Three CTEM and three CISTEM surveys were performed on large area environmental sites on the west coast in 1987. One of the surveys was "Truth Tested" to 300 feet and found to be quite accurate in determining stratigraphy and locating contamination plumes from grade to depths greater than 100 feet. The survey's abilities were established, but were judged to be too expensive for the environmental market. The surveys were not accepted by the environmental engineering consultants. Environmental efforts were limited to characterizations from grade to less than 25 feet in 1987.

In order to advance geophysical survey capability on environmental sites, Pritchard developed and "Beta Tested" the three techniques described herein.

The 2D RECON survey (initially known as the surface EM gradiometer survey) was "Beta Tested" in Santa Clara County (South Bay area). The objective was to find vertical irrigation well casings lopped off 15 feet below the surface. The gradiometer surveys did not prove successful for the original objective, but they were successful in mapping hydrocarbon plumes along oil pipelines criss-crossing the county.

The 2D DEPTH SCAN survey was "Beta Tested" around large, surface oil tanks on a site in the SW San Francisco Bay area. The survey was highly successful. LNAPL plumes located on the water table at 12 feet were mapped.

The EOL survey (initially known as the MagnaScan Survey and later 3DR survey) was "Beta Tested" to 200 feet on a chromium-plume site in the Silinas Valley. The valley is located just south of the Bay area. The results proved to successful for imaging stratigraphy and free-chromium plumes. The survey QAQC was provided by the many borehole and monitor wells on the site. Starting in 1989, the surveys successfully imaged hydrocarbon plumes to over 50 feet of depth at many oil pipeline terminals and refineries in the Los Angeles and San Francisco Bay areas.

In 1991, all of the Pritchard Technology surveys were moved to Texas and the Gulf Coast States to map and image hydrocarbon plumes. Plumes at forty-one sites were characterized in Texas alone.

In late 1994, Pritchard joined Gehm Environmental to provide 3D EOL survey imaging of hydrocarbon plumes on military sites and at many sites in Missouri. In 1997, Pritchard Geophysics was joined by Dave Gehm to provide LNAPL hydrocarbon plume mapping at military sites, fractured bedrock sites, and soil contaminated sites. Pritchard Geophysics and Gehm Environmental began integrating the two surveys in 1998.

The history of David Gehm and the initial Gehm Environmental EOL surveys, in 1995, are presented on www.gehm.com  web site. The two EOL surveys reported were processed, modeled, and analyzed by James Pritchard.

Contact James Pritchard at www.jip.gp-1@worldnet.att.net  for other geophysical survey characterizations. 

James I. Pritchard BIO

Environmental and Exploration Geophysical Specialist

Ph.D., 1971, Geophysics & Geology, Colorado School of Mines, Golden, Colorado
M.Sc., 1964, Geophysics & Geology, Colorado School of Mines, Golden, Colorado
Degree of Geophysical Engineer, 1958, Colorado School of Mines, Golden, Colorado

Licensed geophysicist in California, GP 691, from 1974 to 1990

Pritchard has performed research and development and directed operations worldwide for several EM, DC, and IP geophysical processes. His efforts include surveys for environmental, geothermal, mineral, oil & gas, and potable water investigations during a 45-plus year career. His research efforts include development of systems for imaging recoverable hydrocarbons, mapping Karst features and fault/fracture reservoirs (in limestone, dolomite, volcanic, and metamorphic sections), and mapping reef, channel sand, and Saprolite reservoirs. Pritchard's geophysical research, from 1961 through 1972, was performed at CSM, the USGS (Denver), the Sinclair Research Lab (Tulsa, OK), and the Newmont Mining Research Lab (Danbury, CT).

In 1988, Pritchard developed the 3D EOL imaging process and the 2D RECON and 2D DEPTH SCAN Surveys in California. The EOL is a spin-off from Newmont Mining's EMP (EM Pulse) technique.

From 1976 through 1986, Pritchard directed, modeled, and evaluated 44 multi-channel EM surveys of oil and gas prospects. These surveys were performed for the CSM Exploration Reassert Lab (ERL), Pritchard Geophysics, INDESO (Midland, TX), and Electrodyne Surveys Services (Reno, NV).

While on staff at CSM in the mid-80s, Pritchard, CSM, and Prairie Eagle Exploration (Denver, CO) used a multi-channel seismic system to gather digital EM-data. Pritchard and Seismograph Service Corporation (Denver, CO) developed an EM processing work-station utilizing many standard seismic software modules to model and analyze the multi-channel data. Two techniques and software systems evolved: CTEM (Continuous Time-domain EM profiles) and CISTEM (Continuous Integrated Seismic and EM/DC/IP profiles).

From 1966 through 1977, Pritchard modeled and analyzed resistivity surveys of geothermal reservoirs at 65 USA prospects and 10 world prospects, one each in Java, New Zealand, Honduras, Greece, Israel, Ethiopia, and Kenya and three in Nicaragua. In 1966, Pritchard performed the first "deep" USA electrical resistivity geothermal survey (to 500 feet) at the Soldier Meadows Hot Springs and the Fly Ranch Hot Springs, geothermal areas in the Black Rock Desert in northwest Nevada.

During the 1970s, Pritchard pioneered, developed, and analyzed multi-channel EM surveys to detect and map potable-water reservoirs in California and mineral-deposits in Arizona, Alaska, Tennessee, and Australia.