*U.S. Department of the Interior
National Irrigation Water Quality Program
U.S. Geological Survey*

## Using Geochemical and Statistical Tools
to Identify Irrigated Areas That Might
Contain High Selenium Concentrations in
Surface Water

|Irrigated agriculture has a long history in the Western United States,
beginning with Native American Indians. After passage of the Reclamation
Act of 1902, the United States Government began building and subsidizing
irrigation projects to foster settlement and development of the arid and
semi-arid areas of the Western United States (National Research Council,
1989). Precipitation in the mountainous areas of the West (fig. 1) is stored
in reservoirs and used for irrigation of farmland. With the development
of irrigated agriculture, unforeseen environmental problems have 
occurred.*(Click on image for a larger version, 211K)***Figure 1.** U.S. Geological Survey hydrologist and able
assistant surveying Upper Fremont Glacier in the Wind River Range of Wyoming.
This glacier is a source of irrigation water to the Riverton Reclamation
Project in central Wyoming.As an example, concern is increasing about the quality of surface and
subsurface water draining from irrigated land and the potential effects
of irrigation drainage on human health, fish, and wildlife. Incidences of
mortality, congenital defects, and reproductive failures in waterfowl were
discovered by the U.S. Fish and Wildlife Service
in 1983 at Kesterson National Wildlife Refuge in western San Joaquin Valley,
California. Because of concern about possible adverse effects from irrigation
drainage elsewhere in the United States, the U.S.
Department of the Interior (DOI) implemented the National
Irrigation Water Quality Program (NIWQP) in 1985 and to date (1996)
has evaluated 26 DOI irrigation projects in the Western United States (fig.
2). | *(Click on image for a larger version, 211K)* | **Figure 1.** U.S. Geological Survey hydrologist and able
assistant surveying Upper Fremont Glacier in the Wind River Range of Wyoming.
This glacier is a source of irrigation water to the Riverton Reclamation
Project in central Wyoming. | *(Click on image for a larger version, 
127K)***Figure 2.** Location of National Irrigation Water Quality
Program study areas, 1986-96.Initial evaluation of the data from the NIWQP study areas indicates that
selenium is the constituent most commonly found at elevated concentrations
in water, bottom sediment, and biota (Feltz and others, 1991; Presser and
others, 1994; and Presser, 1994). Because of these consistently elevated
concentrations of selenium, factors controlling the occurrence of selenium
in water need to be better defined. Water-quality data collected from the
NIWQP study areas throughout the Western United States provide an opportunity
to determine important and regionally significant geochemical sources and
processes that control the concentration of selenium in irrigation drainwater.
This information can then be used to predict where other "selenium
problem areas" might occur in other parts of the Western United States
and can be extrapolated to irrigated areas around the 
world. | *(Click on image for a larger version, 
127K)* | **Figure 2.** Location of National Irrigation Water Quality
Program study areas, 1986-96.
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|*(Click on image for a larger version, 211K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Figure 1.** U.S. Geological Survey hydrologist and able
assistant surveying Upper Fremont Glacier in the Wind River Range of Wyoming.
This glacier is a source of irrigation water to the Riverton Reclamation
Project in central Wyoming.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|*(Click on image for a larger version, 
127K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|**Figure 2.** Location of National Irrigation Water Quality
Program study areas, 1986-96.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

## Geochemical and Statistical Tools Used to Identify Surface Water with
Elevated Concentrations of Selenium

|The NIWQP summary data base contains results of thousands of water-quality
analyses and each analysis includes many different physical and chemical
properties, such as water temperature and selenium concentration. Geochemical
and statistical techniques can be used to extract information from this
large multivariate data set. For example, concentration of chemicals such
as major ions might be used to predict whether or not a water sample from
an irrigated area contains an elevated concentration of selenium.

