Approximately 23 percent of the estimated 115 million occupied homes in the United States are served by onsite wastewater systems. The vast majority of onsite wastewater treatment systems include a septic tank, grease trap, or both for primary treatment. These units are efficient, simple, low-energy treatment units whose performance is critically important to the overall functioning of onsite wastewater systems. Regulations, industry standards, guidance materials and engineering texts vary widely and are often incomplete in their consideration of the factors that may influence primary unit...