Subregional Soil Column Study

The City of Santa Rosa is considering indirect discharge as part of the Incremental Recycled Water Program (IRWP) Discharge Compliance Project (DCP). Indirect discharge is considered application of recycled water to soils relatively close to the river where local geology allows for a direct subsurface pathway to the river. Indirect discharge is being considered because of the potential water quality benefits associated with soil aquifer treatment. The primary water quality goals are the attenuation of California Toxics Rule (CTR) constituents copper, nickel and lead in the soils. A soil column pilot was constructed at the Laguna Subregional Water Reclamation Facility (Laguna Plant), which produces disinfected tertiary recycled water for unrestricted use (recycled water), to quantify water quality benefits of indirect discharge. The pilot was designed to observe CTR constituent as well as other water quality changes (e.g., nutrients). CTR constituents were spiked to the pilot feed water as the recycled water levels of CTR constituents are variable and too low to accurately quantify attenuation trends. With this in mind, attenuation goals were based on percent removal values based upon historical levels and anticipated future regulatory levels