Acceptance rates for on-site wastewater systems

Studies have shown that the wastewater infiltration rate in drainfield trenches declines over time due to the formation of a dense biomat at the soil-trench interface that impedes infiltration and causes ponding in the trench. An estimate of the final steady wastewater infiltration rate is needed to specify the trench bottom area required for onsite wastewater systems. This is known as the Long Term Acceptance Rate (LTAR). UGA crop and soil scientists used a two-dimensional computer model to determine the steady flux through the trench bottom for 12 USDA soil textural classes with a fully developed biomat under normal operating conditions. They also developed an Excel spreadsheet that uses the modified Bouma equation to calculate LTAR for the 12 USDA soil textural classes. The scientists worked with a soils subcommittee to develop a proposal to be presented to the Georgia Department of Human Resources Technical Review Committee to convert from the current method of estimating LTAR to our method using the spreadsheet.