The geochemical computer program SNORM (Bodine and Jones, 1986) was the
"geochemical tool" used to calculate concentrations of simple
salts from the results of the chemical analyses of surface-water samples
from NIWQP study sites. The 12 different simple-salt concentrations calculated
with the SNORM program for each water sample are representative of the minerals
("salts") that would remain after a water sample was completely
evaporated. To evaporate the thousands of water samples collected at all
the NIWQP study areas and determine the amount and type of salt remaining
would be quite labor intensive; instead, the SNORM computer program simulates
this evaporation almost instantly. The abundance and type of simple salts
calculated with the SNORM program provides useful geochemical information
on what kind of minerals (selenium or non-selenium bearing) the water might
have contacted and partially dissolved. This is analogous to determining
where a person lives on the basis of his or her accent. | After the concentrations of simple salts were calculated for the thousands
of NIWQP water samples, the next step was to determine if groupings of simple
salts could characterize water samples with high or low selenium concentrations.
A "statistical tool" called pattern-recognition modeling (Meglen
and Sistko, 1985) was used to evaluate the large simple-salt data base generated
with the SNORM computer program. Pattern-recognition modeling techniques
enhance the interpretation of large multivariate data bases such as the
one used in the NIWQP data synthesis study. Pattern-recognition modeling
uses statistical and graphical techniques to "chemically fingerprint"
the groups of simple salts representing different types of minerals (selenium
or non-selenium bearing) that might have contacted and partially dissolved
in water sampled during the NIWQP. The selenium concentration for all the
NIWQP samples was already known; thus, calculating the association between
the simple-salt group and the selenium concentrations in water samples was
explicit. This simple-salt group/selenium association could then be applied
to other areas in the Western United States for which selenium concentrations
in water were not measured to predict if selenium toxicity problems might
exist.
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

## Pattern-Recognition Modeling of Simple-Salt Data Identifies Samples
with Elevated Selenium Concentrations

|A three-dimensional plot showing the results of the pattern-recognition
modeling of the simple-salt data generated from the NIWQP data base is shown
in figure 3A. The three axes are linear combinations of the original simple-salt
data set and can be thought of as a new set of plotting axes. Instead of
each axis representing the concentration of a particular simple salt, each
axis represents combinations of the simple salts, thereby representing a
property of interest (affected by the type and amount of many simple salts).
In this particular application, the property of interest is the types and
amounts of simple salts that would most likely identify water samples with
high or low concentrations of selenium.*(Click on image for a larger version, 71K)***Figure 3.** Results of pattern-recognition modeling of
the National Irrigation Water Quality Program data base.The individual points in figure 3A show where the simple salts for each
of the NIWQP water samples plot on these newly defined axes. The points
are grouped into three distinct clusters when viewed in three dimensions
and are classified as groups 1, 2, and 3. Water samples in group 1 have
the greatest percentage of selenium concentrations higher than 5 micrograms
per liter (\f5 m\f4 g/L) (fig. 3B). Group 1 samples are distinguished from
group 2 and 3 samples by elevated concentrations of the sulfate simple salts
and sodium chloride simple salt combined with very low concentrations of
the calcium carbonate simple salt. On the basis of the simple salt "chemical
fingerprint" for group 1 samples, selenium is mobilized during irrigation
by the oxidation of sulfide minerals or re-solution of sulfate salts that
have selenium substituted for sulfate in the mineral structure. | *(Click on image for a larger version, 71K)* | **Figure 3.** Results of pattern-recognition modeling of
the National Irrigation Water Quality Program data base. | *(Click on image for a larger version, 103K)***Figure 4.** Proportion of samples from each National Irrigation
Water Quality Program study area falling within the group 1 scores cluster
and groups 2 and 3 scores cluster shown in figure
3A.Simple-salt groupings that identify water samples with elevated selenium
concentrations also are evident at individual NIWQP study areas. The majority
of study areas with at least 25 percent of water samples belonging to the
group 1 simple-salt association consistently contained the greatest percentage
of samples with selenium concentrations higher than 2.0 \f5 m\f4 g/L (fig.
4). With the exception of the Riverton Reclamation Project, Tulare Lake
Bed Area, and Salton Sea Area, all study areas have irrigated soils developed
on upper Cretaceous marine sediments. These sediments contain the necessary
sulfide minerals required for sulfide weathering reactions, and the resulting
simple-salt "chemical fingerprint" for group 1 sites. Most study
areas with at least 75 percent of water samples classified in groups 2 or
3 consistently contain the greatest percentage of samples with selenium
concentrations less than 2.0 \f5 m\f4 g/L (fig. 4) and do not have irrigated
soils developed from upper Cretaceous marine sediments. On the basis of
these pattern-recognition modeling results, the simple-salt "chemical
fingerprint" of water samples can help differentiate samples with elevated
selenium concentrations from samples with low selenium concentrations. | *(Click on image for a larger version, 103K)* | **Figure 4.** Proportion of samples from each National Irrigation
Water Quality Program study area falling within the group 1 scores cluster
and groups 2 and 3 scores cluster shown in figure
3A.
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------- | ----------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|*(Click on image for a larger version, 71K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Figure 3.** Results of pattern-recognition modeling of
the National Irrigation Water Quality Program data base.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|*(Click on image for a larger version, 103K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|**Figure 4.** Proportion of samples from each National Irrigation
Water Quality Program study area falling within the group 1 scores cluster
and groups 2 and 3 scores cluster shown in figure
3A.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

