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-9- in addi tion to those effects caused by \~ater use, \-/ill be the seasonal chanGe in the quantity of water discharrJed to the Gunnison River. After the Project is built, water that rreviously had fl~/ed into the Gunnison River durin'! the winter nonths and to a certain extent durillo the snrino runoff oeriod will be stored for irrioation. l-lith the storaoe facilities, \'/ater Hill be available for release for irri- gation and other uses durino the full irriqation season. Decreased f101'IS duri nl! the wi nter I"onths rresent a [lotenti a 1 for freezi ng and may result iil dilnaoe to the fishery i1nd habitat. r.lInnison River v/ater is used to irrioate approximately 250 acres of orchard crops, 250 acres of corn, and 500 acres of alfalfa in the f1ed1and r,lesa area of Grand Junction. As a result of the Grand Hesa Project, the averaoe total dissolved solids concentration of the Gunnison River durino the irriqation season will be improved by lowerinq the concentration Trom 714 Mq!l to 695 fllrJll. This seasonal iMProvement in water quality will result in an averaoe annual benefit to tile Project of approximate 1y $200. The nost sionificant imflacts from the Project \',ill be due to the increased salinity concentrations in the lower Colorado River ~/here salinity concentrations have already reached critical levels. Present uses of lower Colorado P.iver water include irriqated aoricu1ture in ~rizona and Southern California and nunicioa1 and industrial uses in ,'1rizona, ,California and ilevada. The lower' Colorado River is a major source of supply for municiflal and industrial users in the Metropolitan Los Anoe 1 es area and uflon COMpleti on of the Central Ari zona Project the river will provide a \'/ater sUllp1y for metropolitan Phoenix. Studies (5) by the Colorado l1iver Basin :Jater Ouality Control Project of the Environ- mental Protection Aoency indicate that a 3.0 mo!l annual salinity increase at Lake Head ~Jill result in an average annual equivalent penalty castlJ to Vlater users of about $205,000 based on 197U economic conditions; The equivalent penalty cost include a direct cost of ~142,OOO and an indirect cost of $63,000. Detriments to \'later users in ',lexico and to recreation and fisllery users in the Salton Sea are not included in the estinates. Direct penalty costs are yield reductions for irrigated aqriculture, treatment costs for industrial users, and the acceptance of undesirable effects or ~/atersofteninq expenditures for municipal users. Indirect costs are spinoff effects 011 the secondary or supportino indus tri es . The imoact of present and nrojected uses of Basin water on the mineral rJuaiity of tile Colorado River beCOMes oreater nroceedino dO\'/I1- streaM from Lake Head. A prol'lressive increase in sa1initv concentrations occurs in the dO\mstreaM direction resultinq prinCipally from the salt concentra ti no effects of cons umnti ve users. 11 ^ [lena 1 ty cos t is defi ned as the di fference be~leen the detriments associated \/ith the use of ~IO different levels of \'/ater rJuality; thus, it is based on similar economic conditions l'/hich remit the cost effects of \'later oua1ity to be isolated. Detriments are user cost incurred when a specific quality of water is used.