Mt. Solo Reservoir Fill Line
Client—City of Longview, Washington
Gibbs & Olson provided planning, design, permitting, easement acquisition support, and construction phase engineering services for the replacement of the City of Longview’s Mt. Solo Reservoir fill line. The existing 20-inch ductile iron water main, constructed in 1975, had become vulnerable to failure due to ongoing slope erosion and landslide activity along portions of the pipeline corridor.
Working closely with the City, our team evaluated alternative alignments, completed geotechnical investigations, performed surveying, prepared the SEPA checklist, secured temporary and permanent easements and developed bid-ready construction documents for a new pipeline route below the landslide-prone area.
The project included installation of approximately 750 linear feet of 26-inch HDPE water main using horizontal directional drilling (HDD), along with additional HDPE and ductile iron pipe installed through conventional open-cut methods. The new alignment replaced approximately 1,000 feet of aging water main and connected to the City’s existing water distribution system.
During construction, Gibbs & Olson provided engineering support by reviewing contractor submittals, leading on-site progress meetings, responding to RFIs, evaluating and processing change orders, and observing HDPE installation and HDD operations. The completed project delivers a more resilient water transmission system, protects critical infrastructure from future slope instability, and improves long-term reliability of the City’s water supply.
