CHAPTER A - THE TECHNICAL BASIS FOR GROUNDWATER PROTECTION 



Cape Cod Aquifer Management Project Final Report Page 29 



4. 10 Protection of the Resource 



Once the resource area has been defined and mapped, attention must 

 focus on the management of potential sources of contamination. The 

 Aquifer Assessment Committee developed technical guidance documents in two 

 areas: (1) nitrate loading in wellhead-protection areas and (2) management 

 and understanding of common land uses which may threaten groundwater 

 quality. These two documents were designed to provide local officials 

 with the technical basis for managing their groundwater-protection 

 programs. These documents are clearly written on topics such as contam- 

 inant mob i 1 i ty . 



4.10.1 Nitrate Loading in Municipal Wellhead-Protection Areas 



Contamination by nitrate-nitrogen (nitrate) is one of the most 

 widespread threats to groundwater quality on Cape Cod. Sources of nitrate 

 include domestic on-site sewage disposal systems, municipal waste water 

 treatment plants, industrial waste water, and fertilizer. Nitrate was 

 chosen as the contaminant of concern by the Aquifer Assessment Committee 

 for several reasons. Nitrate is assumed to act as a conservative chemical 

 species in groundwater unaffected by sorption materials or by chemical 

 reaction. The principal mechanism by which nitrate is attenuated is by 

 dilution. It has been commonly demonstrated that the presence of nitrate 

 in groundwater, also indicates the presence of other, more toxic, 

 contaminants associated with waste water discharges. Adverse health 

 effects associated with nitrate have prompted a federal drinking water 

 standard of 10 milligrams per liter. However, on Cape Cod a maximum 

 nitrate concentration of 5 milligrams per liter is widely used as the 

 planning goal. 



The Aquifer Assessment Committee reviewed and found inadequate the 

 current approach of limiting development to one house per acre or greater 

 as a protective measure. In an effort to address the potential for 

 exceeding the recommended concentration of nitrate in municipal 

 water-supply wells, a subcommittee developed an approach for evaluating 

 the cumulative impacts of nitrogen-contributing land uses on water 

 quality. This approach is the subject of a CCAMP Technical Report by 

 Frimpter, Donohue , and Rapacz, "A Mass Balance Model for Predicting 

 Groundwater Quality in Municipal Wellhead Protection Areas" which is 

 available separately from NTIS. 



The publication provides an approach for evaluating the cumulative 

 impacts of nitrogen- contributing land uses to water quality in 

 public-supply wells. The model, which employs a mass-balance accounting 

 equation, calculates the resultant steady- state nitrate concentration at 

 the wellhead. In simplified form, the equation is as follows: 



Nitrate Concentration - Nitrate Load: Precipitation + Nitrate Load: 



Sources 



in Well Water Total Volume of Water 



