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< . . . . . United States Department of the Interior U. S. GEOLOGICAL SURVEY Box 25046 M.S. 415 Denver Federal Center Denver, Colorado 80225 IN REPLY REFER TO: WATER RESOURCES DIVISION COLORADO DISTRICT January 9, 1998 Dr. Kirk Johnson Curator of Paleontology Denver Museum of Natural History 2001 Colorado Boulevard Denver, CO 80205-5798 Dear Dr. Johnson: Your National Science Foundation proposal for paleobiological and geological studies of core from a 2,000 ft. deep core hole near Kiowa, Co., is an interesting and unique study that has considerable merit. I am particularly interested in this study because of the potential that exists to couple your work with hydrologic analyses of the core to provide important gains in knowledge about the Denver Basin aquifers. The proposed core-hole site at Kiowa is very near the geographic center of the Denver Basin, and the hole will penetrate all four principal bedrock aquifers of the Denver Basin. Hydrologic analyses of the core could provide perhaps the single most important measure of the hydrologic characteristics of the aquifers ever made in the Basin. In the Laramie-Fox Hills aquifer for example, the core could provide the first data on porosity, hydraulic conductivity, transmissivity, and specific yield of the aquifer in the 2,000 square-mile central part of the Basin where no such data now exist. Similar important gains in information about the overlying Arapahoe, and Denver aquifers also could be made. State water law for the nontributary Denver Basin aquifers is based on estimates of the specific yield of the bedrock aquifers. Specific yield has been determined at fewer than 100 sites in the 7,000 square-mile basin, and most of these sites are near the margin of the aquifers. As a result, important water rights decisions are now made without knowledge of the specific yield in a large area in the center of the Basin. Better administration and promulgation of water law could be achieved with better knowledge of the aquifers in this area. As we have discussed previously, the U.S. Geological Survey (USGS) is willing to support and assist you in the hydrologic analyses of the core. I would be happy to serve as a hydrologic coordinator for your project with responsibility for coordinating hydrologic-core analyses, aquifer testing, and water-quality sampling and analyses. The scope of this work is as follows: About 50 core samples will be selected by USGS for hydrologic analyses to determine hydraulic conductivity, porosity, and specific yield of the aquifer materials from the lower Dawson, Denver, Arapahoe, and Laramie-Fox Hills aquifers. Core hydraulic-conductivity data with thickness data from geophysical logs will define the transmissivity of each principal aquifer, as well as that of