Hydrostratigraphy of the Edwards Aquifer as Evaluated by Hydrophysical and Geophysical Logging

Pedler, William H.

Tuesday, April 30, 2013: 1:35 p.m.

Regency West 4 (Hyatt Regency San Antonio)

Steven Truesdale Sr., P.G., RAS, Inc. Integrated Subsurface Evaluation

William H. Pedler, RAS, Inc. Integrated Subsurface Evaluation

During the past eight years hydrophysical and geophysical borehole methods have been used to evaluate the hydrostratigraphy of the Edwards Aquifer. Work was conducted under EAA contract, however numerous DOD wells were evaluated. The EAA data were collected from wells completed within the Maverick Basin, the Devils River Trend, and the San Marcos Platform. The DOD data were collected from wells at Camps Stanley and Bullis, located within the San Marcos Platform. The purpose of the logging program was to cost-effectively develop a hydrophysical, geophysical and lithologic regional database to assist in water supply management and future groundwater development. Between 2005 and 2012, fourteen wells were logged for EAA using a combination of mechanical caliper, natural gamma, induction resistivity, analog video, and acoustic and optical televiewers to gather information on the lithologic and structural characteristics of the formations in which the wells were developed. Between 2004 and 2008 numerous additional wells were evaluated at Camps Stanley and Bullis. The same methods as applied to EAA wells were conducted in addition to nuclear logs (well integrity analysis), straddle packer testing and scanning colloidal borescope flowmeter methods (horizontal flow evaluation). Hydrophysical logging (HPL) was conducted in six wells under both ambient and stressed pressure conditions, to assess and identify the locations/depths of water-bearing intervals; evaluate the rate of flow from each of these identified intervals; and estimate interval-specific hydraulic conductivity, transmissivity, and fluid electrical conductivity (FEC/TDS). Formation structural data (fracture or karst feature frequency and aperture) were then compared with hydrophysical and geophysical data to generate a relationship profile specific to water-bearing intervals, on a regional stratigraphic basis. The unique combination of geophysical and hydrophysical methods used - in conjunction with the comparison to published stratigraphic data - was successful in effectively developing an empirically based hydrostratigraphy of the Edwards Aquifer.

Steven Truesdale Sr., P.G. , RAS, Inc. Integrated Subsurface Evaluation

Steven Truesdale, PG, is a hydrogeologist, geophysical log analyst, and project manager for RAS Inc., Integrated Subsurface Evaluation, in Golden, Colorado. RAS is a recognized leader in the development of unique downhole tools for use in integrated aquifer solution planning. The RAS project team has successfully applied unique combinations of geophysical and hydrophysical methods with traditional geophysics and hydraulic testing methods, such as their newly developed wireline straddle packer system and single/multiple well pump rates to increase the level of understanding of the environment being tested.

William H. Pedler , RAS, Inc. Integrated Subsurface Evaluation

William Pedler is the President of RAS, Inc. Integrated Subsurface Evaluation, in Golden, Colorado. A graduate of the Colorado School of Mines, he has over twenty five years of experience in researching, developing and applying methods for aquifer characterization and the evaluation of subsurface flow. As the original developer of the Hydrophysical Logging technology in the late 80s, he has improved the understanding of the science as well as the integration of both new and traditional techniques in the field. William Pedler has been involved in 100’s of projects ranging from nuclear waste isolation studies to water resource development/management.

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Hydrostratigraphy of the Edwards Aquifer as Evaluated by Hydrophysical and Geophysical Logging