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The floor of the excavation was treated with an oxidant prior to backfill. The oxidant (potassium permanganate, KMnO4) was applied to further degrade the PCE in groundwater and soil beneath the water table. The excavation was backfilled with clean soil that had been excavated onsite to attain a safe grade on the sidewalls of the pit, as well as clean soil imported from offsite. Backfill and grading of the site was completed in late October, 2011.
Cleanup of Groundwater: Timeline for Pilot Studies and Remedy Selection
The proposed timeline for cleanup of groundwater was provided at the Community Meeting held in Las Vegas on October 26, 2011. Since that time, delays in performing the field tests and pilot studies have modified that schedule. The previous date for completion of pilot studies and submittal of the Corrective Action Report for Groundwater was June 29, 2012. However, drilling for additional characterization did not begin until mid-July, 2012. Data collected from deep drilling and pumping tests called for a reassessment of pilot studies. As of November, 2012, designs for pilot testing were being revisited. Consequently, preparation of the Corrective Action Report, and selection and implementation of the remedy will be delayed while additional site characterization is being conducted. The NDEP will provide a revised timeline for cleanup of groundwater after the Corrective Action Report is submitted by the responsible parties, but a delay of 12 months (from the October 2011 schedule) is not unlikely.
Cleanup of Groundwater: What are the Challenges?
Not all technologies are appropriate for all sites, due to geochemical, hydrological, geological or engineering issues. This is why additional laboratory and field testing are required to determine which technologies are most likely to be effective in cleaning up the groundwater. In the Las Vegas Valley, cleanup of PCE-contaminated groundwater is technically difficult due to the types of geologic deposits and the geochemistry of the shallow groundwater. The remedy must be selected and designed to avoid spreading the plume into areas that are currently unaffected. Ideally, some form of hydraulic containment would be employed to prevent further migration of the PCE mass underneath the residential neighborhood.
Data from the laboratory and field tests will be evaluated, and a preferred remedial technology will be proposed based on criteria outlined in the CAP. The Corrective Action Report will summarize these data and describe the preferred remedy. The NDEP will prepare a "Proposed Plan" summarizing the remedy and requesting public input. All comments and responses on the Proposed Plan will be compiled and provided as an appendix to the Record of Decision (ROD). The ROD is the document that describes the remedy selected to clean up the Site.
After a groundwater treatment system is put in place, groundwater will continue to be monitored on a regular basis. Currently, wells showing a statistical trend of increasing concentration are monitored and sampled every quarter; all other wells are sampled semi-annually or annually. In the future, the frequency of monitoring and sampling may be adjusted to provide adequate data for managing the site, depending on the type of remedy selected and implemented.
Chronology of Actions and Investigations
Additional information on the chronology of the investigation is provided in the Background Document for the Maryland Square PCE Site and in the Administrative Record portion of this website.
Reports and the Administrative Record
Recent reports (from 2007 to 2012) are located here and the entire administrative record, including all reports and correspondence, for the case can be found here. The administrative record is updated as new documents are produced.
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