Johnson County Wastewater - Middle Basin - Executive Summary |
|
EXECUTIVE SUMMARY Introduction Johnson County operates nine wastewater treatment facilities and thirty-nine pump stations. Three of the wastewater treatment facilities and two of the pump stations utilize chlorine for disinfection. One of these three treatment facilities also utilizes sulfur dioxide for dechlorination. The Middle Basin Plant is a 9-million gallon per day facility serving the central Johnson county area. This Risk Management Plan (RMP) covers the Section 112(r) regulated substances maintained at Middle Basin Plant, which will be referred to herein as the Plant. The county is in the process of replacing their chlorination systems with UV treatment. As systems are replaced with non-regulated systems, the 112(r) program will be terminated at each location. Plant Description The Plant is located at 10001 College Boulevard, Overland Park, KS, which is in an urban area. The surrounding population includes commercial and residential properties as well as public acces s sites. The Plant is approximately 800 feet east of Highway 69 and approximately 3500 feet south of Interstate 435. The Plant maintains two regulated substances on site: chlorine and sulfur dioxide. The maximum chlorine storage capacity is 24,000 pounds, which exceeds the RMP threshold quantity of 2,500 pounds. The maximum Sulfur dioxide storage capacity is 10,000 pounds, which exceeds the RMP threshold quantity of 5,000 pounds. Both the chlorine and sulfur dioxide are stored in the same storage room (see Figure 1). Cylinders of both compounds are maintained on raised platforms which extend along the east and west sides of the structure. The center of the structure is the truck loading and unloading area. The chlorine feed system begins on the east side of the building. Empty cylinders of chlorine and sulfur dioxide are also stored on this side. The sulfur dioxide feed system begins on the west side of the building. Full chlorine and sulfur dioxide cylinders are also stored on this side. When a load of full cylinders arrives, the delivery truck backs into the center of the building for unloading. An overhead hoist removes cylinders from the truck bed and places the cylinder on the west platform. Empty cylinders are collected from the east platform in a similar manner. A description of the chlorine and sulfur dioxide systems is included at the end of this section. The Worst Case Release Scenario Chlorine The worst case release scenario for chlorine was calculated as the loss of a single one-ton cylinder over a ten minute period in accordance with the definition provided in the Environmental Protection Agency guidance for RMP development. Only passive control systems were taken into consideration, such as the containment provided by the building. The conditions of the scenario, including release time and weather status are those provided in the EPA Off-Site Consequence Analysis Guidance. Determination of the area of potential impact was determined using RMP*Comp, modeling software developed by the EPA. The results of the Off-Site Consequence Analysis indicated that the chlorine would travel approximately 4750 feet (0.9 miles) under the specified weather conditions before dispersing in the atmosphere to a harmless concentration. Within that radius of the Plant, an estimated 7,041 persons could potentially be affected. Maps of the area and a list of the types of receptors in the potential impact area are provided in the Off-Site Impact Analysis Section. Potential receptors include: - One major commercial and/or industrial area - One recreation area - One school This type of release would only occur if the cylinder valve were broken off, or the cylinder were breached. Historically, there have been no recorded releases of a fusible plug blowout from stationary chlorine tanks (White, 1999). The likelihood of such an incident occurring is minimal. Sulfur Dioxide The worst case release scenario for sulfur dioxide was calculate d as the loss of a single one-ton cylinder over a ten minute period in accordance with the definition provided in the Environmental Protection Agency guidance for RMP development. Only passive control systems were taken into consideration, such as the containment provided by the building. The conditions of the scenario, such as release time and weather status are those provided in the EPA Off-Site Consequence Analysis Guidance. Determination of the area of potential impact was determined using RMP*Comp, modeling software developed by the EPA. The results of the Off-Site Consequence Analysis indicated that the sulfur dioxide would travel approximately 4750 feet (0.9 miles) under the specified weather conditions before dispersing in the atmosphere to a harmless concentration. Within that radius of the Plant, an estimated 7,041 persons could potentially be affected. Maps of the area and a list of the types of receptors in the potential impact area are provided in the Off-Site Impact Analysis Section. The list of potential receptors is the same as for the Chlorine Worst Case Release Scenario. This type of release would only occur if the cylinder valve were broken off, or the cylinder were breached. Historically, there have been no recorded releases of a fusible plug blowout from stationary sulfur dioxide tanks (White, 1999). The likelihood of such an incident occurring is minimal. Alternative Release Scenario Chlorine The alternative release scenario is, by definition, a more likely release scenario than the worst case. Engineered controls, such as the chlorine detection system and alarm, are considered in the analysis. The type of system failure selected for the alternative release was the loss of chlorine due to failure of the cylinder valve leading from the cylinder to the chlorine feed system. Failure of the cylinder valve would allow for loss of chlorine directly from the cylinder to the chlorine storage room. The leak would continue until the chlori ne detection alarm sounded and the system with the defective cylinder valve could be switched to another of the two tank systems on-line and the defective cylinder valve repaired. Because chlorine would have