U.S. Department of the Interior

U.S. Geological Survey

National

Water-Quality

Assessment

Program

Collection and Analysis of Ground-Water Samples

in the Sierra Vista Basin, Arizona, 1996

(A Cooperative Program Between the USGS and the

Arizona Department of Environmental Quality)

Introduction

In 1996, the U.S. Geological Survey

(USGS) and the Arizona Department of

Environmental Quality (ADEQ)

completed a cooperative ground-water

data-collection program in the Sierra

Vista ground-water basin of southeastern

Arizona. This Federal-State cooperative

effort fulfilled the goals of both

programs, increased the number of

ground-water samples and associated

data available to each agency, and

provided an opportunity for quantifying

differences between the agencies’

sampling and analytical techniques.

Sampling in the Sierra Vista Basin by

the USGS was part of the National

Water-Quality Assessment Program

(NAWQA) for the Central Arizona

Basins (CAZB) study area. The goals of

the NAWQA program include providing

a nationally consistent description of

current water-quality conditions for a

large part of the Nation’s water

resources, defining long-term trends in

water quality, and understanding the

natural and human factors that affect

water quality (Gilliom and others, 1995).

In 1994, the USGS began ground-water,

surface-water, and biological studies in

the CAZB study area. Ground-water

studies within the CAZB study area are

focused on basins in which water quality

has been substantially affected by human

activities or has the potential to be

substantially affected.

Sampling by the ADEQ was

completed as a part of the Ambient

Groundwater Monitoring Program,

which is based on the legislative

mandate in the Arizona Revised Statutes

§49-225 (Arizona Department of

Environmental Quality, 1995) that

authorizes the “ongoing monitoring

of the wa t e rs of the St a t e ,

including...aquifers.” Objectives of this

mandate include determining the

presence of pollutants and compliance

with applicable water-quality standards,

evaluating the effectiveness of the best

management practices and effects of

National Water-Quality Assessment Program (NAWQA) of the U.S. Geological Survey

and Arizona Department of Environmental Quality (ADEQ) ground-water sampling

sites in the Sierra Vista Basin part of the Central Arizona Basins (CAZB).

0 10 MILES

EXPLANATION

GROUND-WATER

SAMPLING SITES

BEDROCK

SPRING—ADEQ sample

WELLS

ADEQ sample

USGS sample

Split sample

Split sample (does not

represent a specific

equal-area cell)

0 10 KILOMETERS

Fort

Huachuca

Sierra

Vista

UNITED STATES

MEXICO

32°

31°30'

110°30'

110°

Pedro

River San

Bisbee

Benson

Sierra

Vista

Basin Sierra

Vista Basin

Central

Arizona

Basins

The assessment was based on data

collected between 1971 and 1996 for 23

wells with available depth, perforation

interval, and major-ion chemistry.

Analyses having a cation/anion balance

with a difference greater than 5 percent

were not used in the assessment. The

selected analyses indicated that cation

content in ground water was primarily

more than 50-percent calcium, and anion

content was primarily more than

50-percent bicarbonate. The sulfate

concentration in one analysis exceeded

the U.S. Environmental Protection

Agency maximum contaminant level for

drinking water, and the fluoride

concentration in one analysis exceeded

the secondary maximum contaminant

level for drinking water (U.S.

Environmental Protection Agency,

1996).

Tombstone

pollutants on public health and the

environment, and identifying waterquality trends. Random sampling on a

basin -wide basis is used by the

Ambient Groundwater Monitoring

Program to determine regional groundwater quality; targeted higher-density

sampling that is related to specific land

uses is conducted to determine potential

effects on ground-water quality.

Retrospective Data

A retrospective assessment of

ground-water quality in the Sierra Vista

Basin was completed by the USGS

before the cooperative data-collection

effort began by using the USGS waterq u a lit y d a t a b a s e (DGNWIS).
Methods

The USGS and ADEQ each planned

to sample 20 wells as part of the

cooperative data-collection effort. To

ensure that the wells chosen for sampling

were randomly distributed throughout the

Sierra Vista Basin, computer software

(Scott, 1990) was used to subdivide the

basin into 20 equal-area polygons,

referred to as cells. Within each cell,

primary, secondary, and tertiary points

were randomly assigned by the computer

software. Different sets of random points

within each cell were used by the ADEQ

and USGS.

