Listing of Geochemical Data and Assessment of Variability for Soils and 
Alfalfa of the Uncompahgre Project Area, Colorado

J.G. Crock

K.C. Stewart

R.C. Severson

Introduction

	The Department of Interior (DOI), in response to Congressional 
requests, formed a multi-agency task group in the fall of 1985, including 
members from the Water Resources Division (WRD) and the Geological Division 
(GD) of the U.S. Geological Survey (USGS), the U.S. Fish and Wildlife Services 
(USFWS), the U.S. Bureau of Reclamation (USBR), and the Bureau of Indian 
Affairs, to investigate and examine the potential for damage to the lands 
affected by DOI irrigation projects in the Western U.S. The objective of 
this task group is to determine if irrigation practices have the potential 
to cause harmful effects on human health, fish, wildlife, and other water 
users, or to reduce the suitability of the water for beneficial uses.

	In 1988, reconnaissance studies were completed at ten areas in the 
Western U.S. (Harms and others, 1990) where wildlife management areas received 
irrigation drainage water from federally managed irrigation projects. The 
purpose of these studies was to recognize potential problems and problem 
elements from a limited sampling of water, bottom sediments, and biota, but 
not to characterize the areas in detail.

	The Uncompahgre Project Area (UPA) in west-central Colorado was 
one of these ten study areas. The UPA includes parts of the Gunnison River and 
the Uncompahgre River basin. Currently, approximately 86,000 acres in the area 
are under irrigation. Also included in the UPA is Sweitzer Lake, a Colorado 
State Park (1.3 km southeast of Delta, CO) that has been previously reported 
to contain high levels of selenium (Se) in biota, water, and bottom 
sediments (Harms and others, 1990). Preliminary results from a 
reconnaissance study in the UPA are given in detail by Butler and others 
(1991); the results indicate that the UPA is a major source of Se and 
molybdenum (Mo) and other dissolved and suspended loads to the Gunnison and 
Uncompahgre Rivers. The Gunnison River discharges into the Colorado River at 
Grand Junction, Colorado.

	As a result of the studies by Butler and others (1991), the DOI 
task group recommended the lower Gunnison River and the Uncompahgre River 
basins for a detailed study, which was initiated in early 1991. The detailed 
studies were to meet the following goals: (1) determine whether irrigation-
induced water-quality problems exist, and if so, (2) provide the scientific 
understanding to mitigate or resolve identified problems.

	The USBR Uncompahgre Irrigation Project supplies water to irrigate 
land primarily in the Uncompahgre River basin between Colona and Delta, 
Colorado (figure 1). Irrigation in the study area dates to the late 1800's 
when over 30,000 acres were irrigated with water diverted from the Uncompahgre 
River by 1890. Additional irrigation was possible with the completion of the 
Gunnison Tunnel in 1909 which brought additional water into the UPA from the 
Gunnison River. The diversion dam on the Gunnison River was completed in 1912. 
Additional canals were later completed and the UPA reached its present size. 
The Taylor Park Reservoir and the Ridgway Reservoir also added to the 
storage capacity for the UPA. Irrigated crops in the UPA include onions, 
broccoli, beans, potatoes, barley, sweet corn, alfalfa, feed corn, hay, 
various small grains, and fruit orchards.

	This report describes the results of the detailed study of the UPA 
conducted by the USGS-GD personnel during 1991-92. The specific objectives 
of this report are to: (1) determine the chemical composition and 
variability of the irrigated, agricultural soils developed on various parent 
geologic units within UPA; and (2) estimate the availability of mobile element 
fractions and its variability among geologic units by sampling and analyzing 
alfalfa from each soil sampling locality. Selenium is a primary element of 
concern, however, other elements will also be reported and investigated. 
This report addresses only the total element concentrations in both the 
soils and alfalfa and their inter-relations. Extractable, or water-soluble, 
element concentrations and their relationships with the total soil and alfalfa 
elemental contents are addressed in Stewart and others (1993).

	Studies by other scientists of the USGS, USFWS, and USBR are being 
conducted to: (1) determine the sources, distribution, movement, and fate of 
contaminants within the hydrologic and biota systems; and (2) measure 
contaminant concentrations, determine exposure pathways, and document 
effects as seen in biota.