There is a demonstrated need for better wastewater alternatives, even in the United States. On-site septic systems serve approximately 25% of the US population (USEPA 1997), and in 1995 alone, over 2.5 million septic systems malfunctioned (NODP). Contrary to the belief that regional wastewater facilities are solving the nation's problems, more Americans are using septic systems now than in 1990 (NODP). Many areas currently served by failed or non-existent septic systems cannot be corrected through regionalization due to low population densities, low per-capita income, rugged terrain, and other barriers, leaving on-site and small cluster facilities as the only viable wastewater option (Drake, 2000). In addition, residential clusters are becoming more widespread as a land-planning tool (Arendt, 1999), resulting in the increasing need for community wastewater treatment facilities (Sykes & Kopischke, 1996). Hydraulic failure is recognized as a leading cause of premature wastewater soil absorption system (WSAS) failure (Sherman et al. 1998). Often failure is caused by the slow or limited vertical movement and lack of adequate lateral movement of groundwater, resulting in "mounding" of the water table in the vicinity of the WSAS. Mathematical models are recognized as a potential solution to this design problem (Siegrist et al. 2000) but have not become established as a tool for WSAS designers due to a lack of understanding and field calibration.

In 2002, the NDWRCDP funded a proposal submitted by the Colorado School of Mines (CSM) to evaluate the application of hydrogeologic models to WSAS designs. This project is intended to complement the ongoing CSM effort. Up to five large-scale WSAS systems will be evaluated using a variety of field techniques. The objective of this effort will be to determine the accuracy and applicability of the information gathered through different field techniques as applied to the problem of WSAS mounding. Actual mounding will be measured; and different sets of field data will be input into the models recommended by CSM as being appropriate for the hydrogeologic setting. The relative accuracy of the model predictions vs. actual mounding will be used to evaluate the appropriateness of the field investigative method. The following field techniques will be evaluated:

• Use of soil survey and background information.
  
  
• Hand auger borings.
  
  
• Perc tests.
  
  
• Backhoe pits.
  
  
• In-situ hydraulic conductivity (Amoozometer) in conjunction with backhoe pits.
  
  
• Geotechnical borings; borings logs used as input data.
  
  
• Laboratory grain-size distribution tests to predict hydraulic conductivity used with geotechnical boring logs.
  
  
• Laboratory hydraulic conductivity tests used with geotechnical boring logs.
  
  
• Slug tests to measure hydraulic conductivity in existing monitoring wells.