Airborne And Ground Geophysical Surveys For Locating And Mapping Underground Storage Tanks At Bellows Air Force Station, Hawaii: An Integrated Approach

Abstract

Airborne and ground based geophysical surveys were conducted at Bellows Air Force Station (BAFS), Oahu, Hawaii to locate buried metal potentially representing underground storage tanks (USTs) and other buried debris of environmental concern. The airborne survey was used for reconnaissance to screen approximately 3,000 acres of land and shallow offshore areas at BAFS for buried debris. Once the airborne anomalies were evaluated for their potential to have a UST source, focussed ground surveys were conducted to confirm the location and to more accurately characterize anomaly source objects. BAFS was established in 1917 as the Waimanalo Military Reservation and was deactivated in 1970. Throughout BAFS’ history, USTs along with their associated pipelines were installed to maintain base activities. Over the years, structures associated with the USTs have been demolished resulting in the uncertainty of the UST locations. Over 650 geophysical anomalies were identified in the airborne survey (both electromagnetic and magnetic data). Following review of the flight path videos and further scrutinizing of the data, most of the anomalies were attributed to surface cultural features or geology and were eliminated from further investigation. The remaining 73 anomalies were located on the ground and visual field reconnaissance at these locations eliminated some anomalies from further investigation based on the terrain being unsuitable for construction and surface metal hidden under thick canopy. Eighteen of the 73 anomalies were selected for detailed ground surveys. The follow-up ground-based geophysical surveys were conducted using frequency- and time-domain EM, magnetics and ground penetrating radar. Select anomalies identified in the ground geophysical data were trenched and the sources excavated. The technical approach of integrating site knowledge with airborne geophysical targets to select ground geophysical survey locations proved to be efficient and successful in locating and characterizing buried debris at Bellows Air Force Station.