WSP08083

• File Number: 8220.114.I
• Description: Dolores Participating Project
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 1/1/1977
• Author: USGS
• Title: Field Screening of Water/Soil/Bottom Sediment and Biota Associated with Irrigation Drainage in the Dolores Project and Mancos River Basin - Southwestern Colorado - 1994
• Water Supply Pro - Doc Type: Report/Study

per liter. Mud Creek contributed about 74 percent
of the selenium load to the upper Mancos River in
March 1994. Selenium concentrations were much
higher in Navajo Wash; a sample collected in
March had 97 micrograms per liter of selenium.
Bottom-sediment samples from two ponds in the
Mancos Project exceeded the concentration of
concern of 4 micrograms per gram.
The highest selenium concentrations in
biota samples from streams in the Mancos River
Basin were for samples from Navajo Wash. Most
concentrations in biota in the upper Mancos River
Basin were less than guidelines. Mean selenium
concentrations in eggs from aquatic birds
collected at three ponds in the Mancos Project
slightly exceeded the guideline associated with
reduced hatchability. Five bird livers had a mean
selenium concentration of 32.6 micrograms per
gram dry weight, which slightly exceeded the
mean concentration of 30 micrograms per gram
dry weight that is associated with reproductive
impairment. Two of the ponds had a high
selenium-hazard rating; however, mallard
reproduction was observed in 1994 at one of the
ponds that had a high selenium-hazard rating.

INTRODUCTION

During 1990-91, water, bottom-sediment, and
biota samples were collected for a reconnaissance
investigation of the Dolores Project area in
southwestern Colorado (fig. I). The investigation was
part of the National Irrigation Water Quality Program
(NIWQP), which was started by the U.S. Department
of the Interior in 1985 to identitY the nature and extent
of irrigation-induced water-quality problems in the
Western United States. Results of the reconnaissance
investigation were published in Butler and others
(1995).

Background

Selenium was elevated in some water, bottom-
sediment, and biota samples collected in 1990 in the
Dolores Project area (Butler and others, 1995). Many

of the water and biota samples collected in the newly
irrigated area (since 1987) of the Dolores Project
between Cortez and Dove Creek (the Dove Creek
area in fig. 1) had elevated selenium concentrations.
Samples of irrigation drainage from three washes in
the Dove Creek area had selenium concentrations
ranging from 3 to 12 14g/L (Butler and others, 1995).
Selenium concentrations in 10 of 11 aquatic-
invertebrate samples from the Dove Creek area
exceeded a guideline for food items consumed by
fish and wildlife. Selenium in bird eggs was in the
range of uncertainty for biological risk. The highest
selenium concentration in a biota sample collected
for the study in 1990 was 37.5 l1g/g dry weight in a
mallard liver collected from a pond in Woods Canyon
in the newly irrigated area of the Dolores Project
(fig. 1).
The long-lenn irrigated area of the Dolores
Project is the service area of the Montezuma Valley
Irrigation Company (MVIC) shown in figure 1. The
MVIC area also was sampled in 1990, and generally,
selenium concentrations in water, bottom sediment,
and bi!>ta were not elevated in samples collected from
streams and ponds north of Mc Elmo Creek (Butler
and others, 1995). However, samples from Navajo
Wash, which receives irrigation drainage from
areas on Mancos Shale in the southern part of the
Montezuma Valley, had high selenium concentrations.
The maximum selenium concentration in water
samples collected for the reconnaissance investigation
was 88 14g/L in a sample from Navajo Wash (Butler
and others, 1995).
Selenium concentrations were elevated in some
water and biota samples collected from the lower
Mancos River in 1990 (Butler and others, 1995).
During 1989, the U.S. Fish and Wildlife Service
(USFWS) collected biota samples at five sites in the
Mancos River Basin, and some samples had selenium
concentrations that exceeded guideline concentrations.
Bird livers collected from a pond in the irrigated
area of the Mancos Project (fig. I) in 1989 had high
selenium concentrations; one liver had a concentration
of 69 l4g/g dry weight (Butler and others, 1995).
No sampling was done in the upper part of the basin
in the Mancos Project area for the reconnaissance
investigation in 1990.

2 FIeld ScrMnlnll of W_, SoIl, Botlom Secllm8ll1, end Blo,," Auoclellld with Irrlgallon Dnllnege In the Dolo.- ProJ80t
..d the Mule... River Belin, SouthwMlllm Coloredo, 1994