Quality-Assurance Data for Routine Water

Analyses by the U.S. Geological Survey

Laboratory in Troy, New York —

July 1995 through June 1997

Open-File Report 2004-1327

U.S. Department of the Interior

U.S. Geological Survey
This page has been left blank intentionally. 
Quality-Assurance Data for Routine Water 

Analyses by the U.S. Geological Survey 

Laboratory in Troy, New York—

July 1995 through June 1997

By Tricia A. Lincoln, Debra A. Horan-Ross, Michael R. McHale, 

and Gregory B. Lawrence

Open-File Report 2004-1327

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For additional information about this report write to: 

U.S. Geological Survey 

425 Jordan Road 

Troy, NY 12180 

Email: askny@usgs.gov 

World Wide Web: http://ny.usgs.gov/

For more information about the USGS and its products: 

Telephone: 1-888-ASK-USGS 

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

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.
iii

FIGURES

1-5. Graphs showing results of quality-control data for water-sample analyses from 

July 1995 through June 1997.

1. High- and low-concentration quality-control samples

A. Acid-neutralizing capacity ...........................................................................................................12

B. Aluminum, total monomeric .........................................................................................................12

C. Aluminum, total...............................................................................................................................12

D. Ammonium.......................................................................................................................................12

E. Calcium.............................................................................................................................................13

F. Carbon, dissolved organic .............................................................................................................13

G. Carbon, dissolved organic (soil expulsions)..............................................................................13

H. Chloride............................................................................................................................................13

I. Fluoride..............................................................................................................................................14

J. Magnesium......................................................................................................................................14

K. Nitrate (ion chromatography).......................................................................................................14

Contents

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

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

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

Participating Projects ..........................................................................................................................2

Quality-Assurance/Quality-Control (QA/QC) Program Description.......................................................2

Quality-Control Samples......................................................................................................................2

Filter Blanks and Analytical Blanks ...................................................................................................3

Triplicate Environmental Samples......................................................................................................3

U.S. Geological Survey’s Standard Reference Sample Program..................................................4

NWRI Ecosystem Interlaboratory QA Program ...............................................................................4

Blind Reference Samples....................................................................................................................4

Control-Chart Development and Evaluation..............................................................................................4

Quality-Control Samples......................................................................................................................4

Filter Blanks and Analytical Blanks ...................................................................................................4

Triplicate Environmental Samples......................................................................................................6

NWRI Ecosystem Interlaboratory QA Program ...............................................................................6

Blind Reference Samples....................................................................................................................6

Summary of Results.......................................................................................................................................6

A. Quality-Control Samples .................................................................................................................6

B. Filter Blanks and Analytical Blanks ..............................................................................................8

C. Triplicate Environmental Samples .................................................................................................9

D. U.S. Geological Survey’s Standard Reference Sample (SRS) Program..................................9

E. NWRI Ecosystem Interlaboratory QA Program.........................................................................10

F. Blind Reference Samples ..............................................................................................................10

Selected References...................................................................................................................................10
iv

L. Nitrate (colorimetric method)...................................................................................................14

M. pH .........................................................................................................................................15

N. Potassium ...................................................................................................................................15

O. Silicon .........................................................................................................................................15

P. Sodium .........................................................................................................................................15

Q. Specific conductance...............................................................................................................16

R. Sulfate .........................................................................................................................................16

2. Filter blank and analytical blank samples

A. Aluminum, total monomeric.....................................................................................................17

B. Aluminum, organic monomeric ...............................................................................................17

C. Calcium........................................................................................................................................17

D. Carbon, dissolved organic .......................................................................................................17

E. Chloride........................................................................................................................................17

F. Magnesium..................................................................................................................................17

G. Nitrate (ion chromatography)..................................................................................................17

H. Potassium....................................................................................................................................17

I. Silicon .........................................................................................................................................18

J. Sodium .........................................................................................................................................18

K. Sulfate .........................................................................................................................................18

3. Triplicate environmental samples

A1. Acid-neutralizing capacity (for triplicate means not in the range of ±20 μeq/L) ..........19

A2. Acid-neutralizing capacity (for triplicate means in the range of ±20 μeq/L).................19

B. Aluminum, total monomeric.....................................................................................................19

C. Aluminum, organic monomeric ...............................................................................................19

D. Aluminum, total ..........................................................................................................................19

E. Calcium ........................................................................................................................................19

F. Carbon, dissolved organic.........................................................................................................19

G. Chloride .......................................................................................................................................19

H. Magnesium.................................................................................................................................20

I. Nitrate (ion chromatography) ...................................................................................................20

J. pH .........................................................................................................................................20

K. Potassium....................................................................................................................................20

L. Silicon .........................................................................................................................................20

M. Sodium........................................................................................................................................20

N. Sulfate .........................................................................................................................................20

4. NWRI Ecosystem Interlaboratory QA Program

A1. Acid-neutralizing capacity (for samples not in the range of ±20 μeq/L) .......................21

A2. Acid-neutralizing capacity (for samples in the range of ±20 μeq/L) ...............................21

B. Ammonium..................................................................................................................................21

C. Calcium........................................................................................................................................21

D. Carbon, dissolved organic .......................................................................................................21

E. Chloride........................................................................................................................................21

F. Magnesium..................................................................................................................................21

G. Nitrate (ion chromatography)..................................................................................................21

H. pH .........................................................................................................................................22
v

I. Potassium.....................................................................................................................................22

J. Silicon .........................................................................................................................................22

K. Sodium.........................................................................................................................................22

L. Sulfate .........................................................................................................................................22

5. Blind Reference Samples

A. Calcium .......................................................................................................................................23

B. Chloride ......................................................................................................................................23

C. Magnesium ................................................................................................................................23

D. pH .........................................................................................................................................23

E. Potassium....................................................................................................................................23

F. Sodium .........................................................................................................................................23

G. Specific conductance ..............................................................................................................23

H. Sulfate .........................................................................................................................................23

TABLES

1.Number of environmental samples and quality-control samples analyzed by the Troy 

Laboratory, and summary of quality control (QC) data for each constituent from July 

1995 through June 1997.............................................................................................................................3

2.Reporting limits and data-quality objectives for accuracy, precision, and blanks for 

solution analyses performed by the U.S. Geological Survey Laboratory in Troy, N.Y., 

July 1995 through June 1997 ....................................................................................................................5

3. Results obtained by the Troy Laboratory for U.S. Geological Survey Standard Reference 

Sample (SRS) Program, October 1995 through April 1997 ..................................................................7

ABBREVIATED UNITS OF MEASUREMENT

mg/L milligrams per liter

μeq/L microequivalents per liter

μmol/L micromoles per liter

μS/cm microSeimens per centimeter

μg/L micrograms per liter

Other Abbreviations

ANC acid-neutralizing capacity

CV coefficient of variation

DI deionized water

DQO data-quality objective

LRTAP Long-Range Transport of Atmospheric Pollutants

MCV mean concentration value

MPV most probable value

NWRI National Water Research Institute

QA quality assurance

QC quality control

QC-high high-concentration quality-control sample

QC-low low-concentration quality-control sample

SRS Standard Reference Sample

USGS U.S. Geological Survey 
Abstract

The laboratory for analysis of low-ionic-strength water 

at the U.S. Geological Survey (USGS) office in Troy, N.Y. 

analyzes samples collected by USGS projects in the Northeast. 

