At our client’s sawmill in northern California, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), and zinc all exceeded general industrial stormwater permit numeric action levels (NALs). And the stormwater required treatment to reduce concentrations of COD, BOD, TSS, and zinc. COD/BOD treatment is challenging because those constituents are soluble and not easily reduced with settling or filtering alone.
We performed pre-design hydrologic and bench-scale treatability studies to identify the best treatment combination for COD, BOD, TSS, and zinc. Our engineers completed all design and permitting actions—including the basis of design report, drainage report, permitting and construction plans and specifications, construction cost estimate, construction schedule, construction permits and approvals, and the treatment system O&M manual.
Our treatability studies demonstrated that chemical treatment followed by biofiltration was the most cost-effective option. Our engineers oversaw system construction, starting with contractor bid support through to quality assurance/quality control during construction. Once operational, effluent concentrations were significantly reduced and met all permit-required NALs.