Also, over the last several decades, the City has observed a continuous decline in its basalt well water levels at an average rate of 3 feet per year.
Membranes provide a physical barrier for the removal of microscopic organisms and sediment.
One of the advantages of membrane filtration is the high quality of the finished water in comparison to convention filtration or slow sand filtration. The City completed a pilot study using four different membranes in 2000 and found the membranes to be extremely effective for filtering water from the Umatilla River. When the City can no longer use water from the Umatilla River during the summer and fall months for injection purposes, the stored treated water will be pumped back out of the wells and served to the community. The City believes it is critical to provide the most consistent high quality water possible for ASR purposes. This is another reason that membrane filtration is preferred by the City of Pendleton.