|ALASKAN CITY USES WATER PRESSURE MONITORING TO ENSURE COMMUNITY HAS ADEQUATE WATER SUPPLY
Herring Cove is located eight miles south of the center of the Ketchikan Gateway Borough (KGB). Ketchikan
is a separately governed City and Borough, called the "First City" as it is the first seaport in Alaska voyaging
from the south.
In 2011, Ketchikan's combined population was about 12,400, with approximately 5,000 residing outside the City. The
KGB operates a small potable water system for the South Tongass Service Area (STSA) serving approximately 350 residences,
an elementary school, and a few businesses. The water system averages a daily consumption of 120,000 gallons. Due
to most southeast Alaska communities hugging mountainous terrain, communities are built linearly making this small
utility have close to 15 miles of service main.
Historically, it was assumed, that either the Civilian Conservation Corp (CCC) or the Works Progress Administration
(WPA) constructed the area's original water system which eventually served a total of 35 homes and two businesses. Water
mains were built using 4 inch wood stave, cast iron, ductile iron, and PVC. The supply was the pristine Whitman
Creek with more than ample supply volume. No treatment was provided, thus the customers were under a continuous
boil water notice from the Alaska Department of Conservation, Division of Environmental Health. This system has
since been replaced with 6 and 8 inch High Density Polyethylene (HDPE).
Approximately ten years ago, the KGB realized that the source of water for the STSA was inadequate and layed out a plan
to use Whitman Creek and Herring Cove as new supply sources. The plan, soon after, became reality.
The first phase of the plan required the construction of a dual main leading from the Whitman Creek intake dam to the
existing STSA water treatment plant (WTP) located four miles from Whitman Creek. This enabled potable water to be
returned to Herring Cove and other customers along the route.
Ketchikan, Alaska is approximately 235 miles south of Juneau and covers a total area of 4.1 miles.
Prior experience had proven that constructing a new municipal potable water system to serve properties which were relying
on individual supplies, such as roof catchment or adjacent streams, were likely to have piping with deficient pressure
capacities. The deficiency along with the fact that there were no building or plumbing codes enforced in the KGB
compounded the situation. These factors, made the possibility of plumbing deficiencies, a potential reality.
The original Herring Cove operating pressure was set by the intake elevation at Whitman Creek, which provided between
40 and 60 psi across the customer base. The KGB decided to maintain the new supply as close as possible to this
pressure base. Maintaining this pressure base would help prevent possible property damage by boosting the pressure
to allowable Code limits. To provide necessary documented proof of the pressure consistency (or lack thereof) a
constant reading data logger was installed. Global Water's PL200-G
(Garden Hose Thread) was chosen to gather this data. The pressure logger was attached to a fitting at the water
The PL-200-G was compact and extremely easy to use, simply connected to a computer with a USB cable to gather data.
The KGB PL-200-G was set to collect data points every ten-seconds. That data was downloaded once per week. Data
was examined daily and differential readings were reported to the KGB Department of Public Works.
The original intent was to prove that the STSA pressure was well below the Code maximum. The data gathered by the
PL200-G proved the opposite had occurred. Pressures rose to above 90 psi. A new theory has since been developed based
on this data: debris in the new mains is clogging the pressure-reducing valve (PRV) at the Herring Cove connection on
numerous occasions. Thus, pressure has actually risen above Code maximums.
Global Water's PL200-G pressure logger is expected to be operating for at least another year, essentially until the cause
of the differential pressures has been positively identified.
For more information about the PL200-G pressure logger click HERE.
PL200-G Pressure Logger installation.
To download a pdf version of this application story please click HERE.