Laura Jo Welter, The Triplicate

Feasibility study narrows options down to seven

Shedding fully half of the alternate routes initially proposed, Caltrans is left with seven possible solutions to a section of highway that is being sloughed off the hillside.

The options put forward by the Last Chance Grade Engineered Feasibility Study, completed last month, to fix the troubled section of U.S. Highway 101 were chosen for having lower financial costs and causing less damage to, or loss of, prized natural and cultural resources.

Options include maintaining the grade in its current position, which saddles 200 active slides between Crescent City and Klamath, and six new routes that would hopefully skirt or bore through the problem zones.

By law, Caltrans must consider a "no build" option, that is, what it would cost to maintain the highway where it lies. This will be used as a "baseline" for assessing alternate routes. The Feasibility Study found that maintaining Last Chance Grade in perpetuity has the potential to take the greatest toll on natural resources because a catastrophic road failure would not give officials the time to consider potential impacts while a hasty fix to reopen the road is pursued.

Among the choices recommended for further consideration is a mile-long tunnel that is the shortest proposed alternative with limited impact on National and State Park resources. It does have the potential to affect up to an acre of old growth redwood forest, and extensive geological study will need to take place to assess its feasibility. Soil instability at the portals may constrain construction and maintenance, the study says.

The remaining five routes all diverge from the current highway at Rudisill Road, north of Wilson Creek, re-entering at different points between the Damnation Creek Trailhead and Hamilton Road. They range from 3.3 miles of new road to 11.9, and estimated costs correlate with the length. The longer options, while being costly, are the least likely to have impact on old growth redwoods, though longer length mean the potential for more long-term impact on the watersheds of Wilson and Mill Creeks.

The two-year feasibility study process included sorting through historical responses to the slumping road, including prior studies, seeking public input, as well as consulting with the parks and tribes' experts on potential impacts, all of which is documented in the Last Chance Feasibility Study, available to read at the project's webpage:

All proposed routes will be more thoroughly vetted in the coming years before a selection is made. Caltrans will complete a report next summer on the proposed projects' cost, so that Caltrans can seek funding.

"As stewards of the State Highway System, Caltrans must make sure the public receives a cost effective highway within a reasonable construction period, and that these impacts are considered appropriately," the study reads.

As such, the seven options that were dropped are those that would have more impact on wildlife, watersheds and woodlands "with no added value" over the other options, Project Manager Talitha Hodgson said.

Options exiting the highway at Wilson Creek were excluded to avoid impacts on the cultural resources found there, as well as the added impact on the creek.

The most expensive proposed alternative (its initial cost estimate being up to $1 billion) was 15.1 miles long, swinging out east of the current highway, appears to avoid the slides mapped by Caltrans. But as the majority of geological studies have been conducted near the road, it's possible that the option may not avoid other slide-prone areas, not yet mapped.

"The alternative alignments propose a difficult choice between a short bypass with impacts to old-growth redwoods, and a much longer bypass with greater cost, a larger footprint, and its own ecological impacts. During the Project Study Report process, Caltrans will continue to work with the partners and community stakeholders to develop a solution to Last Chance Grade," the report says.

Barring an act of Congress or a natural disaster, a new route will not be settled on until 2025, and construction will not start until 2031 - meeting California Environmental Quality Act and National Environmental Policy Act requirements takes that long, Hodgson said.

Meanwhile, in the past year, Last Chance Grade has continued to slide, and at an accelerated rate. Geotechnical staff confirmed a 1.1-foot vertical drop and a 1.42-foot horizontal creep between January and April - the movement in those four months nearing the totals of the previous two years.

Reach Laura Jo Welter at .