Application of Health-Based Screening Levels

to Ground-Water Quality Data in a State-Scale

Pilot Effort

Scientific Investigations Report 2004-5174

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the New Jersey Department of Environmental Protection

and Oregon Health & Science University

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

NATIONAL SYNTHESIS ON VOLATILE ORGANIC COMPOUNDS

Application of Health-Based Screening 

Levels to Ground-Water Quality Data

in a State-Scale Pilot Effort

By Patricia L. Toccalino, Julia E. Norman, Robyn H. Phillips, Leon J. Kauffman, 

Paul E. Stackelberg, Lisa H. Nowell, Sandra J. Krietzman, and Gloria B. Post

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the New Jersey Department of Environmental Protection and 

Oregon Health & Science University

Scientific Investigations Report 2004-5174
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

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.

Suggested citation:

Toccalino, P.L., Norman, J.E., Phillips, R.H., Kauffman, L.J., Stackelberg, P.E., Nowell, L.H., Krietzman, S.J., and Post, 

G.B., 2004, Application of health-based screening levels to ground-water quality data in a state-scale pilot effort: U.S. 

Geological Survey Scientific Investigations Report 2004-5174, 64 p.
 iii

Contents

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

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

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

Need for and History of the Human-Health Pilot Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Development and Use of Health-Based Screening Level Values . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Well Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Design of Public-Supply Well Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Design of Domestic-Well Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Design of Monitoring-Well Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Analytical Considerations for Ground-Water Quality Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Minimum Reporting Levels and Estimated Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Interpreting Detection Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Minimum Reporting Levels Compared to Human-Health Benchmarks . . . . . . . . . . . . . . . . . . . . 8

Guidance for Interpreting Water-Quality Data in a Human-Health Context . . . . . . . . . . . . . . . . . . . . . 8

Step 1: Identify Human-Health Benchmarks and Compare to Measured

Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Tier 1 – Benchmarks for Regulated Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Tier 2 – Benchmarks for Unregulated Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 2: Identify Contaminants of Potential Human-Health Concern Using

Benchmark Quotients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Step 3: Interpret the Occurrence of Contaminants of Potential HumanHealth Concern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Assessment of Ground-Water Quality in New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Step 1: Human-Health Benchmarks Identified and Compared to Measured

Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Tier 1 – Regulated Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Tier 2 – Unregulated Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Volatile Organic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Tier 1 – Regulated Volatile Organic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Tier 2 – Unregulated Volatile Organic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Step 2: Contaminants of Potential Human-Health Concern Identified . . . . . . . . . . . . . . . . . . . . 30

Step 3: Occurrence of Contaminants of Potential Human-Health Concern Interpreted . . . . 30

Magnitude of BQ Values and Detection Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

MRL Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Well Type and Use of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Occurrence by Well Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Occurrence by Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Occurrence by Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Contaminant Sources and Physicochemical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
iv 

Patterns of Occurrence of the Contaminants of Potential Human-Health Concern . . . . . . . . .38

Pattern 1: BQmax Greater than or Equal to 1 and Frequently Detected . . . . . . . . . . . . . .39

Pattern 2: BQmax Greater than or Equal to 1 and not Frequently Detected . . . . . . . . . . .39

Pattern 3: BQmax Less than 1 but Greater than or Equal to 0.1 and

Frequently Detected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Pattern 4: BQmax Less than 1 but Greater than or Equal to 0.1 and not

Frequently Detected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Health-Based Comparison of Wells with Multiple Contaminants . . . . . . . . . . . . . . . . . . . . . . . .41

Benchmark Quotient Computations for Multiple Contaminants in Individual Wells . . . .42

Occurrence of Multiple Contaminants by Well Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

Occurrence of Multiple Contaminants by Aquifer and Land Use . . . . . . . . . . . . . . . . . . . .46

Benefits of Applying Health-Based Screening Levels to Water-Quality Data . . . . . . . . . . . . . . . . . . .46

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

1. U.S. Environmental Protection Agency and New Jersey MCL values (current as

of August 2004) for regulated pesticides and VOCs analyzed in groundwater samples from the Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . .58

2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs

analyzed for in ground-water samples from the Long Island-New Jersey

Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

3. Unregulated pesticides and VOCs analyzed in ground-water samples

from the Long Island-New Jersey Study Unit that have no humanhealth benchmarks (as of August 2004). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Figures

1. Map showing ground-water sampling regions in the Long Island-New Jersey

Coastal Drainages Study Unit and the Glassboro study area. . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Map showing location of (a) public-supply and monitoring wells in the Glassboro

study area of the Kirkwood-Cohansey aquifer system, New Jersey, and (b) domestic

wells, by aquifer (sampling region), in the Long Island-New Jersey Coastal

Drainages Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3-13. Graphs showing:

3. Number of detected, unregulated pesticides and VOCs with human-health

benchmarks before and after HBSL calculations in all well types in the

Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4. Distributions of concentrations and detection frequencies of pesticides

detected at concentrations that met or exceeded human-health

benchmarks in at least one well type in the Long Island-New

Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5. Distributions of concentrations and detection frequencies of VOCs

detected at concentrations that met or exceeded human-health

benchmarks in at least one well type in the Long Island-New

Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
 v

6. Distributions of Benchmark Quotient values and detection frequencies,

by well type, for pesticides detected at concentrations within a factor

of 10 of their human-health benchmarks in the Long Island-New

Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

7. Distributions of Benchmark Quotient values and detection frequencies,

by well type, for VOCs detected at concentrations within a factor of 10

of their human-health benchmarks in the Long Island-New Jersey

Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

8. Detection frequencies and Maximum Benchmark Quotient values for

(a) pesticides and (b) VOCs detected in public-supply wells, domestic

wells, and monitoring wells in the Long Island-New Jersey Study Unit . . . . . . . . . . . .36

9. Relation between Maximum Benchmark Quotient values for

(a) pesticides and (b) VOCs detected in public-supply wells and

those in domestic wells in the Kirkwood-Cohansey aquifer

system, New Jersey. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

10. Cumulative distributions and ratios of maximum and summed Benchmark

Quotient values for individual wells for (a) pesticides, (b) VOCs, and

(c) pesticides and VOCs with human-health benchmarks detected

in public-supply, domestic, and monitoring wells in the Long IslandNew Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

11. Cumulative distributions of Benchmark Quotient values for (a) pesticides,

(b) VOCs, and (c) pesticides and VOCs with human-health benchmarks

detected in individual domestic wells in the Kirkwood-Cohansey aquifer

system, and aquifers in the New England and Piedmont Physiographic

Provinces in the Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . .47

12. Cumulative distributions of Benchmark Quotient values for (a) pesticides,

(b) VOCs, and (c) pesticides and VOCs with human-health benchmarks

detected in individual shallow monitoring wells representing agriculture, 

old urban, new urban, and undeveloped land uses in the KirkwoodCohansey aquifer system in the Long Island-New Jersey Study Unit. . . . . . . . . . . . . .48

13. Detection frequencies and Maximum Benchmark Quotient values

for unregulated pesticides and VOCs with new HBSL values detected

in (a) public-supply wells, (b) domestic wells, and (c) monitoring wells

in the Long Island-New Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

Tables

1. Pesticides and VOCs that have Minimum Reporting Levels that exceed

human-health benchmarks in ground-water samples from the Long 

Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

2. Descriptions of human-health benchmarks related to drinking water

used in this report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

3. Numbers of (1) pesticides and VOCs analyzed and detected in ground-water

samples and (2) detected unregulated compounds with human-health

benchmarks in ground-water samples from the Long Island-New

Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

4. Concentrations, detection frequencies, and MCL values for regulated

pesticides detected in public-supply wells, domestic wells, and

monitoring wells in the Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . .16
vi 

5. Concentrations, detection frequencies, and HBSL values for unregulated

pesticides detected in public-supply wells, domestic wells, and monitoring

wells in the Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6. Concentrations, detection frequencies, and MCL values for regulated VOCs

detected in public-supply wells, domestic wells, and monitoring wells in

the Long Island-New Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7. Concentrations, detection frequencies, and HBSL values for unregulated

VOCs detected in public-supply wells, domestic wells, and monitoring

wells in the Long Island-New Jersey Study Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8. Detection frequencies and BQmax and BQmed-det values for pesticides and

VOCs detected at concentrations within a factor of 10 of human-health

benchmarks in samples from public-supply wells, domestic wells, and (or)

monitoring wells in the Long Island-New Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9. Frequency of detection and frequency of exceedance of human-health

benchmarks for pesticides and VOCs detected at concentrations that

met or exceeded human-health benchmarks in samples by well type,

sampling region, and land use in the Long Island-New Jersey Study Unit . . . . . . . . . . . . . . 35

10. Numbers of (1) individual wells with contaminant detections and (2) compounds

detected with human-health benchmarks in individual wells in the Long IslandNew Jersey Study Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

11. Hypothetical BQSiteMax and BQSiteSum example calculations for three

compounds in three wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Conversion Factors, Abbreviations, and Acronyms

Multiply By To obtain

foot (ft) 0.3048 meter

gallon per day (gal/d) 0.003785 cubic meter per day

square mile (mi2) 2.590 square kilometer

kilogram (kg) 2.205 pound avoirdupois

liter (L) 0.2642 gallon

micrograms per liter (μg/L) 1.0 parts per billion

< less than

> greater than or equal to

μg/L micrograms per liter

BQ Benchmark Quotient

BQmax Ratio of maximum detected concentration to drinking-water benchmark

BQmed-det Ratio of median of detected concentrations to drinking-water benchmark

BQmed-all Ratio of median of all samples (including non-detections) to drinking-water

benchmark

BQSiteMax Maximum of BQ values for detected compounds in a given well

BQSiteSum Sum of all BQ values for detected compounds in a given well

CASRN Chemical Abstracts Service Registry Number

E Estimated Concentration
 vii

GWQC Ground Water Quality Criteria (New Jersey Department of Environmental 

Protection)

GWQS Ground Water Quality Standards (New Jersey Department of Environmental 

Protection)

HBSL Health-Based Screening Level

HEAST Health Effects Assessment Summary Tables

HI Hazard Index

HQ Hazard Quotient

IRIS Integrated Risk Information System (U.S. Environmental Protection Agency)

Lifetime HA Lifetime Health Advisory

LINJ Long Island – New Jersey

LRL Laboratory Reporting Level

LT-MDL Long-Term Method Detection Level

MCL Maximum Contaminant Level

MRL Minimum Reporting Level

MTBE Methyl tert-butyl ether

NAWQA National Water-Quality Assessment Program

NJDEP New Jersey Department of Environmental Protection

NWQL National Water Quality Laboratory

OHSU Oregon Health & Science University

OPP Office of Pesticide Programs (U.S. Environmental Protection Agency)

ORD Office of Research and Development (U.S. Environmental Protection 

Agency)

OW Office of Water (U.S. Environmental Protection Agency)

PCE Tetrachloroethylene

PQL Practical Quantitation Level

q1* Cancer Potency Factor (see also SF)

RfD Reference Dose

RSD Risk-Specific Dose

SF Slope Factor

SOC Synthetic Organic Chemical

TCE Trichloroethylene

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC Volatile Organic Compound

Application of Health-Based Screening Levels to GroundWater Quality Data in a State-Scale Pilot Effort

By Patricia L. Toccalino1, Julia E. Norman1, Robyn H. Phillips1, Leon J. Kauffman2, Paul E. Stackelberg2,

Lisa H. Nowell3, Sandra J. Krietzman4, and Gloria B. Post4

Abstract

A state-scale pilot effort was conducted to evaluate a 

Health-Based Screening Level (HBSL) approach developed for 

communicating findings from the U.S. Geological Survey 

(USGS) National Water-Quality Assessment Program in a 

human-health context. Many aquifers sampled by USGS are 

used as drinking-water sources, and water-quality conditions 

historically have been assessed by comparing measured contaminant concentrations to established drinking-water standards 

and guidelines. Because drinking-water standards and guidelines do not exist for many analyzed contaminants, HBSL 

values were developed collaboratively by the USGS, U.S. 

Environmental Protection Agency (USEPA), New Jersey 

Department of Environmental Protection, and Oregon Health & 

Science University, using USEPA toxicity values and USEPA 

Office of Water methodologies. The main objective of this 

report is to demonstrate the use of HBSL approach as a tool for 

communicating water-quality data in a human-health context by 

conducting a retrospective analysis of ground-water quality data 

from New Jersey. Another important objective is to provide 

guidance on the use and interpretation of HBSL values and 

other human-health benchmarks in the analyses of water-quality 

data in a human-health context.

Ground-water samples collected during 1996-98 from 30 

public-supply, 82 domestic, and 108 monitoring wells were 

analyzed for 97 pesticides and 85 volatile organic compounds 

(VOCs). The occurrence of individual pesticides and VOCs was 

evaluated in a human-health context by calculating Benchmark 

Quotients (BQs), defined as ratios of measured concentrations 

of regulated compounds (that is, compounds with Federal or 

state drinking-water standards) to Maximum Contaminant Level 

(MCL) values and ratios of measured concentrations of unregulated compounds to HBSL values. Contaminants were identified 

as being of potential human-health concern if maximum 

detected concentrations were within a factor of 10 of the associated MCL or HBSL (that is, maximum BQ value (BQmax) 

greater than or equal to 0.1) in any well type (public supply, 

domestic, monitoring). Most (57 of 77) pesticides and VOCs 

with human-health benchmarks were detected at concentrations 

well below these levels (BQmax less than 0.1) for all three well 

types; however, BQmax values ranged from 0.1 to 3,000 for 6 

pesticides and 14 VOCs. Of these 20 contaminants, one pesticide (dieldrin) and three VOCs (1,2-dibromoethane, tetrachloroethylene, and trichloroethylene) both (1) were measured at 

concentrations that met or exceeded MCL or HBSL values, and 

(2) were detected in more than 10 percent of samples collected 

from raw ground water used as sources of drinking water 

(public-supply and (or) domestic wells) and, therefore, are 

particularly relevant to human health. 

The occurrence of multiple pesticides and VOCs in individual wells also was evaluated in a human-health context because 

at least 53 different contaminants were detected in each of the 

three well types. To assess the relative human-health importance 

of the occurrence of multiple contaminants in different wells, the 

BQ values for all contaminants in a given well were summed. 

The median ratio of the maximum BQ to the sum of all BQ 

values for each well ranged from 0.83 to 0.93 for all well types, 

indicating that the maximum BQ makes up the majority of the 

sum for most wells. Maximum and summed BQ values were 

statistically greater for individual public-supply wells than for 

individual domestic and monitoring wells. 

The HBSL approach is an effective tool for placing waterquality data in a human-health context. For 79 of the 182 compounds analyzed in this study, no USEPA drinking-water standards or guidelines exist, but new HBSL values were calculated 

for 39 of these 79 compounds. The new HBSL values increased 

the number of detected pesticides and VOCs with human-health 

benchmarks from 65 to 77 (of 97 detected compounds), thereby 

expanding the basis for interpreting contaminant-occurrence 

data in a human-health context.

1Oregon Health & Science University, Department of Environmental & 

Biomolecular Systems, Beaverton, Oregon.

2

U.S. Geological Survey, Long Island – New Jersey Coastal Drainages 

NAWQA Study, West Trenton, New Jersey.

3U.S. Geological Survey, Pesticides National Synthesis Project, Sacramento, 

California.

4

New Jersey Department of Environmental Protection, Trenton, New Jersey.
2 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Introduction

An interagency pilot effort was conducted to test an 

approach for communicating water-quality findings in a 

human-health context in state- and local-scale reports. There 

were two stages to this pilot effort. In the first stage, consensus 

was reached on the development of Health-Based Screening 

Level (HBSL)1 values for unregulated contaminants, that is, 

those for which drinking-water standards have not been 

established. The U.S. Geological Survey (USGS) conducted a 

study, in cooperation with the U.S. Environmental Protection 

Agency (USEPA), the New Jersey Department of Environmental Protection (NJDEP), and Oregon Health & Science University (OHSU), to collaboratively develop the HBSL approach for 

application to state- and local-scale water-quality assessments. 

The systematic procedures used to develop HBSL values are 

described in Toccalino and others (2003). The second stage of 

the pilot effort, the subject of this report, consists of the application of HBSL values as tools for describing water-quality data 

in a human-health context in a state-scale water-quality assessment.

The ground-water data described in this report were collected for the Long Island-New Jersey (LINJ) Coastal Drainages Study Unit (Ayers and others, 2000) as part of the USGS 

National Water-Quality Assessment (NAWQA) Program. 

Work in the LINJ Study Unit, which includes some of the most 

heavily urbanized and populated areas in the United States, 

began in 1994 (Ayers and others, 2000). The HBSL approach 

was applied to ground-water quality data collected from 220 

wells in the LINJ Study Unit during 1996-98. These groundwater quality data have been presented previously in numerous 

publications (Ayers and others, 2000; Clawges and others, 

1999; Kauffman and others, 2001; Stackelberg and others, 

1997, 2000, and 2001), but the potential human-health implications of these water-quality data have not been interpreted 

previously using HBSL values. 

Purpose and Scope

The objective of this report is two-fold. A major objective 

is to demonstrate the HBSL approach as a tool for communicating water-quality data in a human-health context by performing 

a retrospective analysis of ground-water quality data collected 

as part of the USGS NAWQA Program in New Jersey. One 

ground-water sample was collected from each public-supply, 

domestic, and monitoring well in the study unit during 1996-98. 

Samples were analyzed for a total of 97 pesticides and 85 volatile organic compounds (VOCs), and measured concentrations 

were compared to USEPA and New Jersey Maximum Contaminant Level (MCL) values or HBSL values. The use of HBSL 

values allows for an extended interpretation of the potential 

human-health implications of water-quality data because HBSL 

values exist for some compounds that previously had no 

human-health benchmarks. Another important objective of 

this report is to provide guidance on the use and interpretation 

of HBSL values and other human-health benchmarks in the 

analyses of water-quality data in a human-health context by 

considering factors such as the magnitude of detected concentrations relative to human-health benchmarks, detection 

frequency, well type, and use of water.

The scope of this pilot effort is confined to the consideration of ground-water data because ground water is the principal drinking-water source in the study unit area (Stackelberg 

and others, 1997). This pilot effort primarily examines the 

occurrence of individual (single) chemicals detected in groundwater samples in a human-health context, although initial 

efforts also are undertaken to evaluate the relative occurrence of 

multiple contaminants in individual wells in a human-health 

context because numerous contaminants were detected in each 

well type. Additionally, this pilot effort does not attempt to provide estimates of the numbers of people potentially exposed to 

the ground-water resources in the study unit, which is beyond 

the scope of this report, although factors that affect potential 

exposure, such as well type and the physicochemical properties 

of contaminants, are discussed. 

Need for and History of the Human-Health

Pilot Effort 

In 1991, the USGS began the NAWQA Program to (1) 

provide a consistent description of current water-quality conditions for a large part of the Nation’s water resources; (2) define 

any long-term trends in water quality; and (3) identify, describe, 

and explain, to the extent possible, the major natural and human 

factors that affect observed water-quality conditions and trends 

(Leahy, 1990). The USGS has been asked with increasing frequency about the public-health implications of the NAWQA 

findings. The NAWQA Program originally was designed to 

characterize the Nation’s water resources and was not designed 

to answer questions about the potential safety of these water 

resources for drinking-water use. Nonetheless, if interpreted 

carefully, NAWQA data on ground-water quality can provide 

valuable information to state agencies, the USEPA, and others 

interested in drinking-water quality.

To date, NAWQA has assessed water-quality conditions 

using two approaches. The first approach ranks water-quality 

conditions at individual surface-water sites and among networks of ground-water wells within a study unit in relation to 

conditions at surface-water sites and ground-water networks, 

respectively, in other study units. The second approach compares measured contaminant concentrations against established 

drinking-water standards and guidelines for the protection of 

human health (Gilliom and others, 1998). The first approach 

provides no information on whether the contaminant-concentration levels detected are of potential concern to human health, 

and the second approach is limited by the fact that drinkingwater standards and guidelines do not exist for many of the 1

Words in bold are defined in the glossary at the end of the report.
Introduction 3

contaminants analyzed in NAWQA studies. Therefore, the 

USGS has undertaken this HBSL initiative to more comprehensively evaluate its water-quality findings in a human-health 

context. 

Over a 3-year period beginning in October 1998, a consensus HBSL approach was developed collaboratively by the 

USGS, USEPA, NJDEP, and OHSU. During this time, multiple 

procedures for assessing water-quality data in a human-health 

context were considered for this pilot effort, including procedures used by different programs and offices within USEPA 

(including Office of Water (OW), Office of Pesticide Programs 

(OPP), Office of Research and Development (ORD), and Office 

of Solid Waste and Emergency Response). The consensus decision was to use USEPA OW methodologies in developing the 

HBSL approach because this pilot effort addresses groundwater resources that are, or contribute to, drinking-water 

resources. The decision also was made to begin by applying the 

HBSL approach to a state-scale pilot effort. The LINJ Study 

Unit was selected as an appropriate pilot study for state-scale 

analyses because water-quality data were available from multiple well types and hydrogeologic settings. A complete history 

of this pilot effort, as well as the HBSL approach and methods, 

is described in Toccalino and others (2003). The HBSL 

approach is summarized in the following section. 

