The Pee Dee Regional Water Treatment Plant (SWTP) treats raw water from the Great Pee Dee River to produce safe and clean drinking water. A series of water treatment processes and water analysis is completed to accomplish this goal. The present permit capacity of the facility is 10 million gallons per day (MGD). Currently, the facility produces an average of 3.5 MGD.
Pee Dee Regional Water Treatment Plant
Once the raw water reaches our plant, it is treated with ferric sulfate (coagulation process). The ferric sulfate (primary coagulant) makes particles clump together to form a floc, which will settle out in the sedimentation basin. After raw water is fed with ferric sulfate, it goes to rapid mix. The rapid mix (Flocculation process) gives enough time for the raw water and the ferric to mix properly to form the floc. The purpose of coagulation and flocculation process is to remove particulate impurities, especially non-settleable solids and color from treated water. A coagulant aid (Polymer) is also used to assist ferric sulfate with coagulation. Caustic (Sodium Hydroxide) is used for pH adjustment when needed.
Once all components are well mixed, the water goes to the sedimentation basin. The sedimentation basin is for detention time and complete treatment with chemicals and to allow solids to settle out. Detention time in the sedimentation basin is approximately 4 to 4.5 hours depending on the flow rate.
Once the water leaves the sedimentation basin, it goes to the settle water channel where water is treated with sodium hypochlorite (chlorine). After the settle water channel, the water goes to the filters. The purpose of filtration is for the removal of particulate impurities and floc from the water being treated. Filtered water should have a NTU (Nephelometric Turbidity Unit) less than 0.3 NTU as required by the South Carolina Department of Health and Environmental Control (SCDHEC).
Upon the water leaving the filters, it goes to the transfer well where lime (Calcium Hydroxide) is added to increase the pH to 7.5 – 8.0. Lime also helps to control pipe corrosion. Sodium hypochlorite is also added to achieve a dose of 1.0 mg/L – 1.5 mg/L for bacteriological disinfection. The SWTP measures water quality parameters with on-line instrumentation that monitors pH, temperature, turbidity and residual chlorine (Free & Total). Also, jar testing is conducted to help choose the best coagulant, polymer and caustic dose for treatment. Jar testing is a laboratory procedure that simulates the plant's coagulation and flocculation process.
Lab Test Schematic for the SWTP
The SWTP laboratory is certified by the Laboratory Certification Division of SCDHEC. Additionally, each operator within the water production work group is a licensed, certified operator by the Environmental Certification Division of the South Carolina Labor, Licensing, and Regulation Board.
SCDHEC conducts an annual Sanitary Water Survey inspection of the entire water production and distribution system. This inspection normally spans three days so SCDHEC can thoroughly investigate each work group involved in the production, treatment, and distribution of potable water. Also, quarterly, SCDHEC collects random samples from the water distribution system to ensure quality water is being produced.