HomeMy WebLinkAbout2021-12-09 Council Work Session Agenda PacketCouncil Work Session Agenda
December 9, 2021 - 5:30 pm
1.Call to Order / Roll Call
2.Water Supply Planning*
3.Unscheduled Items
4.Adjournment
*Includes Materials - Materials relating to these agenda items can be found in the Council Chambers Agenda
Packet book located by the entrance. The complete Council Agenda Packet is available electronically on the City website
at www.corcoranmn.gov.
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Memo
To: Kevin Mattson, PE From: Ash Hammerbeck, PE
Steve Hegland, PE
City of Corcoran Stantec
File: 227704426 Date: December 3, 2021
Reference: Water Storage Options Evaluation – Follow Up Memo, December 9th Work Session
Background
At the October 28th City Council Work Session, Stantec and Staff discussed with the City Council alternatives
for constructing a water storage system within the neighborhood park of the Bellwether Development. The
report presented multiple water storage options for the Northeast Corcoran Water System including an
elevated water tower, above-ground storage tank (GST), and a buried storage tank and provided information
based on aesthetics, costs, water system functionality .
During that work session the City Council discussed the pros and cons of both systems within this park and
briefly discussed whether the park was the appropriate location for water storage. Through those discussions,
the City Council elected to continue with the geotechnical investigation at the water treatment plant/storage
site and discuss further.
Additional Information
Since the October work session, the City has contracted with Braun Intertec to provide soil borings at the
water treatment plant site and the proposed water storage location in Bellwether Park to identify groundwater
elevations and soil conditions. This information was needed to further evaluate the feasibility of a buried or
partially buried GST in the park location as well as confirm that soil conditions are conducive for the storage
foundations.
Based on a preliminary boring at the Bellwether Park site, the groundwater was identified at approximately
36-feet below the surface elevation and the soils were comprised of sandy lean clay and poorly graded sands.
The preliminary boring information indicates that the soils within the Bellwether Park would be suitable for an
elevated water tower or water storage tank with a typical foundation. Based on these initial results, deep pile
foundations or substantial subgrade corrections would not be anticipated.
The soils borings for the treatment site also indicated reasonable soils for constructing that facility. Braun is
working on finalizing the borings they could get access to and performing laborat ory testing on the material
prior to issuing the final report to confirm site suitability.
Stantec has also reviewed the hydrology and floodplain elevations as part of the adjacent Bellwether and
Newman West Development plans. The estimated high-water level (HWL) within the wetland complex
directly south of the water storage location is at an elevation of 937.8 This is approximately 8’ below the future
ground elevation of the park.
The state regulations for a water storage facility require that the sump of a ground storage tank be located
above the high-water levels of adjacent waterbodies and at least two feet above the groundwater table. This
means that, at most, a ground storage tank at the park location could be buried to a depth of approximately 8’
(elev. 938) and approximately 30’ of the tank would be above grade. At this height, it would not be reasonable
to mounded soils around the tank to visually hide due to substantial grading impacts and the enlarged
footprint it would require.
Agenda Item: 2
December 3, 2021
Kevin Mattson, PE
Page 2 of 3
Reference: Water Storage Options Evaluation – Follow Up Memo, December 9th Work Session
A fully above ground tank at the park location would cost less to construct and maintain versus a partially
buried and would have a height of approximately 40’ above grade.
Based on this additional information, we believe an elevated water tower and at-grade water storage tank are
viable alternatives within the Bellwether Park.
At the previous Work Session, additional questions were raised relative to the tower footprint as compared to
a ground storage tank and how that may impact or limit the park space available for other uses. For both
options, a footprint of approximately 200’x200’ would be required for the infrastructure itself, as well as area to
complete maintenance activities in the future. While much of this space could be greenspace and
landscaping to screen the structures, no park features could be located within that footprint for either option.
See below for a figure showing that approximate footprint within the park
Figure 1: Water Storage Footprint
City Council Considerations
At the Work Session, we would ask the City Council to consider and discuss the following :
• Is the park the preferred water storage system location for staff to proceed with or should staff look for
alternate locations outside the park?
o If the park is preferred, what storage option (elevated water tower or above-ground storage
tank) is preferred?
December 3, 2021
Kevin Mattson, PE
Page 3 of 3
Reference: Water Storage Options Evaluation – Follow Up Memo, December 9th Work Session
• If the Council directs staff to look for alternative locations, our recommendation would be to identify a
site suitable for a water tower in lieu of a ground storage tank. We would ask Council to discuss and
provide direction on what criteria should be used in sel ecting alternative sites as it relates to existing
and proposed land uses or other factors.
Changing the water storage location from the Bellwether Park will likely have additional costs to extend the
utility infrastructure to the location and purchase land rights. To maintain the current schedule, purchase
agreements and site work should be completed by Fall 2022. Additional details on these impacts would be
further discussed and quantified dependening on the site selection.
Additional Work Session Topics
If time allows, Stantec will review with City Council the results of the Architectural Survey, which is attached to
this memo.
11/22/21, 9:09 AM Architecture preference survey
https://docs.google.com/forms/d/1kProLRXTr38xX-zm3Spc8WGIsWjeG34nC6hzwZjxRhM/edit 1/10
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Architecture preference survey
Please rate each of the building styles below.
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11/22/21, 9:09 AM Architecture preference survey
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11/22/21, 9:09 AM Architecture preference survey
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11/22/21, 9:09 AM Architecture preference survey
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