U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 03–4316

Prepared in cooperation with the

KANSAS WATER OFFICE

Summary of Available State Ambient Stream-WaterQuality Data, 1990−98, and Limitations for National 

Assessment
Summary of Available State Ambient 

Stream-Water-Quality Data, 1990–98, and 

Limitations for National Assessment

By Larry M. Pope, Stacy M. Rosner, Darren C. Hoffman, and Andrew C. Ziegler

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

KANSAS WATER OFFICE

Water-Resources Investigations Report 03–4316
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

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Telephone: 1-888-ASK-USGS

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endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Pope, L.M., Rosner, S.M., Hoffman, D.C., and Ziegler, A.C., 2004, Summary of available State ambient stream-waterquality data, 1990–98, and limitations for national assessment: U.S. Geological Survey Water-Resources 

Investigations Report 03–4316, 55 p.

Prepared by the U.S. Geological Survey in Lawrence, Kansas (http://ks.water.usgs.gov)
 iii

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

General Investigative Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Selection of Water-Quality Constituents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Selection of Time Period and Acquisition of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Data Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Quality Assurance of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Summary of Available State Ambient Stream-Water-Quality Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Suspended Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fecal Coliform Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Ammonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Nitrite Plus Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Dissolved Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Sulfate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Limitations of State Ambient Stream-Water-Quality Data for National Assessment . . . . . . . . . . . . . . . . . . . . . . . . . 30

Design of Monitoring Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Selection of Water-Quality Constituents and Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Quantity and Comprehensiveness of Water-Quality Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figures

1. Schematic showing general procedures and decision processes used for data acquisition, handling, 

and summary ofState ambient stream-water-quality monitoring sites for selected water-quality consitituents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2. Graphs showing relations between numbers of ambient stream-water-quality monitoring sites and 

selected minimum numbers of electronically available data for 10 water-quality constituents or

measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3. Graph showing relation between the national average percentage of monitoring sites for 10 waterquality constituentsor measurementsand selected minimum numbers of electronicallyavailable 

data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
iv 

Tables

1. Water-quality constituents and physical measurements considered for summary . . . . . . . . . . . . . . . . . .4

2. Number of ambient stream-water-quality monitoring sites per State with electronically available 

data for at least one of the selected water-quality constituents or measurements and source of 

data and Internet uniform resource locator, 2001–02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

3. Total miles of streams in the States and percentage assessed for water-quality degradation in 

1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

4. Constituent or measurement descriptions and parameter codes for data retrieved from 

U.S. EnvironmentalProtection Agency, U.S. Geological Survey, or State databases . . . . . . . . . . . . . . . . .8

5. Data remark codes and descriptions and statistical summary action for remarked water-quality data 

from the U.S. EnvironmentalProtection Agency STORET, U.S. Geological Survey National Water 

Information System, or State data-management systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6. Summary of median suspended solids concentrations in water from State ambient stream-waterqualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7. Number of State ambient stream-water-quality monitoring sites with data for parameter codes 

of fecal coliform bacteria densities in water, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8. Summary of median fecal coliform bacteria densities in water from State ambient stream-waterqualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9. Number of State ambient stream-water-quality monitoring sites with data forparameter codes 

of ammonia as nitrogen concentrations in water, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

10. Summary of median ammonia as nitrogen concentrations in water from State ambient streamwater-quality monitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

11. Number of State ambient stream-water-quality monitoring sites with data forparameter codes of 

nitrate and nitrite plus nitrate as nitrogen concentrations in water, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . 19

12. Summary of median nitrite plus nitrate as nitrogen concentrations in water from State ambient 

stream-water-quality monitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

13. Summary of median total phosphorus concentrations in water from State ambient streamwater-quality monitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

14. Summary of median total arsenic concentrations in water from State ambient stream-waterqualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

15. Number of State ambient stream-water-quality monitoring sites with data forparametercodes of 

dissolved-solids concentrations in water, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

16. Summary of median dissolved-solids concentrations in water from State ambient stream-waterqualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

17. Number of State ambient stream-water-quality monitoring sites with data fortotal and 

dissolved chloride concentrations in water, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

18. Summary of median chloride concentrations in water from State ambient stream-waterqualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

19. Number of State ambient stream-water-quality monitoring sites with data fortotal and dissolved 

sulfate concentrations in water, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

20. Summary of median sulfate concentrations in water from State ambient stream-water 

qualitymonitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

21. Summary of median pH measurements in water from State ambient stream-water-quality 

monitoring sites, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

22. Selected water-quality criteria for State ambient stream-water-quality data . . . . . . . . . . . . . . . . . . . . . . 35

23. Fecal coliform bacteria criteria for primary and secondary contact recreation for streams in

50States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
 v

24. Number of State ambient stream-water-quality monitoring sites available for selected 

combinations of water-quality constituentsper monitoring site and analyses per constituent, 

1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

25. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for suspended solids, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

26. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for fecal coliform bacteria, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

27. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for ammonia as nitrogen, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

28. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for nitrite plus nitrate as nitrogen, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

29. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for total phosphorus, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

30. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for total arsenic, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

31. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for dissolved solids, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

32. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for chloride, 1990–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

33. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for sulfate, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

34. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for pH, 1990–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
vi 

Conversion Factors, Abbreviations, and Datum

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32) / 1.8.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

microgram per liter (μg/L) 1.0 part per billion (ppb)

micrometer (μm) 0.00003937 inch (in.)

milligram per kilogram (mg/kg) 0.002 pound per ton (lb/ton)

milligram per liter (mg/L) 1.0 part per million (ppm)

milliliter (mL) 0.0338 ounce, fluid (oz)

pound per acre (lb/acre) 1.121 kilogram per hectare (kg/ha)

square mile (mi2) 2.590 square kilometer (km2)
Summary of Available State Ambient Stream-WaterQuality Data, 1990–98, and Limitations for National 

Assessment

By Larry M. Pope, Stacy M. Rosner, Darren C. Hoffman, and Andrew C. Ziegler

Abstract

The investigation described in this report summarized data 

from State ambient stream-water-quality monitoring sites for 

10 water-quality constituents or measurements (suspended solids, fecal coliform bacteria, ammonia as nitrogen, nitrite plus 

nitrate as nitrogen, total phosphorus, total arsenic, dissolved 

solids, chloride, sulfate, and pH). These 10 water-quality constituents or measurements commonly are listed nationally as 

major contributors to degradation of surface water. Waterquality data were limited to that electronically accessible from 

the U.S. Environmental Protection Agency Storage and 

Retrieval System (STORET), the U.S. Geological Survey 

National Water Information System (NWIS), or individual 

State databases. Forty-two States had ambient stream-waterquality data electronically accessible for some or all of the constituents or measurements summarized during this investigation. “Ambient” in this report refers to data collected for the 

purpose of evaluating stream ecosystems in relation to human 

health, environmental and ecological conditions, and designated uses. Generally, data were from monitoring sites assessed 

for State 305(b) reports.

Comparisons of monitoring data among States are problematic for several reasons, including differences in the basic 

spatial design of monitoring networks; water-quality constituents for which samples are analyzed; water-quality criteria to 

which constituent concentrations are compared; quantity and 

comprehensiveness of water-quality data; sample collection, 

processing, and handling; analytical methods; temporal variability in sample collection; and quality-assurance 

practices. Large differences among the States in number of 

monitoring sites precluded a general assumption that statewide 

water-quality conditions were represented by data from these 

sites. Furthermore, data from individual monitoring sites may 

not represent water-quality conditions at the sites because sampling conditions and protocols are unknown. Because of these 

factors, a high level of uncertainty exists in a national assessment of water quality.

 The purpose of this report is to present a summary of electronically available State ambient stream-water-quality data for 

10 selected constituents and measurements from monitoring 

sites with nine or more analyses for 1990–98 and to discuss limitations for use of the data for national assessment. These analyses were statistiscally summarized by monitoring site and 

State, and the results presented in tabular format. Most of the 

selected constituents or measurements have U.S. Environmental Protection Agency criteria or guidelines for aquatic-life or 

drinking-water purposes. A significant finding of this investigation is that for a large percentage of monitoring sites in the 

Nation, there are insufficient data to meet U.S. Environmental 

Protection Agency recommendations for determining if waterquality conditions are degraded and for making informed decisions regarding total maximum daily loads.

Introduction

In 1972, Congress passed the Federal Water Pollution 

Control Act (Public Law 92–500), commonly referred to as the 

Clean Water Act (U.S. Environmental Protection Agency, 

1972). This act and subsequent amendments set goals for eliminating the discharge of contaminants into the Nation’s waters, 

provided Federal funding for construction of municipal sewagetreatment plants, directed the States to set water-quality criteria 

for waters within their boundaries, and funded development of 

programs to control nonpoint sources of contamination. The act 

also directed the States to submit biannual reports to the U.S. 

Environmental Protection Agency (USEPA) that presented a 

comprehensive water-quality assessment (305(b) report) and 

listed the water-quality impaired (degraded) streams or stream 

segments (303(d) report) within the States. These reports were 

named after the sections in the Clean Water Act that required 

their preparation (U.S. Environmental Protection Agency, 

1972).

In response to the provisions of the Clean Water Act, 

States established, modified, or enhanced their ambient streamwater-quality monitoring networks to provide the data necessary to assess stream water quality relative to State-established 

criteria. Data from these monitoring networks have been used to 

produce the biannual 305(b) and 303(d) reports to USEPA and, 

ultimately, to the Congress in the form of National Water Quality Inventory reports (compilation of State 305(b) reports). State 
2 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

networks have been operated to meet the specific goals and 

objectives established by the individual States. However, a 

national summarization of water quality can be accomplished in 

one of two ways. One approach would require that the States 

design and execute their individual monitoring approaches 

using identical designs so that the results can be summed to provide a national assessment. The other would be an analytical 

approach (some combination of statistical and deterministic 

models) that combine the 50 data sets in a manner that produces 

inferences about water quality that take into consideration the 

different sampling designs. Neither of these requirements has 

been met to date, and thus, the data are not suitable for national 

assessment or State-to-State intercomparisons, even though the 

data sets may be highly useful for purposes of State assessments 

and management.

The U.S. General Accounting Office (USGAO, 2000) 

examined USEPA’s National Water Quality Inventory reports 

and the adequacy of water-quality data for key water-quality 

decisions required by the Clean Water Act. The USGAO concluded that assessment data in State 305(b) reports are incomplete because the data do not represent all of the States’ waters. 

Additionally, USGAO identified substantial differences among 

States in virtually every aspect of monitoring and assessment. 

These differences stem from a combination of factors including 

variability in the (1) water-quality criteria (including designated 

or beneficial uses) for determining which water is degraded; 

(2) types of monitoring practices used to ascertain whether or 

not the criteria are exceeded; and (3) procedures used to assess 

water-quality data for determining if water-quality conditions 

are degraded. Much of this variability is the result of the flexibility allowed the States by the Clean Water Act to decide 

which streams to assess, what uses to designate for streams, and 

what water-quality criteria to assign for the designated uses. 

USEPA (2002a) has attempted to minimize some of these 

State-to-State differences through the development and recommendation of consistent methodology in network design, sampling protocols, and evaluation criteria. Targeted, statistically 

based (probabilistic), and geographically based sampling 

designs are used in some State monitoring programs to provide 

the water-quality information required by the Clean Water Act 

to evaluate potential stream-water-quality degradation relative 

to designated uses and appropriate water-quality criteria. When 

appropriate designs are used, this information also may be used 

to describe cause-and-effect relations, seasonal variability and 

time trends, mass transport, and as an aid to management decisions. However, the variability in network designs and operational characteristics, such as the distribution of sites and frequency of sampling, among the States inhibits the use of 

available information for comparison of results among 

the States.

Because of the aforementioned differences in State ambient stream-water-quality monitoring networks and programs, 

water-quality officials in Kansas generally questioned the validity of previous national water-quality comparisons, such as 

those of Hall and Kerr (1991) and Brown and Marshall (1993), 

produced on the basis of information presented in State 305(b) 

and (or) 303(d) reports and, specifically, previous summaries of 

water-quality conditions in Kansas. In 2001, the U.S. Geological Survey (USGS) in cooperation with the Kansas Water 

Office (KWO), supported in part by the State Water Plan Fund, 

conducted an investigation of the comparability and representativeness of State ambient stream-water-quality databases for 

assessment of national water-quality conditions. However, it 

was beyond the scope of this investigation to evaluate the adequacy of the network designs, field and laboratory activities, 

and quality-assurance practices used in the various State monitoring programs. The investigation described in this report will 

provide additional information to support or contrast with previous investigations by the USGS that indicated data in many 

electronically accessible databases are of unknown quality and 

hydrologic context (Childress and others, 1989; Norris and others, 1992; Rinella and others, 1992). 

For example, a comparison of data availablity in Colorado 

and Ohio indicated that fewer than 15 percent of water-quality 

analyses met the screening criteria judged necessary for the data 

to be included in a consistent database suitable for addressing 

broad-scope water-quality questions (Norris and others, 1992). 

Norris and others (1992) also determined that for 12 evaluated 

water-quality constituents an average of only 22 percent of 

stream-water-quality monitoring sites in Colorado and 8 percent in Ohio had 10 or more analyses with concurrent streamflow data during 1977–84. Concurrent streamflow data are necessary for hydrologic assessment such as water-quality trend 

analysis and constituent transport (load) calculations. Furthermore, Norris and others (1992) concluded that, on average, less 

than 10 percent of the stream-water-quality monitoring sites in 

Colorado and Ohio yield sufficient data for determining 

changes in water-quality conditions.

Purpose and Scope

The purpose of this report is to present a summary of available State ambient stream-water-quality data, 1990–98, and to 

examine some of the characteristics of the data that would limit 

its use in producing a national evaluation of stream water quality. Ambient stream-water-quality data are information collected by an integrated activity for the purpose of evaluating the 

physical, chemical, and biological character of water ecosystems in relation to human health, environmental and ecological 

conditions, and designated uses. Therefore, “ambient” in this 

report refers to data collected for those purposes and does not 

mean or is it used to indicate pristine water-quality conditions. 

On the contrary, States may have established monitoring sites in 

their ambient networks for many reasons to include the documentation of stream-water-quality effects from human-related 

sources. These sources may be both point and nonpoint sources 

of contamination. Water-quality conditions determined in 

many or all State ambient stream networks probably are biased 

toward the water-quality effects generated from human-related 

activities because of the interest in these effects and their general pervasiveness. 
General Investigative Approach 3

The scope of this report is limited to States with electronically available water-quality data for sampling sites in their 

ambient stream-water-quality monitoring networks for 1990–

98 (a maximum of 42 States). Water-quality data are statistically summarized by State. 

General Investigative Approach

The water-quality data used for the investigation described 

in this report were from monitoring sites representing each 

State’s ambient stream-water-quality monitoring network for a 

common time period. No attempt was made to normalize for 

how and why monitoring sites were selected such as targeted or 

probabilistic-based selection, the number of sites within each 

State, spatial distribution of sites, or temporal distribution of 

streamflow samples collected at those sites. Procedures used for 

accounting for differences in constituents analyzed (dissolved 

or total constituent concentrations) and laboratory reporting 

methods are discussed in the “Summary of Available State 

Ambient Stream-Water-Quality Data” and “Quality Assurance 

of Data” sections of this report. A general schematic of the procedures used and assessment steps taken in the conduct of this 

investigation is presented in figure 1.

Selection of Water-Quality Constituents

Water-quality constituents considered for summary in this 

report (table 1) were those most commonly responsible for 

Retrieved data for State ambient stream-water-quality monitoring sites, 1990–98

Lists of State ambient stream-water-quality monitoring sites developed

using State contacts, 305(b) reports, or STORET codes

Individual State databases created in Microsoft ACCESS

Determine number of States with water-quality

data for constituents listed in table 1

25 or more

States with data

Less than 25

States with data

Constituent evaluated

Merge similar data (for example, total

chloride with dissolved chloride)

Examine database of each monitoring site

Determine number of analyses in merged database

Less than

Nine analyses

Nine or

more analyses

Data from monitoring site not

statistically summarized

Data from monitoring site

statistically summarized

Constituent not evaluated

Data from monitoring sites in

States statistically summarized

Figure 1. General procedures and decision processes used for data acquisition, handling, and summary of 

State ambient stream-water-quality monitoring sites for selected water-quality consitituents.
4 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

water-quality degradation in the Nation’s streams. In preparation for the 1998 USEPA National Water-Quality Inventory 

Report to Congress, States and tribes assessed 840,402 mi of 

rivers and streams in the Nation and determined that 35 percent 

of those miles (291,263 mi) were degraded with respect to some 

water-quality factor. Of the degraded river and stream miles in 

1998, 38 percent were degraded by sediment/siltation, 36 percent by fecal bacteria, and 29 percent by nutrients (species of 

nitrogen and phosphorus). Smaller percentages were degraded 

by trace metals and pesticides. River and stream miles may have 

been degraded by more than one water-quality constituent (U.S. 

Environmental Protection Agency, 2000b).

Selection of Time Period and Acquisition of Data

The data summary period for the investigation described in 

this report was 1990–98. The ending date of 1998 was selected 

because it represented the date of closure on USEPA’s 

STORET (short for STOrage and RETrieval) data-management 

system, which traditionally has been the repository for State 

ambient stream-water-quality data. Currently (2004), this 

historical system is known as the USEPA STORET Legacy 

Data Center and since 1998 has been a static system; no additional data entry or update to existing data is allowed. Data submitted to USEPA after 1998 have been stored in a more modern, 

relational-based version of the original STORET database now 

(2004) known as STORET (U.S. Environmental Protection 

Agency, 2003a). When this investigation began in 2001, many 

States were not using or had not submitted post-1998 ambient 

stream-water-quality data into the modern STORET system; 

therefore, a decision was made to limit the data for the study 

to 1998 for consistency.

The beginning date (1990) for data used in the investigation described in this report was selected to provide a timeframe 

of sufficient length to produce State databases of reasonable 

size for statistical analysis. The purposes for which monitoring 

sites were selected vary among the States. Associated with these 

purposes are certain operational characteristics that may affect 

or establish the timing and frequency of water-quality sample 

collection. Some States have long-term monitoring sites that are 

sampled several to many times annually. Other States have sites 

that are part of a rotational network established on the basis of 

watersheds or geographic areas. These rotational sites may be 

sampled one to several times every 3 to 5 years, thereby taking 

several rotations to produce a database sufficient to document 

natural within-site water-quality variability and to produce a 

reasonable estimate of central tendency of this variability. 

Some States have a combination of these or other approaches.

An ideal data time period for a water-quality investigation 

such as described in this report is one that maximizes the potential for collection of water-quality samples. However, long time 

periods may introduce water-quality variability associated with 

time trends (water-quality changes over time resulting from 

changes in natural or human factors). Time trends at monitoring 

sites increase the degree of water-quality variability over a time 

period and reduce the prospect of commonality and comparability among monitoring sites. A 9-year (1990–98) time period 

was selected for the acquisition of data for the investigation 

described in this report. Admittedly, this time period was 

somewhat subjectively selected, but it was believed that a 

9-year period would provide two or three sampling cycles for 

rotational sites and be short enough to mitigate the effect of time 

trends in water-quality data.

The main source of water-quality data used for the investigation described in this report was the USEPA STORET Legacy Data Center (table 2). Of the 42 States with electronically 

available water-quality data, 28 State databases were acquired 

from the Legacy system. Data were acquired for five States 

(Colorado, Montana, New Hampshire, North Dakota, and Utah) 

from the modern STORET system that currently (2004) contains the 1990–98 data, and from State-located databases for 

three States (Maryland, Oklahoma, and Virginia). The USGS 

National Water Information System (NWIS) served as the primary or ancillary source of water-quality data for seven States 

Table 1. Water-quality constituents and physical measurements 

considered for summary.

Constituent or measurement

Sediment

Suspended solids

Bacteria

Fecal coliform

Nutrients

Ammonia as nitrogen

Nitrite plus nitrate as nitrogen

Total phosphorus

Trace elements

Arsenic

Selenium

Dissolved solids and major ions

Dissolved solids

Chloride

Sulfate

Pesticides

Alachlor

Atrazine

Physical measurements

Water temperature

pH
General Investigative Approach 5

Table 2. Number of ambient stream-water-quality monitoring sites per State with electronically available data for at least one of the 

selected water-quality constituents or measurements and source of data and Internet uniform resource locator (URL), 2001–02.

[USEPA, U.S. Environmental Protection Agency; STORET, U.S. Environmental Protection Agency STOrage and RETrieval data-management system; 

USGS, U.S. Geological Survey; NWIS, National Water Information System; --, not available]

State Number of 

sites Source of data Internet uniform resource locator (URL)

Alabama 49 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Alaska -- No ambient stream-water-quality network --

Arizona -- State database not electronically accessible --

Arkansas 133 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

California -- No centralized database --

Colorado 537 USEPA modern STORET http://oaspub.epa.gov/storpubl/warehousemenu

Connecticut 32 USGS NWIS http://waterdata.usgs.gov/ct/nwis/qw

Delaware 109 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Florida 874 do. Do.

Georgia 421 do. Do.

Hawaii -- No ambient stream-water-quality network --

Idaho 53 USGS NWIS http://waterdata.usgs.gov/id/nwis/qw

Illinois 373 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Indiana 107 do. Do.

Iowa 68 do. Do.

Kansas 290 do. Do.

Kentucky 89 do. Do.

Louisiana 174 do. Do.

Maine -- Bioassessment ambient network only --

Maryland 40 Chesapeake Bay Program http://www.chesapeakebay.net/data/index.htm

Massachusetts -- State database not electronically accessible --

Michigan 295 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Minnesota 68 do. Do.

