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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