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<:-j (J:) .-l o '--) ::) Chapter II I AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES carry the water to fields where it is typically spread across the fields through furrows. Impacts In limited areas, lands below the Price and stubb Ditches that are presently too wet and alkali to farm successfully due to ditch seepage, would experience increased crop production when the ditches are improved. It is anticipated that with newly designed and balanced supply ditches, the supply of water would be more dependable. Soils Present Conditions Most of the soils in the Grand Valley are either alluvial deposits or residual soils formed on and from the Mancos Shale; they generally have low permeabilities and high water-holding capacities. Localized areas of high saline-alkaline concentrations are scattered throughout the valley. Poor drainage conditions and high water tables have resulted in accumulations of salts, which adversely affect roughly one-third of the available agricultural acreage in the valley. Soil erosion is a problem, particularly in uncultivated areas, because of the low density of natural vegetation. Impacts Improving the two ditches would lower the water tables and subsequently reduce upward capillary movement of salt carrying water, thus decreasing salt deposits at the land surface in localized areas. The results would be a better crop growth in agricultural fields. During construction of either alternative, erosion would be a problem when vegetation was cleared and soils were exposed to wind and water. Construction material sites along washes would constitute potential erosion problems if the channels of the washes were disturbed; however, these sites would be developed with buffer zones along the washes so that this problem would be avoided. Impacts associated with the use of the borrow areas were describeG in the Grand Valley FEIS. Water Qualitv Present Conditions Surface Water.--As the Colorado River flows through the Grand Valley, its salinity increases. The historic flow-weighted mean TOS increases from about 383 mg/L at the Cameo gauging station to about 557 mg/L at the Colorado River above the Dolores River. The monthly flow-weighted averages range from 166 to 962 mg/L and from 210 to 1,737 mg/L at these points, respectively. Table 4 shows the average concentration at the major river stations above and below the Unit area. 19