ISDS 



**A policy evaluation manual describing waste water management issues 

 should be prepared for town and state officials and the Rhode Island 

 courts, as a companion to similar volumes addressing other non-point 

 source pollution problems. The publication should reference available documentation 

 regarding the costs of sprawl and the need to channel growth into sewered areas or areas 

 where soils can accommodate properly installed and maintained ISDS effectively and 

 safely. The handbook should address the need for protection of water supply aquifers and 

 other natural resources, the pervasive impacts which improperly treated sewage effluent can 

 create across property lines and jurisdictional boundaries,the costs and benefits which both 

 ISDS and commumty sewers present, and other issues of concern. 



CRITICAL AREAS 



Findings and Concerns 



Delineation 



Given die severe limitations which many watershed soils present with respect to effluent 

 disposal, provision of adequate buffer distance and groundwater separation becomes 

 critical in providing a margin of safety for receiving waters. Nitrates, in particular, are 

 capable of moving beyond any buffer distance under highly permeable or saturated 

 conditions. Other nutrients and pathogens are attenuated by transport through a buffer 

 zone, albeit less effectively in highly permeable soils, or under saturated conditions. 



Cuirent ISDS site suitability evaluation procedures and policies governing the issuance 

 of variances are unable to address these concerns effectively. Water table separation 

 requirements provide a key example. Areas where the water table is to 24 inches below 

 the ground suiface are considered unsuited to ISDS construction. However, applicants are 

 generally allowed by variance to construct ISDS in areas where the water table is at 2 feet 

 below ground level, even where soil suitability is marginal or unsatisfactory and effluent 

 contaminants may leach directiy into groundwater. 



In the Scituate Watershed, 60 percent of the land area falls into SCS soil group 

 categories associated with water table levels at 18 to 36 inches below ground level. 

 Variances now being issued in this rapidly developing area may seriously compromise 

 water quality in the Scituate Reservoir, which serves 60 percent of the state's population. 



In areas where the water table lies between two 2 and 4 feet below ground level, 

 groundwater effects depend on soil and saturation factors, while effects on surface 

 receiving waters depend on density of development and buffer size. To address these 

 interrelated factors, the present research effort proposes a two-tiered sensitive area 

 definition, identifying Sensitive Areas on the basis of soil characteristics and potential water 

 supply resource availability, and Critical Areas on the basis of (in addition to these factors) 

 current water supply utilization, and location in geographic zones influencing coastal 

 resources. (The ISDS Task Force did not designate all public water supply watersheds as 

 critical areas, but instead focused its designation on the Scituate Reservoir due to its 

 importance and severe soil vulnerability. The Task Force noted the possibility that other 

 water supply watershed areas should be considered for future criticaJ area inclusion.) 



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