Ponca City Wastewater Treatment Plant - Executive Summary
Executive Summary |
Ponca City Wastewater Treatment Plant
Risk Management Plan
The Ponca City Wastewater Treatment Plant (PCWWTP) houses chlorine (Cl2) and sulfur dioxide (SO2) in quantities that exceed the threshold limits defined by the Environmental Protection Agency (EPA), 40 CFR, Part 68, under Section 112 ( r ) of the Clean Air Act.
The City of Ponca City and its facilities are devoted to the prevention of accidental releases of covered chemicals. This is evident by the long established training procedures utilized by the City coupled with the extensive maintenance program that is followed at the plant. As an additional measure of safety, an emergency scrubber remains ready for automatic activation in the event a gas leak is detected.
The PCWWTP is the only City-owned plant used for processing raw sewage. The plant is capable of handling flows up to 9 mgd through the process, and flows as high as 42 mgd may be handled by storing the excess flow until it may be sent throug
h the process. The City uses chlorination for disinfecting (inactivating pathogens) effluent discharge. Chlorine is removed from the effluent by dechlorination (or removal of chlorine) with sulfur dioxide. The chlorination and dechlorination systems are each gas fed under a vacuum. The presence of the vacuum prevents gas from escaping into the atmosphere in case of piping failure. This vacuum feed begins at the regulators, which are mounted directly to the ton containers, which eliminates all pressure piping in the system.
The impact areas for both the worst case and alternate release scenarios were based on the results from RMP*Comp. The worst case release scenario for each system utilized a one-ton release within a 10-minute period. This resulted in a 1.3 mile radius impact area, with an estimated population of 8,100 persons. This analysis ignored any mitigation from the emergency scrubber.
The alternate release scenario for each system was based on a gas release created by
a valve breaking from the one-ton container since the rest of the system operates under a vacuum. This resulted in a release rate of 15 lbs/min of Cl2 and 7 lbs/min of SO2. However, the plant's emergency scrubber is designed to remove 99.9% of both Cl2 and SO2 up to 78 lbs/min. This reduction resulted in the release of 0.015 lb/min Cl2 and .007 lb/min of SO2. Each of the release scenarios has an impact radius of 0.1 miles. Since the chlorination/dechlorination facilities are more then 0.1 miles from the plant fenceline, then most likely, the impact population includes plant personnel. The City currently has 15 employees at the PCWWTP.
The chemical system components at the plant comply with one or more of the following standards: NFPA 58, ASTM Standards, ANSI Standards, and ASME Standards. However, regular maintenance and thorough training sessions will minimize the potential for an accidental release. If a release were to occur, then the impact would be greatly lessened d
ue to the existence of the emergency scrubber.
The PCWWTP has not had any accidental chemical releases within the last five years. If an emergency were to occur, then the scrubber would be automatically activated and plant personnel notified through the plant SCADA system. When notified of a leak, plant personnel will call 9-1-1 to notify the fire department. Next, personnel would contact the Ponca City Emergency Management at (580)767-0380. Other regulatory agencies would be contacted as required. The fire department and emergency management would work with plant personnel to minimize the impact of the release as drilled in accordance with the county emergency response procedures manual.
The chemical feed system in place at the plant was installed in 1998 and in good working condition. At this time, no improvements are planned.