ITEM 8 70th Street Pond status11
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MINNESOTA V
DEPARTMENT INFORMATION
Request for
City Council Action
ORIGINATING DEPARTMENT:
REQUESTOR:
MEETING DATE:
Public Works
City Engineer Wagner
August 22, 2016
PRESENTER(s):
REVIEWED BY:
ITEM #:
City Engineer Wagner
City Administrator Johnson
8
AGENDA ITEM DETAILS
RECOMMENDATION:
Recommend review of 701h Street pond status and previous Council direction. No action is requested.
ARE YOU SEEKING APPROVAL OF A CONTRACT? IS A PUBLIC HEARING REQUIRED?
No I No
BACKGROUND/JUSTIFICATION
Storm Pond #5 located along the south side of the 70th Street/CSAH 37 project, on the Valerius Meadows
property, has been holding water without draining down as designed. Many discussions and site visits
have occurred since February 2016 and a few options have been presented to the Council and the
affected property owners.
Staff recommends continuing pursuit of Option #4 as previously directed by Council as it would be a long
term fix to the situation and the pond could be redesigned and repurposed someday as a regional storm
pond. Other proposed options would not have that ability and either have not been met favorably by
adjacent landowners or would require ongoing operational and/or maintenance costs.
Option #1 was presented to and approved by the City Council April 251h, 2016. This option required
replacing the plugged draintile (being used by the pond as an outlet) with 1,285 feet of new draintile from
the pond to the existing discharge point to the southeast. This option required a temporary easement to
construct the draintile. This option was rejected by the property owners as the installation of the new
draintile would have required an agreement in which the draintile would have been the property owners
to use and maintain. A quote of $19,734.00 was received from Fehn Companies, the general contractor of
70th Street project. It should be noted that this option probably may have incurred additional costs to
repair existing draintile that may have been cut/damaged by installing the new draintile across the farm
fields.
Option #2 was to provide an infiltration layer outlet system at the bottom of the pond. This option was
previously directed by Council to pursue. At that time we were working with the geotechnical engineer
(NTI) who performed a soil boring to determine the depth to the existing glacial washout (drainage layer).
We were informed over the phone that they hit this layer at 21' below the bottom of the pond. Upon
receiving the soil boring report we discovered that under the sandy layer at 21' down were more
impermeable soils, indicating we had not hit the glacial washout needed. NTI revisited the site and
extended the soil boring, per the initial contract, to locate the required soils. These soils were an
additional 15' deeper. This additional depth makes this option not feasible due to cost and
constructability. The original estimated cost for the 21' deep infiltration layer was $24,069.75. MNDOT
has stated in writing that the work would have been State Aid eligible.
Option (#3), this option includes regrading the east side of the pond to provide a separating berm
between the pond and farm field, constructing an concrete outlet structure, and directionally drilling
—2,100 feet of 8" pipe from Pond #5 to Pond #6 located on the southwest side of the Roundabout at the
intersection of 70th Street and Oakwood Avenue. This option was previously presented but not pursued
as it is much more costly and provides less than ideal pipe grades. There is 4 feet of fall in 2,100 feet from
one pond to the next which provides a pipe with 0.19% grade. Typically directional drilling is not
recommended for grades less than 1% as keeping the pipe on this exact of a grade is impossible. We were
also proposing 4 cleanouts along the way so that if the pipe did plug there would be access for the City's
jetting equipment.
,A preliminary quote in the amount of $137,528.00 was received from contractor specializing in
directionally drilling. The cost would be MSA eligible but 100% City cost, no County. This does not include
the cost of the grading around the pond, the concrete outlet structure at the pond, or open cutting and
installing the first 200 feet of pipe supplied by the directional drilling contractor or any engineering fees.
Option #4 is to redesign a larger pond capable of handling all flow without the need of an outlet. As per
direction of Council, staff has redesigned Storm Pond #5 so that no outlet is required. Staff has reviewed
and sized the pond both to accommodate a worst case short term need created if back to back 100 year
events were to occur (approx. 14" of rain over a couple of days) and also accommodate long term
scenarios during prolonged wet cycles in climate. No outlet is needed due to the additional storage
created and the ability over a long period for the runoff to either evaporate or infiltrate. The design used
very conservative values for infiltration and total runoff and is evaluated over a year's timeline. This is the
option recommended by City staff. This option requires purchase of additional property.
A last alternative would be Option #5. This would require an interim storm water lift station with a
shallow small force main until adjacent property develops and allows positive outflow to occur. The utility
department would have to maintain the lift in much the same way they do sanitary lifts. The lift would
not require SCADA and would not need to be very deep. There would be power consumption after most
rainfall and the lift and forcemain would need to be taken out of service each late fall and put into service
again each spring. Staff is not recommending Option #5.
All storm water improvements are 100% State Aid eligible.
SUPPORTING DOCUMENTS: x ATTACHED ❑ NONE
List: Plan Sheet of Pond Improvements
Preliminary Quote for Pond Regrading (not yet received — to be handed out @ meeting)
Preliminary Estimate for Option #5 (Storm Water Lift)
POSSIBLE MOTION
This information is provided for background only. Council has previously approved Option #4 so no
action is necessary at this time.
gUDGFT INFORMATION
FUNDING: BUDGETED: YES
MSAS Funds
Region 7W Federal Funds XNO
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