Mississippi 85 do. Do.

Missouri 44 USGS NWIS http://waterdata.usgs.gov/mo/nwis/qw

Montana 1,114 USEPA modern STORET http://oaspub.epa.gov/storpubl/warehousemenu

Nebraska 22 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Nevada 71 do. Do.

New Hampshire 435 USEPA modern STORET http://oaspub.epa.gov/storpubl/warehousemenu

New Jersey 96 USGS NWIS http://waterdata.usgs.gov/nj/nwis/qw

New Mexico 16 do. http://waterdata.usgs.gov/nm/nwis/qw

517 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

New York 19 do. Do.

North Carolina -- State database not electronically accessible --

North Dakota 91 USEPA modern STORET http://oaspub.epa.gov/storpubl/warehousemenu

Ohio 42 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Oklahoma 261 Oklahoma Conservation Commission http://www.okcc.state.ok.us

Oregon 148 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

Pennsylvania 202 do. Do.

Rhode Island 5 USGS NWIS http://waterdata.usgs.gov/ri/nwis/qw

South Carolina 351 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

South Dakota 100 do. Do.

Tennessee 109 do. Do.

Texas 980 do. Do.

Utah 64 USEPA modern STORET http://oaspub.epa.gov/storpubl/warehousemenu

Vermont -- Bioassessment ambient network only --

Virginia 1,997 Virginia Department of Environmental Quality http://www.deq.state.va.us/water/monitoring.html

Washington 208 USEPA STORET Legacy Data Center www.epa.gov/storpubl/legacy/gateway.htm

West Virginia 26 do. Do.

Wisconsin 50 do. Do.

Wyoming 47 USGS NWIS http://waterdata.usgs.gov/wy/nwis/qw
6 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

(Connecticut, Idaho, Missouri, New Jersey, New Mexico, 

Rhode Island, and Wyoming). These seven States had cooperative agreements with the USGS to collect and analyze all or part 

of the water-quality samples for their ambient stream-waterquality monitoring networks. The repository for USGScollected data is NWIS.

Eight States (Alaska, Arizona, California, Hawaii, Maine, 

Massachusetts, North Carolina, and Vermont) did not have 

electronically available data (table 2). Alaska and Hawaii did 

not have ambient stream-water-quality networks during 

1990–98. Arizona, Massachusetts, and North Carolina had 

ambient stream-water-quality networks, but chemical and physical data were not stored in the STORET system or in a Statelocated database that was electronically accessible. Maine and 

Vermont conducted only biological water-quality assessments; 

therefore, they did not have data for the chemical and physical 

characteristics summarized during the investigation described 

in this report. California did not have a centralized, electronically accessible State database. Ambient stream-water-quality 

responsibilities in California were divided among nine Regional 

Water-Quality Control Boards, each of which varied as to 

amount, availability, and accessibility of data.

Water-quality data were acquired for ambient streamwater-quality monitoring sites in each of 42 States. Ambient 

stream-water-quality monitoring sites generally were those 

sites assessed for State 305(b) reports and were identified either 

through direct contact with the State agencies responsible for 

water-quality assessment and preparation of 305(b) reports, 

through information contained in 305(b) reports, or as identified 

in the STORET system. Water-quality data for identified monitoring sites were retrieved from the sources listed in table 2, 

generally, through Internet access to those sources.

State 305(b) reports provide, in part, an assessment of the 

number of stream miles that meet or fail water-quality criteria 

for designated uses. These assessments are conducted using 

water-quality data from many or all of the stream-water-quality 

monitoring sites used for the investigation described in this 

report. These monitoring sites, however, provide data to assess 

only a small percentage of the total stream miles (a combination 

of perennial and intermittent streams) in many States (table 3) 

(U.S. Environmental Protection Agency, 2000b; Appendix A–

1). Percentages of assessed stream miles, reported by the 

States, ranged from 0 percent in Alaska to 100 percent in 

Hawaii, Maine, and New York with a median for all States of 

20 percent. These percentages included stream miles assessed 

on the basis of macroinvertebrate surveys or other biological 

indices. 

The information presented in table 3 (as reported by the 

States to USEPA) was not calculated consistently among the 

States and should be used only as a general comparison. For 

instance, Arizona did not include river miles on Indian lands in 

their estimate of total river miles; Hawaii used assessed stream 

miles as total miles because total miles were unknown; the percentage of stream miles assessed in Missouri was calculated on 

the basis of the number of perennial miles (not shown in table 3) 

instead of total miles; and the number of perennial stream miles 

was used for the number of total miles in Virginia (U.S. Environmental Protection Agency, 2000b; Appendix A–1). In some 

States, intermittent streams account for a large percentage of 

total stream miles, particularly in the arid and semiarid western 

States. Water-quality conditions for intermittent streams may 

not be determined in many of these States; therefore, percentages of assessed stream miles calculated on the basis of total 

stream miles may be small in these States relative to States with 

fewer intermittent streams.

The number of stream miles assessed for water-quality 

conditions in many States is determined from an assumption 

that conditions at stream monitoring sites represent the conditions for some defined stream segment. This assumption 

imparts uncertainty in statewide water-quality assessments. If 

monitoring sites are to be used to assess statewide conditions, 

there must be a process whereby water-quality measurements 

are used to infer conditions throughout the network of stream 

reaches in the State. Although statistical methods exist that provide the means of extending these data (Smith and others, 1997; 

Larson and Gilliom, 2001; National Research Council, 2001), it 

seems that these methods have not been used by the States. 

Rather, the States use point (monitoring-site) data to infer conditions over some finite reach upstream and downstream from 

the monitoring site and then assume that they have no knowledge beyond those reaches, referring to this remaining part of 

the stream network as unassessed. The use of statistical or deterministic models is necessary if the monitoring data are to 

achieve their full utility in providing meaningful estimates of 

water-quality statewide or nationwide or to achieve any understanding of the uncertainty of the statewide or nationwide 

estimates.

The number of ambient stream-water-quality monitoring 

sites with data for constituents or measurements listed in table 1 

varied among the States. Some of this variation may be 

attributed to geographical size differences among the States. 

State surface areas reported in this paragraph are from the U.S. 

Bureau of Census (2002). For example, the smaller States of 

Rhode Island (1,231 mi2

) and Connecticut (5,544 mi2) have few 

monitoring sites (table 2) relative to many of the larger States 

such as Montana (147,046 mi2

) and Texas (267,277 mi2). 

However, many exceptions are evident such as New York 

(53,989 mi2

) with 19 monitoring sites and Nebraska 

(77,358 mi2

) with 22 monitoring sites. Clearly, factors other 

than size determine the number of ambient stream-water-quality monitoring sites in some States. These factors may be economic, political, a limitation in surface-water resources, or, as 

in the case of New York, a function of monitoring-network 

design and operation. New York, during 1990–98, operated a 

monitoring network consisting of sites for both water-quality 

chemical and biological assessments with the major emphasis 

on the latter. Consequently, New York had few monitoring sites 

with data available for the investigation described in this report. 

In contrast to New York, Virginia (42,326 mi2

) operated almost 

2,000 ambient stream-water-quality monitoring sites during 

1990–98. The number of monitoring sites indicated in table 2 

represents the number with at least one analysis of any 
Data Management 7

Table 3. Total miles of streams in the States and percentage assessed for water-quality degradation in 1998 (U.S. Environmental 

Protection Agency, 2000b; Appendix A–1).

State Total stream miles Percentage

assessed State Total stream miles Percentage assessed

Alabama 77,274 5 Alaska 365,000 0

Arizona 90,373 5 Arkansas 87,617 10

California 211,513 8 Colorado 107,403 27

Connecticut 5,830 16 Delaware 2,509 95

Florida 51,858 10 Georgia 70,150 12

Hawaii 3,905 100 Idaho 115,595 11

Illinois 87,110 33 Indiana 35,673 24

Iowa 71,665 14 Kansas 134,338 12

Kentucky 49,105 19 Louisiana 66,294 9

Maine 31,752 100 Maryland 17,000 39

Massachusetts 8,229 18 Michigan 51,438 40

Minnesota 91,944 13 Mississippi 84,003 47

Missouri 51,978 42 Montana 176,750 10

Nebraska 81,573 5 Nevada 143,578 1

New Hampshire 10,881 24 New Jersey 6,450 59

New Mexico 110,741 4 New York 52,337 100

North Carolina 37,853 89 North Dakota 54,373 22

Ohio 29,113 10 Oklahoma 78,778 14

Oregon 114,823 47 Pennsylvania 83,260 15

Rhode Island 1,392 54 South Carolina 29,898 65

South Dakota 9,937 32 Tennessee 61,075 88

Texas 191,228 7 Utah 85,916 10

Vermont 7,099 16 Virginia 49,350 39

Washington 70,439 98 West Virginia 32,278 24

Wisconsin 57,698 40 Wyoming 108,767 87

constituent or measurement listed in table 4. Data were 

retrieved for a total of 10,812 sites from 42 States.

The data retrieved for this investigation came from multiple sources—STORET, NWIS, or State databases. Data for a 

given constituent may have been associated with one or more 

parameter codes that resulted from the analysis of different 

phases or mode of transport (total and dissolved, or whole water 

and filtered) or from different analytical methods. Parameter 

codes are the five-digit numbers that uniquely identify a chemical constituent or water-quality measurement in STORET or 

NWIS. A total analysis of a water-quality constituent was 

determined on a whole (unfiltered) water sample and included 

all occurrence or transport phases of the constituent as defined 

by the analytical laboratory method. A dissolved analysis of a 

water-quality constituent was determined on a filtered water 

sample, most commonly water filtered through a 0.45-μm poresize filter. Data were retrieved for all available constituents or 

measurements listed in table 4. 

The modern STORET system, however, does not distinguish water-quality constituents by parameter code. Data in the 

modern STORET system are organized by constituent characteristic name and cannot be retrieved by parameter code. Therefore, water-quality data acquired from modern STORET for 

Colorado, Montana, New Hampshire, North Dakota, and Utah 

were retrieved on the basis of characteristic name (suspended 

solids, fecal coliform, and so forth) and not by parameter codes. 

A total or dissolved analysis in modern STORET was identified 

on the basis of a sample fraction characteristic.

Data Management 

Data management and selection or development of common data-summary criteria were essential components of the 

investigation described in this report. The management of data 
8 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 4. Constituent or measurement descriptions and parameter codes for data retrieved from U.S. Environmental Protection 

Agency, U.S. Geological Survey, or State databases.

[STORET, U.S. Environmental Protection Agency STOrage and RETrieval system; NWIS, U.S. Geological Survey National Water Information System; o

C, degrees Celsius; mg/L, milligrams per liter; MF, membrane filtration; M-TEC, fecal coliform agar; col/100 mL, colonies per 100 milliliters of water; 

M-FC, fecal coliform broth or agar; MPN, most probable number; EC, fecal coliform agar; μm, micrometer or micron; N, nitrogen; NO3, nitrate; 

P, phosphorus; μg/L, micrograms per liter; As, arsenic; Se, selenium]

Constituent or measurement description STORET/NWIS 

parameter code1

1

NWIS code is the same as the STORET code unless otherwise indicated. STORET codes are used in the Legacy system and State 

databases but are not used in the modern STORET system.

Suspended solids

Residue, total nonfilterable, residue on evaporation at 105 oC, mg/L 00530

Solids, suspended, residue on evaporation at 180 oC, mg/L 70299

Bacteria

Fecal coliform, MF, M–TEC, 44.5 oC, col/100 mL 31611

Fecal coliform, MF, M–FC agar, 44.5 oC, 24 hour, col/100 mL 31613

Fecal coliform, MPN, EC medium, 44.5 oC, col/100 mL 31615

Fecal coliform, MF, M–FC broth, 44.5 oC, col/100 mL 31616

Fecal coliform, MF, M–FC, 0.7-μm porosity filter, 44.5 oC, col/100 mL 31625

Nutrients

Ammonia, dissolved, mg/L as N 00608

Ammonia, total, mg/L as N 00610

Nitrite, dissolved, mg/L as N 00613

Nitrite, total, mg/L as N 00615

Nitrate, dissolved, mg/L as N 00618

Nitrate, total, mg/L as N 00620

Nitrate, total, mg/L as NO3 71850

Nitrate, dissolved, mg/L as NO3 71851

Nitrite plus nitrate, total, mg/L as N 00630

Nitrite plus nitrate, dissolved, mg/L as N 00631

Phosphorus, total, mg/L as P 00665

Phosphorus, dissolved, mg/L as P 00666

Trace elements

Arsenic, total recoverable in water, μg/L as As 00978

Arsenic, total, μg/L as As 01002

Selenium, total recoverable in water, μg/L as Se 00981

Selenium, total, μg/L as Se 01147

Dissolved solids and major ions

Residue, total filterable, dried at 105 oC, mg/L 00515

Residue, total dissolved, unspecified calculation, mg/L 70294

Residue, total filterable, dried at any temperature, mg/L 70295

Residue, total filterable, dried at 180 oC, mg/L 70300

Solids, dissolved, sum of constituents, mg/L 70301

Chloride, total, mg/L 00940/none

Chloride, dissolved, mg/L 00941/00940

Sulfate, total, mg/L 00945/none

Sulfate, dissolved, mg/L 00946/00945

Pesticides

Alachlor, dissolved, μg/L 46342

Alachlor, whole water, μg/L 77825

Atrazine, whole water, μg/L 39033

Atrazine, dissolved, μg/L 39632

Physical measurements

Temperature, water, oC 00010

pH, standard units 00400
Quality Assurance of Data 9

from more than 10,000 ambient stream-water-quality monitoring sites in 42 States required a relational-based data-management system to store data and to produce the site and State 

summaries necessary for the investigation.

Data retrieved from STORET, NWIS, or State databases 

were placed into a Microsoft ACCESS data-management system at the USGS office in Lawrence, Kansas. Separate 

ACCESS databases were created for each State. Data in each 

State ACCESS database consisted of ambient stream-waterquality analyses for the constituents and measurements listed in 

table 4. A merged database for water-quality constituents and 

measurements of interest (table 1) was prepared by combining 

data for multiple parameter codes, and the combined data for 

each constituent or measurement were used for statistical summary. The utility and comparability of multiple parameter codes 

for selected constituents and measurements for the merged 

database will be discussed later in the “Summary of 

Available State Ambient Stream-Water-Quality Data” section 

of this report. 

Water-quality constituents or measurements from ambient 

stream-water-quality monitoring sites were summarized only if 

the site databases contained nine or more constituent analyses 

or measurements (fig. 1). The nine-analysis threshold was 

selected as a compromise between the desire to include as many 

ambient stream-water-quality monitoring sites per State as possible but still have enough analyses to provide an estimate of 

range and central tendency (median value) for each site’s data 

population. Additionally, nine samples represent an average of 

one sample per year for the selected time period (1990–98). 

This low threshold for data quantity is not consistent with 

USEPA recommendations or compatible with data quantity preferred by USGS (Hooper and others, 2001; Gilliom and others, 

1995). USEPA (2002a) recommends at least 30 analyses per 

monitoring site for determining water-quality degradation for 

the 305(b) assessment cycle (2 years); however, the number of 

analyses required by the States for these determinations varies. 

For example, Kansas currently (2004) requires a minimum of 

12 analyses (Kansas Department of Health and Environment, 

2002). Some States require a minimum data set of 10 analyses, 

whereas other States, such as Nevada and Arizona, require as 

few as four analyses for determining degradation (U.S. General 

Accounting Office, 2002). Time frames within which the minimum number of samples can be collected also vary. Wyoming 

requires 10 samples collected over 3 years, whereas Nebraska 

requires 10 samples collected over 5 years (U.S. General 

Accounting Office, 2002). Although States generally require 

analysis of data collected over 1 to 3 years in determining 

water-quality degradation, USEPA (2002a) recommends that 

States analyze data over longer time periods when available. 

Relative to the 30 analyses recommended by USEPA 

(2002a), the minimum of nine analyses required to summarize 

data from an ambient stream-water-quality monitoring site for 

the investigation described in this report is small. The potential 

disadvantage of a relatively small number of analyses is the possibility that the range and central tendency in sample analyses 

may not be representative of the population range and central 

tendency in water-quality constituent concentrations or measurements at monitoring sites. The implication of this possibility is that water-quality summaries made on the basis of a few 

analyses may be biased. 

Quality Assurance of Data

The ambient stream-water-quality merged database 

assembled for the investigation described in this report consists 

of more than 2 million individual water-quality constituent 

analyses or measurements from more than 10,000 monitoring 

sites in 42 States (table 2). An assumption was made for this 

investigation that the States or their cooperators had reviewed 

and approved the ambient stream-water-quality data prior to 

submission to the STORET, NWIS, or State database systems. 

Normal quality-assurance procedures include an examination 

of (1) “outlier” data values to determine erroneous or incorrectly entered data; (2) historical variability in sample collection methods; (3) accuracy, precision, and detection levels of 

analytical methods; (4) potential for positive or negative bias in 

the data sets; and (5) verification of entered data with laboratory 

results. 

Qualitative data remark codes (table 5) were retrieved 

with water-quality data from the STORET or NWIS datamanagement systems. These remark codes document instances 

where analytical values are less than or greater than an analytical method or reporting limit; presumptive evidence of material 

(chemicals) is present but not quantifiable; bacterial enumeration is outside ideal counting ranges; or bacterial colonies are 

too numerous to count. There were many qualified data in the 

merged database used in this investigation (table 5). For 

instance, most chemical data values coded as “less than” an analytical method or reporting level were used for calculation of 

water-quality constituent median values for ambient streamwater-quality monitoring sites. 

Fecal coliform bacteria densities retrieved from the 

STORET or NWIS data-management systems frequently were 

qualified “less than” or “greater than” a large range of numeric 

values. This range was from less than 1 to greater than several 

hundreds or thousands of bacteria. 

Chemical concentrations or bacteria densities qualified 

with “less than” or “greater than” were used in calculation of 

median values in water from ambient stream-water-quality 

monitoring sites. These qualified data were ranked according to 

their numeric value either before (in the case of “less than”; <) 

or after (in the case of “greater than”; >) the corresponding nonqualified numeric values (assuming a ranking order from smallest to largest); for example, 1, 5, <10, 10, 20, 40, >40, 50, and 

so forth.
10 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 5. Data remark codes and descriptions and statistical summary action for remarked water-quality data from the U.S. 

Environmental Protection Agency STORET (STOrage and RETrieval), U.S. Geological Survey National Water Information 

System (NWIS), or State data-management systems.

[U, data used for assessment; NU, data not used for assessment]

Data 

remark 

code

Description Statistical 

summary action

STORET System1

1

U.S. Environmental Protection Agency (2001a).

A Value reported is the mean of two or more determinations. U

B Results are based upon colony counts outside the acceptable range. U

C Calculated. Value stored was not measured directly but was calculated from other available data. U

I Value reported is less than the practical quantification limit and greater than or equal to the method 

detection limit.

U

J Estimated. NU

K Off-scale low. Actual value not known but known to be less than value shown. U

L Off-scale high. Actual value not known but known to be greater than value shown. U

M Presence of material verified but not quantified. Indicates a positive detection at a level too low to permit accurate quantification.NU

N Presumptive evidence of presence of material. NU

O Sampled for, but analysis lost. Accompanying value is not meaningful for analysis. NU

P Too numerous to count. NU

Q Sample held beyond normal holding time. U

T Value reported is less than the criteria of detection. (Best judgement value). U

U Material was analyzed for but not detected. Value stored is the limit of detection for process in use. 

(Added “less than” qualifier to data value).

U

Z Too many colonies were present to count (TNTC); the numeric value represents the filtration volume. NU

$ Calculated by retrieval software. Numerical value was neither measured nor reported in the database but 

was calculated from other available data during generation of the retrieval report.

U

NWIS System2

2

U.S. Geological Survey (2003).

< Actual value is known to be less than the value shown. U

> Actual value is known to be greater than the value shown. U

A Average value. U

E Estimated value. U

M Presence of material verified but not quantified. NU

N Presumptive evidence of presence of material. NU

S Most probable value. U

V Value affected by contamination. NU

U Analyzed for, not detected. U
Summary of Available State Ambient Stream-Water-Quality Data 11

Summary of Available State Ambient 

Stream-Water-Quality Data

Water-quality data for selected constituents (table 1) from 

ambient stream-water-quality monitoring sites in 42 States were 

statistically summarized. Water-quality constituents and measurements were summarized only if 25 or more States (one-half 

of the States) had electronically available data. Monitoring-site 

median values were calculated for each assessed water-quality 

constituent or measurement, statistically summarized by State, 

and presented in tabular format. Because of few data among the 

States for selenium, alachlor, and atrazine, these constituents 

were not summarized. Water temperature was not summarized 

because national climatic differences in water temperature 

make comparability among monitoring sites difficult.

Suspended Solids

Suspended solids in water samples may consist of organic 

or inorganic materials from sources such as decaying vegetation, algae, solids discharged by industries and municipalities, 

urban and agricultural runoff, soil erosion, and physical degradation of geologic formations (Mays, 1996). Suspended solids 

in streams can serve as a heat sink by absorbing solar radiation, 

which ultimately may increase water temperatures, stress 

aquatic organisms, and may create conditions favorable to 

disease in fish populations. Suspended solids also can serve as 

a transport mechanism for toxic water-quality constituents such 

as mercury, pesticides, and industrial organic compounds. 

