Instream PH Standards

GEI Chadwick Ecological Division successfully assisted Metro Wastewater Reclamation District (Metro) in negotiations with the Water Quality Control Division (WQCD) by setting a new site specific pH standard for the mixing zone of the Metro effluent discharge. The new standard allowed Metro to discharge at current treatment levels and be in compliance with appropriate pH standards.Metro was concerned about potential compliance issues for their effluent and instream pH standards related to the installation of upgraded nitrogen treatment. Our ecological division provided the client with detailed ecotoxicological support. We conducted technical review of EPA pH criteria and determined that fish expected to occur below Metro were more tolerant of pH than species in the national database. We then conducted technical review of EPA pH standards, accumulated additional scientific literature, and evaluated pH against freshwater biota (especially fish) expected to be present downstream of the Metro discharge. We determined that the EPA pH range (6.5 – 9.0) was driven by coldwater species and that warmwater fish below Metro were more tolerant of lower pH values (6.0 – 9.0). A technical report was prepared summarizing the findings for submission by Metro to the Water Quality Control Commission. The study was conducted over a 4-month period.