HomeMy WebLinkAboutX-A-01 Consider Permanent Installation of Water System Disinfection City Council Memorandum
To: Mayor Fasbender & City Councilmembers
From: Nick Egger – Public Works Director
Date: May 29, 2019
Item: Water System Disinfection
COUNCIL ACTION REQUESTED
Staff is recommending the Council decide to implement permanent ongoing disinfection of the water
distribution system by way of gas chlorination. I will provide a brief presentation touching on the history
of the issue and the key points of this memo at Monday evening’s meeting.
BACKGROUND INFORMATION
Coming out of the water system contamination incident of late September 2018, the City’s water supply
has been treated with a low dose of liquid chlorine (sodium hypochlorite) as a precautionary measure,
while City staff were directed to take up a feasibility study of measures the City could consider for
combatting future contamination threats.
The City hired Stantec in early November of 2018 to perform technical analysis work and furnish a report
to the City covering various technological and logistical measures, approximate costs of those methods,
and the effectiveness each would have at countering microbiological contamination risks.
City staff and representatives of Stantec, with assistance of Minnesota Department of Health staff,
presented the results of the report to the City Council in an initial workshop held in late January. An
additional workshop with the Council was held in early March, at which staff presented its
recommendation to implement the use of gas chlorination. Finally, the City held a public open house on
April 4th, where City staff, representatives of the MDH, Stantec, and other industry experts presented
the findings of the feasibility report, staff’s recommendation, and held an extensive Q & A period for
attendees to become as fully informed as possible about the subject matter. This open house was also
live-streamed via HCTV’s Facebook page, where members of the viewing audience could engage and ask
questions.
Since last fall, and along the way through the feasibility study phase, public outreach and
communications efforts by the City have been extensive. Information on this topic has been
continuously posted on the City’s website, with links to resources also provided via the City’s social
media platforms. Many stories and interviews with City staff have been featured by local and metro-
area media outlets. Lastly, City staff have fielded hundreds of phone calls and many in-person
conversations with concerned citizens, answering numerous questions throughout the last eight
months.
Staff’s recommendation of gas chlorination comes after extensive discussion with industry experts and
the Minnesota Department of Health on the threats to public health, the vulnerabilities of a large public
water supply system, and the risks presented by those vulnerabilities; research of the available and
effective methods to combat threats; and strong consideration of the risks and consequences the City
would be exposed to if it were to return the water system to one without ongoing disinfection; coming
to rest on the following rationale.
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• The risks of another contamination event are difficult to quantify, but vulnerability to threats is
large, and the consequences of another event are potentially very significant on multiple fronts
o Impacts to public health, as well as the social and economic bottom lines are many times the
cost of implementing physical protection
• The entire water distribution system needs to be protected, as threats can come from any one
of 7,500+ service connections, as well as other entry points connected to the system
• Chlorination is highly effective at protecting against microbial contamination (bacteria, viruses,
protozoa, etc.), and is the only method available that is able to provide protection of the water
on its journey from the source (wells) to the tap. Filtration and other treatment interventions
provided at the source do not offer this protection.
• Chlorination is a proven and safe technology with widespread use and a great track record
o Chlorine gas leaks from these systems are extremely rare – as reported by the MDH, there
has been less than one leak/year statewide, all have been localized around the source, and
none have required evacuations
• Gas chlorine dose concentrations are much easier to control and balance compared to liquid
chlorine, and this may help minimize taste/odor experiences
o Note: taste and odor sensitivity widely varies from person to person
• MDH Recommends permanent ongoing disinfection via chlorination
• Systems can be designed to account for future integration with other treatment implements
should they be necessary
• Gas chlorination has a lower operations and maintenance efforts, and thus costs, compared to
the liquid chlorination method
If implemented, the City would be one of the last communities in Minnesota with a population of 10,000
or greater which did not previously have ongoing permanent chlorination on its water supply. Staff and
Stantec representatives’ project that all physical work could be completed and all sites’ equipment
online in about one-year’s time.
