Willow Lake Wastewater Treatment Plant - Executive Summary |
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Introduction City of Salem's Willow Lake Wastewater Treatment Plant (WWTP) serves the people of Salem, Keizer, and unincorporated areas of Marion County. Willow Lake WWTP is designed to effectively treat 35 million gallons of wastewater per day and is capable of handling a peak of 105 million gallons per day during the Northwest's wet weather season. The wastewater is treated and disinfected prior to discharge to the Willamette River. The disinfection of the wastewater involves the use of chlorine. The U.S. Environmental Protection Agency (EPA) Risk Management Program (RMP) regulations 40 CFR Part 68, require facilities that have regulated substances above the listed threshold quantities to develop a formal Risk Management Program. EPA also requires these facilities to register and submit a Risk Management Plan to EPA using RMP*Submit by June 21, 1999. Willow Lake WWTP maintains quantities of chlorine above the RMP threshold quantity of 2,500 pounds and as such is subject to th e requirements of Program 3 in 40 CFR Part 68. The elements of the RMP are listed below: X Hazard Assessment - Assess the potential impacts of worst-case and alternative release scenarios and compile a 5-year accident history. X Prevention Program - Implement a comprehensive management program that affects a wide variety of operation, training, and maintenance activities. The requirements of the prevention program are identical to OSHA 1910.119 Process Safety Management Standard which the facility is also subject to. X Emergency Response - Implement an emergency action program for the covered processes. X Risk Management Plan - Register and submit an RMP plan that includes an executive summary, RMP data elements, results of the hazard assessment, and summarizes how all other requirements are met. The RMP is to be submitted to EPA by June 21, 1999. The information presented in the next section is intended to describe the elements of Willow Lake WWTP's Risk Management Program. T he format of the section corresponds to the executive summary data elements as dictated in 40 CFR Part 68 Executive Summary Section. EPA's RMP*Submit User's Manual was used as a guidance document for explanation of the regulation's intent of how the Executive Summary is to be structured. Executive Summary Data Elements According to EPA guidance the executive summary must include a brief descripton of the facilty's Risk Management Program. The following sections list each of the required executive summary data elements by rule citation. 68.155(a) Accidental Release and Emergency Response Policies Willow Lake Wastewater Treatment Plant has operated their chlorination system without serious incident since its construction in 1963. This successful operating record is due to the City of Salem's commitment to training programs, operating procedures, and maintenance activities. In recognition of the potential hazards associated with chlorine, Willow Lake WWTP has invested its re sources in implementing an alternative disinfection process. The City of Salem is currently designing a liquid sodium hypochlorite disinfection process to replace the chlorine system at Willow Lake WWTP. The City of Salem is expected to start construction on the sodium hypochlorite system in the year 2000. Although more expensive to operate, hypochlorite was chosen because of safety concerns with chlorine. Hypochlorite is not one of the hazardous chemicals listed by EPA. Once the system is in place and operating satisfactory, the existing chlorine disinfection system will be removed from service. 68.155(b) Stationary Source and the Substance Handled As stated earlier Willow Lake WWTP serves the people of Salem, Keizer, and unincorporated areas of Marion County. Willow Lake WWTP is designed to effectively treat 35 million gallons of wastewater per day and is capable of handling a peak of 105 million gallons per day during the Northwest's wet weather season. The wastewater is tr eated and disinfected prior to discharge to the Willamette River. Chlorine is used to disinfect the wastewater. Chlorine is stored in 1-ton cylinders. Usually two cylinders are in service delivering chlorine. The chlorine building houses the chlorinator units. The chlorine cylinder area is covered but not totally enclosed. Leak detectors are used to alert facility personnel in the event that a leak occurs. The chlorine monitoring system consists of seven strategically placed chlorine leak detectors. There are four chlorine-detecting probes placed around the chlorine cylinder tanks. One probe is located on each side of the chlorine storage area. Placement of the leak detectors around the storage area provides coverage not limited by wind direction. In addition to the storage area, there is a leak detector in the evaporator-chlorinator room. There are also two