Cape Rock Treatment Plant - Executive Summary
The city of Cape Girardeau, Missouri (City) operates a 4.5-million gallon per day, public water supply treatment plant, Cape Rock Treatment Plant (Plant). This Risk Management Plan (RMP) fulfills the requirements of the Clean Air Act's Section 112(r) for the Plant.
PLANT DESCRIPTION AND REGULATED SUBSTANCES HANDLED
The Plant uses one regulated substance, chlorine, for disinfection to make the treated water safe for human consumption. A maximum of six (6) 2,000-pound chlorine cylinders are stored and used inside the chlorination room of the Plant. The potential maximum chlorine storage of 12,000 pounds exceeds the RMP threshold quantity of 2,500 pounds. This RMP addresses the storage, management, and use of the chlorine cylinders.
The Plant is located at 20 East Cape Rock Drive, Cape Girardeau, Missouri. It is on a bluff overlooking the river. The surrounding area is residential. Alliance Water Resources operates the Plant for the City.
THE WORST-CASE RELEASE SCENARIO
The worst-case scenario for a chlorine release at the Plant was determined to be the complete discharge of a full 2,000-pound chlorine cylinder in 10 minutes. This is in accordance with the definition provided in the United States Environmental Protection (EPA) guidance for RMP development. The release would be inside the chlorine room but there will be no response to reduce the effect of the release. The conditions of the scenario such as time, weather and windspeed are those given in EPA's Off-Site Consequence Analysis Guidance. The area of potential impact from the chlorine release was determined using RMP*Comp. The modeling software developed by the United States National Oceanic and Atmospheric Administration and the EPA for this determination.
The result of the Off-Site Consequence Analysis indicated that the release could travel 0.9 miles downwind from the chlorine room under the specified weather conditions before dispersing in the atmosphere to a harmless concentration. Sin
ce the winds can come from any direction around the Plant, the possible effected area is a circle with a radius of 0.9 miles. According to the 1990 census there are 410 people living within the 0.9-mile radius circle. In case of the worst-case release described above, only a small part of the area inside the circle would be exposed to chlorine concentrations exceeding EPA's minimum values, the area downwind of the release. The actual area effected would look similar to a cigar pointing downwind from the source to the edge of the circle. Those not located within the narrow band of the plume would not be adversely effected by the release.
This type of release would only occur if the cylinder was in a fire with very high temperatures or if the cylinder was to fail, causing all the liquid to escape. Since the cylinders are stored inside a concrete building with no other materials, the likelihood of either incident occurring is minimal.
THE ALTERNATIVE RELEASE SCENARIO
The alternative re
lease scenario is, by definition, a more likely release scenario than the worst-case. A more likely scenario for a chlorine release at the Plant that might have an offsite effect is the leaking of a chlorine line from the chlorine cylinder or the supply regulator at the cylinder. The release would be inside the chlorine room. The largest release rate would be a complete break of the line right after the valve on the cylinder. According to the American Water Works Association Research Foundation, the release rate would start at 10.5 pounds per hour, then slow down as the pressure inside the cylinder was reduced. Since EPA's RMP*Comp Model does not have provision for variable flows, the 10.5 pound per hour release rate was used for the entire duration of the release. The Plant does have a chorine detection system, which would alarm if there was a chlorine leak in the chlorine room. To give the fire department time to respond to the release and shut off the valve, a release time of 2 hou
rs was used.
The result of the Off-Site Consequence Analysis, indicated that the release could travel less than 0.1 miles downwind. According to the 1990 census, there are 21 people living within the 0.1-mile radius circle. Similar to the worst-case scenario, only the individuals located in the downwind path of the released plume could be exposed to excessive levels of chlorine. Because the Plant is located on a bluff and chlorine is heavier than air, the chlorine is likely to roll down the bluff to the river.
ACCIDENTAL RELEASE PREVENTION PROGRAM
The Plant has operation, maintenance, and inspection procedures designed to review the chlorination system routinely. Personnel receive significant training before being allowed to work on the chlorination 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 operating procedures for startup, shutdown, normal operation, and emergency operatio
ns. Personnel are trained routinely on safety concerns and general operation procedures as well as emergency procedures.
The chlorination room is equipped with chlorine detectors and alarms that would sound if a leak occurred. Ventilation is provided in the chlorination room only when a worker is present.
FIVE-YEAR ACCIDENT HISTORY
The Plant has not had a chlorine release in the past 5 years.
EMERGENCY RESPONSE PROGRAM
In an event of an emergency involving any release of chlorine at the Plant, the fire department will be called to handle the response.
PLANNED CHANGES TO IMPROVE SAFETY
Because of the past work, there are no planned changes to improve safety at this time