Kansas Geological Survey, Open-file Report 88-39
Great Plains and Cedar Hills Aquifers--Page 16 of 25
delta D = 8 ( delta 18O ) + 10
is based on precipitation data collected on a world-wide basis. This line is shown in Figure 32 as a reference for the data collected in this study. The D and 18O content in precipitation from any locality will plot on this line. The D and 18O values for precipitation from Manhattan, KS, (delta D= -53, delta 18O = -7.5, Chadhuri, personal communication, 1988) are shown in Figure 32 for reference.
Figure 32. 18O and Deuterium Composition of Ground Waters and Oil-field Brines from Study Area (see Table 4 for Labels).
The data collected in this study shows a parallel best fit line to the meteoric line. This indicates that the source of the water at the tested sites was primarily from meteoric water although the age of that water may have been Pleistocene or older. 18O and deuterium are not used for age dating.
A wide variety of sources of waters were collected for this study in order to determine if any mixing scenarios were occurring between the brines that might be disposed of in the Cedar Hills formation and the overlying formations. The scatter on the delta 18O - delta D diagram (Figure 32) suggests that mixing is not occurring between water types but is occurring vertically at some test sites. The 18O and D isotopes indicate that the waters from the Hays North site (C, D, E) are similar to each other.
Samples L, M, and N from the Gorham site are also similar to each other. These isotopes also emphasize the difference in water chemistry between these two sites. For the Gorham monitoring site, vertical variations in the overall water chemistry, together with the relative changes in Oxygen-18 and D, suggest that the lower part of the Great Plains aquifer is being recharged by the upper Great Plains and the Cedar Hills aquifers (Figures 17 and 36). At the Hays North well site, the difference between the isotope values for the Dakota, Cheyenne, and Cedar Hills aquifers and various brine samples supports the Br/Cl data that the source of salt water is from halite solution rather than from oil-field brine sources. These topics are discussed further in section 7.0.
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