The San Diego County Water Authority board approved change orders to the SDCWA’s contract with NEWest Construction Company, Inc., for the Twin Oaks Valley Water Treatment Plant Expanded Service Area project.
The September 24 CWA board vote accepted three change orders totaling $315,145 which had been authorized by CWA staff under the authority of CWA general manager Maureen Stapleton while also authorizing Stapleton to execute an additional change order for $93,392. The $400,537 change order amount increases the total contract amount to $4,090,537.
A change order for $282,599 includes the replacement of the existing pump inlet piping and valves which were smaller than shown on the record drawings. The change order for $42,046 was executed after the presence of slurry backfill beyond the limits shown on the record drawings led to the decision to relocate the Hauck Mesa Valve Vault and to excavate and backfill the original location. An administrative modification credit of $9,500 corresponds to reduced CWA field office requirements. The new $93,392 change order allows for modifications required to the heating ventilation and air conditioning (HVAC) system.
The Carlsbad seawater desalination plant is expected to be in service this fall and will relieve demand on the CWA’s Twin Oaks Valley Water Treatment Plant, which will allow for a redistribution of water from Twin Oaks through the Valley Center Pipeline and reduce the amount of treated water needed from the Metropolitan Water District of Southern California (MWD).
Treated water from the Twin Oaks Valley Water Treatment Plant is initially distributed along the CWA’s Second Aqueduct which includes Pipelines 3, 4, and 5. The Valley Center Pipeline runs from the Gopher Canyon area to Valley Center and connects the Second Aqueduct to Pipelines 1 and 2 on the First Aqueduct. Pipelines 1, 2, and 4 currently convey treated water to CWA turnouts while Pipelines 3 and 5 carry untreated water through the San Diego Aqueduct system.
The Valley Center Pipeline currently carries 20 cubic feet per second (cfs) while the CWA takes 60 cfs from the MWD delivery point to provide 80 cfs of treated water along the First Aqueduct south of the Valley Center Pipeline.
The Valley Center Pump Station itself was completed in 2001. A review of the station’s mechanical, structural, electrical, and security systems determined that the pump station could be expanded to increase the pumping capacity to 41 cfs, which would satisfy day-to-day and emergency treated water needs projected through 2035.
The retrofit includes replacing the existing pumps, motors, electrical system, computer control system, and certain valves and modifying the building roof to comply with current building code requirements.
Conveying additional water from the Twin Oaks plant would cost less than importing treated water from MWD, and the expected return on investment period is five to eight years.
The Valley Center Pump Station expansion will also increase the CWA’s chances of meeting water demands in an emergency event. In August 2014 the CWA board authorized a $3,682,000 design-build contract with NEWest Construction Company, Inc., for the capacity expansion.
In August 2014 the CWA board authorized a $3,682,000 design-build contract with NEWest Construction Company, Inc., for the capacity expansion.
The inlet piping was believed to be 24 inches in diameter, but some segments had a smaller diameter. That piping will be replaced and will be 26 inches in diameter to meet current standards.
As work was being performed, additional concrete slurry surrounding the Hauck Mesa Valve Vault was encountered. Relocation was determined to be preferable to removing the slurry backfill, so the vault will be moved ten feet to the west.
NEWest or a subcontractor had been required to retrofit the pump station’s existing HVAC system based on the maximum design indoor temperature of 104 degrees for electronic equipment and an average outdoor air high temperature of 91 degrees in the Escondido area. Since the Valley Center Pump Station is in Valley Center, the more appropriate average outdoor air high temperature was 100 degrees. The HVAC modifications will include procuring and installing additional air conditioning units and ducting, high- temperature alarms on the variable frequency drives and active harmonic filter equipment, and seismic bracing for the roof-mounted HVAC equipment.
The capacity expansion has a January 2016 completion estimate.