HomeMy WebLinkAbout2020-01-17; Tierra Del Oro Water Main Impact; Gomez, PazTo the members of the:
CITY COUNCIL
Date I Ii,/')£) CA .i cc~
CM ,..1::_ COO~ DCM_ (3) !:_,_
Jan. 17, 2020
To:
From:
Via:
Re:
Council Memorandum
Honorable Mayor Hall and Members of the City Council
Pai Gomez, Deputy City Manager, Publi} Works
Elaine Lu key, Chief Operations Officer tfr
Tierra Del Oro Water Main Impact
-(cityof
Carlsbad
' Memo ID# 2020006
On Jan. 14, 2020, the water main serving the homes on Tierra Del Oro Street was isolated to
make a repair. This was the fifth service interruption in recent months. Some residents on
Tierra Pel Oro Street have exp~essed frustration with the outages. This memorandum provides
an update on _recent events affecting the water main on Tierra Del Oro Street.
Background
The existing water main on Tierra Del Oro Street was completed in June 1967 and was installed
as a 4" Asbestos Concrete Pipe (ACP) distribution main. As observed in the field, the depth of
the line ranges from approximately 12" to 24". Current City of Carlsbad Engineering Standards
no longer allow 4" water main pipe nor the ·installation of ACP pipe. Current standards require
water mains to be 8" diameter (minimum), polyvinylchloride (PVC) and installed at a minimum
depth of 42" from the top of the pipe to the finished surface. The larger pipe diameter and
increased coverage provides protection of the pipe from damages and from breaks.
Currently, there are two separate private development projects for the construction of single-
family residence homes on Tierra Del Oro Street. Grading permit GR150017 was. issued to Mike
Lloyd Excavating and Thomas J. Taylor Construction for the construction of the home located at
· 5039 Tierra Del Oro Street (Site 1). Grading permit GR2017-0061 was issued to Zavatto Brothers
Construction for the construction of the home located at 5015 Tierra Del Oro Street (Site 2).
In recent months, there have been five incidents involving the existing water main on Tierra Del
Oro Street. Each incident has required c1n isolation of the water main to allow for repairs
resulting in a temporary shutdown of water for the residents on Tierra Del Oro Street
(approximately 20-30 single family homes).
Discussion
Below is a list and brief description of events from the five incidents that have resulted in a
water out~ge to facilitate repairs:
1-Site 1: A fence post impacted a water main in private property at the edge of right-of-
way. The _line impacted was a 4" ACP pipe at a depth of 18". Had the water main been
installed per current stan-dards, it is likely the fence post would not have impacted the
line.
Public Works Branch
Construction Management & Inspection Department
Faraday Center 1635 Faraday Ave I Carlsbad, CA 92008 I 760-602-2730
Honorable Mayor Hall and Members of the City Council
Jan. 17, 2020 ·
Page 2
2-Site 1: The contractor was using a jumping jack tamper (commonly called a Wacker) to
compact soil in an open excavation approximately 5-ft from the subject 4" ACP water
main. The vibration from the activity caused a break in the pipe. The contractor did not
directly impact the water main and the water main was buried (confined in soil) at the
time of the incident.
3-Site 2: The contractor identified _an existing direct tap on the subject 4" ACP water main.
A direct tap to a collar is not allowed per the City of Carlsbad's Engineering Standards. ·
The contractor submitted a Request for Information for direction on how to make the
repair. The contractor installed the new pipe section per CMWD's recommendation and
under the observation of the city's inspector. Following the installation, CMWD
energized the line and verified no leaks. Approximately 10 hours later (in the middle of
the night), the subject line broke nearby/adjacent to the repair location. The break was
not at the immediate repair location or within the excavation/trench limits of the repair.
4-Site 1: The contractor mobilized a boom (crane) truck to install a tree as a part of the
close-out/ landscape phase of work. The boom truck's outrigger was placed on a
secondary crane pad on private property at the edge of right-of-way. As the boom truck
swung its load (tree) into position the ground beneath the crane pad settled
compromising the subject 4" ACP water main. The impacted line was approximately 18"
deep.
5-Site 1: On Tuesday, Jan. 14, 2020, CMWD received a report of a ruptured water line.
Upon arrival, the city's inspector identified the compromised water line to be the
subject 4" ACP water main. The location of the break was under a finished (completed)
driveway. No inspections were scheduled for the day and the contractor's
superintendent stated that no construction activity took place that day.
It is not typical for the common construction activities listed above to cause harm or to impact
existing infrastructure such as a water main. While it is difficult to definitively determine any
one causal factor for the recent breaks on Tierra Del Oro Street, recent events suggest that the
condition of the water main, and the depth in which it was installed over 50 years ago, may
have likely contributed to the recent breaks.
Next steps
When a water main is impacted, CMWD reviews the causal factors of the ir:npact to determine
mitigation measures. If/when multiple breaks occur on any given water main, CMWD reviews
those mains for possible inclusion in its pipeline replacement program. Staff reviews factors
such as the age of pipe, number and cause of breaks, location and consequence of failure when
making decisions about whether to replace mains and the priority for doing so.
According to CMWD's Maintenance & Operations Division, the recent breaks on the Tierra del
Oro Street water main may likely be the result of the shallow depth at which the pipe is buried,
making it more susceptible to problems when ground disturbing activities (such as construction,
· heavy vehicles or vibrations) occurs nearby.
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Honorable Mayor Hall and Members of the City Council
Jan. 17, 2020
Page 3
The subject pipeline was constructed in 1967 and, due to recent events, has been observed to
have a shallow depth of burry ranging from 12" to 24". Given the age of the pipe, location,
depth and the number of recent breaks, CMWD has determined that this water main is a
candidate for replacement and has given this project to Utilities Engineering staff to be included
on the list of water main replacement projects.
Additionally, a pipe sample was taken from the main break that occurred on Jan. 14, 2020. The
sample will be sent to a lab for testing to determine remaining useful life. This, along with the·
criteria mentioned above, will be used to determine the priority for replacing the water main.
cc: Scott Chadwick, City Manager
Celia Brewer, City Attorney
Vicki Quiram, Utilities Director
Ken Knatz, Engineering Manager
Babaq Taj, Engineering Manager
Amanda Guy, Deputy City Attorney
Valerie Airey, Municipal Projects Manager
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