Carmel Area Wastewater District treatment facility - Executive Summary
Carmel Area WasteWater District's WasteWater Treatment Facility has already complied with requirements as set forth in California's Risk Management Prevention Program legislation: California Health and Safety Code section 25531 et. seq. AND Cal-OSHA's Process Safety Management legislation: California Code of Regulations Title 8, section 5189. |
The Monterey County Department of Health has evaluated the Carmel Area WasteWater District's WasteWater Treatment Facility for the risk that it poses to the surrounding community from an accidental release of the acutely hazardous material - CHLORINE GAS. The CAWD facility was ranked relative to all other facilities in Monterey County which handle acutely hazardous materials pursuant to the requirements of California Health and Safety Code Section 25534 (b). Based upon the evaluation, the CAWD facility was ranked #14 out of 137 facilities (#1 being the highest risk).
An extensive program was originally developed in 1992 to meet the requirements
of the Risk Management Prevention Program requirements, using the Hazard and Operability Study (HAZOP) methodology and an Offsite Consequence Analysis. The document was reviewed and modified to accomodate Process Safety Management (PSM) requirements in 1997. Plant safety regulations with regard to process management were not significantly changed to accomodate the new law, as CAWD already had in practice the highest level of safety management possible with existing equipment. Members of the public are welcome to call the treatment plant at 831-624-1249 at any time to request tours/visits to the facility or to review safety documentation at the treatment facility.
Chlorine System: Overview and process chemistry.
Gaseous chlorine is stored in a building at the western boundary of this facility in 1-ton containers. The greatest possible amount of chlorine that could possibly be stored at any given time is 20,000 pounds (or 10 containers). Often, there may b
e as much as 16,000 pounds present, but typically there are fewer than 16,000 pounds present. This chlorine is injected into treated wastewater at several points within the CAWD WasteWater Treatment Facility, resulting in a chemical mixture of water, free chlorine, and bound chlorine in a concentration of approximately 10 parts per million. The purposes of the chlorine are to:
Disinfect Secondary Effluent prior to ocean discharge or tertiary treatment,
Disinfect Tertiary Effluent prior to reuse,
Disinfect Return Activated Sludge to control nuisance organism growth in MLSS,
Disinfect Plant influent flow to control odors and oxidize organics.
The points of injection are as follows:
Chlorine contact tank, (Effluent Disinfection)
Effluent pump station, (Emergency Effluent Disinfection)
Return Activated Sludge sump, (Nuisance Organism Control)
CAWD/PBCSD trunk manhole, (Odor Control & Organics Oxidation)
Influent Pump Station manhole, (Odor Control & Organics Oxidation)
le, (Odor Control & Organics Oxidation)
The source of chlorine to all of the above points of injection is the chlorine storage, injection, and distribution system located within the Chlorination / Dechlorination structure located at the western most boundary of the facility. All vacuum ejectors supplying the six control points are located within the contained structure as well. Chlorine is transported to the points of injection in a 15 mg/l (approximate) chlorine/water solution. Chlorine gas or liquid does not leave the chlorination/dechlorination structure except as a solution.
Chlorine System Components:
The chlorine storage system consists of the following components:
One to eight on-line liquid chlorine cylinders ( 2000 pounds each),
Four flexible couplings (pigtails),
Two pressure gauges with diaphragm seals,
Four scale gauges (cylinder weight),
Two pressure switches,
Two 1" line valves,
Two automatic switchover, vacuum regulator check valves,
Two vacuum gauges,
Two 1' isolation valves,
One chlorine leak detector (set to alarm at 1p.p.m. atmospheric chlorine),
Two exhaust fans (normal),
One exhaust fan (emergency).
The chlorine distribution system consists of the following:
Two 2" vacuum ejectors,
One 1" vacuum ejector,
Three 500 lb/day chlorinators,
4 chlorine distribution lines,
Effluent pump station emergency injection, &
Plant influent injection (CAWD/PBCSD Manhole, Influent manhole, & Headworks manhole).
The chlorine injection system consists of several chlorine solution injectors located at:
Chlorine contact tank influent piping,
Effluent pump station wet well,
RAS wet well,
CAWD/PBCSD trunk manhole,
Influent manhole, &
Chlorine gas is drawn from two of the four chlorine cylinders attached to the header. As each tank is drawn empty, the automatic switchover vacuum regulator aligns the next full cylinder with the header. If loss of vacuum occurs at any point
downstream of the switchover valve, the regulator automatically isolates the chlorine cylinders and header from the distribution system. Items #1 through #10 listed under Section B, chlorine storage system, are shown on this detailed drawing.
Chlorine distribution system as contained within the chlorination/dechlorination structure: Plant effluent pumped through the chlorine ejectors induces a vacuum which draws the chlorine from the chlorine header. Chlorine gas is mixed with the effluent creating a 15 to 20 mg/l chlorine solution which is piped to the various points of injection.
