Environmental Science and Engineering

Qualitative Tools to Determine the Expected Performance of Wastewater Soil Treatment Units

Publication Date: December 2010
C ooperating Institution:
Colorado School of Mines
Principal Investigator: John McCray
Project Budget: $1,390,116
Project Identifier: DEC1R06A


Onsite wastewater treatment systems (OWTS) are an important part of water management infrastructure in the United States. Thus, proper OWTS selection, design, installation, operation and management are essential. To aid this life-cycle, a toolkit was developed to enable evaluation and design of expected soil treatment unit (STU) performance.

The toolkit includes a Guidance Manual, a companion Toolkit User’s Guide, two Excel-based spreadsheet tools (STUMOD and N-CALC), and a supplemental volume of visual-graphics information.  The toolkit also includes a literature and model review (published in 2009). This framework provides detailed information to less experienced users while enabling more experienced users to start directly with STUMOD or other tool implementation referring to limited sections of the Guidance Manual or User’s Guide.

The toolkit was developed for a wide range of users faced with different needs of varying complexity when evaluating treatment of nitrogen, microbial pollutants (bacteria and virus), and organic wastewater contaminants (OWCs). Progressing through simple to more complex tools ultimately guides the user to the simplest tool that is appropriate, but discourages using a tool that is too simple for the decision at hand. The simplest tools include look-up tables and cumulative frequency distributions (CFDs) to direct the user to available pertinent information. Nomographs enable initial screening and quick insight into expected nitrogen removal based on the predicted output from STUMOD. Cumulative probability graphs illustrate modeling results in a risk-based framework while numerical model simulations demonstrate the usefulness of complex tools. Finally, two spreadsheet tools were developed, N-CALC and STUMOD, allowing the user to evaluate a range of STU operating conditions, soil hydraulics, and/or treatment parameters, as well as the relative influence of these factors on performance.

Associated Documents:
Guidance Manual, User’s Guide, and Visual-Graphics Tools
See also: State of the Science: Review of Quantitative Tools to Determine Wastewater Soil Treatment Unit Performance