C. Water Treatment UpdateCITYOF
CHAN SEN
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MEMORANDUM
TO: Todd Gerhardt, City Manager '~,~.
FROM: Paul Oehme, City Engineer/Dir. of Public Works
DATE: May 19, 2004
SUB J: Water Treatment Update - Project No. 04-08
DISCUSSION
On Monday, April 12, 2004, staff met with Council and recommended several
steps to plan for design and construction treatment for the Lotus Lake well field.
These steps include conducting a pilot plant to determine the most cost effective
way to treat the water and conduct a pump test and model the groundwater. Short
Elliott Hendrickson, Inc. was hired to conduct a pilot plant study and conduct a
pump test and model the groundwater at the Lotus Lake well field. The pilot
plant operated 24 hours per day from May 3, 2004 to May 6, 2004. The intent of
the study was to establish methods to remove iron, manganese and arsenic from
the City of Chanhassen's water supply. Water from Well No. 6 was treated with
the pi lot treatment plant and treatment methods were established for the water
source. Well No. 6 was picked because it has some of the highest concentrations
of iron, manganese and arsenic. The purpose for the groundwater modeling was
to evaluate six potential locations, in the vicinity of existing of the Lotus Lake
well field, for three new municipal wells and determine whether the buried glacial
drift aquifer or the Prairie du Chien-Jordan bedrock aquifer should be utilized.
After the pilot plant was conducted, Short Elliott Hendrickson, Inc. also looked at
the two sites cun'ently available to the City for water treatment sighting. These
sites are the "Ready Mix" site east of the cul-de-sac at 79th St. W. and the Lotus
Lake well field.
The pilot study proved that the traditional approach of aeration followed by
chlorine addition, 30 minute detention and potassium permanganate addition for
the removal of manganese works, but does not work better than no detention.
Therefore, detention is not recommended which will save on significant costs in
the construction of the plant. The filter columns with no detention removed the
iron and manganese better over a longer period of time than the ones that were
provided with 30 minutes of detention.
The pilot plant showed the proposed treatment plant should be constructed with
pressure aeration, chlorine addition for the removal of iron followed by potassium
permanganate for the oxidation of the manganese with green sand filtration. The
green sand media will also prevent the escape of pink water into the distribution
system.
Todd Gerhardt
May 19, 2004
Page 2
A pump test was conducted for 34 hours at Well Nos. 2, 5, and 6 in the Lotus
Lake well field. Currently, Municipal Well No. 2 utilizes the Prairie du Chien-
Jordan bedrock aquifer, and Municipal Well Nos. 5 and 6 utilize a buried glacial
drift aquifer. The six potential well sites were assessed on hydrogeologic
conditions, site access, engineering logistics, and well code requirements,
potential contaminant sources, and potential well interference. Based on the
results of aquifer pumping tests performed, it appears that the buried glacial drift
aquifer can sustain at least two additional 900 to 1,000 gpm municipal wells.
Furthermore, it appears that the capacity of Municipal Well No. 5 could be
increased to 1,000 to 1,200 gpm, to obtain an additional 500 gpm. Well No. 5
will need to be physically explored to ensure a larger pump can be accommodated
through the well shaft.
No potential contaminant sources were identified as immediate threats to the
potential wells or aquifers. In addition, no wells (domestic-supply or high-
capacity) were identified that would likely significantly impact or be impacted by
the new municipal wells.
The most feasible locations for the three new municipal wells in the Lotus Lake
area are in South Lotus Lake Park and on the "Ready Mix" site. Two of the new
municipal wells should utilize the buried glacial drift aquifer and one well should
utilize the Prairie du Chien-Jordan bedrock aquifer. It also appears that a second
Prairie du Chien-Jordan bedrock aquifer well could also be constructed at either
site if a backup well is needed or desired.
Based on the groundwater modeling report, the following recommendations are as
follows for new municipal wells in the Lotus Lake area:
· Test wells should be constructed and installed at proposed Well Sites in
the "Ready Mix" site and South Lotus Lake Park to verify and confirm the
presence, capacities, and water quality of the buried glacial drift aquifer
and the Prairie du Chien-Jordan bedrock aquifer.
· Following the construction of the test wells, this report and all
hydrogeological data collected from the test wells should be forwarded to
the Minnesota Department of Health to obtain approval for proceeding
with construction of the new municipal wells.
· The City should consider constructing a total of four municipal wells -
two utilizing the buried glacial drift aquifer and two utilizing the Prairie du
Chien-Jordan bedrock aquifer at "Ready Mix" site and South Lotus Lake
Park. One buried glacial drift aquifer well and one Prairie du Chien-
Jordan bedrock aquifer well would be nested and installed at both
locations.
Todd Gerhardt
May 19, 2004
Page 3
· Well No. 5 should be further evaluated to determine the feasibility of
increasing its capacity from 650 gpm to 1,000-1,200 gpm.
After the pilot plant was conducted and the proposed treatment process known,
Short Elliott Hendrickson, Inc. evaluated the sites that are cu~Tently available to
the City for water treatment. Based on the treatment process recommended, the
"Ready Mix" site does not appear to be a viable option at this time. Due to the
nan'ow property, the setback requirements by the Minnesota Department of
Health, and the topography of the site, designing, constructing and operating a
water treatment plant would be very difficult. The Lotus Lake well field site,
although challenging, offers a better site to construct and operate a water
treatment facility. The existing tennis courts would need to be removed during
construction, but could be built back on site. Delivery trucks would likely access
the plant via South Shore Drive. Staff will present more detailed information on
sighting the water treatment plant at the worksession.
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