The laboratory’s quality-assurance program is based on 

internal and interlaboratory quality-assurance samples and 

quality-control procedures developed to ensure proper sample 

collection, processing, and analysis. For the time period 

addressed in this report, the quality-assurance/quality-control 

data were stored in the laboratory’s SAS data-management 

system, which provides efficient review, compilation, and 

plotting of quality-assurance/quality-control data. This report 

presents and discusses samples analyzed from July 1995 

through June 1997.

Quality-control results for 19 analytical procedures were 

evaluated for bias and precision. Control charts show that data 

from ten of the analytical procedures were biased throughout 

the analysis period for either high-concentration or lowconcentration samples but were within control limits; these 

procedures were: acid-neutralizing capacity, total monomeric 

aluminum, ammonium, calcium, chloride, dissolved organic 

carbon, magnesium, nitrate (ion chromatography), nitrate 

(colorimetric method), and sulfate. Four of the analytical 

procedures were occasionally biased but were within control 

limits; they were: fluoride, pH, silicon, and sodium.

Results from the filter-blank and analytical-blank 

analyses indicate that all analytical procedures in which blanks 

were run were within control limits, although values for a few 

blanks were outside the control limits. 

Sampling and analysis precision are evaluated herein 

in terms of the coefficient of variation obtained for triplicate 

samples in 14 of the 19 procedures. Data-quality objectives 

(DQO’s) were met by at least 92 percent of the samples 

analyzed in all procedures except acid neutralizing capacity 

(80 percent of samples met objectives), total monomeric 

aluminum (87 percent of samples met objectives), organic 

monomeric aluminum (89 percent of samples met objectives), 

and chloride (89 percent of samples met objectives). The data 

are insufficient to evaluate the DQO’s for total aluminum.

Results of the USGS interlaboratory Standard Reference 

Sample Program indicated acceptable data quality for most 

constituents over the time period. The results of the P-sample 

(low-ionic strength constituent) analysis indicated high data 

quality with good ratings in all studies. The T-sample (trace 

constituent) had unacceptable ratings in two studies, but 

received satisfactory ratings in the others. The N-sample 

(nutrient constituent) studies had an unacceptable rating in one 

and an excellent rating in the other.

Environment Canada’s NWRI program results indicated 

that at least 90 percent of the samples met data-quality 

objectives in 9 of the 12 analyses; exceptions were calcium, 

chloride, and silicon. Data-quality objectives were not met for 

calcium samples in two NWRI studies, but all of the samples 

analyzed were within control limits for the remaining studies. 

Data-quality objectives were not met for 32 percent of samples 

analyzed for chloride and 27 percent of samples analyzed for 

silicon.

Results from blind reference-sample analyses indicated 

that data-quality objectives were met by at least 90 percent of 

the calcium, pH, potassium, and sodium samples. Data-quality 

objectives were met by 77 percent of the chloride samples, 

83 percent of the magnesium samples, and 80 percent of the 

sulfate samples. There is insufficient data to evaluate the 

specific conductance samples.

Introduction

The U.S. Geological Survey (USGS) maintains a 

laboratory at its Troy, N.Y. office to analyze low-ionicstrength water for USGS watershed-research projects that 

require major-ion analyses of precipitation, soil-water, shallow 

ground-water, and stream-water samples. The methods used in 

this laboratory are described in detail in Lawrence and others 

(1995). During this time period quality-assurance/quality 

control data were collected, stored, and reviewed using the 

laboratory’s SAS data-management system.

Analyses done during the 2-year period (July 1995-

June 1997) represented by this report were: acid-neutralizing 

Quality-Assurance Data for Routine Water Analyses by 

the U.S. Geological Survey Laboratory in Troy, New York,

July 1995 through June 1997

By Tricia A. Lincoln, Debra A. Horan-Ross, Michael R. McHale, and Gregory B. Lawrence
capacity (ANC), total monomeric aluminum, organic 

monomeric aluminum, total aluminum, ammonium, calcium, 

dissolved organic carbon (DOC), DOC (soil expulsions), 

chloride, fluoride, magnesium, nitrate (ion chromatograph and 

colorimetric method), pH, potassium, silicon, sodium, specific 

conductance, and sulfate.

Purpose and Scope

This report documents the quality-assurance practices 

and quality-control data of this laboratory and is intended for 

use by current and prospective cooperating agencies. It (1) 

describes quality-control and quality-assurance procedures 

of the laboratory, (2) presents graphs showing the results 

from analyses of quality-control samples, filter blanks and 

analytical blanks, triplicate environmental samples, and blind 

reference samples, and (3) describes analytical biases and 

outliers and the corrective actions taken.

Participating Projects

The numbers and types of samples analyzed by the 

laboratory during the 2-year period are summarized below, 

by the project for which they are associated; numbers in 

parentheses are USGS project numbers.

Project: Neversink Watershed Study (NY91-200)

Cooperator: New York City Department of Environmental 

Protection

Analyses: 181 samples (stream water, shallow ground water, 

and snow).

Project: Biogeochemical Processes that Control Nitrogen 

Cycling and Associated Hydrogen and Aluminum Leaching in 

an Undeveloped Headwater Basin (NY91-204)

Cooperator: New York City Department of Environmental 

Protection

Analyses: 4,385 samples (stream water, shallow groundwater, soil water solution, soil water by expulsion method, 

and snow).

Project: Long-Term Monitoring of Five Streams in the 

Catskill Mountains (NY85-152)

Cooperator: U.S. Environmental Protection Agency 

Analyses: 331 stream-water samples.

Project: Forest-Floor Aluminum and Calcium Chemistry—

Relations with Acid Deposition, Root Vitality, Stand 

Dynamics, and Red Spruce (NY92-208)

Cooperator: U.S. Forest Service

Analyses: 67 samples (stream water, soil water solution, and 

soil water by expulsion method).

Project: The effects of the Clean Air Act on water quality of 

medium-scale rivers in the Northeastern United States (NY97-

322)

Cooperator: US Geological Survey, Office of Water Quality

Analysis: 22 stream samples.

Additional information on projects of the New York District is 

given in Lee (1996).

Quality-Assurance/Quality-Control 

(QA/QC) Program Description

The quality of the data produced at this laboratory is 

maintained by adherence to the standard operating procedures 

described in Lawrence and others (1995) and by participation 

in externally administered quality-assurance (QA) programs. 

