ISDS 



c) Fill systems have exhibited a higher failure rate than conventional systems, due to 

 surface seepage, groundwater mounding, and localized overloading (ISDS Task 

 Force, 1987). 



Section SD 15.03 (b) of the ISDS regulations authorizes construction of filled systems 

 in site conditions otherwise not conforming to regulatory requirements, but provides no 

 standards for design or construction of filled systems. 



Present inspection procedures, which provide for inspection of the dug pit before 

 installation, and of the top material prior to covering with topsoil, are inadequate to ensure 

 satisfactory installation of properly protective material throughout the fill system. 



Recommendations 



Revise ISDS regulations to: 



**Prohibit use of filled systems in sensitive areas as defined in CRITICAL 

 AREAS, above, where a) depth to groundwater from original ground surface is less than 

 four feet, except in excessively permeable soils (per rate exceeding 5 minlinch), where five 

 feet is required, and b) where impervious material, including fractured rock, "rotten" rock, 

 or shale is less than six feet from the original ground surface. 



**For situations where use of filled systems is permitted, establish specific regulatory 

 construction standards to: 



a) retain surface runoff on site by requiring a ten foot bi^erfrom the edge of a 

 leaching system to any adjacent property line; and 



b) require that a layer of slowing material be used with gravel fill to ensure that 

 sufficient effluent treatment is achieved. A formula for use of fill material 

 component layers should be prepared, with governing factors provided to the 

 engineer/installer by the Site Evaluator, or licensed evaluation professional. 



MOUND SYSTEMS 



Findings and Concerns 



In an effort to address the many limitations of filled systems, much engineering research 

 effort has focused on the development of practical designs for raised fill or "mound" 

 systems. The advantages and disadvantages of mound systems, along with other 

 alternative systems, were analyzed in depth by an ISDS Task Force Subcommittee. Mound 

 system construction involves considerable engineering analysis, and systems require 

 careful maintenance, two factors that limit their usefulness. Nevertheless, the Task Force 

 recommended use of mounds as replacement for failed systems in situations where existing 

 development prevents installation of a conventional system. The Task Force specified that 

 proper monitoring of systems installed under these specific conditions should be provided 

 for, and encouraged the development of training courses and materials which could ensure 

 their proper siting, design, and construction. 



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