leaked into the chlorine storage room and plant personnel are not trained for emergency responses, response would be made by the Overland Park Fire Department under their agreement with the Plant. The time for the response was estimated at 10 minutes. Once on site, the fire response personnel would enter the room in protective clothing and manually close all the valves to the leaking tank. The results of the Off-Site Consequence Analysis using RMP*Comp, indicated that the chlorine would travel approximately 1580 feet (0.3 mile) under the specified weather conditions in order to disperse in the atmosphere to a harmless concentration. Within that radius of the Plant, an estimated 543 persons could potentially be affected. Maps of the area and a list of the types of receptors in the potential impact area are provided in the Off-Site Impact Analysis Section. Sulfur Dioxide The alternative release scenario is, by definition, a more likely release scenario than the worst case. Engineered controls, such as the sulfur dioxide detection system and alarm, are considered in the analysis. The type of system failure selected for the alternative release was the loss of sulfur dioxide due to a break in the flexible tubing leading from the cylinder to the vacuum regulator. The sulfur dioxide would leak from a 3/8" opening. The leak would continue until the sulfur dioxide detection alarm sounded and the valve on the cylinder could be closed. Because sulfur dioxide would have leaked into the sulfur dioxide storage room and plant personnel are not trained for emergency responses, response would be made by the Overland Park Fire Department under their agreement with the Plant. The time for the response was estimated at 10 minutes. Once on site, the fire response perso nnel would enter the room in protective clothing and manually close all the valves to the leaking tank. The results of the Off-Site Consequence Analysis using RMP*Comp, indicated that the sulfur dioxide would travel approximately 1580 feet (0.3 mile) under the specified weather conditions before it disperses in the atmosphere to a harmless concentration. Within that radius of the Plant, an estimated 543 persons could potentially be affected. Maps of the area and a list of the types of receptors in the potential impact area are provided in the Off-Site Impact Analysis Section. Process Hazard Assessment A process hazard assessment was performed of both the chlorine and sulfur dioxide systems beginning with cylinder unloading and ending with the chlorine or sulfur dioxide in solution. A combination checklist and modified "What if" type of analysis was used for each. General questions regarding the storage and use areas as well as practices and protocols associated with the managemen t of the chlorination and dechlorination systems were answered. Copies of the checklists are included in this plan. Following the checklist, each valve, line and piece of equipment in each of the system was assessed from the cylinder to the point of chlorine or sulfur dioxide injection using system flow diagrams. The valves and other points in the systems where chlorine or sulfur dioxide could be released are numbered on the respective flow diagrams. The assessments are formatted in accordance with those numbers. Compliance with code requirements, considerations of potential failure, maintenance and inspection concerns, and standard operating procedures were reviewed for each point in the system. Comments are summarized in the Process Hazard Assessment section. Prevention System The Plant has an operation, maintenance and inspection system designed to review each element of the chlorination and dechlorination systems routinely. There are Operation and Maintenance manuals for ea ch major piece of equipment, and personnel receive significant training before being allowed to work on the system. At the beginning and end of the daily operating period and as each cylinder is changed, the valves and piping are tested for leaks. There are standard operating procedures (SOPs) for startup, shutdown, normal operation, and emergency operation. The SOPs are written and posted in the appropriate areas. Personnel are trained routinely on safety concerns and general operation procedures as well as emergency procedures. The storage area, which houses both the chlorine and sulfur dioxide (see figure), is equipped with chlorine and sulfur dioxide detectors and alarms that indicate leaks. The tanks are stored and used inside the building. Ventilation is provided in the chlorine feed and storage rooms. Emergency Response Plan Plant personnel are allowed and trained to respond to leaks that can be managed by turning off a valve. Any response requiring entry in a dangero us atmosphere or use of a chlorine repair kit is to be managed by the Overland Park Fire Department. The Plant has an agreement with the Fire Department, which is included in this plan. A complete copy of the Emergency Response Plan is also included in this plan. Accident History The plant had two chlorine releases in 1996. The first release occurred on June 24, 1996 at approximately 1:00pm. Approximately 1100 pounds of chlorine were released in a 90 minute period. The release was due to the failure of a cylinder valve. Off-site responders were notified and responded to the release. One employee and one public responder were slightly injured during the incident. No off-site receptors were affected by the release though the people in the immediate vicinity of the plant were sheltered-in-place. Several trees and patches of grass on-site were burned from the release. The second release occurred on September 29, 1996 at approximately 3:00am. Approximately 680 pounds of chlorine were released in a 90 minute period. The release was due to the rupture of the diaphragm on the pressure reducing valve. Off-site responders were notified and responded to the release. No one was injured during the incident. No off-site receptors were affected by the release. There were no environmental impacts associated with the release. As a result of these incidents, training procedures were revised, the process was modified and new process controls were installed. |