When the Job Site Has No Set Perimeters

Construction projects that fall into the category of being “linear” include those that don’t have or adhere to a set grid or perimeter. Utility projects such as pipeline renovation or installation are commonly linear. Power and cable utility towers that will be on an irregular piece of ground, as well as rail and highway projects, are all classified as linear.

Construction General Permit: Background and 2017 Update
In 2017, EPA’s new Construction General Permit (CGP) became effective in all areas where EPA is the permitting authority for the National Pollutant Discharge Elimination System (NPDES), replacing the 2012 CGP.

Rock Creek Sewer Collection Improvements Project
Many linear construction projects are department of transportation jobs or infrastructure or utility projects. This category can also include installation or renovation of sewer lines as part of a larger project.

The city of Twin Falls, ID, has a long history with water. In general, bringing water to the south-central area of Idaho dates back to the Carey Act of 1894. A long-time resident and historian of the area, Paul Smith, writes, “Located in south-central Idaho, Twin Falls is the regional center for a rich agricultural area whose development can be solely attributed to the vast reclamation network constructed during the first two decades of the century. The various reclamation projects were known as ‘tracts.’ The one specifically responsible for the genesis of Twin Falls [is] the Twin Falls South Side Irrigation Tract.”

In spite of the vision of pioneers and investors, large-scale reclamation of the high-desert, arid valley slipped through their fingers until the early 1900s. One problem was getting across the Snake River Canyon, referred to as the “Great Snake.” The 500-foot-deep, quarter-mile-wide canyon was daunting to bridge until the railroad invested along with one of the pre-reclamation pioneers who knew the area well. Together, the railroad and Ira Perrine, a pioneer and visionary of his time, brought water to more than 200,000 acres south of the Snake River by building the Milner Dam.

One of the Snake River tributaries runs through the 300-foot-deep rocky and craggy-edged Rock Creek Canyon. After the surrounding land was irrigated, it made good farmland, but the basalt rock layer beneath the topsoil didn’t allow water to drain easily from the fields. The drainage problem was so bad that farmers would often stand in rubber boots knee-deep in the muddy fields.

“They dug tile drainages and drilled wells,” says Twin Falls Canal Company general manager Brian Olmstead. “But what they found was that by digging tunnels 30 to 40 feet below the surface, they could drain some of that water from the top and bottom.”

The idea seemed pretty simple: Cut tunnels, and then drill vertically from the surface to create drains that would empty directly into Rock Creek Canyon. In all, 49 tunnels were created by packing holes in the canyon wall with dynamite. The unfortunate side of this was that many tunnelers lost their lives in premature blasts.

The tunnels were finished in 1951. The temperatures deep in the 6-foot by 4-foot rock tunnels remain a near-constant 54°. Water covers approximately 18 inches of the tunnel floors, which allows today for vegetation to grow in and across the tops of the tunnels. Although not being used, Olmstead says, they should be preserved as part of the area’s history. Inconspicuous as they are from the outside, the tunnels are still there and are in direct path of rapid expansion on the south side of the Rock Creek Canyon.

In addition to farming on the drained land, other industries grew up along the Rock Creek Canyon throughout the 1950s and 1960s. Before the Clean Water Act, the city of Twin Falls ran sewer pipes that dumped sewage directly into Rock Creek. The south side of Twin Falls grew up to be the industrial side with activities like those of the “hide and tallow” company that disposed of byproducts of dead horses and cows. The local hospital, a sugar processing plant, a potato processing plant, and others all dumped waste into Rock Creek. The picturesque river that was once so beloved by pioneers was forgotten and neglected. Work is still going on to clean up the river bottom and canyon sides where waste once poured into the small canyon and then to the Snake River.

The first Twin Falls wastewater treatment plant was constructed in the 1960s. Sewer lines were gradually installed to carry wastewater from the city’s residential, commercial, and industrial districts to the treatment plant. Currently, the system has one anaerobic pretreatment facility and approximately 157 miles of line ranging in size from 6 inches to 42 inches in diameter. The system includes five pumping stations, one air injection station, two measuring stations, and approximately 2,750 manholes. The Wastewater Collection Department’s responsibilities include inspections and repairs of the lines, looking for and repairing root damage, and performing routine cleaning. Additionally, the department replaces sewer pipelines as necessary. In Twin Falls, the typical 4-inch sewer service line that runs from a homeowner’s property and connects to the city sewer main falls under the responsibility of the individual homeowner.

Citizens of Twin Falls approved a $38 million bond election to fund a major expansion of the wastewater treatment plant in March 2013. This included work on service lines as needed. In April 2014, construction began on the largest expansion to the wastewater treatment plant since 1965. A new clarifier and aeration tanks have almost doubled capacity of the plant from 9.6 million gallons per day to 16 million gallons per day.

Lee Glaesemann, staff engineer and project manager for the city of Twin Falls, says the city’s sewer model and Wastewater Collection System Master Plan was updated in 2015 to make better use of the approved bond funds.

