Construction Update 10/27/16

On October 28 Thompson Bros. Excavating (TBE) will begin the breaching of the summer levee located along the Tillamook and Trask rivers. Sediment control during breaching, and on all phases of the project, has been and continues to be of paramount importance.

For example, prior to the storms of October 13-17, a coffer dam was constructed at the east end of the project area where a gated spillway is under construction in the last opening of a newly constructed set back levee. The purpose of this emergency action was to confine storm surge within the project area and away from private lands adjoining Highway 101.

When the highest tides of the year overtopped the summer levees, about 6 small breaches and two larger ones resulted in storm waters entering the project. These breaches brought sediment into the interior project area. One of the benefits of the completed project is the collection of even more sediment in this area during flooding events. This area is subsided by 2-3 feet due to the existing levees that have for decades disconnected the interior project lands from the floodplain. Removal of these legacy levees will not only reconnect 521 acres to the flood plain, but will also reopen about 14 miles of ancient channels that will provide critical over wintering habit for juvenile coho salmon. Substantial flood reduction benefits over a 3,000 acre area will also result from the levee breaching.

Throughout the storm the project was continually monitored by the contractor and project managers until the waters subsided. The breaches were then repaired to allow completion of the final interior work prior to the final large scale breaching that will begin on October 28th. The final breaching will start at the furthest point away from the Hall Slough and work eastward along the Trask River, finalizing the breaching at the new levee.

TBE will be using two excavators along with two dozers to complete this work. With two, two-man crews working, TBE anticipates the levee breaching being completed in seven days. Work will begin at low tide and continue as the tide moves landward at the high tide current. Starting at low tide allows TBE to monitor any turbidity that may occur. A project monitor will also be present with turbidity monitoring equipment throughout the breaching. The project team expects some turbidity and sediment to occur during breaching. TBE’s strategy of working their way out of the project and stopping while the tides become higher in elevation allows turbidity to be accumulated back on to the project.

Along the Trask River there are a total of five interior tidal channels to be connected to the Trask River. TBE will be placing a floating silt curtain at the connection points. Placing the silt curtain will help confine turbidity that may occur in the Trask River at the time of connection. TBE will remove the curtains as they continue to remove the summer levee. TBE and the project monitor will be taking pictures throughout the breaching.

Construction Update 10/24/16

Despite a few challenges, project work for 2016 is drawing to a close. The recent storm, which included extreme high tides and storm surge, caused some overtopping of the remnant summer levees as well as a few breaches. In anticipation of the storm, a temporary coffer dam was constructed at the East end of the project area to close off the opening in the middle levee where the new gated spillway is under construction. This action by Thompson Bros. Excavating, Inc. (TBE) confined storm waters to the interior project area and off of adjoining private lands. SFC project managers and TBE actively monitored the site during the storm.

While one TBE crew is busy with final shaping of the south levee, other crews are grass seeding and installing coir matting and fabric over the sides and top of the north and middle levees as well as over the recently completed repairs to the Hall Slough Levee. The middle levee gated spillway is formed and rebar tied in place. The first concrete pour was completed on October 21. The final concrete pour is slated for October 26. The six floodgates will be hung on the spillway as soon as concrete tests demonstrate the desired strength; likely in a week following the final pour.

Excavation of contaminated soil at the former mill sites is also nearly complete. The discovery of 300 cubic yards of asbestos roofing caused some delays while specially-trained crews were brought in to wrap and dispose of the material at a licensed facility. Despite the excavation and hauling of additional solid waste mixed with soils contaminated with decades-old machine lubricants, TBE completed the placement of soils in the containment cell last weekend. There are still several weeks of installing the vent pipes, welding a geotextile membrane and then capping the cell with 18 inches of topsoil. Using funds provided by the City of Tillamook, TBE will also construct a gravel parking lot on top of the east side of the cell for public recreational access to the newly restored wetland and Hoquarten Slough. Hydro seeding of exposed topsoil will complete the cell’s construction.

Some of the summer levees along the Wilson River were recently removed just prior to the recent storm in a location that is not hydrologically connected to the remaining project area. As a result of recent storms and extreme tides, this breached area is already showing promising response to tidal exchanges, resulting in widening and deepening of the reconnected channels. Although the south end of the bay tends to be dominated by freshwater during this time of year, as expected the return of brackish water in the spring and summer will bring about a change in vegetative cover to more of a saltwater marsh over much of the project area.