Chlorine System Safety Features:
The chlorine system has been designed with specific features to safeguard against the accidental release of chlorine gas or liquid. These features include:
All chlorine cylinders stored at the chlorine building are held securely in high impact resistant trunions, which are set in concrete, and are held securely to the trunions by high tensile strength webbed belts and
buckles. The possibility of accidental cylinder relocation during a natural disaster or an operational evolution is infinitesimally small.
Chlorine cylinders fusible plug - Each one ton chlorine cylinder is fitted with a fusible plug which will melt at extreme temperatures to prevent the rupture of the cylinder in the event of a local fire.
One ton cylinder leak repair kit - The CAWD currently maintains two Type "B" chlorine cylinder repair kit for use in repairing on-site chlorine cylinder leaks. Employees receive yearly training in the use of this kit.
Flexible connectors (Pigtails) - Each one ton chlorine cylinder is attached to the chlorine header via flexible metallic tubing specifically designed for this purpose. The connections on either end of the tubing are sealed with fiber gaskets to prevent leakage at the joint. Pigtails are replaced yearly, before corrosion degrades their performance.
Pressure/Vacuum gauges are located throughout the chlorine storage, distribution, and i
njection systems to allow for the monitoring of system integrity and proper operation.
An automatic switchover/vacuum regulator shuts to isolate the chlorine cylinders and header from the chlorine distribution system should a loss of vacuum in the distribution system occur.
Pressure reducing valves are installed in the chlorine header to ensure that chlorine supply pressure is maintained within the manufacturers specifications.
Each of the three 500 lb/day chlorinators used to regulate the chlorine supply is equipped with a vacuum regulator which permits chlorine gas flow only when adequate vacuum (supplied by the ejectors) is present. If ejector vacuum drops to an unacceptable level, chlorine gas flow stops.
A chlorine leak detector is installed in the chlorine storage room which will activate local and remote alarms in the event of a chlorine cylinder or header leak. The detector is set to alarm at 1 ppm of atmospheric chlorine.
A large red strobe light has been installed on the out
side wall of the chlorine storage room where it is clearly visible from all areas of the plant. The light is activated by the chlorine leak detector.
A computerized automatic dialing alarm system has been installed at the facility to which the chlorine leak detector has been wired. Upon the activation of the chlorine leak detector, the automatic dialer pages the on-call operator who in turn calls a preset number for the dialer and is in turn informed, by synthesized voice communications with the computer, that a chlorine leak has been detected.
The ventilation system servicing the chlorine storage room is also wired to the chlorine leak detector which allows for securing the ventilation system in the event of a leak. An emergency override switch has been provided for local control of the emergency ventilation system. This allows for controlled evacuation of the storage room at timed intervals. Inwardly opening ventilation louvers installed in the chlorine storage room remain shut until
a negative pressure is exerted on the room by the emergency exhaust fan. These measures serve to create containment for atmospheric chlorine in the event of a release.
A wind sock has been installed on the roof of the chlorine storage building to assist emergency response teams in determining prevailing wind direction.
Emergency breathing apparatus have been located just outside the chlorine storage room so as to facilitate near immediate entry procedures if needed.
Condition of Chlorine Storage, Distribution, and Injection System Equipment:
The chlorine storage, distribution, & injection system as it exists today, was primarily built and/or installed during the 1985 expansion project and either meets or exceeds building standards for equipment of this nature. Equipment longevity is related to the level and degree of preventative maintenance performed by the operating staff. Resultingly, manufacturers' recommendations for preventive maintenance are strictly adhered to and monitored
by a computerized tracking system.
Chlorine exists as a gas at standard pressure and temperature conditions. Chlorine gas is 2.5 times as dense as air, and thus, is likely to form clouds at the ground surface. Although classified as a nonflammable gas, chlorine may cause fire on contact with combustible materials as a result of the heat released when highly reactive chlorine combines with those materials. Chlorine forms hydrochloric acid upon contact with water and becomes extremely corrosive (therefore water must never be used in the presence of a chlorine leak). The primary health hazards consist of effects on the respiratory system of hydrochloric acid, including severe irritation and possible severe injury of eyes, throat, and lungs. Formation of HCl not only causes respiratory damage but corrodes the opening of the leak, causing the leak to increase in volume. Inhalation of chlorine gas may also result in death from suffocation. MSDS sheets for chl
orine are located in the chlorine building, and in the plant office (master MSDS book).
A significant liquid chlorine release, slug release, at the CAWD WasteWater Treatment Facility could occur as a result, and only as a result, of extensive damage to a chlorine cylinder. This could occur as a result of an accident during maintenance activities in the vicinity of the storage rooms, as a result of operator error during handling, or as a result of an external event such as an earthquake. The likelihood of a significant rupture is not probable as indicated by the lack of such occurrences within the industrial community. Nevertheless, for the purposes of further evaluation, the liquid release scenario is the rupture or damage to one or more of the four chlorine cylinders resulting in the release of the entire liquid contents of X number of cylinders - (X x 2000 lbs/cylinder). In the case of a puncture in the liquid phase of the cylinder, liquid will be expelled through the hole until
the liquid level drops to the lip of the opening. Most of the liquid expelled will evaporate or "flash off" as it comes out of the tank, but some may spill on the ground. The evaporation rate of the spilled liquid depends on heat input from the ground and from the sun. It should be noted that at standard conditions, the weight of one volume of liquid chlorine equals the weight of 456.5 volumes of chlorine gas. The boiling point of liquid chlorine at one atmospheric unit of pressure is -33.97 :C (-29.15 :F).