Results of QA data are evaluated by the laboratory supervisor 

and primary analysts, and appropriate corrective action is 

taken when needed. The data quality objectives (DQO’s) 

are based on (1) the precision and accuracy levels generally 

required in projects using the Troy Laboratory, and (2) the 

analytical limits of the methods used.

Quality-Control Samples

Quality-control (QC) samples are used to determine 

the accuracy of an instrument’s calibration and to detect 

variations in instrument response within an analytical run. 

Source material for all QC samples either is obtained from a 

manufacturer other than the producer of the source material 

used to make calibration standards, or is obtained from a 

different lot.

The concentrations of QC samples are chosen to 

bracket the expected range of the environmental-sample 

concentrations. A high-concentration QC sample and a lowconcentration QC sample (referred to herein as QC-high 

and QC-low) are prepared for most analyses; exceptions are 

inorganic monomeric aluminum, for which column efficiency 

is used to determine the acceptability of the data, and fluoride, 

for which only one mid-level QC sample is prepared because 

the concentrations encountered by the laboratory are within a 

narrow range.

Quality-control samples are analyzed immediately after 

calibration, after every 10 analyses of environmental samples, 

and at the end of each run. Exceptions to the frequency of 

QC-sample analyses are ANC (after every 17 environmental 

samples), and pH (after every 7 to 13 environmental samples). 

QC samples that do not meet DQO’s for accuracy are rerun, 

and if the value is acceptable, the run is continued. If the 

rerun QC-sample value is unacceptable, the environmentalsample data preceding it are considered to be out-of-control 

data. The data are rejected and the instrument is recalibrated. 

Only accepted QC-sample and environmental-sample data are 

entered into the database. An exception to this practice occurs 

when the volume of an environmental sample is insufficient 

for a rerun. In this case, the environmental-sample and QC 

data are entered into the database and flagged, and the project 

chief then decides whether to accept or reject these data. 

Analytical results of QC samples are included in this report to 

 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997
indicate (1) the frequency of out-of-control data that are not 

rerun, and (2) biases and trends of within control data. The 

number of samples analyzed and a summary of the qualityassurance data are given in table 1.

Filter Blanks and Analytical Blanks

A filter blank and an analytical blank are included in each 

group of 50 environmental samples. 

Filter blanks are aliquots of deionized (DI) water that are 

processed and analyzed in the same manner as environmental 

samples. Filter blanks are analyzed only for constituents that 

require filtration. Filter-blank analysis indicates whether 

contamination has occurred during bottle-washing procedures, 

filtration, sample preservation, or laboratory analysis.

Analytical blanks are aliquots of DI water that are 

processed and analyzed as environmental samples, except 

that the filtration step is omitted. Contamination found in 

analytical blanks may be attributed to bottle washing, sample 

preservation, or laboratory analysis, but not to filtration.

Triplicate Environmental Samples

One set of triplicate environmental samples is included 

in each group of 50 samples. An environmental triplicate 

set consists of three consecutive samples taken from one 

field site. The purpose of environmental triplicate samples 

is to determine long-term analytical precision. Precision can 

be affected by bottle washing, sample-collection, sample 

processing procedures, and analysis. Environmental samples 

Table 1. Number of environmental and quality-control (QC) samples analyzed by the Troy Laboratory, and summary of quality-control 

data for each constituent, July 1995 through June 1997. 

[QC-high = high concentration quality-control sample. QC-low = low concentration quality-control sample.]

Number of samples analyzed

Number of QC samples 

exceeding control limits 

where environmental 

sample data are not 

rejected

Number of QC samples 

exceeding control limits by 

more than 5 percent where 

environmental sample data 

are not rejected

Constituent Environmental 

samples

QC-high 

Samples

QC-low 

Samples QC-high QC-low QC-high QC-low

Acid-neutralizing capacity 3458 62 317 0 1 0 0

Aluminum, total monomeric 3722 548 548 0 1 0 1

Aluminum, organic monomeric* 3722 0 0 0 0 0 0

Aluminum, total 1098 140 140 0 0 0 0

Ammonium 2943 453 453 2 5 0 1

Calcium 3019 615 615 0 1 0 0

Carbon, dissolved organic 3885 535 535 2 3 0 1

Carbon, dissolved organic (soil 

expulsions)

67 18 18 0 0 0 0

Chloride 3937 647 647 0 0 0 0

Fluoride 1792 0 312 1 0 0 0

Magnesium 3801 601 601 0 0 0 0

Nitrate (ion chromatography) 3922 647 647 0 4 0 2

Nitrate (colorimetric method) 988 175 171 5 0 0 0

pH 3760 125 489 0 1 0 0

Potassium 3765 587 585 0 3 0 3

Silicon 3684 546 546 1 4 0 1

Sodium 836 539 539 0 0 0 0

Specific conductance 316 36 88 0 0 0 0

Sulfate 935 647 647 0 3 0 1

*Column efficiency is used to determine the acceptability of the data.

Quality-Assurance/Quality-Control (QA/QC) Program Description 
are selected for triplicate analysis on a random basis to ensure 

a wide range of sample concentrations from various field sites. 

The laboratory alternates between analyzing a triplicate set 

consecutively and separating the triplicate set over the day’s 

analytical run.

U.S. Geological Survey’s Standard Reference 

Sample Program

The USGS Standard Reference Sample Program (SRS) 

conducts a national interlaboratory analytical evaluation 

program semiannually. The Troy laboratory participates in 

the low-ionic strength, nutrient, and trace components of 

this program. Typically, the reference samples consists of 

snow, rain, surface water, or deionized water that is collected, 

filtered, and possibly spiked with reagent-grade chemicals 

to meet the goals of the SRS program. Low-ionic strength 

constituent reference samples are prefixed by a P and are 

analyzed for calcium, chloride, fluoride, magnesium, pH, 

potassium, sodium, specific conductance, and sulfate. Nutrient 

constituent reference samples are prefixed by an N and are 

analyzed for ammonium. Trace constituent reference samples 

are prefixed by a T and are analyzed for aluminum, calcium, 

magnesium, potassium, silicon, and sodium. Laboratory 

personnel are aware of the presence of the SRS sample 

at the time of analysis but do not know the constituent 

concentrations until a published report is received from the 

USGS after the conclusion of each study. The most probable 

value (MPV) for each constituent is equal to the median value. 

Individual laboratory performances are rated numerically; the 

highest score is 4.0, and the lowest is 0.0.

NWRI Ecosystem Interlaboratory QA Program

In 1996, Environment Canada changed the name of 

the LRTAP interlaboratory study to the NWRI Ecosystem 

Interlaboratory QA program. The Troy Laboratory participates 

in the quality-assurance program, in which a set of 10 samples 

is analyzed two times per year. The samples are obtained from 

predominantly low-ionic-strength waters from various sources, 

such as precipitation, snow, lakes, and streams throughout 

North America. The concentrations of the constituents in 

the NWRI samples are similar to those of the environmental 

samples analyzed at the Troy Laboratory. Laboratory results 

are compared with a median concentration value (MCV) 

calculated from results from all participants in the NWRI 

program. Laboratory personnel are aware of the presence of 

NWRI samples at the time of analysis but do not know the 

MCV of the constituents until Environment Canada publishes 

a report at the conclusion of each study. 

