Devil’s Slide Mitigation

Montara, CA

CalTrans
Summer/Fall 2005 - 2010

Wetland Mitigation is fortunately now an integral part of development. Construction of the Devil’s Slide Tunnel on Highway 1 between Pacifica and Montara, Ca. is causing impacts to sensitive coastal wetland and scrub habitat. Hanford ARC was contracted in 2005 to restore and mitigate for the impacts to red legged frog and sensitive coastal habitat for a majority of the Devils Slide construction impacts.

The contract involved excavation of a large wetland swale, pond, and associated upland in Montara, on the East side of Highway 1. Mobilization included grading and stabilizing a roadway with base rock and fabric. Straw barriers and silt fencing were installed to protect from wind and water erosion. Street sweeping and vacuuming were required to maintain strict water quality controls. Hanford ARC excavated approximately 20,000 cubic yards of soil, which was offhauled to a common disposal site for the Devils Slide project.

In addition to the earthwork, the project included revegetation with over 4,000 native container plants and seed. The soil was amended with 11,620 pounds of mulch and 1,650 lbs of mycorrhizal inoculum. Hanford crews hydroseeded the area with 745 lbs of pure live seed, and harvested and installed approximately 1500 willow cuttings.

Irrigation systems of PVC pipe, drip lines, sprinklers and emmiters were installed. Water sourcing proved challenging, and Hanford ARC must truck water from Pacifica to fill a series of five 2500 gallon water storage tanks to maintain the watering operations. A new electrical service powers a pressure pump and irrigation controller. The project includes a three year plant-establishment period, during which time Hanford ARC regularly maintains the irrigation system and provides invasive weed control.