chlorine-detecting probes in the reclaimed water pump station. These are placed on the upper floor and in the bas ement of the building to detect any possible chlorine leaks in the chlorine piping located in this building. Each of the chlorine detecting probes is connected to a local and remote alarm system. The local system consists of a flashing red light and an audible horn. The remote system is tied into the plant wide computerized DCS alarm system. Any chlorine leak detection can be monitored for location and strength in parts per million (ppm) from four locations in the plant. These locations are the administration building, the reclaimed-water pump station, the UNOX control room, or the flotation thickener building. All of the chlorine leak detectors are operationally checked bi-weekly and calibrated monthly. The safe operation of the Willow Lake WWTP is further illustrated by the awards the facility has received. A few of the awards received by the facility are listed below: The 1997 Pacific Northwest Pollution Control Association (PNPCA), Division A, "Safety Award." Association of Metropolitan Sewerage Agency (AMSA), Silver Awards of 1997 and 1995. AMSA Gold awards for 1994, 1993, 1991, 1990, and 1989. 1993 &1990 EPA, Operation & Maintenance Excellence Award. 1990 Oregon Region, PNPCA Award of Excellence. 68.155(c) Offsite Consequence Analysis One worst-case release scenario and one alternative release scenario was assessed for the chlorine process. To ensure a common basis for comparisons the EPA defined the worst-case scenario as the release of the largest quantity of a regulated substance from a single vessel or process line that results in the greatest distance to an endpoint. The alternative release rate is a release that is considered more reasonable or "more likely." Active mitigation measures can be used in determining the alternative release scenario while the worst-case scenario is only allowed consideration of passive mitigation measures. The toxic endpoint for chlorine has been defined by EPA to be 0.0087 mg/L (3 ppm). This airborne conc entration that is used as the toxic endpoint is the maximum airborne concentration below which it is believed that nearly all individuals can be exposed for up to one hour without experiencing or developing irreversible or other serious health effects. The distance to the toxic endpoint becomes a radius for a circle around the regulated substance. Residential population within the circle is required to be determined based on available census information. The population number is reported as part of the EPA submittal. This method greatly over estimates the population potentially exposed to a single chlorine release, because the chlorine plume would seek lowest elevations in the direction of the wind during a release. Since wind direction cannot be anticipated for an accidental release, EPA mandated the circle estimation method. Release scenarios and distances to toxic endpoints are discussed in more detail in the subsequent paragraphs. Worst-Case Release Scenario Worst-Case Rele ase Scenario is determined in accordance with the requirements provided in 40 CFR 88.22 and 40 CFR 68.25(b & c). As described in USEPA 40 CFR Part 68.25(b) the worst-case release shall be the greater of the following: 1. The greatest amount held in a single vessel or 2. The greatest amount in a pipe. For the chlorine process at Willow Lake WWTP the worst-case release is that of a 2,000 pound chlorine cylinder (maximum amount held in a single vessel) ruptures and its contents escape to the atmosphere in 10 minutes. In the event the cylinder would release its entire contents to the atmosphere in 10 minutes the release rate would be 200 pounds per minute. The distance to the toxic end point worst-case release distance was taken from Exhibit 4-4 of EPA's Risk Management Program Guidance for Wastewater Treatment Plants. The residential population within the 3-mile radius of influence was determined to be approximately 15,585. The population was determined by block group proratio n method using LandView. III, Environmental Mapping Software developed by the U.S. Department of Commerce Economics and Statistics Administration Bureau of the Census. The software will estimate the residential population within a given area using 1990 census information. USGS Quadrangle maps were used to determine environmental and public receptors. The environmental and public receptors in the impact zone are listed in the RMP plan. The USGS Quadrangle maps used are listed below: ( Mission Bottom, Oreg., last revision 1993 ( Gervais, Oreg., photo revised 1986 ( Salem East, Oreg., photo revised 1986 ( Salem West, Oreg., photo revised 1986 Alternative Release Scenario One alternative release scenario was evaluated for the chlorine process per USEPA 40 CFR 68.165(a)(2). The alternative release scenario considered is in accordance with the guidelines provided