ARCHIVED REPORTS_REMOVAL ACTION COMPLETION REPORT

Home Browse Search

Draft Removal Action Completion Report Neighborhood C, Mountain House,CA Page 2 Assessment Report Southern Portion of Neighborhood C, dated February 12, 2007 (Condor); and the Final Removal Action Workplan, dated July 9,2007(Condor). The RAW included a plan for conducting the removal action, a description of the on-Site contamination, and the goals to be achieved by the removal action, as required by the California Health and Safety Code (H&SC) Section 25323.1. The RAW is also consistent with the criteria specified in the H&SC Section 25356.1(c). Several Environmental Site Assessments (ESAs) were conducted between 2004 and 2007. Dieldrin was found at elevated concentrations in the upper six inches of soil within the agricultural field portion of the Site. The ESAs identified areas with elevated concentrations of dieldrin corresponding with an increased potential for lifetime human health risk of cancer. Based on the results, Condor recommended that surface soil be removed from the Site prior to residential development. There were sufficient data to support a removal action as proposed in the RAW. Due to the physical and chemical nature of dieldrin, the sole constituent of concern (COC), elevated concentrations would likely remain in shallow soil. Due to timing and cost constraints, Condor recommended that soil removal be performed as the preferred remediation measure to mitigate the identified potential threat to human health and the environment prior to development of the Site for residential use. The preferred remediation method identified in the RAW was to remove the upper six inches of soil from the agricultural field portion of the Site and place in a pre-excavated entombment trench beneath the southbound lanes of Great Valley Parkway. The RAW was designed to mitigate exposure of future residents and maintenance workers to the contaminated soil on the Site, with planned areas and depths of excavation based on previous sampling results. The RAW presented the cleanup goal for dieldrin of 0.035 milligrams per kilogram (mg/kg). Excavation boundaries were conservatively planned to encompass identified contamination and include the nearest investigation sample with COC concentrations below the cleanup goal. To ensure adequate contaminant removal, the confirmation sampling plan was designed to constrain each area of contamination in three dimensions. Waste characterization sampling was planned to be performed for each approximately 2000 cubic yards (yds3) of waste soil to characterize disposal concentrations within the entombment area below Great Valley Parkway. The RAW specified exclusion zone and fenceline action levels for dust in air related to soil movement activities at the Site to protect public health. 3.0 REMOVAL ACTION ACTIVITIES The following section and subsections describe specific removal action activities from Site preparation to Site restoration.All stages of the removal action activities were monitored by the Site Manager,Mr.Keith Sprague of MHD and the Professional Geologist, Alex Dewitt of Condor. All personnel working on Site were required to familiarize themselves with and adhere to the Site Specific Health and Safety Plan, Dust Control Plan, and other procedures defined in the RAW. All removal, transportation, and disposal activities were performed in general accordance with the RAW. Variances to the RAW were necessary to accommodate the volume of impacted soil and the construction schedule and are described in the following sections. 3.1 SITE SURVEY AND EXCAVATION DELINEATION Prior to commencement of Removal Action activities, a survey was conducted by Carlson, Barbee & Gibson, a California licensed surveyor, to stake RAW excavation areas, and establish local survey control. The individual excavation sub-parcels and sampling locations were staked with four-foot wood