Within the remainder of the 521-acre portion of the project that will soon become subject to daily tidal inundation, TBE crews are finishing the removal of old fence posts, utility poles, and other man-made remnants. Prior to the final breaching of the remaining summer levees along the Trask and Wilson rivers, crews have to complete a “punch list” that includes final interconnections of ancient sloughs, removal of a few legacy tide gates and final filling of the remaining drainage ditches. TBE expects to begin final breaching this week. This will coincide well with a series of tides that are expected to remain below 7 feet elevation at high tide. TBE will work three crews day and night breaching the levees down to the final design height of 8 feet Mean Sea Level. As levees are removed, crews will also reconnect existing and ancient channels to the river and bay at depths that result in a positive gradient for runoff. Work will not occur in the water but the equipment will operate only when tide levels are below the work area. TBE expects the breaching to take four to five days.

The removal of these levees is the project element that is expected to provide the most flood reduction. Work for 2016 is expected to be completed by mid-November. The remaining work scheduled for midsummer 2017 will be summarized in the next project update.

Construction Update 9/9/16

The Southern Flow Corridor Project (SFC) is intended to provide flood level reduction benefits by removing man-made impediments to flood flow and to permanently restore and protect tidal wetland habitats. This is being accomplished by extensive removal of existing levees and fill around the Trask and Wilson rivers and the smaller sloughs. This project will provide a substantial public benefit through the reduction of life safety risk from floods, reduce flood damage to property, improve freshwater and estuarine water quality, and enhance the quality of the habitat for native fish and wildlife species including the federally-listed Oregon Coast coho salmon.

The SFC project is removing approximately 234,000 cubic yards (cy) of fill including about 35,000 cy from an area along Hoquarten Slough that once housed several mills. The property was undeveloped until the 1920’s when the Tillamook Spruce Veneer Company opened a veneer mill on the east end of the property near Douglas Street and Front Avenue. The mill was built on pilings in the low-lying, marshy area. Logs were transported to the mill from Hoquarten Slough and into a narrow inlet on the north side of the mill. The mill included saws, dry kilns, a woodworking house, a boiler house, a machine shop, and an oil house. It is believed that the mill was powered by steam generated from wood waste from the mill.

In 1944, the mill was abandoned and a new mill (referred to as the west mill), operated by Aberdeen Plywood Company, was constructed west of the original mill. A log pond was created in the low-lying area west of the mill and the Hoquarten Slough inlet was no longer used for log delivery to the mill. The entire mill was also built on pilings and had a lathe room, a filing room (for saw and knife sharpening), a clipper room (for trimming veneer) and a power room. A second log pond was created west of the existing pond in the mid- to late-1950’s. The west mill reportedly operated on diesel-powered equipment.

The green veneer was shipped from the new mill to the company’s plywood plant in Tacoma, Washington for further processing. There is no evidence that plywood manufacturing was ever performed on the subject property.

The mill closed in the mid-1960’s and the log ponds were drained. Fill material, possibly from the areas around the former mill buildings, was placed on the southeast corner of the west log pond around the same time as the closure of the mill. The fill material was sampled during an environmental site assessment in 2014.

Some of the fill materials are contaminated by petroleum byproducts as identified in recent investigations by Anderson Geological. The physical composition of the fill material varies from mineral soils (sand, silt and clay) to wood waste (sawdust, wood chips, logs) and construction waste composed primarily of large pieces of concrete.

To fulfill the flood-control requirements for the Southern Flow Corridor (SFC) project, the ground surface across the entire 5 acre mill property is being excavated to a common elevation of approximately 8 feet above mean sea level. Soils that are planned for removal are referred to as “take” soils. The soils that will be left exposed after the excavation are referred to as the “leave” soils.

The leave surface will include areas of contamination that slightly exceed ecological risk concentrations. The leave surface will be covered with a veneer of topsoil with the expectation that periodic inundation of the area from high water levels in Hoquarten Slough will result in the deposition of additional sediment and the establishment of wetland vegetation, further stabilizing the leave surface. Areas where the leave surface is over-excavated due to grossly-contaminated soil or landfill debris will be backfilled with clean soil and covered with clean topsoil.

It is not the intent of this project to remove all soil and groundwater that exceeds cleanup levels. Only the contaminated material that must be removed to allow the completion of the SFC project, material that would result in higher exposure point concentrations than currently exist, and materials containing garbage and/or free product contaminants, will be removed. Material that would result in higher exposure point concentrations than currently exist will be placed onsite in a containment cell. It is estimated that approximately 900 cy of materials containing garbage and/or free product contaminants will require disposal at an approved solid waste disposal facility.