## Classification Model Successfully Identifies Surface Water with Elevated
Concentrations of Selenium in Utah and Wyoming

|Pattern-recognition modeling of the simple-salt data has indicated that
selenium- and non-selenium-producing areas can be identified using only
simple-salt data calculated with the SNORM geochemical program. On the basis
of these results, a classification program called Soft Independent Modeling
by Class Analogy (Wold and Sjostrom, 1977), or SIMCA for short, was applied
to the NIWQP simple-salt data set to construct a classification model. Once
constructed, the classification model can be used to determine the selenium-producing
potential of areas with unknown or poorly known selenium concentrations
in water samples.

The first step in building a SIMCA classification model is to "train"
the model to recognize the sample groups to be classified by the simple-salt
concentrations. The data are referred to as a training data set and consist
of the NIWQP data set used in the pattern-recognition modeling described
previously, with each of the samples classified according to groups 1, 2,
or 3 (fig. 3A). After the classification
model is constructed and optimized with the training data set, the model
is ready to classify unknown samples in what is termed a "test"
data set. | The test data set used to evaluate the performance of the SIMCA model
consisted of data from more than 2,000 samples of surface water from Wyoming
and Utah compiled from the National Water Data Storage and Retrieval (WATSTORE)
System of the U.S. Geological Survey. Data from Wyoming and Utah were selected
because of the diverse geologic environments represented in these areas
and the documented presence of selenium in surface-water samples. The model
classified more than 75 percent of the samples with elevated selenium concentrations
(higher than 2.0 \f5 m\f4 g/L) correctly into group 1. More than 80 percent
of the samples with low selenium concentrations were correctly classified
into groups 2 or 3.
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

