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

Table 1. Distribution of soil-sampling sites by geologic units in townships 01 the Uncompahgre Project area
[Numbers under geologic unil indicate the number of sites in each unil within each township; geologic units are defined as follows:
Kd. Upper CretaceOus Dakota Sandstone; KIn. Upper Creaaceous Mancos Shale; Qt. Quaternary terrace and alluvial-fan deposits;
Qrn. Quaternary (Holocene) alluvium overlying Mancos Shale: Qr. Quaternary (recent) flood-plain alluvium deposited by the
Uncompahgre River and other streams; Qd. Quaternary alluvium derived from Dakota Sandstone; --, no samples]
Townlhlp Range Geologic unR
number Townlhlp (III well) Kd Km Ql am ad
(lIg.6) ar
I 15 south 96 3 3 3 3
2 15 south 95 3 3 3 3
3 15 south 94 3 3
4 51 north II '4 3
5 51 north 10 3 3 3 3
6 5 t north 09 3 3
7 50 north II 3 3
S 50 north 10 3 3 3 3
9 50 north 09 3 3
10 49 north 10 3 3 3 3 3
II 49 north 09 3 3 3
12 49 north OS 3 3
13 4S north 10 3 'I
14 4Snorth 09 3 3 3
15 4Snorth OS 3 3
I Analytical data for all sites included for calculation of geometric means and ranges, but only first three sites ured for analysis of
variance (ANOVA).
2Analytical data included for calculation of geometric means and ranges, but not for ANOVA.

using tap water, rinsed several times in demineralized
water, redried at ambient room temperature, and
ground to pass a 2-mm screen in a Wiley mill. Each
ground sample was mixed and split, and a part was
ashed at 4500C in a muffle furnace for 24 hours.
Soils and plant ash were decomposed using a
low-temperature mixed acid digestion (Crock and
others, 1983). Solutions were analyzed simulta-
neously for 40 constituents using inductively coupled
plasma atomic-emission spectroscopy (ICP-AES)
(Crock and others, 1983). Soils and dried plant
material for arsenic and selenium determinations were
decomposed by mixed acids and hydrogen peroxide
(Crock and others, 1994). Determinations were made
by hydride-generation atomic absorption spectroscopy
(HGAAS) (Crock and Lichte, 1982; Sanzolone and
Chao, 1987).
Extractions on soils were done using deionized
water (one part soil to five parts water, by weight) by
agitation for 16 hours on a horizontal reciprocating
shaker (Stewart and others. 1990). Solutions were
clarified by centrifugation and filtration (0.45-j!m

filter). Conductivity, pH, and anion concentrations
were determined in solution by conductivity meter,
standard combination pH electrode, and ion chromato-
graph (Wilson and others, 1987; Stewart and others,
1990). A part of each solution was predigested to
oxidize organic malter, according to a modification
developed by Presser and Barnes (1985), prior to
arsenic and selenium determination by HGAAS.

Selenium Concentrations
in Soils and Alfalfa

The geometric means and ranges for total
selenium in all soil samples from the Uncompahgre
Project area and in soil samples from each geologic
unit (Crock and others, 1994) are listed in table 2.
Total-selenium concentrations in the 142 soil samples
ranged from 0.1 to 8.6j!glg (table 2). The geometric
mean selenium concentration for all soil samples was
1.4j!glg, compared to a geometric mean of 0.23 j!g1g
for Western soils (Shacklelte and Boerngen, 1984).

18 Detailed StUdy of Selenium and Other Constituents In Water. Bottom Sediment, Soli, Alfalfa, and Biota Associated with
Irrigation Drainage In the Uncompahgre Project Area and In the Grand Valley, West-Central Colorado, 1991-93