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<br />i <br /> <br />, <br /> <br />this drying temperature. Differences in TDS between the sum cf <br /> <br />constituehts and residue methods can be as high as plus or minus <br /> <br />40 mg/l depending on the constituents present and the laboratory <br /> <br />,... <br />""-l <br />tv <br />N <br /> <br />procedures used. <br /> <br />Flow-weighted salinity used in the Board's monthly water <br /> <br />reports is calculated for each of the measuring stations by the <br /> <br />Bureau of Reclamation. The Bureau aPplies a daily EC-to-TDS <br /> <br />" <br />~ I <br />;va ue. <br /> <br />conversion factor to daily EC readings to obtain the daily TDS <br /> <br />Tqe daily TDS is then applied to the average daily flow; <br /> <br />Daily EC-to-TDS conversion factors are derived by interpolating <br /> <br /> <br />between two base EC-to-TDS conversion factors, determined from <br /> <br />laboratory analyses of water samples for two consecutive time <br /> <br />periods. <br /> <br />For Imperial Dam and the Northerly International Boundary <br /> <br /> <br />~,,' <br /> <br />stations, base EC-to-TDS conversion factors are dete=mined for <br /> <br />samples taken twic€ a month. In the case of the Parker Dam and <br /> <br />Palo Verde Canal stations, base EC-to-TDS conversion factors are <br /> <br /> <br />determined from monthly samples. With respect to the Hoover <br /> <br />Dam station, base conversion factors are determined. from samples <br /> <br />taken every other month. <br /> <br />Below Hoover Dam Station <br /> <br />The sampling point below Hoover Dam is a USGS National S'tream I. <br /> <br />Quality Accounting Netwe-a (NASQAN) station. Samples at NASQAN <br /> <br />stations are taken by the USGS. NASQAN stations were originally <br /> <br />sampled monthly but have been reduced to a bi-monthly frequency <br /> <br />because of ;fiscal limitations. Water samples are sent to the <br /> <br />USGS's Denver, Colorado laboratory, one of its two automatetl <br /> <br />-2- <br /> <br />; <br /> <br />;'<j <br /> <br />1. <br /> <br />, _"'~"'.~~i.-:b1-"< ~~ '~'$..i~~/ <br />