City of Sacramento
City of Sacramento
SCOPE OF SERVICES
Identify Source of PCE Impacted Soil and Groundwater
Use of Direct Sensing Technology
Removal of Contaminated Soil
Monitoring and Sampling Existing Groundwater Pump and Treat System
Samuel C. Pannell Meadowview Community Center, Sacramento, California
Stratus personnel were contracted by the City of Sacramento to identify the source for tetrachloroethylene (perchloroethylene, PCE) impacted soil and groundwater resulting from a former dry-cleaning business operated at the site prior to development of the community center. For speed and efficiency, Stratus personnel utilized a direct sensing technology (membrane interface probe [MIP]) to map the source area in-place and produce volatile organic compound (VOC) profiles. This reduced the need to bring actual samples to the surface for lithologic or chemical analysis, thus reducing analysis time and sample handling, as well as minimizing contaminant exposure. Utilizing MIP technology also eliminated disposal costs associated with investigative derived waste. Chlorinated volatile results were obtained quickly and reporting was completed in the field, facilitating rapid visualization and mapping of the contaminant data both horizontally and vertically. Direct push technology (DPT) was utilized following the MIP investigation to collect discrete soil samples at depths and locations identified by the MIP as containing VOCs. PCE ranging in concentrations from 18 to 73,000 micrograms per kilogram (ug/kg) and its breakdown products (e.g. trichloroethylene [TCE] and cis-1,2-dichloroethene) were detected in soil samples collected in two areas of the investigation zone. Until this investigation was completed, the source of the PCE contamination had not been identified.
Source removal action was undertaken in 2008 by Stratus personnel in the area identified with the highest soil concentrations during the MIP survey. Stratus personnel prequalified the PCE impacted soil for landfill acceptance, and provided oversight during remediation of the PCE source which consisted of excavation, screening, and segregation of contaminated and highly-contaminated soil using a photoionization detector (PID), and coordinated transportation, disposal, and site restoration activities. Approximately 12 tons of highly impacted soil was disposed at the US Ecology facility in Beatty, Nevada for thermal treatment, and approximately 40 tons of impacted soil was disposed at the Waste Management Kettleman Hills Class I facility, Kettleman City, California. The segregation of soil for disposal resulted in that portion of the project coming in approximately 30% under budget. Approximately 30 pounds of PCE were removed from the site during the removal action.
An existing onsite groundwater treatment system was operated intermittently during the past several years. Stratus has been responsible for monitoring and sampling the treatment system, and continues quarterly sampling of numerous groundwater monitoring wells and technical reporting. The amount of PCE extracted by the treatment system between 2014 and 2017 was approximately 0.52 pounds. Due to the diminishing VOC removal and persistent PCE levels in the source area groundwater, alternative remedial solutions were evaluated and discussed with Central Valley Regional Water Quality Control Board staff during an April 2017 project update meeting. Additional source area excavation and treatment (3-D Microemulsion® addition) alternative was selected as the preferred method of remediation.
Stratus completed the second source area removal action between December 2017 and May 2018 in the area of the monitoring well that has historically exhibited the highest concentrations of PCE during quarterly groundwater monitoring (considered the source area well). Excavation in this area was completed to depths of 28 feet below the ground surface, at approximately the groundwater level. Screening with a PID was also conducted during this round of remediation to separate impacted soil from clean overburden soil. A total of approximately 1,500 cubic yards of soil were excavated from the targeted area, and 307 tons of that were determined to be impacted with PCE and disposed at the Recology Class II disposal facility in Vacaville, California. The offsite disposal of the impacted soil along with volatilization of VOCs during the excavation and stockpiling process resulted in removal of an additional approximately 9 pounds of PCE in the vicinity of the source well. Following completion of the excavation and while the excavation was open, approximately 800 pounds of 3-D Microemulsion® treatment product provided by REGENESIS® Remediation Solutions was applied to treat any residual PCE contamination in the excavation area. This in-situ treatment is intended to promote anaerobic biodegradation to breakdown chlorinated solvents in the groundwater through the enhanced reductive dechlorination process in a three-stage electron donor release profile, for a period of up to 2-4 years.