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Eurekas Water

Some of the naturally cleanest in the state

March 25, 2016

The Kansas Rural Water Association represents rural water systems state-wide. They also work closely with cities that supply water to those districts, Eureka being one of those. The city has worked with KRWA on projects such as smoke testing the sewer system, sludge testing the sewer lagoons, leak determination on city mains, and chemical treatment calculations for the cities water. The annual KRWA convention in Wichita is a must attend event for cities in the central states region.


Reprinted by permission from The Kansas Lifeline, a publication of the Kansas Rural Water Association, published in the March 2016 issue.

Written by Pat McCool, Chemical and Environmental Engineer, KRWA Consultant



Meeting MCLs for THMs and HAAs

A Rule and the One Exception


The Rule:

Surface water treatment plants must control and limit the free chlorine

contact time in order to meet MCLs for THMs and HAAs.

The Exception:

The city of Eureka has a water supply lake northwest of town. This lake is

not accessible by public road or right-of-way. The lake was constructed many

years ago at which time the city ceased using Fall River on the west edge of

the city.

The lake’s watershed is the natural Bluestem Prairie of the Flint Hills. The

watershed has only prairie grass, has maybe some cattle some of the time,

and maybe is “burnt off” in some years. The lake water is deep and pristine

probably as good as or better than an unpolluted Rocky Mountain stream.

The natural organic matter in the lake water is very low. The TOC of the

lake water is around 3 mg/L on an average annual basis. The treated water

has an average annual TOC of around 2 mg/L. This is by far the lowest TOCs

for any surface water source that any Kansas PWSs uses.

The city operates the treatment plant and the distribution system with

free chlorine residual. No ammonia is added. In addition to having a “top

notch” water supply lake, the city treatment plant is very well operated and


The city sells water to Greenwood Co. RWD #1 and Greenwood Co. RWD

#2. Both RWDs also maintain free chlorine residual in their system for many

miles from Eureka. Both RWDs are also in compliance with THMs and HAAs.

Over the last 10 years the city sample results for THMS and HAAs have

been in compliance with MCLs. The THMs have averaged 40 μg/L with a high

of 58 μg/L and a low of 21 μg/L. The numbers for HAAs are also very low.

That data is for 19 samples of which 13 samples were taken during the

month of July when THMs and HAAs are expected to be the highest.

It is not the low levels of TOC in that lake water that are responsible for

the low levels of THMs and HAAs that are formed with long free chlorine

contact time. It is the very low levels of a particular type(s) of natural organic

matter (NOM) in the lake water that are responsible for the Exception to the

Rule. More than 99 percent of the TOC does not react with free chlorine.

The city of Eureka and those two RWDs have one good “Best of Show”

water supply.



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