HomeMy WebLinkAboutIR 7942 INFORMAL REPORT TO CITY COUNCIL MEMBERS No,. 7942
TERFO To the Mayor and Members of the City CouncIl August 8, 1995
X Subject:
1873 WATER TREATMENT DISINFECTION PROCESS INADEQUACY
The four Fort Worth water treatment plants that provide drinking water are subject to various
National and State regulations. The regulations became more stringent in 1993 when the Texas
Natural Resource and Conservation Commission (TNRCC) enacted new disinfection requirements
on surface water treatment plants in the state. The Fort Worth Water Department has made many
improvements in its operations to meet the more stringent requirements, and has begun making
infrastructure improvements to continue meeting regulations.
An incident occurred on July 27, 1995 which led to the Rolling Hills Water Treatment being in
violation of the TNRCC regulations. Federal standards were not violated, and the water met all
standards for bacteria, protozoa and turbidity (a measure of water clarity) despite the violation. It
should be noted that the TNRCC regulations are more strict than the National Environmental
Protection Agency regulations. The violation of the Surface Water Treatment Plant Disinfection
Rule will necessitate a notice being placed in the newspaper. Although it did not pose a threat to
health, the disinfection level did not meet the level required by the state for a period of twelve hours.
Of a total 205 million gallons being treated, 33 million gallons did not meet the daily TNRCC
requirement.
Disinfection at the Rolling Hills Water Treatment Plant is accomplished by using chlorine, later
adding ammonia to form a longer lasting chlorainiine disinfectant. The chlorine is added to raw water
from a lake source as it enters the plant. The purpose for adding chlorine is to inactivate or remove
pathogenic bacteria, protozoa cysts, and enteric viruses. It should be noted that no protoa cysts or
enteric viruses have been found in raw water samples to date. If the ability to feed chlorine into the
raw water as it enters the plant is stopped, the Disinfection Rule is adversely impacted.
The chlorine application point experienced a mechanical failure on July 26, 1995, making it
necessary to feed the chlorine from another, less effective point in the plant. On July 27 with three
treatment "trains" in service, applicable chlorine levels existed in two of the trains treating 66 million
gallons per day (MGD). However, the third train which was treating 33 MGD had chlorine levels
below those required by the state. Inadequate mixing of the chlorine in the common raw water line
coming into the plant was not detected until two of the samples taken at four hour intervals had taken
place, at noon and 4 p.m. on July 27. When discovered, corrective measures were taken about 6
p.m. The next sample was also low at 8 p.m. due to lag time for water already in process. By
midnight, the disinfection levels were once again in compliance with state rules.
The rules require that the disinfectant, chlorine, be in contact with the water for a specific period of
time to be termed in compliance. The time for the interaction of the disinfectant is the time it takes
for the water to pass through the various plant processes. This is termed the "CT" or the
"C"oncentration of disinfectant for a period of contact "T"ime. The TNRCC uses CT numbers to
indicate 99.9% removal of protozoan cysts and this requirement was met. TNRCC uses the
numbers to show inactivation/removal of enteric virus at 99.99%, but the tct
Hills Plant showed 99.94% inactivation/removal. CITY
ISSUED BY THE CITY MANAGER FORT WORTH,TEXAS
INFORMAL REPORT TO CITY COUNCIL MEMBERS No. 7942
To the Mayor and Members of the City Council August 8, 1995
Page 2 of 2
X Subject:
xers WATER TREATMENT DISINFECTION PROCESS INADEQUACY
The processed water met the TNRCC requirement for pathogenic bacteria indicated by no coliform
bacteria being found in the routine sampling on July 27. Additionally, the protozoan cyst
requirement was met. Another indicator of treatment performance is the amount of turbidity
(particles in water) removed. During the July 27 episode, the maximum turbidity was 0.16 ntu
(nephelometric turbidity unit), well under the TNRCC requirement of 0.50 ntu.
On July 28, 1995, the TNRCC was notified as prescribed in the regulations, and they have forwarded
a letter to the Water Department describing the steps to take in notifying the public of the
malfunction. The disinfection process was closely monitored and a temporary mechanical feed
mechanism was constructed for installation at the chlorine application point, with the installation
taking place July 29, 1995.
A permanent repair feed system for the chlorine was ordered, and should be installed the week of
July 31, 1995.
In addition to the repair of the chlorine feed point, other steps are being taken to ensure that this type
violation does not reoccur:
• Strengthening testing procedures and testing more frequently.
• Adding automated monitoring equipment.
• Installing improvements to the chlorine and ammonia systems at both the Holly and
Rolling Hills water treatment plants.
Re-emphasizing operator training.
Bob Terrell
City Manager
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ISSUED BY THE CITY MANAGER FORT WORTH,TEXAS