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.