Discharge of water treatment residuals to the receiving waters including lime softening solids, has been allowed by state agencies and USEPA in the past. However, USEPA is
currently considering limiting treatment residual discharges into receiving waters because of violation of instream Water Quality standards and potential (but undocumented) impacts to aquatic life and discoloration of the water in the near vicinity of discharge. In lieu of discharge, many treatment plants would be faced with disposing of these solids in a landfill or elsewhere, resulting in significant cost in disposal. This paper presents a modeling case study to assess whether the current Water Quality standards could be achieved through the implementation of plant level BMP’s and diffuser.
Cornell Mixing Zone Expert System (CORMIX) model was used to simulate the hydrodynamics in the receiving water. The results of the CORMIX model were used along with the in stream and effluent concentrations in a Water Quality (WQ) spreadsheet model to simulate the in stream water quality at various downstream locations in the river. The simulated instream concentration was compared to the instream water quality standards for pH, Total Suspended Solids (TSS), Turbidity and Color. The modeling results indicated that Water Quality standards could be met through the use of diffuser at different flow conditions.