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<br />OO~2S0 <br /> <br />Ferry gage from October 1921 and are used to represent pre-dam conditions in the Colorado River <br />(U.S. Geological Survey, 1985-1996) <br /> <br /> <br />b. Time Series of Physical Parameters <br /> <br /> <br />-"- "-:'c. _Th~..varying..qualityof Glen Canyon Dam releases-were studied using data from two Soll!'Ces~~'" n____ <br /> <br /> <br />The USGS has maintained water quality monitoring for salinity and specific conductance at the <br /> <br /> <br />Colorado River at Lees Ferry gage (09380000) since 1944. These data exist in USGS daily values <br /> <br /> <br />tables. Prior to 1977 single daily measurements for specific conductance were made (daily values <br /> <br /> <br />statistic code 00011). Since that time, specific conductance has been measured at specific <br /> <br /> <br />intervals with automated mini-monitor instrumentation; mean daily values are calculated from <br /> <br /> <br />these data (daily values statistic code (00003). <br /> <br /> <br />Reclamation began its water quality monitoring of the Glen Canyon Dam taiIwater as part of <br /> <br /> <br />Phase I of the Glen Canyon Environmental Studies program in August 1988. This program was <br /> <br /> <br />begunwith measurements of temperature and specific conductance at bi-hourly intervals. As <br /> <br /> <br />instrumentation improved, measurement of dissolved oxygen was added in June 199 I; pH <br /> <br /> <br />measurements began in July 1995. Monitoring at Lees Ferry was initiated in October 1991. This <br /> <br /> <br />monitoring has been conducted with various versions of the Hydrolab™ Corporation's Datasonde <br /> <br /> <br />and Recorder submersible multi-parameter data logging instrumentation (Hydrolab, 1994). These <br /> <br /> <br />monitors are serviced on a monthly basis. The Grand Canyon Monitoring and Research Center <br /> <br />(GCMRC) currently maintains this program. <br /> <br /> <br />c. Chemical Analysis <br /> <br /> <br />The Colorado River at Lees Ferry gage (09380000) gage is maintained as part of the USGS <br /> <br /> <br />National Stream-Quality Accounting Network. Analysis of a broad range of water quality <br /> <br /> <br />parameters and contaminants is conducted on samples collected on a bimonthly basis. <br /> <br />03/06/98 <br /> <br />DRAFr <br /> <br />Page 14 of62 <br />