South 10th Street Storm Drain Reroute Project

Project details updated June 3, 2019

In February 2019, work began on a St. Helens Engineering Division project to reroute storm drain lines in the South 10th Street and Plymouth Street areas. A new gravity-flow stormwater system was installed from the City’s stormwater pump station at South 10th Street and Old Portland Road to an existing 24-inch storm drain on South 11th Street and Plymouth Street.

The installation of this new storm drain system will allow the City to decommission the existing stormwater pump station which is unable to adequately handle the stormwater runoff that it receives, especially during heavy rainfalls.

The project consisted of:

• Construction of over 1,000 linear feet of high density polyethylene pipe (HDPE) of 8-inch, 10-inch, 12-inch, and 14-inch diameters
• Installation of seven new stormwater manholes
• Installation of six new catch basins and ditch inlets

Most of the pipe was installed by the trenchless construction method known as HDD or Horizontal Directional Drilling. This method of construction was selected by the St. Helens Engineering Department because:

1. It would greatly reduce construction time and costs
2. It would minimize traffic disruption to residents, as well as reduce construction noise
3. Horizontal Directional Drilling is one of the few trenchless construction methods that works very well in hard rock

As many residents in St. Helens may already know, the utilities in town are generally constructed less than five feet underground due to the presence of un-weathered, solid basalt bedrock with a compressive strength greater than 40,000 psi (that’s A LOT…. Concrete has a psi of around 5,000. Granite is about 19,000 psi. Our St. Helens basalt has about the same psi as stainless steel!).

The main portions of the new storm drain have been constructed at a depth of 17 feet in solid rock. Not only was the project a great success and constructed within budget, but the new storm system is flowing nicely. Previously surcharged manholes are now drained of standing water for the first time. The Engineering Division expects this system to greatly improve the storm drainage issues in the areas between South 8th Street and South 11th Street.

• The design of the new storm drain system was completed in-house by the City’s Engineering Division
• The general contractor on the project was Emery & Sons Construction, Inc. out of Salem
• The drilling contractor was Downing Diversified, LLC out of Kalama, WA
• The $580,000 project began in early February and was completed at the end of May