“As part of the plan, a list of capital improvement projects was determined and prioritized,” he says. “The Rock Creek Trunkline project was given a high priority due to its age, size, service area, and its difficulty of construction. The section of sewer line that this project upgrades was originally built in the 1960s when the city’s sewer discharge was diverted from Rock Creek to the new treatment plant that is now located in the Snake River Canyon.”

Glaesemann explains that when a political subdivision, such as the city of Twin Falls, contemplates expenditures for public works construction in excess of $100,000, Idaho statute 67-2805(3) applies. “This statute requires a competitive sealed bid process where the purchase of construction services is made from a qualified public works contractor submitting the lowest bid complying with the bidding procedures.”

Extreme Excavation of Shoshone, ID, won the bid at $2,496,853. The bid was higher than the engineer’s estimate because of difficulties and potential risks associated with this unique project. Glaesemann says the project runs a mile long in total, with a half mile upward and a half mile downward of the bridge that crosses Rock Creek Canyon.

“The overall budget is $3 million, roughly. That will include sewer pipe replacement, repairs, restoring the site, and hydroseeding the area when complete. The sewer pipe was actually put in to catch the drains and move it to the lift station down in the canyon. We’re just making the pipe bigger,” he says.

J-U-B Engineers of Twin Falls was retained by the city to act as the city’s representative. Although this is a joint construction project between the city of Twin Falls and Extreme Excavation, each has its own Notice of Intent in place and will later file a separate Notice of Termination when the job is complete.

J-U-B Engineers is a full-service civil engineering firm that began in 1954 in Nampa, ID. The company opened its first Twin Falls office in the 1970s, says Mark Holzven, engineer on the project, and currently has 16 offices throughout the western US.

Extreme Excavation, the contractor, will be responsible for the construction on the city’s 2017 Rock Creek sewer collection improvements. The project involves more than 5,000 linear feet of 8- to 36-inch gravity sewer main, 449 linear feet of 8-inch cured-in-place pipe, bypass pumping, clearing and grubbing, abandonment of existing sewer collection system components, 2,353 linear feet of paved recreational trail, 1,937 linear feet of gravel roadway, repair and replacement of storm drain culverts, sewer manholes, manhole coating and linings, and an open-trench crossing of Rock Creek.

Holzven says most of the challenges have involved the rock excavation and the fact that access to the site is so limited. “There are only three access points for getting material in and out. It’s a remote site. Crossing the Rock Creek—running the pipeline under it—is also a challenge.”

“Additional challenges are that it’s such a close area between the creek and the canyon wall on the east side,” explains Dave Everson, project manager and department manager with Syman LLC. Syman designed and wrote the SWPPP on the Rock Creek Sewer Collection Improvement project. “It’s going to be a real challenge to fit it [construction equipment] all in down there.”

Syman is an environmental compliance firm specializing in design, supply, and installation of practices that prevent the pollution of Idaho’s water. Services offered by the Nampa firm include SWPPP and erosion and sediment control plans; temporary and permanent BMPs; temporary silt fencing; inlet protection and check dams; and installation of wattles, including reusable Gator Guard or biodegradable wattles. The company also provides dewatering and hydroseeding services.

“Ninety percent of the SWPPP BMPs on the site will be temporary,” says Everson. “The revegetation will be permanent. There will be some silt fence between the trench and the creek. Silt fence will also be used where they’re staging at the north end.”

The SWPPP’s description of site conditions notes, “A trail with surrounding vegetation covers the old sewer line. The trail runs along the creek.” Above the creek are railroad tracks that are currently in service and a four-lane bridge. Although the project is only one mile in length, the total property size is 16 acres, with the area of construction disturbances being the same. Mobilization and groundbreaking took place on July 5, 2017, and will continue through November.

All inlet protection and other BMPs are supplied by Syman and were in place before ground-disturbing activities began. Temporary BMPs will remain in place until final stabilization of the project. Mass excavations completed in the first week allowed for the utility installations. When utilities are installed, trenches will be backfilled and the ground around the area compacted as per the plan specifications.

Once compaction is complete, grading and base preparation and paving will begin. During this stage of construction, it is imperative for all pollution prevention and other good housekeeping measures to be observed. Dewatering activities will be required for the open-trench crossing of Rock Creek.

“A creek bypass method will be used to create a work area within the stream channel. A trench-specific dewatering method will be utilized to dewater the trench excavation within the work area, if needed. No other dewatering is anticipated,” says Everson.

Finally, the site will be hydroseeded and landscaped. The trail will be paved and all construction equipment will be removed from the site, as well as all temporary stormwater controls. Final stabilization, to be completed by November 2017, will be achieved once all disturbed areas are either fully stabilized with hard surfaces such as paving, or have a vegetative cover that is at least 70% of the density of the native background vegetative cover that existed prior to construction.

Idaho Interstate I-84 Project
In the arid, high-desert town of Eden, ID, where the population is only 405, it comes as no surprise that the entire area is rural and agricultural land. The 0.32-square-mile town is located in Jerome County on the north side of the Snake River in southeast Idaho. Rural roads in the Eden area are left over from the early days when the Hudson Bay Fur Company ran its trapping business. Few travelers wanted to traverse the sharp canyon walls at that point with their wagons. The Idaho State Historical Society records describe methods using chains attached to nearby trees to lower wagons over the steep areas that would have otherwise been impassable. Along documented emigrant roads in Idaho, and at a few preserved trading posts on the Oregon Trail, some of the trees still carry chain and rope marks of the past.