Blind Reference Samples

The Troy Laboratory disguises USGS SRS samples 

from previous studies as routine environmental samples. 

These blind reference samples are processed and analyzed as 

environmental samples and therefore assumed by the analyst 

to be a project sample. The blind reference samples have most 

probable values that are reported by the USGS SRS program. 

The SRS samples are rotated as supplies are exhausted, and 

periodically the identity of the blind reference sample is 

changed. One blind reference sample is included in each set of 

50 environmental samples.

Control-Chart Development 

and Evaluation

Control charts (figs. 1-5) are plots of QC data in 

relation to time; in this report, they are used to (1) confirm 

that laboratory DQO’s are met for individual QC samples, 

(2) detect long-term biases within the control limits, and (3) 

provide comparisons with results from other laboratories. 

A constituent analysis is considered biased if 70 percent 

or more of the points on a chart are above or below the 

theoretical value.

Quality-Control Samples

Results of QC sample analyses are plotted on control 

charts in which the central line is equal to the theoretical value 

of the control sample. Each analyte has prescribed control 

limits that have been established to meet project DQO’s (table 

2). The limits are represented by the upper and lower controllimit lines on each chart. QC-high and QC-low samples are 

plotted on separate graphs by constituent and date of analysis, 

and the control charts are evaluated for trends and(or) bias 

and precision. All data are reported in micromoles per liter 

(μmol/L) except pH (pH units), ANC (microequivalents per 

liter, μeq/L), and specific conductance (microSeimens per 

centimeter, mS/cm).

During the period represented by this report, two qualitycontrol sample concentrations were changed to reflect typical 

environmental-sample concentrations (see fig. 1N and 1P). 

The concentration changes are discussed in the summary of 

results. 

Filter Blanks and Analytical Blanks

Results from blank analyses (fig. 2) are plotted on control 

charts by constituent. The control limits were established to 

meet project DQO’s (table 2) and are represented by horizontal 

lines on the control charts. Data are plotted as concentration 

in relation to date of collection. Negative blank concentrations 

are encountered frequently. The standard curve is extrapolated 

beyond the lowest standard in order to evaluate blank samples 

and negative concentrations reflect the practical limitations of 

the extrapolation. The control charts are evaluated to identify 

possible contamination or positive interferences.

 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997
Control-Chart Development and Evaluation   

Table 2. Reporting limits and data-quality objectives for accuracy, precision, and blanks for solution analyses performed by the U.S. 

Geological Survey Laboratory in Troy, N.Y., July 1995 through June 1997.

[DQO, data-quality objective. μmol/L, micromoles per liter. CV, coefficient of variation. ANC, acid-neutralizing capacity.]

Accuracy Precision

Constituent or property

Low-concentration 

quality-control sample

High-concentration 

quality-control sample Environmental 

Triplicate 

Samples 

DQO (CV) 

Filter and 

analytical 

blanks 

DQO (μmol/L)

Reporting 

limit 

(μmol/L)

DQO 

(percent 

error) 

Concentration 

(μmol/L)

DQO

 (percent 

error)

Concentration 

(μmol/L)

Acid-neutralizing capacity 1 none 10 (-39.9) 10 (125) 15 none

Aluminum, total monomeric 1.5 15 7.41 10 18.5 15 1.0

Aluminum, organic 

monomeric 2 1.5 none none none none 15 1.0

Aluminum, total 1.0 20 3.0 10 15.0 10 none

Ammonium 2.0 15 7.14 10 17.9 none none

Calcium 2.0 10 25.0 10 99.8 10 1.0

Carbon, dissolved organic3 41.0 15 83.3 10 416 10 18

Carbon, dissolved organic 

(soil expulsions)3 41.0 10 416 10 1665 none none

Chloride 3.0 10 8.47 10 84.7 10 2.0

Fluoride 0.5 15 1.58 none none none none

Magnesium 1.0 10 10.3 10 41.1 10 0.5

Nitrate (ion chromatography) 2.0 10 4.84 10 48.4 10 0.3

Nitrate (colorimetric method) 5.0 15 42.9 10 100 none none

pH4 none 10 (4.44) 20 (6.88) 10 none

Potassium 1.0 10 6.40 10 25.6 10 0.5

Silicon 6.0 10 35.6 10 107 10 3.0

Sodium 1.0 10 8.70 10 43.5 10 1.0

Specific conductance5 none 10 (17.0) 10 (39.0) none none

Sulfate 2.0 10 8.33 10 83.3 10 0.3

1

 ANC: Values in parentheses are in microequivalents per liter. For values within ±20 microequivalents per liter, an absolute data-quality objective of ±6 

microequivalents per liter is used for precision. 

2

 Quality-control samples for organic monomeric aluminum are unavailable.

3

 Concentrations are expressed as micromoles carbon per liter.

4

 pH: Percent error and coefficient of variation determined from [H+]. Values in parentheses are in pH units.

5

 Specific conductance: Values in parentheses are in microSiemens per centimeter.
Triplicate Environmental Samples

The coefficient of variation (CV) for each triplicate 

sample concentration is plotted by constituent and date of 

collection in figure 3. Data with mean concentrations less than 

the defined reporting limit (table 2) are excluded. The DQO 

for all constituents is a CV of less than 10 percent, with the 

exception of ANC, total monomeric aluminum and organic 

monomeric aluminum, which are 15 percent. Each circle 

within the control charts represents the CV of a triplicate 

environmental sample. 

cv = (100)

where: s = standard deviation, and

x = arithmetic mean of triplicate samples

ANC triplicate sample means were plotted on two 

graphs. The first graph shows the CV for triplicate sample 

means outside the range of -20 to +20 μeq/L (fig. 3A1); the 

absolute value of the mean is used to calculate the CV. The 

second graph shows values that fall between -20 and +20 

μeq/L (fig. 3A2); each symbol on the second graph represents 

the difference between the triplicate sample mean and the 

individual values of that triplicate sample.

NWRI Ecosystem Interlaboratory QA Program

Interlaboratory comparison graphs (fig. 4) are based on 

results from NWRI samples and represent NWRI studies from 

September 1995 through April 1997. Samples with MCV’s 

less than the reporting limits were excluded from the graphs. 

The MCV and the control limits are represented by lines on 

the graphs; the percent difference (D) is calculated as:

D = [(AV - MCV)/MCV] x 100

where: AV = analyzed value, and

MCV = mean concentration value

A separate graph is shown for ANC values in the +20 

to -20 μeq/L range; results for these samples are plotted as the 

difference between the laboratory value and the MCV (fig. 