Oversight and monitoring for this phase of the project is being performed by Erik Anderson, R.G., a professional geologist registered in the state of Oregon, under a plan approved by the Oregon Department of Environmental Quality.

The estimated volume of in-place soil to be excavated is 35,800 cy. This includes:

-13,500 cy of clean soil/fill and 1,500 cy of waste concrete in which no contaminants have been detected or are present below ecological screening levels and Clean Fill Criteria. Metals are present at or below natural background concentrations. These materials are classified as Type 1 and are being used to construct a setback levee designed to keep the daily tide off the farmland adjoin the southern project area. That levee is presently about 60% completed.

-5,000 cy of soil/fill in which organic contaminants have been detected above aquatic ecological screening levels but below Clean Fill Criteria. Metals are present at or below natural background concentrations. These materials are classified as Type 2.

-5,700 cy of mineral soil and organic soils/wood waste in which organic contaminants have been detected above terrestrial ecological screening levels and Clean Fill Criteria. Metals are present above natural background concentrations. These materials are classified as Type 3.

-900 cy of oil-saturated soil and garbage, classified as Type 2 or Type 3, is being disposed offsite at a Subtitle D landfill.

It is estimated that approximately 10,700 cy of Types 2 and 3 contaminated soil and fill will be removed in this area and placed in an on-site containment cell that is currently being constructed along Front Street on city and county property west of Douglas Avenue. Once completed and capped, a gravel parking area will be constructed on top of the cell to facilitate public recreational access to Hoquarten Slough and the newly created wetland area.

The mill sites, location of contaminants, containment cell and progress of work at site through September 2, 2016 is shown on the enclosed attachment.

Construction Update 8/12/16

Despite summer rainfall, the project is on schedule. Work on the north setback levee is proceeding well with completion of this element expected by the end of August. This is one of three setback levees designed to keep daily tides off adjoining farm land that is outside the project area. The approximate 2 ½ miles of these levees are specially designed with a clay-type soil core. Once fully dried and compacted, the core will prevent water infiltration through the levee that might otherwise cause erosion and levee failure. The levee core will be capped with a granular material, also available on site, and graded to a 1/5 slope to minimize erosion during overtopping flood events. The three setback levees are in locations that enable efficient flood discharge over the remainder of the overland flow corridor.

The City of Tillamook, one of the many project partners, is presently contemplating an expansion of a planned parking area on the so-called “containment cell” that is being constructed along the north side of Front Street between Douglas Avenue and an old mill pond channel located west of Cedar Avenue. The proposed revision would accommodate parking for 30 vehicles instead of the 14 contemplated in the initial design. The lot will be available for recreational access to Hoquarten Slough and the surrounding area.  A decision by the City on the possible expansion is dependent on a revised bid proposal from the project contractor, Thompson Brothers Excavating, Inc.

In any event, parking atop the containment cell is a creative use for the earthen berm that will be used to encapsulate the slightly contaminated soils that remain on the project site from the two veneer mills that operated from about 1920-1965. The contaminants in the soil consist of remnant motor oil and machine lubricants used at the mills. Although the contamination levels do not pose a risk to humans, the worst of the soils will be transported to a licensed treatment facility in Hillsboro.  The lesser contaminants will be encased within the cell and monitored long term. Currently those contaminants are uncontained at the site and pose a risk to the environment.

Further questions may be directed to Project Manager Paul Levesque at 503 842-1809.

Construction Update 7/15/16

With the onset of drier weather the pace of construction has increased. Thompson Brothers Excavating, the prime contractor from Vancouver, Washington, will bring on additional crews and machinery early next week. The Oregon Department of Environmental Quality (DEQ) has given final approval on the cleanup plan for the two former mill sites just north of Front Street in Tillamook. Clearing and grubbing of the mill sites is just about finished but continues elsewhere on the 640 acre project site. The new crew will begin excavation and disposal of contaminated soils as well as removal of the surrounding clean soils that will help with the discharge flood waters.

