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NAVEL BASE VENTURA COUNTY, PORT HUENEME, CALIFORNIA EPA CHARACTERIZATION TEST CELL REPORT ON ELECTROMAGNETIC SURVEYS IN THE TEST CELL AREA
Citation:
Werkema, D. NAVEL BASE VENTURA COUNTY, PORT HUENEME, CALIFORNIA EPA CHARACTERIZATION TEST CELL REPORT ON ELECTROMAGNETIC SURVEYS IN THE TEST CELL AREA. U.S. Environmental Protection Agency, Washington, DC, EPA/600/S-04/073 (NTIS PB2004-106608), 2004.
Impact/Purpose:
Research is being conducted to improve and evaluate the resolution of the CR, EM, seismic, and GPR methods over complex geological formations (such as fractured geologies) and to evaluate the capability of these geophysical methods to delineate subsurface organic contaminants.
Description:
The objective of the geophysical surveys at the EPA Characterization Test Cell (CTC) area (Site) at Naval Base Ventura County, Port Hueneme, California is to locate geophysical anomalies indicative of metallic objects within the area of the cell. The goal was to provide background metallic object content at the Site for future construction and research activities. To achieve the objective, detailed reconnaissance geophysical mapping using Electromagnetic Induction (EMI) was conducted throughout the Site. The EMI survey was performed using the Geonics EM-31 and the Geonics EM-61. The following series of geophysical property maps were produced from the survey results: an EM-31 Quadrature response (bulk ground conductivity), EM-31 In-Phase response, EM-61 Bottom Channel, EM-61 Top Channel, and the EM-61 Normalized Differential Channel. The EM- 31 revealed bulk ground conductivities, while the EM-61 revealed responses due to ferrous and/or non-ferrous metallic objects. The EM-31 maps show no anomalous responses within the area surveyed. An increasing bulk ground conductivity gradient was observed along the eastern and southeastern portions of the Site interpreted as due to a nearby chain- link fence as well as an underground utility along the southeastern boundary. The EM-61 maps reveal several discrete anomalies indicative of small metallic objects throughout the site and one large discrete anomaly of no known cause. In addition a few north-south trending linear anomalies may represent elongate pipe-like metallic objects or surface material contrasts. Overall, the EMI surveys suggest the locations of several subsurface metallic objects, which may be encountered during excavation and construction and if so, should be removed prior to construction of the CTC.