Development and Use of Health-Based 

Screening Level Values

Health-Based Screening Level values are defined as estimates of benchmark concentrations (for noncarcinogens) or 

concentration ranges (for carcinogens) of contaminants in water 

that (1) may be of potential human-health concern; (2) can be 

used as threshold values against which measured concentrations 

of contaminants in ambient water samples can be compared; 

and (3) are consistent with USEPA OW methodologies for 

setting drinking-water Lifetime Health Advisory (Lifetime 

HA) and Risk-Specific Dose (RSD) values (Toccalino and 

others, 2003; U.S. Environmental Protection Agency, 1988, 

1993). HBSL values are not drinking-water standards, nor are 

they USEPA or NJDEP guideline values. HBSL values are useful thresholds, however, for determining when measured concentrations meet or exceed concentrations relevant to human 

health. HBSL values are developed by using USEPA OW 

methodologies and USEPA toxicity values, so they are as comparable as possible to USEPA drinking-water guideline

values (that is, Lifetime HA and RSD values). As used in this 

report, new HBSL values refer to HBSL values calculated for 

unregulated contaminants that (1) have no existing USEPA 

drinking-water guideline values or (2) have more recent 

USEPA toxicity data than that used to calculate existing 

USEPA drinking-water guideline values, resulting in different 

benchmark values.

The USGS, USEPA, NJDEP, and OHSU participants in 

this pilot effort came to a consensus agreement to pursue the 

following two-tiered, screening-level-based methodology for 

placing NAWQA water-quality data in a human-health context 

for state- and local-scale analyses and reports (Toccalino and 

others, 2003):

• Tier 1: For regulated compounds (compounds for 

which Federal and (or) state drinking-water standards 

have been established), compare measured contaminant-concentration data with USEPA MCL values and 

applicable state drinking-water standards.

• Tier 2: For unregulated compounds (compounds for 

which Federal and (or) state drinking-water standards 

have not been established), compare measured contaminant-concentration data with HBSL values developed 

using USEPA OW methodologies (U.S. Environmental 

Protection Agency, 1988 and 1993) and USEPA toxicity data.

This two-tiered approach for state- and local-scale analyses entails listing regulated compounds separately from unregulated compounds. For regulated compounds, measured concentration data will continue to be compared with Federal and 

(or) state drinking-water standard values as has been done historically. Standard values are threshold values that are legally 

enforceable by Federal or state government agencies. For 

purposes of comparison with contaminant concentrations 

measured by the USGS in raw water, these standards will not be 

used as regulatory values; rather, these standards will be used as 

benchmarks that provide some information about the potential 

health effects if the sampled water resources were to be consumed over a lifetime by the average adult. HBSL values will 

be used only for compounds for which no drinking-water standards have been established by USEPA or NJDEP (that is, 

unregulated compounds). Other states may have a different 

number of compounds with drinking-water standards than New 

Jersey; therefore, the number of compounds for which it is 

appropriate to apply HBSL values will vary from state to state.

HBSL values were developed for unregulated compounds 

by using USEPA OW methodologies to calculate Lifetime HA 

and RSD values (U.S. Environmental Protection Agency, 1988 

and 1993) and toxicity values published by the USEPA Integrated Risk Information System (IRIS), OW, OPP, and in the 

Health Effects Assessment Summary Tables (HEAST). A 

detailed description of the methodologies used to develop 

HBSL values is presented in Toccalino and others (2003).

When MCL values (Tier 1) or HBSL values (Tier 2) are 

used as benchmarks for communicating water-quality data in a 

human-health context, there are important caveats to consider. 

Exceedance of MCL or HBSL values does not necessarily mean 

that people who potentially consume the water are adversely 

affected because (1) the USEPA OW models used to develop 

these benchmark values are intentionally conservative (protective) and include safety factors; (2) the models assume lifetime 

exposure to these concentrations, whereas the concentrations 

of contaminants may change seasonally or over time; and 

(3) the raw water resources from some well types typically 

sampled may be treated prior to consumption, and contaminant 

concentrations may be reduced substantially by treatment 

methods (Toccalino and others, 2003). Not all well types 
4 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

receive treatment, however, and the treatment methods may not 

be designed to remove specific contaminants from the water 

resources.

Description of Study Area

The LINJ Coastal Drainages Study Unit includes all of 

New Jersey, except for those areas that drain to the Delaware 

and Hudson River Basins, and all of Long Island (fig. 1) (Ayers 

and others, 2000). The ground-water data described in this 

report were collected in New Jersey, with the exception of data 

from three samples that were collected in New York State. The 

extent of the sampled area also includes the Glassboro study 

area, a 380-square-mile section of southern New Jersey. Part of 

the Glassboro study area falls outside of the LINJ Study Unit 

boundary (fig. 1). 

The study area includes three ground-water sampling 

regions in New Jersey (fig. 1). The Kirkwood-Cohansey aquifer 

system in southern New Jersey consists of unconsolidated sedimentary deposits (sands and gravels) (Ayers and others, 2000), 

whereas aquifers in the New England and Piedmont Physiographic Provinces in northern New Jersey consist of fractured 

bedrock (Clawges and others, 1999). The chemical quality of 

ground water in these three aquifers is of concern because they 

are important sources of drinking water (Ayers and others, 

2000). All three aquifers are vulnerable to contamination introduced at or near the land surface. The vulnerability of the 

Kirkwood-Cohansey aquifer system results from the highly 

permeable unconsolidated sands and gravels composing the 

aquifer system (Stackelberg and others, 1997) and the shallow 

depth to ground water; the average depth to ground water in the 

Glassboro study area is about 15 feet below ground surface 

(Stackelberg and others, 2000). The vulnerability of the bedrock aquifers in the New England and Piedmont Physiographic 

Provinces varies depending on soil and rock type and the degree 

of fracturing of the rock (Clawges and others, 1999); fractures 

can serve as conduits to deeper parts of the aquifers. The New 

England Physiographic Province is equivalent to the Highlands, 

which is the physiographic term used by NJDEP.

The chemical quality of ground water in the Glassboro 

area, which is part of the Kirkwood-Cohansey aquifer system, 

is of particular concern because this is a fast-growing region of 

New Jersey and because ground water provides most of the 

public and domestic supply in the area (Stackelberg and others, 

1997). As a result of NJDEP-mandated restrictions on withdrawals from deeper confined aquifers (New Jersey Department 

of Environmental Protection, 1996), the surficial KirkwoodCohansey aquifer system has experienced increased withdrawals to meet growing water-supply demands in the area (Stackelberg and others, 1997). About half of the water withdrawn from 

the Kirkwood-Cohansey aquifer system in the Glassboro area is 

for public- and domestic-water supplies. The remaining half is 

withdrawn for industrial and irrigation purposes (Kauffman and 

others, 2001). 

Well Networks

Raw (that is, untreated) ground-water samples were collected from three different well types: public-supply wells (30 

samples), domestic wells (82 samples), and monitoring wells 

(108 samples). Water-quality data from each of these well types 

contributes different information towards the objective of communicating contaminant-occurrence data in a human-health 

context. Except for domestic-well samples, which were collected from three major sampling regions throughout the LINJ 

Study Unit (fig. 1), the remaining ground-water samples discussed in this report were collected from the Glassboro study 

area.

Design of Public-Supply Well Network

Thirty public-supply wells (fig. 2a) in the Glassboro study 

area were sampled once either in 1997 or 1998 to determine the 

chemical quality of ground water in the part of the KirkwoodCohansey aquifer system used for public supply. Data from 

these wells also were used in conjunction with data from the 

land-use monitoring wells and a ground-water model to better 

understand how contaminants enter and move through the 

aquifer to water-supply wells and streams (Kauffman and 

others, 2001). Public-supply wells usually are in urban areas.

The public-supply wells are screened over intervals ranging from 15 to 47 feet, and have well depths ranging from 71 to 

180 feet below ground surface. The average pumping rate during 1992-96 was about 270,000 gallons per day (unpublished 

data on file at USGS New Jersey District office, West Trenton, 

N.J.). Because public-supply wells withdraw large volumes of 

water, they have correspondingly large contributing areas that 

generally encompass multiple land uses (Stackelberg and 

others, 2001).

If water from a public-water system exceeds USEPA or 

New Jersey MCL values, the supplier of that water is required 

to eliminate the problem by changing to or adding another water 

source or by improving water treatment within 1 year (New 

Jersey Department of Environmental Protection, 2000). The 

ground-water samples in this study were collected prior to any 

treatment and do not represent finished drinking-water samples. 

As a result, any measured contaminant concentration in the raw 

water resources that exceeds Federal or state MCL values does 

not indicate a violation of drinking-water standards, and no 

corrective action is required (although the NJDEP generally is 

notified in these cases).

Design of Domestic-Well Networks

Ground-water samples were collected from 82 domestic 

(household) wells in New Jersey to characterize water quality 

that is representative of three sampling regions (fig. 2b). 

Ground-water samples were collected from domestic-well 

networks located in an unconsolidated sediment aquifer 
Well Networks 5

(30 domestic wells in the Kirkwood-Cohansey aquifer system) 

and in fractured bedrock aquifers (30 domestic wells in the New 

England Physiographic Province and 22 domestic wells in the 

Piedmont Physiographic Province). Each of the 82 domestic 

wells was sampled once. Wells in the New England and Piedmont Physiographic Provinces were sampled in 1997, and wells 

in the Kirkwood-Cohansey aquifer system were sampled in 

1998 (Ayers and others, 2000).

Domestic wells are private sources of water supply primarily found in rural or agricultural settings rather than dense 

urban areas. Domestic wells tapping the unconsolidated sediments of the Kirkwood-Cohansey aquifer system are screened 

over 5- to 10-foot-long intervals to depths ranging from 38 to 

175 feet below ground surface. In contrast, domestic wells in 

the fractured bedrock aquifers have open intervals over much of 

their length. In the New England Physiographic Province, the 

domestic wells are open over intervals ranging from 6 to 

263 feet, and to depths ranging from 150 to 300 feet below 

ground surface. In the Piedmont Physiographic Province, 

domestic wells are open over intervals ranging from 90 to 

200 feet, and to depths of 125 to 250 feet below ground surface. 

Domestic wells pump an average of 82 gallons of water per day 

per person, equivalent to approximately 320 gallons per day for 

a four-person household (Nawyn, 1998). 

Figure 1. Ground-water sampling regions in the Long Island-New Jersey Coastal Drainages Study Unit and the Glassboro 

study area (modified from Ayers, 1994).

74o

74o

75o

75o

41o 41o

73o

73o

40o 40o

39o 39o

41o 41o

Valley

and 

Ridge

Coastal Plain

Fall Line

New York City

Philadelphia

Atlantic City

EXPLANATION

Ground-water sampling regions

Glassboro study area

Kirkwood-Cohansey aquifer system

Piedmont Physiographic Province

New England Physiographic Province

Long Island-New Jersey Study Unit boundary

Physiographic Province boundary

New York

Long Island

New Jersey New Jersey New Jersey

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 1:200,000, 1985

Universal Transverse Mercator projection, Zone 18

North American Datum of 1983 
6 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Figure 2. Location of (a) public-supply and monitoring wells in the Glassboro study area of the Kirkwood-Cohansey aquifer

system, New Jersey, and (b) domestic wells, by aquifer (sampling region), in the Long Island-New Jersey Coastal Drainages 

Study Unit (from Ayers and others, 2000).

0 5 MILES

0 5 KILOMETERS

39o30' 39o30'

39o45' 39o45'

75o

75o

75o15'

75o15'

a

74o

74o

75o

75o

41o 41o

40o 40o

39o 39o

0 20 MILES

0 20 KILOMETERS

Glassboro study area

New England bedrock

Piedmont bedrock 

Kirkwood-Cohansey 

Study wells, by aquifer

EXPLANATION

b

Study wells in Glassboro area

Undeveloped

Agricultural

New urban 

Old urban

Public supply

EXPLANATION

Base from U.S. Geological Survey digital data, 1:200,000, 1985

Universal Transverse Mercator projection, Zone 18

North American Datum of 1983 

New York

New Jersey

Design of Monitoring-Well Networks

Ground-water samples were collected from a network of 

108 monitoring wells in the rapidly urbanizing Glassboro study 

area (fig. 2a), including 78 shallow monitoring wells (about 

10 feet below the water table) and 30 moderate-depth monitoring wells (about 40-50 feet below the water table). Monitoringwell data provide a great deal of information about contaminant 

sources, the environmental fate and transport of contaminants, 

and trends in contaminant concentrations over time. Ground 

water collected from monitoring wells also can be a source to, 

and a predictor of, contaminant concentrations in parts of the 

aquifer used for domestic and public supply at some later period 

of time (Stackelberg and others, 1997).

The 78 shallow monitoring wells were used to measure the 

effects of land use on shallow ground-water quality and to 

assess the chemical quality of recently recharged (shallow) 

ground water in the surficial Kirkwood-Cohansey aquifer 

system (fig. 2a) of southern New Jersey. Four land-use settings 

were investigated: agricultural areas (15 wells), areas of residential and commercial development less than 25 years old (30 

new urban wells), areas of residential and commercial development more than 25 years old (20 old urban wells), and undeveloped areas (13 wells) (Ayers and others, 2000; Stackelberg and 

others, 1997). The undeveloped land uses primarily are forested 

areas and wetlands, but may contain small amounts of urban or 

agricultural land. Each of the 78 shallow monitoring wells was 

sampled once during September-December 1996. 

Additionally, 30 ground-water samples were collected 

from a network of 30 moderate-depth monitoring wells in the 

Glassboro study area that are co-located with 30 shallow monitoring wells in urban land-use areas. Each of the moderatedepth monitoring wells was sampled once during fall 1997. 

Samples from these wells were collected in order to evaluate the 

quality of ground water recharged in urban areas 10 to 20 years 

ago (Stackelberg and others, 2000). The chemical quality of 

10- to 20-year-old water is of concern because ground-water 

modeling results indicate that water withdrawn from the 

Kirkwood-Cohansey aquifer system for domestic and public 

supply is composed partly of water from this age interval. Additionally, the quality of this water resource is an indicator of the 

fate of contaminants known to be contributing to the contaminant load at the water table in areas of urban development 

(Stackelberg and others, 2000).

The shallow monitoring wells typically were screened 

over 2-foot-long intervals approximately 10 feet below the 

water table (Stackelberg and others, 1997). Shallow monitoring 

wells were sampled at depths near the water table (Ayers and 
Analytical Considerations for Ground-Water Quality Data 7

others, 2000) and, therefore, capture water flowing in paths 

that originate in relatively small areas at the land surface 

(Stackelberg and others, 2000). In contrast, the moderate-depth 

monitoring wells typically were screened over 2- to 2.5-footlong intervals (Stackelberg and others, 2000), approximately 40 

to 50 feet below the water table (Ayers and others, 2000). Wellscreen depths were selected by using ground-water flow modeling tools developed by the USGS (Stackelberg and others, 

2000). All monitoring wells were pumped only during sampling 

and at very low rates (generally less than 1 gallon per minute) 

for short periods of time (generally less than 1 hour).

Analytical Considerations for

Ground-Water Quality Data

Several analytical considerations need to be accounted for 

when interpreting water-quality data in a human-health context. 

These considerations include reporting Minimum Reporting 

Level (MRL) values for detected contaminants, identifying estimated concentrations of confirmed detections, explaining how 

detection frequencies were calculated, and comparing MRL 

values to human-health benchmarks. These considerations are 

described further below.

Minimum Reporting Levels and Estimated 

Concentrations

Sampling and analytical methods used in this study 

allowed for the quantification of pesticide concentrations with 

MRL values ranging from 0.001 to 1.2 micrograms per liter 

(μg/L) and VOC concentrations with MRL values ranging from 

0.026 to 9 μg/L in ground-water samples. The MRL is defined 

as the smallest measured concentration of a compound that may 

be reliably reported by using a given analytical method (Timme, 

1995). MRL values can change over time and can vary for different analytes within the same analytical method. Protocols 

and procedures used for sample collection are described in 

Koterba and others (1995). Analytical methods for pesticides 

and VOCs are described in Zaugg and others (1995), Werner 

and others (1996), and Connor and others (1998). The USGS 

National Water Quality Laboratory (NWQL) has implemented 

a procedure for establishing a default “less than” reporting 

level, called the laboratory reporting level (LRL), which is calculated from the long-term method detection limit (LT-MDL) 

(Oblinger Childress and others, 1999). In this report, MRL 

values are used because LRL and LT-MDL values did not come 

into use by the NWQL until 1999 (that is, after the data used in 

this report were generated).

The NWQL reports non-detections as less than (<) the 

MRL values and assigns E codes to estimated concentrations of 

confirmed detections of pesticides and VOCs that are less than 

the MRL (Oblinger Childress and others, 1999). A variety of 

conditions can justify evoking the E code, including results that 

were extrapolated beyond the calibration range used in the analytical method and matrix interferences in the sample (Kolpin, 

2001; Oblinger Childress and others, 1999). All E-coded data 

are believed to be reliable detections but with greater than 

average uncertainty in quantification (U.S. Geological Survey, 

1999). For most data analysis applications, E codes can be 

ignored because the qualitative difference in reliability is not 

substantial. If attention is placed on individual measured concentration values, then E-coded values are considered to be 

estimates only. All estimated concentrations are included in the 

calculation of detection frequencies and are presented in the 

figures and tables in this report. 

Interpreting Detection Frequencies

Each of the 220 wells considered in this study were sampled once. The detection frequencies (that is, the percentage of 

samples with detections) in this report are given for all detections to provide a measure of how often a compound was 

detected in samples from a given well type. Detection frequencies tend to vary with the sensitivity of the analytical method 

used; if the MRL is lowered for a given compound, the detection frequency for that compound will tend to increase because 

lower concentrations of that compound can be detected. Therefore, the detection frequencies reported here are not directly 

comparable among compounds because the MRL varies 

between compounds (Kolpin, 2001), and sometimes for the 

same chemical over time as a result of changes in the analytical 

method or sample matrix effects. To aid in comparisons 

between compounds, the most common MRLs for each 

detected pesticide and VOC are included in this report. 

A method commonly used by NAWQA to compare detection frequencies among compounds is to censor data to a common reporting level. The use of a common reporting level (or 

detection threshold) facilitates comparisons among compounds 

by bringing most of the data to a common reference point. 

Adjustments of this type are used to address questions such as 

“Is compound x detected more frequently than compound y?” 

(Kolpin, 2001). The data presented in this report are not censored to a common reporting level, however, because the 

primary focus of this report is to communicate water-quality 

results in a human-health context. Human-health benchmark 

concentrations such as HBSL and Ground Water Quality 

Criteria (GWQC) values are developed using toxicity data without consideration of analytical detection limits. Therefore, some 

HBSL values may be close to, or occasionally less than, MRL 

values, and censoring data to a common (typically higher) 

reporting level could lead to a loss of data that are relevant to 

human health. Censored data from LINJ studies that allow for 

comparison of detection frequencies between different compounds are available in previous publications (Ayers and others, 

2000; Stackelberg and others, 2000). 
8 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Minimum Reporting Levels Compared to 

Human-Health Benchmarks

In order to ensure that the analytical methods are adequate 

to detect concentrations of potential human-health concern, the 

analytical MRL must be less than the human-health benchmark 

value. Fortunately, of the 87 pesticides and 55 VOCs analyzed 

in this study that have human-health benchmarks, 76 pesticides 

(87 percent) and 45 VOCs (82 percent) were reported with 

MRLs at least 10-fold less than the MCL or HBSL. This is a 

result of the low MRLs that can be achieved with USGS analytical methods.

Only five compounds (one pesticide and four VOCs) analyzed in ground-water samples from the LINJ Study Unit were 

reported with MRLs greater than their human-health benchmarks (MCL for regulated compounds and HBSL for unregulated compounds) (table 1). Two of the five compounds are regulated (1,2-dibromo-3-chloropropane and 1,2-dibromoethane), 

and three of the compounds are unregulated (aldrin, acrylonitrile, and methyl acrylonitrile). Only 1,2-dibromo-3-chloropropane and 1,2-dibromoethane were detected in ground-water 

samples collected from the LINJ Study Unit (table 1). The MRL 

for 1,2-dibromo-3-chloropropane (0.214 μg/L) is slightly 

greater than its MCL (0.2 μg/L), and the MRL for 1,2-dibromoethane (0.036 μg/L) is somewhat less than its MCL (0.05 μg/L) 

in most well types, although the MRLs for both compounds are 

approximately two-fold greater than their MCLs in shallow 

monitoring-well samples (table 1). Uncertainty in quantitation 

increases as detected concentrations approach the MRL. Benchmark exceedances for compounds with benchmarks below or 

near their respective MRL values also have greater uncertainty 

than for compounds with benchmarks greater than their MRL 

values.

Guidance for Interpreting WaterQuality Data in a Human-Health 

Context

An important objective of this report is to provide guidance on the use and interpretation of HBSL values and other 

human-health benchmarks in the analyses of water-quality data 

in a human-health context. This guidance is intended primarily 

for USGS personnel conducting state- or local-scale waterquality studies; however, it can also be applied more generally 

by other agencies or organizations to facilitate the interpretation 

of water-quality data in a human-health context. Effective use 

of human-health benchmarks in water-quality assessments 

requires an understanding of what the individual benchmarks 

mean, as well as information about the specific hydrologic system being studied. Three general steps are presented here for 

interpreting water-quality data in a human-health context. First, 

all applicable human-health benchmarks for detected contaminants are compiled and compared with measured concentrations. Second, contaminants of potential human-health concern 

are identified by assessing the differential between measured 

concentrations and human-health benchmarks. Lastly, the 

Table 1. Pesticides and VOCs that have Minimum Reporting Levels that exceed human-health benchmarks in ground-water samples 

from the Long Island-New Jersey Study Unit.

