Analysis of Intake and Discharge Salinity Regimes for a Desalination Plant

A desalination facility in Swansea, Massachusetts is under design to withdraw water from the Palmer River during the six-hour period around low tide while the brine discharge is scheduled during the 6-hr period around high tide. These time periods minimize the discharge salinity relative to ambient conditions. An analysis to determine the likely variation of ambient salinities at both the intake and discharge during plant operation was needed both as part of the information needs for plant design as well as an assessment of environmental impacts. The analysis required characterization of the present salinity structure so a field program was undertaken. Both a continuous time series of salinity and a series of vertical salinity profiles at the intake and discharge locations were part of this field program. The long term data was processed to determine the 6-hr block average salinities centered at low tide and high tide, corresponding to times of water withdrawal and discharge. Using exponential regressions the low tide and high tide salinities were related to river flow. The vertical profile data were then used to estimate the salinity at the intake and discharge. Using linear regressions, the intake and discharge salinities were calculated from the low tide and high tide salinities predicted from the exponential regressions. Typical seasonal salinities based on seasonal river flows were calculated