By Greg Glass
The mobilization for Phase II cleanup activities started on July 21st. As of the first week of September, Phase II appears to be on schedule and probably more than half finished. I have made 7 site visits since Phase II began to observe site conditions and progress.
The additional “data gaps” sampling results documented soil contamination up to almost six times the criterion for soil excavation (maximum reported total TPH concentration over 17,000 parts per million) located south of the eastern end of Detention Basin 1, where the former asphalt warehouse was once located. As a result, the temporary water treatment plant was moved at the start of Phase II to allow access for additional soil removal in that area. The treatment plant was set up at a location in the central Lower Yard where cleanup actions were already done in Phase I.
ARCADIS, Chevron’s contractor, has estimated that the total soils plus sediments to be excavated during Phase II will be about 12,000 tons. That is a small fraction of the volume removed during Phase I or the Upper Yard cleanup program. A few small excavation areas in the southwest Lower Yard and next to Willow Creek near Detention Basins 1 and 2 were addressed at the beginning of Phase II. The major soil removal work so far has been in the southeast Lower Yard, where area B1 was not completed during Phase I. Site airphotos show a history of soil disturbance and fill activities in the southeast Lower Yard, which was not used for any of the UNOCAL bulk fuel plant operations. Soil excavations at area B1 have turned up assorted debris (e.g., broken concrete foundation materials) as well as crushed drums or drum fragments, with petroleum product frequently observed. These observations suggest that the southeast Lower Yard was used historically for disposal activities. Site reports have also documented the use of this area for treatment of some TPH-contaminated soils brought onto the site from other UNOCAL facilities. By the end of Phase II almost all open areas in the southeast Lower Yard will have been excavated to treeline.
By early September backfilling of the excavation at area B1 had started. Soil confirmation sampling showed a few sidewall locations where additional soil removal is needed. They will be addressed as backfilling proceeds.
Soil removals at other areas adjacent to Willow Creek along the western property boundary were starting in early September. Those limited areas were easier to address at the same time as sediment remediation, and therefore were held over from Phase I to Phase II. The former “slops pond” that was used when the asphalt plant operated is also located in this area. It will be addressed either directly by excavation or through additional sampling to confirm its status with respect to cleanup criteria.
The last area of soil removal during Phase II will be the former asphalt plant warehouse area, located south of Detention Basin I and east of the major Phase I excavations in the central Lower Yard. Given the restricted time period for working in Willow Creek (fish window), ARCADIS wanted to complete those in-stream activities first. Cleanup at the former asphalt plant warehouse area will probably start by late September and be completed during October. The full spatial extent of that excavation is not well-defined by sampling results, but assuming the contamination is associated with former warehouse operations the footprint of that building may be a rough indication. Soil removals will be guided by the existing sampling results, visible indicators of contamination, and additional confirmation sampling as the excavation proceeds.
A major focus of Phase II is cleanup of a segment of Willow Creek along the western property boundary of the UNOCAL site, just upstream from the tidal basin. That segment of the creek was isolated by construction of two temporary coffer dams. Fish within this isolated segment were collected and transplanted as cleanup work in the creek started. All water from dewatering activities within this isolated reach was routed through the treatment plant before discharge. Temporary piping runs were laid out to allow for pumping creek and tidal flows around the isolated segment. Late August saw unusually high amounts of rainfall – several inches within a week or so. ARCADIS installed additional pumps to handle the larger flows. For a while, water was ponded behind the upstream coffer dam, resulting in higher water levels in the marsh. By early September ARCADIS had successfully pumped down the water ponded upstream. Progress on the sediment cleanup activities has been steady; removal of the coffer dams and re-establishment of normal creek flows should occur in late September.
All of the excavations for the creek channel and associated overbank areas and slopes have been done from the UNOCAL side, using long-reach excavation equipment. Except for some of the sideslopes along the UNOCAL side (residual excavation areas held over from Phase I), sediment removals are essentially complete. There was much less obvious evidence of contamination (odors, product sheens) in the sediments than for the onsite soil excavations. The original elevations were surveyed before excavations started, and clean backfill was placed to re-establish the original grades. Backfill materials had to meet criteria specific to their use within the creek (e.g., organic matter content, grain size). After backfilling, thin erosion control mats consisting of straw and a degradable netting are being placed all along the remediated reach of the creek. They are held by 6-inch long wire “staples” pushed into the soils.
The final stages of restoring the creek and completing nearby excavations are expected to take a few weeks. The sediment cleanup component of the Interim Actions should be finished around the end of September.
Overall, my impression is that the Phase II cleanup actions are going well. When they are completed the ground water monitoring programs will commence, starting with the installation of a number of new monitoring wells. Those activities may start around mid- to late October.
Feel free to contact me Greg Glass via (HYPERLINK"gglassenviro@comcast.net"gglassenviro@comcast.net)
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