[VOC, volatile organic compound; CASRN, Chemical Abstracts Service Registry Number; MRL, Minimum Reporting Level; μg/L, micrograms per liter; 

%, percent; SMW, shallow monitoring well; HBSL, Health-Based Screening Level; PSW, public-supply well; DW, domestic well; MDMW, moderate-depth 

monitoring well; MCL, Maximum Contaminant Level]

Compound CASRN MRL in μg/L

(well type)

Human-health 

benchmark in μg/L

(benchmark type)

Detection frequency

(%)

Pesticides

Aldrin 309-00-2 0.01 (SMW) 0.002 to 0.2

(HBSL range)

Not detected

VOCs

Acrylonitrile 107-13-1 1.23 (PSW, DW, MDMW); 2 (SMW) 0.06 to 6

(HBSL range)

Not detected in any well type

1,2-Dibromo-3-chloropropane 96-12-8 0.214 (PSW, DW, MDMW); 0.5 (SMW) 0.2

(MCL)

1.2 in DW only

1,2-Dibromoethane 106-93-4 0.036 (PSW, DW, MDMW); 0.1 (SMW) .05

(MCL)

13.3 in PSW only

Methyl acrylonitrile 126-98-7 0.57 (PSW, DW, MDMW); 2 (SMW) .7

(HBSL)

Not detected in any well type
Guidance for Interpreting Water-Quality Data in a Human-Health Context 9

occurrence of the contaminants of potential concern is interpreted in a human-health context by considering factors such as 

detection frequency and well type. These three general steps are 

elucidated in the next three sections. 

Step 1: Identify Human-Health Benchmarks and 

Compare to Measured Concentrations

The first step in interpreting water-quality data in a humanhealth context is to identify all applicable Federal (USEPA) and 

state human-health benchmarks, as well as HBSL values, for 

detected compounds, and to compare measured concentrations 

to these benchmarks. Historically, USGS has used USEPA 

MCL, Lifetime HA, and RSD values (defined in table 2) to 

assess water-quality conditions (Gilliom and others, 1998). For 

contaminants that have more than one of these three benchmarks available, the USGS has historically used the MCL, if 

available; otherwise, either the Lifetime HA (for noncarcinogens) or the RSD, usually at a 10–5 cancer risk level (for potential carcinogens), was used. For the few compounds with both a 

Lifetime HA and an RSD value, the lower value was used in 

order to be protective of both noncancer and cancer effects. 

USGS also historically has compared water-quality data to state 

standards and guidelines, where they exist, in state- and localscale water-quality studies.

HBSL values supplement USEPA and state standards and 

guidelines for drinking water. The two-tiered HBSL approach 

for interpreting water-quality data in a human-health context 

was introduced in the section “Development and Use of HealthBased Screening Level Values” and is described in more detail 

in the “Tier 1: Benchmarks for Regulated Compounds” and the 

“Tier 2: Benchmarks for Unregulated Compounds” sections 

below. This two-tiered HBSL approach entails listing waterquality data for regulated compounds separately from unregulated compounds. In both Tier 1 and Tier 2 analyses, the listed 

water-quality data may include the contaminant name, number 

of samples collected, percentage of samples with detections, 

MRL values, human-health benchmarks, and measured concentrations. 

Determining which measured concentrations (for example, maximum concentrations and median concentrations) to 

compare with human-health benchmarks depends, in part, on 

the hydrologic system being studied. Contaminant concentrations in ground-water systems tend to change relatively slowly 

as a function of time, and, depending on the objectives of the 

analysis and the nature of the data set, it may be appropriate to 

compare a variety of concentrations with human-health benchmarks (examples include median and maximum concentrations, 

a median-detected concentration (which excludes non-detected 

values), and (or) a range of percentiles). The median-detected 

concentration may be biased towards the high end of the concentration distribution, particularly when there are a substantial 

number of samples without detections, and comparisons 

between maximum detected concentrations and human-health 

benchmarks may be conservative (Toccalino and others, 2003). 

In data sets with low detection frequencies, comparisons of 

median concentrations and some percentile concentrations with 

human-health benchmarks have limited utility because these 

concentrations will be equivalent to non-detected values.

Tier 1 – Benchmarks for Regulated Compounds

For Tier 1 analysis, measured concentrations of regulated 

compounds are compared to drinking-water standards. In this 

study, there are two applicable drinking-water standards: 

USEPA MCL values and New Jersey State MCL values, both 

of which are legally enforceable (table 2). The State of New 

Jersey’s drinking-water standards are equal to, or more stringent than, the USEPA standards. MCL values protect public 

health by limiting the levels of contaminants in drinking water. 

MCL values are established on the basis of health effects, but 

are not strictly health-based values. Analytical and bestavailable treatment technology limitations also are considered, 

and for noncarcinogens only, costs may be considered in the 

development of MCL values (New Jersey Department of 

Environmental Protection, 2000). 

Tier 1 analysis begins with listing all detected, regulated 

compounds, along with their Federal and state MCL values. The 

USEPA and New Jersey MCL values (current as of 2004) used 

in this report for regulated pesticides and VOCs are provided in 

Appendix 1. The most current USEPA MCL values are published in the Code of Federal Regulations and in periodic 

USEPA compilations of drinking-water contaminants and their 

MCL values (U.S. Environmental Protection Agency, 2002b, 

2003b, and 2004). Current New Jersey MCL values are 

available on the NJDEP web site (New Jersey Department of 

Environmental Protection, 2002). MCL values for other states 

typically are published on state drinking-water program web 

sites (for example see, Association of State Drinking Water 

Administrators, 2003). 

Tier 2 – Benchmarks for Unregulated 

Compounds

For Tier 2 analysis, measured concentrations of unregulated compounds are compared to HBSL values. HBSL values 

are estimates of benchmark concentrations in water that may be 

of potential human-health concern. Measured concentrations 

are compared to HBSL values in lieu of USEPA OW Lifetime 

HA and RSD values; however, HBSL values typically are 

equivalent to USEPA OW Lifetime HA and RSD values, when 

available, because HBSL values were developed using USEPA 

OW methodologies and USEPA toxicity data. HBSL values 

may be different from published Lifetime HA or RSD values for 

compounds with USEPA toxicity values that are more recent 

than those used to develop Lifetime HA or RSD values. Additionally, HBSL values exist for some compounds with no published Lifetime HA or RSD values. HBSL values are described 

further in section “Development and Use of Health-Based 

Screening Level Values” and in table 2. 
10 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Table 2. Descriptions of human-health benchmarks related to drinking water used in this report.

[Maximum Contaminant Levels (Federal and State) are enforceable standards; the remainder of the listed benchmarks are unenforceable guidelines or publichealth goals; USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; OW, Office of Water (USEPA); kg, kilogram; L, liter; 

ORD, Office of Research and Development (USEPA); μg/L, micrograms per liter; NJDEP, New Jersey Department of Environmental Protection]

Human-health 

benchmark Acronym Agency Description References

Health-Based 

Screening 

Level

HBSL USGS Estimates of benchmark concentrations (for noncarcinogens) or concentration ranges (for carcinogens) in water that (a) may be of potential human-health concern; (b) can be used as threshold values 

against which measured concentrations of contaminants in ambient 

water samples can be compared; and (c) are consistent with USEPA 

Office of Water methodologies for setting drinking-water Lifetime 

Health Advisory and Risk-Specific Dose values (U.S. Environmental 

Protection Agency, 1988 and 1993).

(Toccalino and others, 

2003)

Maximum Contaminant Level 

(Federal)

USEPA 

MCL

USEPA 

(OW)

The maximum permissible level of a contaminant in water that is 

delivered to any user of a public water system. MCLs are set as close 

to Maximum Contaminant Level Goals (MCLGs) as feasible using 

the best available treatment technology and taking cost into consideration. The MCLG is the concentration of a contaminant in drinking 

water at which no known or anticipated adverse health effects occur 

and which allows an adequate margin of safety. 

(U.S. Environmental 

Protection Agency, 

2003a and 2004)

Lifetime Health 

Advisory

Lifetime HA USEPA 

(OW)

The concentration of a contaminant in drinking water that is not 

expected to cause any adverse noncarcinogenic effects over a lifetime of exposure (70 years). The Lifetime HA is based on exposure 

of a 70-kg adult consuming 2 L of water per day, and assumes that 

only part (generally 20 percent) of the total exposure to a contaminant is from drinking water. 

(U.S. Environmental 

Protection Agency, 

1993 and 2004)

Risk-Specific 

Dose 

RSD USEPA 

(OW & 

ORD)

The concentration of a contaminant in drinking water that corresponds 

to a specific estimated lifetime cancer risk (typically 1 in 10,000, 1 in 

100,000, or 1 in 1,000,000). The RSD is always associated with a 

specific cancer risk level. A related benchmark is the unit drinkingwater risk, which is risk per microgram per liter concentration.

(U.S. Environmental 

Protection Agency, 

2001 and 2004)

Maximum 

Contaminant 

Level (State)

New Jersey 

MCL

NJDEP The maximum permissible level of a contaminant in water measured 

at the point of entry to the distribution system or at the free-flowing 

outlet of the ultimate user of a public water system or other water 

system to which State primary drinking water regulations apply. For 

carcinogens, the health-based goal is a 1 in 1,000,000 excess cancer 

risk over a lifetime of exposure; for noncarcinogens, the health-based 

goal is a level at which no known or anticipated health effects would 

be expected to occur. 

(New Jersey Department of Environmental Protection, 2000)

Ground Water 

Quality Criteria

GWQC NJDEP Contaminant concentrations that, when not exceeded, will not prohibit 

or significantly impair the use of ground water for potable water or 

conversion to potable water through conventional water treatment. 

Values are human-health risk-based criteria based on the available 

evidence regarding each constituent’s carcinogenicity or toxicity, as 

appropriate for the protection of potable-water use. 

(New Jersey Department of Environmental Protection, 1993 

and 2004a)

Interim Specific 

Ground Water 

Quality Criteria

Interim

Specific 

GWQC

NJDEP Contaminant concentrations in ground water for chemicals where a 

specific GWQC is not available. Values are based on the same 

methodologies and risk assessment approach applied to the development of the specific GWQC. 

(New Jersey Department of Environmental Protection, 1993 

and 2004b)
Guidance for Interpreting Water-Quality Data in a Human-Health Context 11

For Tier 2 analysis, measured concentrations of unregulated compounds also may be compared to state guideline 

values, if available. The State of New Jersey published two 

numerical criteria—the GWQC and the Interim Specific 

GWQC Criteria (table 2)—that were developed as part of the 

New Jersey Ground Water Quality Standards (GWQS). The 

GWQS specify the quality criteria (numerical values) and 

designated uses for ground water (New Jersey Department of 

Environmental Protection, 1993). Like HBSL values, GWQC 

and Interim Specific GWQC values also were developed using 

USEPA OW methodologies. NJDEP also publishes Interim 

Generic GWQC that are not health-based values, but are used as 

default values for synthetic organic chemicals (SOC) when no 

specific criterion exists or when published health information is 

lacking (New Jersey Department of Environmental Protection, 

2004b). Interim Generic GWQC values are not included in 

table 2 or in the remainder of this report because they are not 

health-based values.

Tier 2 analysis begins with listing all detected, unregulated 

compounds, along with their applicable HBSL values and stateguideline values. The HBSL values used in this report (current 

as of August 2004) for unregulated pesticides and VOCs are 

provided in Appendix 2. HBSL values are updated on a monthly 

basis to incorporate any new or updated toxicity values published by USEPA. Up-to-date GWQC and Interim Specific 

GWQC values are available on NJDEP’s web sites (New Jersey 

Department of Environmental Protection, 2004a and 2004b).

Step 2: Identify Contaminants of Potential 

Human-Health Concern Using Benchmark 

Quotients

The second step in interpreting water-quality data in a 

human-health context is to identify contaminants of potential 

human-health concern by assessing the differential between 

measured concentrations and human-health benchmarks. For 

ground-water data collected in this study, a Benchmark 

Quotient (BQ) value, the ratio of the measured concentration of 

a detected contaminant to its USEPA MCL value (for a regulated compound) or to its HBSL value (for an unregulated compound), was calculated for individual pesticides and VOCs. For 

regulated compounds with New Jersey MCL values but no 

USEPA MCL values, the BQ values were calculated using New 

Jersey MCL values. For unregulated carcinogens, the HBSL 

value used to calculate BQ values corresponds to a 10-6 cancer 

risk (that is, the low end of the HBSL concentration range). 

HBSL values were rounded to one significant figure to be consistent with USEPA OW practices (Toccalino and others, 

2003); therefore, all BQ values also were rounded to one significant figure. 

Different types of BQ values can be calculated for detected 

compounds; three types of BQ values were calculated for each 

well type in this study. Maximum BQ (BQmax) values were 

calculated for each detected compound (with a human-health 

benchmark) in each well type, where the BQmax value represents the maximum detected concentration of a compound in a 

given well type divided by the compound’s MCL or HBSL 

value. Median BQ (BQmed-det) values were calculated for 

compounds with BQmax values greater than or equal to (≥) 0.1. 

BQmed-det values represent the median of detected concentrations of a compound (that is, the median value of all detected 

concentrations only) in a given well type divided by the MCL 

or HBSL value for the compound. 

A third type of BQ value was calculated to represent the 

median of all samples (including non-detections) divided by the 

MCL or HBSL value (BQmed-all), where non-detections were 

assigned a concentration equal to the MRL for a given compound. BQmed-all values are not presented in this report, 

because most detected compounds with human-health benchmarks were detected less than 50 percent of the time in any well 

type and therefore BQmed-all values are equivalent to the ratio 

of the MRL to the human-health benchmark. 

In this report, contaminants of potential human-health 

concern are defined as pesticides and VOCs with maximum 

detected concentrations within a factor of 10 of applicable 

human-health benchmarks (that is, BQmax ≥ 0.1) in any of the 

three well types. The selection of 0.1 as the BQ threshold for 

identifying contaminants of potential human-health concern is 

consistent with various state and USEPA practices. For example, USEPA published a draft final rule defining a waterreference level as the level at or above which the agency wants 

to be informed of the presence of a pesticide in water resources. 

The water-reference level was further defined as 10 percent of 

the MCL or other applicable level in order to provide an early 

warning of potential problems with pesticides in water 

resources (U.S. Environmental Protection Agency, 1996). 

Furthermore, the USEPA final Federal Register notice on 

reporting requirements for risk/benefit information for pesticides indicated that, if a pesticide is detected in ground water, 

surface water, or finished drinking water, then the detections 

should be reported in three categories: (1) detections at levels 

greater than the MCL or other applicable criterion, (2) detections at levels greater than 10 percent of the MCL but not to 

exceed the MCL or other applicable criterion, and (3) detections 

at levels less than 10 percent of the MCL or other applicable 

criterion (U.S. Environmental Protection Agency, 2003c). In 

this report, the magnitude of pesticide and VOC detections in 

ground water, relative to their benchmark values, is reported in 

these same three categories.

Step 3: Interpret the Occurrence of 

Contaminants of Potential Human-Health 

Concern

The third step in interpreting water-quality data in a 

human-health context is to evaluate the occurrence of the contaminants of potential human-health concern (that is, those 

contaminants with BQmax ≥ 0.1) by considering five primary 
12 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

factors. These five factors are (1) magnitude of the BQ values, 

(2) detection frequency, (3) MRL considerations, (4) well type 

and use of water, and (5) sources and physicochemical properties of the contaminants.

First, although contaminants of potential human-health 

concern are defined in this report as contaminants with BQmax 

≥ 0.1, contaminants with BQ values ≥ 1 have more humanhealth importance than contaminants with BQ values < 1. BQ 

values ≥ 1 indicate that measured concentrations met or 

exceeded a human-health benchmark (MCL or HBSL value). 

For example, a BQ value of 10 indicates that the measured concentration of a chemical was 10-fold greater than the humanhealth benchmark; it does not mean that the chemical is 10-fold 

more toxic than a chemical with a BQ value equal to 1. BQ values less than 1 indicate that measured concentrations were less 

than the applicable human-health benchmarks. BQ values that 

are less than 1 also provide useful information about the potential for human-health effects. For example, a BQ value less than 

0.001 indicates that measured concentrations of a contaminant 

were more than a factor of 1,000 less than the applicable 

human-health benchmark, and therefore, this contaminant is not 

likely to be of concern to human health. In contrast, a BQ value 

in the range of 0.1 to 1 indicates that the measured concentration 

of a contaminant was within a factor of 10 of the MCL or HBSL 

value. As a result, it may be desirable to monitor future concentrations of this contaminant to account for variability in sample 

collection and analysis, and to track trends in the occurrence of 

this contaminant over time. 

Second, compounds that are frequently detected are more 

likely to be of concern than compounds that are detected infrequently. In this report, frequently detected compounds are 

defined as those compounds that are detected in at least 

10 percent of samples from any given well type. This definition 

of frequently detected compounds is consistent with usage in a 

previously published report of the LINJ Study Unit (Stackelberg and others, 2000). This definition also generally follows 

USEPA human-health risk assessment guidance that discusses 

the evaluation of contaminants of potential concern based on 

frequency of detection (U.S. Environmental Protection Agency, 

1989b). This USEPA guidance focuses assessments on contaminants that are consistently detected, rather than on those that 

are detected infrequently. The USEPA guidance provides an 

example in which assessments are focused on compounds 

detected in at least 5 percent of samples, assuming that at least 

20 samples were collected (one detection in 20 samples equals 

a 5 percent frequency of detection), but this guidance also 

allows the use of a different detection frequency (U.S. Environmental Protection Agency, 1989b).

Third, contaminants of potential human-health concern 

and detection frequencies are evaluated in the context of MRL 

values for the analytical method used. If the MRL value for a 

contaminant is greater than the human-health benchmark for 

that contaminant, then (1) any detections of that contaminant 

will be greater than the human-health benchmark (that is, BQ 

value > 1), unless estimated concentrations less than the MRL 

are reported, and (2) there is the possibility that the contaminant 

could be present at concentrations that are of human-health concern (that is, BQ value ≥ 0.1), even in samples where that contaminant is not detected. In general, the detection frequency for 

a given contaminant will tend to decrease as the MRL increases. 

See the section “Interpreting Detection Frequencies” for additional considerations regarding the MRL in a human-health 

context. 

Fourth, well type is important because it affects potential 

human exposure (through possible drinking-water consumption) to contaminants present in the water. The relevance of 

water-quality data from the public-supply, domestic, and monitoring wells considered in this study to human-health concerns 

differs markedly.

Ground-water samples collected from public-supply wells 

are relevant to human health because these water resources currently are used as drinking-water sources for large numbers of 

people. Ground water from public-supply wells typically is 

treated (disinfected) before it is consumed, however, the 

NAWQA Program primarily collects and analyzes raw water 

samples (that is, water sampled prior to treatment). If water 

from public-supply wells contains measured concentrations of 

contaminants that exceed MCL values, then the water supply is 

treated to remove the contaminants (New Jersey Department of 

Environmental Protection, 2000). Therefore, contaminants 

measured in raw water from public-supply wells may not be 

present at the same concentrations in the water consumed by the 

people who are served by those wells. Further, estimating the 

potential exposure to consumers of water from public-supply 

wells is complicated by the fact that public-supply distribution 

systems could contain water that is blended from multiple water 

sources. Beginning in 2004, the NAWQA Program’s Source 

Water Quality Assessment component monitors both raw and 

treated ground-water samples.

Ground-water data collected from domestic wells are particularly relevant to human health because (1) the ground water 

is a current drinking-water resource and (2) these water 

resources typically are consumed with little or no treatment. 

Ground water from domestic wells is consumed by smaller 

numbers of people (typically one family per well) than ground 

water from public-supply wells (typically thousands of people 

per well). The estimation of the potential exposure to consumers 

of water from domestic wells is limited, however, because only 

one sample was collected per well; this prevents the estimation 

of representative exposure over time (this limitation also is true 

for the other well types).

In contrast, ground-water data collected from monitoring 

wells are not immediately relevant to human health because 

water from these wells is not consumed (non-potable wells). 

Although the water collected from monitoring wells is not a current source of drinking water, contamination in these wells can 

be both a contributor to, and a predictor of, future contaminant 

concentrations in deeper aquifers that may be used, now or in 

the future, for domestic and public supplies. Data from monitoring wells also can provide substantial insight about contaminant 

sources, their environmental fate and transport, and trends in 

concentrations over time.
Assessment of Ground-Water Quality in New Jersey 13

Examining ground-water data by well type (as was done in 

this study) can provide regional water-quality information, as 

well as identify local concerns. For example, if a chemical is 

detected in only one well at a concentration greater than the 

MCL or HBSL value, this chemical may not have noteworthy 

regional importance, but it could have local importance. 

Lastly, it also is useful to characterize the sources and 

physicochemical properties of contaminants that are identified 

as being of potential human-health concern, and (or) those that 

are frequently detected, to help understand potential human 

exposure to these contaminants. The physicochemical properties of a contaminant provide information about its fate and 

transport, biodegradability, persistence in water resources, and 

migration to other water resources. Such information helps in 

assessing the potential human exposure to a contaminant. Contaminants that are mobile and (or) persistent in the environment 

are of greater relevance to potential human exposure than contaminants that are not mobile and (or) that readily degrade in the 

environment. Contaminants that are highly water soluble, 

poorly sorbed to soil and aquifer matter, and highly persistent 

(resistant to degradation) pose the greatest likelihood of contaminating ground water. The sources and physicochemical 

properties of contaminants that were frequently detected in the 

LINJ Study Unit were described in detail by Stackelberg and 

others (2000), and therefore, are not explained in depth in this 

report.

