JOHNSON COUNTY WASTEWATER-75TH STREET PUMP STATION - Executive Summary
EXECUTIVE SUMMARY |
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 75th Street Pump Station is a wastewater holding station serving the central Johnson county area. This Risk Management Plan (RMP) covers the Section 112(r) regulated substances maintained at 75th Street Pump Station, 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.
The Plant maintains only one regulated substance on site: chlorine. The maximum chlorine storage capacity is 4,000 pounds, which exceeds the RMP threshold quantity of 2,500 pounds. A des
cription of the chlorine system is included in this section.
The Plant is located on the northwest corner of 75th and Nall, Overland Park, KS, which is in an urban area. The surrounding population includes commercial and residential properties as well as public access sites.
The Worst Case Release Scenario
The worst case release scenario for chlorine was calculated as the loss of a single one-ton cylinder 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 approxima
tely 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 12,104 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:
- Three schools
- One major commercial and/or industrial area
- One recreational area
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.
Alternative Release Scenario
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 ana
lysis. The type of system failure selected for the alternative release was the loss of chlorine due to a break in the flexible tubing leading from the cylinder to the vacuum regulator. The chlorine would leak from a 3/8" opening. The leak would continue until the chlorine detection alarm sounded and the valve on the cylinder could be closed. Because chlorine would have leaked into the chlorine storage room, response would be made by the Overland Park Fire Department under their agreement with the Plant. The time for the response was estimated at 15 minutes. Once on site, the fire response personnel would enter the room in protective clothing and manually switch the chlorine feed to the unaffected 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 1,545 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 the chlorine system beginning with cylinder unloading and ending with the chlorine in solution. A combination checklist and modified "What if" type of analysis was used. General questions regarding the storage and use areas as well as practices and protocols associated with the management of the chlorination system were answered. A copy of that checklist in included in this plan. Following the checklist, each valve, line and piece of equipment in the system was assessed from the cylinder to the point of chlorine injection using system flow diagrams. The valves and other points in the systems where chlorine could be released are numbered on the flow diagrams. The assessment is formatted in accordance with those numbe
rs. 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.
The Plant has an operation, maintenance and inspection system designed to review each element of the chlorination system routinely. There are Operation and Maintenance manuals for each 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 loading and unloading chlorine cylinders and changing chlorine cylinders. 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
The chlorine storage area is equipped with chlorine detectors and alarms that indicate leaks. The tanks are stored and used inside the building. Ventilation is provided in the chlorine feed room only when a worker is present. However, if a release is detected, the ventilation system will shut down to contain the leak.
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 dangerous 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.
There have been no accidents at the plant in the last five years.