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<br />- 'L i"'~ ....~.,.. <br /> <br />0!l1318 <br /> <br />5. Grand Valley geology: (A) surficial geology, (B) generalized extent of Ihe cobble aquifer, and <br />(C) generalized geologic section .................................................................................................................... 10 <br />6. Distribution of soil-sampling sites within townships in irrigated weas of the Uncompahgre Project........... 17 <br />7. Graph showing percent of variance in selenium concentrations in soils and alfalfa for different levels <br /> <br />in the sampling design....... .......... .......... ...... .......... ........... .......... ......... ......... ........... .......... ............ .................. ........ 20 <br />8. Map showing locations of type weas and locations of wells and springs in the Uncompahgre Project <br />area where samples were collected for chemical analysis ...................................................................................... 22 <br />9. Map showing location of type wea and wells in the Grand Valley where samples were collected for <br /> <br />chemical analysis.. .................. ........ .......................... ...... ...... ............. ........... ................ ........... .......... ...... ..... ........... 23 <br />10. Schematic showing hydrogeologic selling and ground.waler flow in (A) Reed Wash type area and <br /> <br />(8) Dry Creek type area. ......................................................................................................................................... 26 <br />II. Graph showing water-level altitude and specific conduclance ofwaler in welll43NO. Grand Valley, <br /> <br />March 1992-March 1993 ........................................................................................................................................ 27 <br />12. Graphs showing historical water-level aJtitudes and dissolved-solids concentrations in water from <br />wells 125Q5 and 208KO located in the Grand Valley ............................................................................................. 29 <br />13. Trilinear diagram showing percentages of major ions in water from selected wells during the irrigation <br />season in the Uncompahgre Project area and in the Grand Valley.......................................................................... 30 <br />14. Graphs showing oxygen and hydrogen stable isotope values in waler from selected wells, streams. and <br />rivers in the Uncompahgre Project area and in the Grand Valley........................................................................... 33 <br />15. Stability-field diagram for selenium species in natural waters and data points calculated from selenium- <br />speciation data collected for this study ................................................................................................................... 34 <br />16. Schematic showing conceptual model of the occurrence of selenium in Mancos Shale, shale residuum, <br />alluvium, and ground water in the Uncompahgre Project area and in the Grand Valley........................................ 38 <br />17. Graph showing platinum-electrode potential and concentrations of dissolved selenium in water from <br />wells in Mancos Shale residuum............................................................................................................................. 40 <br />18. Graph showing dissolved selenium in water from wells in shale residuum and alluvium during the <br />irrigation season and nonirrigation season .............................................................................................................. 40 <br />19. Graphs showing correlation of dissolved solids and dissolved selenium in water from wells in alluvium <br /> <br />and shale residuum....... .............. ..... ..... ............ .................. .................. ................ ........ ........... .................. .............. 42 <br />20. Scanning-electron photomicrograph of framboidal pyrile collected on 0.45-micrometer water-filter <br />paper from a well located outside the irrigated Grand Valley area, October 1991 ................................................. 43 <br />21. Graphs showing correlations of dissoJved selenium with various dissolved constituents in water from <br />wells in the Uncompahgre Project area and in the Grand Valley............................................................................ 46 <br />22. Graph showing dissolved-selenium concentrations and the LOWESS smoothed curves of selenium <br />concentrations for the Gunnison River at Whitewater and the Colorado River near the Colorado-Utah <br /> <br />Slale line, 1975-92.............. ...... .............. ............... .......... ........................ ....... ....................... ................................. 50 <br />23. Schematic diagram showing the lower Gunnison River Basin and relative locations of selected surface- <br /> <br />waler-sampling sites............ ................ ................. ........................... ........... ........... ....... ........... .................. .............. 52 <br />24. Graph showing selenium loads in the Gunnison River at Whitewater and the Colorado River near the <br />Colorado-Utah State line, July 1991-August ]992, and the residual loads............................................................ 54 <br />25. Schematic diagram showing the southern part of the Uncompahgre ProjecI, relative locations of surface- <br />water-sampling sites, and seJenium concentrations in samples coJlecred during synoptic surveys, <br /> <br />January-March 1992 .......... ........... ......... .............. ........................... ...... ...................... .................... ..... ............. ...... 56 <br />26. Schematic diagram showing the northern part of the Uncompahgre Project, relative locations of surface- <br />water-sampling sites, and selenium concentrations in samples coUected during synoptic surveys, <br />January-March 1992...... ........ ..... ............... .... .......................... ....... ...................... ........... ............ ........ ........ ........... 57 <br />27-29. Graphs showing: <br />27. Selenium concentrations in samples from Dry Creek al site DRY I, Cedar Creek al site CD I, <br />Loutsenhizer Arroyo at sites LZAM and LZA I, and an unnamed drainage at site RD], <br /> <br />July 1991-August 1992 .................................................................................................................................. 60 <br />28. Selenium concentrations in the Uncompahgre River al Delta, ]987-92........................................................ 62 <br />29. Selenium concentrations in the Uncompahgre River, February 19-20, 1992 ................................................ 63 <br /> <br />CONTENTS V <br />