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.