Water Pollution Control Facilities - Executive Summary |
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The Cedar Rapids Water Pollution Control Facilities (CRWPCF) is located on approximately 40 acres in the southeastern quadrant of Cedar Rapids and currently serves the cities of Cedar Rapids, Marion, Hiawatha, and Robins. The plant became operational in 1980 and offers treatment of up to 56 million gallons of wastewater per day. Advanced biological treatment provides state-of-the-art processing of industrial and domestic waste. Administration, Operations, Maintenance and Warehouse buildings provide the support and control functions for the wastewater treatment and solids handling facilities. CRWPCF is designed and operated to maintain discharge compliance with the Clean Water Act [33 U.S.C. 1342(b)]. Federal and state requirements are defined in a National Pollutant Discharge Elimination System (NPDES) Permit, which allows the City to operate the plant and to discharge treated effluent to the Cedar River. The NPDES permit establishes daily maximum and monthly average effluent lim itations for the plant. The WPCF handles, uses, and stores chlorine, an EPA-regulated substance, in amounts exceeding the regulatory threshold of 2,500 pounds. The process of chlorination for disinfection of wastewater is not included in the North American Industry Classification System (NAICS) codes listed by EPA in 40 CFR 68.10(d) although the WPCF is subject to OSHA Process Safety Management (PSM) requirements. This qualifies the Water Pollution Control Facilities as a Program 3 process. The plant conducts continuous chlorination and dechlorination of the wastewater going to the Cedar River between April 1 and October 31 as required by the NPDES Permit issued by the Iowa Department of Natural Resources. Chlorination of the wastewater is conducted by injecting and dissolving chlorine gas directly into the effluent. This process is necessary to kill potentially harmful bacteria that may be present in wastewater. Chlorine is removed from the effluent with the addition of ma gnesium bisulfite to reduce potential impacts on aquatic organisms. All chlorine and magnesium bisulfite is stored and processed in the Disinfection Building. The Disinfection Building includes a chlorine container room, a magnesium bisulfite (MBS) room, chlorination room, and a sample room. Four one-ton containers are on-line at any one time with an additional four ton-containers on standby. Between 18 and 22 containers (36,000 to 44,000 pounds of chlorine) may be maintained in the inventory. The Disinfection Building is normally unmanned but operators visit the facility daily and respond to any trouble alarms which may occur. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst-case release" and "alternate release scenario." The worst case scenario is defined by the Environmental Protection Agency (EPA), which states that "the owner or operator shall assume that the maximum quantity in the largest vessel is released as a gas over 10 minutes," due to an unspecified failure. The alternate scenario is defined as "more likely to occur than the worst-case release scenario." EPA regulations require the use of tables or atmospheric dispersion modeling to determine the distance traveled by the chlorine released before its concentration decreases to the toxic endpoint. The endpoint is the distance a toxic gas/vapor cloud will travel before dissipating to the point that serious injuries from short-term exposures will no longer occur. The toxic endpoint selected by EPA for chlorine is 3 parts per million (ppm), which is the Emergency Response Planning Guideline Level-2 (ERPG-2). The ERPG-2 concentration is defined by the American Industrial Hygiene Association as the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an i ndividuals ability to take protective action. The residential population within a circle with a radius corresponding to the toxic endpoint distance has to be defined, "to estimate the population potentially affected." The worst-case release scenario at the WPCF involves the failure of a single one-ton container (a total of 2,000 pounds of chlorine). The offsite consequence analysis was performed using the conditions pre-defined by EPA, namely the release of the entire amount as a gas in 10 minutes, use of the one-hour average ERPG-2 as the toxic endpoint, and consideration of the population within a full circle with the radius corresponding to the toxic endpoint distance. EPA sets these conditions to simplify the off-site consequence analysis and ensure a common basis for comparison even though these assumptions may be unrealistic or not even possible. Look-up tables in EPAs publication, "Risk Management Guidance for Wastewater