Download Inverted Siphon Rehabilitation and Odor Control

CITY COMMISSION AGENDA MEMO
September 4, 2009
FROM:
Robert W. Pugh, P.E., Assistant Director of Public
Works - Utilities
MEETING:
October 13, 2009
SUBJECT:
As-Built Change Order ~ Inverted Siphon
Rehabilitation and Odor Control Project (SP0702P)
PRESENTER:
Robert W. Pugh, P.E., Assistant Director of Public
Works - Utilities
BACKGROUND
Gravity sanitary sewers lines sometimes meet obstacles that need to be passed. A method
of crossing such an obstruction for sewer lines is for the sewer line to drop and run
horizontally beneath the obstruction. The sewer line then rises back to the proper
elevation. This type of piping is called an inverted siphon or a depressed sewer. The
sewer line on both sides of the inverted siphon flows by gravity. However, the inverted
siphon flows under pressure.
The City has experienced odor problems for many years near the inverted siphon located
near the intersection of Fort Riley Boulevard and East Poyntz Avenue (US Highway 24).
The odor problems occur intermittently; however, when the odor occurs, it is quite
strong. The current odor control improvement is based on recommendations in the City’s
Water Distribution System and Sanitary Sewer Collection System Master Plan Update,
dated July 2003.
On August 24, 2007, CDM, Inc., of Wichita, Kansas, completed the Preliminary Design
Report for this Plan. Significant physical repair and rehabilitation of the existing inverted
siphon and the construction of a new gas phase carbon-type odor control system at the
siphon location were the main recommendations of the Preliminary Design Report.
On January 22, 2008, the City Commission authorized City Administration to execute an
amendment to the agreement with CDM for Engineering Services for the Odor Control
System for the Sanitary Sewer Collection System Inverted Siphon.
The City’s consultant (CDM) and its sub-consultant (BG Consultants, of Manhattan,
Kansas) prepared the project specifications and the project was let out for bid. The
project was advertised for bid in The Manhattan Mercury for three consecutive days. Bid
notices and project specifications were also posted on the City’s web site and mailed
directly to interested contractors.
A bid letting was held on January 30, 2009. On February 5, 2009, the City Commission
authorized a contract with Walters-Morgan Construction, Inc., of Manhattan, Kansas, in
the amount of $327,424.65 for the project.
The siphon repair includes rehabilitation of the existing inlet structure interior surface,
replacement of the top of the structure with vent and access doors, and a siphon gate
replacement.
The construction of the gas phase odor control system includes a new carbon-type odor
control system at the siphon location.
DISCUSSION
Subsequent to the bid opening, the U.S. Army Corps of Engineers required that an
emergency backfill plan be prepared for the project, in the event that the Kansas River
level would rise, thereby raising groundwater levels on the landward side of the levee,
which, in turn, could provide potentially damaging uplift pressures on the inverted siphon
foundation and structure. The Corps of Engineers requested that this emergency backfill
plan be provided for a 3-year flood event, or river stage of 1001.0’ Accordingly, Walters
Morgan was required to have sufficient volume of backfill material delivered to the site,
and have a contingency plan to backfill the excavation if the river level reached 1001.0’.
This resulted in a mobilization cost of $5,439. Additional additions required to meet the
Corps directive were additional uplift calculations ($1,344), additional concrete haunch at
existing top of slab interface to new vertical wall extensions ($7,723), and additional
epoxy coated reinforcement ($3,500). Additionally, it was observed during bypass
pumping operations that the upstream manhole on Ft. Riley Boulevard had deteriorated,
and required rehabilitation to sustain traffic loads. Accordingly, the manhole was
replaced with a 42” pipe and adjoining pavement replaced to prevent future structural
problems for $2,527.00. Also, there were minor additions to the quantities of elevated
slab concrete ($682.50) and foundation concrete ($476.00). Finally, a rock driveway
was added to provide access to the structure for inspection in maintenance ($2722), and a
step down transformer was added to provide power between 480V, 3-phase II power feed
and the 230V, one-phase odor control motor ($1,000). These additions were partially
offset by a deduction for decreasing the size of sluice gates for the structure ($1,995). The
total proposed net additions to the contract are $23,418.50 (+7.2%), resulting in a final
contract amount of $350,843.15. However, the necessity of having a transformer addition
was determined to be a design error by the consultant, CDM, Inc. Accordingly, $1,000
amount will be deducted from their final pay request to the City.
The project engineer for the construction phase, BG Consultants, has reviewed all the
changes and concurs with City Staff as to their appropriateness and costs.
FINANCING
Temporary notes are being used as an interim financing mechanism for this project. Once
the project is completed, general obligation bonds will be issued and the proceeds will be
used to pay off the temporary notes. The bonds are anticipated to be for a ten-year term
and will be paid from the Wastewater Fund. In the bond resolution, the City factors in all
costs that could be incurred when a project is bonded. These costs include possible
contingencies and all financing and bonding costs as recommended by Bond Counsel.
ALTERNATIVES
It appears the Commission has the following alternatives concerning the issue at hand.
The City Commission may:
1. Approve Change Order No. 1-Final for the Inverted Siphon
Rehabilitation and Odor Control Project (SP0702), resulting in a net
increase in the amount of $23,418.50 (+7.2%) to the contract with
Walters-Morgan Construction, Inc., of Manhattan, Kansas.
2. Reject the As-Built Change Order.
3. Modify the request to meet the needs of the Commission.
4. Table the request.
RECOMMENDATION
City Administration recommends the City Commission approve the As-Built Change
Order for the Inverted Siphon Rehabilitation and Odor Control Project, in the amount of
$23,418.50, for a final contract amount of $350,843.15.
POSSIBLE MOTION
Approve Change Order No. 1-Final for the Inverted Siphon Rehabilitation and Odor
Control Project (SP0702), resulting in a net increase in the amount of $23,418.50
(+7.2%) to the contract with Walters-Morgan Construction, Inc., of Manhattan, Kansas.
09036
Enclosure:
1. Change Order No. 1-Final
CHANGE ORDER
CITY OF MANHATTAN, KANSAS
CHANGE ORDER NO.: 1 FINAL
SP0702P
CONTRACTOR: Walters Morgan
2008 INVERTED SIPHON
2616 Tuttle Creek Boulevard
IMPROVEMENT: REHABILITATION AND ODOR CONTROL
Manhattan, Kansas 66502
PROJECT NO.:
DISTRICT NO.:
PROJECT TITLE:
NATURE OF CHANGE: Amend Original Contract
TELEPHONE: 785-532-9440
PLAN
ITEM NO.
ADD
DESCRIPTION
Add items to address uplift
requirements, and other
miscellaneous items.
BENEFIT DIST.: 100%
QUANTITY
UNIT
0
LS
CITY-AT-LARGE: 0%
ACTUAL
QUANTITY
UNIT
QUANTITY
CHANGE
PRICE
1
1 $ 23,418.50
Total:
Page 1
NET PRICE
CHANGE
$
23,418.50
$
23,418.50