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HomeMy WebLinkAboutPPP.04.02-P2-89 Construction Contingency Increase - Ops Committee Meeting Solids Thickening and Dewatering at Plant No . 2 Project No. P2-89 y S A N l Tq Q � CD Orange County SanitationDistricil THE Request for Additional Construction Contingency P2-89 Solids Thickening and Processing Upgrades • Project Scope includes: — Rehab and upgrade 4 dissolved air flotation thickeners ( DAFTs) — Modify two sludge holding tanks to allow use as active digesters • Construction contract $26 million • Schedule — Construction started June 2012 — Construction complete by January 2017 Dissolved Air Flotation Thickeners • Rehab and upgrade 4 dissolved air flotation thickeners ( DAFTs) • 2 of 4 now complete and in service • Performance of new units exceeds expectations l ii Y 9. • ,, I 9+ •yv ... I k C 1 ++i l vy ? Z' w ANI s ,\•��., Imo: � r F, J•6. Construction Challenge : Only 1 DAFT could be rehabbed at a time Original Implementation Plan Ste p 1 Step 2 Step 3 Step 4 Original in service O O O A B O B 000 000 000 OOCO In construction- New in service Revised Implementation Plan based on higher than expected capacity of the modified units Step 1 Step 2 Step 3 Original in service O O O 000 000 000 Revised approach avoided delays cause by other construction problems Construction Challenge : Center Foundation for 4th DAFT • New collector was to be anchored to existing foundation • Existing foundation very different than shown on as-builts • High costs, delays and construction risks were avoided by re- engineering the anchorage to avoid cutting into the existing slab. • Re-engineering results in substantial supplier effort LC V CLIIVL 2'MAX h LTS 2"BELOW STRUCT ;OFMu.; FACE&FILL stt n.z a uee— 4"DEEP SHEAR EMBEDMENT IT z rom OPENN s ri""I is.e•mrcaa _ .. _ ' � I ttso._ d ii I RoT meL 4 ei a d I I "`OMLL EMBEDMENT I (TYP) L a 1F �(TYP BED.w! IATE),AT (E) APPROXIMA. TYPE. S WAS PIPE.V YP), ° ' 4 0.a" IGLE I ° rr4pII� F EXISTIr OF "Mover -#5 REINF x 6' SILLTRUCTUR' NVIE "' "T^'r" rRnT.SEI Record Drawings ( H(N u E)FC Final Anchorage Design Biosolids Holding ( DigestersTanks I & J • Modify to work as active digesters or holding tanks • Rehab mechanical & electrical • Address concrete dome corrosion 41: „ram e f e t x : ae.a OM Y `• I ' I 1 7 -1 4! f Construction Challenge : Digester Concrete Issues • Digester dome required patching and repair (ala Plant 1 Digester Rehab project) • Cracks in digester floor needed sealing • Joint between wall and floor required complex sealing detail • Replacement of pipe penetrations through wall required reinforcement of existing concrete a�M—WW Construction Challenge : Digester K Transfer Pump • Digester K rehab was not part of project • Digester K transfer pump started to fail during construction — single point of failure • Decision made to replace pump on this project due to critical nature of pump low-A Costs of addressing unknown conditions requires additional contingency a g y Amounts Original construction contract $26,383,400 Authorized contingency $2,107,242 8.0% Changes to date $1,941,724 7.4% Remaining contingency $165,748 0.6% �41JM2MMMIF Reservation for remaining construction risks $692,616 2.6% Contingency Remaining $165,748 0.6% Requested contingency increase $526,868 2.0% Total requested contingency $2,634,340 10.0% No additional project budget is needed — only construction contingency. Despite chan es, project is still g highly cost effective • DAFT is lowest operating cost thickening technology • Temporary thickening facilities avoided - saved millions & minimized risks • Bid climate in 2012 was highly favorable • - � • • . ion Cost qd 7" Project Development Estimate 2008 $46 million Temporarythickening eliminated Predesign Estimate 2011 $31 million Favorable Construction Contract 2012 $26 million Bid climate New DAFTs use $250,000 less polymer annually than old.