Wells that do not correspond to positive anomalies may be uncased. The USGS has 50 years of experience in the development and application of aeromagnetic and ground magnetic survey methods. In particular, the USGS has taken the leading role in the study of abandoned well sites through the use of magnetic anomaly data. Isostatic residual gravity anomaly maps are produced by subtracting long-wavelength anomalies, produced by masses deep within the crust or mantle, from the Bouguer anomaly map. Isostatic residual gravity anomaly maps therefore reveal more clearly than Bouguer anomaly maps the density distributions within the upper crust that are of interest in many geologic and tectonic studies.
Benefits Locating abandoned wells is an important step toward reducing groundwater contamination.
Once located, the wells can be sealed to prevent the transmission of contaminants into and between aquifers. Unfortunately, older well locations are frequently unrecorded or inaccurately recorded. Aeromagnetic and ground magnetic surveys provide an efficient direct method for locating these abandoned wells.