Stafford Lake Treatment Plant - Executive Summary |
|
EXECUTIVE SUMMARY The North Marin Water District (NMWD) owns and operates the Stafford Water Treatment Plant (STP) located 4 miles west of Novato. The treatment plant takes raw water from Stafford Lake and processes it to produce a potable water supply for the community of Novato. In order to meet public health disinfection requirements the water is chlorinated using chlorine gas. While chlorine gas is an extremely valuable chemical for drinking water purification, it is also regulated as an extremely hazardous substance by the U.S. Environmental Protection Agency (EPA). EPA regulation FR 6[120],p.31668 requires facilities that use an extremely hazardous regulated substance above the listed threshold quantities to develop a formal Risk Management Program (RMProgram) and to register and submit a Risk Management Plan (RMPlan). In addition, Article 2, Division 20, Chapter 6.95 of the California Health and Safety Code and Title 19, Division 2, Chapter 4.5, Articles 1 through 11 of the California Code of Regulations require a Risk Management Program be submitted to the County of Marin, Department of Public Works , Office of Waste Management. This summary details the RMProgram for the STP. The STP is a conventional surface water treatment plant with a rated production capacity of 6.2 MGD. It was built in 1952 and had a major renovation in 1973. STP is typically operated spring through fall and provides about 20% of the community supply. The other 80% is purchased fully treated from the Sonoma Co. Water Agency. The plant uses 5 main water treatment processes to purify the lake water. These are coagulation, flocculation, sedimentation, filtration, and disinfection. Of these processes only disinfection uses an extremely hazardous substance, chlorine gas. The maximum quantity of chlorine on hand at any time is 8000 lbs, which exceeds the EPA threshold of 2500 lbs. The chlorine is store d in 2000 lb. containers and 150 lb. cylinders. NMWD has always recognized the importance of safety in handling the various chemicals at STP with regard to both our own employees and the general public. As evidence of that there has never been an accidental release of chlorine or sulfur dioxide gas with off-site consequences documented at STP over the 47-year history of plant operations. In 1994 a Risk Management Prevention Program was created by NMWD at the request of the Marin County Office of Waste Management to address the hazards to the community associated with the use of extremely hazardous substances at STP. In support of the RMPP, the NMWD performed various studies all using standard engineering practices in accordance with current industry practices. Seismic analyses were performed to evaluate the treatment plant structures vulnerabilities to earthquakes. A Hazard and Operability Study (HazOp) evaluated the design and operation of the chlorine feed system at ST P, identifying possible problems which may result in an uncontrolled release of the chemical to the surrounding environment. As a result of the HazOp the chlorine system was converted to a remote vacuum feed configuration yielding substantial safety benefits. Additional safety measures have been adopted such as the installation of seismic restraints for the chlorine feed scale, a sun shield and traffic barrier for the chlorine storage area, and the installation of an overhead electric hoist and trolley for safer loading and unloading of the chlorine containers from the delivery truck. In addition it has become standard procedure to have only factory trained service technicians perform the annual chorinator overhauls. This practice has resulted in virtually trouble free equipment operation between the annual service visits. Another important part of the accidental release prevention plan is well-trained operators. The STP operator's average experience operating STP is 12 years. They receive annual refresher training in using chlorine leak repair kits and self- contained breathing apparatus, as well as vendor led workshops on chlorine safety. In the next few months our STP operating staff will be receiving a 16 hour Hazmat training program to become certified First Responders - Operations Level; this training will be given by the local Fire Protection District, and should serve to further enhance the skills of an already experienced staff. Both in the 1994 RMPP and this current RMProgram Off-site consequence analyses were performed to identify what, if any, impacts to the public or the environment could occur with an accidental release of chlorine gas. The 1994 OSCA utilized the Aloha model, while the 1999 OSCA utilized EPA's RMP*comp. The worst case scenario modeled would have off-site impacts, primarily to local ranchers, the adjacent public golf course, and the county park, as well as pedestrians and bicyclists in the area of the bike path . This would result from a release of 2000 lbs. of chlorine gas in 10 minutes due to either a snapped off valve or a fusible plug failure. This type of event is rated as an unlikely event ("The probability of occurrence is considered "unlikely" during the expected lifetime of the facility").This event is considered unlikely to occur due to a combination of factors such as the ruggedness of the chlorine containers, the structural protections in place at STP, and the specific handling procedures employed by the staff. An alternative release scenario considered to be more likely to occur than the worst case event was also modeled. This could be caused by an operator error committed during the changeout of a chlorine cylinder, a defective gasket, or a loose valve packing nut. This event is considered probable ("the probability of occurrence is considered "possible" during the expected lifetime of the facility"). The model utilized a very extreme release scenario of 31lbs of ch lorine in 60 minutes, and is beyond that which would be released in a "real world" event resulting from a leak due to a gasket or valve packing problem. This event would have only marginal off-site impacts with the only public receptor being the bike path some 500 feet north of the plant. NMWD emergency response planning is focused on likely events with County assistance for potential releases with off-site consequences. The County HAZMAT response program is documented and NMWD personnel have participated in a County training program related to the general concepts of the plan. The Novato Police and Fire Departments will assume the roles of first responders incident commanders for releases of chlorine gas with potential for off-site consequences. Pedestrians, bicyclists, and automobiles access to the threatened areas will be controlled by Police, Fire, and Sheriff personnel. Notification of the local ranchers, Indian Valley Golf Course, Stafford Lake County Park, and any other citizens at risk will be a priority. Notification of news media is not considered to be a primary concern because of the minimal population exposure. Work involved in abating the chlorine leak will be a coordinated effort between STP staff and the Novato Fire Districts incident command with assist from the County HAZMAT team if required. Through development and implementation of this RMProgram, the risks associated with the use of chlorine gas at STP will be maintained at an acceptably low level. This does in no way infer that there are no risks associated with this facility or that a release of chlorine gas could not occur. NMWD will ensure that the RMProgram described in this document will be developed further, and established and maintained such that the risks are managed throughout the lifetime of the facility. |