Combined Sewer Overflow Remediation

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Geotechnology engineers working at project siteGeotechnology engineers working at project site

The St. Louis Metropolitan Sewer District (MSD) began its $4.7 billion, 23-year, Combined Sewer Overflow (CSO) remediation in 2011 and to date, Geotechnology has assisted Jacobs Engineering with subsurface exploration services including drilling and geophysics on three primary elements of the project.

Drilling services have included drilling 113 borings into rock depths between 150 to 300 feet below ground surface and angle borings through known or suspected faulted zones to depths of 180 feet to 450 feet. Two of the angle borings were drilled at 45-degree angles and three at 35-degree angles.

To perform these borings and gather the required data the crew drilled with a 6 ¼ inch hollow stem auger to 15 feet below the ground surface, utilized HWT casing with casing advancer to bedrock refusal and then set those casings into rock 6 inches to 12 inches. An HQ3 coring system was used and HQ wireline packer tests were performed every 10 feet for the entirety of the angled borehole depths. In the two 450-foot deep angle borings we conducted high-flow-rate pump-in packer tests at two intervals in each boring. The pump-in rate was 50 gallons per minute for 2 hours. After testing was complete the boring was backfilled with cement-grout and surface patched.

Angle drilling was agreed upon for the area based on previous site knowledge and the goal to retrieve as much data as possible by intersecting the major rock-joint sets orthogonally.

For further information on Geotechnology drilling services contact your area’s Drilling Manager. In St. Louis, MO and Fairview Heights, IL, John Bostwick, R.G.; Overland Park, KS, Sheryl Gallagher, P.E.; Memphis, TN,  Mike Kosydor.