C. Water Treatment Plant Updatee.
MEMORANDUM
CITYOF
CHANHASSEN
7700 Ma ,~et Bvulevard
PO Box 147
Chanhass~:n MN 55317
Phone: 952227' 1!00
Fax 952 227 1! 10
Phone 952 227 1180
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Phone 952 227 1400
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Natural Resources
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Public Works
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Web Site
TO:
FROM:
DATE:
SUB J:
Todd Gerhardt, City Manager
Paul Oehme, City Engineer/Dir. of Public Works
July 20, 2004
Water Treatment Plant Site Selection Update - Project No. 04-08
DISCUSSION
The Preliminary Investigation Report for the proposed Lotus Lake Water
Treatment Plant (dated May 24, 2004) was presented to the City Council at the
June 14, 2004 work session. Since that time, there have been some questions
about some of the items stated in that report such as setback requirements,
possible treatment plant site constraints, and new well locations.
As a brief review of the items addressed in the May 24, 2004 Preliminary
Investigation Report, following are the Water Treatment Plant (WTP) constraints
that were investigated:
Potential Constraints
1. Distribution System Capacity
2. Feasible Well Locations
3. Treatability of the Well Water
4. Suitability of Available WTP Sites
An amendment to the Preliminary Investigation Report will address questions
raised about Items 2 and 4, Feasible Well Locations and Suitability of Available
WTP Sites, and will be discussed in more detail at the worksession.
Suitability of Available WTP Sites
A critical sheet included in Subsection 4.4, Suitability of Available WTP Sites, of
the May 24, 2004 Preliminary Investigation Report, was the sheet showing the
Minnesota Department of Health (MDH) setback requirements and separation
distances for wells and WTP facilities. That critical sheet identified 50 feet as the
setback requirement for any WTP structures from the property line. Utilizing a
50-foot setback for siting a 6,000 gpm WTP at the Ready Mix site appeared to
render that site unusable. It also made the Lotus Lake Wellfield site very tight but
workable. As a result, SEH, Inc. was led to believe that the Ready Mix site was
not usable if the 50-foot setbacks had to be maintained.
Upon review of the regulations and discussions with the MDH staff, it seemed
reasonable to review these requirements at a meeting on site with representatives
The City of Chanhassen · A growing community with clean lakes quality schools a c arl~q qg. do'¢,ntown ti ri;, nO businesses winding trails, and beautiful parks· A nr~a',,o, place w,,, live w,nrk a~,C pla',
Todd Gerhardt
July 20, 2004
Page 2
from the MDH, the City, and SEH, Inc. On July 1, 2004, representatives from the City, MDH,
and SEH, Inc. met and reviewed both potential treatment plant sites. What came out of that
meeting was that the 50-foot setback requirement could be reduced to a 20-foot setback. In
addition, information must be obtained about potential contaminant threats from potential spills
that could occur from the railroad tracks. Also, verification of the existing sanitary sewer lines
must be shown where they may impact the water treatment plant sites.
Because of this new information, the Ready Mix site now comes back into play as a viable site
for the WTP. Using 20 feet as the setback requirement for the building, the Ready Mix site
becomes workable.
Since both sites are now viable, the pros and cons of each site must be reviewed to compare the
two sites. Both the Ready Mix site and the Lotus Lake Wellfield site have issues concerning
design, construction, security, safety, expandability, etc. that must be considered in selecting a
potential site. Also, if the plant were to be located at the Ready Mix site, what would be the best
location to maximize future development of the site? The following is a brief comparison of the
pros and cons for each site.
Ready Mix Site - West End
Pros:
· Site allows more design flexibility
· Not close to residential homes
· Large clearwell possible
· Detached backwash tanks possible
· Excavated material may be able to be
left on site
· Better protection from railroad spill then
east end of Ready Mix site
· Better use of site for future development
· Opportunity cost for sale of east half of
property
Ready Mix Site - East End
Pros:
· Site allows more design flexibility
· Not close to residential homes
· Large clearwell possible
· Detached backwash tanks possible
· Visible location for security
· Room to alter plant in the future if
necessary
· Most of the excavated material could
be left on site
Lotus Lake Wellfield Site
Pros:
· Well controls located within WTP
(remove existing well houses)
· Visible location for security
· Redevelopment of Ready Mix site
Cons:
· Construction staging somewhat limited
· Limited width for building design
· Limited access to plant area
· Less visible location for security then
east end of Ready Mix site
· Possible railroad spill hazard although
not as great a east end of Ready Mix site
· Additional raw and distribution
watemain necessary.
· More costly then building at east end of
Ready Mix site
Cons:
· Construction staging somewhat limited
· Limited width for building design
· Limited access to plant area
· Possible railroad spill hazard
· Additional raw and distribution
watemain necessary.
· Additional cost to construct access to
site
Cons:
· Construction staging limited
· Cost to remove excavation material
· Limited size of site reduces design
flexibility
· Close to residential homes
· Limited clearwell capacity
· Well isolation distances
· Disruption to residents during
construction
· Shared use of site by public
· Elimination of open space at park
· Tennis courts required to be replaced
· No room to alter plant in the future if
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Todd Gerhardt
July 20, 2004
Page 3
PRELIMINARY COST ASSUMPTIONS
necessary
A preliminary project cost of $10.5 million for a 6,000 gpm gravity filtration WTP was reported
in the May 24, 2004 report for the Lotus Lake Wellfield site. Costs to construct the treatment
plant at the east side of the Ready Mix site will not alter significantly the project cost estimate of
$10.5 million. The Ready Mix site will need additional raw water and distribution watermain
installed and additional work to construct access to the site. However, the Ready Mix site allows
for greater staging opportunities over the Lotus Lake Wellfield site which will reduce the
construction cost. In addition the Ready Mix site may allow for the excavated material to be left
on site unlike the Lotus Lake Wellfield site. If the treatment plant were to be built at the west
end of the Ready Mix site, additional costs would be incurred over the east end of the Ready Mix
site due to the additional amount of excavation, sheet piling of the footings for the pedestrian
bridge, additional waterproofing of the plant, and removal of the existing cul-de-sac and
landscape features. A more detailed cost analysis will be discussed at the work session.
Construction costs will also vary for each site depending on the groundwater table. Also,
construction costs will vary depending on the architectural and landscape features included in the
project.
OPPORTUNITY COST FOR READY MIX SITE
The preliminary findings showed a portion of the Ready Mix site could be developed in the
future if a treatment plant were sited at this location. The area with the most redevelopment
potential appears to be the easterly end of the site. Approximately 1.2 acres could be
redeveloped at this location if a WTP were construed at the west end. However, if future wells
were to be constructed at this location, development area would be smaller. Due to the
topography of the site, development of the west end of the site would be more difficult. More
detailed information on future development and opportunity costs will be discussed at the work
session.
CONCLUSION
While each of the sites have potential drawbacks and issues to resolve, it now appears that the
Ready Mix site is a viable location for a WTP based upon discussions with the MDH concerning
this site. Site selection should be based on the perceived best benefit to the City.
C:
Randal Leppala, SEH, Inc.
Jim Norton, SEH, Inc.
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