FINANCIAL IMPACT
A preliminary and conservative cost of $440,000 is estimated for initial retrofitting work that would
need to be completed at four well houses and at the water treatment plant. This figure includes
engineering and project management costs that are part of project delivery. The annual operating costs
are estimated to be $44,000 per year. If approved, staff is recommending financing project costs using
fund balance from the City’s Trunk Water Fund (WAC) account rather than making a change to the
incremental increases already being applied to water consumption rates. Annual operating costs would
be linked to consumption rates, however this requires a very, very small incremental change.
RECOMMENDATION
Staff recommends that the Council approve implementation of permanent disinfection of the water
system using gas chlorination.
ATTACHMENTS
Table of various methods studies, answering important questions about effectiveness, costs,
complexities, etc.
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City of Hastings
Water System Disinfection Alternatives Analysis
Alternative
Provide Residual
Protection in
Distribution System
by itself?
Additional Disnfection
Implements Needed
for Distribution
Protection?
Risks of Microbiological
Contamination
Reduced?
Physical
Space/Facility
Modification Needs
Can Additional Treatment
Types (i.e. Nitrates, PFCs)
be integrated afterward?
Operational
Management
Effort
Initial Capital
Costs Annual Operational Costs
Capital Cost when
paired with method for
residual protection
Annual Operational Cost
when paired with method
for residual protection
Costs per
singular action
Chlorine Gas Yes No Yes - continual
protection.
Small to Modest,
depending on facility
Yes - easily configured.
System can be designed in
anticipation of future
treatment methods.
Low - dosing levels can be
set and do not require
frequent checking.
$440,000 $44,000 N/A N/A N/A
Sodium
Hypochlorite
(Liquid)
Yes No Yes - continual
protection.
Small to Modest,
depending on facility
Yes - easily configured.
System can be designed in
anticipation of future
treatment methods.
Low to moderate -
management of dosing levels
requires more attention than
Gas option.
$195,000 $99,000 N/A N/A N/A
Ozone
No - eliminates
pathogens and
microbiological
contaminants only
from source water.
Yes - required by
standards.
Only when paired with
method for protection
in distribution system.
Small to Modest,
depending on facility
Yes. Moderate to
significant impact
depending on size, scale,
and type of additional
treatment.
Significant $3,750,000 $104,000 $3,155,000 to
$3,351,000 $148,000 to $203,000 N/A
Ultraviolet Light
No - eliminates
pathogens and
microbiological
contaminants only
from source water.
Yes
Only when paired with
method for protection
in distribution system.
Significant
Yes. Moderate to
significant impact
depending on size, scale,
and type of additional
treatment.
Moderate $938,000 $22,000 $905,000 to $1,101,000 $66,000 to $121,000 N/A
Shock
Chlorination
No - temporal and
performed only once
or twice annually.
No
No. This method does
not offer continual
protection.
None N/A
Moderate and intermitent -
intense staffing needs during
operation, with significant
communcations efforts.
N/A N/A N/A N/A
Estimated
$10,000 of
staffing costs
and chemicals
Filtration
No - removes
contaminants only
from source water.
Yes - required by
standards.
Only when paired with
method for protection
in distribution system.
Small to Modest,
depending on facility
Yes. Moderate to
significant impact
depending on size, scale,
and type of additional
treatment.
Low to moderate depending
on type of filtration.
$15 to $20+
Million,
depending on
type*
$50,000-$120,000 (sand
filtration)
Minimal for membrane
filtration, but periodic
replacement of membrane is
required ($600,000)
$15.2-$20.5+ Million
$100,000-$220,000 (sand
filtration)
$50,000-$100,000
(membrane filtration)
Periodic membrane
replacement ($600,000)
N/A
Ongoing
Comprehensive
Inspection &
Enforcement
No N/A
No, but likelihood of
discovering potential
risks is increased.
N/A
Yes. Moderate to
significant impact
depending on size, scale,
and type of additional
treatment.
Significant - requires
examination of all private
plumbing work on 7,800+
served properties in the City.
Requires intense efforts in
scheduling visits to
properties, and consent of
owners.
None
Significant - would require
several full-time staff
dedicated to task.
N/A N/A N/A
Do Nothing No N/A No None N/A None None None None None N/A
*Membrane filtration requires extensive operational efforts and costs, and process results in up to 30% of source water being sent to waste. Sand filtration system requires large amount of space, but minimal operation and maintenance efforts.
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