WSP05795 - Laserfiche WebLink

Home Browse Search

SUMMARY (Continued) ,'....-.. :~~;1:~ Imperial Dam was about 710 mg/L. In 20 of the last 23 years, how- ever, the 8verage concentration has exceeded 800 mg/L. In response to the Federal Water Pollution Control Act and its amendments, the seven Colorado River Basin States adopted and the Environmental Protection Agency approved numeric criteria for three locations on the Colorado River, as listed in the table below. The goal of the salinity control program i8 to maint8in concentrations at or below these criteria. Numeric criteria for the lower Colorado River Co lorado River location Below Hoover Dam Below Parker Dam At Imperial Dam Annual flow-weighted concentration (mg/L) 723 747 879 In the Uinta B88in, the estimated average annual salt contribution of the Duchesne River into the Colorado River for the period 1941-78 is 330,000 tons. An additional 90,000 tons of salt are contributed annu- ally by Pariette Draw and Ashley Creek, and 30,000 tons of salt are contributed by small tributaries that flow directly into the Green River. The total estimated average contribution of salt from the Uinta Basin to the Colorado River is 450,000 tons per year. Reclamation divided the Uinta Basin Unit into 17 irrigated sub- areas for evaluation purposes. Approximately 407,700 acre-feet of water entered the 17 subareas annually during the 8tudy period (1972-77), in- cluding canal diversion8 from rivers and creeks, precipitation, inter- cepted flow from up8tream irrigation, and subsurface inflows. This inflow carried a salt load of approximately 138,300 tons annually. About 262,500 acre-feet annually were consumptively used by crops and phreatophytes, and 145,200 acre-feet left the 17 subareas as return flow. The salt load of the return flow was about 312,900 tons. S8lt pickup from the 17 subareas was approximately 174,600 tons annually. Much of the salt pickup from the 17 subareas is from the dissolu- tion of salt8 from the 80il and subsurface materials, principally from soils of marine origin (Uinta, Duchesne River, and Mancos Formations) which underlie most of the Uinta B8sin. Seepage from conveY8nce systems and deep percolation resulting from irrigation are the prim8ry processes which di8solve salts from the soils and shales and convey the 8alt8 to natural drainages and ultimately to the Duchesne, Green, and Colorado Ri ver"s. Existing Environment The Uinta Basin Unit area is largely rural, and agriculture is ex- pected to remain an important aspect of the economy of the basin. M08t of the irrigated lands and nearly all of the population of Duche8ne and S-2 OdC<jS7