## Classification Model Can Be Used to Assess Other Irrigated 
Areas

|The demonstrated use of the classification model in differentiating selenium-producing
areas from non-selenium-producing areas indicates that the model can be
applied successfully to areas where selenium concentrations have not been
determined. Numerous circumstances contribute to the lack of selenium data
for water samples. Examples of the applicability of the model include (1)
areas within the United States or other countries that might be expanding
agriculture and where there is a limited selenium data base; (2) situations
in which the analytical reliability of selenium data from an area might
be in question but the major-ion data used to calculate the simple-salt
data are of good quality; and (3) situations in which the concentrations
of selenium and other chemical constituents are determined simultaneously
and the detection limits for selenium are so high that only the very high
concentrations of selenium are measured. | *(Click on image for a larger version, 114K)*Shocking fish at Stewart Lake, Wildlife Management Area near Vernal,
Utah. Stewart Lake is the Middle Green River Basin, Utah, study area.*(Click on image for a larger version, 170K)*Gill-netting operations during reconnaissance-phase investigations at
a wetland site in the Middle Green River Basin, Utah, study area. | *(Click on image for a larger version, 114K)* | Shocking fish at Stewart Lake, Wildlife Management Area near Vernal,
Utah. Stewart Lake is the Middle Green River Basin, Utah, study area. | *(Click on image for a larger version, 170K)* | Gill-netting operations during reconnaissance-phase investigations at
a wetland site in the Middle Green River Basin, Utah, study area.
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ | --------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------
|*(Click on image for a larger version, 114K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Shocking fish at Stewart Lake, Wildlife Management Area near Vernal,
Utah. Stewart Lake is the Middle Green River Basin, Utah, study area.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|*(Click on image for a larger version, 170K)*                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Gill-netting operations during reconnaissance-phase investigations at
a wetland site in the Middle Green River Basin, Utah, study area.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

## Sources of Additional Information

|The following publications contain additional information on the occurrence
of selenium in irrigation drainwater and the geochemical and statistical
tools used to identify and predict the occurrence of selenium-producing
landscapes. Details on pattern-recognition and classification modeling of
the NIWQP data sets can be found in Naftz (in press).


Bodine, M.W., and Jones, B.F., 1986,
The salt norm: A quantitative chemical- mineralogical characterization
  of natural waters: U.S. Geological Survey Water- Resources Investigation
  Report 86-4086, 130 p.Feltz, H.R., Sylvester, M.A., and Engberg, R.A., 1991,
Reconnaissance investigations of the effects of irrigation drainage
  on water quality, bottom sediment, and biota in the Western United States,*in*Mallard, G.E., and Aronson, D.A., eds., Proceedings of the U.S.
  Geological Survey Toxic Substance Hydrology Program, Monterey, Calif.,
  March 11-15, 1991: U.S. Geological Survey Water-Resources Investigations
  Report 91-4034, p. 319-323.Meglen, R.R., and Sistko, R.J., 1985,
Evaluating data quality in large data bases using pattern-recognition
  techniques, *in* Breen, J.J., and Robinson, P.E., eds., Environmental
  Application of Chemometrics, American Chemical Society Symposium Series
  292, Wash., D.C., American Chemical Society, p. 18-33. | Naftz, D.L., in press,
Pattern-recognition analysis and classification modeling of selenium-producing
  areas: Journal of Chemometrics.National Research Council, 1989,
  Irrigation- induced water quality problems, Wash., D.C., National Academy
  Press, 157 p.Presser, T.S., 1994,
  The Kesterson effect: Environmental Management, v. 18, no. 3, p. 437-455.Presser, T.S., Sylvester, M.A., and Low, W.H., 1994,
  Bioaccumulation of selenium from natural geologic sources in Western
  States and its potential consequences: Environmental Management, v. 18,
  no. 3, p. 423-436.Wold, Svante, and Sjostrom, Michael, 1977,
  SIMCA: A method for analyzing chemical data in terms of similarity
  and analogy, *in* Kowalski, B.R., ed., Chemometrics Theory and Application,
  American Chemical Society Symposium Series 52, Wash., D.C., American Chemical
  Society, p. 243-282.
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Information on technical reports and hydrologic data related to the National
Irrigation Water Quality Program can be obtained from:



*--David L. Naftz*

> *from U.S. Department of the Interior, U.S. Geological Survey, Fact
>   Sheet FS-077-96*



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### For more information contact any of the following:

- More information on the National Irrigation Water Quality 
  Program is located on their World Wide Web at 
  http://www.usbr.gov/niwqp/
- For more information on all USGS reports and products (including
  maps, images, and computerized data), call 1-888-ASK-USGS

### This fact sheet is available in two formats:

- For more information on the fate of contaminants in the environment
  check out the USGS's Toxic Substances
  Hydrology Program home page.



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