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(';:") :,'i PUBLIC HEALTH SERVICE All irrigation return flows from project lands will be to the San Juan River dre,inage basin, Return flows from the Montezuma Valley have been used to irrigate lands i" the McElmo Creek Canyon west of Cortez, Colorado. New return flows from the project developments in Montezuma Valley are expected to be of equal if not better quality than past flows of McElmo Creek. The effect on quality of San Juan Biver water below the confluence with McElmo Creek and Montezuma Creek will be negligible. About 1,000 acres of land in the vicinity of the Cortez airport are presently waterlogged and underlaid by beds of Mancos shale. The depth to Mancos shale in the area varies from 0 to about 30 feet. Applica- tion of additional water to these and adjacent areas will increase the necessity of providing adequate drainage facilities. The availability of an adequate water supply for irrigation in the Towoac area may also increase the necessity for construction of drainage facilities. The extent of the drainage facilities necessary in this area will be deter- mined later. The topography of the Dove Creek area is such that nat- ural drainage should suffice to remove the excess irrigation water applied to these areas. A few scattered strips of bottom land of draws and swales in the northern part of the Montezuma Valley area are now waterlogged; however, these lands have been excluded from the project area. Chemical quality data for selected surface ;later stations and pub- lic water supplies in the area are shown in Tables 4 and 5, respectively. Under the present stream regimen the effluent from the Dolores sew- age treatment is discharged to the Dolores River below the tu,"mel now utilized in diverting Dolores River water for the Cortez public water supply. However, under the potential project plans stored water in the McPhee Reservoir. including the effluent from the Dolores sewage treat- ment plant, will be utilized as a raw water supply for Cortez and Dove Creek. Under the potential project plans the bacteriological quality of the stored water in McPhee Reservoir is of great importance to any community using the water for domestic purposes. Under authority contained in Chapter 66-1-7, Colorado Revised Stat- utes, 1953, together with amendments "enacted by the General Assembly in 1955 and 1959," the Colorado State Department of Public Health has established the minimum standards allowable for effluents of sewerage system and trade wastes discharged upon the land or into the surface or ground waters. These adopted standards are summarized below: 1, The effluent of sewerage system and trade wastes shall not contain (a) substances in quantities toxic to man, (b) set- tleable matter exceeding five-tenths milliliter per liter, (c) suspended matter exceeding seventy-five parts per million. or (d) floating matter. 124