All five of the factors described above need to be considered when interpreting water-quality data in a human-health 

context. Combinations of these factors help identify which 

detected contaminants could pose the greatest human-health 

concern. For example, contaminants that both (1) have 

measured concentrations that exceed human-health benchmarks 

and (2) are frequently detected in ground-water resources that 

are used for drinking water (that is, domestic or public-supply 

wells) are likely the most important contaminants from a 

human-health perspective. In contrast, contaminants that are 

detected infrequently and are present at concentrations well 

below their human-health benchmarks are least likely to be of 

concern. Other notable contaminants are those that are frequently detected in domestic or public-supply wells, but have 

no available toxicity data with which to calculate HBSL values. 

Identifying such compounds can assist Federal and state 

drinking-water agencies with prioritizing future data-collection 

and toxicity-evaluation activities.

Assessment of Ground-Water Quality 

in New Jersey

A total of 182 compounds (97 pesticides and 85 VOCs) 

were analyzed in this study, and 97 of these compounds were 

detected in samples from at least one of the three well types. 

The numbers of pesticides and VOCs that were analyzed and 

detected in the public-supply wells, domestic wells, and monitoring wells in the study area are summarized in table 3. The 

number of detected, unregulated pesticides and VOCs that have 

human-health benchmarks (before and after HBSL calculations) for comparison with measured concentrations also are 

provided in table 3 and illustrated in figure 3.

Table 3. Numbers of (1) pesticides and VOCs analyzed and detected in ground-water samples and (2) detected unregulated compounds 

with human-health benchmarks in ground-water samples from the Long Island-New Jersey Study Unit.

[VOC, volatile organic compound; HBSL, Health-Based Screening Level; PSW, public-supply well; DW, domestic well; MW, monitoring well; Lifetime HA, 

Lifetime Health Advisory; USEPA, U.S. Environmental Protection Agency; RSD, Risk-Specific Dose]

Well type

Number of compounds

All compounds Detected compounds Detected, unregulated compounds with

human-health benchmarks

Analyzed Detected Regulated Unregulated Before HBSL calculations1 After HBSL calculations

Pesticides

PSW 47 15 4 11 8 10

DW 85 21 7 14 9 12

MW 97 30 8 22 17 21

VOCs

PSW 85 38 24 14 4 6

DW 85 47 27 20 4 9

MW 85 45 24 21 5 9

1

Human-health benchmarks before HBSL calculations are Lifetime HA values from USEPA Office of Water and RSD values from either USEPA Office of 

Water or the USEPA Integrated Risk Information System database.
14 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Figure 3. Number of detected, unregulated pesticides and VOCs with human-health benchmarks before and after HBSL 

calculations in all well types in the Long Island-New Jersey Study Unit.

17

7

24

12

0

10

20

30

Pesticides

n = 26

VOCs

n = 30

NUMBER OF DETECTED,

UNREGULATED COMPOUNDS

WITH HUMAN-HEALTH BENCHMARKS

65% 92% 23% 40%

Detected, unregulated compounds

with new HBSL values

Pesticidesb,c

1. Acetochlor

2. Benfluralin

3. EPTC

4. Linuron

5. Napropamide

6. Norflurazon

7. Pendimethalin

VOCs

1. Acetone 

2. Carbon disulfide

3. Ethyl ether

4. Isopropylbenzene

5. 1,1,2-trichloro1,2,2-trifluoroethane

a Human-health benchmarks before HBSL calculations are Lifetime HA values from USEPA Office of Water and RSD values

from either USEPA Office of Water or the USEPA Integrated Risk Information System database.

b Carbaryl has a USEPA Lifetime HA value (700 μg/L). Carbaryl also has a new HBSL range (40-4,000 μg/L) based on updated

toxicity data published by USEPA Office of Pesticide Programs. Because carbaryl had a human-health benchmark before

HBSL values were calculated, it is not included as a compound with a new benchmark in this figure. 

[VOC, volatile organic compound; HBSL, Health-Based Screening Level; USEPA, U.S. Environmental Protection Agency; Lifetime HA, Lifetime

Health Advisory; RSD, Risk-Specific Dose; %, percent; n, number of unregulated compounds detected; EPTC, 5-ethyl dipropylthiocarbamate]

Before HBSL calculationsa

 (Lifetime HA + RSD)

After HBSL calculations

 (Lifetime HA + RSD + HBSL)

c Diuron has a USEPA Lifetime HA (10 μg/L). Diuron also has a new HBSL range (2-200 μg/L) based on updated toxicity data

published by USEPA Office of Pesticide Programs. Because diuron had a human-health benchmark before HBSL values

were calculated, it is not included as a compound with a new benchmark in this figure. 

EXPLANATION

Step 1: Human-Health Benchmarks Identified 

and Compared to Measured Concentrations

Comparisons of measured ground-water contaminant 

concentration data with human-health benchmarks for pesticides and VOCs for all well types are presented in the following 

sections “Pesticides” and “Volatile Organic Compounds,” 

respectively (tables 4-7). For each of these two contaminant 

classes, Tier 1 analysis for regulated compounds (that is, comparisons with USEPA and New Jersey drinking-water MCL 

values) is presented first (tables 4 and 6). Tier 2 analysis for 

unregulated compounds (that is, comparisons with HBSL 

values and with New Jersey GWQC and Interim Specific 

GWQC values) is presented second (tables 5 and 7). 

Pesticides

Of the 97 total pesticides analyzed in this study, 38 

(39 percent) were detected in at least one well type. Twelve of 

the 38 detected pesticides are regulated (that is, have a USEPA 

or New Jersey MCL value) and 26 are unregulated. Nearly all 

of the detected, unregulated pesticides (24 of 26) have humanhealth benchmarks, and seven of these benchmarks are new 

HBSL values (fig. 3). 

Detection frequencies for pesticides ranged from less than 

2 percent to 47 percent of samples in a given well type. Nine 

pesticides were frequently detected (that is, detected in 

10 percent or more of samples) in samples from at least one of 

the well types (tables 4 and 5). All but one of these nine 

frequently detected pesticides has a human-health benchmark 

value; the exception is the herbicide metabolite, deethylatrazine.

Tier 1 – Regulated Pesticides

Twelve regulated pesticides were detected (out of 19 regulated pesticides analyzed) in ground-water samples collected 

from all well types (table 4). All regulated pesticides were 

detected at concentrations less than USEPA and New Jersey 

MCL values, with the exception of dinoseb in samples from 

monitoring wells (table 4). Dinoseb was detected in 4 of 72 
Assessment of Ground-Water Quality in New Jersey 15

monitoring-well samples, and measured concentrations 

exceeded the MCL in 2 of these 4 samples (table 4; fig. 4). Both 

of the detected concentrations (40 μg/L and 8 μg/L), which 

exceeded the USEPA and New Jersey MCL values of 7 μg/L, 

were estimated concentrations. The other two detections of 

dinoseb were at concentrations at least 100-fold below the MCL 

value. Estimated concentrations have greater uncertainty in 

their quantitation than concentrations that are not estimated, and 

this uncertainty also applies to the exceedance, particularly for 

the sample with 8 μg/L dinoseb, for which the estimated concentration was close to the MCL of 7 μg/L. Dinoseb was not 

detected in any samples from domestic wells and was not analyzed in public-supply well samples. Dinoseb was, however, 

analyzed and detected in public-supply well samples collected 

in a study by Vowinkel and others (1996).

Three regulated pesticides—atrazine, carbofuran, and 

simazine—were detected in all well types; however, none was 

detected at concentrations that exceeded USEPA or New Jersey 

MCL values (table 4). The maximum carbofuran concentration 

detected was more than 100-fold less than the MCL for all well 

types. Three regulated pesticides—atrazine, heptachlor 

epoxide, and simazine—were detected within a factor of 10 

of their MCL values, but only in monitoring-well samples 

(table 4). Atrazine and simazine were frequently detected in all 

well types except for domestic wells; atrazine and simazine 

were detected in 9.9 percent and 8.6 percent, respectively, of 

the domestic wells. Heptachlor epoxide was analyzed only in 

monitoring-well samples, and was not frequently detected.

Tier 2 – Unregulated Pesticides

Twenty-six unregulated pesticides were detected (out of 

78 unregulated pesticides analyzed) in ground-water samples 

collected from all well types, and measured concentrations were 

compared to HBSL values and New Jersey GWQC values, 

when available (table 5). Measured concentrations of two of 

these pesticides—dieldrin and diuron—met or exceeded their 

HBSL values in ground-water samples from at least one well 

type (table 5). 

Dieldrin was detected in all well types, and all but 2 of the 

31 measured concentrations of dieldrin exceeded the low end of 

the HBSL concentration range (10-6 cancer risk) and the New 

Jersey GWQC, which also is based on a 10-6 cancer risk 

(table 5; fig. 4). The low end of the HBSL concentration range 

and the New Jersey GWQC value for dieldrin are the same 

(both 0.002 μg/L) because New Jersey also uses USEPA OW 

methodologies for calculating GWQC values. Measured dieldrin concentrations in four monitoring-well samples also 

exceeded the high end of the HBSL concentration range 

(0.2 μg/L), which is based on a 10-4 cancer risk. In the two 

samples in which detected dieldrin concentrations did not 

exceed the low end of the HBSL concentration range, dieldrin 

was detected at concentrations within a factor of 10 of the 

HBSL (fig. 4).

The New Jersey practical quantitation level (PQL) for 

dieldrin is 0.03 μg/L (New Jersey Department of Environmental Protection, 2004a), which was exceeded in samples from 

three public-supply wells and six monitoring wells. The PQL is 

not a human-health benchmark but is equivalent to the concentration that can be reliably quantitated by NJDEP analytical 

methods (New Jersey Department of Environmental Protection, 

2004b). The MRL for dieldrin analyzed in this study, using 

USGS methods, is 0.001 μg/L. This MRL is less than the low 

end of the HBSL concentration range and the New Jersey 

GWQC value (0.002 μg/L), thus allowing quantitation of dieldrin at concentrations that are relevant to human health.

Diuron was detected in 2 of 60 samples from domestic 

wells and in 5 of 72 samples from monitoring wells (table 5), 

but was not analyzed in public-supply well samples. The maximum detected concentration in domestic wells (1.9 μg/L) was 

approximately equal to the low end of the HBSL concentration 

range (2 μg/L). The maximum detected concentration of diuron 

in monitoring-well samples (2 μg/L) was an estimated concentration, equal to the low end of the HBSL concentration range 

(based on a 10-6 cancer risk) (table 5; fig. 4). In the five samples 

in which detected diuron concentrations were less than the low 

end of the HBSL concentration range, diuron was detected at 

concentrations within a factor of 10 of the HBSL (fig. 4). 

Because the maximum detected concentration in monitoringwell samples was an estimated concentration, which was equal 

to the human-health benchmark concentration, the uncertainty 

in this estimated concentration indicates that there also is uncertainty in the exceedance. Diuron has a Lifetime HA value of 

10 μg/L; this value was not exceeded in any sample.

Five other unregulated pesticides with human-health 

benchmarks—carbaryl, p,p’-DDE, metolachlor, prometon, and 

terbacil—were detected in all well types; however, the detected 

concentrations were all well below their applicable HBSL 

values and New Jersey GWQC values (table 5). The maximum 

detected concentration of these five unregulated pesticides 

ranged from about 20-fold to more than1,000-fold less than 

their respective HBSL values. 

Two unregulated pesticide analytes—deethylatrazine and 

fenuron—were detected but have no human-health benchmarks 

(Lifetime HA, RSD, HBSL, or GWQC values) to use for comparison against measured concentrations (table 5; Appendix 3). 

These compounds do not have human-health benchmarks 

because the toxicity data needed to calculate HBSL values are 

lacking. Deethylatrazine (a degradation product of the herbicides atrazine and propazine) was detected in all well types in 

25 to 42 percent of the samples (table 5). Fenuron was analyzed 

in samples from domestic wells and monitoring wells, but was 

detected in only 1 of 60 domestic-well samples (table 5). 
16 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Table 4. Concentrations, detection frequencies, and MCL values for regulated pesticides detected in public-supply wells, domestic

wells, and monitoring wells in the Long Island-New Jersey Study Unit.

[MCL, Maximum Contaminant Level; Bold type indicates measured concentrations exceed USEPA or New Jersey MCL values; CASRN, Chemical Abstracts 

Service Registry Number; MRL, Minimum Reporting Level; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; BQmax, Benchmark 

Quotient = ratio of maximum detected concentration to USEPA MCL value; <, less than; E, estimated value; 2,4-D, 2,4-dichlorophenoxyacetic acid; 2,4,5-TP, 2-

(2,4,5-trichlorophenoxy) propionic acid]

Compound CASRN

Number

of

samples

Number of

samples

with

detections

Percentage of

samples

with

detections

MRL

(μg/L)

Maximum

detected

concentration

(μg/L)

USEPA

MCL

(μg/L)

New 

Jersey 

MCL

(μg/L)

BQmax1

Public-supply wells (30 wells)

Alachlor 15972-60-8 30 7 23.3 <0.002 0.0671 2 2 0.03

Atrazine 1912-24-9 30 9 30.0 <.001 .0341 3 3 .01

Carbofuran 1563-66-2 30 3 10.0 <.003 E.0773 40 40 .002

Simazine 122-34-9 30 8 26.7 <.005 .22 4 4 .06

Domestic wells (82 wells)

Aldicarb

sulfoxide

1646-87-3 60 1 1.7 <0.021 E0.23 4 4 0.06

Atrazine 1912-24-9 81 8 9.9 <.001 .0793 3 3 .03

Carbofuran 1563-66-2 81 2 2.5 <.003 E.218 40 40 .005

2,4-D 94-75-7 60 1 1.7 2<.15, 

<.035

.15 70 70 .002

Picloram 1918-02-1 60 1 1.7 <.05 E.05 500 500 .0001

Simazine 122-34-9 81 7 8.6 <.005 .265 4 4 .07

2,4,5-TP 93-72-1 60 1 1.7 <.021 .06 50 50 .001

Monitoring wells (108 wells)

Alachlor 15972-60-8 108 3 2.8 <0.002 0.099 2 2 0.05

Atrazine 1912-24-9 108 51 47.2 <.001 .676 3 3 .2

Carbofuran 1563-66-2 108 6 5.6 <.003 E.173 40 40 .004

Chlordane, 

technical

12789-03-6 69 1 1.4 <.1 .1 32 30.5 .05

Dinoseb 88-85-7 72 4 5.6 <.035 E40 7 7 6

Heptachlor

epoxide

1024-57-3 69 4 5.8 <.01 .07 0.2 0.2 .4

Lindane 58-89-9 108 1 0.9 <.004 .0128 0.2 0.2 .06

Simazine 122-34-9 108 41 38.0 <.005 1.38 4 4 .3

1

BQmax values for regulated compounds were calculated using USEPA MCL values and were rounded to one significant figure.

2

MRL value that applies to the largest number of samples (when more than one MRL exists for a given compound).

3

USEPA MCL and New Jersey MCL are for chlordane (CASRN 57-74-9).
Assessment of Ground-Water Quality in New Jersey 17

Figure 4. Distributions of concentrations and detection frequencies of pesticides detected at concentrations that

met or exceeded human-health benchmarks in at least one well type in the Long Island-New Jersey Study Unit.

30 26.7

81

108

60

72

60

NA

NA

72

3.7

18.5

NA

0

5.6

NA

3.3

6.9

EXPLANATION

Public-supply wells

Domestic wells

Monitoring wells

Detected concentration

Estimated concentration 

U.S. Environmental Protection Agency

 Maximum Contaminant Level 

New Jersey Maximum Contaminant Level

New Jersey Ground-Water Quality Criteria

Low end of Health-Based Screening Level

 range (10-6 cancer risk)

Minimum Reporting Level

Multi-colored lines indicate multiple

 benchmarks at the same value 

Diuron has a USEPA Lifetime HA (10 μg/L). Diuron also has a new HBSL range (2-200 μg/L) based on

updated toxicity data published by USEPA Office of Pesticide Programs.

*

CONCENTRATION, IN MICROGRAMS PER LITER

102 101 100 10-1 10-2 10-3 10-4

Dieldrin

Dinoseb

Diuron*

[n, number of samples; %, percent; NA, not analyzed; USEPA, U.S. Environmental Protection Agency; HBSL, Health-Based

Screening Level; Lifetime HA, Lifetime Health Advisory; μg/L, micrograms per liter] 

Detection

frequency

(%)

n
Table 5. Concentrations, detection frequencies, and HBSL values for unregulated pesticides detected in public-supply wells, domestic wells, and mLong Island-New Jersey Study Unit.[HBSL, Health-Based Screening Level; Bold type indicates measured concentration exceeds New Jersey Ground-Water Quality Criteria (GWQC) or HBSL value; CASRN, Che

Number; MRL, Minimum Reporting Level; μg/L, micrograms per liter; BQmax, Benchmark Quotient = ratio of maximum detected concentration to HBSL value or low end of H

than; --, not available; E, estimated value; USEPA, U.S. Environmental Protection Agency; RSD, Risk-Specific Dose; OPP, Office of Pesticide Programs (USEPA); q1*, cancer p

time Health Advisory; p,p’-DDE, p,p’-dichlorodiphenyl dichloroethylene; IRIS, Integrated Risk Information System; SF, oral slope factor; PQL, practical quantitation level; RfDEPTC, 5-ethyl dipropylthiocarbamate]

Compound CASRN Number of samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL 

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New 

Jersey 

GWQC 

(μg/L)

HBSL 

concentration

or range1

(μg/L)

BQmax2 

Public-supply wells (30 wells)

Acetochlor 34256-82-1 30 1 3.3 <0.002 0.0604 -- 2 to 200 0.03 RSD apCarbaryl 63-25-2 30 1 3.3 <.003 E.019 -- 40 to 4,000 .0005 RSD ap

Note: 

Cyanazine 21725-46-2 30 1 3.3 <.004 .0087 -- 1 .009 Lifetimp,p'-DDE 72-55-9 30 2 6.7 <.006 E.00063 0.1 0.1 to 10 .006 RSD apDeethylatrazine 6190-65-4 30 12 40.0 <.002 E.0234 -- -- -- No HBSDieldrin 60-57-1 30 8 26.7 <.001 .046 .002

PQL=0.033

0.002 to 0.2 20 RSD ap

Linuron 330-55-2 30 1 3.3 <.002 .0123 -- 1 .01 Lifetim

carcin

Metolachlor 51218-45-2 30 11 36.7 <.002 .671 -- 100 .007 LifetimMetribuzin 21087-64-9 30 2 6.7 <.004 .008 -- 200 .00004 LifetimPrometon 1610-18-0 30 3 10.0 <.018 E.0084 -- 100 .00008 LifetimTerbacil 5902-51-2 30 4 13.3 <.007 E.0978 -- 90 .001 Lifetim

Domestic wells (82 wells)

Benfluralin 1861-40-1 81 1 1.2 <0.002 0.0057 -- 2,000 0.000003 Lifetim

RfD

Carbaryl 63-25-2 81 2 2.5 <.003 E.539 -- 40 to 4,000 .01 RSD ap

Note: 

Dacthal 1861-32-1 81 1 1.2 <.002 E.0015 -- 70 .00002 Lifetimp,p'-DDE 72-55-9 81 3 3.7 <.006 E.0056 .1 0.1 to 10 .06 RSD apDeethylatrazine 6190-65-4 81 20 24.7 <.002 E.0801 -- -- -- No HBS
Table 5. Concentrations, detection frequencies, and HBSL values for unregulated pesticides detected in public-supply wells, domestic wells, and mLong Island-New Jersey Study Unit.—Continued

Compound CASRN Number of samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL 

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New 

Jersey 

GWQC 

(μg/L)

HBSL 

concentration

or range1

(μg/L)

BQmax2 

Domestic wells (82 wells)—Continued

Dieldrin 60-57-1 81 3 3.7 <0.001 0.0251 0.002 

PQL=0.033

0.002 to 0.2 10 RSD ap

Diuron 330-54-1 60 2 3.3 <.02 1.9 -- 2 to 200 1 RSD ap

Note: L

EPTC 759-94-4 81 1 1.2 <.002 .182 -- 200 .0009 Lifetim

RfD

Fenuron 101-42-8 60 1 1.7 <.013 .05 -- -- -- No HBSMetolachlor 51218-45-2 81 3 3.7 <.002 .102 -- 100 .001 LifetimNapropamide 15299-99-7 81 1 1.2 <.003 .005 -- 700 .000007 Lifetim

RfD

Prometon 1610-18-0 81 7 8.6 <.018 .025 -- 100 .0002 LifetimTerbacil 5902-51-2 81 3 3.7 <.007 E.891 -- 90 .01 LifetimTrifluralin 1582-09-8 81 1 1.2 <.002 .0066 -- 5 .001 Lifetim

Monitoring wells (108 wells)

Bentazon 25057-89-0 72 2 2.8 <0.014 0.2 -- 200 0.001 LifetimButylate 2008-41-5 108 1 .9 <.002 E.0025 -- 400 .000006 LifetimCarbaryl 63-25-2 108 7 6.5 <.003 E.781 -- 40 to 4,000 .02 RSD ap

Note: 

Cyanazine 21725-46-2 108 1 .9 <.004 .023 -- 1 .02 LifetimDacthal 1861-32-1 108 1 .9 <.002 E.001 -- 70 .00001 Lifetimp,p'-DDE 72-55-9 108 2 1.9 <.006 E.0018 .1 0.1 to 10 .02 RSD apDeethylatrazine 6190-65-4 108 45 41.7 <.002 E.48 -- -- -- No HBSDicamba 1918-00-9 72 1 1.4 <.035 E.45 -- 200 .002 LifetimDieldrin 60-57-1 108 20 18.5 <.001 5.6 .002 

PQL=0.033

0.002 to 0.2 3,000 RSD ap
Monitoring wells (108 wells)—Continued

Diuron 330-54-1 72 5 6.9 <0.02 E2 -- 2 to 200 1 RSD ap

Note: L

Fluometuron 2164-17-2 72 1 1.4 <.035 .04 -- 90 .0004 LifetimLinuron 330-55-2 108 1 .9 <.002 .024 -- 1 .02 Lifetim

carcin

Methomyl 16752-77-5 72 1 1.4 <.017 E.04 -- 200 .0002 LifetimMetolachlor 51218-45-2 108 30 27.8 <.002 .466 -- 100 .005 LifetimMetribuzin 21087-64-9 108 2 1.9 <.004 .159 -- 200 .0008 LifetimNapropamide 15299-99-7 108 1 .9 <.003 .043 -- 700 .00006 Lifetim

RfD

Norflurazon 27314-13-2 72 1 1.4 <.024 .53 -- 30 .02 Lifetim

carcin

Pendimethalin 40487-42-1 108 3 2.8 <.004 .028 -- 30 .0009 Lifetim

carcin

Prometon 1610-18-0 108 20 18.5 <.018 4.83 -- 100 .05 LifetimTebuthiuron 34014-18-1 108 6 5.6 <.01 E1.43 -- 500 .003 LifetimTerbacil 5902-51-2 108 5 4.6 <.007 E.495 -- 90 .006 LifetimTrifluralin 1582-09-8 108 2 1.9 <.002 .014 -- 5 .003 Lifetim

1HBSL range corresponds to a 10-6 to 10-4 cancer risk range for unregulated carcinogens. 2BQmax values for unregulated compounds were calculated using the HBSL concentration, or for carcinogens, the low end of the HBSL concentration range and were round3The Practical Quantitation Level (PQL) is the lowest concentration of a constituent that can be reliably achieved among laboratories within specified limits of precision and 

laboratory operating conditions (New Jersey Department of Environmental Protection, 2001).