4A2). The NWRI pH results consist of two sets of data—pH 

values less than 6.00, and pH values equal to or greater than 

6.00. The two sets of data have different DQO’s, which are 

represented by a short dashed line and a long dashed line on 

the pH graph (fig. 4H).

Blind Reference Samples

Results from blind reference sample analyses (fig.5) are 

plotted on separate control charts, by constituent and date of 

analysis. Samples with MPV’s less than the reporting limits 

were excluded from the graphs. The MPV and the control 

limits of ±10 percent are represented by lines on the graphs; 

the percent difference (D) is calculated as:

D = [(AV-MPV)/MPV]x100

where: AV = analyzed value, and

MPV = most probable value

Summary of Results

The following sections summarize the results for (A) 

quality-control samples (fig. 1, p. 12-16), (B) filter blanks and 

analytical blanks (fig 2, p. 17-18), (C) triplicate environmental 

samples (fig. 3, p. 19-20), (D) SRS samples (table 3), (E) 

LRTAP samples (fig. 4, p. 21-22), and (F) blind samples (fig. 

5, p. 23).

A. Quality-Control Samples

Acid-Neutralizing Capacity (fig. 1A).– DQO’s were met 

by 99 percent of the samples. The QC-high sample had a 

negative bias during this time period. The QC-low sample 

had a positive bias from June through December 1996.

Aluminum, Total Monomeric (fig. 1B).–DQO’s were met by 

99 percent of the samples. The QC-high sample had a slight 

positive bias during this time period. The QC-low sample 

had a slight positive bias through 1996 and a slight negative 

bias through 1997.

Aluminum, Organic Monomeric.–A QC sample has not 

been developed for this analysis. Column efficiency is used 

to determine acceptability of the data.

Aluminum, Total (fig. 1C).–DQO’s were met by 100 percent 

of the samples. No apparent trends or biases were evident 

among the QC-high and QC-low samples.

Ammonium (fig. 1D).–DQO’s were met by 99 percent of the 

samples. No apparent trends or biases were evident among 

the QC-low samples. The QC-high sample had a slight 

positive bias during this time period.

Calcium (fig. 1E).–DQO’s were met by 99 percent of the 

samples. A slight positive bias was observed for most 

analyzed QC-high and QC-low samples during this period.

Carbon, Dissolved Organic (fig. 1F).–DQO’s were met by 99 

percent of the samples. A positive bias was observed for the 

QC-high sample in 1995 which reappeared in September of 

1997. The QC-low sample had a negative bias during this 

period.

Carbon, Dissolved Organic (soil expulsions) (fig. 1G).–

DQO’s were met by 100 percent of the samples. The data 

are insufficient for trend analysis.

Chloride (fig. 1H).–DQO’s were met by 100 percent of the 

samples. The QC-high graph illustrates a negative bias 

which was due to an error in preparation of QC stock 

 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

s

_

x
Control-Chart Development and Evaluation   

Table 3. Results obtained by the Troy Laboratory for U.S. Geological Survey Standard Reference Sample (SRS) Program, October 

1995 through April 1997.

[MPV, most probable value; TV, Troy Laboratory value. All values are in milligrams per liter except aluminum (μg/L), pH (pH 

units) and specific conductance (microSiemens per centimeter). Dashes indicates no results reported.] 

a Laboratory rating system: 4 is highest score; 0 is lowest

b Sample described in Long and Farrar (1994a) c Sample described in Long and Farrar (1994b)

d Sample described in Long and Farrar (1995a) e Sample described in Long and Farrar (1995b)

Analyte

MPV, TV, 

and ratinga

SRS sample number and date of sample distribution

P-25

10-95b

T-137

10-95b

P-26

4-96c T-1394-96c T-1414-96c N-494-96c P-279-96d

T-143

9-96d

N-51

9-96d

P-28

4-97e T-1494-97e

Aluminum MPV 

TV 

Rating

--

--

--

--

--

--

--

--

--

22.4

11.1

0

75.4

26.4

0

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

Ammonium MPV 

TV 

Rating

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

0.155

0.269

0

--

--

--

--

--

--

0.07

0.10

4

--

--

--

--

--

--

Calcium MPV 

TV 

Rating

1.67

1.68

4

38.1

38.2

4

0.450

0.280

0

50.3

33.9

0

19.1

13.0

0

--

--

--

2.53

1.45

0

53.7

55.0

3

--

--

--

1.64

1.64

4

42.3

42.9

4

Chloride MPV 

TV 

Rating

1.30

1.25

4

--

--

--

7.79

7.46

3

--

--

--

--

--

--

--

--

--

1.20

1.13

4

--

--

--

--

--

--

3.30

3.39

4

--

--

--

Fluoride MPV 

TV 

Rating

0.139

0.139

4

--

--

--

0.040

0.027

3

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

0.06

0.04

3

--

--

--

Magnesium MPV 

TV 

Rating

0.350

0.330

2

10.1

9.5

2

0.060

0.050

3

10.00

8.00

0

5.48

4.33

0

--

--

--

0.461

0.450

4

10.4

8.3

0

--

--

--

0.883

0.850

3

13.1

12.9

4

pH MPV 

TV 

Rating

6.52

6.49

4

--

--

--

4.70

4.78

3

--

--

--

--

--

--

--

--

--

6.92

7.03

4

--

--

--

--

--

--

6.75

6.94

4

--

--

--

Potassium MPV 

TV 

Rating

0.55

0.56

4

1.19

1.19

4

0.146

0.160

4

2.73

2.82

4

2.32

2.42

3

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

2.00

2.31

0

Silicon MPV 

TV 

Rating

--

--

--

6.96

8.01

1

--

--

--

9.31

10.24

0

8.70

9.44

1

--

--

--

--

--

--

23.4

25.4

2

--

--

--

--

--

--

--

--

--

Sodium

MPV 

TV 

Rating

1.28

1.27

4

22.0

20.6

2

4.40

4.28

4

90.9

109.3

0

33.0

35.1

1

--

--

--

1.34

1.32

4

34.0

33.0

3

--

--

--

3.25

3.20

4

42.8

37.1

0

Specific 

conductance

MPV 

TV 

Rating

20.9

20.2

4

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

Sulfate

MPV 

TV 

Rating

2.34

2.36

4

--

--

--

0.67

0.68

4

--

--

--

--

--

--

--

--

--

2.42

2.34

4

--

--

--

--

--

--

6.14

6.18

4

--

--

--
solution and has been corrected. The QC-low sample shows 

a positive bias during this time period.

Fluoride (fig. 1I).–DQO’s were met by 99 percent of the 

samples. The positive bias in 1995 and 1997 is attributed to 

the QC stock solution, which was replaced.

Magnesium (fig. 1J).–DQO’s were met by 100 percent of the 

samples. The QC-high sample had a negative bias. The QClow sample had a negative bias in 1995.

Nitrate (ion chromatography) (fig. 1K).–DQO’s were met 

by 99 percent of the samples. The QC-high sample had 

a negative bias during this period. No apparent trends or 

biases were evident among the QC-low sample.

