by:  This photograph, looking north, shows the primary area of excavation in the two previous stages of the tunnel project under the intersection of S.E. Insley Street at 18th. One final excavation of Insley, starting this month and running through August, will connect the collector pipe under Insley – conduit for most Inner Southeast sewage – to the small “big pipe” drilled from this point northward to the “CSO Big Pipe” southern terminus, on the north side of McLoughlin between 17th and 18th Streets.

The Portland Bureau of Environmental Services advises that the final stage of opening the six-mile-long 'East Side Combined Sewer Outflow' tunnel will begin in mid-June.

The huge tunnel was completed last October, and the finishing work involved with putting it into service has been underway since then - including closing the access excavations, installing bubbler tubes to measure the water level in the tunnel, and restoring the areas around the excavations.

Starting in the middle of June, BES will begin redirecting the outfalls to the tunnel; the outfalls to the Willamette River will not be blocked, but no longer will be used unless a very heavy rain event overflows the 22-foot-diameter Eastside CSO tunnel.

This means that instead of sewage mixed with rainwater going to the river every time a sprinkle occurs, as has been the case in the past, overflows to the river may only occur two or three times per winter, and occasionally once a year or less in the summer and fall. Reducing the overflows to the river has been the main purpose of the hugely expensive Combined Sewer Overflow (CSO) tunnel project.

The Eastside CSO tunnel runs north to Swan Island, where it will join with the already-in-use Westside CSO tunnel. The combined output of both tunnels will enter the new sewage pumping station on Swan Island, where the sewage will be pumped north to Columbia Boulevard for treatment.

As part of this final connection project, BES reports that the southernmost point in the Eastside project - the intersection of S.E. 18th and Insley - will, for the third and final time, be closed from mid-June through the month of August, to divert the 'Insley Collector' pipe to the tunnel shaft.

The Eastside tunnel project will have taken five years to complete.

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