Treatment Plants (40 CFR Part 68)," was used to det ermine the distance to the toxic endpoint for worst-case and alternate release scenarios. The distance to the toxic endpoint for chlorine taken from Exhibit 4-3 of the EPA Guidance Document was determined to be 1.3 miles with a potentially affected population of 300. The complete failure of a one-ton chlorine container with the loss of the entire contents within a 10 minute period is not a likely event and has not been known to have occurred in the almost 100 years of chlorine use in the United States. Also, only the population within an elliptical plume extending downwind of the release point is potentially affected. The plume area, or footprint, is approximately 6 percent (one-twentieth) of the area of a full circle. The alternative release scenario involves the failure of a 1-inch forged steel pipe connected to four 1-ton containers. The amount of chlorine released is 3,504 pounds, at an average rate over one hour (the duration of the release) of 14.6 pounds/minute. Thi s release is limited by the flow through the 5/16-inch valves on each of the one-ton containers. The distance to the toxic endpoint for chlorine (taken from Exhibit 4-12 of the EPA Guidance Document) was determined to be 0.2 miles with a potentially affected population of 10. The toxic endpoint was calculated using the formula for a vapor release (QR = 190 x Ah), where: QR = Quantity Released (pounds) 190 = Chemical-specific factor for chlorine at a tank pressure of 113 psia and temperature of 77 0F Ah = Hole area (square inches) The alternate release scenario described would take place indoors where the chlorine leak would be partially contained in the enclosed building. If a gas is released in an enclosure such as a building, the release rate to the outside air may be lessened considerably. The release rate from the building will be approximately 55 percent of the worst-case scenario release rate. Accidents reported to EPA involving chlorine systems have been caused by rust h oles, failure of a diaphragm, leaks during hookup to a tank, a packing nut leak, faulty cylinders, removal of a valve in error, faulty valves, leaking gaskets, and a blown pressure gauge. Each of these incidents, while potentially serious, can be easily controlled through maintenance or process system safety features that would prevent a catastrophic release. Chlorine is historically the preferred disinfecting agent for water, having been first introduced to the United States for water treatment in 1908. The general WPCF accidental release prevention program is based on the following key elements: 7 High level of training of the operators 7 Preventive maintenance program which includes an annual operations and maintenance pre-startup safety review 7 Use of state-of-the-art process and safety equipment 7 Use of accurate and effective operating procedures, written with the participation of the operators 7 Performance of a hazard review of equipment and procedu res 7 Implementation of an auditing and inspection program Chemical-specific prevention steps include the availability of respiratory protection devices [a supplied air respirator (SAR) is worn by mechanics during the connection / disconnection of chlorine ton-containers and a self contained breathing apparatus (SCBA) is available for emergency use], awareness of the hazardous and toxic properties of chlorine, and the presence of chlorine detectors throughout the Disinfection Building. Wastewater Treatment Plant Operators are required to maintain an operator license issued by the Iowa Department of Natural Resources. Operators must complete a minimum of 10 - 20 hours of continuing education credits every two years to keep their license current. No accidental releases of chlorine have occurred at the WPCF since the plant became operational in 1980. The WPCF has an emergency response program which has been coordinated with the City of Cedar Rapids Fire Department (CRFD). The C RFD has a professional, well-trained and well-equipped Hazardous Materials (HAZMAT) Response Team and the CRFD is a member of the Linn County Local Emergency Planning Committee (LEPC). The CRFD HAZMAT Response Team periodically conducts training and drills in responding to a chlorine ton-container leak. A Chlorine Institute Emergency "B" Kit, which includes the necessary tools and equipment for repairing ton container leaks, is available on-site for use by the HAZMAT Team. The CRFD also has an agreement for mutual aid and assistance with the City of Marion Fire Department. WPCF operators have been trained to provide a controlled response to chlorine leaks but limited to conducting an initial assessment and providing any necessary technical advice and support to the CRFD HAZMAT Team. |