ISDS 



drains may intercept ISDS effluent due to groundwater mounding or natural 

 variations in groundwater surface levels. 



b) Given the risk of effluent interception by subdrains, the impacts of drain discharge 

 are of critical importance. Subdrains may discharge any of the range of 

 contaminants contained in ISDS effluent and may also cause erosion and channeling 

 of substrates and banks creating significant water quality degradation. 



c) Potential for failure of subdrains is high, due to clogging of the filter bed, 

 obstruction of the discharge point, and backup of overland flow to receiving 

 waters. 



DEM regulations regarding subdrains arc insufficiendy clear as to permitted method of 

 discharge and required setback to receiving waters. Presentiy, the 100-foot required buffer 

 from ISDS to public water supplies is defined to include "tributaries, drains and subdrains 

 thereto." Task Force findings state that, in practice, only those drains and subdrains which 

 arc direcdy connected to natural wetiands or tributaries are included in this definition. 



Further, manmade stormwater drainage ways and drains which discharge flow overland 

 before reaching reservoir waters arc protected by 25-foot, rather that 100-foot buffers. 



Although DEM's policy is to prcvent dircct discharge of subdrains to surface waters, no 

 minimum distance of overland flow is recommended. Unless some effluent treatment is 

 provided by overland flow, the actual buffer distance may consist only of the 25-foot 

 required setback between the subdrain and the ISDS. 



Recommendations 



**Revise ISDS regulations to establish deHnitions of tributaries and drains 

 which are based on flow characteristics. The regulatory definitions applied under 

 the Freshwater Wetiands program provide that "areas subject to storm flowage" include 

 naturally occurring intermittent streams connecting wetiands, which may be classified as 

 rivers requiring 100 foot buffers. In order to provide consistency with the 

 freshwater wetlands definition, which also addresses manmade stormwater 

 drainageways within the "flowage" definition, the ISDS definition of 

 tributaries and drains should similarly address flow characteristics. In both 

 programs, the definition of intermittent streams should be clarified so as to be tied to soil 

 characteristics. (For example, intermittent highly meandering streams are characteristic of 

 Ridgebury soils). 



***Revise ISDS regulations to prohibit use of subdrains in all critical areas 

 as defined in CRITICAL AREAS above. 



**If subdrains are permitted in areas outside of critical areas, adopt the 

 following regulatory standards for ISDS, which expand on those recommended by 

 tiie ISDS Task Force: 



a) The minimum distance from a subsurface drain to any part of a sewage disposal 

 system shall not be less than 25 feet where located uphill of the system and no less 

 than 75 feet on the downhill side. Where pre-existing subdrains occur on lots 



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