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<br />. <br /> <br />. <br /> <br />. <br /> <br />1~4r. <br /> <br />J4-'1~-Lr~fti"'-~-t:"~.., -_ <br />.. : 1~ rl'v,It::.JAR\p '-;G-:;;~-'- <br />if ML.:" I.... <br />, - t-....,.- ...~ <br />~ _.',_ i ""r"~ r:: ""-"\: - <br /> <br />Figure 13 near here. <br /> <br />Table 7 near here. <br /> <br />Specific conductance at station 07109500 exhibited less variability between the pre-Pueblo Reservoir (1969- <br /> <br />74) and post-Pueblo Reservoir (1975-94) periods (fig. 14) than was observed at station 07099400. Although the <br /> <br />annual minimum and maximum specific conductance tended to increase after 1974, the median specific conduc- <br /> <br />tance for 1969-74 (778 J.LS/cm) was nO[ significantly different (p=0.16) from the median specific conductance for <br /> <br />1975-94 (812 \lS/cm). The annual minimum spedfic conductance increased from about 200-400 J.LS/cm in 1969- <br /> <br />74 to about 250-600 \lS/em in 1975-94 (fig. 14). The annual maximum specific conductance increased from about <br /> <br />1,000-1,100 JlS/cm in 1969-74 to about 1,000-1,450 flS/cm in 1975-94 (fig. 14). Monthly specific conductance dif- <br /> <br />fered between the two periods of 1969-74 and 1975-94 (fig. 15), but most of the differences were not statistically <br /> <br />significant (table 8). The small number of significam differences may be paniy due to the small number of specific- <br /> <br />conductance data in the 1969-74 period (table 8). Significant increases in specific conductance occurred during <br /> <br />December, June, and August The increase in the median specific conductance in December (900 to 1,120 JlS/cm) <br /> <br />coincided with a significant decrease in discharge (table 7). 1bis relation in specific conductance and discharge <br /> <br />trends is typical, because discharge and specific conductance are inversely proportional to one another. The <br /> <br />increased median specific conductance in June (338 to 450 J.LS/cm) and in August (470 to 550 J.LS/cm) coincided <br /> <br />with increased discharge for those months (table 7). This relation between discharge and specific-conductance <br /> <br />trends is unusual, because one would expect increased discharge to result in increased dilution and decreased spe- <br /> <br />cific conductance. There are two likely causes of the increased specific conductance in June and August: (1) Mix- <br /> <br />ing of low-conductance and high-conductance water within Pueblo Reservoir resulted in increased specific <br /> <br />conductance in the reservoir outflow during months that historically had the lowest specific conduc1ance; and (2) <br /> <br />dissolved solids loads from major tributaries increased. It is likely that both drcumstances occurred and have acted <br /> <br />in concen to increase specific conductance during June and August A lack of data prevented an analysis of spe- <br /> <br />26 "'- <br />