Table 5. Concentrations, detection frequencies, and HBSL values for unregulated pesticides detected in public-supply wells, domestic wells, and m

Long Island-New Jersey Study Unit.—Continued

Compound CASRN Number of samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL 

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New 

Jersey 

GWQC 

(μg/L)

HBSL 

concentration

or range1

(μg/L)

BQmax2 
Assessment of Ground-Water Quality in New Jersey 21

Volatile Organic Compounds

Of the 85 total VOCs analyzed in this study, 60 

(71 percent) were detected in at least one well type. Half of the 

60 detected VOCs are regulated, and half are unregulated. 

Twelve of the 30 detected, unregulated VOCs have humanhealth benchmarks, and 5 of these benchmarks are new HBSL 

values (fig. 3). 

In general, VOCs were detected in ground-water samples 

more frequently than pesticides, with VOC detection frequencies ranging from less than 1 percent to 100 percent of samples 

from a given well type (tables 6 and 7). Twenty-two VOCs were 

frequently detected (that is, detected in 10 percent or more of 

samples) in samples from at least one of the well types (tables 6 

and 7). All of the 22 frequently detected VOCs have humanhealth benchmarks (MCL or HBSL values). 

Tier 1 – Regulated Volatile Organic Compounds

Thirty regulated VOCs were detected (out of 33 regulated 

VOCs analyzed) in ground-water samples collected from any 

one of the three well types (table 6). Four regulated VOCs had 

maximum detected concentrations that exceeded their USEPA 

or New Jersey MCL values in public-supply and (or) domestic 

well samples (table 6; fig. 5). These four VOCs are 1,2-

dibromo-3-chloropropane, 1,2-dibromoethane, tetrachloroethylene (PCE), and trichloroethylene (TCE).

Measured concentrations of 1,2-dibromo-3-chloropropane 

in ground-water samples exceeded USEPA and New Jersey 

MCL values in the only sample in which it was detected (in 1 of 

82 domestic-well samples) (table 6; fig. 5). The maximum 

detected concentration of 0.481 μg/L exceeded the USEPA and 

New Jersey MCL values of 0.2 μg/L by slightly more than twofold. The MRL for 1,2-dibromo-3-chloropropane in domesticwell samples (0.214 μg/L) is slightly greater than the MCL 

value (table 6). Consequently, the possibility exists that some 

samples without detectable residues of 1,2-dibromo-3-chloropropane (as analyzed by this method) nonetheless could contain 

concentrations (greater than 0.2 but less than 0.214 μg/L) that 

exceed the MCL.

1,2-Dibromoethane was frequently detected (4 of 30 

samples) in public-supply wells but was not detected in samples 

from any of the other well types (table 6). The maximum 

detected concentration of 1,2-dibromoethane (0.066 μg/L) in 

public-supply wells exceeded the USEPA and New Jersey 

MCL of 0.05 μg/L (table 6; fig. 5). The other three detections of 

1,2-dibromoethane were at concentrations less than, but within 

a factor of 10 of, the MCL value; all four detected concentrations were estimated concentrations (table 6; fig. 5). Estimated 

concentrations have greater uncertainty in their quantitation, 

and this uncertainty also applies to the exceedance of a benchmark, particularly because the maximum detected concentration of 1,2-dibromoethane was close to the MCL (table 6; 

fig. 5). 

PCE was frequently detected in all well types, but maximum detected concentrations exceeded the USEPA MCL 

(5 μg/L) and New Jersey MCL (1 μg/L) values in only 1 of 30 

samples from public-supply wells (table 6; fig. 5). PCE was 

detected in 2 of 30 public-supply wells and 1 of 82 domestic 

wells at concentrations less than, but within a factor of 10 of, 

the USEPA MCL (fig. 5). PCE was detected in 9 of 30 publicsupply wells, 5 of 82 domestic wells, and 5 of 108 monitoring 

wells at concentrations less than, but within a factor of 10 of, the 

New Jersey MCL (fig. 5). 

TCE was frequently detected in all well types (table 6; 

fig. 5). Measured concentrations of TCE exceeded the USEPA 

MCL value (5 μg/L) in two samples (one sample each from the 

30 public-supply and 82 domestic wells), and exceeded the New 

Jersey MCL value (1 μg/L) in four samples (two samples each 

from the 30 public-supply and 82 domestic wells) (table 6; 

fig. 5). TCE was detected in one of 30 public-supply wells and 

in one of 82 domestic wells at concentrations less than, but 

within a factor of 10 of, the USEPA MCL (fig. 5). TCE was 

detected in 10 of 30 public-supply wells, 3 of 82 domestic wells, 

and 2 of 108 monitoring wells at concentrations less than, but 

within a factor of 10 of, the New Jersey MCL (fig. 5).

In addition to PCE and TCE, 17 other regulated VOCs 

were detected in all well types. None were detected at concentrations that exceed USEPA or New Jersey MCL values, however, and nine of these regulated VOCs were detected at concentrations at least 10-fold less than the MCL values (table 6). 

Ten regulated VOCs—benzene, chloroethylene, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloroethene, cis-1,2-dichloroethylene, 1,2-dichloropropane, methyl tert-butyl ether 

(MTBE), methylene chloride, and trichloromethane—were 

detected within a factor of 10 of their human-health benchmarks 

for at least one well type. All of these VOCs were present in 

both public-supply wells and domestic wells (water that is consumed as drinking water), except methylene chloride, which 

was detected only in domestic wells (table 6). 

Tier 2 – Unregulated Volatile Organic Compounds

Thirty unregulated VOCs were detected (out of 52 unregulated VOCs analyzed for) in ground-water samples collected 

from any well type, and measured concentrations were compared to HBSL values and to New Jersey GWQC and Interim 

Specific GWQC values, when available (tables 3 and 7). None 

of the unregulated VOCs were detected at concentrations that 

exceeded HBSL values (table 7). All unregulated VOCs were 

detected at concentrations at least 10-fold less than the HBSL 

values, and all but two VOCs (1-chloro-2-methylbenzene in 

public-supply wells and methyl chloride in monitoring wells) 

were detected at concentrations more than 100-fold less than the 

HBSL values. Isopropylbenzene and trichlorofluoromethane 

were the only unregulated VOCs with human-health benchmarks that were detected in all well types. 
22 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Table 6. Concentrations, detection frequencies, and MCL values for regulated VOCs detected in public-supply wells, domestic wells, 

and monitoring wells in the Long Island-New Jersey Study Unit.

[MCL, Maximum Contaminant Level; VOC, volatile organic compound; Bold type indicates measured concentrations exceed USEPA or New Jersey MCL 

values; CASRN, Chemical Abstracts Service Registry Number; MRL, Minimum Reporting Level; μg/L, micrograms per liter; USEPA, U.S. Environmental 

Protection Agency; BQmax, Benchmark Quotient = ratio of maximum detected concentration to USEPA (or New Jersey) MCL value; <, less than; --, not 

available; E, estimated value]

Compound CASRN

Number

of 

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

USEPA 

MCL 

(μg/L)

New 

Jersey 

MCL 

(μg/L)

BQmax1

Public-supply wells (30 wells)

Benzene 71-43-2 30 5 16.7 2<0.032, <0.1 0.212 5 1 0.04

Bromodichloromethane 75-27-4 30 3 10.0 <.048 .369 380 380 .005

Bromoform 75-25-2 30 2 6.7 <.1, 2<.104 .72 380 380 .009

Chlorobenzene 108-90-7 30 5 16.7 <.028 .128 100 50 .001

Chlorodibromomethane 124-48-1 30 2 6.7 <.18, 2<.182 .595 380 380 .007

Chloroethylene 75-01-4 30 1 3.3 <.11, 2<.112 E.054 2 2 .03

1,2-Dibromoethane 106-93-4 30 4 13.3 <.036 E.066 0.05 0.05 1

1,2-Dichlorobenzene 95-50-1 30 7 23.3 <.048 .729 600 600 .001

1,3-Dichlorobenzene 541-73-1 30 4 13.3 <.054 .104 -- 600 .0002

1,4-Dichlorobenzene 106-46-7 30 10 33.3 <.05 .178 75 75 .002

1,1-Dichloroethane 75-34-3 30 13 43.3 <.066 .563 -- 50 .01

1,2-Dichloroethane 107-06-2 30 2 6.7 <.13, 2<.134 .299 5 2 .06

1,1-Dichloroethene 75-35-4 30 16 53.3 <.044 .722 7 2 .1

cis-1,2-Dichloroethylene 156-59-2 30 15 50.0 <.038 12.1 70 70 .2

trans-1,2-Dichloroethylene156-60-5 30 4 13.3 <.032 .18 100 100 .002

1,2-Dichloropropane 78-87-5 30 3 10.0 <.068 1.42 5 5 .3

Methyl tert-butyl ether 1634-04-4 30 15 50.0 2<.112, <.17 1.41 -- 70 .02

Tetrachloroethylene 127-18-4 30 22 73.3 2<.038, <.1 71 5 1 10

Tetrachloromethane 56-23-5 30 5 16.7 <.088 E.031 5 2 .006

1,1,1-Trichloroethane 71-55-6 30 21 70.0 <.032 1.13 200 30 .006

Trichloroethylene 79-01-6 30 17 56.7 <.038 8.74 5 1 2

Trichloromethane 67-66-3 30 30 100.0 <.052 2.5 380 380 .03

Xylenes

(sum of isomers)4

1330-20-7 30 2 6.7 <.06, 2<.064 .241 10,000 1,000 .00002
Assessment of Ground-Water Quality in New Jersey 23

Table 6. Concentrations, detection frequencies, and MCL values for regulated VOCs detected in public-supply wells, domestic wells, 

and monitoring wells in the Long Island-New Jersey Study Unit.—Continued

Compound CASRN

Number

of 

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

USEPA 

MCL 

(μg/L)

New 

Jersey 

MCL 

(μg/L)

BQmax1

Domestic wells (82 wells

Benzene 71-43-2 82 3 3.7 <0.032, 2<0.1 0.926 5 1 0.2

Bromodichloromethane 75-27-4 82 2 2.4 <.048 .331 380 380 .004

Bromoform 75-25-2 82 1 1.2 <.1, 2<.104 E.044 380 380 .0006

Chlorobenzene 108-90-7 82 2 2.4 <.028 3.51 100 50 .04

Chloroethylene 75-01-4 82 1 1.2 <.11, 2<.112 .386 2 2 .2

1,2-Dibromo-3-chloropropane96-12-8 82 1 1.2 <.21, 2<.214 .481 0.2 0.2 2

1,2-Dichlorobenzene 95-50-1 82 2 2.4 <.048 .143 600 600 .0002

1,3-Dichlorobenzene 541-73-1 82 3 3.7 <.054 E.044 -- 600 .00007

1,4-Dichlorobenzene 106-46-7 82 5 6.1 <.05 1.15 75 75 .02

1,1-Dichloroethane 75-34-3 82 10 12.2 <.066 .416 -- 50 .008

1,2-Dichloroethane 107-06-2 82 1 1.2 <.13, 2<.134 .205 5 2 .04

1,1-Dichloroethene 75-35-4 82 6 7.3 <.044 E.031 7 2 .004

cis-1,2-Dichloroethylene 156-59-2 82 2 2.4 <.038 2.99 70 70 .04

1,2-Dichloropropane 78-87-5 82 2 2.4 <.068 E.073 5 5 .01

Ethylbenzene 100-41-4 82 1 1.2 <.03 .103 700 700 .0001

Methyl tert-butyl ether 1634-04-4 82 25 30.5 <.112, 

2<.166, <.17

30.2 -- 70 .4

Methylene chloride 75-09-2 82 2 2.4 <.38, 2<.382 .674 5 3 .1

Naphthalene 91-20-3 82 1 1.2 <.25 2.47 -- 300 .008

Styrene 100-42-5 82 1 1.2 <.042 E.005 100 100 .00005

Tetrachloroethylene 127-18-4 82 22 26.8 <.038, 

2<.102, <.1

.598 5 1 .1

Tetrachloromethane 56-23-5 82 2 2.4 <.088 .123 5 2 .02

Toluene 108-88-3 82 12 14.6 <.038, <.05, 

2

<.054

E.069 1,000 1,000 .00007

1,1,1-Trichloroethane 71-55-6 82 19 23.2 <.032 .883 200 30 0.004

Trichloroethylene 79-01-6 82 12 14.6 <.038 14.3 5 1 3

Trichloromethane 67-66-3 82 56 68.3 <.052 13.5 380 380 .2

Xylenes

(sum of isomers)4

1330-20-7 82 3 3.7 <.06,

2

<.064

.2356 10,000 1,000 .00002
24 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Monitoring wells (108 wells)

Benzene 71-43-2 108 3 2.8 <0.032, 

2<0.05

0.333 5 1 0.07

Bromodichloromethane 75-27-4 108 5 4.6 <.048, 2<.1 E.05 380 380 .0006

Bromoform 75-25-2 108 2 1.9 <.104, 2<.2 E.04 380 380 .0005

Chlorobenzene 108-90-7 108 3 2.8 <.028, 2<.05 E.012 100 50 .0001

Chlorodibromomethane 124-48-1 108 4 3.7 2<.1, <.182 E.04 380 380 .0005

1,2-Dichlorobenzene 95-50-1 108 7 6.5 <.048, 2<.05 E.086 600 600 .0001

1,3-Dichlorobenzene 541-73-1 108 4 3.7 2<.05, <.054 E.043 -- 600 .00007

1,4-Dichlorobenzene 106-46-7 108 7 6.5 <.05 .457 75 75 .006

1,1-Dichloroethane 75-34-3 108 9 8.3 2<.05, <.066 5.6 -- 50 .1

1,2-Dichloroethane 107-06-2 108 2 1.9 2<.05, <.134 .69 5 2 .1

1,1-Dichloroethene 75-35-4 108 10 9.3 <.044, 2<.1 .1 7 2 .01

cis-1,2-Dichloroethylene 156-59-2 108 3 2.8 <.038, 2<.05 .305 70 70 .004

1,2-Dichloropropane 78-87-5 108 1 0.9 2<.05, <.068 E.04 5 5 .008

Ethylbenzene 100-41-4 108 3 2.8 <.03, 2<.05 E.01 700 700 .00001

Methyl tert-butyl ether 1634-04-4 108 41 38.0 2<.1, <.112 43.8 -- 70 .6

Naphthalene 91-20-3 108 1 0.9 2<.2, <.25 E.01 -- 300 .00003

Styrene 100-42-5 108 1 0.9 <.042, 2<.05 E.003 100 100 .00003

Tetrachloroethylene 127-18-4 108 35 32.4 <.038, 2<.05 .946 5 1 .2

Toluene 108-88-3 108 8 7.4 <.038, 2<.05 .133 1,000 1,000 .0001

1,1,1-Trichloroethane 71-55-6 108 34 31.5 <.032, 2<.05 .64 200 30 .003

Trichloroethylene 79-01-6 108 11 10.2 <.038, 2<.05 .434 5 1 .09

Trichloromethane 67-66-3 108 88 81.5 2<.05, <.052 5.6 380 380 .07

Xylenes

(sum of isomers)4

1330-20-7 108 3 2.8 2<.05, <.064 E.03 10,000 1,000 .000003

1BQmax values for regulated compounds were calculated using USEPA MCL values. For compounds with New Jersey MCL values but no USEPA MCL 

values, the BQmax values were calculated using New Jersey MCL values. All BQmax values were rounded to one significant figure. 

2

MRL value that applies to the largest number of samples (when more than one MRL exists for a given compound).

3Under the USEPA 1998 final rule for disinfectants and disinfection byproducts, the total for trihalomethanes is 80 μg/L (U. S. Environmental Protection 

Agency, 2004).

4Sum of Xylenes = m- & p-xylene (CASRN 108-38-3 & 106-42-3) + o-xylene (CASRN 95-47-6). 

Table 6. Concentrations, detection frequencies, and MCL values for regulated VOCs detected in public-supply wells, domestic wells, 

and monitoring wells in the Long Island-New Jersey Study Unit.—Continued

Compound CASRN

Number

of 

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

USEPA 

MCL 

(μg/L)

New 

Jersey 

MCL 

(μg/L)

BQmax1
Assessment of Ground-Water Quality in New Jersey 25

Figure 5. Distributions of concentrations and detection frequencies of VOCs detected at concentrations that met or

exceeded human-health benchmarks in at least one well type in the Long Island-New Jersey Study Unit.

30 0

82

108

82

108

82

30

30

108

1.2

0

13.3

0

0

73.3

26.8

32.4

EXPLANATION

Public-supply wells

Domestic wells

Monitoring wells

Detected concentration

Estimated concentration 

U.S. Environmental Protection Agency

 Maximum Contaminant Level 

New Jersey Maximum Contaminant Level

Minimum Reporting Level*

Multi-colored lines indicate multiple benchmarks

 at the same value 

The MRL for some compounds varies for samples in a given well type. The most commonly reported MRL

for each well type is shown in this figure.

*

CONCENTRATION, IN MICROGRAMS PER LITER

102 101 100 10-1 10-2 10-3 10-4

1,2-Dibromo-3-chloropropane

1,2-Dibromoethane

Tetrachloroethylene (PCE)

[VOC, volatile organic compound; n, number of samples; %, percent; MRL, Minimum Reporting Level] 

82

30

108

56.7

14.6

10.2

Trichloroethylene (TCE)

Detection

frequency

(%)

n
Table 7. Concentrations, detection frequencies, and HBSL values for unregulated VOCs detected in public-supply wells, domestic wells, and monitor

New Jersey Study Unit.

