19 - ELDEN PUMPING STATION DOWNSPOUTTo:
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Subject:
Item 19
Costa Mesa Sanitary District
... an Independent Special District
Board of Directors
Scott Carroll, General Manage
Rob Harriers, District Engineer
January 24, 2013
Elden Pumping Station Downspout on Incoming Gravity Line
Summary
In December 2012, the District's General Manager gave a report on the success of
downspouts on incoming lines at pumping stations in reducing hydrogen sulfide odors and
corrosion. Because staff had successfully installed a downspout on the incoming Irvine
force main at the Elden pumping station and the reduction in hydrogen sulfide was
significant, staff desired to have a second downspout installed on the incoming gravity line
at the Elden station to further reduce hydrogen sulfide and corrosion. Because of the
complicated nature of the hydraulics of the Irvine /Elden pumping system, both attempts at
installing the downspout on December 3rd and December 19th were unsuccessful;
however, staff made important progress in planning for the replacement of the remaining
37 -year old valves and piping at the Elden station.
Staff Recommendation
That the Board of Directors directs the General Manager to include replacement of the
section of 37 -year piping and valves at the Elden Pumping Station in the District's force
main rehabilitation program and to install the second downspout when the piping and
valves are replaced.
Analysis
The reason for the complicated hydraulic condition is the profile of the Irvine force main as
designed and constructed by the previous District Engineer in the 1970s along with the
design by the same engineer to tie the Irvine force main into the Elden force main. A copy
of the Irvine force main profile is attached hereto and the profile has stretches where there
19 Protecting our community's health and the environment by providing solid waste and sewer collection services.
www.crosdca.gov
Board of Directors
January 24, 2013
Page 2 of 3
are flat slopes, which traps air in the line. There should never be a flat slope in a force
main due to hydraulics and the opportunity for corrosion to occur. The decision by the
same engineer to tie the force mains together presented a condition where both the Irivne
and Elden pumps are actually pumping against each other when they are pumping
simultaneously. This second condition was rectified in 1990 when the current District
Engineer connected the Irvine force main directly into the Elden station wet well.
When the District rehabilitated the Irvine force main in 2012 by installing a liner, the profile
of the line did not change, but air release valves were strategically located to remove the
air from the system. Because of the profile, when the air was removed from the line, a
siphon condition was created that caused self- draining of the Irvine force main into the
Elden station. There was never a siphon condition before the 2012 construction because
the Irvine force main had air in at least two places and the air stopped the siphon condition
from occurring.
Before the siphon condition was discovered, it was thought one of the 37 -year old valves
was not completely closing and replacement of this valve was included during the second
attempt to install the downspout. The good news is the 14" valve does work (it was
exercised during the work) so it is possible to install the second downspout in Elden.
Additionally, it is now known how long it takes to remove the wastewater from the Elden
force main during a shutdown project such as replacing valves and piping or installing a
downspout.
Besides the two valves and piping at Elden that need replacing, three valves on the 18"
Elden force main (one on the east side of the Mesa bridge and two on the west side of the
Mesa bridge) that did not close properly will be replaced.
In the overall picture, the replacement of the piping and valves noted above should be
placed high on the priority list because the Elden system is the largest force main and has
the largest pumps the District owns. When this work is done, the installation of the second
downspout can easily be accomplished.
Strategic Plan Element & Goal
This item complies with Strategic Plan Element 1.0, Sewer Infrastructure and Strategic
Goal No. 1.4 System Wide Sewer Replacement and Repair Program.
Legal Review
Not applicable.
Financial Review
The cost for the two attempts by Schuler Engineering Inc. to install the second downspout
and replace the 14" valve was $30,406.86 (the replacement valve, downspout, and piping
included in this amount will eventually be used); the cost for traffic control was $3,407, and
Board of Directors
January 15, 2013
Page 3 of 3
the cost for the fleet of pumper trucks for the second attempt was $1,058. The grand total
was $34,871.86. These expenses were appropriated from Project #164, Miscellaneous
Sewer Maintenance account.
Committee Recommendation
On January 15, 2013 the Operations Committee discussed this item and recommends that
the Board approves staff's recommendation.
Public Notice Process
Copies of this report are on file and will be included with the agenda packet for the
January 24, 2013 Board of Directors regular meeting at District Headquarters and on the
District's website.
Alternative Actions
1. Refer the matter back to staff for additional information.
Attachment A: Irvine Force Main Profile
Reviewed by:
Marc Davis
District Treasurer /Acting Accounting Manager
SCALE 1" =100'
SCALE 1" =100'