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Geophysical Survey Summary Report for AOC-65
Section 1 - Introduction
1.1 - Purpose of Report
A subsurface geophysical investigation was performed at Camp Stanley Storage Activity (CSSA) Area of Concern (AOC)-65 to delineate structural and stratographic conditions that may be influencing groundwater and contaminant migration. The investigation was performed in conjunction with a soil vapor extraction (SVE) treatability study at the unit. The SVE treatability study is being conducted to evaluate the effectiveness of SVE at reducing the volatile contaminants present in the subsurface materials at the site. Additionally, a groundwater recharge study is planned for the AOC-65 area to assess the infiltration and migration of water through the unsaturated zone and to evaluate its effect on the migration of contaminants from the unit.
The geophysical investigations were performed to identify subsurface features that may be controlling the migration of contaminants such as fractures, faults, and karst dissolution features. Identification of these features was used to direct installation of piezometers and an SVE system in the vicinity of Building 90. Additionally, the geophysical results were used to select locations for the Westbay® (WB) multi-level sampling point wells installed during the TO-0042 task order activities. A discussion of the Westbay® well locations and installation is included in CSSA Environmental Encyclopedia, Volume 5, Groundwater, TO-0042 Well Installation Report (Parsons, currently draft).
The investigation included performing surface and down-hole geophysical surveys and detailed evaluation of rock core collected during drilling at AOC-65.
Surface geophysical methods included electrical resistivity imaging, microgravity, very low frequency electromagnetics, seismic reflection, induced polarization, and spontaneous potential. The methods utilized at the unit were selected based on their applicability for detecting physical contrasts associated with the features. The different methods were utilized in a phased approach, where the results of each provided guidance for successive phases. Borehole geophysical surveys were completed at some of the drilling locations to aid in characterization of geologic conditions. These surveys included caliper, spontaneous potential, gamma-ray, and resistivity logging.
Drilling activities were conducted at AOC-65 to characterize geologic conditions at the unit. The coreholes were completed as vapor extraction wells (VEW), vapor monitoring points (VMP) for the SVE system, as groundwater piezometers (PZ) to be used in a groundwater recharge study at AOC-65. Drilling locations were selected based on locations of anomalies identified in the surface geophysical survey.
This report describes work performed under contract F41624-00-D-8024, Task Order 0058 (Parsons project number 740999). Geophysical surveys were performed under work breakdown structure (WBS) 04010. Drilling activities for the groundwater recharge study and the SVE system installation were completed under WBS 04030 and 04040, respectively. Preparation of this report was completed under WBS 05020.
This document outlines characterization activities conducted at Building 90 and AOC‑65 in conjunction with SVE treatability and groundwater recharge studies. Section 2 of this report describes site conditions, and Section 3 details the geophysical surveys completed. Section 4 presents results of the surface geophysical surveys. Section 5 discusses drilling activities conducted in conjunction with the treatability and groundwater recharge studies, and Section 6 presents the conclusions and recommendations. References can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).