When transported to and deposited in lakes or reservoirs, suspended solids can shorten the useful life of a lake or reservoir 

by increasing the rate of sedimentation, thereby reducing storage volume, smothering rooted vegetation, and adversely 

affecting the ecosystem of aquatic benthic (bottom-dwelling) 

organisms. Also, suspended solids in lake and reservoir water 

can increase turbidity, reduce the available light that reaches 

aquatic plants and organisms, restrict biodiversity, and inhibit 

photosynthesis and primary productivity (Horne and Goldman, 

1994).

All States with suspended solids concentrations in water 

from ambient stream-water-quality monitoring sites analyzed 

suspended solids according to the methodology associated with 

parameter code 00530 (table 4) and subsequently stored those 

data in STORET Legacy, NWIS, or State databases under that 

parameter code or as “suspended solids” in the modern 

STORET system. Florida is the lone exception, which also had 

two monitoring sites with suspended solids concentrations 

stored under parameter code 70299. For the purpose of the summary presented in this report, it was assumed that data under 

both parameter codes were analytically comparable and, therefore, were merged into one database. 

Forty States had electronically accessible suspended solids 

concentrations for water from ambient stream-water-quality 

monitoring sites with at least nine analyses. State medians of 

monitoring-site median concentrations of suspended solids 

ranged from 2.0 mg/L in New Hampshire to 42.5 mg/L in 

Nebraska (table 6).

Fecal Coliform Bacteria

Fecal coliform bacteria are indigenous to the intestinal 

tract of all warmblooded animals, and their presence in stream 

water indicates fecal contamination and possible presence of 

pathogenic microorganisms, such as entero-, rota, reovirus, that 

may cause human disease, ranging from mild diarrhea to respiratory disease, meningitis, and polio (Pepper and others, 1996). 

Possible sources of fecal coliform bacteria contamination in 

streams include municipal-wastewater discharges, seepage 

from domestic septic systems, runoff or seepage from livestockproducing areas, and wildlife. Because of the potential humanhealth implications of fecal bacteria contamination, all States 

have implemented an ambient stream-water-quality criterion 

for either fecal coliform or Escherichia coli (E. coli) bacteria 

densities. E. coli is the predominant bacterium in the fecal 

coliform group (McKinney, 1962) and may be more indicative 

of fecal contamination from warmblooded animals than the 

fecal coliform group (Cabelli, 1977; Dufour and Cabelli, 1984). 

The fecal coliform bacteria group may include species of the 

Klebsiella, Enterobacter, and Citrobacter genera (Gleeson and 

Gray, 1997). Rasmussen and Ziegler (2003) developed sitespecific relations and ratios between E. coli and fecal coliform 

bacteria such that densities of one may be used to estimate densities of the other. Historically, most States relied on the enumeration of fecal coliform bacteria as an indicator of sanitary 

quality particularly for the time period 1990–98. Therefore, 

indicator bacteria for most States consisted of the fecal coliform 

group in this report. In 1986, USEPA revised the ambient waterquality criteria for marine and freshwater (U.S. Environmental 

Protection Agency, 1986) and recommended that criteria for 

either E. coli or Enterococci organisms replace criteria for fecal 

coliform bacteria. However, many States may have been reluctant to switch from a fecal coliform criteria because of concern 

of long-term comparability.

Thirty-nine States had electronically accessible fecal 

coliform bacteria densities in water from ambient stream-waterquality monitoring sites stored in STORET Legacy, NWIS, or 

State databases under one or more parameter codes (table 7) or 

as “fecal coliform” in the modern STORET system. Although 

monitoring sites for most States had fecal coliform bacteria densities stored under only one parameter code (most commonly 

31616), five States (Connecticut, Florida, Rhode Island, South 

Carolina, Virginia) had data from monitoring sites stored under 

two parameter codes, and Texas had data stored under three 

parameter codes. The division of fecal coliform bacteria densities among more than one parameter code within and among the 

States necessitated a data-merging procedure prior to the monitoring-site and State summaries presented in this report.

The merging procedure of ambient stream-water-quality 

monitoring sites with different parameter codes for fecal 

coliform bacteria densities was, for the most part, a simple 
12 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 6. Summary of median suspended solids concentrations in water from State ambient 

stream-water-quality monitoring sites (with nine or more analyses), 1990–98.

[--, not available; <, less than]

State

Number of 

assessed 

monitoring sites1

1Nine or more analyses per site.

Monitoring-site median concentration

(milligrams per liter)

Minimum Median Maximum

Alabama 45 1.0 9.0 32.0

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 1.0 7.5 116

California -- -- -- --

Colorado 214 <10 <10 260

Connecticut 0 -- -- --

Delaware 103 2.0 10.5 111

Florida 602 <1.0 4.0 153

Georgia 196 <1.0 9.0 37.0

Hawaii -- -- -- --

Idaho 0 -- -- --

Illinois 11 8.0 26.0 108

Indiana 105 <4.0 19.0 93.0

Iowa 26 12.5 40.5 190

Kansas 124 5.0 33.0 108

Kentucky 60 3.0 15.0 48.5

Louisiana 171 4.0 22.0 251

Maine -- -- -- --

Maryland 40 4.0 8.0 18.0

Massachusetts -- -- -- --

Michigan 96 <4.0 12.0 54.1

Minnesota 63 1.2 25.0 145

Mississippi 66 1.0 13.5 140

Missouri 22 2.5 10.8 181

Montana 132 <1.0 5.2 340

Nebraska 22 5.0 42.5 254

Nevada 67 1.0 <10.0 108

New Hampshire 25 <1.0 2.0 6.5

New Jersey 65 3.0 6.0 27.0

New Mexico 219 <3.0 8.0 832

New York 19 2.0 10.0 41.0

North Carolina -- -- -- --

North Dakota 28 <5.0 25.8 1,030

Ohio 41 <5.0 14.0 65.0

Oklahoma 182 <1.0 7.9 129

Oregon 144 <1.0 4.0 62.5

Pennsylvania 173 <2.0 6.0 26.0

Rhode Island 5 2.0 5.0 6.0

South Carolina 52 1.4 6.7 27.0

South Dakota 96 2.0 17.0 2,160

Tennessee 68 3.0 11.8 101

Texas 396 <1.0 21.0 622

Utah 64 <3.0 34.2 938

Vermont -- -- -- --

Virginia 945 <3.0 6.5 64.0

Washington 204 1.0 5.0 114

West Virginia 26 <5.0 8.8 29.0

Wisconsin 46 3.0 10.2 56.0

Wyoming 1 13.0 13.0 13.0
Summary of Available State Ambient Stream-Water-Quality Data 13

Table 7. Number of State ambient stream-water-quality monitoring sites with data (nine or more 

analyses) for parameter codes of fecal coliform bacteria densities in water, 1990–98.

[M–TEC, fecal coliform agar; M–FC, fecal coliform agar or broth; MPN, most probable number; MPF, micrometer porosity

filter; --, not available]

State

Number of sites with data for parameter code1

1

See table 4 for complete descriptions of parameter codes. Data not organized by parameter code in the modern STORET 

system.

Number of 

sites in 

merged 

database

31611

(M–TEC)

31613

(M–FC agar)

31615

(MPN)

31616

(M–FC broth)

31625

(M–FC, 

0.7 MPF)

Alabama -- 45 -- -- -- 45

Alaska -- -- -- -- -- --

Arizona -- -- -- -- -- --

Arkansas -- -- -- 113 -- 113

California -- -- -- -- -- --

Colorado -- -- -- -- -- 124

Connecticut -- -- -- 32 3 32

Delaware -- -- -- -- -- 0

Florida -- 108 -- 268 -- 372

Georgia -- -- 255 -- -- 255

Hawaii -- -- -- -- -- --

Idaho -- -- -- -- 42 42

Illinois -- -- -- 3 -- 3

Indiana -- -- -- -- -- 0

Iowa -- -- -- 17 -- 17

Kansas -- -- -- 249 -- 249

Kentucky -- -- -- 59 -- 59

Louisiana -- -- 103 -- -- 103

Maine -- -- -- -- -- --

Maryland -- -- -- 40 -- 40

Massachusetts -- -- -- -- -- --

Michigan -- -- -- -- -- 0

Minnesota -- 63 -- -- -- 63

Mississippi -- -- -- 50 -- 50

Missouri -- -- -- -- 39 39

Montana -- -- -- -- -- 2

Nebraska -- -- -- 22 -- 22

Nevada -- 60 -- -- -- 60

New Hampshire -- -- -- 8 -- 8

New Jersey -- -- -- -- 5 5

New Mexico -- -- -- -- 9 9

New York -- 8 -- -- -- 8

North Carolina -- -- -- -- -- --

North Dakota -- -- -- -- -- 39

Ohio -- -- -- 40 -- 40

Oklahoma 14 -- -- -- -- 14

Oregon -- 83 -- -- -- 83

Pennsylvania -- -- -- 53 -- 53

Rhode Island -- -- -- 1 5 5

South Carolina -- -- 43 276 -- 310

South Dakota -- -- -- 96 -- 96

Tennessee -- -- -- 60 -- 60

Texas -- 33 -- 422 67 457

Utah -- -- -- -- -- 16

Vermont -- -- -- -- -- --

Virginia -- -- 460 790 -- 1,086

Washington -- -- -- 202 -- 202

West Virginia -- -- -- 26 -- 26

Wisconsin -- 44 -- -- -- 44

Wyoming -- -- -- -- 18 18
14 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

combining of monitoring sites into a single State database. 

Occasionally, however, individual water-quality samples from 

monitoring sites contained fecal coliform bacteria densities 

analyzed and stored under more than one parameter code. In 

these situations, densities stored under parameter code 31616 

were selected in preference over densities stored under other 

parameter codes. Generally, densities under parameter code 

31616 were the most commonly occurring for monitoring sites 

within the six States with multiple parameter codes for fecal 

coliform bacteria and, therefore, the most reasonable selection. 

For the purpose of summaries presented in this report, it 

was assumed that densities under all fecal coliform bacteria 

parameter codes among or within the States were 

analytically comparable even though there may be analytical 

variability between the methods associated with the different 

parameter codes. State medians of monitoring-site median densities of fecal coliform bacteria ranged from 19.2 col/100 mL in 

Colorado to 2,650 col/100 mL in Montana (on the basis of two 

sites) (table 8).

Ammonia

Ammonia as nitrogen (hereinafter referred to as ammonia) 

is a reduced form of nitrogen. Rooted aquatic plants and algae 

require dissolved forms of nitrogen as nutrients essential for 

growth and reproduction (Horne and Goldman, 1994). Compounds of nitrogen such as ammonia or the oxidized forms of 

nitrogen such as nitrite and nitrate are the basic building blocks 

for protein synthesis. However, large inputs of nitrogen compounds into the aquatic environment may cause excessive algal 

growth. This growth ultimately may produce taste-and-odor 

problems in drinking water, reduce the aesthetic and 

recreational value of water, and stress aquatic organisms resulting from depleted dissolved oxygen concentrations when algal 

blooms die.

Concentrations of ammonia ranging from 0.44 to 

18.7 mg/L (uncorrected for pH) were shown to be acutely toxic 

to 19 freshwater invertebrate species, whereas acute toxicity 

among 29 fish species ranged from 0.068 to 3.78 mg/L, uncorrected for pH (U.S. Environmental Protection Agency, 1986). 

Concentrations of ammonia acutely toxic to fish may cause 

increases in respiratory activity, oxygen uptake, and heart rate; 

reductions in hatching success and growth and morphological 

development; and injury to gills, liver, and kidneys. At larger 

concentrations, fish may experience convulsions, coma, or 

death (U.S. Environmental Protection Agency, 1986). 

Therefore, it is desirable to mitigate the introduction of 

excessive ammonia.

Major nonpoint sources of ammonia include agricultural 

activities such as the application of synthetic fertilizers (anhydrous ammonia) and pasturing and confined feeding of livestock. Farm livestock can produce large amounts of nitrogenous 

organic waste (urine, manure, and organic wastes) in areas 

where large numbers of animals are pastured or confined. The 

decomposition of organic waste can release ammonia and other 

nutrients into the aquatic environment. Discharges from 

industrial and municipal-wastewater treatment plants also may 

be a major point source of ammonia and other nutrients to 

streams in the United States.

Unionized ammonia (NH3) readily dissolves in water to 

form its derivative ionic species ammonium ion (NH4

+). 

Because the acid-base ionization constant for NH4

+ is relatively 

large (9.26), most ammonia in water within natural environmental pH ranges (6.0 to 9.0 standard units) is present as NH4

+

rather than NH3 (Manahan, 1994). Analytical methods for 

ammonia (as nitrogen) are conducted on either a whole water 

sample (total ammonia analysis) or a filtered water sample (dissolved ammonia analysis). In both cases, the resultant analytical 

determination will represent a combined concentration of 

unionized and ionized forms of ammonia. However, because of 

the large solubility of ammonia in water at natural pH ranges 

and the preponderance of the dissolved ionic species (NH4

+), 

analytical determinations of ammonia (as nitrogen) in whole 

(total) and filtered (dissolved) water samples will produce similar ammonia concentrations.

Forty-one States reported ammonia concentrations (as 

nitrogen) in water from ambient stream-water-quality 

monitoring sites (table 9). Most States reported ammonia concentrations determined from whole water samples (total ammonia; parameter code 00610) for 1990–98. Two States (Nevada 

and Wisconsin) reported ammonia concentrations determined 

only on filtered samples of water (dissolved ammonia; parameter code 00608), whereas 12 States reported both total and dissolved ammonia concentrations. Total and dissolved ammonia 

analyses were assumed to produce similar concentrations of 

ammonia in water from most monitoring sites; therefore, data 

for parameter codes 00608 and 00610 were combined to create 

merged State databases prior to the water-quality summary for 

ammonia. Ammonia data acquired from the modern STORET 

system included total and dissolved analyses for Colorado and 

Montana and required a similar merging procedure.

Creation of merged databases for ammonia concentrations 

determined in water from ambient stream-water-quality monitoring sites consisted of merging dissolved ammonia determinations into the database for total ammonia determinations. In situations where both a total and dissolved concentration existed 

for a water sample, the total concentration was included rather 

than the dissolved concentration. Total ammonia concentrations 

were preferred for inclusion because of the preponderance of 

these data among the State water-quality databases. Merged 

State databases (table 9) were used for the water-quality summary of ammonia presented in this report. State medians of 

monitoring-site median concentrations of ammonia ranged 

from 0.003 mg/L in Colorado to 0.46 mg/L in Rhode Island 

(table 10).

Nitrite Plus Nitrate

Nitrite and nitrate are inorganic oxidized forms of nitrogen 

produced during various stages of the nitrogen cycle (Manahan, 

1994, p. 41). In most oxygenated surface water, nitrate is by far
Summary of Available State Ambient Stream-Water-Quality Data 15

Table 8. Summary of median fecal coliform bacteria densities in water from State 

ambient stream-water-quality monitoring sites (with nine or more analyses), 1990–98.

[mL, milliliters; --, not available; <, less than; >, greater than]

State

Number of 

assessed 

monitoring 

sites1

1Nine or more analyses per site.

Monitoring-site median density

(colonies per 100 mL of water)

Minimum Median Maximum

Alabama 45 18.0 115 1,950

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 113 8.5 75.5 500

California -- -- -- --

Colorado 124 <2.0 19.2 4,300

Connecticut 32 11.0 148 5,650

Delaware 0 -- -- --

Florida 372 <1.0 80.0 2,250

Georgia 255 <20.0 200 7,900

Hawaii -- -- -- --

Idaho 42 2.0 24.0 265

Illinois 3 220 230 2,450

Indiana 0 -- -- --

Iowa 17 3.0 200 1,900

Kansas 249 <10.0 155 6,000

Kentucky 59 10.0 128 650

Louisiana 103 8.0 200 30,000

Maine -- -- -- --

Maryland 40 4.0 265 2,300

Massachusetts -- -- -- --

Michigan 0 -- -- --

Minnesota 63 <4.0 64.0 950

Mississippi 50 10.0 152 640

Missouri 39 4.0 57.0 1,000

Montana 2 2,260 2,650 3,040

Nebraska 22 17.0 71.2 720

Nevada 60 <10.0 20.0 3,100

New Hampshire 8 55.0 230 430

New Jersey 5 7.0 28.0 210

New Mexico 9 14.0 51.0 330

New York 8 20.0 48.0 600

North Carolina -- -- -- --

North Dakota 39 <10.0 30.0 160

Ohio 40 72.5 235 2,700

Oklahoma 14 50.0 450 2,150

Oregon 83 <4.0 140 >600

Pennsylvania 53 10.0 60.0 1,800

Rhode Island 5 27.0 56.0 160

South Carolina 310 1.0 170 2,600

South Dakota 96 <2.0 65.0 1,100

Tennessee 60 <2.0 210 4,250

Texas 457 <3.0 106 13,000

Utah 16 2.0 40.0 750

Vermont -- -- -- --

Virginia 1,086 <1.8 100 16,000

Washington 202 <1.0 20.8 510

West Virginia 26 <10.0 144 3,000

Wisconsin 44 <10.0 47.5 1,300

Wyoming 18 11.0 69.5 325
16 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 9. Number of State ambient stream-water-quality monitoring sites with data (nine or 

more analyses) for parameter codes of ammonia as nitrogen concentrations in water, 1990–98.

[--, not available]

State

Number of sites with data for parameter code1

1

See table 4 for complete descriptions of parameter codes. Data not organized by parameter code in the 

modern STORET system.

Number of sites in 

00608 merged databases

(dissolved)

00610

(total)

Alabama -- 18 18

Alaska -- -- --

Arizona -- -- --

Arkansas -- 131 131

California -- -- --

Colorado -- -- 163

Connecticut 29 24 29

Delaware 17 103 103

Florida 284 566 793

Georgia -- 283 283

Hawaii -- -- --

Idaho 45 12 47

Illinois -- 11 11

Indiana -- 106 106

Iowa -- 39 39

Kansas -- 251 251

Kentucky -- 60 60

Louisiana -- -- 0

Maine -- -- --

Maryland -- 40 40

Massachusetts -- -- --

Michigan -- 70 70

Minnesota -- 66 66

Mississippi -- 58 58

Missouri 14 35 39

Montana -- -- 140

Nebraska -- 22 22

Nevada 67 -- 67

New Hampshire -- -- 41

New Jersey 67 80 82

New Mexico 14 223 228

New York -- 19 19

North Carolina -- -- --

North Dakota -- -- 55

Ohio -- 41 41

Oklahoma -- 38 38

Oregon -- 143 143

Pennsylvania 2 174 174

Rhode Island 5 5 5

South Carolina -- 337 337

South Dakota -- 96 96

Tennessee -- 65 65

Texas 90 444 446

Utah -- -- 64

Vermont -- -- --

Virginia 67 902 957

Washington -- 204 204

West Virginia -- 26 26

Wisconsin 40 -- 40

Wyoming 21 11 21
Summary of Available State Ambient Stream-Water-Quality Data 17

Table 10. Summary of median ammonia as nitrogen concentrations in water from State ambient 

stream-water-quality monitoring sites (with nine or more analyses), 1990–98.

[<, less than; --, not available]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration

(milligrams per liter)

Minimum Median Maximum

Alabama 18 <0.01 <0.01 0.27

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 <.05 <.05 4.2

California -- -- -- --

Colorado 163 <.001 .003 .12

Connecticut 29 .02 .08 .85

Delaware 103 .03 .07 .66

Florida 793 <.01 .04 3.1

Georgia 283 .02 .03 2.3

Hawaii -- -- -- --

Idaho 47 .007 .03 .09

Illinois 11 .02 .12 .40

Indiana 106 <.10 <.10 .60

Iowa 39 .05 <.10 .11

Kansas 251 <.02 <.05 .88

Kentucky 60 <.05 <.05 .19

Louisiana 0 -- -- --

Maine -- -- -- --

Maryland 40 .01 .03 .14

Massachusetts -- -- -- --

Michigan 70 .01 .04 .30

Minnesota 66 <.02 .04 .22

Mississippi 58 <.10 .16 .46

Missouri 39 .01 .03 .10

Montana 140 <.01 <.01 2.9

Nebraska 22 .02 .06 .20

Nevada 67 .006 <.10 9.7

New Hampshire 41 <.01 <.10 <.10

New Jersey 82 .03 .07 .76

New Mexico 228 .02 <.10 5.3

New York 19 .008 .04 .17

North Carolina -- -- -- --

North Dakota 55 <.01 .03 .94

Ohio 41 <.05 <.05 .48

Oklahoma 38 .01 .07 1.4

Oregon 143 <.02 .02 .31

Pennsylvania 174 <.02 .02 .74

Rhode Island 5 .03 .46 1.3

South Carolina 337 <.05 <.05 .18

South Dakota 96 <.02 <.03 10.6

Tennessee 65 <.02 .03 .23

Texas 446 <.01 <.05 .68

Utah 64 <.05 <.05 .59

Vermont -- -- -- --

Virginia 957 .01 <.04 10.4

Washington 204 <.01 .01 2.9

West Virginia 26 <.50 <.50 <.50

Wisconsin 40 <.02 .05 .19

Wyoming 21 .02 .03 2.6
18 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

the most predominant ion because of the rapid oxidation of 

nitrite to nitrate.

Nitrate is the form of nitrogen most easily used by rooted 

green plants and algae and usually occurs in relatively small 

concentrations in uncontaminated surface water with a world 

average of 0.30 mg/L as nitrogen (Reid and Wood, 1976, 

p. 235). Larger concentrations may stimulate the growth of 

rooted plants or accelerate algal production to an extent that 

algae may produce a taste-and-odor problem in finished drinking water. Because most aquatic organisms can tolerate nitrite 

plus nitrate concentrations far in excess of what normally might 

be found even in contaminated surface water, no water-quality 

criteria have been established for protection of aquatic life. 

