By Michael Raffety 8-29-14
Since Aug. 1 contractor Excavating Engineers Inc. out of San Diego County has been working on the Camp 2 Bridge reconstruction project for the El Dorado Irrigation District.
The first order of business was deconstructing the rickety Erector Set-like bridge and its wooden bridge deck. The remains are stacked in the marshaling yard a short walk before the bridge abutment. Other pieces are on the east abutment where they will serve as a protection for the stacked rock abutment in case a rock falls on it.
To lift out the old superstructure and its timber deck, the contractor brought in a crane. To make enough space for the small construction crane, some of the rock face next to the west abutment had to be “shaved back.” To knock out enough space for the crane, the rock was drilled in about half a dozen places. The holes were then filled with grout. After the grout dried, it expanded and cracked off the rock face, creating room for the crane.
The crewman who lives in the Camp 2 House now walks across the South Fork on a bridge behind the St. Pauli Inn and hikes up a path to get to the house, since the bridge is out for several months and Camp 2 can’t be accessed by vehicle until a new bridge is completed.
The bridge and its road approaches were constructed by Western States Electric on the bed of an original canal and flume route that was replaced by the Plum Creek Syphon. A siphon is shaped like the curved pipe under your kitchen sink. Only in this case it is 5 to 6 feet in diameter and moves water from a canal down a canyon and up another hill to the another canal — 1,444 feet long. The narrow diameter is near the bottom of the siphon to increase velocity and pressure to avoid accumulating detritus at the bottom of the siphon.
The crewman at the Camp 2 House is in charge of keeping the trash rack clean to ensure that the siphon doesn’t get plugged up. The siphon has been buried in the ground since the Western States Electric Co. acquired the mining water system built in 1876. Western States bought it in 1916, reached agreement to provide water to Placerville in 1919 and began increasing canal capacity. The project received its federal power license in 1922 and went operational in 1924. Four years later, it sold it to PG&E. EID acquired in 1999.
The Plum Creek siphon and the Alder Creek Siphon were two ways to reduce the total number of miles of canal and flume that needed to be enlarged to bring enough water to run the hydroelectric project. Alder Creek Siphon is 1,835 feet long.
Beside cleaning bits of dead fall and assorted material that accumulates in the trash rack, the Camp 2 crewman also must prevent ice buildup going down the siphon. He tends just under a mile of flume and canal and two spillways as far back as the Mill Creek to Bull Creek tunnel. In the winter sometimes snow conditions mean food supplies have to be brought in on a snow cat.
Excavating Engineers was the lowest of three bidders at $1.488 million. The contract was approved June 9 on a 3-2 vote, with Directors Greg Prada and Alan Day voting no.
Engineer Jake Eymann had been working on this project for eight years. It took the last three years to get a permit from the Forest Service for the project, with two years to complete the collection process, so EID could pay the Forest Service to review the project and issue a permit. Also, the project needed a permit from the Army Corps of Engineers because it would be dropping rocks and boulders into Plum Creek. Additonal required permits were the state Department of Fish & Wildlife and the Regional Water Quality Control Board.
The bridge site is daunting. The rock face is at a 45 degree angle, making a 90 percent grade.
“Everything’s hard about this job,” Eymann said. All work is done by men tied off with harnesses and cables.
Near the east abutment two men were suspended from cables drilling into a huge boulder. They looked like film of drillers who carved Mt. Rushmore. Viewed from the west abutment, the rock they were drilling on looked like the body of a moa statue from Easter Island. Closest to the west abutment is a large nose that will get broken off to make room for the new road bed.
Orange circles mark where the surveyor and the suspended subcontractors from Access Limited — the rock jumpers and drillers — determined that new concrete retaining walls will be anchored after a shelf is chipped out of the rock face.
Once the boulders that are considered hazardous are removed from above the project site and any other loose rock and trees are removed, then work will begin on building the bridge base concrete forms.
Those forms will be a series of boxes with anchored steel. The boxes will be backfilled with gravel and the actual bridge steel superstructure will be cantilevered out from the concrete box, Eymann said.
The challenge will be to complete the concrete work before it gets too cold. While Wednesday morning the overnight low at the Mountain Democrat weather station on Ray Lawyer Drive was 63 F, at the bridge site it was 47 F.
At the same time while work was proceeding to prepare the large boulder formation above the bridge for dropping, drilling was under way on the rock face below the west bridge abutment. Drillers had found a 1-foot void 20 feet into the rock below the abutment and that would have to be anchored into bedrock with very long anchor bolts. A stack of about 14 long bolts were lying at the construction site waiting to be installed in the mountain. At lenghts from 23 to 28 feet, they each had screw ends that would allow another bolt to be added to increase their length.
Before the bid was let, EID hired a group to do a LiDAR survey of the rocks. That stands for Light Detection And Ranging. LiDAR when used from a helicopter can determine the terrain beneath a tree canopy. In this case it was ground-based equipment that mapped “the boulder units,” enabling Eymann do a simulation of that rock removal and estimate the yardage of the rocks to be removed.
Once the bridge is complete, that will allow access by vehicle to bring in lumber to replace a rotting Flume 30, perform maintenance on the Camp 2 House and keep the land clear along the siphon route so trees don’t grow along it and destroy it with roots. Two other projects required by the project’s license from the Federal Energy Regulatory Agency include removing an old warming shed and a boat house. The bridge will save $13,000 of helicoper expense everytime a propane tank must be replaced with a full one.
Total funding for the project is $1.969 million (less a $35,000 balance), which includes the $14.488 million construction contract, $248,800 for contingency and possible additional rock scaling, $218,700 in capitalized labor that includes an EID inspector on the job every day and $48,000 for geotechnical engineering.