Pendleton water technology on country’s cutting edge

Published 6:31 am Friday, June 7, 2013

The?Pendleton water treatment plant was the first of its kind in the world to use a siphon design for filtering water through drinking water membranes.

The plant first went online June 13, 2003, with an original production capacity of 6 million gallons per day. This production was targeted for storage in the winter and spring months when the Umatilla River has high flows and customers use about 2.5 million gallons per day. That allows filtered water through the membranes to be stored in the basalt aquifer beneath Pendleton by flowing the water down existing wells to help recharge the aquifer. Prior to aquifer storage, the city relied on 62 percent of its source water from native groundwater, with annual water level declines of over three feet per year.

Through nine years of operation, an average of 441 million gallons has been stored and recovered each year and more than 5 billion gallons of native groundwater has been left in the aquifer. This has successfully reduced native groundwater declines from an average of more than three feet per year to an average of less than a foot per year. It also changed our reliance on native groundwater from 62 percent to an average of 18 percent each year for our annual water supply. Pendleton has the largest municipal storage program in Oregon and is considered one of the most drought-resistant water systems in the country.

In December 2011, new replacement membranes were purchased at 45 percent of market cost and added to the treatment plant. This expanded production from 6 million to about 10 million galls per day during the winter and spring months. It also allowed half of the older membranes to be retired to the wastewater treatment plant, where recent upgrades have been completed.

During this same period, the aquifer storage program was expanded to include two new wells, bringing the total to five, to take advantage of the additional treatment plant production capacity. With our current year of operation, 885 million gallons have been stored and we are just beginning to recover the stored water as we move into the summer months. It is expected that about 100 million will remain in the basalt aquifer after this ASR season and a measurable increase in native groundwater levels will occur.

With the expansion of the water treatment and storage programs, Pendleton also pursued development of hydropower production within the last decade. These new facilities came online in late 2012 and early 2013.

Five of the six new power producing facilities use regenerative drive technology, whereby the existing motors and pumps serve as the catalyst for making power by spinning backwards. A variable frequency drive is used as an electric brake to control the speed of the motor when water flows down into the aquifer. The regenerative drive captures excess power produced at the motor and the power is provided to our local utility company through a net-metering agreement. In our first year, about 345,000 kilowatt hours of power was produced, or more than a $20,000 offset to our overall annual water system power bill of about $380,000. We are the first municipality to use this type of technology for producing power.

Pendleton is recognized as a leader in water supply innovation.

Bob Patterson is the public works director for the city of Pendleton.