Adverse human-health effects of large concentrations of nitrate 

(greater than 10 mg/L) in drinking water include methemoglobinemia (blue-baby syndrome) in infants (U.S. Environmental 

Protection Agency, 1986). 

Sources of nitrite plus nitrate nitrogen in the aquatic environment are similar to those for ammonia. Point sources include 

municipal and industrial discharges, and nonpoint sources are 

mostly related to agricultural activities such as crop (fertilizer 

application) and livestock (manure distribution) production and 

urban uses such as lawn fertilizers.

Nitrite (NO2

-

) and nitrate (NO3

-

) ions are completely soluble in water (Follett, 1995). Therefore, determinations of 

nitrite plus nitrate as nitrogen concentrations in whole (total) or 

filtered (dissolved) water from ambient stream-water-quality 

monitoring sites generally should be comparable. Nitrite, generally, is an insignificant component of the nitrite plus nitrate 

determination because in most natural water nitrite is readily 

oxidized to nitrate (Hem, 1992). 

Historically, States have reported nitrite and nitrate determinations in several ways—only nitrate, nitrite and nitrate individually, and (or) combined determinations of nitrite and nitrate 

(table 11). These determinations have been made on filtered and 

unfiltered stream-water samples. Kansas, for example, currently (2004) determines concentrations of nitrite plus nitrate as 

nitrogen on unfiltered water samples (parameter code 00630) 

but historically had reported nitrate concentrations on filtered 

water samples (parameter code 00618). For the purpose of this 

report, the representation of inorganic oxides of nitrogen in 

stream-water samples was concentrations of nitrite plus nitrate 

as nitrogen (either parameter code 00630 or 00631). In the 

absence of either of these determinations, however, concentrations of nitrate as nitrogen (parameter codes 00618 or 00620) or 

as nitrate (parameter code 71851, subsequently expressed as 

nitrogen in this report) were used as surrogates for nitrite plus 

nitrate as nitrogen determinations under the assumptions that 

nitrite concentrations were small (relative to nitrate concentrations) in natural stream water and that no substantial differences 

existed between determinations made on filtered or unfiltered 

water samples. Hereinafter, all determinations of nitrate or 

nitrite and nitrate used in this report will be referred to as nitrite 

plus nitrate as nitrogen.

Most of the 42 States with electronically accessible nitrite 

plus nitrate as nitrogen concentrations analyzed for total 

concentrations (table 11). Some States, however, also analyzed 

for dissolved concentrations of nitrite plus nitrate either in combination with or instead of total concentrations. Because of the 

similarity in total and dissolved concentrations of nitrite plus 

nitrate as nitrogen, monitoring sites with these data were combined into merged State databases using a merge procedure 

identical to that used for merging ammonia data, with total concentrations having preference. State medians of monitoring-site 

median concentrations of nitrite plus nitrate as nitrogen ranged 

from 0.05 mg/L in Nevada to 5.7 mg/L in Iowa (table 12).

Phosphorus

Phosphorus is an essential nutrient for plant growth; however, in excess of critical concentrations, it may contribute to 

the eutrophication of surface-water resources. Eutrophication 

(nutrient enrichment) is characterized by an abundance of nutrients, decreases in dissolved oxygen, excess growth of algae, and 

an acceleration of the normal rate of ecological succession 

(Reid and Wood, 1976). Sources of phosphorus in surface water 

are similar to those previously identified for ammonia and 

nitrite plus nitrate as nitrogen. 

Phosphorus is ubiquitous in streams in much of the Nation. 

Some of this occurrence is due to the natural weathering of 

phosphorus in soil and rock, but a large part of the phosphorus 

in streams is the result of human activities. These activities may 

include point-source discharges from municipal and industrial 

facilities or nonpoint-source contributions related to runoff 

from urban and agricultural areas. Fertilizers containing phosphorus are routinely applied in crop production, often in conjunction with nitrogen fertilizers. Phosphorus compounds also 

are a component of livestock manure, and the land disposal of 

manure from confined animal-feeding operations and pasturing 

of livestock establish a substantial source of nonpoint-source 

phosphorus to the Nation’s rivers and streams (Heathwaite, 

1997; Sharpley and Rekolainen, 1997; U.S. Geological Survey, 

1999).

Data from 41 States were summarized for total phosphorus 

concentrations in water from ambient stream-water-quality 

monitoring sites. All phosphorus data retrieved were stored 

under a single parameter code (00665, table 4) or retrieved as 

“total phosphorus” from the modern STORET system. Therefore, a data-merge procedure was not necessary for total phosphorus concentrations. State medians of monitoring-site median 

concentrations of total phosphorus ranged from 0.02 mg/L in 

West Virginia to 0.33 mg/L in Illinois (table 13).

Arsenic

Arsenic is a nonmetallic element that has potential toxicological effects on aquatic organisms (U.S. Environmental Protection Agency, 1986). Arsenic occurs in the Earth’s crust at 

concentrations of about 2 to 5 mg/kg and has been distributed 

throughout the environment by natural weathering and human 

activities. One distribution mechanism is the burning of fossil 
Summary of Available State Ambient Stream-Water-Quality Data 19

Table 11. Number of State ambient stream-water-quality monitoring sites with data (nine or more analyses) for parameter 

codes of nitrate and nitrite plus nitrate as nitrogen concentrations in water, 1990–98.

[--, not available]

State

Number of sites with data for parameter code1

1

See table 4 for complete descriptions of parameter codes. Data not organized by parameter code in the modern STORET system.

Number of sites 

in merged 

database

00618

(dissolved)

00620

(total)

00630

(total)

00631

(dissolved)

718512

(dissolved)

2

Reported nitrate as nitrate (NO3) concentrations were converted to nitrate as nitrogen concentrations for use in this report.

Alabama -- 44 -- -- -- 44

Alaska -- -- -- -- -- --

Arizona -- -- -- -- -- --

Arkansas -- -- 131 -- -- 131

California -- -- -- -- -- --

Colorado -- -- -- -- -- 210

Connecticut -- -- 24 28 -- 30

Delaware -- 3 103 17 -- 103

Florida 11 351 696 105 -- 825

Georgia -- -- 283 -- -- 283

Hawaii -- -- -- -- -- --

Idaho -- -- 9 41 -- 45

Illinois -- -- 11 -- -- 11

Indiana -- -- 106 -- -- 106

Iowa -- -- 39 -- -- 39

Kansas 152 -- 168 -- -- 251

Kentucky -- -- 60 -- -- 60

Louisiana -- -- 172 -- -- 172

Maine -- -- -- -- -- --

Maryland -- -- 40 -- -- 40

Massachusetts -- -- -- -- -- --

Michigan -- 51 73 28 -- 85

Minnesota -- -- 66 -- -- 66

Mississippi -- -- 65 -- -- 65

Missouri -- -- 37 25 -- 40

Montana -- -- -- -- -- 235

Nebraska -- -- 22 -- -- 22

Nevada 63 -- -- -- 64 64

New Hampshire -- -- -- -- -- 46

New Jersey -- -- 85 72 -- 87

New Mexico -- -- 221 13 -- 230

New York -- -- 19 -- -- 19

North Carolina -- -- -- -- -- --

North Dakota -- -- -- -- -- 57

Ohio -- -- 41 -- -- 41

Oklahoma -- -- 3 111

3Concentrations of nitrite plus nitrate as nitrogen at some monitoring sites were calculated from individual nitrite and nitrate as nitrogen concentrations.

-- -- 111

Oregon -- -- 143 -- -- 143

Pennsylvania 1 171 -- -- -- 171

Rhode Island -- -- 5 5 -- 5

South Carolina -- -- 340 -- -- 340

South Dakota -- 47 50 -- -- 96

Tennessee -- -- 65 -- -- 65

Texas -- 266 180 102 -- 449

Utah -- -- -- -- -- 64

Vermont -- -- -- -- -- --

Virginia 85 901 -- 55 -- 957

Washington -- -- 204 -- -- 204

West Virginia -- -- -- -- -- 4 24

4No single monitoring site had nine or more analyses for any one parameter, but when merged, 24 monitoring sites had nine or more analyses 

of the combined parameters.

Wisconsin -- -- -- 42 -- 42

Wyoming -- -- 6 29 -- 29
20 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 12. Summary of median nitrite plus nitrate as nitrogen concentrations in 

water from State ambient stream-water-quality monitoring sites (with nine or 

more analyses), 1990–98

[--, not available; <, less than]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration

(milligrams per liter)

Minimum Median Maximum

Alabama 44 <0.01 0.45 3.7

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 <.02 .21 8.8

California -- -- -- --

Colorado 210 <.05 <.50 6.0

Connecticut 30 .13 .46 3.7

Delaware 103 .08 1.7 15.2

Florida 825 0 .07 9.7

Georgia 283 <.02 .26 3.5

Hawaii -- -- -- --

Idaho 45 .06 .22 2.4

Illinois 11 .18 4.3 11.4

Indiana 106 <.10 2.5 7.2

Iowa 39 .50 5.7 11.0

Kansas 251 .04 .54 6.8

Kentucky 60 .13 .48 5.3

Louisiana 172 <.02 .16 2.2

Maine -- -- -- --

Maryland 40 .39 1.4 5.7

Massachusetts -- -- -- --

Michigan 85 .01 .90 9.0

Minnesota 66 <.05 .53 32.0

Mississippi 65 <.02 .16 .64

Missouri 40 .08 .47 10.5

Montana 235 0 .07 33.5

Nebraska 22 .06 1.2 1.9

Nevada 64 0 .05 3.0

New Hampshire 46 <.02 .19 .68

New Jersey 87 .10 1.1 4.4

New Mexico 230 <.04 <.10 7.2

New York 19 .18 .44 1.2

North Carolina -- -- -- --

North Dakota 57 <.005 .08 .47

Ohio 41 .32 2.7 5.2

Oklahoma 111 .02 .24 7.1

Oregon 143 <.02 .12 4.1

Pennsylvania 171 <.04 .71 12.8

Rhode Island 5 .25 .71 .90

South Carolina 340 <.02 .18 6.5

South Dakota 96 <.10 .30 19.2

Tennessee 65 .07 .38 2.8

Texas 449 <.01 .39 29.0

Utah 64 <.02 .25 3.0

Vermont -- -- -- --

Virginia 957 0 .19 71.7

Washington 204 <.01 .20 9.4

West Virginia 24 .16 .43 2.0

Wisconsin 42 .05 .45 4.1

Wyoming 29 .06 .16 3.3
Summary of Available State Ambient Stream-Water-Quality Data 21

Table 13. Summary of median total phosphorus concentrations in water from 

State ambient stream-water-quality monitoring sites (with nine or more 

analyses), 1990–98.

[--, not available; <, less than]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration

(milligrams per liter)

Minimum Median Maximum

Alabama 45 0.01 0.09 4.5

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 <.03 .07 4.7

California -- -- -- --

Colorado 209 <.01 .05 2.7

Connecticut 32 .01 .05 .52

Delaware 103 .03 .10 .62

Florida 790 .002 .07 5.8

Georgia 283 <.02 .07 3.4

Hawaii -- -- -- --

Idaho 44 .005 .04 .49

Illinois 11 .06 .33 2.8

Indiana 106 <.03 .10 .38

Iowa 28 .10 .20 .50

Kansas 251 .04 .15 1.9

Kentucky 60 <.005 .04 .74

Louisiana 172 .03 .15 1.0

Maine -- -- -- --

Maryland 40 <.01 .05 .24

Massachusetts -- -- -- --

Michigan 83 .009 .06 .35

Minnesota 63 .01 .15 3.5

Mississippi 65 .03 .08 .39

Missouri 34 .02 .05 4.1

Montana 175 <.01 .04 2.7

Nebraska 22 .02 .18 .80

Nevada 67 .01 .06 .48

New Hampshire 46 .007 .03 .12

New Jersey 82 .02 .07 .45

New Mexico 225 <.01 <.09 4.6

New York 0 -- -- --

North Carolina -- -- -- --

North Dakota 57 <.02 .17 .64

Ohio 41 <.05 .11 1.2

Oklahoma 194 <.01 .04 .64

Oregon 141 .01 .05 .44

Pennsylvania 174 .02 .03 .64

Rhode Island 5 .02 .22 .34

South Carolina 339 <.02 .05 1.2

South Dakota 96 .01 .12 1.8

Tennessee 65 <.01 .05 .45

Texas 439 <.01 .12 4.7

Utah 64 <.01 .06 .98

Vermont -- -- -- --

Virginia 936 .01 <.10 13.8

Washington 206 <.01 .03 3.1

West Virginia 26 <.02 .02 .14

Wisconsin 44 .03 .09 .35

Wyoming 21 .02 .05 2.4
22 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

fuels (particularly coal) with potential contamination of surface-water resources (Manahan, 1994). Arsenic also has been 

introduced into the aquatic environment through industrial discharges and use as a component in some pesticides, most of 

which are currently (2004) banned (Manahan, 1994). However, 

arsenic (roxarsone) is still used as a feed additive for poultry for 

increased weight gain, feed efficiency, improved pigmentation, 

and prevention of parasites (Miller and others, 2000). Some 

ground water, particularly of geothermal origin, may contain 

relatively large natural concentrations of arsenic (Hem, 1992). 

Discharge of arsenic-enriched ground water may contaminate 

surface-water resources.

Data from 28 States were summarized for total arsenic 

concentrations in water from ambient stream-water-quality 

monitoring sites. All total arsenic data from monitoring sites 

with at least nine analyses had these data stored in STORET 

Legacy, NWIS, or State databases under parameter code 00978 

(total recoverable arsenic) or parameter code 01002 (total 

arsenic) or as “total arsenic” in the modern STORET system. 

However, only Washington stored data under parameter code 

00978 for a total of five monitoring sites. Total and total recoverable analyses generally are distinguished by the degree of 

digestion of a water/sediment sample. Total is used when the 

analytical procedure assures measurement of at least 95 percent 

of a constituent in both the dissolved and suspended phases. 

Total recoverable is used to represent something less than the 

“total” amount (less than 95 percent) (Fishman and Friedman, 

1989). However, for the purpose of the summary presented in 

this report, it was assumed that total arsenic concentrations 

stored under both parameter codes were analytically comparable. Because no monitoring site in Washington contained both 

total and total recoverable concentrations of arsenic, a merging 

procedure and selection of a preferred parameter were not 

required. State medians of monitoring-site median concentrations of total arsenic ranged from 0.80 μg/L in Washington to 

11.5 μg/L in South Dakota (table 14).

Dissolved Solids

Dissolved solids in surface water result from natural dissolution of rocks and minerals or discharges from municipal, 

industrial, or agricultural sources. The major constituents of 

dissolved solids are the cations (positively charged ions) calcium, magnesium, sodium, and potassium, and the anions (negatively charged ions) bicarbonate, carbonate, sulfate, and chloride. Natural variability in dissolved-solids concentrations 

depends on chemical characteristics of drainage-basin soils, 

composition of surficial material, and in some situations the 

minerals in deeper geologic strata. Larger dissolved-solids concentrations in surface water may be expected in areas underlain 

by ancient marine sediment containing large salt deposits (Bevans, 1989; Gillespie and Hargadine, 1994). Ground water dissolves the salt, which eventually discharges into surface water. 

Point-source discharges such as from industrial or municipal 

wastewater-treatment plants (Pope and Putnam, 1997) and 

nonpoint-source discharges from areas of extensive irrigation 

(Klein and Bradford, 1980; Libermann and others, 1989) also 

may increase dissolved-solids concentrations in surface water.

Excessively large concentrations of dissolved solids may 

be objectionable in drinking water because of possible physiological effects, unpalatable mineral taste, and greater cost 

because of (1) corrosion of plumbing, boilers, or other watertransfer or utility equipment, or (2) the necessity for additional 

treatment to remove the ions responsible for objectionable taste 

or corrosion. Because dissolved solids may not be removed 

from source water during traditional drinking-water treatment 

processes, more expensive reverse osmosis procedures (Chu 

and others, 1986, for example) may be required to produce 

drinking water of desirable quality.

Twenty-nine States had electronically accessible dissolved-solids concentrations in water from ambient streamwater-quality monitoring sites (table 15). Data from monitoring 

sites with nine or more analyses for dissolved solids were stored 

in STORET Legacy, NWIS, or State databases under one or 

more of four parameter codes for dissolved solids (00515, 

70294, 70300, 70301) or as “dissolved solids” in the modern 

STORET system. Although monitoring sites for most States 

had dissolved-solids concentrations stored under only one 

parameter code (most commonly 70300), Florida also had calculated dissolved-solids concentrations (parameter code 

70301). For the purpose of the summary presented in this report, 

it was assumed that all State analytical and calculated determinations of dissolved-solids concentrations were comparable 

and, therefore, were merged into State databases with a common dissolved-solids parameter (table 15). During the merge 

process for Florida, parameter code 70300 was used in preference over parameter code 70301. State medians of monitoringsite median concentrations of dissolved solids ranged from 

37.2 mg/L in Mississippi to 711 mg/L in South Dakota 

(table 16).

Although an assumption of comparability of State analytical and calculated results was made for the statistical summary 

of dissolved-solids concentrations (table 16), there may be evidence of an inconsistency in this assumption. The small median 

dissolved-solids concentration (37.2 mg/L) for Mississippi was 

determined from the medians of 46 monitoring sites that used 

the somewhat ambiguous parameter code 70294 (unspecified 

calculation). Relative to the bordering States of Alabama and 

Louisiana, which had median concentrations of 204 and 

196 mg/L, respectively, the median for Mississippi seems 

anomalous and possibly the result of a lack of computational 

comparability (not all of the same constituents may have been 

included in the dissolved-solids calculation).

Chloride

Chloride ion is the most common oxidation state (-1) of the 

element chlorine and is the only ion of major environmental significance in the hydrologic cycle. Chloride occurs mostly in 

small concentrations in all natural freshwater except for those 
Summary of Available State Ambient Stream-Water-Quality Data 23

Table 14. Summary of median total arsenic concentrations in water from State 

ambient stream-water-quality monitoring sites (with nine or more analyses), 1990–98.

[<, less than; >, greater than; --, not available]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration 

(micrograms per liter)

Minimum Median Maximum

Alabama 27 <5.0 <10.0 <10.0

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 0 -- -- --

California -- -- --- --

Colorado 0 -- -- --

Connecticut 0 -- -- --

Delaware 20 <10.0 <10.0 <10.0

Florida 128 .57 <1.5 <10.0

Georgia 0 -- -- --

Hawaii -- -- -- --

Idaho 0 -- -- --

Illinois 2 <1.0 1.1 1.1

Indiana 61 .30 1.5 3.2

Iowa 1 <10.0 <10.0 <10.0

Kansas 251 <1.0 4.0 <21.0

Kentucky 59 <2.0 <2.0 3.0

Louisiana 12 2.4 3.2 5.8

Maine -- -- -- --

Maryland 0 -- -- --

Massachusetts -- -- -- --

Michigan 48 <1.0 1.2 2.9

Minnesota 0 -- -- --

Mississippi 22 <3.0 <5.0 <5.0

Missouri 0 -- -- --

Montana 8 <1.0 >1.0 15.5

Nebraska 13 2.9 5.0 6.8

Nevada 59 <3.0 4.0 251

New Hampshire 1 <5.0 <5.0 <5.0

New Jersey 4 1.0 1.5 3.0

New Mexico 15 <1.0 <5.0 <5.0

New York 0 -- -- --

North Carolina -- -- -- --

North Dakota 24 1.4 3.2 7.9

Ohio 41 <2.0 <2.0 4.0

Oklahoma 0 -- -- --

Oregon 0 -- -- --

Pennsylvania 31 <4.0 <4.0 <4.0

Rhode Island 1 2.0 2.0 2.0

South Carolina 0 -- -- --

South Dakota 20 <5.0 11.5 37.1

Tennessee 70 <1.0 <2.0 6.0

Texas 9 1.0 2.0 3.0

Utah 54 <5.0 <5.0 20.0

Vermont -- -- -- --

Virginia 75 <5.0 <10.0 <10.0

Washington 5 .58 .80 3.7

West Virginia 0 -- -- --

Wisconsin 2 <10.0 <10.0 <10.0

Wyoming 0 -- -- --
24 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 15. Number of State ambient stream-water-quality monitoring sites with data (nine or more 

analyses) for parameter codes of dissolved-solids concentrations in water, 1990–98.

[

οC, degrees Celsius; --, not available]

State

Number of sites with data for parameter code1

1See table 4 for complete descriptions of parameter codes. Data not organized by parameter code in the modern 

STORET system.

