Cullman Wastewater Treatment Plant - Executive Summary
Executive Summary |
In 1996, The U.S. EPA promulgated titled Part 68Chemical Accident Prevention Provisions, after this, called the "Regulations." The Regulations, in part, require owners of wastewater treatment plants using toxic substances, to take efforts to prevent and/or reduce accidental releases of those substances, and to document those efforts in a Risk Management Plan (RMP). This Executive Summary highlights the main points of the Risk Management Plan.
Accidental Release Prevention and Emergency Response Policies at the Cullman Wastewater Treatment Plant (WWTP)
The City of Cullman, Alabama, strives to prevent accidental releases of toxic chemicals at its WWTP. They have accomplished this through adherence to recommendations from the chemical manufacturers and equipment suppliers, periodic training of City personnel, and an ongoing preventive maintenance program on the equipment.
Mr. Jerry L. Paul, Superintendent, oversees implementation of the Risk Management Plan and
has overall responsibility for the development, implementation, and integration of the RMP into WWTP operations. Cullman has accomplished this through adherence to recommendations from the chemical manufacturers and equipment suppliers, periodic training of City personnel, and an ongoing preventive maintenance program on the equipment. The City has trained and equipped WWTP staff to respond to small leaks whether in the chemical containers, container valves and fuse plugs, or system piping. To date, Cullman's efforts have been successful. Only a very few minor releases of either chemical have occurred, were due to minor system leaks, and WWTP staff repaired those leaks without any injuries or property damage.
Description of the Cullman WWTP and Regulated Substances in Use
The City of Cullman, Alabama, a municipal corporation, owns and operates the existing 4.75 MGD Cullman Wastewater Treatment Plant (WWTP) which discharges into Eight Mile Creek. The plant currently serves 5,140
homes and 1,014 commercial or industrial entities. The plant currently serves an estimated 14,110 persons and serves commercial or industrial users. Most of the major industrial discharges have pretreatment and are under SID Permits with the State. Due to the stringent nature of these SID's, the plant's influent is primarily domestic in nature.
Sewage enters the treatment plant via three 24" diameter gravity sewers. After screening and grit removal, centrifugal pumps pump sewage to the influent flow measurement flume, flowing by gravity through a pre-aeration chamber, primary clarifiers, primary trickling filter and intermediate clarifiers. Effluent is then pumped to a secondary trickling filter and flows by gravity to final clarifiers, disinfection, an effluent flow measurement flume, and then cascades down to Eight Mile Creek.
Cullman accomplishes disinfection of the wastewater through the addition of chlorine. When using chlorine and similar-type chemicals for disinfection
of sewage, byproducts are developed that are harmful to the receiving water. Sulfur dioxide is added to the effluent after chlorination but before discharge to neutralize any unused chlorine. Both chlorine and sulfur dioxide are toxic and are the only regulated substances used at the Cullman WWTP. Cullman stores both chlorine and sulfur dioxide at the WWTP in one-ton containers. There are no more than four containers each for chlorine and sulfur dioxide at any one time on the plant site.
Worst-Case and Alternative Release Scenarios
To develop a worst-case scenario for the release of toxic substances like chlorine or sulfur dioxide, deciding the maximum amount of substance that could be released is necessary, and at what rate of release. For the Cullman WWTP, the Regulations require that the effects of the release of the contents of a full one-ton container over a ten minute period be evaluated. This release volume and rate are used to develop the location of the toxic endpoint
The toxic endpoint is the maximum airborne concentration below which the EPA believes that nearly all individuals can be exposed for up to one hour without experiencing or developing irreversible or other serious health affects or symptoms that could impair an individual's ability to take protective action. The Regulations estimate the distance to the Toxic Endpoint, from the Cullman WWTP for either chlorine or sulfur dioxide in a forested area, will be approximately 1.3 miles.
We also developed alternative release scenarios for both chlorine and sulfur dioxide. We assumed that a valve or fuse plugs, either of which are 1" in diameter and can be below the liquid level in the one-ton cylinder, failed completely. The Regulations predict that the release rates for the chemicals are approximately 2,500 and 1,600 pounds per minute respectively for chlorine and sulfur dioxide. Under the conditions described in the Regulations for the alternative scenarios, the distance to the toxic e
ndpoint would be approximately 0.7 and 0.6 miles respectively for chlorine and sulfur dioxide.
General Accidental Release Prevention Program and Chemical-Specific Prevention Steps
The City of Cullman compiled and maintains safety information related to chlorine and sulfur dioxide and associated process equipment. Material Safety Data Sheets (MSDSs) provide important data on the composition and characteristics of the chemicals. Cullman maintains extensive operation and maintenance data on all chemical equipment and piping. Operators can reference this material to ensure that they maintain all pressures, temperatures, and flows within safe limits.
Periodically, operating procedures and equipment are reviewed to identify specific hazards and safeguards. Opportunities for equipment malfunctions or human errors are identified that lead to development of safeguards to control and/or prevent those malfunctions and errors. Finally, all devices and steps that will detect and/or monitor
releases are evaluated.
Standardized procedures developed by the chemical industry are used wherever appropriate. These procedures allow employees to work safely and are a source of information to prevent or mitigate the release of toxic substances.
All employees undergo on-the-job training in the safe handling of chlorine and sulfur dioxide. Additionally, at a minimum of approximately once every two years employees attend training conducted by outside organizations.
Preventive maintenance, inspection, and testing of equipment critical to safe operations have a high priority for the Cullman WWTP. This program reduces downtime due to equipment failures and lessens the risks of accidental substance releases.
Five-year Accident History
There have been no accidental releases of either chlorine or sulfur dioxide in the past five years that have cause onsite or offsite personal injury or property damage, and offsite environmental damage, evacuation, or in-place sheltering.
If releases of chlorine or sulfur dioxide beyond the capabilities of WWTP staff should occur, the Cullman County Emergency Management Agency (EMA) will immediately be contacted. The Cullman County EMA serves as a single-point coordination of fire, police, rescue, and all other agencies that may be necessary to respond to both natural and man-made emergencies. For a significant chemical release at the Cullman WWTP, the City's hazardous material response team, that is part of the fire department, will respond to the WWTP site. The City has trained this group in all emergency response procedures regarding chlorine and sulfur dioxide. Cullman County also has a hazardous material response team that the EMA can contact, if necessary.
Planned Changes to Improve Safety
Cullman has successfully operated their chlorine and sulfur dioxide equipment to disinfect and dechlorinate treated wastewater for many years. Within two years, Cullman should complete construction of a
UV disinfection system that will replace the use of chlorine and sulfur dioxide for disinfection and dechlorination of the WWTP's treated wastewater. When this occurs, this will greatly reduce the risks associated with the use of toxic chemicals.