Grapevine Water Treatment Plant - Executive Summary

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INTRODUCTION 
The Accidental Release Prevention Risk Management Program rule (40 CFR Part 68) is similar to the Occupational Safety and Health Administration's Process Safety Management Program, which is designed to protect workers from accidental releases of hazardous substances.  The Risk Management Program rule addresses over 100 chemical substances, 77 of which are acutely toxic and 63 of which are flammable gases, and the accidental release of these substances. The United States Environmental Protection Agency (USEPA) estimates that over 100,000 sources are covered by the rule, including chemical manufacturers and wholesalers, certain retailers, potable water treatment systems, wastewater treatment plants, ammonia refrigeration systems, and federal facilities. 
The Grapevine Water Treatment Plant (WTP) falls under this regulation because of the on-site storage of chlorine.  The amount of chlorine stored is above the threshold limit specified by the USEPA thereby making the facility  
subject to compliance with the regulation.  The Grapevine WTP personnel have complied with the USEPA Risk Management Program rule and have completed an Accidental Release Prevention Program (ARPP) Plan that contains the following required information: 
7  A management system; 
7 A hazard assessment that establishes the worst-case and alternate release scenarios and their impact on the population and the environment (40 CFR Part 68 Subpart B); 
7 A prevention program that includes safety information, a hazard review, operating procedures, training, maintenance, compliance audits, and incident investigations. (40 CFR Part 68 Subpart C); and 
7 An emergency response plan (40 CFR Part 68 Subpart E); 
The following subsections discuss details of the plan that has been implemented at the Grapevine WTP. 
RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES 
The Grapevine WTP facility in Grapevine, Texas has an excellent record in preventing and minimizing releases of chlorine.  The emergency response  
policies at this facility ensure that there is emergency response coverage 24 hours per day, 7 days per week.  There are also adequate provisions for coordination with outside agencies, such as the Grapevine Fire Department in the event of an emergency.   In the event of a release, plant staff will contact the Grapevine Fire Department, relaying information regarding the release prior to implementing plant evacuation to a location outside the plant gates, awaiting the arrival of the fire department to inform its personnel of all information about the release and to provide assurance that the plant has been totally evacuated.   
 
REGULATED SUBSTANCE 
The Grapevine WTP uses chlorine as a component of a chloramine disinfectant in the water treatment process.  The Grapevine WTP regularly has a storage maximum quantity of 12 one-ton containers of chlorine at its facility that is stored outside.  This is above the threshold limit (2,500 pounds) set by the USEPA.  
 
PROCESS DESCRIPTION 
The Grape 
vine WTP receives raw water from the City of Grapevine's Lake Grapevine water supply which is pumped into the treatment plant located at 2600 Fairway Drive, in Grapevine, Texas.  Water is treated at the plant and subsequently pumped to the distribution network of pipelines, pump stations, and storage tanks.   
The existing chlorine feed facility at the Grapevine WTP consists of  (1) up to twelve one ton chlorine containers, (2) a vacuum regulator mounted on an automatic switchover module with gas piping and miscellaneous valves, (3) four flow proportionate feed chlorinators, (4) gas piping and ejectors, and (5) chlorine solution diffusers.  On treatment plant grounds, the only area in which chlorine has a potential to generate a gaseous release is the chlorine storage area (items 1 and 2 above).  Chlorine is delivered to the Grapevine WTP by truck and chlorine containers are stored in the outside storage area located to the north of the Chemical Building. Chlorine is removed as a gas un 
der pressure of the liquid in the individual containers; however the majority of the chlorine feed is operated through a water injection induced vacuum, making the system extremely safe and minimizing potential pressurized leaks along the feed lines.   
 
WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS 
The chlorine storage and process areas have associated hazards that can potentially affect on-site employees and the off-site population and environment.  The U.S. EPA requires that one worst-case scenario and one alternate release scenario is reported for each regulated chemical.  
 
Worst-Case Scenario 
The largest potential release of chlorine would occur through a valve failure on one of the one ton cylinders located on the north side of the plant.  This valve failure could potentially release all 2,000 pounds of the chlorine as a gas.  Under Section 68.25(c)(1), the release time for a chemical such as chlorine is 10 minutes.  Passive mitigation controls were not applicable to the worst-c 
ase release at this plant. 
 
The EPA-approved modeling program DEGADIS+ was used to characterize the effects of the worst case scenario at the Grapevine WTP facility.  The distance to the toxic endpoint of 3 ppm was determined to be 1.66 miles.  The estimated affected residential population is 2,590 people.  Commercial/industrial areas and residential areas would be affected in the worst-case release scenario. 
 
Alternate Scenario 
One alternate scenario was modeled for the Grapevine WTP. The release was established as a leak that would potentially develop in the gaseous piping from between the cylinder and the vacuum regulator on a < inch line.  A release of chlorine through the <-inch diameter line would occur for about 10 minutes, and is presumed to be observed or detected.  The release rate of chlorine caused by leakage through this opening is calculated to be 73.8 lb/min.  DEGADIS+ was also used to characterize the effects of the alternative case scenario at the Grapevine WTP.  The 
distance to the USEPA defined toxic endpoint of 3 ppm was determined to be 1.34 miles.  The estimated affected residential population is 1,400 people.   
 
 
GENERAL ACCIDENTAL RELEASE PRECAUTION PROGRAM 
The Grapevine WTP carries out consistent operation and maintenance of its chlorine equipment utilizing only fully trained personnel in this area.  Grapevine WTP management enforces consistent operation through discipline for operational deviations. 
 
FIVE-YEAR ACCIDENT HISTORY 
The Grapevine WTP's accident history was reviewed for the period from June 1994, through June 1999.  During this period of time, no accidental releases of chlorine had occurred.   
 
EMERGENCY RESPONSE PROGRAM 
As mentioned earlier, this facility has developed an Emergency Response Program involving immediate plant evacuation once the City's Fire Department is called to implement response and repair to leaking chlorine gas.  The plant is staffed 24 hours per day and 7 days per week.  Plant operators are required to mak 
e rounds for inspection and monitoring of the plant processes at least every two hours.  Accordingly, plant staff will detect any releases of chlorine and the Fire Department is trained to respond to this situation.  
 
The Emergency Response Plan includes: (1) procedures to follow in the event of a chlorine emergency, (2) information about the plant evacuation plan, and (3) a detailed description of the emergency responder's plan for handling such an emergency.  
 
The Grapevine County Fire Department has been designated to provide emergency responders and equipment, and will assume Incident Command upon arrivalat the planl.  
 
PLANNED CHANGES TO IMPROVE SAFETY 
Based on the hazard review and prevention evaluation completed for chlorine, a list of action items was developed and is being considered by Grapevine WTP management to determine if implementation is to be accomplished.  The most notable planned changes include the following: 
 
7 Ensure that the delivery driver follows a set procedur 
e in the delivery of chlorine.  MW will coordinate with the staff to develop a procedure for how the chlorine truck driver or vendor should perform while on plant grounds.  It is anticipated that the vendor can then be subjected to this procedure at the time of the plant's next bid for chemical purchase.  However, the existing vendor will likely accept these requirements voluntarily to ensure customer satisfaction; 
 
7 The consideration of remote leak detection for chlorine gas in the area of the outside storage of chlorine cylinders; and 
 
 
7 In the future when the plant facilities are expanded or upgraded, consideration should be given to design and construction of a containment building to encompass the chlorine cylinders designed in conjunction with the capability to chemically neutralize any accidental releases of chlorine.  This option might be compared with the conversion to a nongaseous chlorine compound.
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