Number of 

sites in merged 

database

00515

(dried at 

105 oC)

70294

(unspecified 

calculation)

70300

(dried at 

180 oC)

70301

(sum of 

constituents)

Alabama 42 -- -- -- 42

Alaska -- -- -- -- --

Arizona -- -- -- -- --

Arkansas -- -- 131 -- 131

California -- -- -- -- --

Colorado -- -- -- -- 212

Connecticut -- -- 32 -- 32

Delaware -- -- -- -- 0

Florida -- -- 246 6 253

Georgia -- -- -- -- 0

Hawaii -- -- -- -- --

Idaho -- -- 32 -- 32

Illinois -- -- -- -- 0

Indiana -- -- 23 -- 23

Iowa 28 -- -- -- 28

Kansas -- -- -- 251 251

Kentucky -- -- -- -- 0

Louisiana 172 -- -- -- 172

Maine -- -- -- -- --

Maryland 12 -- -- -- 12

Massachusetts -- -- -- -- --

Michigan -- -- -- -- 0

Minnesota -- -- -- -- 0

Mississippi -- 46 -- -- 46

Missouri -- -- 36 -- 36

Montana -- -- -- -- 84

Nebraska -- -- -- -- 0

Nevada 67 -- -- -- 67

New Hampshire -- -- -- -- 0

New Jersey -- -- 92 -- 92

New Mexico -- -- 228 -- 228

New York -- -- 19 -- 19

North Carolina -- -- -- -- --

North Dakota -- -- -- -- 52

Ohio -- -- 32 -- 32

Oklahoma -- -- -- -- 0

Oregon -- -- 1 -- 1

Pennsylvania 173 -- -- -- 173

Rhode Island -- -- 1 -- 1

South Carolina -- -- -- -- 0

South Dakota -- -- 96 -- 96

Tennessee 23 -- -- -- 23

Texas -- -- 284 -- 285

Utah -- -- -- -- 64

Vermont -- -- -- -- --

Virginia 82 -- -- -- 82

Washington -- -- -- -- 0

West Virginia -- -- -- -- 0

Wisconsin -- -- -- -- 0

Wyoming -- -- 11 -- 11
Summary of Available State Ambient Stream-Water-Quality Data 25

Table 16. Summary of median dissolved-solids concentrations in water from 

State ambient stream-water-quality monitoring sites (with nine or more 

analyses), 1990–98.

[--, not available]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration

 (milligrams per liter)

Minimum Median Maximum

Alabama 42 45.0 204 9,790

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 30.5 144 541

California -- -- -- --

Colorado 212 28.0 190 3,500

Connecticut 32 51.0 98.5 248

Delaware 0 -- -- --

Florida 253 2.0 201 5,960

Georgia 0 -- -- --

Hawaii -- -- -- --

Idaho 32 29.0 214 517

Illinois 0 -- -- --

Indiana 23 167 350 476

Iowa 28 170 335 600

Kansas 251 143 435 6,250

Kentucky 0 -- -- --

Louisiana 172 44.0 196 9,360

Maine -- -- -- --

Maryland 12 72.0 238 642

Massachusetts -- -- -- --

Michigan 0 -- -- --

Minnesota 0 -- -- --

Mississippi 46 .02 37.2 252

Missouri 36 128 201 671

Montana 84 9.0 120 2,920

Nebraska 0 -- -- --

Nevada 67 31.5 159 2,370

New Hampshire 0 -- -- --

New Jersey 92 23.0 136 534

New Mexico 228 28.0 206 8,320

New York 19 42.0 159 438

North Carolina -- -- -- --

North Dakota 52 158 634 2,190

Ohio 32 208 424 739

Oklahoma 0 -- -- --

Oregon 1 140 140 140

Pennsylvania 173 20.0 160 780

Rhode Island 1 74.0 74.0 74.0

South Carolina 0 -- -- --

South Dakota 96 122 711 3,540

Tennessee 23 85.5 162 262

Texas 285 62.0 507 35,100

Utah 64 98.0 437 3,450

Vermont -- -- -- --

Virginia 82 26.5 185 773

Washington 0 -- -- --

West Virginia 0 -- -- --

Wisconsin 0 -- -- --

Wyoming 11 65.0 244 1,890
26 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

that receive discharge of salt-laden ground water, municipal or 

industrial discharges, or are affected by oceanic tides. Seawater 

normally contains about 19,000 mg/L of chloride (Hem, 1992).

Chloride in streams has several natural sources; the dominant source in noncoastal areas probably is the dissolution of 

marine salt from sedimentary rock formations, particularly 

evaporite deposits. In contrast, igneous rock is expected to yield 

little chloride to solution (Hem, 1992). Wet (precipitation) and 

dry (atmospheric) deposition are secondary sources of chloride 

to the land surface (Lynch and others, 1996). These sources 

would have the greatest effects in near-coastal or coastal areas 

where chloride had been entrained in the atmosphere during the 

evaporation of seawater or transported by tidal activity.

Natural concentrations of chloride may be enriched by 

human activities particularly those associated with urbanization. Municipal-sewage discharges may contribute chloride to 

streams (Phillips, 1994; Pope and Putnam, 1997). Road salt can 

be a major contaminant of streams in both urban and rural areas. 

Snowmelt runoff from roads and bridges treated with salt can 

transport large concentrations of sodium and chloride to 

streams that can change water chemistry and stress or kill 

aquatic organisms (U.S. Environmental Protection Agency, 

1995). 

The chloride ion is one of the most conservative of the 

major solutes in natural water and does not enter into oxidation 

or reduction reactions, form solute complexes with other ions, 

or form salts of low solubility (Hem, 1992). Therefore, concentrations of chloride determined from whole water (total 

analysis) samples and filtered water (dissolved analysis) samples should be similar.

An inconsistency in parameter codes exists for total and 

dissolved chloride concentrations between the STORET Legacy and NWIS data-management systems. The STORET Legacy parameter code for total chloride is 00940 (table 4), whereas 

this same code in the NWIS system represents dissolved chloride. Because of this inconsistency, parameter headings in 

table 17 were simplified to “Total” and “Dissolved.”

Thirty-nine States had ambient stream-water-quality monitoring sites with at least nine analyses for chloride concentrations (table 17). Most of these chloride concentrations were 

total analyses; however, 15 States had monitoring sites with 

determinations of total and (or) dissolved chloride concentrations. New Mexico had 15 monitoring sites operated by the 

USGS, with analyses for dissolved chloride concentrations 

only. Other States with USGS-operated monitoring sites with 

dissolved chloride concentrations only included Connecticut, 

Idaho, Missouri, New Jersey, Rhode Island, and Wyoming. 

Because of the suspected similarity in total and dissolved concentrations of chloride, total and dissolved data were combined 

to create merged State databases with a procedure similar to that 

used to combine total and dissolved ammonia concentrations 

previously discussed in this report except that total chloride 

concentrations (the most commonly reported among the States) 

was used in preference over dissolved concentrations. The 

water-quality summary for chloride was conducted on these 

merged State databases. State medians of monitoring-site 

median concentrations of chloride ranged from 0 mg/L in 

Montana to 7,740 mg/L in Georgia (table 18). The exceptionally large monitoring-site median concentration for Georgia 

probably is due to its seven monitoring sites being located near 

the coast on tidal-affected streams subject to chloride fluxes 

from marine water.

Sulfate

Sulfate is an oxidized form of sulfur and occurs naturally 

in surface water as a result of weathering of metallic sulfides in 

igneous and sedimentary rocks. Pyrite (iron disulfide) commonly occurs in sedimentary rocks and coal deposits and can be 

a major source of sulfate ion when oxidized. This natural oxidation process can be enhanced due to mineral- or coal-mining 

operations that may expose large quantities of pyrite to weathering. Gypsum (calcium sulfate) also is a source of sulfate in 

sedimentary rocks (Hem, 1992).

In addition to natural sources, sulfate concentrations in 

streams may be increased as a result of human activities. As previously indicated, sulfate concentrations in streams in mined 

areas may be larger than in unmined areas because of weathering of sulfide- or sulfate-bearing minerals (Powell, 1988). 

Drainage water from irrigated areas, particularly in semiarid 

lands, may contain large sulfate concentrations as a result of 

leaching of solutes (Orlob and Ghorbanzadeh, 1981; Sorenson 

and Schwarzbach, 1991). The additional water supplied by irrigation accelerates the natural leaching process and is especially 

evident in areas that receive little natural precipitation. The 

release of sulfur dioxide during the combustion of fossil fuels 

(Johnson, 1986) may increase stream sulfate concentrations 

(Smith and Alexander, 1986). The conversion of sulfur dioxide 

to particulate sulfate is believed to be an aqueous-enhanced 

chemical reaction in the atmosphere (Lamb and others, 1987). 

Subsequent wet and dry deposition may increase concentrations 

of sulfate in surface water.

Determination of sulfate concentrations in whole (total 

analysis) and filtered (dissolved analysis) water samples should 

provide similar results because of the ionic nature and solubility 

of sulfate (Hem, 1992) and because most of the methods for sulfate analysis incorporate a turbidity removal step (Clesceri and 

others, 1998). Because of the suspected similarity in total and 

dissolved concentrations of sulfate, total and dissolved data 

were combined to create merged State databases with a procedure similar to that used to combine State total and dissolved 

ammonia concentrations previously discussed in this report 

except total sulfate concentrations (the most commonly 

reported among the States) was included in preference over dissolved concentrations. The water-quality summary for sulfate 

was conducted on these merged State databases (table 19).

An inconsistency in parameter codes exists for total and 

dissolved sulfate concentrations between the STORET Legacy 

and NWIS data-management systems. The STORET Legacy 

parameter code for total sulfate is 00945 (table 4), whereas this 

same code in the NWIS represents dissolved sulfate. Because of 

this inconsistency, parameter headings in table 19 were simplified to “Total” and “Dissolved.”
Summary of Available State Ambient Stream-Water-Quality Data 27

Table 17. Number of State ambient stream-water-quality monitoring sites 

with data (nine or more analyses) for total and dissolved chloride 

concentrations in water, 1990–98.

[--, not available]

State

Number of sites with indicated analysis Number of 

sites in 

merged 

database

Total Dissolved

Alabama 45 -- 45

Alaska -- -- --

Arizona -- -- --

Arkansas 131 -- 131

California -- -- --

Colorado -- -- 0

Connecticut -- 31 31

Delaware 95 -- 95

Florida 600 149 653

Georgia 7 -- 7

Hawaii -- -- --

Idaho -- 35 35

Illinois 7 -- 7

Indiana 15 -- 15

Iowa 6 -- 6

Kansas 168 152 251

Kentucky 60 -- 60

Louisiana 172 -- 172

Maine -- -- --

Maryland -- -- 0

Massachusetts -- -- --

Michigan 93 -- 93

Minnesota 10 -- 10

Mississippi 56 -- 56

Missouri -- 35 35

Montana 48 84 132

Nebraska 22 -- 22

Nevada -- 67 67

New Hampshire 12 -- 12

New Jersey -- 92 92

New Mexico 116 15 131

New York 19 -- 19

North Carolina -- -- --

North Dakota -- 52 52

Ohio 40 -- 40

Oklahoma 177 -- 177

Oregon -- 4 4

Pennsylvania 41 -- 41

Rhode Island -- 5 5

South Carolina 14 -- 14

South Dakota 8 -- 8

Tennessee 1 -- 1

Texas 495 -- 495

Utah -- 64 64

Vermont -- -- --

Virginia 897 -- 897

Washington -- -- 0

West Virginia 25 -- 25

Wisconsin 47 1 47

Wyoming -- 19 19
28 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 18. Summary of median chloride concentrations in water from State 

ambient stream-water-quality monitoring sites (with nine or more analyses), 

1990–98.

[--, not available; <, less than]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration

(milligrams per liter)

Minimum Median Maximum

Alabama 45 3.0 12.0 5,160

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 1.9 4.8 124

California -- -- -- --

Colorado 0 -- -- --

Connecticut 31 9.6 19.0 51.0

Delaware 95 8.0 27.0 12,900

Florida 653 1.6 23.0 4,260

Georgia 7 67.1 7,740 14,500

Hawaii -- -- -- --

Idaho 35 .25 5.0 67.0

Illinois 7 24.8 99.6 144

Indiana 15 11.0 41.0 190

Iowa 6 21.1 22.8 23.4

Kansas 251 4.6 29.6 3,220

Kentucky 60 2.3 6.5 36.5

Louisiana 172 2.8 18.3 5,320

Maine -- -- -- --

Maryland 0 -- -- --

Massachusetts -- -- -- --

Michigan 93 2.0 31.5 188

Minnesota 10 7.2 12.0 25.0

Mississippi 56 0 5.6 19.7

Missouri 35 2.2 6.4 136

Montana 132 0 0 36.0

Nebraska 22 1.0 16.6 52.4

Nevada 67 0 5.6 395

New Hampshire 12 10.0 26.5 69.0

New Jersey 92 4.3 23.5 220

New Mexico 131 1.6 5.2 2,140

New York 19 3.8 18.0 96.0

North Carolina -- -- -- --

North Dakota 52 <3.0 14.6 922

Ohio 40 10.0 36.0 162

Oklahoma 177 2.1 <10.0 1,720

Oregon 4 1.6 2.8 17.0

Pennsylvania 41 .66 10.0 63.0

Rhode Island 5 14.0 51.0 57.8

South Carolina 14 8.5 12.9 10,000

South Dakota 8 2.0 24.4 92.0

Tennessee 1 18.0 18.0 18.0

Texas 495 5.0 73.0 17,600

Utah 64 2.5 31.6 792

Vermont -- -- -- --

Virginia 897 .6 9.5 16,700

Washington 0 -- -- --

West Virginia 25 1.6 6.0 24.4

Wisconsin 47 2.0 11.4 158

Wyoming 19 .20 4.5 140
Summary of Available State Ambient Stream-Water-Quality Data 29

Table 19. Number of State ambient stream-water-quality monitoring sites 

with data (nine or more analyses) for total and dissolved sulfate 

concentrations in water, 1990–98.

[--, not available]

State

Number of sites with indicated 

analysis

Number of sites 

in merged 

database Total Dissolved

Alabama -- -- 0

Alaska -- -- --

Arizona -- -- --

Arkansas 131 -- 131

California -- -- --

Colorado 215 -- 215

Connecticut -- 32 32

Delaware -- -- 0

Florida 506 144 593

Georgia -- -- 0

Hawaii -- -- --

Idaho -- 37 37

Illinois 3 -- 3

Indiana 12 -- 12

Iowa 6 -- 6

Kansas 168 152 251

Kentucky -- 59 59

Louisiana 172 -- 172

Maine -- -- --

Maryland 12 -- 12

Massachusetts -- -- --

Michigan 64 -- 64

Minnesota 1 -- 1

Mississippi 2 -- 2

Missouri -- 34 34

Montana 72 91 163

Nebraska -- -- 0

Nevada -- 66 66

New Hampshire 8 -- 8

New Jersey -- 92 92

New Mexico 58 59 132

New York 19 -- 19

North Carolina -- -- --

North Dakota -- 52 52

Ohio 36 -- 36

Oklahoma 178 -- 178

Oregon -- -- 0

Pennsylvania 174 -- 174

Rhode Island -- 5 5

South Carolina 5 -- 5

South Dakota 8 -- 8

Tennessee 2 -- 2

Texas 481 -- 481

Utah -- 64 64

Vermont -- -- --

Virginia 894 -- 894

Washington -- -- 0

West Virginia 26 -- 26

Wisconsin 17 -- 17

Wyoming -- 19 19
30 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Thirty-six States had ambient stream-water-quality monitoring sites with at least nine analyses for sulfate concentrations 

in stream water (table 19). Most of these sulfate concentrations 

were total analyses; however, 14 States had monitoring sites 

with determinations of total and (or) dissolved sulfate concentrations. Many of the monitoring sites in States with dissolved 

sulfate concentrations were operated by the USGS, which only 

analyzed for dissolved sulfate concentrations. These USGSoperated monitoring sites were in the same States as previously 

identified in the “Chloride” section of this report. State medians 

of monitoring-site median concentrations of sulfate ranged 

from 6.5 mg/L in New Hampshire to 232 mg/L in North Dakota 

(table 20).

pH

pH is a measure of the hydrogen-ion activity in a water 

sample and by definition is the negative base-10 logarithm of 

the hydrogen-ion activity (-log10 H+) (Hem, 1992). pH measurements of natural water serve as an indicator of acid-base 

equilibrium of various dissolved compounds, salts, and gases. 

The principal equilibrium system controlling pH in natural 

water is the carbonate system—carbon dioxide (CO2), carbonic 

acid (H2CO3), bicarbonate ion (HCO3

-1), and carbonate ion 

(CO3

-2) (U.S. Environmental Protection Agency, 1986). The 

degree of dissociation of weak acids, bases, and salts 

(compounds) is affected by changes in pH that subsequently 

can affect the toxicological properties of those and other compounds (Franklin and others, 2000; Pyle and others, 2002). 

Therefore, knowledge of the pH of natural water may provide 

insight into the potential for detrimental effects on aquatic 

ecosystems.

Uncontaminated stream water generally has a pH in the 

range of 6.5 to 8.5 standard units (Hem, 1992) and may display 

diurnal fluctuations similar to those for dissolved oxygen 

(Simonsen and Harremoes, 1978). These diurnal pH fluctuations probably are associated with photosynthetic/respiratory 

processes of aquatic organisms that use dissolved carbon dioxide during the day and release it at night. Snowmelt runoff, 

which may increase during the warmth of the day and 

decrease during the cool of the night, also may produce diurnal 

pH fluctuations.

All 42 States with electronically accessible pH measurements in water from ambient stream-water-quality monitoring 

sites had these data stored in STORET Legacy, NWIS, or State 

databases under a single parameter code (00400, table 4) or as 

“pH” in the modern STORET system. Therefore, a data-merge 

procedure was not necessary for pH measurements. State medians of the monitoring-site median measurements of pH ranged 

from 6.7 standard units in Rhode Island and South Carolina to 

8.2 standard units in several other States (table 21).

Limitations of State Ambient Stream-WaterQuality Data for National Assessment

The use of stream-water-quality data from State ambient 

monitoring networks has certain inherent limitations for producing a “picture” of national water-quality conditions. The 

Clean Water Act granted the States the independence to establish stream-water-quality monitoring networks to fulfill the 

requirements of the act and to develop monitoring procedures 

and protocols to satisfy unique blends of ecological, social, 

political, and economic conditions within each State. The very 

nature of this independence, however, created potential variability in the factors necessary to produce a nationally consistent water-quality assessment. These factors include (1) the 

basic spatial design of monitoring networks (selection of 

streams and location of monitoring sites); (2) water-quality constituents for which samples are analyzed; (3) water-quality criteria to which constituent concentrations are compared; 

(4) quantity and comprehensiveness of water-quality data; 

(5) sample collection, processing, and handling; (6) analytical 

methods; (7) temporal variability in sample collection; and 

(8) quality-assurance practices implemented to ensure reliability in data produced. National assessment of ambient streamwater quality using State-generated databases, therefore, consists of a compilation of 50 individual monitoring networks 

with varying degrees of comparability. Furthermore, in a study 

of water-quality assessment procedures of the Great Lake 

States, the Environmental Integrity Project (2004) concluded 

that no meaningful attempt to standardize or analyze widely disparate State approaches to water-quality assessment has been 

conducted and that the biannual National Water Quality Inventory reports may not present a true picture of national or 

regional water-quality conditions. USEPA (2004) also has recognized that many of these factors make it “...difficult to use 

existing data to give a complete and accurate picture of the state 

of U.S. surface waters to support aquatic life... .” Although a 

detailed evaluation of the variability among States in all these 

factors was beyond the resources and scope of the investigation 

described in this report, aspects of factors 1–4 will be discussed 

relative to the variability among State ambient stream-waterquality programs identified in this or previous reports.

Design of Monitoring Networks

The implementation of water-quality monitoring is a key 

aspect of the Clean Water Act. Monitoring forms the basis of 

environmental assessment, the ability to determine time trends 

in water quality, and provides the information required for regulatory decisions related to contaminant-load allocation (total 

maximum daily loads), discharge permitting, and human health. 

Without reliable stream-water-quality data, government agencies, the Congress, and the public can not make the informed 

decisions necessary to protect and conserve the Nation’s water 

resources.
Limitations of State Ambient Stream-Water-Quality Data for National Assessment 31

Table 20. Summary of median sulfate concentrations in water from State 

ambient stream-water-quality monitoring sites (with nine or more analyses), 

1990–98.

[--, not available; <, less than]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median concentration 

(milligrams per liter)

Minimum Median Maximum

Alabama 0 -- -- --

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 2.7 9.9 181

California -- -- -- --

Colorado 215 <5.0 41.0 1,920

Connecticut 32 5.5 11.0 31.0

Delaware 0 -- -- --

Florida 593 0 12.1 651

Georgia 0 -- -- --

Hawaii -- -- -- --

Idaho 37 .60 17.0 120

Illinois 3 70.0 85.0 108

Indiana 12 24.0 40.0 86.5

Iowa 6 38.8 58.1 78.4

Kansas 251 10.1 81.5 2,170

Kentucky 59 5.5 31.0 290

Louisiana 172 1.4 10.7 728

Maine -- -- -- --

Maryland 12 27.8 122 650

Massachusetts -- -- -- --

Michigan 64 3.0 29.0 82.0

Minnesota 1 12.0 12.0 12.0

Mississippi 2 <10.0 15.4 15.4

Missouri 34 2.3 15.0 160

Montana 163 0 13.0 2,980

Nebraska 0 -- -- --

Nevada 66 0 12.5 960

New Hampshire 8 1.0 6.5 7.0

New Jersey 92 4.2 18.0 54.0

New Mexico 132 <5.0 21.6 4,700

New York 19 6.1 16.5 82.5

North Carolina -- -- -- --

North Dakota 52 12 232 742

Ohio 36 38.0 85.2 160

Oklahoma 178 1.3 12.4 1,870

Oregon 0 -- -- --

Pennsylvania 174 4.1 28.0 348

Rhode Island 5 6.8 19.0 20.9

South Carolina 5 <10.0 <10.0 22.0

South Dakota 8 15.6 208 400

Tennessee 2 107 147 187

Texas 481 2.3 52.6 3,340

Utah 64 9.8 75.4 1,640

Vermont -- -- -- --

Virginia 894 1.2 11.8 2,240

Washington 0 -- -- --

West Virginia 26 10.0 23.2 190

Wisconsin 17 <5.0 31.0 76.0

Wyoming 19 2.2 54.4 940
32 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 21. Summary of median pH measurements in water from State ambient streamwater-quality monitoring sites (with nine or more analyses), 1990–98.