in 40 CFR 68.22 and 68.28. The scenario for the alternative release follows: The regulation dictates an alternative release scenario that results in an offsite impact. To achieve this end a liquid release from a one ton cylinder was chosen for the alternative release scenario. In this scenario the flexible hosing on a one ton cylinder is dislodged while the valve is open. The dislodgment could be caused by a heavy object ramming against the valve/flexible connection, however the impact would have to be at a specific angle to result in the damage theorized. Due to the construction of the storage area and the cylinders, dislodging the connection is thought to be very unlikely. The cylinder valve opening is 5/16 inches according to the "Handbook of Chlorination and Alternative Disinfectants." Once dislodged, liquid chlorine under pressure would be released through valve opening. The liquid chlorine would pool and gaseous chlorine would flash off the liquid surface. According to EPA Guidance document a Flashing Liquid Chlorine Release will have a release rate of: Quantity Released (QR) = 3, 140 x Ah Where Ah = the area of the hole 3,140 = factor applicable to chlorine liquefied under a pressure of 98.5 psig. Ah = p r2 = 3.14 x 0.024 = 0.077 inches square An opening of 5/16 equates to a release rate of approximately 241 pounds a minute (actually greater than the worst-case). Based on Table exhibit 4-12 of The EPA's Risk Management Program Guidance for Wastewater Treatment Plants the distance to the toxic endpoint is 0.68 miles in a rural area. The development in the area of Willow Lake WWTP is predominately agriculture and low buildings. Areas like this are considered rural setting per the EPA Guidance document. The reason the distance is far lower than the worst-case even though the release rate is higher (241 vs. 200 pounds per minute) is due to the meteorological conditions used for the alternative case. The residential population within the 0.68-mile radius of influence was determined to be approximately 287. The population was determined by block group pror ation method using LandView. III, Environmental Mapping Software developed by the U.S. Department of Commerce Economics and Statistics Administration Bureau of the Census. The software will estimate the residential population within a given area using 1990 census information. USGS Quadrangle maps were used to determine environmental and public receptors. The environmental and public receptors in the impact zone are listed in the RMP plan. The USGS Quadrangle maps used are listed below: ( Mission Bottom, Oreg., last revision 1993 ( Salem West, Oreg., photo revised 1986 68.155(d) Accidental Release Prevention Program The Prevention Program required for compliance with 40 CFR Part 68 for Program 3 processes is identical to the prevention program required under OSHA PSM. Willow Lake WWTP aligned its prevention program with OSHA in 1997. Willow Lake WWTP continuously evaluates and updates their safety and prevention procedures as needed. Willow Lake WWTP revalidated their existin g prevention program during the development of the Risk Management Plan. 68.155(e) Five-year Accident History The chlorination facility has been in place since 1963. No accidents, as described under 40 CFR 68.42(a), have occurred at this facility since it began operation. 68.155(f) Emergency Response Program The emergency response program established by the City of Salem does not require personnel to act as the site incident commander. In the case of an incident the Keizer Fire Department becomes the incident commander and assumes the role of directing response activities including any community emergency evacuation measures. Fire department staff have visited the Willow Lake WWTP facility for site orientation on an annual basis for the last two years. 68.155(g) Safety Improvements The facility completed the recommendations from the initial PHA completed in March of 1997. Since 1997, Willow Lake WWTP has decided to switch from chlorine to liquid sodium hypochlorite as the disinfecting agent. Hypochlorite is not listed as an EPA hazardous substance and does not trigger 40 CFR Part 68. The new disinfection process is currently being designed. Construction of the system is anticipated to be completed October of the year 2000. Once the new disinfection system is on line, chlorine will be removed from service. Conclusion As part of Willow Lake WWTP's commitment to safety and respect for the hazards associated with handling and storing chlorine, Willow Lake WWTP had an existing chlorine management system in place prior to the EPA RMP mandate. To comply with RMP, Willow Lake WWTP re-evaluated their current system for handling chlorine and updated and modified elements as necessary. The RMP*Submit satisfies Willow Lake WWTP's requirement to register and provide to the EPA a summary of their Risk Management Program for the chlorine system. |