No abstract

Slight tonal differences in images are a result of the quality of the original aerial photographs.

George Bales, Drew Goins, Bobby Robinson, and Tom Wiedmeier of the Augusta Utilities Department provided valuable assistance with various project activities. Joe Beard of East Central Regional Hospital provided well access at the East Central Regional Hospital, Gracewood Campus. Bobby Robinson at the Augusta Utilities Department Water Plant provided access to production wells for both water-quality sampling and an aquifer test, and provided a pumping record for Well Field 2 for a few days prior to the test. Numerous private land owners allowed access to their wells for the collection of water-level data. Michael Hamrick of the U.S. Geological Survey collected water-level data during the 24-hour aquifer test at Well Field 2.

Borehole geophysical logs and flowmeter data were collected in April 2011 from eight boreholes to identify the depth and orientation of cavernous zones within the Miocene Tampa Limestone in the vicinity of Jim Woodruff Lock and Dam in Jackson County, Florida. These data are used to assess leakage near the dam. Each of the eight boreholes was terminated in limestone at depths ranging from 84 to 104 feet. Large cavernous zones were encountered in most of the borings, with several exceeding 20-inches in diameter. The cavernous zones generally were between 1 and 5 feet in height, but a cavern in one of the borings reached a height of about 6 feet. The resistivity of limestone layers penetrated by the boreholes generally was less than 1,000 ohm-meters. Formation resistivity near the cavernous zones did not show an appreciable contrast from surrounding bedrock, probably because the bedrock is saturated, owing to its primary permeability. Measured flow rates in the eight boreholes determined using an electro magnetic flowmeter were all less than ± 0.1 liter per second. These low flow rates suggest that vertical hydraulic gradients in the boreholes are negligible and that hydraulic head in the various cavernous zones shows only minor, if any, variation.