[--, not available]

State

Number of 

assessed 

monitoring 

sites1

1

Nine or more analyses per site.

Monitoring-site median measurement

 (standard units)

Minimum Median Maximum

Alabama 45 5.1 7.4 7.9

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 6.2 7.3 8.2

California -- -- -- --

Colorado 205 4.6 8.1 9.1

Connecticut 32 7.1 7.4 8.2

Delaware 103 6.5 7.2 8.0

Florida 690 3.8 7.0 8.4

Georgia 284 3.9 7.0 7.9

Hawaii -- -- -- --

Idaho 51 7.1 8.2 8.7

Illinois 11 7.2 7.6 8.3

Indiana 101 7.4 7.8 8.2

Iowa 36 7.9 8.2 8.5

Kansas 247 6.9 8.0 8.6

Kentucky 60 6.6 7.5 8.0

Louisiana 172 5.9 7.1 8.0

Maine -- -- -- --

Maryland 40 7.0 7.8 8.3

Massachusetts -- -- -- --

Michigan 79 7.3 8.0 8.3

Minnesota 66 7.5 8.2 8.4

Mississippi 66 6.0 7.1 7.8

Missouri 38 7.2 7.9 8.2

Montana 276 2.8 7.6 8.8

Nebraska 22 7.9 8.1 8.3

Nevada 35 7.8 8.2 8.7

New Hampshire 55 6.1 7.0 7.6

New Jersey 89 4.3 7.6 8.3

New Mexico 211 4.6 8.2 9.0

New York 19 7.3 7.7 8.3

North Carolina -- -- -- --

North Dakota 72 7.2 8.2 8.7

Ohio 39 7.0 8.0 8.3

Oklahoma 133 2.6 7.5 8.5

Oregon 140 6.8 7.6 8.6

Pennsylvania 174 4.6 7.4 8.3

Rhode Island 5 6.6 6.7 6.9

South Carolina 339 5.4 6.7 8.0

South Dakota 96 4.8 8.2 8.7

Tennessee 43 6.2 7.3 7.9

Texas 546 6.0 7.8 8.9

Utah 64 7.8 8.2 8.5

Vermont -- -- -- --

Virginia 898 3.7 7.2 8.4

Washington 207 6.8 7.6 8.7

West Virginia 24 6.8 7.6 8.3

Wisconsin 38 7.1 7.9 8.6

Wyoming 36 7.6 8.2 8.6
Limitations of State Ambient Stream-Water-Quality Data for National Assessment 33

Stream-water-quality monitoring data are produced from 

networks composed of monitoring sites (specific locations on 

streams) from which streamflow samples are collected over 

some specified interval of time. Although this is a simplistic 

description, monitoring networks, in practice, are composed of 

a complex set of operational variables that can make individual 

State networks functionally unique and may restrict the Stateto-State comparability necessary to produce a national assessment of stream-water quality. Network operational variables 

include (1) the basic design option (census, judgemental or targeted, statistical or probabilistic survey), (2) type of monitoring 

network (physical, chemical, biological), (3) selections of 

streams and sampling locations on streams, and (4) temporal 

coverage (hour, day, week, month, or year).

Variability in network design stems from a need for States 

to meet State-defined water-quality management objectives, 

which may not be limited solely to Clean Water Act goals. 

Other objectives may include acquisition of data to establish 

water-quality criteria, determination of water-quality status and 

trends—including areal and temporal extent of known contamination, identification of causes and sources of water-quality 

problems, implementation and evaluation of water-quality management programs, and calculation of constituent transport 

(U.S. Environmental Protection Agency, 2003b). 

These objectives are met by the States, in part, through the 

design of their ambient stream-water-quality monitoring networks. The census option, or monitoring of all streams and rivers within a State, is rarely, if ever, used as the sole monitoring 

design because of the staff and funding necessary to conduct 

such an ambitious effort. More commonly used in State monitoring networks are the judgemental- or statistical-based design 

options (U.S. General Accounting Office, 2002). The judgemental design may target monitoring-site locations or limited 

monitoring resources on areas with suspected or known waterquality problems or on areas that are used frequently by the public. The statistical-based option uses randomized site-selection 

processes to provide statistically valid information that may be 

extrapolated to all State water of a similar type. In reality, States 

may use a combination of design options to fulfill the requirements of State-defined water-quality objectives.

The type of monitoring networks used for ambient streamwater-quality assessment may vary among States. Most States 

use some form of physical and chemical water-quality analysis 

for assessment purposes to meet the objectives of the Clean 

Water Act. Some of these physical and chemical water-quality 

constituents were summarized in this report, but States often 

analyze for a much broader suite of constituents to include pesticides, volatile organic chemicals, and toxic contaminants. 

Some States (Maine and Vermont, for example) rely almost 

exlusively on biological monitoring, whereas others such as Illinois, Kansas, New York, and Ohio incorporate physical, chemical, and biological data into their 305(b) assessments (U.S. 

General Accounting Office, 2002).

The criteria and rational used in selection of streams and 

sampling sites to assess may be keyed to the network design 

chosen by the States. For example, a substantial reliance on 

statistical-survey design will dictate stream and site selection on 

the basis of random selection, whereas target-based designs 

may incorporate more professional judgement in selection of 

suspected or known problem areas or areas with intensive 

human-use activity. Other factors that may control or limit site 

selection include the need for point- or nonpoint-source definition, a desire to “piggy back” upon other State or Federal water 

programs and sites such as the USGS streamgaging network, or 

requests or constraints mandated from political or economic 

entities. The variability among States in network design, type of 

monitoring, and stream and site selection makes a compilation 

of State data into a national picture of stream-water quality 

problematic.

Prior to the mid-1980s, no program existed to integrate 

information from the local or regional scale to the national scale 

to provide a consistent description of water quality across the 

Nation and insight on the major factors that control water quality in different regions. Hirsch and others (1988) outlined a 

national assessment design (program) that would integrate 

information from a large set of hydrologic systems to provide 

regional and national overviews. Results from hydrologic study 

units would be linked together by a core set of consistent operational protocols that include (1) study approaches, (2) sample 

collection, processing, and handling, (3) laboratory methods 

and quality assurance, (4) selection of water-quality constituents, (5) collection of ancillary information pertinent to the 

hydrologic setting and possible cause-and-effect relations, and 

(6) storage of all assessment data. This proposed design evolved 

into the USGS National Water-Quality Assessment (NAWQA) 

Program.

Implemented in 1991, the purpose of the NAWQA Program is to describe the status of current water-quality conditions, long-term trends (or lack of trends) in water quality, and 

to identify, describe, and explain possible cause-and-effect relations for the water-quality conditions (Gilliom and others, 

1995). Information from individual hydrologic study units 

(river basins or ground-water systems) would provide detailed 

descriptions of local and regional water-quality conditions, 

identify water-quality concerns and problem areas, and provide 

the consistent data necessary for national assessments (national 

synthesis) of priority water-quality issues such as nutrients, pesticides, volatile organic contaminants, and trace elements. 

National synthesis integrates information from individual 

study units into multiple study-unit analyses and incorporates 

existing information from other agencies and researchers to 

produce regional- and national-scale assessments. National synthesis develops comprehensive assessments issue by issue at the 

national scale by comparative analysis of study-unit findings 

(Gilliom and others, 1995). These comparative analyses are 

possible only because of the consistency in assessment network 

design and operation among the study units. The regular accumulation of consistent and comparable water-quality assessments for some of the largest and most important hydrologic 

systems of the Nation provides a major contribution to the 

knowledge of regional and national water quality (National 

Research Council, 2002).
34 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Selection of Water-Quality Constituents and Criteria

The selection of water-quality constituents for which 

States choose to analyze may have substantial effect on the utility of State ambient stream-water-quality data to provide a reliable national water-quality assessment. It was previously mentioned that the type of stream-water-quality monitoring 

(physical, chemical, biological) that States conduct may vary. 

This lack of commonality in monitoring practices makes direct 

State-to-State comparisons difficult. Not only is it difficult to 

make water-quality comparisons among States, but also, variability in monitoring practices within States (among monitoring 

sites) makes it difficult to get reliable pictures of within State 

water-quality conditions when the types and number of waterquality constituents vary among the sites.

USEPA (2002c) has determined that some of the most 

common causes of streams being listed in State 303(d) reports 

(degraded water quality) are the result of excessive concentrations of sediment, bacteria, nutrients, and metals. All States, 

however, do not analyze for the same set of water-quality constituents. For example, electronically accessible fecal coliform 

bacteria data were not available for Delaware, Indiana, or Michigan, seven other States had data for less than 10 monitoring 

sites (table 8), and total phosphorus concentrations were not 

available for monitoring sites in New York (table 13).

Differences in data collected among monitoring sites 

within States produce a skewed or biased overall assessment of 

water quality for the States. For example, Oklahoma had 

14 monitoring sites with nine or more analyses for fecal 

coliform bacteria (table 8), but substantially more monitoring 

sites were analyzed for total phosphorus (194; table 13), chloride (177; table 17), and pH (133; table 21). Median monitoringsite densities of fecal coliform bacteria were relatively large in 

Oklahoma (50 to 2,150 col/100 mL; table 8), so it is possible 

that water at many of these sites may have been assessed as 

degraded, but because the 14 monitoring sites represent only a 

small percentage of all the sites potentially assessed, the percentage of stream miles degraded for sanitary quality may be 

small relative to what it may have been had more of the total 

number of monitoring sites been assessed. The variability in 

constituents analyzed among monitoring sites within a State 

and among the States also makes an assessment of national 

water-quality conditions from State databases problematic.

Most stream-water-quality constituents analyzed by States 

have associated criteria to measure whether the designated use 

of the stream is being achieved. USEPA (1999a; 1999b) has 

recommended water-quality criteria for aquatic-life protection 

for many of the constituents summarized in this report 

(table 22). Public drinking-water criteria (U.S. Environmental 

Protection Agency, 2002b) also exist for most of these constituents. USEPA currently (2004) has not implemented waterquality criteria for suspended solids, fecal coliform bacteria, or 

total phosphorus. States have the flexibility, however, to establish their own stream-water-quality criteria for aquatic-life protection on the basis of unique sets of conditions that include designated uses of streams, ecological characteristics such as 

aquatic-life community structure, and State-determined concentration levels necessary for protection of human health 

through direct or indirect contact. The resulting variability in 

these water-quality criteria among the States reduces the potential for State-generated assessments of ambient stream-water 

quality to produce a national perspective of water-quality 

conditions.

Some water-quality constituents, such as suspended solids, 

do not have numeric criteria in most States. Instead, these States 

use a narrative criteria that generally state that the occurrence of 

suspended material in rivers and streams shall not be of such 

magnitude as to inhibit the intended use of the water and shall 

not have a detrimental effect on growth or reproduction of 

aquatic life. However, five States (Hawaii, Nevada, New Jersey, South Dakota, and Utah) do have numeric criteria for suspended solids, which range from a minimum concentration of 

35 mg/L in Utah to a maximum of 158 mg/L in South Dakota 

(U.S. Environmental Protection Agency, 2001b). The absence 

of numeric criteria for most States introduces subjectivity into 

the water-quality assessment process and reduces the comparability of State assessments and the potential for collating these 

assessments into a reliable national perspective of stream-water 

quality.

In contrast to the absence of State numeric criteria for suspended solids, the States generally had numeric criteria for fecal 

coliform bacteria (table 23). Primary contact recreation criteria 

range from 50 (Washington) to 1,000 col/100 mL (colonies per 

100 mL of water) in four States. The larger criteria, however, 

generally are single-sample (SS) criteria, whereas most State 

criteria are expressed as a geometric mean (GM). The GM is the 

mean of the logarithms of data transformed back to the original 

unit of measure and, in positively skewed or log-normally distributed data, approximates the median (Helsel and Hirsch, 

1995). As defined by USEPA, a GM for bacteria is the GM of 

at least five samples collected in separate 24-hour periods during a 30-day period (U.S. Environmental Protection Agency, 

2000a). However, few States collect the required five bacteria 

samples in a 30-day period necessary for calculation of a 

USEPA-defined geometric mean; therefore, in practice States 

either have not assessed streams for degradation relative to fecal 

bacteria, used the geometric mean of the data available or some 

other measure of central tendency, or compared bacteria densities to the numeric value of the geometric mean. Because few 

sites had more than one bacteria sample in a single 30-day 

period, the geometric mean for that period is the same as the 

single-sample value.

Fewer States have a secondary contact recreation 

criterion for fecal coliform bacteria than have a primary 

contact recreation criterion (table 23). Secondary contact 

recreation is defined as activities where ingestion of water 

is unlikely, such as fishing or wading. State criteria for 

secondary contact recreation range from 200 col/100 mL in 

five States to 5,000 col/100 mL in Ohio. 

The criteria discussion for bacteria presented in this report 

was restricted to fecal coliform bacteria, the most common measure of sanitary quality of streams in the 1990s. However,
Limitations of State Ambient Stream-Water-Quality Data for National Assessment 35

Table 22. Selected water-quality criteria for State ambient stream-water-quality data.

[mg/L, milligrams per liter; col/100 mL, colonies per 100 milliliters of water; N, nitrogen; P, phosphorus; μg/L,micrograms per liter; CMC, Criterion Maximum 

Concentration; CCC, Criterion Continuous Concentration; MCL, Maximum Contaminant Level; SDWR, Secondary Drinking-Water Regulation (nonenforceable 

recommendations); HAL, Health Advisory Level; --, not available]

Water-quality constituent or measurement

U.S. Environmental Protection Agency criteria

Stream-waterquality goal

Aquatic life1

1U.S. Environmental Protection Agency (1999a).

Public drinking water2

2

Criteria apply to post-treatment water; U.S. Environmental Protection Agency (2002b).

CMC CCC MCL SDWR HAL

Solids, suspended, mg/L -- -- -- -- -- --

Bacteria, fecal coliform, col/100 mL -- -- -- 0 -- --

Ammonia, total, as N, mg/L -- 3

--

3

pH dependent; U.S. Enviromental Protection Agency (1999b).

4--

4

pH and temperature dependent; U.S. Environmental Protection Agency (1999b).

-- -- 30

Nitrite plus nitrate, total, as N, mg/L -- -- -- 10 -- --

Phosphorus, total, as P, mg/L 5

0.10

5

U.S. Environmental Protection Agency (1986).

-- -- -- -- --

Arsenic, total, μg/L -- 340 150 10 -- --

Solids, dissolved, mg/L -- -- -- -- 500 --

Chloride, total, mg/L -- 860 230 -- 250 --

Sulfate, total, mg/L -- -- -- -- 250 --

pH, standard units -- -- 6.5–9.0 -- 6.5–8.5 --

USEPA (1986, 2000a) has recommended and some States have 

adopted the use of Escherichia coli (E. coli) bacteria as the indicator organism for sanitary quality. For example, Kansas made 

the switch to E. coli in 2003.

USEPA currently (2004) has a recommended, nonenforceable water-quality goal of 0.10 mg/L for total phosphorus in rivers and streams (U.S. Environmental Protection Agency, 1986). 

Ecoregion-specific criteria for total phosphorus currently 

(2004) are being or have been developed through a collaborative partnership between the States and USEPA. These criteria 

range from 0.01 to 0.128 mg/L. Information concerning this 

development process and resultant ecoregion-specific criteria 

may be found on the World Wide Web at URL 

http://www.epa.gov/ost/standards/nutrient.html (accessed 

July 1, 2003).

Differences in water-quality constituents analyzed and the 

criteria to which the resultant concentrations are compared 

make it difficult to use State stream-water-quality data or State 

water-quality assessments to produce a national picture of 

ambient stream-water-quality conditions (U.S. General 

Accounting Office, 2002). These differences are the result of 

the selection of constituents that States choose to emphasize, the 

phase for which constituents are analyzed (total or dissolved), 

the designated uses that States apply to streams, and the waterquality critieria associated with these uses. Criteria differences 

among the States may result in different rates of stream degradation and limit State-to-State comparability. The reliance on 

narrative instead of numeric criteria also limits the comparability of State data or assessment results as presented in their biannual 305(b) reports. These limitations reduce the development 

of a reliable national water-quality assessment using these data.

Quantity and Comprehensiveness of Water-Quality 

Data

States vary in the quantity of ambient stream-water-quality 

data collected and comprehensiveness in geographical coverage 

of those data and type and number of constituents analyzed. 

This variability, in part, limits the use of State water-quality 

data or assessments of those data to compile a reliable picture of 

national water-quality conditions and restricts the capability to 
36 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 23. Fecal coliform bacteria criteria for primary and secondary contact 

recreation for streams in 50 States.

[GM, geometric mean of at least five samples collected in separate 24-hour periods during a 

30-day period; SS, single sample; --, no criteria or not available]

State

Fecal coliform bacteria criteria1

(colonies per 100 milliliters of water)

1U.S. Environmental Protection Agency (2001b).

Primary contact Secondary contact

Alabama 200 (GM) 2,000 (GM)

Alaska 200 (GM) --

Arizona 200 (GM)

800 (SS)

1,000 (GM)

4,000 (SS)

Arkansas 200 (GM) 1,000 (GM)

California 200 (GM) 2,000 (GM)

Colorado 200 (GM) 2,000 (GM)

Connecticut 200 (GM) --

Delaware -- --

Florida 200 (GM) --

Georgia 200 (GM)

--

1,000 (GM)

4,000 (SS)

Hawaii 200 (GM) --

Idaho -- --

Illinois 200 (GM) --

Indiana -- --

Iowa 200 (GM) --

Kansas 200 (GM) 2,000 (SS)

Kentucky 200 (GM) 1,000 (GM)

Louisiana 200 (GM) 1,000 (GM)

Maine -- --

Maryland -- --

Massachusetts 200 (GM) 1,000 (GM)

Michigan -- --

Minnesota 200 (GM) --

Mississippi 200 (GM) 2,000 (GM)

Missouri 200 (GM) --

Montana 200 (GM) --

Nebraska 200 (GM) --

Nevada 200 (GM) 2,000 (GM)

New Hampshire -- --

New Jersey 200 (GM) --

New Mexico 200 (GM)

400 (SS)

--

--

New York 200 (GM) 2,000 (GM)

North Carolina 200 (GM) 200 (GM)

North Dakota 200 --

Ohio 1,000 (GM) 5,000 (GM)

Oklahoma 200 (GM) --

Oregon 126 (GM)

406 (SS)

--

--

Pennsylvania 200 (GM) 2,000 (GM)

Rhode Island 200 (GM) 200 (GM)

South Carolina 200 (GM) 200 (GM)

South Dakota 200 (GM)

400 (SS)

1,000 (GM)

2,000 (SS)

Tennessee 200 (GM)

1,000 (SS)

--

--

Texas 200 (GM) 2,000 (GM)

Utah 200 (GM) 200 (GM)

Vermont 200 (GM)

1,000 (SS)

--

--

Virginia 200 (GM)

1,000 (SS)

--

--

Washington 50–100 (GM) 200 (GM)

West Virginia 200 (GM) 2,000 (GM)

Wisconsin 200 (GM) --

Wyoming 200 (GM) --
Limitations of State Ambient Stream-Water-Quality Data for National Assessment 37

answer status and trends questions about the nation’s streamwater quality.

An analysis of the quantity of electronically available 

water-quality data was conducted by determining the number of 

monitoring sites in each State that had selected numbers of analyses of the 10 water-quality constituents examined in this report 

(tables 25–34 in the “Supplemental Information” section at the 

back of this report). States do not necessarily analyze ambient 

stream-water samples for the same water-quality constituents or 

to the same extent. Nationally, more than 9,000 monitoring sites 

had one or more analysis for total phosphorus (table 29) and pH 

(table 34), but less than 3,500 sites had one or more analysis for 

total arsenic (table 30). The presence of arsenic in streams is 

found mostly near where it occurs naturally in soils and rocks, 

and the geographic variability in the natural occurrence of 

arsenic in soil and rocks is probably responsible for much of this 

difference in State emphasis on arsenic.

Relative to the number of monitoring sites with total phosphorus and pH data, other constituents showed marked reductions in the number of monitoring sites with electronically 

available data for 1990–98. For example, slightly less than 

6,100 monitoring sites (nationally) had one or more analyses for 

fecal coliform bacteria (table 26), about a 33-percent reduction 

in the number of sites relative to those numbers of total phosphorus and pH. Much of this difference may be attributable to 

operational constraints in the collection and analysis of bacterial samples. Holding times (time between collection and analysis) for bacterial samples generally are short relative to many 

chemical constituents. These reduced holding times may 

increase sample transportation costs as well as staff time for collection and analysis. Increases in sample collection and analysis 

costs for some State programs may be offset with reductions in 

the number of sites at which data are collected.

In addition to differences in the number of monitoring sites 

with selected constituents, monitoring sites have different numbers of analyses of particular constituents (tables 25–34; fig. 2). 

USEPA (2002a) recommended a minimum of 30 water-quality 

analyses at monitoring sites for degradation assessment purposes; however, on average (for the 10 constituents evaluated in 

this report) only about 30 percent (fig. 3) of the monitoring sites 

(relative to the number with one or more analyses) examined 

had the quantity of electronically available data that met this 

minimum recommendation between 1990 and 1998. Substantial 

reduction in monitoring sites reduces the spatial distribution 

and (or) density of monitoring sites possibly to a point (1) that 

States may not meet the requirement of the Clean Water Act to 

assess all surface water (U.S. Environmental Protection 

Agency, 2002a), (2) that State assessments may be biased 

toward the water-quality characteristics of larger river systems 

where long-term (more samples collected) monitoring sites may 

predominate, or (3) that the overall quality or representativeness 

of the State assessment may be reduced.

