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Show Madison- Effects of Causeway on Chemistry of Great Salt Lake Table 4. Results of tracer studies at Southern Pacific Co. causeway during August - September 1969. Distance from Time from injection pointy/ beginning of M easured stage Dye injection point to measuring injection to difference ( see fig. 1) point 2/ first appearacross causeway ( railroad milepost) ( feet) ance of dye ( feet) 737.6 89 > 7 hours 0.83 741.5 75 45 minutes .89 743.6 78 < 33 minutes .93 745.2 74 3 hours 3/. 03 747.2 78 < 19 minutes .97 748.5 72 1 hour 1.02 750.0 75 45 minutes .99 751.5 80 1 hour 1.24 752.8 149 > 8 hours 1.07 1/ Water surface on south side. 2/ Water surface on north side. 3/ Measuring point was inside of berm on north side of causeway. Stage inside berm was approximately 0.9 foot higher than stage in north part of lake. length that was about 60- 80 feet west of the injection point. The dye appeared visually on the north side of the causeway about 60- 80 feet west of the injection point, 41 minutes after injection was started. Because of the dispersion, however, it was impossible to know whether dye entered the causeway at depth and moved through the causeway in 41 minutes or whether it dispersed upward and entered a " pipe" at some other depth, moving through in less than 41 minutes. Dye was also injected 18 feet below the water surface. This dye had been concentrated to approximately 0.01 density units greater than the water in situ at a depth of 18 feet in order to avoid the dispersion problem that had occurred at 10.5 feet. Dispersion occurred again, however, and within 7- 10 minutes the dye cloud had reached the surface. Because of the masking effects caused by dispersion, the information obtained for travel time of water from south to north through the lower sections of the fill is not considered reliable. The third phase of the tracer study was an attempt to trace movement from north to south through the fill. The site chosen for the injection was again at railroad milepost 747.2. This site was chosen because it was hoped that the travel time there would be less than 8 hours- the maximum uninterrupted time available for measuring. The following information was gained from two injections which were made a week apart: 1. A " piping" effect occurs with the north to south flow. Both dye injections were at the same injection point and at the same depth- 5.5 feet below the water surface on the north side. After the first injection, dye appeared in 3.5 hours on the south side of the causeway directly across from the injection point, which was about 30 feet east of the point on the surface where the travel time south to north was less than 19 minutes. The dye entered the south side at a point below the top of the deep layer of brine. The exact point of entry could not be determined because the dye dispersed through the entire depth of the deep layer of brine. After the second injection, dye appeared south of the causeway in 1 hour, directly across from the point of injection. 2. The actual point on the north side where the dye entered the causeway cannot be determined because of dispersion at the injection point. 3. Sampling on the south side gave no indication of movement from north to south above the deep layer of brine. If there is any such movement, the flow is small enough so that the southward- moving brine trickles down through the rocks on the south side and is undetectable before it enters the deeper layer of brine. GENERAL CONCLUSIONS FROM THE TRACER STUDY 1. A large amount of water moves through the fill from south to north near the lake surface. The approximate average velocity of movement through the new fill ranges from about 1 to 5 feet per minute. If any water moves through the old sections of the fill, the quantity is insignificant compared to that which moves through the new section. 2. Visual observations indicate that the rate of water movement is not uniform through the fill, but it may vary from very slow to very fast over a span of a few feet. 3. The thickness of the layer discharging from the north side of the causeway cannot be measured accurately, but it is estimated to be from 2 to 6 inches at the edge of the fill. 4. Water moves from north to south through the fill, and it probably discharges at or below the level of the deeper, more dense layer of brine south of the causeway. The maximum velocity observed was about 1 foot per minute. Because the depth of discharge makes visual observation impossible, however, the first observed dye may not represent the first dye actually through the causeway. Thus the 34 |