[HBSL, Health-Based Screening Level; VOC, volatile organic compound; Bold type indicates measured concentration exceeds New Jersey Ground-Water Quality Criteria (GW

Abstracts Service Registry Number; MRL, Minimum Reporting Level; μg/L, micrograms per liter; BQmax, Benchmark Quotient = ratio of maximum detected concentration to 

--, not available; Lifetime HA, Lifetime Health Advisory; E, estimated value; IRIS, Integrated Risk Information System; RfD, oral reference dose; PQL, practical quantitation leProtection Agency]

Compound CASRN

Number

of

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New Jersey 

GWQC

(μg/L)

HBSL 

concentration

(μg/L)

BQmax1 

Public-supply wells (30 wells)

1-Chloro-2-methylbenzene 95-49-8 30 2 6.7 <0.042 2.73 -- 100 0.03 LDibromomethane 74-95-3 30 1 3.3 <.05 E.014 -- -- -- N1,3-Dichloropropane 142-28-9 30 1 3.3 2<.116, <.12 E.056 -- -- -- NDiisopropylether 108-20-3 30 1 3.3 <.098 .172 320,000 -- -- NEthyl ether 60-29-7 30 1 3.3 <.17 .814 31,000 1,000 .0008 L1-Ethyl-2-methylbenzene 611-14-3 30 1 3.3 <.1 .174 -- -- -- NIsopropylbenzene 98-82-8 30 2 6.7 <.032 E.027 3800 700 .00004 L1,1,1,2-Tetrachloroethane 630-20-6 30 1 3.3 <.044 E.011 10 70 .0002 L1,2,3,4-Tetramethylbenzene 488-23-3 30 1 3.3 <.23 E.029 -- -- -- NTrichlorofluoromethane 75-69-4 30 6 20.0 <.09, 2<.092 .665 32,000 2,000 .0003 L1,2,3-Trichloropropane 96-18-4 30 1 3.3 2<.07, <.16 .164 3.005

4PQL=2

540 .004 L

1,2,3-Trimethylbenzene 526-73-8 30 1 3.3 <.12, 2<.124 .186 -- -- -- N1,2,4-Trimethylbenzene 95-63-6 30 1 3.3 <.056 E.055 -- -- -- N1,3,5-Trimethylbenzene 108-67-8 30 1 3.3 <.044 E.017 -- -- -- N
Table 7. Concentrations, detection frequencies, and HBSL values for unregulated VOCs detected in public-supply wells, domestic wells, and monitor

New Jersey Study Unit.—Continued

Compound CASRN

Number

of

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New Jersey 

GWQC

(μg/L)

HBSL 

concentration

(μg/L)

BQmax1 

Domestic wells (82 wells)

Acetone 67-64-1 82 1 1.2 2<4.9, <5 E6.88 700 6,000 0.001 n-Butylbenzene 104-51-8 82 1 1.2 2<.186, <.19 E.036 -- -- -- Carbon disulfide 75-15-0 82 8 9.8 <.08, 2<.37 .216 3800 700 .0003 Chloroethane 75-00-3 82 1 1.2 <.12 .689 -- -- -- Dichlorodifluoromethane 75-71-8 82 7 8.5 <.096, 2<.138, <.14 E.95 31,000 1,000 .001 Diisopropylether 108-20-3 82 3 3.7 <.098 .159 320,000 -- -- Ethyl ether 60-29-7 82 1 1.2 <.17 3.94 31,000 1,000 .004 1-Ethyl-2-methylbenzene 611-14-3 82 1 1.2 <.1 .255 -- -- -- Isopropylbenzene 98-82-8 82 1 1.2 <.032 .389 3800 700 .0006 Methyl chloride 74-87-3 82 3 3.7 <.25, 2<.254 E.02 30 30 .0007 Methyl ethyl ketone 78-93-3 82 1 1.2 <1.6, 2<1.65 3.38 300 4,000 .0008 Methyl iodide 74-88-4 82 1 1.2 <.076, 2<.208, 

<.21

E.13 -- -- -- 

tert-pentyl methyl ether 994-05-8 82 1 1.2 <.11, 2<.112 E.09 -- -- -- n-Propylbenzene 103-65-1 82 1 1.2 <.042 E.074 -- -- -- Tetrahydrofuran 109-99-9 82 2 2.4 <1.15, 2<8.79, 

<9

7.97 310

4PQL=20

-- -- 

1,2,3,4-Tetramethylbenzene 488-23-3 82 1 1.2 <.23 .252 -- -- -- 
Domestic wells (82 wells)—Continued

1,1,2-Trichloro-1,2,2-trifluoroethane 76-13-1 82 1 1.2 <0.032 E0.015 -- 200,000 0.00000008 Trichlorofluoromethane 75-69-4 82 2 2.4 <.09, 2<.092 1.06 32,000 2,000 .0005 1,2,4-Trimethylbenzene 95-63-6 82 1 1.2 <.056 E.056 -- -- -- 1,3,5-Trimethylbenzene 108-67-8 82 1 1.2 <.044 E.051 -- -- -- 

Monitoring wells (108 wells)

Acetone 67-64-1 108 3 2.8 <4.9, 2<5 31.4 700 6,000 0.005 Bromobenzene 108-86-1 108 1 0.9 <.036, 2<.05 E.0088 -- -- -- n-Butylbenzene 104-51-8 108 1 0.9 2<.05, <.186 E.019 -- -- -- sec-Butylbenzene 135-98-8 108 4 3.7 <.048, 2<.05 .281 -- -- -- tert-Butylbenzene 98-06-6 108 3 2.8 2<.05, <.096 E.08 -- -- -- Carbon disulfide 75-15-0 108 41 38.0 2<.05, <.08 E.17 3800 700 .0002 1-Chloro-2-methylbenzene 95-49-8 108 1 0.9 <.042, 2<.05 E.007 -- 100 .00007 Chloroethane 75-00-3 108 2 1.9 2<.1, <.12 .146 -- -- -- Dichlorodifluoromethane 75-71-8 108 5 4.6 <.096, 2<.2 E4.3 31,000 1,000 .004 Diisopropylether 108-20-3 36 1 2.8 <.098 .485 320,000 -- -- 1-Ethyl-2-methylbenzene 611-14-3 108 1 0.9 2<.05, <.1 E.025 -- -- -- 

Table 7. Concentrations, detection frequencies, and HBSL values for unregulated VOCs detected in public-supply wells, domestic wells, and monitor

New Jersey Study Unit.—Continued

Compound CASRN

Number

of

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New Jersey 

GWQC

(μg/L)

HBSL 

concentration

(μg/L)

BQmax1 
Monitoring wells (108 wells)—Continued

Isopropylbenzene 98-82-8 108 1 0.9 <0.032, 2<0.05 E0.042 3800 700 0.00006 Methyl chloride 74-87-3 108 15 13.9 2<.2, <.254 E1.9 30 30 .06 Methyl ethyl ketone 78-93-3 108 4 3.7 <1.65, 2<5 7.06 300 4,000 .002 Methyl iodide 74-88-4 108 6 5.6 2<.05, <.076 E.17 -- -- -- 1-Methyl-4-isopropylbenzene 99-87-6 108 5 4.6 2<.05, <.11 .71 -- -- -- tert-Pentyl methyl ether 994-05-8 108 3 2.8 2<.1, <.112 E.02 -- -- -- Tetrahydrofuran 109-99-9 108 2 1.9 <1.15, 2<5 E2.66 310

4PQL=20

-- -- 

1,1,2-Trichloro-1,2,2-

Trifluoroethane

76-13-1 108 1 0.9 <.032, 2<.05 .12 -- 200,000 .0000006 

Trichlorofluoromethane 75-69-4 108 11 10.2 <.092, 2<.1 17 32,000 2,000 .008 1,2,4-Trimethylbenzene 95-63-6 108 1 0.9 2<.05, <.056 E.003 -- -- -- 

1BQmax values for unregulated compounds were calculated using the HBSL concentration and were rounded to one significant figure.2MRL value that applies to the largest number of samples (when more than one MRL exists for a given compound). 3New Jersey Interim Specific GWQC based on the methodologies and risk assessment approach contained in the ground-water quality standards.4The Practical Quantitation Level (PQL) is the lowest concentration of a constituent that can be reliably achieved among laboratories within specified limits of precision and 

laboratory operating conditions (New Jersey Department of Environmental Protection, 2001).

5HBSL based on Lifetime HA value; 1,2,3-trichloropropane has been found to cause cancer in laboratory animals and an IRIS profile is currently being developed by USEPA 

Environmental Protection Agency, written commun., 2003). 

Table 7. Concentrations, detection frequencies, and HBSL values for unregulated VOCs detected in public-supply wells, domestic wells, and monitor

New Jersey Study Unit.—Continued

Compound CASRN

Number

of

samples

Number of 

samples 

with 

detections

Percentage 

of samples 

with 

detections

MRL

(μg/L)

Maximum 

detected 

concentration

(μg/L)

New Jersey 

GWQC

(μg/L)

HBSL 

concentration

(μg/L)

BQmax1 
30 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

One unregulated VOC, 1,2,3-trichloropropane, was 

detected in 1 of 30 samples from public-supply wells at a concentration that exceeded the New Jersey Interim Specific 

GWQC value (0.005 μg/L) (table 7). New Jersey’s Interim Specific GWQC values are health-based criteria established by 

NJDEP for chemicals without specific GWQC (table 2). The 

maximum detected concentration of 1,2,3-trichloropropane, 

however, was approximately 200-fold less than the HBSL for 

this compound (40 μg/L), which was set equal to the USEPA 

Lifetime HA value. The HBSL and Interim Specific GWQC 

values for 1,2,3-trichloropropane differ because they are based 

on two different toxicity values. The HBSL is based on the oral 

reference dose value published in the USEPA IRIS database. 

Carcinogenicity data for 1,2,3-trichloropropane are not currently available in the IRIS database; however, an IRIS profile 

is being developed by USEPA because 1,2,3-trichloropropane 

has been found to cause cancer in laboratory animals (J.M. 

Donohue, U.S. Environmental Protection Agency, written commun., 2003). In contrast, the New Jersey Interim Specific 

GWQC value was calculated using an oral cancer slope factor

value from USEPA HEAST (G.B. Post, New Jersey Department of Environmental Protection, written commun., 2003). 

1,2,3-Trichloropropane is listed in HEAST as a B2 carcinogen 

on the basis of the results of a 1993 National Toxicology Program study (National Toxicology Program, 1993), which concluded that there was clear evidence of carcinogenicity in rats 

and mice. 

Eighteen detected unregulated VOCs have no humanhealth benchmarks (Lifetime HA, RSD, HBSL, GWQC, or 

Interim Specific GWQC values) to use for comparison against 

measured concentrations (table 7; Appendix 3). These 18 VOCs 

do not have human-health benchmarks because the toxicity data 

needed to calculate HBSL values are lacking. None of these 

18 VOCs were frequently detected, but 3 (diisopropylether, 

1-ethyl-2-methylbenzene, and 1,2,4-trimethylbenzene) were 

detected in all well types (table 7). 

Step 2: Contaminants of Potential HumanHealth Concern Identified

Pesticides and VOCs were identified as being of potential 

human-health concern if maximum detected concentrations 

were within a factor of 10 of their human-health benchmarks 

(that is, BQmax ≥ 0.1) for any well type (see section “Identify 

Contaminants of Potential Human-Health Concern Using 

Benchmark Quotients”). BQmax values were calculated for all 

detected pesticides and VOCs with human-health benchmarks 

(tables 4-7). Twenty contaminants (6 pesticides and 14 VOCs) 

were identified as being of potential human-health concern 

because they had BQmax values ≥ 0.1 (BQmax range, 0.1-

3,000) for at least one well type (table 8; figs. 6 and 7). 

Most detected contaminants with human-health benchmarks (30 of 36 pesticides and 27 of 41 VOCs) were detected at 

concentrations more than10-fold less than human-health benchmarks (that is, BQmax < 0.1). More than half (41 of 77, or 

53 percent) of detected pesticides and VOCs with human-health 

benchmarks had BQ values < 0.01 (that is, more than 100-fold 

less than human-health benchmarks) (tables 4-7).

Step 3: Occurrence of Contaminants of 

Potential Human-Health Concern Interpreted

Interpretation of the occurrence of contaminants of potential human-health concern (that is, those contaminants with BQ 

values ≥ 0.1) entails the consideration of five primary factors: 

(1) magnitude of the BQ values, (2) detection frequency, 

(3) MRL considerations, (4) well type and use of water, and 

(5) sources and physicochemical properties of the contaminants.

Magnitude of BQ Values and Detection 

Frequency

BQmax and BQmed-det values and detection frequencies 

for each of the 20 contaminants with BQmax ≥ 0.1 are listed in 

table 8 for all three well types. Because comparisons between 

maximum detected concentrations and human-health benchmarks (BQmax) may be conservative, the distributions of all 

detections of these 20 contaminants were examined. The distributions of BQ values and the detection frequencies for the 6 

pesticides and 14 VOCs of potential human-health concern are 

shown in figures 6 and 7, respectively, and are discussed further 

in section “Patterns of Occurrence.” Thirteen of the 20 contaminants of potential human-health concern were frequently 

detected in at least one well type (table 8).

Seven of the 20 contaminants of potential human-health 

concern (dieldrin, dinoseb, diuron, 1,2-dibromo-3-chloropropane, 1,2-dibromoethane, PCE, and TCE) had maximum 

detected concentrations that met or exceeded human-health 

benchmarks (that is, BQmax ≥ 1) for at least one well type 

(table 8). The remaining 13 contaminants of potential humanhealth concern had measured concentrations that were less than, 

but within a factor of 10 of, the applicable human-health benchmarks (that is, 1 > BQmax ≥ 0.1) for all well types (table 8). 

Only 2 of the 20 contaminants of potential human-health 

concern (dieldrin and 1,2-dibromo-3-chloropropane) had 

BQmed-det values ≥ 1 for at least one well type, indicating that 

the median of detected concentrations met or exceeded humanhealth benchmarks. For dieldrin, this was a result of measured 

concentrations exceeding the low end of the HBSL concentration range in most of the samples in which it was detected 

(figs. 4 and 6). In contrast, 1,2-dibromo-3-chloropropane was 

detected in only one sample from domestic wells, so its 

BQmed-det value is the same as its BQmax value (figs. 5 and 

7). The median of detected concentrations were within a factor 

of 10 of human-health benchmarks (1 > BQmed-det ≥ 0.1) for 

six additional contaminants of potential human-health concern 

(dinoseb, heptachlor epoxide, diuron, chloroethylene, 1,2-

dibromoethane, and methylene chloride) for at least one well 

type; most of these six contaminants had low detection frequencies, hence the BQmed-det values were similar (or equivalent) 

to the BQmax values.
Table 8. Detection frequencies and BQmax and BQmed-det values for pesticides and VOCs detected at concentrations within a factor of 10 of humasamples from public-supply wells, domestic wells, and (or) monitoring wells in the Long Island-New Jersey Study Unit. [Each compound has a BQmax greater than or equal to 0.1 in at least one well type; BQmax, Benchmark Quotient = ratio of maximum detected concentration to human-health b

Benchmark Quotient = ratio of median of detected concentrations to human-health benchmark value; VOC, volatile organic compound; Bold red type indicates Benchmark Quo

type indicates 0.1 < BQ < 1; >, greater than or equal to; <, less than or equal to; <, less than; CASRN, Chemical Abstracts Service Registry Number; n, number of samples; %, p

ND, not detected] 

Compound CASRN Regulated or unregulated

Public-supply wells Domestic wells M

n

Detection

frequency 

(%)

BQmax BQmed- det n Detection frequency (%) BQmax BQmed- det n Det

freq

(

Pesticides

Atrazine 1912-24-9 Regulated 30 30.0 0.01 0.006 81 9.9 0.03 0.002 108 47Dinoseb 88-85-7 Regulated NA NA NA NA 60 ND ND ND 72 5Heptachlor epoxide 1024-57-3 Regulated NA NA NA NA NA NA NA NA 69 5Simazine 122-34-9 Regulated 30 26.7 .06 .003 81 8.6 .07 .004 108 38Dieldrin 60-57-1 Unregulated 30 26.7 20 4 81 3.7 10 9 108 18Diuron 330-54-1 Unregulated NA NA NA NA 60 3.3 1 .5 72 6

VOCs

Benzene 71-43-2 Regulated 30 16.7 0.04 0.006 82 3.7 0.2 0.004 108 2Chloroethylene 75-01-4 Regulated 30 3.3 .03 .03 82 1.2 .2 .2 108 ND 1,2-Dibromo-3-chloropropane 96-12-8 Regulated 30 ND ND ND 82 1.2 2 2 108 ND 1,2-Dibromoethane 106-93-4 Regulated 30 13.3 1 .5 82 ND ND ND 108 ND 1,1-Dichloroethane 75-34-3 Regulated 30 43.3 .01 .0007 82 1.2 .04 .04 108 81,2-Dichloroethane 107-06-2 Regulated 30 6.7 .06 .05 82 1.2 .04 .04 108 1,1-Dichloroethene 75-35-4 Regulated 30 53.3 .1 .005 82 7.3 .004 .003 108 9cis-1,2-Dichloroethylene 156-59-2 Regulated 30 50.0 .2 .003 82 2.4 .04 .02 108 21,2-Dichloropropane 78-87-5 Regulated 30 10.0 .3 .02 82 2.4 .01 .009 108 Methyl tert-butyl ether 

(MTBE)

1634-04-4 Regulated 30 50.0 .02 .004 82 30.5 .4 .004 108 38

Methylene chloride 75-09-2 Regulated 30 ND ND ND 82 2.4 .1 .1 108 ND Tetrachloroethylene 

(PCE)

127-18-4 Regulated 30 73.3 10 .02 82 26.8 .1 .005 108 32

Trichloroethylene 

(TCE)

79-01-6 Regulated 30 56.7 2 .04 82 14.6 3 .01 108 10

Trichloromethane 67-66-3 Regulated 30 100 .03 .002 82 68.3 .2 .002 108 8
32 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Figure 6. Distributions of Benchmark Quotient values and detection frequencies, by well type, for pesticides 

detected at concentrations within a factor of 10 of their human-health benchmarks in the Long IslandNew Jersey Study Unit.

30 30.0

81

108

81

108

60

NA

30

72

9.9

47.2

26.7

3.7

18.5

NA

0

5.6

EXPLANATION

*

BENCHMARK QUOTIENT VALUE

104 102 103 101 100 10-1 10-2 10-3 10-4

Atrazine

Dieldrin

60

NA

72

NA

3.3

6.9

NA

NA

69

NA

NA

5.8

81

30

108

26.7

8.6

38.0

Dinoseb

Diuron*

Heptachlor epoxide

Simazine

Benchmark Quotient value = 1 

Benchmark Quotient value = 0.1 

Ratio of MRL to

 USEPA MCL or HBSL 

Public-supply wells

Domestic wells

Monitoring wells

[BQ, Benchmark Quotient = ratio of detected concentration to human-health benchmark value; n, number of wells; %, percent;

NA, not analyzed; MRL, Minimum Reporting Level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum

Contaminant Level; HBSL, Health-Based Screening Level; Lifetime HA, Lifetime Health Advisory; μg/L, micrograms per liter] 

Diuron has a USEPA Lifetime HA (10 μg/L). Diuron also has a new HBSL range (2-200 μg/L)

based on updated toxicity data published by USEPA Office of Pesticide Programs. The BQ

values for diuron in this figure were calculated using an HBSL of 2 μg/L. 

Detection

frequency

(%)

n
Assessment of Ground-Water Quality in New Jersey 33

Figure 7. Distributions of Benchmark Quotient values and detection frequencies, by well type, for VOCs detected at 

concentrations within a factor of 10 of their human-health benchmarks in the Long Island-New Jersey Study Unit.

16.7

3.7

2.8

3.3

1.2

0

0

1.2

0

EXPLANATION

BENCHMARK QUOTIENT VALUE

101 100 10-1 10-2 10-3 10-4 10-5

13.3

0

0

43.3

12.2

8.3

6.7

1.2

1.9

53.3

7.3

9.3

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

30

82

108

Benzene

Chloroethylene

1,2-Dibromo-3-chloropropane

1,2-Dibromoethane

1,1-Dichloroethane

1,2-Dichloroethane

1,1-Dichloroethene Trichloromethane

Benchmark Quotient value = 1 

Benchmark Quotient value = 0.1 

Ratio of MRL to USEPA MCL 

Public-supply wells

Domestic wells

Monitoring wells

[BQ, Benchmark Quotient = ratio of detected concentration to human-health benchmark value; VOC, volatile organic compound; n, number of

wells; %, percent; MRL, Minimum Reporting Level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level] 

cis-1,2-Dichloroethylene

1,2-Dichloropropane

Methyl tert-butyl ether (MTBE)

Methylene chloride

Tetrachloroethylene (PCE)

Trichloroethylene (TCE)

Detection

frequency

(%) n

50.0

2.4

2.8

10.0

2.4

0.9

50.0

30.5

38.0

BENCHMARK QUOTIENT VALUE

101 100 10-1 10-2 10-3 10-4 10-5

0

2.4

0

73.3

26.8

32.4

56.7

14.6

10.2

100

68.3

81.5

Detection

frequency

(%) n
34 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

MRL Considerations

For 18 of the 20 contaminants of potential human-health 

concern, analytical MRL values were less than their HBSL or 

MCL values (tables 1 and 4-6), enabling the quantitation of 

these contaminants at concentrations that are relevant to human 

health. The exceptions are 1,2-dibromoethane and 1,2-dibromo3-chloropropane, which had MRL values greater than or near 

their MCL values, resulting in benchmark exceedance rates and 

BQ values that have higher uncertainty than those for the other 

measured contaminants.

Well Type and Use of Water

Well type affects potential human exposure (through 

possible drinking-water consumption) to contaminants present 

in the ground water. Each of the well types considered in this 

study (see section “Well Networks”) provides water-quality 

data of varying relevance to potential human-health concerns; 

water-quality data from each well type are discussed separately 

below. In this study, ground-water quality data were collected 

from multiple aquifers and land-use areas, in addition to multiple well types. Domestic-well samples were collected from 

three sampling regions (aquifers) and monitoring-well samples 

were collected from four land-use areas. In this study, therefore, 

the occurrence of contaminants is discussed as a function of 

well type, aquifer, and land use. The occurrence of three pesticides (dieldrin, dinoseb, and diuron) and four VOCs (1,2-

dibromo-3-chloropropane, 1,2-dibromoethane, PCE, and TCE) 

with maximum detected concentrations that met or exceeded 

human-health benchmarks is summarized by well type, aquifer, 

and land use in table 9 and is discussed further in the following 

three sections. 

Occurrence by Well Type

The patterns of pesticide and VOC detection frequencies 

in relation to BQmax values varied considerably among well 

types (figs. 8a and 8b). Pesticides and VOCs tended to have 

higher detection frequencies in public-supply wells than in the 

other well types. In public-supply wells, one pesticide (dieldrin) 

and three VOCs (1,2-dibromoethane, PCE, and TCE) were frequently detected and detected at concentrations that exceeded 

their human-health benchmark values (BQmax ≥ 1) (figs. 8a 

and 8b). Three additional VOCs (1,1-dichloroethene, cis-1,2-

dichloroethylene, and 1,2,-dichloropropane) were frequently 

detected in public-supply wells and had BQmax values greater 

than 0.1 and less than 1 (fig. 8b). 

In domestic wells, two pesticides (diuron and dieldrin) 

were detected at concentrations that met or exceeded their 

human-health benchmarks, but both were detected infrequently 

(fig. 8a). Only TCE was both frequently detected in domesticwell samples and exceeded its benchmark (BQmax = 3) in 

domestic wells. Measured concentrations of 1,2-dibromo-3-

chloropropane exceeded its benchmark in domestic wells 

(BQmax = 2), but was not frequently detected (fig. 8b). 

