Due to river ice-induced damage to an over 100-year-old, 10-inch diameter, cast iron water main crossing the Des Moines River, the city of Ottumwa had to find a solution to replace this asset to maintain redundancy and fire protection. Complicating the project was subsurface contamination associated with legacy industrial operations on both sides of the river and existing in-service sanitary sewers within the project corridor.
Brierley Associates' solution was to use Horizontal Directional Drilling (HDD) to install 12-inch diameter HDPE DR 9 pipe. To overcome the concern of legacy contamination and the existing sanitary sewer infrastructure, the HDPE water main was inserted through steel casing until bedrock was reached, followed by grouting in the casing and annular space. Further protection of contaminate fluid migration was accomplished by grouting the bedrock annulus around the HDPE pipe. Additionally, a special welded end plate connection was designed, which allowed a ductile iron water main fitting to be connected to the HDPE to prevent subsurface contaminated media from entering the new water main.
The successful Vine Street water main replacement is the first instance of a water main of this material and size being constructed via trenchless methods beneath the Des Moines River in Ottumwa, Iowa. Other river crossings exist in the area, but these consist of pipes fixed to bridges, or dredged along the riverbed. Since Ottumwa Water and Hydro (OWH) was unfamiliar with longer HDD installations like this one, the project team worked collaboratively with OWH to educate, mitigate risks, and develop a level of comfort with the HDD method. The educative approach also aided in the approval of the Iowa DNR variance.
The design team consisted of Brierley Associates as prime consultant with French-Reneker-Associates and Kaskaskia Engineering Group as subconsultants. Construction was provided by Ellingson Construction and K.M. King, Inc.