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<br />PART VI <br /> <br />EVALUATION OF EXISTING SALINITY CONDITIONS <br /> <br />. <br /> <br />Seismograph drilling act1v1t1es may be particularly disruptive to shallow <br />ground water systems and stricter regulation and enforcement should be <br />considered. <br /> <br />to- <br />e,n <br />N <br />OJ <br /> <br />The Meeker Dome Salinity Project described in Part VIII is one <br />area where Reclamat ion has plugged abandoned oil explorat ion drilling <br />holes anticipating that the aquifers are static and the saline water <br />would not find another path back to the surface. <br /> <br />6. Switching the Reporting of TDS from Evaporation Residue at <br />180. C to Sum of the Constituents <br /> <br />It has been found that waters high in calcium sulfate salts <br />retain water at 180. C, and thus yield high TDS results. Between 1968 <br />and 1970, TDS was changed from a measurement of l80.C residue to sum of <br />ionic constituents for all the USGS records used in this report. Since <br />the Colorado River waters are high in sulfates, this may have produced a <br />slight downward shift in the TDS data. <br /> <br />7. Salinity Control Projects <br /> <br />. <br /> <br />The actual implementation of salinity control units is des- <br />cribed in Part VIII. Meeker Dome, Grand Valley Stage I, and possibly <br />research pumping for the Paradox Unit have prevented some salts from <br />reaching the river in the 1980-82 period. While the local impacts of <br />these projects are still being evaluated, no effects are likely to have <br />occurred as yet below Lake Mead because of the 5- to 7-year actual flow <br />hydraulic detention time of the reservoirs. <br /> <br />8. Erosion <br /> <br />Several research projects have shown that steeply sloping <br />saline shales yield high dissolved solids concentrations during runoff <br />events. These and previous studies have primarily focused on conditions <br />caused by summer and fall thundershowers. The total salt contributions <br />from these events have been estimated to constitute less than 10 percent <br />of the total salt budget of the studied tributaries. Lower elevation <br />snowmelt events, particularly associated with saline marine formations, <br />may contribute a greater portion of the salinity budgets. Analyses of <br />the Green River near Green River stat ion indicate that electrical con- <br />ductivity remains high or may increase with flow peaks associated with <br />snowmelt runoff events in January through April. <br /> <br />. <br /> <br />During the McElmo Creek salinity studies (described in Part <br />VIII), it was found that approximately 32 percent of the total salt load <br />could be related to such runoff events. Since some of these salts had <br />previously been assigned to agricultural return flows, the project salin- <br />ity benefits had to be revised. Similarly, recent Pr ice River sal inity <br />studies showed 21 percent, and San Rafael 14 percent of the salt budget <br />related to natural runoff. <br /> <br />31 <br />