After 1860, gold brought miners to southern Idaho in large numbers, and shortly after 1900, cars and trains brought families. Just over a decade later, a new highway system, sometimes utilizing the already existing routes, replaced wagon roads. Irrigation quickly followed in 1906, allowing for greater expansion to the area. Farms were often homesteaded by World War II veterans.

Of course, today the highway system looks nothing like what the pioneers saw when they came to Idaho. Where once they could walk faster than their oxen could pull the wagon, now cars speed along at Idaho’s 80-mile-an-hour speed limit, and in phenomenally greater numbers. The average number of vehicles per day on the I-84 – Eden ramp is 8,970, and the projected average for 2040 is 11,700, according to the Idaho Transportation Department (ITD).

ITD is undertaking a total restoration of the eastbound lanes of I-84 (mile posts 180 to 186) to provide a smoother, safer driving surface, according to ITD public information specialist Nathan Jerke.

“The objective of this project is to strengthen the roadway for heavier loads and to restore the structural integrity,” explains Jerke. “In addition, the horizontal and vertical curve deficiencies associated with the eastbound ramps on I-84 will be updated to meet highway design standard speeds. The purpose is also to prevent pavement distress, cracking, and the formation of potholes on this interstate section, in accordance with federal and state standards.”

He adds, “The existing alignment on I-84 for grading and drainage was constructed in 1966. This section of roadway was rehabilitated in 2000 with a cement recycled asphalt base, and in 2010 this same section of roadway had a pavement preservation treatment. The past rate of deterioration and distress in the pavement requires corrective action [to prevent] failure from top-down cracking and total cracking.”

Douglas Yearsley, project engineer with ITD District 4, says the minimum bedrock depth at the site is zero feet, but varies due to the lava flows that underlie the area.

“The total project size is 107 acres, not including any contractor-provided staging or waste sites,” he says. “The contract consists of two project areas that are approximately 3 miles each for a total of 6 miles of roadway to be constructed.”

The total budget on this project is more than $10 million, and Yearsley says ITD is watching over it very carefully and using as many naturally occurring BMPs as possible. That presents its own challenge, he adds. “Our most employed tactic is to maintain existing vegetation as much as possible, which limits the amount and type of work that we can perform.”

These linear construction projects are short-timeframe, limited-work-window projects, which means that there is not much time to get from start to finish, Yearsley says. “The contractor must move areas from open and disturbed to stabilized in a shorter timeframe and must plan ahead to make sure deadlines and seasonal weather limitations are met.”

The plan for the I-84 site is a full-width restoration on the eastbound side because of crossovers needed for traffic control, says Jerke. The asphalt will be removed, milled, and recycled at an asphalt mixing area conveniently located on a rural section of land close by.

“To control traffic, crossovers will be constructed in the medians on either side of the project at about milepost 180 and 186,” he says. “One travel lane will be open at all times.”

Late July and August in this southern Idaho desert are known to have temperatures in the 100s, so keeping traffic moving is essential. All deteriorated base and subbase will be removed and excavated down to natural ground level. Fortunately, in this area that is a short distance, with the total overlay not more than 3 feet.

The new roadway will consist of 0.5 foot of new surface over a minimum of 1 foot of aggregate over approximately 1.5 feet of rock cap. The roadway elevation under structures will be excavated and repaved to meet Idaho highway design standards.

The shoulders and guardrails will be adjusted to the new elevations. In sections where road elevations will be adjusted under existing structures, Jerke adds, guardrails will be replaced, and in areas with a ramp design change, the guardrails will be either replaced or new ones added.

“Horizontal and vertical ramp curves will be lengthened and heightened to meet highway design standards. Metal cattle guards will be installed on entrance and exit ramps,” he says. “Culverts and irrigation pipes within the project area will be replaced as needed. To eliminate roadside hazards and keep shoulder contour consistent, culvert and pipes will be extended to the ITD right of way. Temporary easements will be obtained as needed to tie the new culverts and pipes to the existing infrastructure. Utilities will also be moved to the edge of the right of way if needed.”

This area is well suited to maintaining natural vegetation. Using IDT hydrographs and historical data to estimate runoff, Yearsley plans on using berms, inlet protection, and wattles primarily for BMPs.

“Inlet protection is being used to protect the inlets where our stormwater will enter the canal system through the existing drop inlets. The wattles are used in areas where open water exists and will serve to capture sediment along with the existing vegetation to keep sediment out of the waterways,” says Yearsley.

The 8-inch Filtrexx SiltSoxx are used in some areas. For inlet protection, Yearsley says, Ultra-Drain Guard by UltraTech International is being used. The inserts, which he says are commonly known onsite as “witch hats” because of their black cone shape, are placed directly inside the drain under the grate.