A significant gaseous chlorine release could occur in the portions of the chlorine storage and supply systems where chlorine exists in the gaseous state under pressure. In the case of a puncture or leak in the upper (vapor) phase of the cylinder or the cylinder supply pigtail to the chlorine header, about one-fourth of the liquid (depending upon liquid temperature) remaining in the cylinder will rapidly flash off. This will cool the remaining liquid to the atmospheric boiling po
int. The evaporation rate of the remaining liquid primarily depends on the heat input from the atmosphere. It is very possible that the atmospheric temperature surrounding the leak will drop low enough to freeze atmospheric moisture around the leak effectively sealing the leak. In the case of a chlorine vapor leak from the chlorine supply header, the installed vacuum/pressure sensor will immediately shut, isolating the leak.As a means of reducing risk associated with the use of acutely hazardous materials (AHM's) at the Carmel Area WasteWater District's Treatment Facility, the Carmel Area WasteWater District has implemented a number of measures as part of the design of the chlorine system and as part of the facility's standard operating and maintenance procedures. Risk reduction measures are aimed at limiting the possibility of an accidental release. In instances where there exists some chance that a release might occur in spite of the measures taken, the CAWD has focused efforts on en
suring rapid response by trained personnel wearing appropriate protective equipment to hazardous conditions to reduce the impact to the surrounding community as well as CAWD employees. This section presents a summary of the risk reduction measures that have been incorporated into the facility design and into the facility's standard operating and maintenance procedures.
System Mitigation Measures:
The particular causes of accidental AHM release include operator error, equipment failure, and uncontrollable external events such as natural disasters. The ultimate goal in this particular circumstance is to encourage that staff adopt an acute awareness of unsafe operating practices where AHM's are concerned. Operator error could result from several causes including not following proper procedures or inadequate training. All operations personnel have received training on the proper use of the chlorine cylinder repair kit. This training is performed annually by the chlorine manufacturer
/supplier. Each employee demonstrates his or her skill with the "B" kit and receives a certificate of competency for chlorine cylinder repair. All 6 regular Operators and the Chief Operator are authorized to take necessary steps to shut the chlorine system down in an emergency. Additionally, the Monterey County Emergency Response Team, including the California Department of Forestry, has conducted emergency response training at the CAWD WasteWater Treatment Facility in preparation for an accidental release of chlorine. CAWD staff members were involved as support personnel.
Extensive written procedures for Receiving Cylinders, have been developed and are to be followed at all times:
These procedures are performed by teams of 3 employees, all wearing SCBA equipment, who run down the procedures in a checklist form, much like an airline crew.
A comprehensive maintenance program is critical to limiting the number of occurrences of equipment failure. The CAWD current
ly contracts with an instrumentation technician, specializing in the type of chlorination equipment installed at the CAWD facility, for regular preventative maintenance routines as well as a separate instrumentation technician who specializes in maintaining the CAWD computerized alarm system. CAWD staff personnel assist the technicians when applicable so as to facilitate in-house maintenance when necessary. In between scheduled maintenance routines, the AHM equipment is inspected daily to ascertain levels of equipment integrity. All other non-electronic equipment AHM equipment such as valving and piping, is maintained as per manufacturers specifications. Additionally, equipment such as the chlorine leak detector is tested on no less than a monthly basis to insure equipment functionality.
External events such as earthquakes or flooding represent a special problem for facilities of this type as it is impossible to predict their frequency or magnitude. No amount of
engineering will prevent the release of an AHM if an earthquake measured at 9.5 occurs. As is noted in previous sections, much thought has gone into designing the chlorine storage room so as to abridge the likelihood of a release of an AHM in a semi-managable catastrophe. To avoid compounding the problem, no flammable material is stored in the chlorine storage room which is constructed solely of concrete and steel. This measure eliminates the possibility of a fire rupturing the chlorine cylinders. Furthermore, the cylinders themselves are designed to execute a controlled release of chlorine, rather than a cylinder explosion, in the event of a fire. If cylinders are engulfed in flames, chlorine leakage is certain, and water shall not be used for firefighting. SCBA and full protective gear shall be used by firefighters.
This facility has been subjected to two major floods during the past 5 years, each of which represents a "worst case" hundred year flood event. In both cases, the ch
lorine process facility was not affected by the flood because it is located on high ground. Additionally, the storage facility itself is approximately 4 feet higher than the adjacent ground.
Carmel Area Wastewater District is proud of its accident history, with no reportable accidents in the entire history of this facility. The District has worked closely with numerous public agencies and developed extensive in-house emergency planning measures to assure the highest degree of safety for the surrounding public.