Cheraw Wastewater Treatment Plant - Executive Summary |
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Executive Summary I. The Town of Cheraw Department of Public Utilities owns and operates a Wastewater Treatment Plant on Roddy Street within the Town of Cheraw limits. The facility is committed to providing Town employees a safe working environment. To ensure this standard, the Town has established safe working practices, standard operating procedures, and accident prevention programs. Management is dedicated to training employees on proper operating procedures, emergency response, and equipment use. To prevent accidental releases of chemicals, the Town follows all applicable sections of the United States Environmental Protection Agency (EPA) Prevention Program. The Town has enlisted the help of the Cheraw Fire Department for emergency response to comply with the EPA Emergency Response Program requirements. II. The Town of Cheraw Wastewater Treatment Plant treats domestic and industrial wastewater from within the Town limits and the surrounding area and is currently expanding i ts capacity to 6.0 million gallons per day. The existing plant consists of a bar screen and grit chamber, two parallel aeration basins, two seventy-five foot diameter clarifiers, a chlorine contact chamber, dechlorination chamber, and a belt press and lime stabilization unit for sludge handling. The expansion will replace the bar screen, grit chamber, chlorine contact chamber, and dechlorination chamber with newer equipment while adding an additional aeration basin, 100-foot clarifier, and belt press to the plant. The chlorination system, installed at the plant to disinfect the effluent flow before discharging the treated wastewater into the Pee Dee River, is housed in a chlorination building where the chlorinators, safety equipment and instrumentation are located. Flow is recorded in the laboratory building at the head of the plant. The chlorine is stored in one-ton cylinders liquefied under pressure outside the building. The maximum quantity of chlorine on site is contained in t hree cylinders totaling 6,000-pounds. III. For the Process Hazard Analysis, two release scenarios, a "worst-case release" and "alternate release scenario", were evaluated for impact on the plant and its surroundings. The worst-case release, as defined by EPA, is the "greater of the following: (1) For substances in a vessel, the greatest amount held in a single vessel, taking into account administrative controls that limit the maximum quantity; or (2) For substances in pipes, the greatest amount in a pipe, taking into account administrative controls that limit the maximum quantity as a liquid under pressure, the owner or operator shall assume that the quantity in the vessel or pipe is released as a gas over 10 minutes." The alternative scenario is one "more likely to occur than the worst-case release scenario". The worst-case scenario for the Cheraw Wastewater Treatment Plant evaluated the release of 2,000 pounds of chlorine as a gas within a ten-minute time span. The releas e was modeled using the EPA modeling tool, RMP*Comp to determine the distance to toxic endpoint. The distance to toxic endpoint is the distance the vapor cloud will travel before the maximum airborne concentration reaches a level that nearly all individuals can be exposed for up to one-hour without experiencing or developing irreversible or other serious health effects. For the chlorine system at the wastewater treatment plant, the release of one ton-cylinder (2,000 pounds) would travel 2.2 miles before reaching its toxic endpoint. This distance accounts for the EPA-mandated meteorological conditions, namely Stability F, wind speed of 1.5 m/sec, highest maximum daily temperature of 116:F and average humidity of 65%. This worst case release would affect approximately 8,750 people, several schools, hospitals, recreation areas, and industrial areas. The Pee Dee River and Huckleberry Creek would be affected as environmental receptors. The alternative release scenario involves a va por release from a 3/16-inch hole for a 60-minute duration. The release was modeled in the EPA's RMP Guidance for Wastewater Treatment Plants Reference Tables or Equations. The release accounted for a wind speeds of 3.0 m/sec, and Stability Class D in a rural environment. The release resulted in a distance to toxic endpoint of 0.1 mile. Approximately 400 people, a recreational area and the environmental receptors above would be affected. No passive mitigation has been considered at the wastewater treatment plant. The installation of chlorine detectors and alarms in conjunction with a trained emergency response team has prepared the Town of Cheraw for a chemical release. In the event of a release, employees are trained to assist the response team with area evacuations while the response team attempts to contain the situation. Emergency Repair Kits for the chlorine cylinders are on hand to control or stop a release. IV. The Department of Public Works follows the EPA guideline s for Risk Management and the guidelines established by OSHA for Process Safety Management. The two codes require the Town to evaluate the on and off site risks associated with a highly hazardous chemical and ensure that proper precautions and plans are implemented to minimize the impact of such release. The Town completed a Process Hazard Analysis to review the causes and effects of a chemical release. The Town of Cheraw developed a preventative maintenance program to ensure the equipment used is in optimum condition. Any equipment not in optimum condition is immediately evaluated for repair or replacement. In addition to a preventative maintenance program, the Town has established standard operating procedures in conjunction with the Chlorine Institute and manufacturer's recommendations. Employees are required to follow the standard procedures at the plant, especially near a highly hazardous chemical area. All employees are trained prior to exposure to equipment and provided refresher training at least every three years. Chemical awareness is discussed both in training and during monthly safety meetings where employees can discuss any hazards or potential hazards of the chlorine system. Chemical specific prevention steps include the installation of the gas monitors and alarm system. Self-contained breathing apparatus, gloves, goggles and aprons are available for employees for protection against a chlorine leak. V. No accidental releases of chlorine have occurred at this facility within the last five years. VI. The Wastewater Treatment Plant is covered under the community emergency response program. The Fire Department, which is a member of the Local Emergency Planning Committee (LEPC), is qualified to handle a chlorine leak or spill at the wastewater treatment plant. The Fire Department has also met with surrounding industries to coordinate training for and response to a chemical spill. Wastewater treatment plant employees are trained on proper eme rgency response during the employee training sessions. VII. The Town of Cheraw is evaluating the installation of secured entrances and exits to the wastewater treatment plant, the installation of pipe bollards around the chlorine cylinders, the posting of "No Hot Work" signs around the chlorine area and the repair of the alarm system at the wastewater treatment plant as a result of the Process Hazard Analysis (PHA). These recommendations will be considered for future implementation at the wastewater treatment plant. |