Zone I consists of two hydro- 

 geologic settings. Two thirds of the area is made up of Barnstable Out- 

 wash Plain deposits of permeable sand and fine gravel with beds of silt 

 and clay. The relief of the land surface is moderate, ranging in eleva- 

 tion from sea level to about 40 feet. Ground water is generally less than 

 50 feet deep. All nine public supply wells are screened in the outwash 



