City of Dover Wastewater Treatment Plant - Executive Summary
DOVER WWTP RISK MANAGEMENT PLAN |
The City of Dover Wastewater Treatment Plant (Dover WWTP) is a 1.5 million gallons per day (MGD) facility located between I-77 and the Tuscarawas River, just southwest of U.S. 211 in Dover, Ohio. The original plant was built in 1956, upgraded in 1988, and modified in 1990. The plant is in operation 24 hours per day. Treatment processes include grinding, grit removal, primary treatment, oxidation, secondary clarification, disinfection, and dechlorination. Chlorine gas is used for disinfection at the Dover WWTP. Chlorine gas is the only regulated substance addressed by the Risk Management Plan (RMP) that is used and/or stored at the plant.
Chlorine is purchased in one-ton cylinders and stored in the chlorine building located at the center of the treatment facility. During normal operating procedures, the maximum number of full cylinders at this location is two. Only one cylinder is in service at any given time. Chlorine gas is f
ed from the cylinder through a 3/8-inch regulator to a 3/4-inch plastic line where it flows to gas chlorinators and is converted to solution. The chlorine solution is then metered to the chlorine tank for disinfection of the plant effluent. Chlorine feed system equipment is currently inspected on a daily basis.
Dover WWTP personnel will shortly enhance their current program for preventing the accidental release of chlorine. A 14-step written procedure for changing chlorine cylinders will be completed and maintained on file for use by employees when changing cylinders. Employees will be required to review the procedure on an annual basis. Employees are already required to view a video on chlorine safety and receive safety training every year in April before the May-October chlorination season starts. A list of chlorine maintenance procedures will be maintained on file and used by employees for the periodic checking, cleaning, and maintaining of all chlorine feed system componen
ts. Safety information and Material Safety Data Sheets (MSDS's) for chlorine already exist and are maintained on file in the plant's Right-to-Know area where they are easily accessible by plant personnel.
An Emergency Procedures Plan for the City of Dover Wastewater Department exists which provides detailed instructions of procedures in response to the accidental release of chlorine. Instructions are provided for detection, notification, and evacuation procedures. The Dover WWTP is covered under the Emergency Response Program of the Local Emergency Planning Committee of Tuscarawas County. Plant employees are not to respond directly to the release of regulated substances but are to call 911 to notify the Dover Fire Department.
As a requirement of the Risk Management Plan, different scenarios for the release of chlorine gas from the Dover WWTP to the environment were performed. The release scenarios were modeled using EPA's RMP*Comp model, and included both worst-case and altern
ative release scenarios.
The worst-case scenario assumes that the largest single container will release its entire contents to the environment over a ten-minute period. For the Dover WWTP, the largest container is a one-ton cylinder that is located in the plant's chlorine building. Criteria used within the RMP*Comp model included a release rate of 110.0 pounds per minute (lbs/min), wind speed of 1.5 meters per second (m/sec), an atmospheric stability class of F, and urban topography. The enclosed storage of the chlorine in the chlorine building is considered a passive mitigation measure that reduces the potential exposure to the environment by approximately 33 percent. The projected area impacted by the worst-case release scenario, based on the EPA model, is presented on Figure 1. The affected area is a circle of 0.9-mile radius that includes educational, residential, recreational, commercial, office and industrial areas within the City. The affected area's population, based on
1990 Census population density information, is approximately 2,900.
Although the worst-case release scenario is a requirement of the Risk Management Plan, there is an extremely low probability that such an event would occur. A more realistic scenario that would be encountered at the Dover WWTP is a leak from the chlorine feed line, which is addressed by an alternative release scenario.
The alternative release scenario assumed that a leak or break would occur at the 3/8-inch regulator connection between the chlorine tank and chlorine feed line. The alternative release scenario assumed that the leak would be released to the environment over a ten-minute period (the release duration did not affect the size of the affected area). Criteria used within the RMP*Comp model included a release rate of 20.9 lbs/min, wind speed of 3.0 m/sec, an atmospheric stability class of D, and urban topography. As with the worst-case release scenario, the location of the chlorine feed equipment in t
he chlorine building is considered a passive mitigation measure that reduces the potential exposure to the environment by about 33 percent. The projected area impacted by the alternative release scenario, based on the EPA model, is presented on Figure 2. The affected area is a circle of 0.1-mile radius that only affects the Dover WWTP staff and does not reach the public off-site.
The Dover WWTP has had no accidents during the last 5 years. In fact, an injury or fatality associated with an accidental chemical release has never occurred at the plant. This success is due to the quality of the staff and the plant's existing chlorine safety handling and training programs.
The Risk Management Plan specifies that WWTPs must have a prevention program in place for each process. For the Dover WWTP, chlorine gas is the only regulated substance and the chlorine feed system is the only regulated process. Since the worst-case release scenario modeling results indicated that the public is w
ithin the potential effected area of a chemical release, the possible prevention programs available to the Dover WWTP included Program 2 (default program) and Program 3 (consistent with Occupational Safety and Health Association [OSHA] program). Although the Dover WWTP could have sought coverage under the less stringent Program 2, plant personnel have chosen to meet Program 3 to be consistent with OSHA's Process Safety Management (PSM) standards.
Program 3/OSHA PSM standards require implementation of a prevention program with several tasks. The Dover WWTP has existing programs for several of these tasks including review of safety information, training programs, and equipment inspections. As part of the Risk Management Plan requirements for Program 3, the plant has developed written procedures for process hazard analysis, operations, maintenance, management of change, employee participation plans, and hot work permits. It is anticipated that these additional management and safety p
rocedures will help ensure that the Dover WWTP will maintain a perfect record of no chemical release accidents in the future.