Coleman Engineering provided planning services (including a successful SRF-grant funding application); preliminary and final design; project management; and inspection and construction contract administration for a new drinking water well and for a consolidation pipeline for the Los Molinos Community Services District, Los Molinos, CA. The water supply pipeline portion of the project consisted of 1,800-feet of 10-inch dia. C900 PVC transmission main within and adjacent to the Caltrans right-of-way for State Highway 99, and two 4-inch dia. C900 PVC distribution mains each approximately 450-feet long. The distribution mains are to connect two mobile home parks into the Los Molinos water supply network so that existing wells can be decommissioned. Three horizontal directional drilling (HDD) / jack-and-bore crossings – two of State Highway 99 and one of Los Molinos Creek – were included in the project.
Key Challenges & Solutions
- Early in construction and after discussions with Caltrans, advantage was taken of a concurrent and adjacent Caltrans stormwater drainage project that allowed one of the Highway 99 crossings to be completed by open-cut trenching instead of HDD.
- After multiple attempts, both of the remaining HDD crossings could not be bored. This was due to adverse ground conditions and caused partial collapse of the drilled holes. Two solutions were adopted. Caltrans allowed for further open-cut trenching across Highway 99, and for the Los Molinos Creek Crossing, a pipe bridge was designed. With piers set above outside of the riparian environment, the need for additional environmental permitting from the State of California Department of Fish and Wildlife was avoided.
February 14, 2022