HomeMy WebLinkAbout4 Frozen line Agenda Item #
l�' e'TRUC E
e Public Utility District
Memorandum
To: Board of Directors
From: Neil Kaufman and Peter Holzmeister
Date: February 14, 2007
Subject: Frozen Water Service Laterals
1. Why this matter is before the board:
On February 7, during the public input portion of the Board of Directors Meeting, Charlie White described
a frozen service line problem experienced at Donner Lake. He stated that our use of plastic service lines
from the street through the service box to the point of connection at the customer-owned metal line made
it impossible to thaw frozen lines using impressed electric current.
The Board requested that the Water Department provide information to the Board regarding this issue.
2. History:
Different portions of the District's water system were constructed at different times. Over the course of
time, a number of pipelines have been replaced due to their poor condition. The first pipeline
replacement work was performed in 1985, and a number of projects have occurred since then.
Starting with the large Tahoe Donner Replacement Project in 1991, the District began installing PE
(plastic) service lateral piping. Components inside the new meter boxes were brass. A dielectric union
was used to make the connection between the between the meter hardware and the metal pipe
downstream of the meter box. A dielectric union is equipped with a plastic bushing that prevents
electricity from being conducted across the connection. This is done to eliminate pipeline corrosion
caused by connecting dissimilar metals buried in corrosive soils.
In 2001, the District changed to a different meter box design which has been used on all projects since
that time. The new meter box is constructed of plastic with plastic tubing and metal fittings. The plastic
tubing is non-conductive. This system also eliminates pipeline corrosion caused by connection of
dissimilar metals.
3. New information:
During January 2007, the Truckee area experienced a period of unusually cold weather, but very little
snow. During January and February 2007, the Water Department dealt with approximately 100 service
calls regarding frozen pipes and broken pipes.
Area Percent of Calls
Tahoe Donner 40%
Donner Lake 30%
Gateway 8%
Glenshire 8%
Other Areas 14%
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Almost all of these cases involved one of two problems.
1. The owner of a second home did not keep the inside of the house warm enough and did not drain
the internal plumbing when the house was unoccupied. Sometimes, the homeowner forgot to
close the crawlspace vents allowing cold air to enter. The pipes inside the house or in the
crawlspace then froze.
2. The customer-owned lateral between the meter box and the house is too shallow. Snow actually
functions as an insulator due to the large amounts of air trapped within a snow bank. The
combination of unusually cold weather and lack of snow led to greater frost penetration and
freezing of a number of underground pipes.
At Donner Lake, many of the older properties were not constructed to be used as year-round
residences. The customer-owned service laterals on these houses are often shallower (12"-18" below
grade in some cases) than current standards allow. Periods of cold weather similar to that experienced
in January will freeze these shallow laterals.
There were six locations where a service lateral froze between the main and the meter box. There are
District-owned pipes and the District was responsible to unthaw the pipe. All of these laterals are original
construction located in within Tahoe Donner. At four of the six locations, a property owner or
homebuilder constructed an access road or driveway that reduced the amount of cover over the service
lateral. The pipe then froze within the access road or driveway. The other two laterals area located in
areas that do not have mush sun exposure. The District also had four locations where a water meter
froze in the meter box but the adjoining buried pipe did not freeze.
When a lateral pipe freezes there are four basic methods to address the problem.
1) Wait and hope that warmer weather will thaw the pipe.
2) Impress an electrical current a metallic pipe. The electric current will cause the metal to heat
up and melt the ice that formed inside the pipe. This requires that access be available to both
ends of the metallic pipe. This method will not work with plastic pipe since plastic pipe is non-
conductive.
3) Force hot water down the pipe to melt the ice. This method will work with both plastic and
metal pipes.
4) If the exact location of the ice formation is known, the pipe can be excavated and heated
externally by a propane torch or similar equipment. This method will work with both plastic
and metal pipes.
Option 1 is often not feasible since the customer needs water service restored quickly. However, some
second homeowners who do not use their house often during the winter have opted to wait until the
Spring.
Option 2 is the 'old school' method of thawing pipes. A number of local plumbers have the equipment to
perform this work and it can be successful if the pipes are all metallic and conductive. This equipment is
also available for rental at Truckee Rents. However, there are safety hazards associated with this
method. On many older homes, the electrical system is grounded to the water piping. If there are any
problems with the house electrically, impressing a current to thaw a water pipe can damage items such
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as appliances and electronics. There are also instances throughout the country where thawing pipes
with an electric current has started an electrical fire. The District used this method in the past but does
not do so currently.
The District uses a hot water thawing machine (Option 3) to thaw frozen laterals owned by the District.
The field crew has found that it is sometimes it is necessary to excavate the lateral and cut it because the
machine cannot navigate sharp bends in a pipe. Not all of the local plumbers have the equipment to
force hot water or steam down a pipe.
Option 4 is often not feasible since the exact location of the ice formation is usually not known.
After a number of internal discussions, the Water Department agreed to provide some assistance to
customers in the Donner Lake area. The Water Department will excavate the connection point between
the customer's metal pipe and the plastic pipe installed by the District as part of the replacement project.
Once the metal pipe is exposed, a plumber (or property owner) could connect an electric thawing
machine to the pipe. An acknowledgement form for signature by the property owner was created to
ensure that owner recognizes that this was a one-time event. The Water Department contacted Charlie
White and a number of local plumbers to let them know that the District would do this excavation work.
As of February 15, one service lateral had been excavated. A second lateral is scheduled for the week
of February 20-23. The property owner at a third house opted to wait until later in the winter to see if the
pipe will thaw by itself.
4. Recommendation:
We have no recommendation for the Board. The District has been conducting pipeline replacement
projects for the last 17 years and during that period, we have installed has no electrical continuity
between the meter box and the house.
January 2007 was the first really cold period in Donner Lake since the mains were replaced. Almost all of
the problems occurred on customer laterals that are too shallow. As home owners at Donner Lake
convert summer cabins to year round homes, the customer-owned water service lines need to be placed
at least four feet deep.
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