Nitrate (colorimetric method) (fig. 1L).–DQO’s were met 

by 99 percent of the samples. The QC-high and QC-low 

samples appear to have a negative bias; this is attributed to 

incomplete conversion of nitrate to nitrite by the cadmiumreduction column. The column was operating at 90-percent 

efficiency during this period. Project chiefs were notified of 

the negative bias; data were not changed.

pH (fig. 1M).–DQO’s were met by 99 percent of the samples. 

The QC-high sample had a positive bias from March 

through August 1996. The QC-low sample had a positive 

bias during 1995.

Potassium (fig. 1N).–DQO’s were met by 100 percent of 

the samples. No apparent trends or biases were evident 

among the QC-high and QC-low samples. The potassium 

QC-low concentration was decreased from 6.40 to 5.12 

μmol/L in January 1996 and reverted to 6.40 μmol/L in 

November of 1996 to reflect typical environmental-sample 

concentrations.

Silicon (fig. 1O).–DQO’s were met by 99 percent of the 

samples. The QC samples had a positive bias from June to 

December of 1996.

Sodium (fig. 1P).–DQO’s were met by 100 percent of the 

samples. No apparent trends or biases were evident among 

the QC sample. The sodium QC-low concentration was 

changed periodically between 8.70 and 10.88 μmol/L to 

reflect typical environmental-sample concentrations. The 

QC-low sample had a negative bias during February of 1997 

and a positive bias in May of 1997. 

Specific conductance (fig. 1Q).–DQO’s were met by 100 

percent of the samples. The data are insufficient for trend 

analysis, but visual inspection appears to indicate a negative 

bias.

Sulfate (fig. 1R).–DQO’s were met by 99 percent of the 

samples. No apparent trends or biases were evident among 

the QC-low sample. The QC-high sample had a positive 

bias during this time period.

B. Filter Blanks and Analytical Blanks

Acid-Neutralizing Capacity.–Blanks were not analyzed for 

this constituent.

Aluminum, Total Monomeric (fig. 2A).–The DQO was met 

by 88 percent of the samples. Although below the DQO, 

there is evidence of some aluminum contamination in 1996.

Aluminum, Organic Monomeric (fig. 2B).–The DQO was 

met by 100 percent of the samples. Although below the 

DQO, there is evidence of some aluminum contamination in 

1996.

Aluminum, Total.–Blanks were not analyzed for this 

constituent.

Ammonium.–Blanks were not analyzed for this constituent.

Calcium (fig. 2C).–The DQO was met by 86 percent of 

the samples. No systematic trends were evident for this 

analysis.

Carbon, Dissolved Organic (fig. 2D).–The DQO was met 

by 93 percent of the samples. No systematic trends were 

evident for this analysis.

Carbon, Dissolved Organic (soil expulsions).–Blanks were 

not available for this constituent.

Chloride (fig. 2E).–The DQO was met by 67 percent of the 

samples. The source of chloride contamination is being 

investigated.

Fluoride.–Blanks were not analyzed for this constituent.

Magnesium (fig. 2F).–The DQO was met by 98 percent of 

the samples. No systematic trends were evident for this 

analysis.

Nitrate (ion chromatography) (fig. 2G).–The DQO was met 

by 97 percent of the samples. No systematic trends were 

evident for this analysis.

Nitrate (colorimetric method).–Blanks were not available for 

this constituent.

pH.—Blanks were not analyzed for this constituent.

Potassium (fig. 2H).–The DQO was met by 99 percent of 

the samples. No systematic trends were evident for this 

analysis.

Silicon (fig. 2I).–The DQO was met by 87 percent of the 

samples. No systematic trends were evident for this 

analysis.

Sodium (fig. 2J).–The DQO was met by 96 percent of 

the samples. No systematic trends were evident for this 

analysis.

 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997
Specific conductance.–Blanks were not analyzed for this 

constituent.

Sulfate (fig. 2K).–The DQO was met by 99 percent of 

the samples. No systematic trends were evident for this 

analysis.

C. Triplicate Environmental Samples

Acid-Neutralizing Capacity (figs. 3A1 and 3A2).–The DQO 

was met by 80 percent of the triplicate samples.

Aluminum, Total Monomeric (fig. 3B).–The DQO was met 

by 87 percent of the triplicate samples.

Aluminum, Organic Monomeric (fig. 3C).–The DQO was 

met by 89 percent of the triplicate samples.

Aluminum, Total (fig. 3D).–The data are insufficient to 

evaluate the DQO’s.

Ammonium.–Triplicate samples were not analyzed for this 

constituent.

Calcium (fig. 3E).–The DQO was met by 94 percent of the 

triplicate samples.

Carbon, Dissolved Organic (fig. 3F).–The DQO was met by 

93 percent of the triplicate samples.

Carbon, Dissolved Organic (soil expulsions).–Triplicate 

samples were not available for this constituent.

Chloride (fig. 3G).–The DQO was met by 89 percent of the 

triplicate samples.

Fluoride.–Triplicate samples were not analyzed for this 

constituent.

Magnesium (fig. 3H).–The DQO was met by 100 percent of 

the triplicate samples.

Nitrate (ion chromatography) (fig. 3I).–The DQO was met 

by 96 percent of the triplicate samples.

Nitrate (colorimetric method).–Triplicate samples were not 

available for this constituent.

pH (fig. 3J).–The DQO was met by 99 percent of the triplicate 

samples.

Potassium (fig. 3K).–The DQO was met by 95 percent of the 

triplicate samples.

Silicon (fig. 3L).–The DQO was met by 98 percent of the 

triplicate samples.

Sodium (fig. 3M).–The DQO was met by 98 percent of the 

triplicate samples.

Specific conductance.–Triplicate samples were not analyzed 

for this constituent.

Sulfate (fig. 3N).–The DQO was met by 100 percent of the 

triplicate samples.

D. U.S. Geological Survey’s Standard Reference 

Sample (SRS) Program

The U.S. Geological’s SRS Program rates laboratory 

performance for each analyte on a scale of 4 to 0:

Rating Performance

4.0 Excellent

3.0-3.99 Good

2.0-2.99 Satisfactory

1.0-1.99 Marginal

0.0-0.99 Unsatisfactory

Overall laboratory mean ratings for each SRS sample 

were:

P-25 3.8 T-137 2.6 N-49 0.0

P-26 3.0 T-139 0.7 N-51 4.0

P-27 3.3 T-141 0.8

P-28 3.7 T-143 2.0

 T-149 2.0

All analyses received an acceptable rating for each 

constituent with these exceptions: 

Aluminum.–Due to the malfunctioning of the graphite 

furnace, aluminum data are erroneous. An inductively 

coupled plasma (ICP) spectrophotometer has been 

purchased and improved results are expected.

Ammonium.–SRS sample N-49 was improperly diluted 

leading to erroneous data.