The information presented in figures 2 and 3 provided 

some insight into the relation between the availability of monitoring sites and numbers of analyses; however, the figures do 

not provide information on the extent of State ambient streamwater-quality monitoring networks and the comprehensiveness 

of databases relative to the modest number of commonly collected water-quality constituents assessed in this report. An 

effort to describe this extent and comprehensiveness was conducted by determining the number of ambient stream-waterquality sites in each State that met selected combinations of 

number of available constituents and minimum number of analyses of each constituent (table 24).

The first category of ambient stream-water-quality monitoring sites in table 24 (sites with 1 or more of the 10 constituents assessed in this report each with nine or more analyses) 

represents the maximum in available monitoring sites and, 

potentially, the minimum in comprehensive data requirements. 

The nine or more required analyses is the same summary criterion used in previous sections of this report. The other three categories are attempts to increase the overall comprehensiveness 

of State databases relative to the constituents summarized in 

this report and required either 8 or more constituents or all 

10 constituents. Also required are either 9 or more analyses per 

constituent or 30 or more analyses per constituent. The nineanalysis criterion was chosen to represent an average of one 

analysis per year for the period used in this report (1990–98). 

The 30-analysis criterion was chosen to correspond to the 

minimum number of analyses recommended by USEPA 

(2002a) for decisions on water quality.

The number of ambient stream-water-quality monitoring 

sites with at least one water-quality constituent (or measurement) with nine or more analyses ranged from 5 in Rhode Island 

to 1,139 in Virginia (table 24). Possible reasons for this variability among the 42 States assessed were discussed in 

previous sections of this report. Nationally, these 42 States 

had 6,783 monitoring sites that met the aforementioned 

criteria.

Large reductions in numbers of available monitoring sites 

occurred as the minimum requirements for both numbers of 

constituents per site and number of analyses per constituent 

increased. The number of available monitoring sites with 8 or 

more of the 10 constituents assessed in this report with at least 

nine analyses decreased to a national total of 3,148 (decrease of 

54 percent) in 37 States (table 24). Five States with data used 

in this report had no sites that met this data criteria, and 

eight States had less than 10 sites. Only 230 monitoring sites 

nationally (in nine States) had at least 9 analyses for all 10 constituents assessed in this report. When the USEPA minimum 

recommendation of 30 analyses per constituent was factored in 

(10 constituents each with 30 or more analyses, table 24), only 

73 monitoring sites nationally (in five States) met those criteria. 

This analysis indicated that some State ambient stream-waterquality networks are lacking in the comprehensiveness of collected data, at least relative to the common constituents summarized in this report, and most monitoring sites in those networks 

do not have the number of analyses recommended by USEPA 

to make appropriate degradation and, ultimately, total maximum daily loads decisions.

USGAO (2002) identified differences in State approaches 

in identifying water-quality degraded surface water (rivers, 
38 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

A. Suspended solids

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0 20 40 60 80 100

Number of monitoring sites

B. Fecal coliform bacteria

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0

0 20 40 60 80 100

C. Ammonia

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0 20 40 60 80 100

D. Nitrite plus nitrate

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000 10,000

0 20 40 60 80 100

E. Total phosphorus

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

0 20 40 60 80 100

F. Total arsenic

0 20 40 60 80 100

G. Dissolved solids

0 20 40 60 80 100

H. Chloride

0 20 40 60 80 100

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

I. Sulfate

0 20 40 60 80 100

J. pH

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0 20 40 60 80 100

Number of analyses (equal to or greater than)

Number of analyses (equal to or greater than)

Figure 2. Relations between numbers of ambient stream-water-quality monitoring sites (nationally) and selected minimum 

numbers of electronically available data for 10 water-quality constituents or measurements.
Summary and Conclusions 39

streams, and lakes). Some of these differences among the States 

were inherent to the implementation of the Clean Water Act, 

which allowed USEPA, in administering the act, some flexibility for the States to develop assessment approaches that were 

appropriate to their specific ecological and environmental conditions. However, as noted by USGAO (2002), some of the variations in approach have no appropriate scientific basis.

Information obtained from the investigation described in 

this report verified some of the inconsistencies noted by 

USGAO (2002). Most notable is the variability in characteristics of State stream-water-quality monitoring networks such as 

the number of monitoring sites and water-quality analyses. 

Additional inconsistencies among States include numeric 

water-quality criteria, particularly for fecal coliform bacteria 

(table 23) and to a lesser degree the absence of or variability in 

numeric criteria for suspended solids. National monitoring is, in 

reality, a compilation of 50 State networks with varying degrees 

of comparability. Differences among the States in water-quality 

criteria and methodologies used in data assessment and waterquality degradation decisions restrict comparability among the 

States and limit the consistency needed to produce a national 

assessment of ambient water quality. An analysis of the extent 

and comprehensiveness of State ambient stream-water-quality 

networks for this report indicated that these networks may be 

lacking in the diversity of collected data and that many monitoring sites in those networks have few samples and do not have 

the number of analyses recommended by USEPA to make 

appropriate degradation and total maximum daily loads decisions.

Because of the differences and inconsistencies among 

State ambient stream-water-quality monitoring programs, a scientifically defensible national assessment of stream-water 

quality for 1990–98 could not be made with the State databases 

produced for the investigation described in this report. Some 

efforts have been made by USEPA (2002a) to produce a more 

uniform system of network operations and assessment of waterquality data. However, the task is enormous and will require 

much coordination with and cooperation between the States and 

USEPA to develop common ground in collection, analysis, 

evaluation, and assessment of stream-water-quality data before 

reliable, scientifically defensible national water-quality assessments are possible.

Summary and Conclusions

Ambient stream-water-quality data were electronically 

acquired for 10 water-quality constituents or measurements, 

stored in a relational-based database (by State), and statistically 

summarized. The electronic availability of data varied among 

the States. Forty-two States had pH data from ambient stream 

monitoring sites, whereas only 26 States had total arsenic data. 

Electronically accessible data were not available for Alaska, 

Arizona, California, Hawaii, Maine, Massachusetts, North 

Carolina, and Vermont.

Data for State ambient stream-water-quality monitoring 

sites were retrieved for 1990–98 from the U.S. Environmental 

Protection Agency Storage and Retrieval System, the U.S. Geological Survey National Water Information System, or Statelocated databases. These data were assembled into individual 

State databases, and each monitoring site was assessed for the 

number of available analyses for 10 water-quality constituents 

or measurements. Monitoring sites with nine or more analyses 

for each of the constituents or measurements were statistically 

summarized, and median concentrations or measurements 

determined. The nine-analysis threshold was selected as a compromise between the desire to maximize spatial distribution but 

still have enough analyses to provide an estimate of range and 

central tendency (median values) for the site data population. 

Also, nine represented an average of one sample per year over 

the time period investigated. Subsequently, the median of monitoring-site medians was calculated for each constituent or measurement in each State, statistically summarized, and the result 

presented in tabular format.

Comparisons of monitoring data among States are problematic for several reasons, including differences in the basic 

spatial design of monitoring networks; water-quality constituents for which samples are analyzed; water-quality criteria to 

which constituent concentrations are compared; quantity and 

comprehensiveness of water-quality data; sample collection, 

processing, and handling; analytical methods; temporal variability in sample collection; and quality-assurance practices. 

Large differences among the States in number of monitoring 

sites precluded a general assumption that statewide water-quality conditions were represented by data from these sites. Furthermore, data from individual monitoring sites may not represent water-quality conditions at the sites because sampling 

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100

Number of analyses (equal to or greater than)

Percentage

Figure 3. Relation between the national average percentage 

of monitoring sites for 10 water-quality constituents or 

measurements and selected minimum numbers of 

electronically available data.
40 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 24. Number of State ambient stream-water-quality monitoring sites available for selected combinations of water-quality 

constituents per monitoring site and analyses per constituent, 1990–98.

[Total number of monitoring sites in State databases (sites with one or more analyses of at least 1 of 10 constituents) were presented previously in table 2. --, not 

available]

State

Number of ambient stream-water-quality monitoring sites

With 1 or more constituents 

with 9 or more analyses

With any 8 or more of 10 

constituents with 9 or more 

analyses

With all 10 constituents with 

9 or more analyses

With all 10 constituents with 

30 or more analyses

Alabama 45 41 0 0

Alaska -- -- -- --

Arizona -- -- -- --

Arkansas 131 131 0 0

California -- -- -- --

Colorado 220 104 0 0

Connecticut 32 28 0 0

Delaware 103 0 0 0

Florida 868 405 8 0

Georgia 290 0 0 0

Hawaii -- -- -- --

Idaho 51 21 0 0

Illinois 11 3 0 0

Indiana 106 14 0 0

Iowa 39 0 0 0

Kansas 251 251 118 40

Kentucky 61 59 0 0

Louisiana 172 105 0 0

Maine -- -- -- --

Maryland 40 12 0 0

Massachusetts -- -- -- --

Michigan 97 47 0 0

Minnesota 66 1 0 0

Mississippi 66 44 0 0

Missouri 40 31 0 0

Montana 334 54 0 0

Nebraska 22 13 0 0

Nevada 68 64 28 0

New Hampshire 56 8 0 0

New Jersey 96 65 0 0

New Mexico 239 115 1 1

New York 19 8 0 0

North Carolina -- -- -- --

North Dakota 73 39 13 0

Ohio 41 40 27 6

Oklahoma 212 8 0 0

Oregon 144 1 0 0

Pennsylvania 174 63 27 24

Rhode Island 5 5 0 0

South Carolina 340 0 0 0

South Dakota 96 28 0 0

Tennessee 73 12 0 0

Texas 576 362 7 2

Utah 64 64 1 0

Vermont -- -- -- --

Virginia 1,139 864 0 0

Washington 207 0 0 0

West Virginia 26 21 0 0

Wisconsin 48 13 0 0

Wyoming 42 4 0 0

Totals 6,783 3,148 230 73
References Cited 41

conditions and protocols are unknown. Because of these factors, 

a high level of uncertainty exists in the results of this 

investigation.

Forty States had electronically accessible suspended solids 

concentrations for water from ambient stream-water-quality 

monitoring sites. State medians of monitoring-site median concentrations of suspended solids ranged from 2.0 mg/L in New 

Hampshire to 42.5 mg/L in Nebraska.

Thirty-nine States had electronically accessible fecal 

coliform bacteria densities for water from ambient streamwater-quality monitoring sites. State medians of monitoringsite median densities of fecal coliform bacteria ranged from 

19.2 col/100 mL in Colorado to 2,650 col/100 mL in Montana.

Forty-one States had electronically accessible ammonia 

concentrations for water from ambient stream-water-quality 

monitoring sites. State medians of monitoring-site median concentrations of ammonia ranged from 0.003 mg/L in Colorado to 

0.46 mg/L in Rhode Island.

Forty-two States had electronically accessible nitrite plus 

nitrate as nitrogen concentrations for water from ambient 

stream-water-quality monitoring sites. State medians of monitoring-site median concentrations of nitrite plus nitrate as nitrogen ranged from 0.05 mg/L in Nevada to 5.7 mg/L in Iowa.

Forty-one States had electronically accessible total phosphorus concentrations for water from ambient stream-waterquality monitoring sites. State medians of monitoring-site 

median concentrations of total phosphorus ranged from 

0.02 mg/L in West Virginia to 0.33 mg/L in Illinois.

Twenty-eight States had electronically accessible total 

arsenic concentrations for water from ambient stream-waterquality monitoring sites. State medians of monitoring-site 

median concentrations of total arsenic ranged from 0.80 μg/L in 

Washington to 11.5 μg/L in South Dakota.

Twenty-nine States had electronically accessible dissolved-solids concentrations for water from ambient streamwater-quality monitoring sites. State medians of monitoringsite median concentrations of dissolved solids ranged from 

37.2 mg/L in Mississippi to 711 mg/L in South Dakota.

Thirty-nine States had electronically accessible chloride 

concentrations for water from ambient stream-water-quality 

monitoring sites. State medians of monitoring-site median concentrations of chloride ranged from 0 mg/L in Montana to 

7,740 mg/L in Georgia.

Thirty-six States had electronically accessible sulfate concentrations for water from ambient stream-water-quality monitoring sites. State medians of monitoring-site median concentrations of sulfate ranged from 6.5 mg/L in New Hampshire to 

232 mg/L in North Dakota.

Forty-two States had electronically accessible pH measurements for water from ambient stream-water-quality monitoring sites. State medians of the monitoring-site median measurements of pH ranged from 6.7 standard units in Rhode Island 

and South Carolina to 8.2 standard units in several States.

National monitoring is, in reality, a compilation of 50 State 

networks with varying degrees of comparability. Differences 

among the States in water-quality criteria and methodologies 

used in data assessment and decisions on water quality restrict 

comparability among the States and limit the consistency 

needed to produce an accurate national assessment of ambient 

stream-water quality. An analysis of the extent and comprehensiveness of State ambient stream-water-quality networks for 

this report indicated that these networks may be lacking in the 

diversity of collected data and that many monitoring sites in 

those networks have few samples and for many basic waterquality constituents do not have the number of analyses recommended (30) by the U.S. Environmental Protection Agency to 

make appropriate water-quality and total maximum daily 

loads decisions for 1990–98.

Targeted, statistically based (probabilistic), and geographically based sampling designs are used in some State monitoring programs to provide the water-quality information required 

by the Clean Water Act to evaluate potential stream-waterquality degradation relative to designated uses and appropriate 

water-quality criteria. When appropriate designs are used, this 

information also may be used to describe cause-and-effect relations, seasonal variability and time trends, mass transport, and 

as an aid to management decisions. However, the variability in 

network designs and operational characteristics, such as the distribution of sites and frequency of sampling, among the States 

prevented the use of available information for a scientifically 

defensible comparison of results among the States.

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bridges: Office of Water, U.S. Environmental Protection 

Agency Report EPA–841–F–95–008a, 6 p.

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25 p.

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ambient water quality criteria for ammonia: U.S. Environmental Protection Agency Report EPA–822–R–99–014, 

147 p.

U.S. Environmental Protection Agency, 2000a, Implementation 

guidance for ambient water quality criteria for bacteria— 

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823–D–00–001, 37 p.

U.S. Environmental Protection Agency, 2000b, National water 

quality inventory—1998 report to Congress: U.S. Environmental Protection Agency Report EPA–841–R–00–001, 

413 p.

U.S. Environmental Protection Agency, 2001a, STORET result 

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on World Wide Web, accessed June 21, 2001, at URL 

http://www.epa.gov/storpubl/legacy/rsultrmk.htm

U.S. Environmental Protection Agency, 2001b, Water quality 

standards: Office of Water, information available on World 

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http://www.epa.gov/waterscience/standards/wqslibrary/

U.S. Environmental Protection Agency, 2002a, Consolidated 

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14 p.
44 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

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accessed April 10, 2003, at URL http://waterdata.usgs.gov/

nwis/help?codes_help
Supplemental Information
46 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 25. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

suspended solids, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 49 45 45 45 45 45 43 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 132 131 131 131 130 128 127 27

California -- -- -- -- -- -- -- -- -- --

Colorado 347 278 262 214 75 63 52 46 28 6

Connecticut 0 0 0 0 0 0 0 0 0 0

Delaware 109 109 108 103 97 86 73 58 22 0

Florida 648 642 627 602 514 431 372 300 197 94

Georgia 284 244 233 196 79 78 76 75 61 11

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 0 0 0 0 0 0 0 0 0 0

Illinois 367 141 24 11 3 3 1 1 1 0

Indiana 107 106 106 105 100 91 84 83 82 0

Iowa 55 55 55 26 14 14 14 14 14 14

Kansas 161 161 153 124 46 40 40 40 14 0

Kentucky 89 88 66 60 49 46 46 45 44 27

Louisiana 172 171 171 171 152 149 148 148 99 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 38

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 261 178 166 96 72 69 65 61 39 6

Minnesota 66 65 65 63 56 51 51 50 17 0

Mississippi 84 72 71 66 58 56 19 17 10 0

Missouri 37 33 30 22 14 9 5 5 1 0

Montana 323 187 162 132 93 81 66 56 13 1

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 69 69 69 67 64 56 53 53 35 10

New Hampshire 228 114 27 25 16 0 0 0 0 0

New Jersey 74 73 70 65 33 4 0 0 0 0

New Mexico 512 415 348 219 75 31 11 1 1 0

New York 19 19 19 19 19 19 19 18 0 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 37 33 32 28 18 11 10 8 7 2

Ohio 42 42 41 41 40 40 40 40 37 10

Oklahoma 245 238 236 182 87 43 34 33 8 1

Oregon 148 148 147 144 126 119 114 98 64 12

Pennsylvania 200 196 191 173 173 173 173 171 153 8

Rhode Island 5 5 5 5 5 3 3 2 0 0

South Carolina 119 62 56 52 48 46 44 39 34 9

South Dakota 100 96 96 96 93 88 86 83 50 31

Tennessee 101 97 90 68 52 40 25 7 2 0

Texas 769 576 486 396 314 235 147 96 22 2

Utah 64 64 64 64 64 64 63 63 60 8

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,342 1,127 1,086 945 807 748 645 569 341 133

Washington 205 205 205 204 106 105 91 91 57 0

West Virginia 26 26 26 26 0 0 0 0 0 0

Wisconsin 50 49 49 46 40 36 32 29 13 5

Wyoming 1 1 1 1 1 1 1 0 0 0

Totals 7,710 6,429 5,886 5,095 3,841 3,367 2,940 2,634 1,736 456

Percentage reduction 16.6 23.7 33.9 50.2 56.3 61.9 65.8 77.5 94.1
Supplemental Information 47

Table 26. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

fecal coliform bacteria, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 47 45 45 45 41 41 35 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 115 115 114 113 84 72 70 70 49 0

California -- -- -- -- -- -- -- -- -- --

Colorado 298 256 212 124 60 51 42 38 21 5

Connecticut 32 32 32 32 32 31 31 31 24 0

Delaware 1 1 0 0 0 0 0 0 0 0

Florida 458 442 427 372 260 214 169 122 75 42

Georgia 392 317 270 255 155 141 132 116 87 5

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 47 47 47 42 36 22 12 7 1 0

Illinois 37 25 7 3 3 2 1 1 1 0

Indiana 0 0 0 0 0 0 0 0 0 0

Iowa 47 33 28 17 17 16 16 16 16 0

Kansas 289 288 276 249 171 145 145 144 54 6

Kentucky 87 83 70 59 48 46 45 44 44 0

Louisiana 167 166 142 103 52 28 0 0 0 0

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 18

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 0 0 0 0 0 0 0 0 0 0

Minnesota 63 63 63 63 56 50 50 50 18 0

Mississippi 68 63 61 50 49 38 4 0 0 0

Missouri 43 42 42 39 39 37 34 32 16 2

Montana 4 2 2 2 1 1 0 0 0 0

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 70 68 68 60 56 55 47 37 23 0

New Hampshire 104 40 8 8 1 0 0 0 0 0

New Jersey 18 10 5 5 5 3 2 0 0 0

New Mexico 175 56 19 9 8 5 4 2 2 0

New York 13 12 10 8 1 0 0 0 0 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 69 64 57 39 23 17 11 7 3 1

Ohio 41 40 40 40 39 36 30 25 13 0

Oklahoma 22 15 14 14 4 0 0 0 0 0

Oregon 132 128 120 83 37 24 11 7 0 0

Pennsylvania 88 77 72 53 50 49 47 46 42 1

Rhode Island 5 5 5 5 5 5 5 5 5 0

South Carolina 338 337 337 310 226 203 197 192 130 5

South Dakota 100 96 96 96 88 83 74 56 47 0

Tennessee 107 99 89 60 41 32 18 3 2 0

Texas 784 659 560 457 346 251 195 140 77 11

Utah 18 16 16 16 15 12 10 6 0 0

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,420 1,195 1,151 1,086 943 834 695 584 335 83

Washington 208 208 208 202 106 105 91 89 57 0

West Virginia 26 26 26 26 0 0 0 0 0 0

Wisconsin 47 46 45 44 36 33 29 25 12 0

Wyoming 19 18 18 18 16 15 13 10 0 0

Totals 6,063 5,301 4,866 4,269 3,216 2,763 2,333 2,007 1,229 179

Percentage reduction 12.6 19.7 29.6 47.0 54.4 61.5 66.9 79.7 97.0
48 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 27. Number of State ambient stream-water-quality monitoring sites with selected numbers of 

analyses for ammonia as nitrogen, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 35 18 18 18 17 3 2 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 133 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 262 232 213 163 61 54 45 40 17 0

Connecticut 29 29 29 29 29 28 28 28 24 2

Delaware 109 109 108 103 97 86 72 57 22 0

Florida 823 823 823 793 647 538 438 353 243 99

Georgia 416 382 323 283 156 147 136 126 92 22

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 49 49 49 47 33 23 19 14 7 1

Illinois 368 142 24 11 3 3 1 1 1 0

Indiana 107 106 106 106 103 93 86 85 84 0

Iowa 68 68 68 39 27 27 27 27 27 27

Kansas 289 289 281 251 169 146 145 145 89 6

Kentucky 89 88 66 60 49 46 46 45 44 24

Louisiana 0 0 0 0 0 0 0 0 0 0

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 40

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 248 146 127 70 65 63 55 49 14 3

Minnesota 67 67 67 66 66 65 63 52 47 0

Mississippi 81 63 63 58 51 50 6 2 1 0

Missouri 43 43 42 39 38 37 26 20 12 0

Montana 380 199 173 140 89 77 53 49 22 0

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 69 69 69 67 64 56 53 53 36 11

