By Greg Glass
Feasibility Study. The first milestone for completion of the Feasibility Study (FS) is submittal of a Draft Work Plan for Ecology review. Chevron expects to submit that Draft Work Plan by the end of September 2011. Ecology schedules indicate that the agency’s review will not be completed until near the end of 2011, with a final revised and approved Work Plan expected early in 2012. Stakeholders, including ECAC and the Washington State Department of Transportation (WSDOT), will receive the Draft Work Plan for review concurrently with Ecology in September. The Work Plan will include a schedule for completion of the Feasibility Study, which is expected to take a year or more. Depending on the time required for selecting and designing final cleanup actions, completion of Lower Yard cleanup could extend to 2014.
Identifying and evaluating alternatives for Lower Yard cleanup in the Feasibility Study will require a sufficient understanding of the nature and extent, and any ongoing sources for, remaining Lower Yard contamination. Part of the Feasibility Study process will therefore be the identification and resolution of any remaining data gaps. Even before submittal of the Draft FS Work Plan, Chevron sought and received Ecology approval for an additional investigation of remaining contamination, including LNAPLs (oil product), in the vicinity of monitoring well MW-510 and the former slops pond (called the Detention Basin No. 2 Investigation by Chevron). Soil samples were collected from 17 borings in this area in August and are now being analyzed at the lab for TPH and benzene, and for cPAHs if TPH levels are sufficiently high. Piezometers were installed at a number of the soil borings and will be observed for water levels and LNAPL occurrence. An LNAPL bail down test was also performed at MW-510 where product has frequently been observed over the past two years of ground water monitoring. The results of this additional investigation are scheduled to be submitted to Ecology by November 2011. Chevron, Ecology, WSDOT, and ECAC representatives visited the site and observed portions of this recent field investigation program by Chevron’s consultant, ARCADIS.
Ground Water Monitoring Results, 2nd Quarter 2011. An additional round of ground water samples – the 13th since the end of Lower Yard Interim Actions in 2008 – was collected in June. Chevron reported the results of that sampling round in its August monthly progress report to Ecology. As outlined in the proposal for continued ground water monitoring, the June 2011 sampling round included both perimeter (point-of-compliance) and interior wells (40 total). The next sampling round will occur in September and will include only the perimeter wells.
For the first time since August 2009 no LNAPLs were reported at MW-510. The total TPH concentration of 15,300 ug/L at that well still indicated significant ground water contamination; this was by far the highest reported TPH result.
Overall the results were similar to the previous sampling round in March 2011. In the southeast corner of the Lower Yard, wells MW-135 and MW-136 repeated their comparatively lower results (still marginally above default cleanup levels) showing a substantial reduction from earlier sampling rounds. MW-136 has had a pretty consistent declining trend since its maximum value in June 2009. MW-135 has had a more up-and-down pattern and rebounded once before from a concentration similar to the June 2011 result to a level almost three times higher. June 2011 results for MW-135 and MW-136 were 785 ug/L and 645 ug/L, respectively.
Three perimeter wells, in addition to MW-510, at locations previously noted for higher TPH concentrations continued to show similar results in June 2011. MW-129R near the southeast corner of DB-1 was slightly lower than previous rounds, at 1,935 ug/L. LM-2 at the far northern corner of DB-1, with 2,345 ug/L total TPH, was the highest in June of all wells other than MW-510. LM-2 TPH levels have declined somewhat over the last 3 rounds but remain well above cleanup levels. On the western site boundary, well MW-104 had its second highest result since the end of Lower Yard Interim Actions; at 2,274 ug/L it was almost twice the previous concentration in March 2011. MW-104 has had one of the most extreme up-and-down patterns for TPH.
One other notable result was for interior well MW-143, which was not sampled in March 2011. In the last sampling round at MW-143, in October 2010, total TPH was very low at 169 ug/L The June 2011 result was more than 10 times higher, at 1,745 ug/L – very close to the round just before October 2010, when 1,585 ug/L was reported in July 2010. MW-143 has also had a very notable up-and-down pattern for total TPH.
The June 2011 results continue the post-Interim Action pattern with several areas along the site perimeter continuing to show the highest residual ground water TPH contamination. MW-143 in the southwest Lower Yard is the interior well with the highest remaining TPH contamination. The focus in these notes on remaining areas of contamination is consistent with the decision by Ecology that the completed Interim Actions are not Final Actions and that a Feasibility Study to evaluate additional cleanup actions is required. But this focus on residual contamination should not obscure the fact that most of the monitoring wells, and nearly all of those in the interior of the site, already show acceptable TPH levels.
(For well orientation check the well map in the categories at the left.)
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