Approximately 234,000 cubic yards of material will be removed or reused as part of this project. The clean soils will be reused in the construction of setback levees, filling of old drainage ditches or spread out on adjoining farmland where landowners are willing to receive it. The purpose for filling the old ditches is to allow natural drainage channels to reform in a more serpentine manner, thereby producing better salmon habitat. Once the levees surrounding the project area are removed, ancient tidal channels will be reconnected to the rivers and the new tidal channels will become established. This project is expected to create approximately 14 miles of new or reconnected tidal channels that will then serve as critical over-wintering habitat for juvenile coho and other fish. The Oregon Department of Fish and Wildlife has just completed the removal of any remaining salmon in the old ditches so that filling of those ditches may now begin.

Construction of the 2 ½ miles of new setback levees has also started. Core material soils for these levees are being place in 1 foot lifts so they can dry out prior to compacting and covering. These levees are located to protect adjoining farmland from the daily tides that will soon regularly inundate much of the new flood corridor.

A substantial amount of concrete is also being demolished and removed from the old mills and former buildings on the site. Most of this concrete will be placed outside the project area in nearby cow pads that have received permits as elevated refuge islands for cows to escape rising waters during floods.

Despite all the activity since February within the project area, an eagle’s nest adjoining the site is once again home to two young eaglets who don’t seem too eager to leave home as young adults.  Regular monitoring of the nest is continuing to occur. Once the eaglets fledge, the work hour restrictions within the buffer area surrounding the nest will be lifted and work can proceed throughout daylight hours as with the remainder of the project area. The eagle’s nest will continue to be protected for future use by the longtime resident nesting parents.

As one of the largest projects of this type ever constructed in the northwest, regular visits are made by state and federal agency staff to monitor progress. Representatives from DEQ were on site last week and officials from the NOAA Fisheries will tour the project next week. For safety reasons, the public is not permitted within the project area until construction is completed.

Construction Update – 6/13/2016

Construction has begun. On April 27, 2016 a contract was signed with the low bidder Thompson Brothers Excavating, Inc. (TBE) out of Vancouver, Washington in the amount of $5,500,930. TBE mobilized to the site the first week of May. The contractor now has a number of crews working throughout the 640 acre project area.

The construction of the Southern Flow Corridor (SFC) will create a “natural overland floodway” that is currently blocked by numerous levees and dikes. The project will remove these blockages and set back remaining levees in order to provide an unobstructed flow corridor. The net result is that flood levels are reduced over a wide area in the lower Wilson floodplain and even to some degree the lower Trask and Tillamook River systems. Although the SFC was developed as a flood project, it also restores tidal wetland habitats and ecological function as a direct consequence of removing levees and reconnecting 14 miles of ancient channels to the river systems. TBE has completed similar projects along the Columbia River and elsewhere, including work for ODOT.

Demolition has almost been completed at the former farm buildings west of the Hall Slough Bridge on Goodspeed Road. The Tillamook Fire Department conducted a practice burn on the house slated for removal at the end of Goodspeed Rd. TBE crews have started clearing and removing brush and trees that were felled within the project area back in February. This wood debris will be chipped to build temporary construction roads. TBE has also started stripping out top soils along 1.75 miles where set back levees will be constructed.

Approval from the Oregon Department of Environmental Quality is expected the week of June 13-17 on final plans for cleanup of the two former mill sites north of Front St. in the City of Tillamook. Excavation of this area will begin following that approval. For public safety, access onto the entire project site is limited for the duration of the project which is expected to be substantially completed by fall. Regrading of the new setback levees will be conducted, as needed, in summer 2017.

Further questions may be directed to Project Manager Paul Levesque at 503 842-1809.

Pre-Construction Work Underway

In early February the SFC Project began pre‐construction activities with tree felling in the Hoquarton and Hall Slough areas west of Highway 101. The SFC project will remove about 8 miles of old levees and dredged material that currently block flood flows to Tillamook Bay. Trees that are growing on top of these levees are being felled before bird nesting begins. The felled trees are being left on‐site until the construction contractor starts major construction work later this spring. Construction work involves the removal of levees and the construction of tidal dikes in order to provide better conveyance of recurrent floodwaters within the Highway 101 Business Corridor. Construction work will last throughout summer 2016; and there will be some followup work in summer 2017.

In addition to mitigating recurrent floodwaters, the SFC Project also provides for wetland
restoration and fish habitat improvement. The SFC Project is the result of many years of public agency and private citizen collaboration.

If you have any questions related to the SFC Project, please contact Paul Levesque, Tillamook County SFC Co‐Project Manager at 503‐842‐1809.