Wells within approximately a 1-mile

radius of each primary point were

identified and randomly ordered. The wells

then were visited sequentially to determine

if they were suitable for sampling. If none

of the wells within a 1-mile radius of the

primary point were adequate, wells around

the secondary point were identified and

randomly ordered. A well was suitable for

sampling if it had a submersible pump, a

sampling point before water entered

storage tanks, and a measuring point to

determine depth to water; if construction

information (depth, perforated interval,

casing diameter, and driller's log) was

available, and if the well owner gave

permission to sample. The wells selected

were for public, domestic, and livestock

use.

The USGS followed NAWQA groundwater sampling protocols and procedures

(Koterba and others, 1995) to quantify and

minimize measurement bias and variability

associated with the data-collection process.

Quality-control samples (blanks, spikes,

and replicates) were collected along with

the environmental samples. The ADEQ

ground-water sampling protocols and

procedures for this study conformed to the

Quality Assurance Project Plan (Arizona

Department of Environmental Quality,

1991) and the Field Manual For Water

Quality Sampling (Arizona Water

Resources Research Center, 1995).

Both agencies planned to collect

additional quality-control samples, referred

to as “split samples,” at a subset of wells.

The split-sample well locations were to be

selected by the ADEQ and represent

ADEQ equal-area cells. NAWQA groundwater sampling protocols and procedures

were to be followed by ADEQ and USGS

for most of the split samples; and one

split sample was to be collected with each

agency following their respective

protocols to determine if a difference was

detectable.

Federal-State Data Collection

The USGS sampled one well in 19 of

the 20 cells; no suitable well was found

in one cell in the northeastern corner of

the basin. ADEQ also sampled a well in

each of the 19 cells; a spring was

sampled in the cell where no suitable

well was available.

Split samples were collected by the

USGS and ADEQ at 6 of the ADEQ’s 19

wells. An additional split sample was

collected at a well not used to represent

a specific equal-area cell.

Ground water from each well was

analyzed for a large number of chemical

constituents and physical properties (see

table). Chemical analyses included as

part of both agencies’ programs were

performed on split samples. Samples

collected by the USGS were analyzed by

the USGS National Water-Quality

Laboratory in Arvada, Colorado.

Samples collected by the ADEQ were

analyzed by the Arizona Department of

Health Services Laboratory in Phoenix,

Arizona.

This Federal-State effort allowed the

USGS and ADEQ to collect more data

than either agency could have collected

alone. These additional data will result in

comprehensive findings that will benefit

both participating agencies and the

general public.

—Alissa Coes and Dorinda Gellenbeck

(USGS), and Doug Towne (ADEQ)

Volatile organic compounds

Dissolved organic carbon

Pesticides

Radon

Isotopes of hydrogen and

oxygen

Field parameters (pH,

dissolved oxygen,

specific conductance,

temperature, turbidity,

alkalinity, acidneutralization

capacity)

—

—

—

—

—

Field parameters (pH,

specific conductance,

temperature)

—

—

—

—

—

Field parameters (pH,

specific conductance,

temperature)

Analyses completed in Sierra Vista Basin during cooperative data-collection effort

[— , not analyzed for]

USGS ADEQ Split samples

Major ions

Trace elements

Nutrients

Major ions

Trace elements

Nutrients

Major ions

Trace elements

Nutrients

References

Arizona Department of Environmental Quality,

1991, Quality assurance project plan: Phoenix,

Arizona, Arizona Department of Environmental

Quality, Water Quality Standards Unit, 209 p.

——1995, Arizona laws relating to environmental

quality: Charlottesville, Virginia, Michie

Company, 200 p.

Arizona Water Resources Research Center, 1995,

Field manual for water-quality sampling:

Tucson, Arizona, University of Arizona College

of Agriculture, 51 p.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995,

Design of the National Water-Quality

Assessment Program—Occurrence and distribution of water-quality conditions: U.S.

Geological Survey Circular 1112, 33 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W.,

1995, Ground-water data-collection protocols

and procedures for the National Water-Quality

Assessment Program—Collection and documentation of water-quality samples and related

data: U.S. Geological Survey Open-File Report

95–399, 113 p.

Scott, J.C., 1990, Computerized stratified random

site-selection approaches for design of a groundwater-quality sampling network: U.S.

Geological Survey Water-Resources

Investigations Report 90 – 4101, 109 p.

U.S. Environmental Protection Agency, 1996,

National primary drinking water regulations:

U.S. Code of Federal Regulations, Title 40,

Parts 141 and 143, revised as of July 1, 1996, p.

p. 288–429 and p. 470– 473.

For more information contact:

District Chief

U.S. Geological Survey

520 N. Park Avenue, Suite 221

Tucson, Arizona 85719

(520) 670-6671

http://wwwdaztcn.wr.usgs.gov

USGS Fact Sheet

August 1997 FS-107-97