City of Stockton Tertiary Treatment Plant - Executive Summary
The Regional Wastewater Control Facility (RWCF) uses Chlorine and Sulfur Dioxide in the treatment of wastewater. These chemicals are stored and used at the Tertiary Facility, located off state highway 4 at John Turk Road. Each of these chemicals has unique properties that could be a hazard to personnel, equipment, and the environment.
Chlorine is used at the Regional Wastewater Treatment Facility to disinfect wastewater to meet state and federal effluent discharge requirement, algae control, and to reduce hydrogen sulfide in the headworks at the Main Plant.
The Regional Wastewater Treatment Facility receives chlorine in 90-ton railroad tank cars. These cars are stored adjacent to the chlorine building, located at the Tertiary Facility. Liquid chlorine is fed directly from the tank cars into the chlorine building where the liquid is converted to a gas by evaporation. The chlorine gas is then metered to various process points in the facility. The gas is
distributed via a vacuum feed system using water driven injectors the pull the gas into a chlorine solution. This chlorine solution is applied to the process. The amount of chlorine used per day varies with treatment requirements. Typically, the amounts vary from 5,000 lbs/day to 12,000 lbs/day. The existing storage area, feed equipment, and piping system were installed in 1979 as part of the Tertiary Plant expansion project. The evaporators, chlorinators, and associated equipment are designed to effectively and safely handle chlorine quantities three times in excess of the current usage. Preventative maintenance is performed by the city's maintenance staff using a computerized maintenance program to ensure that regular maintenance, inspection, and testing is completed on a timely basis.
The Tertiary plant is staffed 24-hours a day, 7 days a week through most of the year. The operations staff are trained and tested annually on the use of self contained breathing apparatu
s (SCBA) and chlorine "C" and "A" kits, used to cap broken valves on the tank car and 150 lbs chlorine cylinders in the event of an emergency. Chlorine drills are periodically conducted to ensure proficiency in the use of the "C" and "A" kits. Written emergency procedures have been established and are practiced on a regular basis. Staff includes review of these procedures throughout the year during "tailgate" safety meetings.
The chlorine building has two chlorine leak detection systems to detect and alarm in the presence of chlorine gas. The alarm indicators include a flashing beacon and audible alarm at the chlorine building. The alarms send a signal to the tertiary plant control room to alert the operations staff in the event of a chlorine leak. Chlorine alarms are displayed on an annunciator and through an audible alarm tone. These units are checked, calibrated, and maintained on a regular basis by the plant instrumentation staff.
The chlorinators and evaporator
s are equipped with automatic shut down features in the event of loss of vacuum, power failure, temperture, or high chlorine pressure. When a shut down occurs, an alarm is sounded and displayed at the chlorine building and the tertiary control room.
Chlorine tank cars, through ICC regulations, are required to have a check valve in the dome so that in the event of a major leak, the valve automatically closes and prevents leakage of chlorine into the atmosphere. Each tank car is double lined to ensure that integrity of the contents is maintained in the event of derailment, or other collision. Additionally, the rail cars are within a locked fenced compound and continuously monitored by gas detectors along the fence perimeter and at the rail car domes, and the compound is continuously video monitored.
The City of Stockton RWCF's Tertiary Plant uses Sulfur Dioxide for effluent Dechlorination. The sulfur dioxide storage area is located at the tertiary facility,
located on the west side of the San Joaquin River adjacent to the Main RWCF on Navy Drive. Sulfur Dioxide is used to remove residual chlorine in the effluent in order to need state and federal effluent discharge requirments. Sulfuric Acid is also used to lower the pH of the wastewater to facilitate the algae removal process.
The facility uses a 5000 gal. tank to store the sulfur dioxide at the tertiary site. Liquid sulfur dioxide is fed to the SO2 building, located adjacent to the storage area, and is evaporated into gas form. The SO2 gas is then metered to sulfinators to use in the process. SO2 use varies depending on time of year and treatment requirements. Typically, the amounts used are in the 4000 lbs/day to 8000 lbs/day range.
During the past three years there have been no major releases of sulfur dioxide from this facility. Minor releases of sulfur dioxide gas have occured because of residual gas in pipes leaking during scheduled maintenance activities, and
during connection and disconnection of liquid sulfur dioxide lines to the tank from a trailer. Staff have been directed and trained, as part of Standard Operating Procedures, to wear respirators as a precaution when openning lines to facilitate maintanance functions.
The sulfur dioxide building has sulfur dioxide leak detection systems to detect and alarm in the presence of sulfur dioxide gas. The alarm indicators include a flashing beacon and audible alarm at the SO2 building. These units are checked, calibrated, and maintained on a regular basis by the plant instrumentation staff. Preventive maintenance is performed by the city's maintenance staff using a computerized maintenance program to ensure that regular maintenance, inspection, and testing is completed on a timely basis.