Calcium.–In 1996, calcium data are erroneous due to a 

method error. The calcium method used during this period 

included a lanthanum chloride reagent whose concentration 

was too low to mask interferences. Environmental-sample 

data were erroneously low. The method was corrected, and 

project samples were reanalyzed for calcium. Initial data 

were flagged as erroneous, and reanalysis data were added 

to the database.

Magnesium.–The most probable cause of erroneous 

magnesium data for high concentration SRS samples is an 

error in dilution of the sample.

Potassium.–The cause of a zero rating for SRS T-149 is 

unexplained.

Silicon.–The erroneous silicon data were due to a matrix 

interference. All SRS T samples are acidified. An acidified 

sample was not compatible with the silicon method utilized 

during this period. SRS silicon analysis was discontinued 

until the purchase of an ICP.

Control-Chart Development and Evaluation   
Sodium.–The most probable cause of erroneous sodium data 

for high concentration SRS samples is an error in dilution of 

the sample.

E. NWRI Ecosystem Interlaboratory QA Program

Environment Canada’s NWRI program does not audit the 

analysis of total monomeric aluminum, organic monomeric 

aluminum, dissolved organic carbon (soil expulsions), 

fluoride, and nitrate (colorimetric method).

The laboratory did not submit results for total aluminum 

or specific conductance analyses during this time period.

Acid-Neutralizing capacity (figs. 4A1 and 4A2).—The DQO 

was met by 100 percent of the NWRI samples. No trend or 

bias was evident.

Ammonium (fig. 4B).—The DQO was met by 92 percent 

of the NWRI samples. NWRI samples were not run for 

ammonium for studies 39 or 68. Environmental samples are 

no longer routinely analyzed for ammonium. Samples are 

selectively analyzed a few times yearly.

Calcium (fig. 4C).—The DQO was met by 58 percent of 

the NWRI samples. The calcium method used during 

this period included a lanthanum chloride reagent, 

whose concentration was too low to mask interferences. 

Environmental-sample data were erroneously low. The 

method was corrected, and project samples were reanalyzed 

for calcium. Initial data were flagged as erroneous, and 

reanalysis data were added to the database.

Carbon, dissolved organic (fig. 4D).—The DQO was met 

by 90 percent of the NWRI samples. The data exhibited a 

positive bias. A new carbon analyzer has been purchased 

and improved results are expected.

Chloride (fig. 4E).—The DQO was met by 68 percent of the 

NWRI samples. Most outliers had a positive bias.

Magnesium (fig. 4F).—The DQO was met by 95 percent of 

the NWRI samples. 

Nitrate (ion chromatography) (fig. 4G).—The DQO was met 

by 90 percent of the NWRI samples.

pH (fig. 4H).—The DQO was met by 100 percent of the 

NWRI samples. No trend or bias was evident.

Potassium (fig. 4I).—The DQO was met by 90 percent of the 

NWRI samples. No trend or bias was evident.

Silicon (fig. 4J).—The DQO was met by 73 percent of the 

NWRI samples. An ICP was recently installed for silicon 

analysis, and improved results are expected.

Sodium (fig. 4K).—The DQO was met by 90 percent of the 

NWRI samples. No trend or bias was evident.

Sulfate (fig. 4L).—The DQO was met by 100 percent of the 

samples. Data indicate a slight negative bias for studies 39, 

68, and 69. The cause is uncertain, but no bias is evident for 

study 70.

F. Blind Reference Samples

Blind reference samples are analyzed for all constituents 

for which the SRS program reports. The blind reference 

samples are not analyzed for acid-neutralizing capacity, total 

monomeric aluminum, organic monomeric aluminum, total 

aluminum, ammonium, dissolved organic carbon, fluoride, 

nitrate and silicon.

Calcium (fig. 5A).–The DQO for calcium was met by 95 

percent of the blind reference samples. The calcium 

method used during this period included a lanthanum 

chloride reagent, whose concentration was too low to 

mask interferences. The method was corrected, and project 

samples were reanalyzed for calcium. Most blind sample 

data are from the time period after the error was corrected.

Chloride (fig. 5B).–The DQO was met by 77 percent of the 

blind reference samples.

Magnesium (fig. 5C).–The DQO was met by 83 percent of the 

blind reference samples.

pH (fig. 5D).–The DQO was met by 100 percent of the blind 

reference samples. No trend or bias was evident.

Potassium (fig. 5E).–The DQO was met by 90 percent of the 

blind reference samples. No trend or bias was evident.

Sodium (fig. 5F).–The DQO was met by 100 percent of the 

blind reference samples. 

Specific conductance (fig. 5G).–There are insufficient data 

for DQO evaluation. The analysis appears to have a low bias 

which subsequent control charts may show.

Sulfate (fig. 5H).–The DQO was met by 80 percent of the 

samples. No trend or bias was evident.

Selected References

Farrar, J.W., 1997, Results of the U.S. Geological Survey’s 

analytical evaluation program for Standard Reference 

Samples: T-147 (trace constituents), T-149 (trace 

constituents), M-142 (major constituents), N-53 (nutrient 

constituents), N-54 (nutrient constituents), P-28 (low ionic 

strength constituents), GW-1 (ground water constituents), 

and Hg-24 (mercury) distributed in April 1997: U.S. 

Geological Survey Open-File Report 97-553, 184 p.

Lawrence, G.B., Lincoln, T.A., Horan-Ross, D.A., Olson, 

M.L., and Waldron, L.A., 1995, Analytical methods of the 

U.S. Geological Survey’s New York District Water Analysis 

Laboratory: U.S. Geological Survey Open-File Report 95-

416, 78 p.

10 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997
Lee, M.P., 1996, U.S. Geological Survey Water-Resources 

Programs in the New York District–fiscal years 1993-94: 

U.S. Geological Survey Open-File Report 96-113, 48 p.

Lincoln, T.A., Horan-Ross, D.A., Olson, M.L., and Lawrence, 

G.B., 1996, Quality-Assurance Data for Routine Water 

Analyses by the U.S. Geological Survey Laboratory in Troy, 

New York: May 1991 through June 1993: U.S. Geological 

Survey Open-File Report 96-167, 22 p.

Lincoln, T.A., Horan-Ross, D.A., McHale, M.R., and 

Lawrence, G.B., 2001, Quality-Assurance Data for Routine 

Water Analyses by the U.S. Geological Survey Laboratory 

in Troy, New York: July 1993 through June 1995: U.S. 

Geological Survey Open-File Report 01-171, 25 p. 

Long, H. K., and Farrar, J. W., 1996a, Report on the U.S. 

Geological Survey’s evaluation program for Standard 

Reference Samples distributed in October 1995 T-137 

(trace constituents), M-136 (major constituents), N-47 

(nutrient constituents), N-48 (nutrient constituents), P-25 

(low ionic strength constituents), and Hg-21 (mercury): U.S 

Geological Survey Open-File Report 96-138, 106 p.

