Simplified Design of ET beds for groundwater protection in the Arid

Flow Variation in Design of Advanced Onsite Systems
A. Hanson, Ph.D., PE, L. E. Mimbela, R. Polka, W. Zachritz1
New Mexico State University, Las Cruces, NM 88003
Currently at the Dry Lands Research Institute, Las Vegas, Nevada.
There is an increase in use of advanced home scale wastewater treatment systems to
protect sensitive environmental areas. In the arid southwest these are both shallow
ground waters used for drinking water, fractured bedrock areas, and riparian areas.
Standard septic tank systems are relatively insensitive to flow variation, but the advanced
systems are extremely sensitive to large fluctuations in flow. This paper will present a
detailed flow study from 3 homes. It will compare the peaks day during the week as well
as hourly peak flows to the typical values presented in engineering design literature.
Flow values are measured at the septic tank effluent not coming out of the house so
hydraulic damping by the septic tank is accounted for.