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Show Utah Geological and Mineralogical Survey, Water- Resources Bulletin 14, 1970 APPENDIX A RESULTS OF TRACER STUDIES Tracer studies using Rhodamine WT dye were conducted during August and September 1969 in an attempt to trace movement of brine through the causeway fill. In the first phase of the study, Rhodamine WT fluorescent dye, adjusted to the density of the south part brine, was injected at the surface on the south side of the fill. Injections were made at nine sites along the causeway. Two sites were along the old fill, constructed in the early 1900' s; and the other seven sites were along the new fill ( figure 1). One liter of dye was injected at each site, at a rate which resulted in a total injection time of approximately one- half hour. Samples for fluorescence analysis using a Turner Model 111 fluorometer were collected on the north side of the fill directly across from the injection points. Sampling began with injection of the dye and continued until a peak fluorescence occurred or until the dye was visually observed on the north side. The following information was gained from these tests: 1. The travel time of water ( at the surface) through the new section of the causeway ranged from less than 19 minutes to 1 hour ( table 4). At milepost 745.2, however, the travel time through the fill was 3 hours. This travel time is representative of only about a half mile stretch of causeway where a berm exists on the north side. The water stage inside this berm is approximately 0.9 foot higher than the stage in the north part of the lake. 2. Water appears to " pipe" through the fill. In a given section of the fill, water moves very rapidly through a " pipe" at one point and much more slowly where no " pipe" exists only a few feet away. These initial observations would seem to indicate that the fill in the causeway is not at all homogeneous. At certain places along the causeway, the material is fairly compact with relatively small, poorly connected pore spaces. At other places, connected openings between larger rocks appear to exist all the way through the causeway. For these reasons, calculating an average travel time for movement through the entire causeway or assigning an average permeability to the entire causeway may give extremely misleading results. 3. Dispersion of the dye at both the injection sites and the measuring points was one of the biggest problems encountered in the first phase of the tests. The dye was injected as far back into the large boulders of the riprap ( figure 1) as possible, but wave action and diffusion of the dye itself still caused considerable dispersion. In addition, the prevailing lake current is from east to west, parallel to the causeway. As a result, dye clouds as much as 300 feet long formed along the causeway at the injection sites. Because of this dispersion, the distance traveled and the travel times through the fill can only be approximated. In some cases, the actual travel time of the water from the point of injection to the measuring point directly across from it may have been considerably longer than the shortest observed travel time of the dye. This would be true where the dye dispersed up or down the length of the causeway on the south side until it hit a " pipe" with much higher permeability than the material at the injection site. The only points where dispersion was not a problem were where the observed travel times were less than about one- half hour. At these points, almost all the injected dye entered the fill at the injection site. 4. Travel time through the older fill at either end of the causeway was much longer than travel time through the new fill. The longer travel times are probably due to the methods used to construct the older fill ( see p. 1) and possibly to compaction of the materials with time. The second phase of the tracer study was made in order to trace movement from below the water surface on the south side of the causeway to the north side. The purpose of these tests was to try to locate the interface between northward and southward moving water and to find the deepest point at which water was moving northward. The site chosen for the test was at railroad milepost 747.2, where the observed travel time at the surface had been the shortest. This site was chosen with the hope of avoiding the dispersion problems that had been encountered previously. A sample was obtained on the south side of the causeway, 10.5 feet below the surface. The density of the sample was determined, and the dye was then concentrated to this same density by adding the proper amount of water from the north part. One liter of the dye was injected into the rocks where the edge of the causeway was 10.5 feet below the water surface. The dye immediately began dispersing from the injection point to the west and upward. Downward dispersion may also have taken place; but if so, it would not have been visible. Within 5- 7 minutes the dye cloud was touching the causeway at the water surface along a 50- 75 foot 33 |