City of Casa Grande Water Reclamation Facility - Executive Summary
1 EXECUTIVE SUMMARY |
1.1 Accident Release Prevention and Emergency Response Policies
At the City of Casa Grande, protecting the environment is a high priority. Accident prevention is the preferred alternative. When a release occurs, we are committed to responding with the maximum of city resources and cooperate with local emergency response agencies. We will provide training and information, as requested, to local emergency response agencies. All management levels support complete compliance for all safety and environmental laws and are committed to implement a RMP plan and achieve plan goals. We encourage and require employee participation in chemical safety.
1.2 Facility Description and Regulated Substances Handled
The City of Casa Grande uses chlorine at its Water Reclamation Facility (WRF) located at 1194 W. Kortsen Rd. Casa Grande, Arizona. The chlorine is received as a liquid in one ton cylinders by truck. Up to four cylinders can be connected to the system at any one time. Thi
s amount (8,000 lb.) is above the 2,500 lb. regulatory threshold for chlorine. All processes that use the chlorine are classified as regulated process for purposes of the RMP rule. For the City, only the chlorination process uses chlorine and is therefor regulated for RMP purposes. All other processes at WRF do not use or have regulated chemicals above the regulatory thresholds.
The chlorine is used for disinfection of the plant effluent. Chlorine gas is dissolved in water using conventional vacuum operated chlorinators. The WRF has three chlorinators fed by one set of two cylinders. The two cylinders feed the chlorine gas as controlled by a vacuum regulator. Vacuum must be present for chlorine to be withdrawn from the cylinder set. The vacuum is provided by process water flowing through ejectors. A second backup set of two cylinders is connected to the system. When the automatic control system detects the first set of cylinders are empty the control system automatically switches to t
he second set of cylinders.
The chlorine solution produced is in the form of hypochlorous acid (HOCl) and hypochlorite ions (OCl). These compounds are unregulated for RMP purposes.
The chlorine is stored and dispensed in a building especially designed to handle the chlorine. It is equipped with chlorine detectors that automatically alarm to the central control system if more than 10 ppm of chlorine is detected. In addition, the chlorine building is equipped with an automatic chlorine scrubber that is automatically or manually activated. The scrubber is designed to treat 4,800 lbs of chlorine before needing to be chemically refilled.
The automatic control system will notify the WRF operator on call during unattended hours of operation.
1.3 Worst Case Scenario
Essentially, the EPA requires all processes to assume that the maximum quantity of the listed chemical is released in 10 minutes. They do no allow credit for any active controls for mitigation of the release rates (i.e. autom
atic shutdown controls). For this facility, the worst case release quantity is 8,000 lbs. This value is the maximum quantity contained in four 1-ton cylinders full of chlorine as received from the City's suppliers. For a 10-minute release period, the yields a release rate of 800 lb./minute of chlorine. EPA default conditions were used.
Using specific guidance for liquid chlorine is found in the EPA document, Risk Management Program Guidance for Wastewater Treatment Plants, the distance to the toxic endpoint (3-ppm) for a release of this amount is 2.7 miles. Within this distance, the City of Casa Grande has identified numerous public receptors, and no environmental receptors. The program, Landview III, estimates the population within the affected area. For this worst case scenario, there are an estimated 176 residents within the 2.7-mile radius.
1.4 Alternate Scenario
For This facility, the alternative scenario is a liquid chlorine leak from a cylinder valve. This type of leak would m
ost likely start small. It is estimated the most likely hole size will be equivalent to 1/4-inch diameter. This size of leak would be quickly detected by the plant operations personnel due to the automatic chlorine detection system. Also, any leaking valve packing, flange leak, or valve leak would, most likely, not leak at a rate greater than the 1/4-inch hole being modeled. The EPA document, Risk Management Program Guidance for Wastewater Treatment Plants, gives a release rate for liquid chlorine through a 1/4-inch hole to be 150 lb./minute (Exhibit 4-13). It is estimated the release will continue for a maximum of 30 minutes before the cylinder and its companion cylinder are empty (4,000 lbs if both cylinders completely full). The total amount leaked is 4,000 lb however a 4,500 lb chlorine release is modeled to account for the possibility of the cylinders being slightly overfilled.
The WRF chlorine building is designed to contain and treat chlorine releases to meet the 1988 Uniform F
ire Code, Article 80 requirements for containment and scrubbing. The chlorine scrubber is assumed to operated per design capabilities for this release. Discharge from the scrubber is 0.0027 lb/min Cl at a concentration of 15 ppm.
The City has selected to use these weather conditions for the alternate release scenario. They are:
Wind Speed 3 meters/sec
Stability Class D
Temperature 25? C (77? F)
Relative Humidity 50%
Using specific guidance for liquid chlorine is found in the EPA document, Risk Management Program Guidance for Wastewater Treatment Plants, the distance to the toxic endpoint (3 ppm) for a 0.0027 lb./min leak of liquid chlorine is 0.08 miles. Within this distance, the City has identified some public receptors, and no environmental receptors. The program, Landview III, estimates the population within the affected area. For this alternate case scenario, there is an estimated 0 residents within the 0.08-mile radius.
1.5 Accidental Release Prevention Program
The City has
prepared a comprehensive accidental release prevention program. The program topics include:
* Hazard analysis
* Operator training
* Mechanical maintenance and inspections
* Management of change
* Pre-startup Review
* Incident investigation
* Contractor safety
* Compliance audits
1.6 Five Year Accident History
The City of Casa Grande WRF has not had any chlorine releases during the previous 5 years.
1.7 Emergency Response Program
The City has prepared an extensive emergency response program. The program includes an emergency response plan, training and coordination with local emergency response agencies and the Pinal County Local Emergency Planning Committee (Pinal LEPC).
1.8 Planned Changes to Improve Safety
The process hazard analysis of the regulated process yielded four recommendations for further evaluation and consideration by the City of Casa Grande:
1. Install a windsock on the exterior of the chlorine building
2. Develop a written procedure to load and unload chlorine cyl
inders from the delivery truck. The procedure should include, inspecting the cylinders before unloading, chocking the vehicle wheels, and inspecting the crane. etc
3. Label all major components, valves and piping in the chlorine building.
4. Train all operators and maintenance personnel on the following topics:
* The danger of mixing chlorine with certain materials
* The toxicity, mobility, and ability of chlorine to sustain combustion
* Consequences of confining liquid chlorine without a thermal expansion device.
* The effect of moisture on the corrosion potential of chlorine.
* The effects of fire and elevated temperature on the pressure of confined chlorine and the potential for release.
They will be completed within the required timetables.
In the alternative scenareo, the RMP Submit program will not allow correct entry of data items for the release quanitity nor the release rate due to error checking and data type limits. The correct amount released for Item 3.5 is 0.08 lb.
The correct release rate for Item 3.6 is 0.0027 lb/min