ISDS 



adjacent to new development, a 75-foot setback shall be applied from the subdrain 

 to the new ISDS. 



b) A minimum buffer of 100 feet from the point of subdrain discharge to any surface 

 water body or wetland must be provided. Such buffers must provide adequate 

 effluent treatment via approved mechanisms, including overland flow, infiltration or 

 vegetated channel passage. The design of buffers should also ensure non-erosive 

 passage through the vegetative buffer and proper discharge from it. Buffers must 

 meet applicable requirements of the Freshwater Wetlands Program, CRMC, and 

 local drainage control requirements. 



c) Use of subdrains in level areas is not recommended due to unreliable performance. 



d) As a component of the ISDS application process, the engineer/ installer must 

 demonstrate that the subsurface drain will effectively lower the water table while 

 maintaining the required 25-foot setback from the ISDS and that overland treatment 

 for a minimum of 75 feet will provide effluent renovation without inducing water 

 quality or erosion impacts to receiving waters. 



e) As a component of the ISDS application process, the engineer/installer and 

 homeowner shall prepare for approval a plan for maintenance of the subdrain buffer 

 area, outlining ownership and maintenance responsibility. When agreed upon, the 

 plan shall become a permit attachment and deed encumbrance, subject to property 

 transfer verification and to inspection by DEM and applicable WWMD. 



FILLED SYSTEMS 



Findings and Concerns 



Where minimum required separation distances to groundwater or impervious surface 

 (four and six feet respectively) cannot be met, current ISDS regulations provide that two 

 and four foot separations may be acceptable if the site is altered via filling or excavation. 

 System designers may fill above the original ground surface to meet separation 

 requirements, or may excavate low permeability material and replace it with more 

 permeable substrate. Variances may be granted to adjust separation distances. 



Use of filled systems presents several concerns: 



a) Runoff from filled systems constructed on small lots frequentiy creates drainage 

 problems on adjacent properties; 



b) Design standards for fill systems inadequately specify requirements for fill material 

 to be used. As a rule, coarse sand or gravel fill is used due to high permeability. 

 Because coarse soils have been found to be much less effective in removing 

 nutrients and microbial pathogens than less permeable soils, these systems can 

 rapidly release improperly treated effluent into groundwater or other receiving 

 waters. The risk of contamination is increased where excavation of natural soil 

 materials within a short distance of the water table creates smearing or compaction 

 of wet soils, severely limiting the soil's capacity to renovate effluent. 



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