<br />76 National Water Summary 1984-Hydrologic Perspectives
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<br />EXPLANATION
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<br />Figure 44. Malimum. mean.
<br />and minimum d,ssolvS<l.
<br />solids loads lor 26 stations
<br />in the Colorado Aiver basin,
<br />1965 to 1983. (Source: Com.
<br />plied by J. E. K,rCher from
<br />U,S, Geological Survey and
<br />U.S. Bureau of Reclamation
<br />data)
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<br />WYOMING
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<br />.~V '8. fi'!> <;], 10 COLORADO
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<br />'COIolUS
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<br />UTAH
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<br />19r:;j--
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<br />NEW
<br />MEXICO
<br />
<br />ARIZONA
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<br />......
<br />
<br />
<br />-------------
<br />
<br />Se\eral faelors may be influencing the gen-
<br />erally decreasing trends in dissol\t~d-solids con-
<br />centration ~hown in figure ':6. These fa..:lOrs
<br />indude reSef\Olr sforage and operation,
<br />dis~ohed-solids control mea'>ure" in Ihe basin,
<br />and \'ariations in natural runoff. The dis-
<br />soh'ed-solids concentration in rhers generally
<br />denease~ wilh increa'eJ streamllo.... on an an-
<br />nual ba~is.
<br />The period from 1%3 to 1980 represents
<br />lhl' most ~ignificant period of re..er\oir filling in
<br />thl' history of\\ater development in the Colora-
<br />do Ri\er ba...in. The amount of .....ater ,>tored in
<br />
<br />.
<br />
<br />.
<br />
<br />.
<br />
<br />Flaming Gorge Resen'oir, L.ake Powell, and
<br />Lake :\kad collecti\e1y increased from Jess Ihan
<br />~O million acre-feet (a<:re-fl) in 1963 to more
<br />than 50 million a<:re-ft in 1980. During lhe
<br />JX'riod of filling, it is possible Ihat the more
<br />dense ....ater (high dis'iohed-solids <:oncen~
<br />trationl moved to the bOllam of the reservoir
<br />and the Jess dense watl."r (10\\ dissolved-solids
<br />..:oncentration) flo\\ed out of the reservoir.
<br />Such a ..ituation \\oulJ l'ause a de<:rease In
<br />di,..ol\ed-solids com.cntratiom downslream of
<br />thC'resenoir.
<br />,\nother po,>sible rea,>on for the trends is
<br />l"hanges in irrigation practi..:es. \luch of Ihe
<br />farmland that had poor drainage and had
<br />excessive dis,ohed ,olids in the soil has been
<br />taken out of produ~"tion. In addition, irrigalion
<br />prauicC\ have changed significantly during the
<br />pa"l 20 years, whkh should de<:rease return
<br />110"'" and decrea,>e the dis..ohed ,olid, input 10
<br />'>treams.
<br />Many aquifers in lhe region contain large
<br />cOI1..:cntratiom of di..,ohed solids but arc con-
<br />fined by hundreds of fect of impermeable
<br />shall."liI and, therefore. ~.k'ld relatively little sa-
<br />line ground waler through springs 10 the
<br />streams under natural conditions. However,
<br />when the ~'onfining layer,> for lhe saline aquifers
<br />are disrupted by mining or drilling, lhe saline
<br />ground water can more readily flo" [0 Ihe
<br />surface or reach the streams. "Iany saline
<br />springs and Ilo....ing ....ell, have been identified
<br />in the ba,in. Some of the.sc: flowing wells have
<br />been plugged as pan of disso]ved-solids-\.'ontrol
<br />proje<:h, such as at \Il'cker Dome, near \feck-
<br />er, Co]o., and, therefore, <:ould be causing a
<br />df'1.:r\.'a,>ing trend in some areas. The iniliation
<br />of other dissol\'ed-solids-control projects dur-
<br />ing this period also may cOlllribute to the
<br />dc:c1ine in dissohed-'olids concentrations in
<br />pans of fhe basin. Each of lhese faclOrs possi-
<br />bly ..:ontribute.. to the prl."dominantly decreasing
<br />trends in dissol\'Cd-.solids concentrations, but
<br />determining the relative imparlance of these
<br />major causes will require fun her ,tudy.
<br />
<br />.
<br />
<br />.
<br />
<br />DISSOLVED-SOLIDS CONTROL
<br />MEASURES
<br />
<br />In 197~, an amendment to the Federal
<br />Water Pollution Control A..:t (Public Law
<br />92-500) 'el fonh goals that included the reslO+
<br />ration and mainlenance of ""ater quality, Iimi.
<br />talion of polluling diluent di~charge~, and
<br />e\t'nlua] lero pollution dis..:hargl.". :-';umeri\.'a]
<br />criteria ,ubsequemly \\ ere l'~tablished for three
<br />station.s t'l\' the Colorado Ri\er Ba~in Salini{\'
<br />Control F~rum, adopll."d bv ea..:h of the se\e~
<br />ba..in Sfates. and apNO\cd by the U.S. Em'i-
<br />ronmental PrOfe..:tion Agcn..:y. The criteria are:
<br />
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