New Hampshire 315 156 57 41 16 7 0 0 0 0

New Jersey 95 95 95 82 70 62 49 35 3 1

New Mexico 521 427 364 228 80 35 17 6 1 0

New York 19 19 19 19 19 19 19 18 1 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 83 71 55 33 24 23 19 7 2

Ohio 42 42 41 41 40 40 40 40 37 10

Oklahoma 195 174 135 38 16 13 11 10 2 0

Oregon 148 148 147 143 126 119 115 99 64 13

Pennsylvania 201 196 192 174 174 174 174 172 169 142

Rhode Island 5 5 5 5 5 5 5 5 5 0

South Carolina 339 339 339 337 276 228 197 196 193 135

South Dakota 97 96 96 96 92 88 86 83 46 10

Tennessee 107 99 88 65 44 40 26 9 2 0

Texas 903 663 561 446 358 282 207 157 67 10

Utah 64 64 64 64 64 64 64 63 59 8

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,424 1,143 1,094 957 809 748 643 566 342 133

Washington 207 205 205 204 106 105 91 91 57 0

West Virginia 26 26 26 26 0 0 0 0 0 0

Wisconsin 49 44 43 40 35 33 27 22 9 1

Wyoming 27 22 22 21 20 15 13 10 3 0

Totals 8,615 7,194 6,525 5,618 4,341 3,851 3,316 2,942 2,020 827

Percentage reduction 16.5 24.3 34.8 49.6 55.2 61.5 65.9 76.6 90.4
Supplemental Information 49

Table 28. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

nitrite plus nitrate as nitrogen, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 48 48 48 44 44 44 44 44 42 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 131 131 131 131 130 129 127 17

California -- -- -- -- -- -- -- -- -- --

Colorado 316 274 259 210 69 69 49 38 22 2

Connecticut 30 30 30 30 30 30 30 30 23 2

Delaware 109 109 108 103 97 84 72 57 20 0

Florida 839 839 838 825 678 572 487 402 264 128

Georgia 416 382 323 283 156 144 136 127 93 16

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 50 50 49 45 35 25 19 18 5 0

Illinois 368 142 24 11 3 3 1 1 1 0

Indiana 106 106 106 106 103 93 86 85 84 0

Iowa 68 68 68 39 27 27 27 27 27 27

Kansas 289 289 281 251 169 146 145 145 89 6

Kentucky 88 87 66 60 48 46 46 45 44 24

Louisiana 173 172 172 172 152 149 148 148 96 0

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 40

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 265 165 154 85 70 67 65 61 27 4

Minnesota 67 67 67 66 66 65 63 52 47 0

Mississippi 85 72 71 65 59 55 20 16 10 0

Missouri 44 43 43 40 37 37 34 32 14 0

Montana 880 418 347 235 165 113 72 65 29 0

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 66 66 66 64 61 54 51 51 34 10

New Hampshire 339 211 92 46 21 11 0 0 0 0

New Jersey 92 91 91 87 73 70 69 67 7 2

New Mexico 521 425 370 230 77 31 16 6 2 0

New York 19 19 19 19 19 19 19 18 1 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 83 72 57 34 25 24 19 7 2

Ohio 42 42 41 41 40 40 40 40 37 10

Oklahoma 221 197 171 111 59 38 29 28 8 1

Oregon 148 148 147 143 126 119 115 98 62 13

Pennsylvania 198 193 189 171 171 171 171 170 167 142

Rhode Island 5 5 5 5 5 5 5 5 5 0

South Carolina 340 340 340 340 301 270 226 216 209 167

South Dakota 97 96 96 96 92 88 86 83 45 0

Tennessee 106 97 88 65 43 40 26 9 2 0

Texas 889 655 571 449 331 257 181 139 72 10

Utah 64 64 64 64 64 64 63 63 60 7

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,419 1,143 1,095 957 812 749 649 568 343 134

Washington 206 205 205 204 106 105 91 90 57 0

West Virginia 24 24 24 24 0 0 0 0 0 0

Wisconsin 50 44 43 42 38 37 32 32 18 3

Wyoming 36 32 31 29 22 14 10 9 0 0

Totals 9,408 7,736 7,067 6,107 4,696 4,169 3,639 3,294 2,240 767

Percentage reduction 17.8 24.9 35.1 50.1 55.7 61.3 65.0 76.2 91.8
50 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 29. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

total phosphorus, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 49 45 45 45 45 45 43 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 133 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 322 274 258 209 71 61 51 45 28 6

Connecticut 32 32 32 32 31 30 30 28 25 2

Delaware 109 109 107 103 96 83 73 57 20 0

Florida 807 806 805 790 655 547 459 406 276 129

Georgia 416 382 323 283 156 147 136 126 92 21

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 50 50 49 44 39 28 22 19 7 1

Illinois 368 141 24 11 3 3 1 1 1 0

Indiana 107 106 106 106 103 93 86 85 84 0

Iowa 57 57 57 28 16 16 16 16 16 16

Kansas 289 289 281 251 169 146 145 145 89 6

Kentucky 89 88 66 60 49 46 46 45 44 26

Louisiana 173 172 172 172 152 149 148 148 98 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 40

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 272 165 155 83 69 67 65 61 28 4

Minnesota 66 65 65 63 56 51 51 51 17 0

Mississippi 85 72 71 65 59 56 20 16 10 0

Missouri 39 38 38 34 28 24 19 16 10 0

Montana 664 264 216 175 128 100 70 54 24 0

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 69 69 69 67 64 56 53 53 36 11

New Hampshire 347 220 93 46 21 15 2 0 0 0

New Jersey 95 95 93 82 71 69 66 58 7 2

New Mexico 521 426 346 225 74 33 17 10 3 0

New York 0 0 0 0 0 0 0 0 0 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 83 72 57 34 25 24 19 8 2

Ohio 42 42 41 41 40 40 40 40 34 9

Oklahoma 258 247 245 194 91 45 35 34 12 1

Oregon 148 148 146 141 126 120 116 99 64 13

Pennsylvania 201 196 191 174 174 174 174 172 169 141

Rhode Island 5 5 5 5 5 5 5 5 4 0

South Carolina 339 339 339 339 277 224 212 210 205 81

South Dakota 97 96 96 96 92 88 86 83 45 0

Tennessee 106 97 88 65 43 40 25 9 2 0

Texas 854 639 547 439 341 253 183 138 55 9

Utah 64 64 64 64 64 64 64 62 56 4

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,408 1,129 1,080 936 808 742 646 566 338 132

Washington 208 207 207 206 106 105 91 91 57 0

West Virginia 26 26 26 26 0 0 0 0 0 0

Wisconsin 50 47 46 44 39 37 34 32 18 6

Wyoming 31 28 28 21 16 10 9 7 3 0

Totals 9,148 7,557 6,891 6,015 4,604 4,030 3,558 3,244 2,197 790

Percentage reduction 17.4 24.7 34.2 49.7 55.9 61.1 64.5 76.0 91.4
Supplemental Information 51

Table 30. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

total arsenic, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 44 27 27 27 24 23 21 5 0 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 0 0 0 0 0 0 0 0 0 0

California -- -- -- -- -- -- -- -- -- --

Colorado 46 2 0 0 0 0 0 0 0 0

Connecticut 0 0 0 0 0 0 0 0 0 0

Delaware 43 22 20 20 20 19 19 17 5 0

Florida 224 175 155 128 90 65 58 48 17 6

Georgia 66 20 2 0 0 0 0 0 0 0

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 2 1 0 0 0 0 0 0 0 0

Illinois 191 51 2 2 2 1 0 0 0 0

Indiana 71 67 66 61 41 40 38 38 35 0

Iowa 1 1 1 1 1 1 1 1 1 0

Kansas 289 289 281 251 168 146 145 144 88 6

Kentucky 89 88 66 59 46 46 46 45 44 19

Louisiana 125 125 124 12 0 0 0 0 0 0

Maine -- -- -- -- -- -- -- -- -- --

Maryland 0 0 0 0 0 0 0 0 0 0

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 216 88 78 48 47 35 4 4 0 0

Minnesota 52 16 11 0 0 0 0 0 0 0

Mississippi 72 69 64 22 9 0 0 0 0 0

Missouri 1 0 0 0 0 0 0 0 0 0

Montana 96 9 8 8 3 3 3 3 0 0

Nebraska 17 13 13 13 0 0 0 0 0 0

Nevada 71 70 70 59 48 19 8 8 7 0

New Hampshire 213 25 16 1 0 0 0 0 0 0

New Jersey 59 28 16 4 0 0 0 0 0 0

New Mexico 323 152 42 15 3 1 1 1 1 0

New York 0 0 0 0 0 0 0 0 0 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 68 38 31 24 12 7 5 0 0 0

Ohio 42 42 41 41 26 26 21 16 7 0

Oklahoma 0 0 0 0 0 0 0 0 0 0

Oregon 1 0 0 0 0 0 0 0 0 0

Pennsylvania 41 33 32 31 31 31 30 29 22 0

Rhode Island 2 2 1 1 1 1 1 1 0 0

South Carolina 2 1 1 0 0 0 0 0 0 0

South Dakota 52 44 23 20 20 19 19 19 7 1

Tennessee 108 99 92 70 56 41 34 12 2 0

Texas 101 33 23 9 8 4 4 4 3 0

Utah 60 58 57 54 50 7 2 2 0 0

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 692 399 226 75 14 4 4 4 0 0

Washington 14 12 11 5 2 1 0 0 0 0

West Virginia 0 0 0 0 0 0 0 0 0 0

Wisconsin 4 2 2 2 1 1 1 0 0 0

Wyoming 0 0 0 0 0 0 0 0 0 0

Totals 3,498 2,101 1,602 1,063 723 541 465 401 239 32

Percentage reduction 39.9 54.2 69.6 79.3 84.5 86.7 88.5 93.2 99.1
52 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 31. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

dissolved solids, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 48 48 47 42 27 27 27 27 25 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 133 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 317 276 262 212 75 63 51 46 28 6

Connecticut 32 32 32 32 32 32 32 32 27 2

Delaware 0 0 0 0 0 0 0 0 0 0

Florida 273 267 260 253 196 151 100 84 44 8

Georgia 0 0 0 0 0 0 0 0 0 0

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 50 50 48 32 11 9 7 6 1 0

Illinois 197 63 1 0 0 0 0 0 0 0

Indiana 30 23 23 23 21 20 20 20 19 0

Iowa 57 57 57 28 16 16 16 16 16 16

Kansas 289 289 281 251 169 146 145 144 86 6

Kentucky 1 0 0 0 0 0 0 0 0 0

Louisiana 173 172 172 172 152 149 148 148 99 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 12 12 12 12 12 12 12 12 12 11

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 15 0 0 0 0 0 0 0 0 0

Minnesota 0 0 0 0 0 0 0 0 0 0

Mississippi 62 49 49 46 42 8 7 4 0 0

Missouri 42 38 38 36 29 23 17 13 6 0

Montana 193 109 96 84 48 29 9 6 2 0

Nebraska 0 0 0 0 0 0 0 0 0 0

Nevada 69 69 69 67 64 56 53 53 35 10

New Hampshire 0 0 0 0 0 0 0 0 0 0

New Jersey 95 95 95 92 76 74 73 70 7 2

New Mexico 521 424 355 228 82 39 16 5 1 0

New York 19 19 19 19 19 19 19 18 1 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 82 70 52 29 19 17 11 0 0

Ohio 38 34 33 32 29 26 24 23 20 10

Oklahoma 0 0 0 0 0 0 0 0 0 0

Oregon 19 4 1 1 1 0 0 0 0 0

Pennsylvania 200 195 186 173 173 172 172 171 167 37

Rhode Island 1 1 1 1 1 1 1 1 1 0

South Carolina 19 0 0 0 0 0 0 0 0 0

South Dakota 100 96 96 96 93 88 86 83 50 30

Tennessee 48 34 31 23 19 16 12 7 0 0

Texas 690 476 387 285 124 62 50 38 2 0

Utah 64 64 64 64 64 64 63 63 58 2

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 246 107 86 82 71 63 61 42 16 0

Washington 0 0 0 0 0 0 0 0 0 0

West Virginia 0 0 0 0 0 0 0 0 0 0

Wisconsin 2 0 0 0 0 0 0 0 0 0

Wyoming 23 19 13 11 7 6 6 6 1 0

Totals 4,168 3,337 3,017 2,580 1,813 1,521 1,375 1,280 853 268

Percentage reduction 19.9 27.6 38.1 56.5 63.5 67.0 69.3 79.5 93.6
Supplemental Information 53

Table 32. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

chloride, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 49 45 45 45 45 45 43 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 132 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 22 0 0 0 0 0 0 0 0 0

Connecticut 31 31 31 31 31 31 31 31 26 2

Delaware 106 103 102 95 88 81 69 45 17 0

Florida 693 687 677 653 507 380 302 257 187 78

Georgia 10 8 8 7 7 7 7 7 7 1

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 47 47 46 35 11 10 9 7 1 0

Illinois 202 50 8 7 3 2 1 1 1 0

Indiana 32 16 15 15 15 15 15 15 14 0

Iowa 6 6 6 6 6 6 6 4 0 0

Kansas 289 289 281 251 169 146 145 145 89 6

Kentucky 89 88 66 60 51 48 48 45 44 28

Louisiana 173 172 172 172 152 149 148 148 99 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 0 0 0 0 0 0 0 0 0 0

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 249 173 163 93 69 66 62 58 36 3

Minnesota 17 11 11 10 9 6 6 6 5 0

Mississippi 80 65 60 56 49 49 7 3 0 0

Missouri 43 39 39 35 25 20 17 9 5 0

Montana 523 250 198 132 65 28 21 17 4 0

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 69 69 69 67 64 56 53 53 35 10

New Hampshire 209 118 32 12 1 0 0 0 0 0

New Jersey 93 93 93 92 73 71 70 67 7 2

New Mexico 507 358 233 131 52 24 18 13 3 0

New York 19 19 19 19 19 19 19 18 1 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 82 70 52 29 19 17 11 0 0

Ohio 42 42 40 40 39 38 37 35 30 3

Oklahoma 252 229 227 177 59 40 23 21 4 1

Oregon 53 6 4 4 0 0 0 0 0 0

Pennsylvania 82 66 59 41 40 40 39 39 37 3

Rhode Island 5 5 5 5 5 1 1 1 1 0

South Carolina 22 15 15 14 14 13 13 13 13 2

South Dakota 16 10 9 8 7 7 7 7 6 0

Tennessee 2 1 1 1 1 0 0 0 0 0

Texas 910 697 597 495 394 319 247 198 77 15

Utah 64 64 64 64 64 64 61 61 58 1

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,216 1,079 1,042 897 765 702 605 511 284 55

Washington 1 0 0 0 0 0 0 0 0 0

West Virginia 26 26 26 25 0 0 0 0 0 0

Wisconsin 50 49 48 47 41 39 34 33 18 4

Wyoming 25 23 22 19 18 14 13 12 7 0

Totals 6,569 5,290 4,761 4,066 3,140 2,708 2,349 2,088 1,288 342

Percentage reduction 19.5 27.5 38.1 52.2 58.8 64.2 68.2 80.4 94.8
54 Summary of Available State Ambient Stream-Water-Quality Data, 1990–98, and Limitations for National Assessment

Table 33. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

sulfate, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 0 0 0 0 0 0 0 0 0 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 132 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 342 277 263 215 73 60 51 39 23 2

Connecticut 32 32 32 32 32 32 32 32 27 2

Delaware 0 0 0 0 0 0 0 0 0 0

Florida 635 622 618 593 471 364 275 199 101 25

Georgia 7 7 7 0 0 0 0 0 0 0

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 46 46 45 37 8 7 6 1 0

Illinois 220 54 3 3 3 2 1 1 1 0

Indiana 22 13 12 12 12 12 12 12 12 0

Iowa 6 6 6 6 6 6 5 0 0 0

Kansas 289 289 281 251 169 146 145 145 89 6

Kentucky 89 88 66 59 49 46 46 45 44 22

Louisiana 173 172 172 172 152 149 148 148 99 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 12 12 12 12 12 12 12 12 12 11

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 192 108 100 64 51 42 41 8 1 0

Minnesota 4 1 1 1 1 1 1 1 0 0

Mississippi 2 2 2 2 2 2 0 0 0 0

Missouri 42 38 38 34 24 20 17 9 5 0

Montana 614 265 240 163 98 41 30 23 3 0

Nebraska 0 0 0 0 0 0 0 0 0 0

Nevada 69 69 68 66 58 45 28 17 10 10

New Hampshire 201 43 10 8 1 0 0 0 0 0

New Jersey 93 93 93 92 74 72 71 68 7 2

New Mexico 511 364 234 132 52 24 18 13 4 0

New York 19 19 19 19 19 19 19 18 1 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 82 70 52 29 19 17 11 0 0

Ohio 42 42 41 36 33 29 26 22 19 0

Oklahoma 245 229 227 178 58 40 23 21 6 1

Oregon 30 0 0 0 0 0 0 0 0 0

Pennsylvania 201 196 192 174 174 174 174 172 169 142

Rhode Island 5 5 5 5 5 1 1 1 1 0

South Carolina 11 5 5 5 5 5 5 4 0 0

South Dakota 19 10 9 8 7 7 7 7 6 0

Tennessee 4 2 2 2 2 0 0 0 0 0

Texas 898 684 584 481 382 304 232 182 72 10

Utah 64 64 64 64 64 64 63 63 58 1

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,219 1,079 1,042 894 764 701 604 512 284 56

Washington 0 0 0 0 0 0 0 0 0 0

West Virginia 26 26 26 26 0 0 0 0 0 0

Wisconsin 20 18 18 17 12 9 9 9 6 0

Wyoming 25 23 22 19 18 16 13 12 7 0

Totals 6,652 5,218 4,761 4,065 3,043 2,603 2,264 1,943 1,197 418

Percentage reduction 21.6 28.4 38.9 54.3 60.9 66.0 70.8 82.0 93.7
Supplemental Information 55

Table 34. Number of State ambient stream-water-quality monitoring sites with selected numbers of analyses for 

pH, 1990–98.

[--, not available]

State Number of analyses (equal to or greater than)

1 3 5 9 15 20 25 30 50 100

Alabama 49 49 49 45 45 45 45 45 43 0

Alaska -- -- -- -- -- -- -- -- -- --

Arizona -- -- -- -- -- -- -- -- -- --

Arkansas 133 133 132 131 131 131 131 131 129 127

California -- -- -- -- -- -- -- -- -- --

Colorado 523 360 265 205 74 63 53 45 24 4

Connecticut 32 32 32 32 32 32 32 32 27 2

Delaware 109 109 108 103 96 87 76 59 21 0

Florida 748 745 739 690 575 490 423 371 281 155

Georgia 391 377 330 284 154 146 132 122 80 8

Hawaii -- -- -- -- -- -- -- -- -- --

Idaho 51 51 51 51 48 32 24 19 9 0

Illinois 367 135 23 11 3 2 1 1 1 0

Indiana 105 105 101 101 87 82 81 80 61 0

Iowa 65 65 65 36 24 24 24 24 24 24

Kansas 289 288 280 247 169 145 145 144 76 6

Kentucky 87 84 65 60 48 47 47 45 44 15

Louisiana 173 172 172 172 152 148 148 148 84 1

Maine -- -- -- -- -- -- -- -- -- --

Maryland 40 40 40 40 40 40 40 40 40 40

Massachusetts -- -- -- -- -- -- -- -- -- --

Michigan 218 157 147 79 65 64 59 57 11 1

Minnesota 67 67 67 66 66 65 63 52 48 0

Mississippi 83 72 71 66 63 60 25 23 10 0

Missouri 43 42 42 38 38 36 34 32 17 2

Montana 871 411 335 276 184 125 96 81 45 5

Nebraska 22 22 22 22 22 22 22 21 0 0

Nevada 55 54 50 35 23 22 0 0 0 0

New Hampshire 429 277 136 55 21 15 5 0 0 0

New Jersey 94 94 94 89 75 74 73 70 8 2

New Mexico 527 425 360 211 65 27 14 14 5 1

New York 19 19 19 19 19 19 18 16 0 0

North Carolina -- -- -- -- -- -- -- -- -- --

North Dakota 90 86 82 72 42 35 30 21 9 0

Ohio 41 41 41 39 38 37 35 35 24 6

Oklahoma 256 250 224 133 71 41 38 36 12 3

Oregon 148 148 147 140 126 120 116 96 63 13

Pennsylvania 200 194 188 174 174 174 174 172 166 96

Rhode Island 5 5 5 5 5 5 5 5 5 0

South Carolina 339 339 339 339 294 244 215 212 208 149

South Dakota 100 96 96 96 93 87 86 79 49 8

Tennessee 102 92 70 43 31 26 23 8 2 0

Texas 935 787 682 546 435 347 296 237 128 39

Utah 64 64 64 64 64 64 64 64 63 60

Vermont -- -- -- -- -- -- -- -- -- --

Virginia 1,278 1,094 1,050 898 770 710 614 527 303 74

Washington 208 208 208 207 106 105 91 90 57 0

West Virginia 26 26 26 24 0 0 0 0 0 0

Wisconsin 48 44 40 38 30 28 27 27 21 5

Wyoming 43 39 36 36 31 29 25 18 6 0

Totals 9,473 7,898 7,093 6,018 4,629 4,095 3,650 3,299 2,204 846

Percentage reduction 16.6 25.1 36.5 51.1 56.8 61.5 65.2 76.7 90.1