ISDS 



methods by which state procedures will be referenced to ensure consistency with more 

 stringent local standards. Describe methods, by which such standards will be enforced by 

 DEM, or referred to towns for enforcement (Again, this recommendation is based on the 

 assumption that DEM must take vigorous action in strengthening regulatory program 

 capability and enforcement, particularly in critical areas.) 



Buffers, Setback Requirements, Separation Distances 



Time of travel of ISDS effluent through unsaturated soil must be sufficient to provide 

 treatment to remove microbial organisms, phosphorus and nitrates to the greatest extent 

 possible. Systems must be constructed so as to function properly without failure via 

 surface breakout or discharge of improperly treated effluent to groundwaters. In the event 

 of system failure, opportunity for effluent renovation must be provided via natural or 

 induced degradation before effluent may be allowed to discharge to surface waters. For 

 these reasons, provision of adequate buffers and separation distances is of great 

 importance. 



Recommendations : Critical Areas Identified by the ISDS Task Force and by 

 the Present Study 



Water Supply Watersheds 



(Note: The Task Force designated only the Scituate Reservoir Watershed as a Critical Area; 

 'this study applies these recommendations, in addition, to water supply watershed Sensitive 

 Areas, to be evaluated in consideration of cumulative non-point source inputs. Here, 

 recommendations are repeated for all critical area classifications to indicate distinctions 

 between Task Force recommendations and those of this study.) 



Given the necessity of protecting water supplies,increase groundwater separation distance 

 requirement to four feet 



***Increase setback requirement to require that distance between all parts 

 of ISDS and reservoir, tributaries thereto, and open or subsurface drains 

 thereto, be a minimum of 200 feet. (This represents an increase of 100 feet over the 

 present setback requirement of 1()0 feet from drmking water sources.) Require that surface 

 runoff from fill or mound systems be contained within 100 feet of the reservoir. 



***Revise ISDS regulations and variance granting procedures to stipulate 

 that variances for standard system construction will not be granted in areas 

 where the water table is less than 3 feet below ground surface. 



**For large systems or subdivisions (combined flow exceeding 2000 gpd), 

 develop regulatory standards which provide for adequate separation based 

 upon soil conditions, effluent characteristics, and other site specific 

 conditions. Use of a point-based system such as that described in SITE EVALUATION, 

 below, may be applied to establish thresholds guiding the level of technical evaluation 

 necessary to establish design and siting requirements. 



** Adopt cumulative impact assessment procedures based upon contaminant 

 loading to consider potential impacts of a) new systems in areas developed beyond 

 carrying capacity; b) large systems and subdivisions in sensitive areas, soil-limited areas, 



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