Edmonds UNOCAL / Chevron Cleanup: December 2010

By Greg Glass

Two Year Ground Water Monitoring Program Ends. The final round of sampling wells at the UNOCAL Edmonds site (Round 11) occurred in October 2010; the results were reported to Ecology by Chevron on December 6^th. What happens next? Ecology and Chevron held a stakeholders meeting on November 16^th to discuss the plans and approximate schedules for further activities.

After extensive Interim Actions in the Lower Yard to remove contamination, wells throughout the Lower Yard were sampled for two years to track trends in ground water quality (including natural attenuation of residual contamination) and see if the cleanup levels for site ground water were met at the Points of Compliance (the site perimeter) by the end of that period. Interim Actions removed and treated large quantities of contaminated ground water, excavated and removed large quantities of contaminated soils, and removed floating product (LNAPLs) from large portions of the Lower Yard. The ground water monitoring data, including Round 11 results, show that despite the extensive cleanup actions multiple Point of Compliance wells have not yet achieved cleanup levels.

A ground water monitoring report will be submitted to Ecology by Chevron by the end of January 2011. We hope that report will provide evaluations and interpretations of the data as a starting point for the development of further actions. Because the Interim Actions already completed cannot be deemed Final Cleanup Actions, a Feasibility Study will be prepared by Chevron to identify and evaluate alternatives for additional cleanup actions to meet site cleanup standards. After completion of the Feasibility Study, Ecology will develop a Cleanup Action Plan and select a preferred alternative. Ecology and Chevron have agreed on this standard MTCA process to develop final cleanup actions. Further Interim Actions to address parts of the remaining contamination problems are not being considered.

The Feasibility Study process will start with development and review of a Work Plan, which will probably be submitted in the first half of 2011. The Feasibility Study schedule will likely include deliverables along the path to a final report; for example, a list of alternatives to be evaluated should be submitted for early review. There will be opportunities for stakeholders to review and comment on the Work Plan, a Draft Feasibility Study report, and a Draft Cleanup Action Plan. At the November 16^th stakeholders meeting Ecology offered a preliminary estimate that completion of a Feasibility Study and Cleanup Action Plan may take two years. That would mean the final cleanup actions could start in 2013. The development schedule for the multi-modal Edmonds Crossing transportation hub, according to the Washington State Department of Transportation, does not conflict with this schedule.

Some additional site data collection can be anticipated as part of the next steps. Chevron will be submitting a proposed plan to Ecology soon for continuing ground water monitoring during the Feasibility Study process. The excavation and backfilling of large portions of the Lower Yard has changed the materials in the shallow ground water zone; a proposal for a tidal influence (hydraulics) study is expected to be submitted soon. Further data collection to clarify the sources and extent of remaining contamination, to support Feasibility Study development and evaluation of alternatives, may also be needed.

Round 11 Ground Water Monitoring Results. In addition to TPH, Round 11 included analyses for benzene, cPAHs, and natural attenuation parameters in all sampled wells. Those additional parameters had been dropped from several preceding rounds when the monitoring program was revised after the first year. The complete analyses in Round 11 provide a snapshot of conditions at the end of the two-year monitoring program. Evaluations of the natural attenuation parameters should be included in the ground water monitoring report due in January 2011.

The overall picture of ground water TPH at the site was largely confirmed in Round 11, although there were notable changes at a few wells. Product continues to be observed at MW-510 at the former slops pond location. Wells MW-129R, MW-135, and MW-136 in the southeast Lower Yard had total TPH between 1,685 and 2,625 ug/L. Well LM-2, at the north end of Detention Basin 1, had the highest TPH concentrations (omitting MW-510 with NAPLs, which was not sampled) in Round 11 at 3,925 ug/L. Three additional Point of Compliance wells along the western site boundary – MW-149R, MW-147, and MW-518 – had total TPH values between 645 and 1,730 ug/L. [Depending on TPH composition, the TPH cleanup levels are between about 500 and 700 ug/L].

As noted in previous rounds, the interior of the Lower Yard has only minor levels of residual ground water contamination compared to perimeter wells. Only two wells, MW-507 and MW-514, slightly exceeded 500 ug/L.

Notable changes in Round 11 included the following:

An almost 90% decrease in TPH at MW-143, in the southwest Lower Yard near the toe of the Upper Yard. The Round 11 TPH result was only 169 ug/L, compared to over 1,500 ug/L in the two previous rounds.

A new maximum TPH concentration for the two years of monitoring at LM-2. The Round 11 value of 3, 925 ug/L is more than 75% higher than the previous maximum value in October 2009. Chevron noted in its December 6^th submittal to Ecology that it planned to resample LM-2 in December to verify this result.

MW-147, along the western site boundary, had TPH at 1,730 ug/L, more than 2.5 times the previous Round 10 value.

Thus, monitoring results continue to show some instances of sharp “up-and-down” patterns in wells rather than steadily decreasing TPH concentrations reflecting typical attenuation processes.

The time trends for selected wells, grouped geographically, over all 11 rounds of sampling are provided below as visual summaries of ground water TPH concentrations at the site since completion of the extensive Lower Yard Interim Actions.

Check Monitoring Well Maps on the left for help in identifying the well locations.