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Crews drilling core samples to prepare for the Sellwood Bridge replacement project will work a long day today in order to get a full-length core sample from one of their drilling sites.

The work will take especially long because crews have found that, in one section of the river, the bedrock is much lower than in other section, said Multnomah County spokesman Mike Pullen. The area at issue is near the east bank of the river at the site where one of the foundations for the new bridge will be placed.

Pullen said that layers of gravel between the river floor and bedrock go about 30 feet deeper in this section of the river.

鈥淭his will make the foundation at that location longer, deeper and more expensive,鈥� Pullen said.

The goal of the preliminary drilling work is to take core samples so crews have a better idea of what work they’ll need to do to install foundations that go all the way down to bedrock, Pullen said.

鈥淲e’d like to know as much as possible in the design phase,鈥� Pullen said. 鈥淚t avoids surprises during construction that could add cost and make the project go over budget or force us to cut parts of the budget.鈥�

Today’s drilling is expected to be the last in-river work for August, according to a release sent by the county. Crews needed to work an extra-long day in order to complete the work all at once because there is a risk that the bore hole will collapse if left open overnight, according to the release.