Geosynthetics April/May 2020 - 38

CSPE performance and history in long-term potable water storage applications

FIGURE 4 Aerial view of Twin Happy Valley
Reservoirs, Adelaide, Australia (Google Earth)

The decision to replace
the CSPE liners and covers
was made taking several
factors into account. This
included that the planned
25-year asset life had been
achieved. Changes to flow
were also necessary as
water-quality standards
had progressed over the
previous 25 years, and
short circuiting was an
issue as the inlets and
outlets were relatively
close to each other.

the fact that South Australia has some
of the highest solar conditions in the
developed world. Specific puncture resistance tests were conducted using material
obtained from the site, and HDPE, CSPE,
ethylene propylene diene monomer
(EPDM) and butanol were all evaluated.
Following the evaluation process,
45-mil (1.14-mm) CSPE was selected as
the most suitable material. Black material
was selected for the liner while the cover
material was black on the underside,
which was in contact with the potable
water, and tan on the top surface to
reduce surface temperatures and provide
a more aesthetic appearance (Figure 4).
The liner and cover for Storage 1 were
factory fabricated off-site. The twin storages were constructed using compacted
cut and fill material with an underfloor
drainage system. After final surface preparation, a heavyweight nonwoven geotextile
cushion layer was installed by the contractor before installation of the prefabricated CSPE liner panels. All field seams
carried out on the liner were performed
using CSPE adhesive. The covers were
installed in the same manner. Storage 1
was completed in 1988, and Storage 2 was
completed a year later. Annual inflation
of the CSPE floating covers were carried
out to facilitate inspection and cleaning
of the liners. Three years after installation
during one of these regular inflations, the
cover on Storage 1 was torn open by a gust
of wind, resulting in a large tear more than
halfway across the cover and displacing
approximately 25% of the cover area. Over
the following days, the cover was manually
pulled back into place and successfully
repaired using the CSPE gluing process.
The repairs carried out in 1991 on the
cover on Storage 1 remained effective for
the full remaining life of the material.
The decision to replace the CSPE liners and covers was made taking several
factors into account. This included that
the planned 25-year asset life had been

achieved. Changes to flow were also necessary as water-quality standards had
progressed over the previous 25 years,
and short circuiting was an issue as the
inlets and outlets were relatively close to
each other.
After 26 years of service, the liner
and cover on Storage 1 were replaced in
2014. While the tan top surface of the
cover was stained, the CSPE material
was still completely pliable and the black
underside surface appeared nearly new.
When the liner material was cleaned, it
appeared to be in close to new condition. The 26-year-old CSPE liner and the
cover material appeared to still have some
life in them and were cut and reused as
drop-in liners, evaporation pit liners,
tarpaulins and haystack covers.
In 2016, after 27 years of service,
the liner and cover on Storage 2 were
replaced. The CSPE material was in the
same near-new condition as in Storage 1
and was again recovered and reused in
other applications. The new replacement
45-mil (1.14-mm) CSPE covers were
constructed with integral CSPE baffle
curtains to improve chlorine contact/residence time and eliminate short circuiting.
Upper Reservoir
* Otay Water District, Spring Valley, Calif.
* 36.7-million-gallon
(139-million-l) capacity
* Potable water storage
* CSPE liner and cover originally
installed in 1988
Otay Water is a water, recycled water and
sewer service provider. The California
State Legislature originally authorized the
establishment of the Otay Water District
in 1956 as a special district. Today, the
district provides water services to customers within 125 square miles (323
km 2) of the densely populated region
of southeastern San Diego County. The
district's facilities service the water and

Geosynthetics | April May 2020

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3/23/20 5:30 PM

Geosynthetics April/May 2020

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