Clear Water Services worked in conjunction with SCS Engineers to develop an advanced treatment BMP to support this waste transfer facility located in Santa Clara, CA. This endeavor was supported by a phased investigative study, which included bench-scale treatability testing, an in-field pilot stormwater treatment system (PSTS), and a retrofitted temporary treatment system that could support the facility's organic loading and organic footprint. The facility had exhibited significant exceedances for all heavy metals, COD, and TSS. Values for COD reached as high as 40x the benchmark value.

Stormwater would periodically exhibit organic decay (anaerobic breakdown), which contributed to the reduction in dissolved oxygen and extremely low pH conditions, posing additional treatment design challenges. The PSTS was developed to determine the most cost-effective and feasible treatment system design by addressing the removal of TSS, COD, and associated metals. The PSTS also had to support management of anaerobic breakdown. The PSTS evaluated the following treatment train: solids separation, hydroxide precipitation, coagulation, and particulate reduction (via sand filtration), as well as various adsorption multimedias and ion exchange resins.

The PSTS included levels of manual and automated operator support necessary for real-time operations to adjust chemical concentrations, control pH, and document treatment system performance in accordance with the NPDES. The PSTS proved successful and supported the design of a 300gpm long-term rental treatment system.

This system implemented a handful of modifications from the pilot to support the variability of stormwater influent. Modifications included larger stormwater structures that supported retention time and freeboard allocation, thereby increasing functionality at the design flow rate and allowing for more time for chemical mixing and solids separation. The new design also included advanced automated pH adjustment, which utilized the feedback from pH monitoring locations to properly adjust (and trim as needed) pH adjustment chemistry and pretreatment chemistry dose rates to support an accurate real-time chemical adjustment. Smart pH adjustment also improved flocculation efficiency, further reduced potential anaerobic conditions, and lowered long-term chemical costs.

The PSTS also confirmed the multimedia selection, which included a mix of adsorption and ion exchange resins, proving sufficient for consistently reducing all contaminants of concern at variable concentrations.