Dalecarlia Water Treatment Plant - Executive Summary
EXECUTIVE SUMMARY |
a) The accidental release prevention policy of the U.S. Army Corps of Engineers, Washington Aqueduct Division, is to prevent releases of extremely hazardous substances through the use of proper equipment and procedures. All equipment that is used on the chlorination system at the Dalecarlia Water Treatment Plant is consistent with design criteria. All procedures for operating and maintaining equipment-handling chlorine are written and are constantly reviewed and revised as needed. In addition, all personnel operating or maintaining chlorine-handling equipment are provided a high level of training.
Chlorine storage and feed areas are in enclosed buildings which contain multiple chlorine sensors. In the event of a leak, these chlorine sensors provide an alarm to indicate to the operators that chlorine gas is at an elevated level in the building atmosphere. In addition, several of the sensors are designed to activate the chlorine scrubber system in the event chlori
ne concentrations within the building exceed their setpoints. Each separate chlorine area (storage and feed) contains its own scrubber system that is capable of scrubbing at least one ton of chlorine.
In the event that a substantial chlorine leak was to occur, specific Dalecarlia Water Treatment Plant personnel are trained and equipped to respond. Personnel are trained to use personal protective equipment, including self-contained breathing apparatus (SCBA), in order to address emergency situations in a safe manner. In the event that a more serious leak was to occur than Dalecarlia personnel are able to address, local emergency responders would be contacted. These local Hazmat personnel are coordinated with in advance as is required by the Risk Management Program regulations.
b) The Dalecarlia Water Treatment Plant is located in Washington, D.C. off of MacArthur Blvd, N.W., along the east bank of the Potomac River. The plant rated capacity is 240 million gallons per day (MGD) an
d the average annual production of potable water is approximately 110 MGD. At the Dalecarlia Water Treatment Plant, the Risk Management Program regulations are applicable to chlorine stored on site. The amount of chlorine stored at the plant exceeds the 40 CFR Part 68 threshold quantity of 2,500 pounds. The storage facility at the Dalecarlia Water Treatment Plant includes 64 one-ton chlorine containers, which equates to 128,000 lbs. of chlorine.
The Dalecarlia Water Treatment Plant is operated 24 hours a day, seven days a week. An electronic gate opener monitors and controls access to the plant, which is surrounded by a security fence. A security guard is stationed at the front grate to admit visitors and deliveries on a 24-hour a day, seven-day a week schedule.
c) The offsite consequence analysis considers two chlorine release scenarios. First is the worst-case release scenario. For the worst-case release scenario, the EPA regulations specify that the greatest amount held in
a single vessel is released as a gas over 10 minutes. At the Dalecarlia Water Treatment Plant, this would involve the release of a ton container of chlorine. This is a very unlikely scenario. The other chlorine release scenario considered is called the alternative release scenario. This scenario is defined within the regulations as being more likely to occur than the worst-case release scenario and to have a toxic endpoint off-site.
As specified by the regulations, all active mitigation measures are assumed to not be working for the worst-case release scenario. At the Dalecarlia facility, even if an event were to occur whereby a ton container were to be released, the scrubber in the storage area would prevent the release of chlorine gas to the environment. Even in the event of a power outage, the on-site emergency generator would allow the scrubber to operate and remove the chlorine gas. For both the worst-case release scenario and the alternative release scenario, the toxic
endpoint considered is the ERPG-2, which is three parts per million by volume. The American Industrial Hygiene Association defines this concentration 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 individual's ability to take protective action."
For the worst-case release scenario, the atmospheric conditions as specified in the regulations are, stability class F, and wind speed of 1.5 m/sec. EPA-developed RMP*Comp software was used to calculate the distance to endpoint of 0.9 miles. This calculation took into account passive mitigation for the fully enclosed building.
The alternative release scenario involves the fracture of a <" pipe connection on a liquid chlorine feed line. This could result from a pressure gage attached to the pipe being struck by a ton container being moved into t
he feed location. The amount of chlorine released is estimated to be 1750 lbs. at an average rate of 70 lb/min for 25 minutes. The distance to the ERPG-2 endpoint is estimated to be 0.1 miles. Passive building mitigation was once again used to dampen the impact of the release. However, it was also assumed that the building scrubber system was not operational. As in the case for the worst-case release scenario above, this alternative release scenario is not very likely, since activation of the building scrubber system would render this type of release to be fully absorbed by the scrubber system. The RMP*Comp software was again used to estimate the distance to an endpoint. Meteorological conditions were assumed to be Stability Class D, with a wind speed of 3.0 m/s in the model. These types of meteorological conditions are more typical than those assumed for the modeling of the worst-case release scenario.
d) The general Washington Aqueduct Division accidental release prevention
program for the Dalecarlia water treatment plant includes the following key elements:
' Comprehensive training of operations and maintenance personnel
' Computerized preventive maintenance tracking system
' Use of process equipment meeting industry design specifications
' Use of state-of-the-art leak detection systems
' Use of effective and constantly reviewed and revised operating procedures with input from operations and maintenance staff
' Performance of in-depth hazard review of Risk Management Program-regulated processes and equipment
' Implementation of a Risk Management Program audit program
Chemical-specific prevention steps include the use of air-line respirators for routine container connect/disconnects, presence of alarmed chlorine detectors in storage and feed areas, and awareness of the hazardous and toxic properties of chlorine in use at the Dalecarlia Water Treatment Plant.
e) In the past five years, there was a single incident at the Dalecarlia Water Treatment Plant
which involved a leak of chlorine where several personnel were exposed and sought medical attention. In August of 1997, during the very late evening hours, a chlorine release occurred from the chlorination system in the Dalecarlia Chemical Building. The release occurred as a result of highly chlorinated water being discharged to a plant drain system. A vent from this drain goes to the roof of the Chemical Building. Off-gassing of the chlorinated water caused a small amount of chlorine gas (less than 1 pound) to be emitted through the vent on the roof. Once this gas was emitted into the air, it was drawn into the building's air conditioning system air intake, which is near the vent on the roof.
Since this event occurred during the very late evening hours, the air conditioning system was not continuously operating and therefore did not disburse the chlorine gas into the building at this time. However, once the building heated up as a result of the morning sun, the air conditioning
system started and discharged the chlorine gas into the building where it affected personnel working near the air conditioning duct. Although no personnel were affected to the extent that emergency medical attention was required, several individuals decided to go to nearby Sibley Hospital where they were provided some medical treatment. There were no known long-term health effects to the individuals who sought medical treatment as a result of this incident.
There were no known, or likely, off-site impacts due to the very low level of chlorine estimated to have been released. No off-site emergency responders were notified. The vent pipe, which was involved in this release, was relocated to a place where the possibility of this reoccurring is reduced.
f) The facility has an emergency response program that has been coordinated with the District of Columbia Fire Department. The D.C. Fire Department will respond in the event of a chemical emergency. The emergency response program c
ontains an emergency response decision tree and notification plan. Emergency response drills have been conducted in the past and one is planned for 1999. Following a drill, emergency response procedures are reviewed and updated.
g) As a result of the process of preparing this Risk Management Program, extensive review of chlorine handling practices has been performed. This review has identified some areas that are being evaluated for further improvements to enhance safe operations. One area where a change has recently been incorporated is in the routine connection and disconnection of chlorine ton containers. Operations personnel performing this task wear an air line respirator. Previously, these personnel would only carry an air-purifying respirator. This change makes it less likely for a significant leak of chlorine to overcome an employee and be unable to quickly address a potential situation.