The Sacramento Regional County Sanitation District discharges treated wastewater to the Sacramento River near Freeport, California, via a multi-port diffuser. Flow in the river near this 181 mgd treatment plant is often strongly tidal. 

 

Since the late 1980’s, Flow Science has conducted field dye studies within the river to determine the mixing behavior of the discharge. Flow Science developed a thermal compliance model to evaluate the effect of the discharge on temperature within the river. This model was incorporated into the Plant’s NPDES permit, which contained an exemption to the Thermal Plan.

Flow Science has also conducted detailed modeling of the near-field and far-field water quality and temperature effects of this discharge. The analyses have utilized several models, including a longitudinal dispersion model to evaluate the effects of reverse flows on wastewater concentrations within the river, Fisher Delta Model (FDM), FLOWMOD, a three-dimensional computational fluid dynamics (CFD) model of the near-field zone, and Monte Carlo modeling to evaluate water quality within the river for a variety of operational and water quality scenarios.

These studies have been conducted in support of NDPES permitting efforts, to evaluate the impact of isolated discharge events, in support of master planning and EIR processes. Flow Science continues to provide on-going support of SRSCD in support of an NPDES permit appeal, permit compliance, TMDL development, and EIR processes.