By Greg Glass
By the first week of October Phase II cleanup activities of the Lower Yard were clearly headed toward completion. The major remaining task is the installation of a large number of new or replacement ground water monitoring wells. An extended ground water monitoring program will start this Fall, and will provide information on the status of site ground water contamination after the large-scale remediation efforts. I have visited the site to observe cleanup activities 12 times from early August through early October.
The cleanup of a segment of Willow Creek along the western margin of the Lower Yard was finished in late September. Sediment removal was done to a planned depth below original grade with no additional confirmational sampling. After sediment removal and re-establishment of the original elevations with clean backfill materials, erosion control mats were placed and both banks were re-vegetated using native plant species. Periods of higher rainfall during the sediment remediation program, while the coffer dams were in place, resulted in some ponding of water in the marsh upstream of the work area. On September 26th (a Friday) when the upstream coffer dam was removed water levels in the marsh were probably between 6 and 12 inches higher than below the dam. I observed the removal of this upstream dam, which was done in a controlled manner to minimize erosion and siltation as water levels equalized. A temporary silt plume still occurred but was contained by the fact that the downstream coffer dam was still in place. It was removed the following Monday, September 29th, after which Willow Creek was again free-flowing.
Soil removal at the few remaining excavation areas was also completed during September. The largest of these Phase II excavations was in the southeast Lower Yard (area B1), a location not used for normal bulk fuel plant (or asphalt plant) operations but apparently a location of some disposal activities. A number of crushed drums, as well as assorted concrete debris, were uncovered during the excavation of that area. A few seeps of product were also observed on hot days along the excavation sidewall, prompting additional soil removal. Sampling of the sidewalls and floor of the excavation at the end of excavation activities showed no contaminant levels above removal criteria.
Small additional excavations were also completed at three locations next to Willow Creek (areas B7, B8, and B9). Excavations at those three areas were suspended at the end of Phase I and the final work next to the creek was done in Phase II at the end of the period when sediment removals were occurring. Based on the results of “data gaps” soil sampling, one new excavation area was added to Phase II near the southeast end of Detention Basin 1. This was the location of the former asphalt plant warehouse. The additional excavation area was relatively small compared to other Lower Yard excavations. As with all of the previous soil excavation areas, confirmational sampling was done at these final Phase II excavation areas and showed no exceedances of soil removal criteria.
The Lower Yard Interim Actions clearly removed a very large fraction of the contamination that was present at the site as late as 2006, some 15 years after the end of bulk fuel plant operations. (Earlier cleanup actions in the Lower Yard, and the Upper Yard, had also removed a substantial mass of contaminants). Cleanup actions included the removal of free product, extensive excavation of contaminated soil, and pumping and treatment of a large quantity of contaminated ground water. While almost all of the residual contamination has been addressed, the Lower Yard is still not pristine. Soils below the removal criterion of almost 3,000 parts per million (ppm) total petroleum hydrocarbons (TPH) did not have to be removed, and confirmational sampling at the excavations has documented some residual soil TPH contamination up to that limit. A small area near the Washington Department of Transportation storm drain line in the middle of the Lower Yard has substantially higher levels of contamination. Those soils have not been removed so far because of the risks of damaging the storm drain line. There is also a possibility (probably slight) that some relatively small areas of significant contamination have not been identified despite the extensive site investigations.
The purpose of monitoring ground water for a period of two years after planned physical cleanup activities have been completed (as they now are) is to document whether the remaining levels of contamination at the site will cause ongoing ground water quality problems. That is, the ground water data will be used to determine whether or not the completed cleanup actions are sufficient. Ground water monitoring will also determine how quickly any remaining ground water contamination, still present because of historic rather than current site contamination, diminishes. The ground water monitoring program includes wells along the perimeter of the Lower Yard (compliance wells) and wells in the interior of the Lower Yard (natural attenuation wells). More than 40 wells will be sampled and evaluated over the two-year monitoring period. Existing wells will be used where they are available, but approximately 28 new wells will also be installed to prepare for the ground water monitoring program. New well installations are scheduled to start on October 8th and should be completed within about 10 days. Ground water monitoring should therefore start by early November.
With completion of Phase II except for well installations, the removal of all of the equipment onsite has started. For example, the automated vehicle wash station has been disassembled and removed, as well as all of the piping and pumps associated with the sediment remediation work and rerouting of Willow Creek flows. Demobilization should remove all of the equipment and materials stored onsite during cleanup efforts, preparing the site for transfer to the Department of Transportation.
A full report documenting all of the Lower Yard Interim Action work will be prepared and submitted to Ecology in a few months. We will be reviewing all of the ground water monitoring results as they are submitted and intend to provide updates here through the blog.
Feel free to call: ( HYPERLINK "mailto:gglassenviro@comcast.net" gglassenviro@comcast.net)
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