Go to ...
RSS Feed

September 18, 2019

Treasure Dam Demolished Using Jackhammer on Suspended Sling


Mitigation work designed to alleviate the potential for high water flooding with debris later this month continues at a fast pace on Henson Creek.
As reported last week, heavy equipment — massive excavators and a log skidder equipped with a gripper — are being manned by personnel from Timber Market Forestry. Also simultaneously at work on Henson Creek is a crew demolishing the Hidden Treasure Dam utilizing a robatic jackhammer suspended from a crane.
Public access up Henson Creek remains closed at a locked gate located a mile up the canyon from Lake City. The public access closure is for safety reasons and allows contractors such as Timber Market Forestry and the Moltz dam demolition crew requisite
room to work.
Yet another contractor, SEMA Construction, began work this week hauling debris materials pulled from the creek. The goal is to relocate the collected debris and not allow it to re-enter the water course in the event of higher water later this month.
Excavators and logging skidder operated by Timber Market Forestry arrived in town two weeks ago and first went to work at the Klondike Slide excavating snow and digging out tree debris brought down by the avalanche. Work conditions at the Klondike are cramped due to the geography of a narrow, snow-filled canyon through which both Henson Creek and County Road 20 pass in extremely narrow proximity.
As a result of the snowslide across Henson Creek, water at the Klondike was for a time flowing across the road surface. Thanks to the excavators’ work, however, water is now back in the natural channel, although it remains close to the road. Road condition at that point are described as “pretty beat up and muddy.”
A challenge in removing debris from the snow at the Klondike Snowslide is where to place the tree debris as it is plucked from the snow. Up to this point the tree detritus has been stacked in close proximity to the slide along the county road or in periodic wide spots. The local emergency response team is now formulating a debris management plan which will address long-term storage of the debris at specific locations.
As of Tuesday this week, Timber Market Forestry has worked its way through the Klondike Snowslide and is now at work clearing snow and removing tree debris just up the road at the Big Casino Snowslide which also partially covered the county road.
UCG Operations Chief Justin Whitesell reported at Tuesday evening’s public briefing that snow and debris at Lee Smelter Gulch has also been cleared at the entrance to Capitol City, as well as the upper end of the Modoc Snowslide just above Ute-Ulay Mine. Whitesell acknowledged that extreme terrain prevents access to some snowslide debris.
Apart from excavators and logging equipment cutting through snowslides on Henson Creek, the most mesmerizing work now taking place in terms of flood mitigation work is the gradual, incremental removal of the 122-year- old Hidden Treasure Dam which is located on mining claims owned by George and Beth Hurd, and just down the canyon from the Hurd’s popular Hard Tack Mine.
Hurd says he agonized with the decision to demolish the dam which, although located on private property, is a popular historic attraction along the Alpine Loop Scenic Byway. “If removal of the dam saves even a single life,” says Hurd, “it’s well worth it.”
Hurd met with a succession of state, local and federal agencies, including the U.S. Army Corps of Engineers, which arrived on the scene to evaluate the flood risk of retaining the 35’-wide, 85’-tall cement dam in its present configuration. Mirroring sentiments first expressed during the flood of 1921 when a crack appeared in the dam, concerns were raised that water-borne debris might block a breach hole at the base of the dam and impound water which posed a threat to Lake City if suddenly released.
It was directly because of the Hidden Treasure Dam and its upstream counterpart — a similar, although more deteriorated concrete dam at the Ute-Ulay Mine — that monitoring equipment was installed on a cable stretched above Henson Creek adjacent to the mouth of Alpine Gulch. The $46,000 monitoring equipment includes a satellite transmitter sending data every 15 minutes throughout the day and night measuring the height of the water surface and water flow. A dramatic fluctuation in the depth or flow of the water might be indicative of an upstream blockage.
Moltz Construction based out of Salida, Colorado, is the contractor selected for removal of the Hidden Treasure Dam, with subcontractor Terry Crane Service, also from Salida, providing the requisite 275-ton, 230’ boom which is being used in the process.
Total on-site crew numbers on the demolition are three men associated with Terry Crane Service and five from Moltz, including project superintendent Chad Carter who hails from Wetmore, near Westcliff, Colorado. Carter and four other men who are here from Moltz are in addition to a behind-the-scenes crew of metal fabricators at the Moltz shop in Salida.
Asked for a chronology on his firm’s fast-paced association with the Hidden Treasure Dam, Supervisor Carter says that after receiving word on the impending demolition, he and fellow team members “plotted and planned” their options. On day five of the project, last Tuesday, May 28, they began crafting a custom metal platform which was designed to straddle the top of the dam while suspended on a sling held in place by the boom of the crane. Mounted onto the platform is a remote control, industrial grade Brokk 110 Demo jack- hammer, powered by an electric generator. As envisioned, the crane, with 170’ boom extension, gently lowers the platform and rock drill into place as the dam cement is pulverized starting at the top and working downward.
Continuing his chronology, Carter says he and his crew arrived on the scene last Wednesday, May 29, met with George Hurd and arranged for gravel which was used to build an access ramp allowing the crane to be positioned just above the dam. Preparation work continued last Thursday with wiring for power, work commencing last Friday, May 31, as an excavator was brought in to gently maneuver close to the dam and knock down a 10’ section of concrete at the dam’s top.
With the crane’s arrival on Friday, the rock drill was loaded onto the custom metal basket and suspended on the sling from the crane boom as the rock drill began to pulverize concrete at the dam’s upper level.
Questioned on Friday afternoon with the rock drill in operation, Superintendent Carter reported top width of the dam was 4’ thick, gradually expanding downward. Target date for the dam’s total removal was next Monday, June 10, in advance of expected higher water. At Tuesday’s public meeting, it was stated that Moltz Construction has been given a 10-day extension for completion of the work.
Removal of the dam was aided by discovery early this week that it is in fact veneered in concrete front and back, and that the interior of the structure consists of sand and rock.
Moltz Construction specializes in repairs and construction of water and wastewater treatment plants in a multistate region including Colorado, Nebraska, and Wyoming. Most recently, the firm’s demolition work included removal of a 150’-tall water tower located at Sanchez Reservoir near San Luis, Colorado. The firm has worked at Homestake Reservoir on Freemont Pass in Lake County, and also made repairs to a large water impoundment dam on Adobe Creek in Las Animas County.

More Stories From 2018