Station II was located 2 miles down- 

 stream from the salt point. The volume of 

 flow was 43.4 cfs, the resistivity 188,000 ohms, 

 and water temperature 44° F. The salt reached 

 this point in 69 minutes and the resistivity 

 dropped to 92,000 ohms or 49 percent of the or- 

 iginal level. After 50 minutes of observation 

 at this station, the resistivity had increased to 

 173,000 ohms and readings were discontinued 

 in order to intercept the salt at the next station. 



At Station UI, 3.5 miles downstream from 

 the salt point, the volume of flow was 51.6 cfs, 

 resistivity 170,000 ohms, and water temperature 

 44° F. The salt reached this station approx- 

 imately 10 minutes before the observer did or 

 about 118 minutes after the block was intro- 

 duced into the stream at the salt point. The 10- 

 minute error was closely estimated from back- 

 calculations and from results of other trials 

 when only Stations I and III were observed. The 

 salt was in the area of Station III for 110 minutes 

 and the resistivity dropped to a low of 110,000 

 ohms or 65 percent of the original. 



The data obtained at the salt point and at 

 Stations I and III were related to the concentra- 

 tion of salt in ppm by two methods . First, the 

 concentration of salt added to the stream at the 

 salt point and the average concentrations of salt 

 as it passed Stations I and UI during the periods 

 of observation were calculated on the basis of 

 the 16 pounds of salt dissolved from the block 

 during the 15 -minute period, the stream flow 

 rates measured in cfs at Stations I and III, and 

 the lengths of time in minutes that the salt was 

 in the station areas. Accordingly, the salt dis- 

 solved into the stream at the salt point at an 

 average rate of 8.3 ppm for the 15-minute period. 

 Its average concentration at Station I during the 

 44 minutes it influenced resistivity was 2.8 ppm. 

 The average concentration at Station III for 110 

 minutes was 0.8 ppm. In the second method, the 

 concentrations of salt at the various levels of re- 

 sistivity measured at Stations I and III were 

 estimated from the curves shown in figure 1 . 

 The concentrations of salt at Station I ranged 

 from 0.1 to 7.6 ppm as the resistivity dropped 

 from 207,000 to 54,500 ohms but the average con- 

 centration for the 44-minute period was 2.6 ppm. 

 The concentrations at Station III ranged from 0. 1 

 to 1.7 ppm as the resistivity dropped from 170,000 



to 110,000 ohms and the average concentration 

 was 0.6 ppm. Despite the dilution of the salt 

 and the stretchout of the bolt over the 3.5 miles 

 between the salt point and Station III, the re- 

 sistivity was appreciably lowered. 



The close agreement at Stations I and III 

 between the calculated average concentrations 

 of salt (2.8 and 0.8 ppm respectively) and the 

 estimated average concentrations (2.6 and 0.6 

 ppm respectively) derived from curves in figure 1 

 supports the validity of the curves and indicated 

 that they can be used in the interpretation of data 

 on resistivity collected in streams. 



Additional, detailed observations were 

 made on Indian Creek and 8 other streams (table 3). 

 One or two blocks of salt were placed in them for 

 varying periods of time and resistivities were 

 greatly reduced. The degree to which the resistiv- 

 ity was reduced in a trial area was roughly con- 

 trolled by placing the salt block in either fast, 

 slow, shallow, or deep spots in the stream . In 

 Roaring Fork (Stream G, table 3), 31 pounds of 

 salt were dissolved at Station I during a 2 -hour 

 period to reduce the resistivity from 106,000 to 

 a range of 37,000 - 66,000 ohms. The stream 

 flow was 12.5 cfs and water temperature 49° F. 

 At Station III, 32 pounds of salt were used in 1.75 

 hours to reduce the resistivity from 103,000 to a 

 range of 40,000 - 52,000 ohms when the flow was 

 11.9 cfs and temperature 50° F. At Station IV, 

 50 pounds of salt were used in 2.5 hours by placing 

 the block in fast water. The resistivity was re- 

 duced from 106,000 to 20,000 ohms, the flow was 

 12.5 cfs, and water temperature was 50° F. The 

 salt used at the rate of 20 pounds per hour at 

 Station IV had greater effect in reducing resistiv- 

 ity than did the rate of 15.5 pounds per hour at 

 Station I. It was found, too, that a block of salt 

 would last from 1 to 4 hours, depending on the 

 size of the stream and the location of a block 

 placed in it . 



The effects of salt on an electric field in 

 water were tested at one of the stations on Roaring 

 Fork. The stream at this point was 33 feet wide, 

 its flow was 25.8 cfs, and its temperature was 50° 

 F. A 6-electrode, alternate -polarity system was 

 stretched across the stream and the relative 

 strengths of the electric fields in the water were 

 measured at input voltages of 230 and 330 volts AC 



1 