Detection frequencies of both pesticides and VOCs were 

higher in public-supply wells than in domestic wells, most 

likely because public-supply wells withdraw larger volumes of 

water from the aquifer. Consequently, public-supply wells capture recharge from relatively large contributing areas at the land 

surface (Stackelberg and others, 2000). In contrast, small volumes of water recharged from relatively small areas at the land 

surface are withdrawn at low rates from domestic wells.

More pesticides and VOCs combined were detected at 

concentrations within a factor of 10 of human-health benchmarks (BQmax ≥ 0.1) in domestic wells (10 compounds) than 

in public-supply wells (7 compounds) (figs. 8a and 8b). More 

pesticides were analyzed in samples from domestic wells (85) 

than public-supply wells (47); however, considering only compounds analyzed in samples from both well types, domestic 

wells contained more compounds with a BQmax greater than or 

equal to 0.1 (9 compounds) than public-supply wells (7 compounds). This finding is important because water from domestic 

wells typically is consumed directly without treatment.

Because ground water from both public-supply wells and 

domestic wells currently is used as drinking water, comparisons 

among the BQmax values for pesticides and VOCs were made 

between these two well types in the same aquifer, the Kirkwood-Cohansey aquifer system (figs. 9a and 9b). Eight pesticides and 19 VOCs with human-health benchmarks were 

detected in samples from the 30 public-supply wells and the 30 

domestic wells in the Kirkwood-Cohansey aquifer system. 

Analysis of the paired BQmax values for these 8 pesticides and 

19 VOCs using the Mann-Whitney test indicated that BQmax 

values for one well type were not significantly different from 

the BQmax values for the other well type. The results of these 

statistical tests were the same when pesticides and VOCs that 

were detected in only one of the two well types were included. 

In monitoring wells, only one pesticide (dieldrin) was 

frequently detected and detected at concentrations that 

exceeded its benchmark value (BQmax = 3,000). Two additional pesticides (diuron and dinoseb) were not frequently 

detected but were detected at concentrations that met or 

exceeded their human-health benchmarks (BQmax = 1 and 6, 

respectively) (fig. 8a). No VOCs were detected in monitoringwell samples at concentrations that exceeded their benchmark 

values. Seven contaminants (three pesticides and four VOCs) 

were detected in monitoring-well samples at concentrations less 

than, but within a factor of 10 of, human-health benchmarks 

(1 > BQmax ≥ 0.1) (figs. 8a and 8b). 

One pesticide (deethylatrazine) was frequently detected in 

all well types, but it has no human-health benchmark with 

which to compare measured concentrations. No VOCs without 

human-health benchmarks were frequently detected in any well 

type. 
Table 9. Frequency of detection and frequency of exceedance of human-health benchmarks for pesticides and VOCs detected at concentrations tha

health benchmarks in samples by well type, sampling region, and land use in the Long Island-New Jersey Study Unit.

[Domestic-well data are presented by sampling region; monitoring-well data are presented by land-use category; VOC, volatile organic compound; Bold type indicates BQmax > Quotient = ratio of maximum detected concentration to human-health benchmark value; n, number of wells sampled; %, percent; PCE, tetrachloroethylene; TCE, trichloroethyleNA, not analyzed; μg/L, micrograms per liter; HBSL, Health-Based Screening Level; U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level]

Well type Sampling region Land use and n wells

% Detected Pesticides 

% Met or exceeded 

human-health 

benchmark

Dieldrin Dinoseb Diuron 1,2-Dibromo-3- chloropropane 

Dib

e

Public-supply 

wells

Kirkwood-Cohansey Aquifer System -- % Detected 26.7 NA NA 0 

n=30 % BQmax >1 23.3 NA NA 0 

Domestic wells Kirkwood-Cohansey Aquifer System -- % Detected 0 0 6.7 3.3 

n=30 % BQmax >1 0 0 13.3 3.3 

New England Physiographic Province -- % Detected 3.3 0 0 0 

n=30 % BQmax >1 3.3 0 0 0 

Piedmont Physiographic Province -- % Detected 9.5 NA NA 0 

n=22 % BQmax >1 9.5 NA NA 0 

Shallow 

monitoringwells

Kirkwood-Cohansey Aquifer System Agricultural

n=15

% Detected 6.7 20 13.3 0 % BQmax >1 6.7 13.3 0 0 

New urban 

n=30

% Detected 26.7 0 0 0 % BQmax >1 26.7 0 0 0 

Old urban 

n=20

% Detected 15 30 321.4 0 % BQmax >1 10 30 37.1 0 

Undeveloped

n=13

% Detected 0 7.7 0 0 % BQmax >1 0 0 0 0 

Moderate-depth 

monitoring wells

Kirkwood-Cohansey Aquifer System New urban

n=14

% Detected 21.4 NA NA 0 % BQmax >1 21.4 NA NA 0 

Old urban 

n=16

% Detected 31.2 NA NA 0 % BQmax >1 31.2 NA NA 0 

1BQmax = 1 for diuron in Kirkwood-Cohansey aquifer domestic wells; diuron was detected at a concentration of 1.9 μg/L, nearly equal to the low end of its HBSL range (2 2TCE exceeded USEPA MCL (5 μg/L) 4.5% of the time and New Jersey MCL (1 μg/L) 9.1% of the time in domestic wells in the Piedmont Physiographic Province.3n =14 for dinoseb and diuron in old urban shallow monitoring wells.
Figure 8. Detection frequencies and Maximum Benchmark Quotient values for (a) pesticides and (b) VOCs detected in public-supply wells, dom

wells in the Long Island-New Jersey Study Unit.

Public-supply wells Domestic wells Mon

MAXIMUM BENCHMARK QUOTIENT VALUE

DETECTION FREQUENCY, IN PERCENT DETECTION FREQUENCY, IN PERCENT

104 102 100 10-2 10-4 10-6 10-8 104 102 100 10-2 10-4 10-6 10-8 

10-4 10-6 10-8

104 102 100 10-2 10-4 10-6 10-8 104 102 100 10-2 10-4 10-6 10-8 

10-4 10-6 10-8

MAXIMUM BENCHMARK QUOTIENT VALUE MAXIMUM BENC

(a)

Pesticides

(b)

VOCs

EXPLANATION

Maximum Benchmark Quotient value = 1 Maximum Benchmark Quotient value = 0.1 Detection frequency = 10 percent 

Public-supply wellsDomestic wellsMonitoring wells

* Diuron has a USEPA Lifetime HA (10 μg/L). Diu

(2-200 μg/L) based on updated toxicity data pubPesticide Programs. The BQmax values for diurusing an HBSL of 2 μg/L. 

[BQmax, Maximum Benchmark Quotient = ratio of maximum detected concentration to human-health benchmark value; VOC, volatile organic compound; compoundlabeled; , greater than or equal to; 1,2-DBCP, 1,2-dibromo-3-chloropropane; 1,2-DBA, 1,2-dibromoethane; 1,1-DCA, 1,1-dichloroethane; 1,2-DCA, 1,2-dichloroethanecis-1,2-DCE, cis-1,2-dichloroethylene; DCM, dichloromethane (methylene chloride); 1,2-DCP, 1,2-dichloropropane; MTBE, methyl tert-butyl ether; PCE, tetrachloroethy%, percent; USEPA, U.S. Environmental Protection Agency; Lifetime HA, Lifetime Health Advisory; μg/L, micrograms per liter; HBSL, Health-Based Screening Level] 

Heptachlor eHeptachlor e

Diuron* Diuron*

Dieldrin Dieldrin

MTBE

PCE

TCE DCM Benzene Benzene

1,2-DBCP 1,2-DBCP

Chloroethylene Chloroethylene

Trichloromethane Trichloromethane

Dieldrin Dieldrin

PAC

TCE 1,1-DCE 1,1-DCE

cis-1,2-DCE -1,2-DCE

1,2-DBA 1,2-DBA

1,2-DCP 1,2-DCP

Heptachlor e

Diuron*

Dieldrin

MTBE

PCE

TCE DCM Benzene

1,2-DBCP

Chloroethylene

Trichloromethane

Dieldrin

PCE

TCE

1,1-DCE

cis-1,2-DCE

1,2-DBA

1,2-DCP

100

80604020

0

100

80604020

0

100

80604020

0

100

80604020

0

100

80604020

0

100

80604020

0
Assessment of Ground-Water Quality in New Jersey 37

Figure 9. Relation between Maximum Benchmark Quotient values for (a) pesticides and (b) VOCs detected in

public-supply wells and those in domestic wells in the Kirkwood-Cohansey aquifer system, New Jersey.

EXPLANATION

MAXIMUM BENCHMARK QUOTIENT VALUE,

DOMESTIC WELLS (n=30)

MAXIMUM BENCHMARK QUOTIENT VALUE,

PUBLIC-SUPPLY WELLS (n=30)

102 10-5

10-5

10-4

10-3

10-2

10-1

100

101

102

101 100 10-1 10-2 10-3 10-4

Maximum Benchmark Quotient value = 0.1 

[BQmax, Maximum Benchmark Quotient = ratio of maximum detected concentration to human-health benchmark value; VOC,

volatile organic compound; compounds with BQmax values 0.1 are labeled; , greater than or equal to; n, number of

samples; PCE, tetrachloroethylene; TCE, trichlorethylene] 

1 to 1 line

MAXIMUM BENCHMARK QUOTIENT VALUE,

DOMESTIC WELLS (n=30)

MAXIMUM BENCHMARK QUOTIENT VALUE,

PUBLIC-SUPPLY WELLS (n=30)

102 10-5

10-5

10-4

10-3

10-2

10-1

100

101

102

101 100 10-1 10-2 10-3 10-4

1 to 1 line

7 VOCs

below line (on the line)

11 VOCs

above line

7 pesticides

below line

1 pesticide

above line

(a)

Pesticides

(b)

VOCs

PCE

Benzene

Chloroethylene

TCE

1,2-Dichloropropane

1,1-Dichloroethene

cis-1,2-Dichloroethylene
38 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Occurrence by Aquifer

Ground-water samples were collected from domestic wells 

in three aquifers (sampling regions) (figs. 1 and 2b). In samples 

from domestic wells, two pesticides (dieldrin, diuron) and two 

VOCs (1,2-dibromo-3-chloropropane and TCE) were present at 

maximum detected concentrations that met or exceeded humanhealth benchmarks (figs. 8a and 8b). Detection frequency and 

exceedance data for these four contaminants are listed by 

domestic-well sampling region in table 9.

Measured concentrations of dieldrin exceeded the low end 

of the HBSL concentration range in every sample from the New 

England and Piedmont Physiographic Provincesin which it was 

detected; dieldrin was not detected in domestic wells in the 

Kirkwood-Cohansey aquifer system. The measured concentration of diuron was approximately equal to the low end of the 

HBSL concentration range in one domestic-well sample from 

the Kirkwood-Cohansey aquifer system; diuron was not 

detected in the New England Physiographic Province and was 

not analyzed in samples from the Piedmont Physiographic 

Province (table 9). 1,2-Dibromo-3-chloropropane was detected 

and exceeded the USEPA and New Jersey MCL value in one of 

the 30 domestic-well samples from the Kirkwood-Cohansey 

aquifer system, but was not detected in samples from the New 

England or Piedmont Physiographic Provinces (table 9). TCE 

was frequently detected in all three domestic-well sampling 

regions, and measured concentrations exceeded the MCL value 

in two of the four samples from the Piedmont Physiographic 

Province in which it was detected (table 9).

Occurrence by Land Use

Ground-water samples were collected from shallow monitoring wells in four land-use areas (agricultural, new urban, old 

urban, and undeveloped areas) (fig. 2a) to measure the effects of 

land-use settings on shallow ground-water quality. In samples 

from monitoring wells, three pesticides (dieldrin, dinoseb, and 

diuron) but no VOCs had maximum detected concentrations 

that met or exceeded human-health benchmarks (figs. 8a and 

8b). Detection frequency and exceedance data for these three 

pesticides are listed by land-use area in table 9. 

Dieldrin, dinoseb, and diuron were detected in shallow 

monitoring wells in the agricultural land-use areas. These three 

pesticides were detected least often in shallow monitoring-well 

samples from undeveloped areas, and no concentrations 

detected from that land use met or exceeded human-health 

benchmarks. Dieldrin was detected in samples collected from 

all land-use categories, except undeveloped areas. Measured 

dieldrin concentrations met or exceeded human-health benchmarks in all but 1 of 12 shallow monitoring-well samples in 

which it was detected and in all of the moderate-depth monitoring wells in which it was detected (table 9; fig. 4), making 

dieldrin a compound of regional importance. Dinoseb was 

detected in samples collected from agricultural and undeveloped land-use areas, and measured concentrations exceeded the 

MCL in two of the three samples from agricultural land-use 

areas in which it was detected. Diuron was detected in samples 

collected in agricultural and old urban land-use areas, and the 

measured concentration was equal to the low end of the HBSL 

range in one of the three samples from the old urban land-use 

areas in which it was detected (table 9; fig. 4). 

All the exceedances of human-health benchmarks in shallow monitoring wells were the result of pesticide detections in 

samples from the agricultural, old urban, and new urban landuse areas (table 9). The total number of pesticides and VOCs 

with BQmax values ≥ 0.1 was comparable for the agricultural 

(4), old urban (5), and new urban (3) land-use areas (data not 

shown). The fewest number of pesticides (8) and VOCs 

(9) were detected in samples from undeveloped land-use areas, 

as would be expected, and no pesticides or VOCs in the undeveloped land-use areas were detected within a factor of 10 of 

their human-health benchmarks (data not shown). Shallow 

monitoring wells were designed to sample parts of shallow 

aquifers that are known or suspected to be associated with 

specific land uses in the recharge area. Therefore, carefully 

located monitoring wells can provide an important indication of 

contamination in targeted parts of a ground-water flow system. 

Contamination detected in these monitoring wells can be both a 

contributor to, and a predictor of, future chemical contamination in deeper parts of the Kirkwood-Cohansey aquifer system, 

which is used for domestic and public supplies. 

Contaminant Sources and Physicochemical 

Properties

Characterization of the sources and physicochemical properties of contaminants of potential human-health concern aids 

in understanding potential human exposure to these contaminants. The sources and physicochemical properties of contaminants that were frequently detected in the study unit were 

described in detail in another report (Stackelberg and others, 

2000), but pertinent data related to the 20 contaminants of 

potential human-health concern are provided below.

Patterns of Occurrence of the Contaminants

of Potential Human-Health Concern

When the 20 contaminants of potential human-health concern were examined in light of the five factors discussed above, 

the following four patterns of occurrence for these 20 contaminants emerged.

1. BQmax greater than or equal to 1, and frequently detected.

2. BQmax greater than or equal to 1, and not frequently 

detected.

3. BQmax less than 1 but greater than or equal to 0.1, and 

frequently detected.

4. BQmax less than 1 but greater than or equal to 0.1, and 

not frequently detected.

The occurrence of the contaminants that follow these four patterns is summarized below.
Assessment of Ground-Water Quality in New Jersey 39

Pattern 1: BQmax Greater than or Equal to 1

and Frequently Detected

One unregulated pesticide (dieldrin) and three regulated 

VOCs (PCE, TCE, and 1,2-dibromoethane) were measured at 

concentrations that exceeded human-health benchmarks and 

were frequently detected in ground water that is used for 

drinking water (that is, domestic or public-supply wells) 

(table 8; figs. 6 and 7). 

Dieldrin stands out because (1) it was measured at concentrations that exceeded the low end of the HBSL concentration 

range (10-6 cancer risk) in samples from all well types and (2) it 

was frequently detected in public-supply and monitoring wells 

(tables 4 and 8; fig. 6). Measured concentrations of dieldrin met 

or exceeded the low end of the HBSL concentration range in 29 

of 31 samples in which it was detected (figs. 4 and 6), resulting 

in BQmed-det values that were ≥ 1 for all well types (table 8). 

Dieldrin was detected at concentrations within a factor of 10 of 

the HBSL in the two samples in which detected concentrations 

did not exceed the low end of the HBSL concentration range 

(figs. 4 and 6). Environmental residues of dieldrin may result 

from the introduction of either dieldrin or aldrin into the environment. Dieldrin and aldrin are organochlorine insecticides, 

which is a highly persistent class of insecticides used extensively in the United States during the 1950s-1960s; dieldrin also 

is a degradation product formed from aldrin. Both dieldrin and 

aldrin are no longer registered for use in the United States 

(Ware, 1989). Their uses were discontinued for agriculture in 

the early 1970s and for termite control in the late 1980s (Nowell 

and others, 1999).

Two VOCs (PCE and TCE) stand out because they were 

(1) detected at concentrations that exceeded their human-health 

benchmarks (USEPA and New Jersey MCLs) and (2) frequently detected in multiple well types. BQmed-det values for 

PCE and TCE were less than 0.1 for all well types (table 8), 

indicating that although these contaminants were frequently 

detected, they were not frequently detected at concentrations 

approaching MCL values.

PCE concentrations exceeded human-health benchmarks 

in only 1 of 30 public-supply well samples, but maximum 

detected concentrations were within a factor of 10 of humanhealth benchmarks in domestic and monitoring wells (tables 6 

and 8; figs. 5 and 7). Unlike many of the VOCs of potential 

human-health concern, PCE is less soluble and more likely to 

sorb to organic matter in the subsurface than other chlorinated 

compounds (Stackelberg and others, 2000). Nonetheless, PCE 

was frequently detected in all well types, and in all sampling 

regions and land-use areas, with the exception of monitoring 

wells in agricultural land-use areas (table 9), reflecting its highvolume production and diverse industrial and commercial uses 

(Harte and others, 1991; Stackelberg and others, 2000). 

TCE was measured in samples from public-supply and 

domestic wells at concentrations that exceeded its humanhealth benchmarks; it also was frequently detected in all well 

types (tables 6 and 8; figs. 5 and 7). TCE concentrations 

exceeded the USEPA MCL value in 1 of 30 samples from 

public-supply wells and 1 of 82 samples from domestic wells, 

and exceeded the New Jersey MCL value in 2 public-supply 

wells and 2 domestic wells (fig. 5). TCE was detected at concentrations within a factor of 10 of the New Jersey MCL in both 

shallow and moderate-depth monitoring wells (data not shown). 

TCE has been produced in large quantities since the 1960s and 

has a wide variety of industrial and commercial uses as a metal 

degreaser and industrial solvent, among other uses (Harte and 

others, 1991). TCE is likely to leach to ground water because it 

is highly water soluble and has a low soil-sorption coefficient 

(Stackelberg and others, 2000).

1,2-Dibromoethane was detected at concentrations that 

exceeded its human-health benchmarks (USEPA and New 

Jersey MCL values), and it was frequently detected, but only in 

samples from public-supply wells. 1,2-Dibromoethane was 

detected in 4 of 30 public-supply-well samples; only one sample had measured concentrations that exceeded the MCL, and 

this was an estimated concentration (tables 6 and 8; figs. 5 and 

7). The other three detections were within a factor of 10 of the 

MCL (fig. 7). The occurrence of 1,2-dibromoethane exclusively in samples from the public-supply wells likely reflects 

historical use patterns and the fact that public-supply wells 

intercept ground water from larger contributing areas than other 

well types (Stackelberg and others, 2000). The analytical MRL 

for 1,2-dibromoethane in shallow monitoring wells was about 

3-fold greater than that for the other well types (table 1), which 

may explain why it was not detected in shallow monitoring 

wells. 1,2-Dibromoethane was used historically as an additive 

to leaded gasoline and as a turf fumigant (U.S. Environmental 

Protection Agency, 2002f), but use of 1,2-dibromoethane has 

decreased with the decline in the use of leaded gasoline and 

because the USEPA banned its use as a turf fumigant in 1984 

(Stackelberg and others, 2000).

Pattern 2: BQmax Greater than or Equal to 1

and not Frequently Detected

One regulated pesticide (dinoseb), one unregulated pesticide (diuron), and one regulated VOC (1,2-dibromo-3-chloropropane) were measured in samples at concentrations that 

exceeded human-health benchmarks in one or more well types, 

but were not frequently detected in any well type (table 8; 

figs. 6 and 7). Neither dinoseb nor diuron were analyzed in 

samples from public-supply wells, domestic wells from the 

Piedmont Physiographic Province, or moderate-depth monitoring wells (table 9).

The USEPA and New Jersey MCL value for dinoseb, a 

regulated pesticide, was met or exceeded (BQmax = 6) in two 

of the four monitoring-well samples in which it was detected, 

and detected concentrations of dinoseb were at least 100-fold 

less than the MCL in the other two samples (fig. 6). The MCL 

exceedances of dinoseb occurred in 2 of 15 samples from shallow, agricultural monitoring wells (table 9). The BQmed-det 

value for monitoring wells was 0.6 (table 8), indicating that at 

least half of the detected dinoseb concentrations were within a 
40 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

factor of 10 of the MCL. Dinoseb was not detected in domesticwell samples and was not analyzed in public-supply well samples (tables 8 and 9; figs. 4 and 6). Dinoseb has a high potential 

for movement in the environment because it is moderately soluble in water and does not sorb appreciably to soil particles 

(Vogue and others, 1994). 

