WSP07583

• File Number: 8270.200
• Description: Selenium
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 1/1/1996
• Author: USGS
• Title: Detailed Study of Selenium and Other Constituents in Water-Bottom Sediment-Soil-Alfalfa and Biota Associated with Irrigation Drainage - Uncompahgre Project Area and in the Grand Valley - 1991-93
• Water Supply Pro - Doc Type: Report/Study

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CONTENTS

Abstract......................... ..................... ............ ............... ........................... ........................................................ ............. ......... I
Introduction ....................................... ............ ......... ...................... ...................................... ............................... ............ ........ 2
Purpose and Scope... ....... ..................... ............. ............ ...... ....... ............................... .................... ............... ........... ..... 3
Description of Study Area ........................................................................................................................................... 6
Physiography, Soils, Climate, and Land Uses ................................................................................................... 6

Geologic Setting ...... ............... ...... .......... ...... ...... ...... ......... .............. ............................. ............. ............. ........... 7
Irrigation Projects .......... ...... ............. ................. .......... ..... ....... ....... ................................. ...... ..... ............. .......... 12
Uncompahgre Project ...... ...... ................ ...... .............. ........................ ....................... .............. ........... ...... 12
Grand Valley.. .................. ............... ...... .......... ........... ........................... ..................... .................. ...... ...... 13
Salinity-Control Projects..... ......... ........................... ........ ........ ........................... .............. ............. .......... 13

Previous Studies....... ............................... ............... ...... .................. ........... ........ .......... ............. ............ ............. .......... 14
Acknowledgments ............... ....................... ............ ....... ..... ....................... ..... .......................... ............ ................. ...... 16
Soils and Alfalfa Investigations ......... ........ ........... ................. .......... ............ ..... ....... ........ ....................... .............. ........... ...... 16
Sample Preparation and Analytical Methods .............................................................................................................. 17
Selenium Concentrations in Soils and Alfalfa............................................................................................................. 18

Ground-Water Investigations. ............ ..... ................ ................... ......... ..... ...... ................................... ........... .............. ............ 21
Sample Collection and Analytical Methods ................................................................................................................ 24

Ground-Water Hydrology........... .......... ........ ...................... ......... ............. ................................ ............ ............. .......... 25
Historical Ground-Water Quality........ ......... ...... ................ ......... .............. ................................ ...... ..... ................. ...... 28
Major-Ion Chemistry......... ...... ...................... .................................. ............... ............... ............... .............. ............ ..... 28
Review of Selenium Geochemistry ............................................................................................................................. 31
Sources of Selenium and Other Trace Constituents .................................................................................................... 35
Occurrence of Selenium in Ground Water................................................................................................................... 37

Distribution............................ .......................... ...... ......... ..... .............. ........ ........ ............. ....... ..... ............... ........ 37
Seasonal Effects. ............ ........ .......................... ............... ..... ................ ............................. ................ ................. 40
Mobilization and Transpan of Selenium ..................................................................................................................... 41

Selenium Oxidation .... ................ ......... ......................... ............................................ ....... ....... .............. ........... ............ 43
Indicators of Microbial Activity............. ...................... .......................................................... ............. ................ ........ 44
Relation of Selenium to Other Constituents ................................................................................................................ 44

Surface-Water Investigations............................... ............................... ..................... ............. ................... ................. ............. 47
Sample Collection and Analytical Methods ................................................................................................................ 47
Selenium Concentrations and Loads in the Gunnison and Colorado Rivers............................................................... 48

Selenium Concentrations........... ............... .......... .......................................................... ........ ......... ........... ......... 48
Selenium Loads ........................................ ......... ...................... ......................................... ..... ............. ............... 51
Distribution, Magnitude, and Variation of Selenium Concentrations ......................................................................... 54

Uncompahgre Project Area...... .... ................ ..... ............ ...... ................ ............. ....................... ................ .......... 54
Tributaries, Canals, and Ditches.............................................................................................................. 54

Uncompahgre River........ ....... ...................... ............ .................................... ...... ................... ........... ........ 61
Adjacent Areas in the Lower Gunnison River Basin .............................................................................. 61

Grand Valley.................................... ................ ............................. ...................................... ..................... .......... 61
Magnitude and Variation of Selenium Loads .............................................................................................................. 69

Uncompahgre Project Area ............................... ........................... .................................................... ................. 70
Grand Valley...... ............ ............... ..................... ............ ............................................... ......................... ............ 74

CONTENTS III