HomeMy WebLinkAboutA001 - Council Action Form dated July 14, 2026ITEM #:39
DATE:07-14-26
DEPT:PW
SUBJECT:13TH STREET EMERGENCY STORM SEWER PIPE REPAIR - APPROVAL
OF CHANGE ORDER NO. 1
COUNCIL ACTION FORM
BACKGROUND:
In late March 2026, City staff responded to reports of sinkholes on the north side of 13th Street
near Veenker Memorial Golf Course. An investigation determined that the existing 12-foot
diameter corrugated metal pipe (CMP) conveying Clear Creek beneath 13th Street has
deteriorated significantly.
The culvert, which was installed prior to the area's annexation into the City of Ames, has
experienced extensive corrosion of the pipe invert beneath the westbound lanes of 13th Street.
As a result, stream flow has migrated beneath the pipe, eroding the supporting soil and
creating large underground voids.
The erosion has resulted in multiple soil voids adjacent to the culvert outlet, extending beneath
and around the pipe. While the voids are currently located north of the roadway,
continued erosion poses a risk of undermining 13th Street and could ultimately lead to
structural failure of both the roadway and the culvert if left unaddressed.
Because of the implications to public infrastructure, staff evaluated repair alternatives with
specialty contractors. Pressure grouting (mudjacking) was selected as the most appropriate
short-term stabilization method because it restores structural support to the existing culvert
without requiring emergency replacement of the crossing. This repair will stabilize the
culvert and roadway while allowing the City to evaluate and program a permanent
replacement or rehabilitation of the crossing within the next five to seven years.
Proposals for the grouting work were solicited and a contract awarded to Denco Highway
Construction of Mingo Iowa, in the amount of $40,360. The original contract included pressure
grouting to fill the voids immediately surrounding the culvert with flowable grout. During
construction, it became apparent that the extent of the voids above the pipe were
substantially larger than originally anticipated and have continued to grow in large rain
events.
This City Council Action is to approve Change Order No. 1 in the amount of $10,130.
The scope of work will include backfilling the remaining upper voids with suitable soil to restore
the surrounding ground to its original condition. Because these upper areas are not subject to
continuous water flow, soil provides a more cost-effective backfill material while the pressure
grout continues to provide structural support where ongoing erosion is occurring.
Revenue for these expenses is available from unobligated Storm Sewer System Improvement
funds, where there is an available balance of $170,965.
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ALTERNATIVES:
1. Approve Change Order No. 1 to Denco Highway Construction, in the amount of $10,130.
2. Direct staff to pursue changes to the project.
CITY MANAGER'S RECOMMENDED ACTION:
The proposed change order will restore the voided areas surrounding the culvert,
stabilize the existing infrastructure, and reduce the risk of continued erosion that could
undermine 13th Street while allowing the City to program a permanent rehabilitation or
replacement of the culvert in a future capital improvement project. Therefore, it is the
recommendation of the City Manager that the City Council approve Alternative No. 1 as
described above.
ATTACHMENT(S):
13th St Culvert Emergency Repair Figure.pdf
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