_____1996b, Report on the U.S. Geological Survey’s 

evaluation program for Standard Reference Samples 

distributed in April 1996: T-139 (trace constituents), T-141 

(trace constituents), M-138 (major constituents), N-49 

(nutrient constituents) N-50 (nutrient constituents), P-26 

(low ionic strength constituents), and Hg-22 (mercury): U.S 

Geological Survey Open-File Report 96-436, 143 p.

_____1997, Report on the U.S. Geological Survey’s evaluation 

program for Standard Reference Samples distributed in 

September 1996: T-143 (trace constituents), T-145 (trace 

constituents), M-140 (major constituents), N-51 (nutrient 

constituents), N-52 (nutrient constituents), P-27 (low 

ionic strength constituents), and Hg-23 (mercury): U.S. 

Geological Survey Open-File Report 97-20, 145 p. 

Control-Chart Development and Evaluation 11
12  Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

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Control-Chart Development and Evaluation 13

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14  Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

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Figure 1. (continued) Results of quality-control data for high- and low-concentration quality-control samples from July 1995 

through June 1997.
Control-Chart Development and Evaluation 15

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#/.42/,3!-0,% 4(%/2%#4)#!,6!,5% 500%2#/.42/,,)-)4 ,/7%2#/.42/,,)-)4

Figure 1. (continued) Results of quality-control data for high- and low-concentration quality-control samples from July 1995 

through June 1997.
16  Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

SPECIFIC CONDUCTANCE, 

IN MICROSEIMENS PER CENTIMETER 

Q. SPECIFIC CONDUCTANCE 

High Concentration Sample 50

40

30

25

Low Concentration Sample 

Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May

1995 1996 1997

DATE OF ANALYSIS 

SPECIFIC CONDUCTANCE, 

IN MICROSEIMENS PER CENTIMETER 

45

35

24

22

16

12

10

18

14

SULFATE, 

IN MICROMOLES PER LITER 

R. SULFATE 

High Concentration Sample 

110

100

80

65

60

Low Concentration Sample

Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May

1995 1996 1997

DATE OF ANALYSIS

SULFATE,

IN MICROMOLES PER LITER

90

70

11.0

10.0

8.0

6.5

6.0

9.0

7.0

20

105

95

75

85

10.5

9.5

7.5

8.5

CONTROL SAMPLE THEORECTICAL VALUE UPPER CONTROL LIMIT LOWER CONTROL LIMIT 

Figure 1. (continued) Results of quality-control data for high- and low-concentration quality-control samples from July 1995 

through June 1997.
Control-Chart Development and Evaluation 17

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Figure 2. Results of quality-control data for filter blank and analytical blank samples from July 1995 through June 1997.
18  Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

3),)#/.

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Figure 2. (continued) Results of quality-control data for filter blank 

and analytical blank samples from July 1995 through June 1997.
Summary of Results 19

COEFFICIENT OF VARIATION 

A1. ACID-NEUTRALIZING CAPACITY 

(for triplicate means not in ±20 μeq/L range) 

60

40

10

0

A2. ACID-NEUTRALIZING CAPACITY

(for triplicate means in ±20 μeq/L range)

Jul Oct Jan Jul

1995 1996 1997

DATE OF COLLECTION 

DIFFERENCE FROM TRIPLICATE MEAN, 

IN MICROEQUIVALENTS PER LITER 

50

20

30

20

-10

-30

0

-20

10

30

COEFFICIENT OF VARIATION 

B. ALUMINUM, TOTAL MONOMERIC 

70

50

20

0

C. ALUMINUM, ORGANIC MONOMERIC 

COEFFICIENT OF VARIATION 

60

30

100

80

20

0

40

10

60

40

10

30

D. ALUMINUM, TOTAL 

20

5

0

E. CALCIUM 

25

10

15

F. CARBON, DISSOLVED ORGANIC 

30

25

10

0

G. CHLORIDE 

15

100

70

10

30

0

50

20

5

20

30

COEFFICIENT OF VARIATION CONTROL LIMIT 

90

50

70

Apr Oct Jan Apr

COEFFICIENT OF VARIATION COEFFICIENT OF VARIATION COEFFICIENT OF VARIATION 

20

5

0

25

10

15

30

COEFFICIENT OF VARIATION 

80

60

40

90

Jul Oct Jan Jul

1995 1996 1997

DATE OF COLLECTION 

Apr Oct Jan Apr

Figure 3. Results of quality-control data for triplicate environmental samples from July 1995 through June 1997.
20 Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

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Figure 3. (Continued) Results of quality-control data for triplicate environmental samples from July 1995 through June 1997.
Summary of Results  21

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.%542!,):).'#!0!#)49

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.72)345$)%34(2/5'( .72)345$)%34(2/5'(

0%2#%.4$)&&%2%.#% -#6 500%2#/.42/,,)-)4 ,/7%2#/.42/,,)-)4

Figure 4. Results of quality-control data for NWRI Ecosystem Interlaboratory QA Program from July 1995 through June 1997.
22  Quality-Assurance Data for Routine Water Analyses by the U.S. Geological Survey Laboratory in Troy, New York, July 

1995 through June 1997

PERCENT DIFFERENCE. pH<6.00 

(Control 10%) 

PERCENT DIFFERENCE. pHr6.00

(Control 20%) 

DIFFERENCE FROM MEAN 

CONCENTRATION VALUE (IN PERCENT) 

DIFFERENCE FROM MEAN 

CONCENTRATION VALUE (IN PERCENT) 

DIFFERENCE FROM MEAN 

CONCENTRATION VALUE (IN PERCENT) 

DIFFERENCE FROM MEAN 

CONCENTRATION VALUE (IN PERCENT) 

DIFFERENCE FROM MEAN 

CONCENTRATION VALUE (IN PERCENT) 

H. pH 

I. POTASSIUM 

J. SILICON 

K. SODIUM 

L. SULFATE 

DIFFERENCE

STUDY 39 STUDY 68 STUDY 69 STUDY 70 

70

60

40

20

10

0

-10

-20

-30

20

15

10

5

0

-5

-10

-15

-20

20

15

10

5

0

-5

-10

-15

-20

10

-10

-20

-30

-40

STUDY 39 STUDY 68 STUDY 69 STUDY 70 

STUDY 39 STUDY 68 STUDY 69 STUDY 70 

STUDY 39 STUDY 68 STUDY 69 STUDY 70 

STUDY 39 STUDY 68 STUDY 69 STUDY 70 

20

0

20

15

10

5

0

-5

-10

-15

-20

NWRI STUDIES 39 THROUGH 70 

NWRI STUDIES 39 THROUGH 70 

PERCENT DIFFERENCE MCV UPPER CONTROL LIMIT LOWER CONTROL LIMIT 

50

30

Figure 4. (Continued) Results of quality-control data for NWRI Ecosystem Interlaboratory QA Program from July 1995 through 

June 1997.
Selected References  23

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Figure 5. Results of quality-control data for blind reference samples from July 1995 through June 1997.