By Greg Glass
The first of two reports documenting all of the 2007-2008 Interim Action cleanup activities has been submitted to Ecology by Chevron’s consultants, ARCADIS (Phase I Remedial Investigation As-Built Report, UNOCAL Edmonds Bulk Fuel Terminal Lower Yard, January 8, 2009). That first report provides information on the major soil excavation, product removal, and ground water treatment activities through the Spring of 2008. ECAC received a copy of the report and will be submitting review comments to Ecology.
A second report (the Phase II As-Built Report) will be submitted within the next few months to document the results of additional site investigations (data gaps sampling), small additional soil excavation activities, and sediment remediation in Willow Creek that occurred later in 2008.
Ecology, the Washington State Department of Transportation, and Chevron have also been discussing the remaining soil contamination adjacent to the WASHDOT storm drain line at the site. A separate report on alternatives to address that remaining contamination will also be prepared and submitted to Ecology by Chevron within the next few months.
Another major flooding event hit western Washington early in January. Areas near Seattle and Edmonds were spared the worst effects this time by virtue of being largely in the rain shadow of the Olympic Mountains; areas to the north and south were hit much harder. I visited the site just after the peak rainfall to observe conditions; water levels in the marsh, in Detention Basin 1, and in Willow Creek were all pretty high, but there was no significant flooding of the Lower Yard.
The planned two-year ground water monitoring program has started. Results from the first round of sampling in late October 2008 are available. Additional rounds of sampling will occur every two months. A map of monitoring well locations and designation numbers has been added to the blog (see below). A total of 40 wells are being sampled each round, with observations but no sampling in 10 additional wells. There are two systems of monitoring wells being sampled: a “perimeter” set of wells for compliance with cleanup levels, and an “interior” set of wells for natural attenuation of any remaining ground water contamination (see the text accompanying the well location map for details). Refer to the map to pinpoint the locations of monitoring wells discussed in this and subsequent postings on the ground water monitoring results.
While the results of each monitoring round are being submitted to Ecology as they are validated, the first data evaluation report will not be prepared until after the first year of monitoring (6 rounds of sampling) is completed. Only significant, and unexpected, observations – for example, the reoccurrence of a significant amount of product in wells - are likely to lead to any earlier decisions for actions beyond the planned ground water monitoring program.
After the soil and sediment excavations were finished, 25 new monitoring wells (numbered 500 through 524) were installed at the site to prepare for the ground water monitoring program. A few replacement wells were also installed where existing wells retained as part of the long-term monitoring program had to be removed during excavations. Those wells were all properly developed before any samples for chemistry analyses were collected. Even so, it has been my experience that the initial round or two of sampling at newly installed wells sometimes produce results not typical of longer duration monitoring, which may reflect a degree of “new well effects”. (Call this a personal bias). Thus, I would suggest caution when reviewing the initial results. Cumulative results over the first 4 to 6 rounds are likely to be more representative.
Results from round 1 sampling from October 2008 were reported to Ecology by ARCADIS in mid-December 2008. No product (LNAPL) was observed in any of the wells. The levels of Total Petroleum Hydrocarbons (TPH) at many of the wells were below detection limits, and overall ground water conditions throughout much of the soil excavation/product removal areas appear much improved. Among the interior wells, the highest remaining concentrations approached 1,500 ug/L TPH, with slightly above 1,000 ug/L TPH-gasoline and lesser amounts of TPH-diesel (wells MW-502 and MW-514).
The highest TPH levels were reported at several of the perimeter monitoring wells. One of the two new wells adjacent to the southeast Lower Yard, MW-501, had over 8,000 ug/L TPH (1,040 ug/L gasoline, 6,690 ug/L diesel, and 597 ug/L oil). Excavations in the southeast Lower Yard were extensive and had indications of previously undocumented disposal activities. The second new well in this area, MW-500, also had relatively elevated contamination with 1,180 ug/L TPH-diesel and 280 ug/L TPH-gasoline. These two new wells provide the first ground water data for parts of the southeast Lower Yard, where the lack of significant historic operations had suggested lower impacts. The high levels at MW-501 were not anticipated. It will be interesting to see what the next several rounds of sampling show in this area.
The second highest TPH results from round 1 were reported for well MW-510, located near the southwest corner of Detention Basin 1 along the western property boundary. The TPH at that well was over 3,700 ug/L, with 3,400 ug/L as TPH-diesel and a lesser amount as TPH-gasoline. This well is at the location of the former “slops pond” associated with operations of the historic asphalt plant. No significant soil TPH contamination was seen during the boring for this well. We identified characterization of this slops pond area as a potential data gap in our comments to Ecology after completion of Phase I of the Interim Actions.
Several additional perimeter wells near the tidal basin and along Willow Creek had TPH concentrations marginally above the required ground water cleanup level of 706 ug/L for the western part of the Lower Yard. The cleanup level for the eastern part of the Lower Yard is 506 ug/L. The difference in cleanup levels reflects the historically different composition of TPH by location. Final compliance decisions will be based on the actual measured composition of TPH at each well.
Results for round 2 sampling should be available within about a month. We will provide an update once they are received.
Feel free to call: ( HYPERLINK "mailto:gglassenviro@comcast.net" gglassenviro@comcast.net)
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