The maximum detected concentration of diuron was equal 

to the low end of the HBSL concentration range (BQmax = 1) 

in 1 of 14 samples from the old-urban monitoring wells, and its 

measured concentration was approximately equal to the low 

end of the HBSL concentration range in 1 of 30 domestic-well 

samples from the Kirkwood-Cohansey aquifer system (tables 8 

and 9). The BQmed-det value for diuron in domestic wells was 

0.5 (table 8), but this was a result of its low detection frequency 

in domestic wells (2 of 60 samples) (fig. 6). Diuron has a new 

HBSL range (2-200 μg/L) based on updated toxicity data 

published by USEPA OPP (U.S. Environmental Protection 

Agency, 2002c). Diuron also has a Lifetime HA value of 

10 μg/L published by USEPA OW; this Lifetime HA value was 

not exceeded in any sample. Diuron has a moderate potential for 

movement in the environment because of its moderate water 

solubility and ability to sorb to soil particles (Vogue and others, 

1994).

1,2-Dibromo-3-chloropropane was analyzed in all well 

types, but was detected in only 1 of 82 domestic-well samples 

(table 8; figs. 5 and 7), in a domestic well in the KirkwoodCohansey aquifer system (table 9). This one measured concentration exceeded the USEPA and New Jersey MCL value for 

1,2-dibromo-3-chloropropane (BQmax = 2), and because 1,2-

dibromo-3-chloropropane was detected in only one sample, the 

BQmed-det value is the same as its BQmax value (table 8). 

Because 1,2-dibromo-3-chloropropane was detected in only 

one domestic well sample and was not detected in any of the 

other well types, it could be a compound of local, but probably 

not regional, importance. The low detection frequency of 1,2-

dibromo-3-chloropropane, however, could be the result of its 

relatively high MRL value (0.214 μg/L) compared to other regulated VOCs (table 6). The MRL value is greater than the MCL 

for 1,2-dibromo-3-chloropropane (0.2 μg/L) in all well types 

(table 1). As a result, it is possible that this contaminant may be 

present, but undetected, at concentrations greater than the MCL 

but less the MRL, which means that the MCL exceedance rates 

could be biased low. 1,2-Dibromo-3-chloropropane is a fumigant with a very high potential for movement in the environment because it has high water solubility and limited ability to 

sorb to soil particles (Vogue and others, 1994).

Pattern 3: BQmax Less than 1 but Greater than

or Equal to 0.1 and Frequently Detected

Two regulated pesticides (atrazine and simazine) and 

seven regulated VOCs (benzene, 1,1-dichloroethane, 1,1-

dichloroethene, cis-1,2-dichloroethylene, 1,2-dichloropropane, 

MTBE, and trichloromethane) were measured at concentrations 

that did not exceed, but were within a factor of 10 of humanhealth benchmarks (1 > BQmax ≥ 0.1) in one or more well 

types; they also were frequently detected in ground water that is 

used for drinking water (that is, domestic and (or) public-supply 

wells) (table 8; figs. 6 and 7). All nine contaminants had 

BQmed-det values of 0.04 or less for all well types (table 8), 

indicating that the median detected concentrations were at least 

a factor of 20 less than the USEPA or New Jersey MCL values.

Atrazine and simazine had BQmax values ≥ 0.1 but less 

than 1 only for monitoring-well samples (table 8; fig. 6) (that is, 

in water that is not immediately consumed as drinking water). 

Atrazine and simazine are high-use herbicides that are highly 

mobile because they are water soluble and do not sorb appreciably to soil particles (Stackelberg and others, 2000). Both atrazine and simazine were frequently detected in public-supply 

wells (table 4) and shallow and moderate-depth monitoring 

wells (data not shown). 

Of the seven frequently detected VOCs with BQmax values ≥ 0.1 but less than 1, only MTBE and trichloromethane 

(chloroform) were frequently detected in all well types (table 8; 

fig. 7), indicating widespread (nonpoint) sources of these contaminants. MTBE was first used to enhance octane levels in 

gasoline in the late 1970s. By the early 1990s, MTBE became 

the most commonly used fuel oxygenate in many parts of the 

Nation (Zogorski and others, 1997). MTBE is more soluble, 

slower to degrade, and more mobile in the subsurface than other 

gasoline constituents such as benzene (Squillace and others, 

1997). Trichloromethane is used in the production of fluorocarbon-22, but it also is a common disinfection byproduct resulting 

from the chlorination of public drinking-water supplies. These 

public supplies can provide widespread (nonpoint-source) 

recharge to surficial aquifers underlying urban areas through a 

variety of mechanisms (Stackelberg and others, 2000).

The remaining five frequently detected VOCs with 

BQmax values ≥ 0.1 but less than 1 are benzene and four chlorinated organic compounds (1,1-dichloroethane, 1,1-dichloroethene, cis-1,2-dichloroethylene, and 1,2-dichloropropane) 

(table 8; fig. 7). Benzene was frequently detected in publicsupply wells (table 6) and moderate-depth monitoring wells 

(data not shown). Benzene is used as a constituent in motor 

fuels, as a solvent for a variety of media, and in the manufacture 

of detergents, explosives, pharmaceuticals, and dyestuffs (U.S. 

Environmental Protection Agency, 2002f). The four chlorinated 

organic compounds were frequently detected in public-supply 

wells (table 6); 1,1-dichloroethane and 1,1-dichloroethene also 

were frequently detected in moderate-depth monitoring wells 

(data not shown). These four chlorinated compounds are used in 

industrial and commercial applications similar to those of PCE 

and TCE, although in much smaller quantities (Stackelberg and 

others, 2000). These four chlorinated compounds have moderate to high water solubilities and low soil-sorption coefficients, 

indicating that they likely leach to ground water after being 

introduced to the subsurface (Stackelberg and others, 2000).
Assessment of Ground-Water Quality in New Jersey 41

Pattern 4: BQmax Less than 1 but Greater than 

or Equal to 0.1 and not Frequently Detected

One regulated pesticide (heptachlor epoxide) and three 

regulated VOCs (chloroethylene, 1,2-dichloroethane, and 

methylene chloride) were measured at concentrations that did 

not exceed, but were within a factor of 10 of human-health 

benchmarks (1 > BQmax ≥ 0.1) in one or more well types, but 

were not frequently detected in any well type (table 8; figs. 6 

and 7). 

Heptachlor epoxide was analyzed only in shallow monitoring-well samples. Heptachlor epoxide had a BQmax value of 

0.4 in these samples, where it was detected infrequently (4 out 

of 69 samples) (table 8; fig. 6). The BQmed-det value for heptachlor epoxide is 0.1 (table 8), indicating that the median 

detected concentration was a factor of 10 less than the USEPA 

MCL. Heptachlor epoxide is a persistent degradation product of 

the organochlorine insecticide heptachlor (U.S. Environmental 

Protection Agency, 2002e), which is no longer used in the 

United States. Heptachlor was used widely to control fire ants 

in the Southeast and as a soil insecticide on corn and other food 

crops until the mid-1970s, and was used in termite control until 

the late 1980s (Nowell and others, 1999).

Chloroethylene was detected infrequently in public-supply 

and domestic wells, and its BQmax value was 0.2 for domestic 

wells. Chloroethylene was detected in only 1 of 82 domesticwell samples; hence, its BQmed-det value for domestic wells 

was the same as its BQmax value (table 8). 1,2-Dichloroethane 

was detected infrequently in all three well types, and its BQmax 

value was 0.1 for monitoring-well samples. Methylene chloride 

was found only in domestic wells, where it was detected in 2 of 

82 domestic-well samples; the BQmax value was 0.1. The 

BQmed-det value for methylene chloride also was 0.1 because 

both detections of methylene chloride were within a factor of 10 

of the USEPA MCL (table 8; fig. 7). These three chlorinated 

solvents typically are used in organic synthesis or as solvents 

and have limited ability to sorb to soil particles due to low soilsorption coefficients (Mackay and others, 1993).

In addition to the 20 contaminants of potential humanhealth concern described above, one additional contaminant, 

deethylatrazine, is noteworthy because it was frequently 

detected in all well types, but it has no human-health benchmarks. This contaminant is formed in the environment from 

degradation of the commonly used herbicides atrazine and 

propazine, which makes deethylatrazine a high priority for the 

collection of toxicity information. In the USEPA OPP HumanHealth Risk Assessment for atrazine, the toxicity of deethylatrazine was considered as equivalent to that of the parent compound atrazine (U.S. Environmental Protection Agency, 

2002d). The consensus-based protocol for HBSL development 

(Toccalino and others, 2003), however, does not currently permit the use of toxicity data from a parent compound to calculate 

an HBSL for a degradation product; the HBSL protocol is based 

on USEPA OW methodologies.

Health-Based Comparison of Wells with 

Multiple Contaminants 

A major objective of this pilot effort is to demonstrate use 

of the HBSL approach as a tool for communicating waterquality data collected for individual contaminants in a humanhealth context. Guidance for interpreting water-quality data for 

multiple contaminants in a human-health context is not provided in the “Guidance” section of this report because such 

interpretations represent an extension beyond typical analyses. 

Additionally, USEPA procedures for assessing potential risks 

or hazards resulting from exposure to multiple contaminants are 

under development (Toccalino and others, 2003). Nonetheless, 

an initial effort was made to communicate water-quality findings for multiple contaminants in a human-health context 

because multiple chemicals (53 in public-supply, 68 in domestic, and 75 in monitoring wells) were detected in each type of 

well (table 3). In this section, a screening tool for interpreting 

the occurrence of multiple contaminants in a human-health 

context is presented as a first step towards estimating relative 

potential human-health concerns associated with individual 

wells.

The long-term cumulative effects of low concentrations of 

multiple contaminants on human health currently are unknown 

and are an area of active research. Early USEPA guidance on 

the assessment of chemical mixtures indicated that when toxicity data are not available for an identical or reasonably similar 

mixture to that being studied, the risk or hazard can be estimated 

from the toxic or carcinogenic properties of the components in 

the mixture. When little or no quantitative information is available on the potential interactions between the components in a 

mixture, additive models are recommended (U.S. Environmental Protection Agency, 1986, 1989b). As these early guidance 

documents note, however, dose-additive models are not the 

most biologically plausible approach if the compounds do not 

have the same mode of toxicological action; more recent 

USEPA guidance documents have begun to address this issue 

(U.S. Environmental Protection Agency, 2000, 2002a, 2003d). 

The approach used in this report does not make assumptions 

about dose additivity or modes of toxicological action. 

Mixtures of contaminants were detected in each of the well 

types considered in this study. Previous analyses examined the 

co-occurrence of pesticides and VOCs in public-supply and 

monitoring wells in the Kirkwood-Cohansey aquifer system 

(Stackelberg and others, 2001). One or more pesticides were 

detected with one or more VOCs in more than 95 percent of the 

samples collected from these well types. Overall, more than 

140,000 and more than 3,000 unique combinations of pesticides 

with VOCs were detected in two or more samples from the 

public-supply and monitoring wells, respectively. The most 

frequently detected pesticides (such as atrazine, simazine, 

deethylatrazine) and VOCs (such as trichloromethane and 

MTBE) constituted the most frequently occurring combinations 

(Stackelberg and others, 2001). 
42 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Benchmark Quotient Computations for Multiple 

Contaminants in Individual Wells

Two BQ indexes were computed to aid in the examination 

of the occurrence of multiple contaminants in individual wells 

in relation to their respective human-health benchmarks. To 

ensure comparability between BQ calculations for different 

well types, aquifers (sampling regions), and land-use areas, 

only the 47 pesticides and 85 VOCs that were analyzed in all 

well types were considered in the analyses; of these, 44 pesticides and 55 VOCs have human-health benchmarks. Waterquality data from 30 public-supply, 82 domestic, and 108 monitoring wells were evaluated. At least one pesticide or VOC 

with a human-health benchmark was detected in most individual wells (100 percent of public-supply wells, 88 percent of 

domestic wells, and 98 percent of monitoring wells) (table 10). 

The maximum numbers of pesticides and VOCs with humanhealth benchmarks that were detected in any individual well 

were 21 for public-supply wells, 24 for domestic wells, and 17 

for monitoring wells (table 10). 

For each individual well, BQ values were calculated for 

every detected compound with a human-health benchmark, and 

these BQ values were used to determine two BQ indexes for 

that well—the maximum BQ value (BQSiteMax) and the sum 

of all BQ values (BQSiteSum). (Computations are shown for a 

hypothetical example in table 11.) BQSiteMax is defined as the 

maximum of BQ values for all detected contaminants in a given 

well. BQSiteMax will be greater than or equal to 1 if measured 

concentrations of any contaminant in the sample exceed or are 

equal to the human-health benchmark. 

BQSiteSum is defined as the sum of all BQ values for a 

given well. In other words, BQSiteSum is a unitless sum of the 

concentrations of individual contaminants in a mixture, with 

each concentration first normalized by dividing the concentration by its respective human-health benchmark; each contaminant with a human-health benchmark is weighted equally. The 

BQSiteSum provides a relative measure of potential for humanhealth effects for individual wells and, therefore, is appropriate 

and valuable to use as a screening-level tool in water-quality 

analyses. For example, BQSiteSum values can be used to compare and rank wells, or well types, on the basis of relative potential human-health concerns to help prioritize future sampling 

efforts. Also, BQSiteSum values observed over time in individual wells can be used to track trends in potential for humanhealth effects.

Because BQSiteSum values provide a relative measure of 

potential human-health effects in individual wells, the biological importance of any absolute BQSiteSum value is unknown. 

A BQSiteSum value ≥ 1 does not necessarily indicate an 

exceedance of any human-health standard or guideline, unless 

measured concentrations of one or more individual compounds 

in a sample exceed their respective human-health benchmarks. 

For example, if 10 compounds are measured at concentrations 

within a factor of 10 of their respective human-health benchmarks in a given well and the BQSiteSum value is ≥ 1, this does 

not necessarily indicate that there is a potential for adverse 

health effects.

BQSiteSum values are analogous to the Pesticide Toxicity 

Index, which can be used to rank sites on the basis of relative 

potential exposure and toxicity of pesticides to aquatic organisms (Munn and Gilliom, 2001). BQSiteSum values also are 

similar to Hazard Index (HI) values used by USEPA to assess 

noncancer hazards. HI values are the sum of more than one hazard quotient (HQ) for multiple substances and (or) multiple 

exposure pathways. An HQ is the ratio of a single substance 

exposure level to a reference dose toxicity value. If the HI is 

greater than 1 as a result of summing several HQs of similar 

magnitude, USEPA segregates the compounds by effects and 

by mechanism of action and then derives separate HIs for each 

chemical group (U.S. Environmental Protection Agency, 

1989b). In contrast to HI values, BQSiteSum values do not distinguish between carcinogens and noncarcinogens or make 

assumptions about modes of toxicological action, nor do they 

imply that contaminant toxicities or carcinogenicities are additive.

Compounds without human-health benchmarks were 

excluded from the BQSiteMax and BQSiteSum calculations. In 

preliminary analyses (data not shown), BQ values for compounds that were not detected, but have human-health benchmarks, were calculated using two methods: (1) assume a concentration of zero, and (2) assume a concentration equal to the 

MRL. These preliminary analyses showed that the treatment of 

nondetects generally had little influence on the results except 

for BQ values calculated for compounds that have MRL values 

near or greater than their MCL or HBSL value; these BQ values 

artificially inflated BQSiteSum values. Therefore, compounds 

that were not detected, but have human-health benchmarks, 

were assigned BQ values of zero (table 11). 

Occurrence of Multiple Contaminants 

by Well Type

Cumulative distribution plots of BQSiteMax and BQSiteSum values for pesticide data, VOC data, and the combination 

of pesticide and VOC data for individual wells in all three well 

types are shown in figure 10. For most individual wells, 

BQSiteMax values were equivalent to, or close to, BQSiteSum 

values, particularly for pesticides. For pesticides, the median 

ratio of BQSiteMax to BQSiteSum values was approximately 1 

for all well types; for VOCs, this median ratio ranged from 0.77 

for public-supply wells to 0.94 for domestic wells (fig. 10), 

indicating that the BQSiteMax value makes up the majority of 

the sum. In all samples and for all analytes (pesticides, VOCs, 

and pesticides plus VOCs combined), the BQSiteMax value 

was within a factor of 10 of the BQSiteSum value. 

For all well types, pesticides with human-health benchmarks were detected in fewer individual wells than were VOCs 

with human-health benchmarks (table 10; figs. 10a and 10b). 

More individual wells had detections of pesticides with 

BQSiteMax values ≥ 1 (28 of 219 wells), however, than had 
Table 10. Numbers of (1) individual wells with contaminant detections and (2) compounds detected with human-health benchmarks in individual we

New Jersey Study Unit.

[n, number of wells sampled; HH benchmark, Human-health benchmark (MCL or HBSL); %, percent; BQ, Benchmark Quotient = ratio of measured concentration to human-he

BQSiteMax, maximum Benchmark Quotient value in an individual well; ≥, greater than or equal to; PSW, public-supply well; DW, domestic well; MW, monitoring well; VOC, 

Well type n

Number (%) of wells 

with detections of 

compounds with

HH benchmarks

Maximum number of 

compounds detected 

with HH benchmarks

in any well

Number (%) of wells with 

detections of compounds 

with BQSiteMax >1

Maximum number of 

compounds detected 

with BQ value >1

in any well

Number (%) of wells w

detections of compou

with BQSiteMax >0

Pesticides

PSW 30 23 (77%) 6 7 (23%) 1 8 (27%DW 81 21 (26%) 5 3 (4%) 1 3 (4%) MW 108 78 (72%) 11 18 (17%) 1 25 (23%

VOCs

PSW 30 30 (100%) 20 3 (10%) 1 12 (40%DW 82 69 (84%) 20 2 (2%) 1 8 (10%MW 108 101 (94%) 13 0 (0%) 0 5 (5%) 

Pesticides and VOCs

PSW 30 30 (100%) 21 9 (30%) 2 18 (60%DW 82 72 (88%) 24 5 (6%) 1 9 (11%MW 108 106 (98%) 17 19 (18%) 1 29 (27%
44 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

detections of VOCs with BQSiteMax values ≥ 1 (5 of 220 

wells) (table 10; figs. 10a and 10b). A BQSiteMax value ≥ 1 

indicated that the maximum detected concentration of at least 

one contaminant in an individual well met or exceeded a 

human-health benchmark (MCL or HBSL value). For pesticides and VOCs combined, public-supply wells had the largest 

percentage of individual wells (9 of 30 or 30 percent) with a 

BQSiteMax value ≥ 1. The BQSiteMax value was ≥ 1 for 5 of 

82 (6 percent) domestic wells and for 19 of 108 (18 percent) 

monitoring wells (table 10 and fig. 10c). In public-supply and 

domestic wells, pesticides contributed approximately twothirds of the measured exceedances, whereas in monitoring 

wells, all exceedances resulted from measured pesticide concentrations (table 10). All BQSiteMax values ≥ 1 for pesticides 

resulted from dieldrin detections. Dinoseb and diuron also had 

BQ values ≥ 1 in domestic and (or) monitoring wells (fig. 6), 

but dinoseb and diuron were not analyzed in all well types. 

Because only contaminants analyzed in all well types are considered for this evaluation, dinoseb and diuron do not contribute 

to BQSiteMax or BQSite Sum values. BQSiteMax values ≥ 1 

for VOCs resulted from exceedances in one public-supply well 

each for 1,2-dibromoethane, PCE, and TCE and one domestic 

well each for 1,2-dibromo-3-chloropropane and TCE (fig. 7). 

For all three well types, the greatest BQSiteMax and BQSiteSum values (20, 10, and 3,000 for public-supply, domestic, and 

monitoring wells, respectively) were the result of pesticide 

(dieldrin) detections (figs. 6, 10a and 10c).

Results of analysis of variance on the ranked-transformed 

BQSiteMax values for pesticides and VOCs combined indicate 

that the BQSiteMax values were statistically different for samples from all three well types in the study area at a 95-percent 

confidence level. A comparison of the means of BQSiteMax 

values for each well type using the Tukey test indicates that 

BQSiteMax values for public-supply wells were significantly 

greater than those for domestic wells and monitoring wells at a 

95-percent confidence level, likely because public-supply wells 

had the largest percentage (30 percent) of individual wells with 

pesticide or VOC concentrations that exceeded their humanhealth benchmarks. Results of these two statistical tests were 

the same using BQSiteSum values. Results for domestic wells 

may not be directly comparable to results for public-supply or 

monitoring wells because public-supply and monitoring-well 

samples are from the Kirkwood-Cohansey aquifer system only, 

whereas domestic-well samples are from three aquifers (the 

Kirkwood-Cohansey aquifer system and aquifers in the Piedmont and New England Physiographic Provinces) (see sections 

“Description of Study Area” and “Well Networks”). Although 

samples from public-supply wells tended to have greater 

BQSiteMax and BQSiteSum values than samples from monitoring wells, the five highest BQSiteMax values for pesticides, 

and for pesticides and VOCs combined, are for monitoring 

wells (fig. 10). 

A comparison of the means of BQSiteMax and BQSiteSum values for domestic and monitoring wells using the Tukey 

test indicates that BQ values for monitoring wells are significantly greater than those for domestic wells at a 95-percent confidence level. This result is expected because shallow monitoring wells were designed to intentionally sample specific points 

in a shallow aquifer that are known, or suspected, to be associated with a part of the ground-water flow system that has been 

affected by contaminant sources that can be linked to known 

surficial land uses (such as pesticides applied to an agricultural 

field) in the recharge area. 

Table 11. Hypothetical BQSiteMax and BQSiteSum example calculations for three compounds in three wells.

[μg/L, micrograms per liter; HH Benchmark, Human-Health Benchmark (MCL or HBSL); MCL, Maximum Contaminant Level; HBSL, Health-Based Screening 

Level; BQ, Benchmark Quotient = ratio of measured concentration to human-health benchmark value; BQSiteMax, maximum Benchmark Quotient value in an 

individual well; BQSiteSum, sum of all Benchmark Quotient values in an individual well; μg/L, micrograms per liter; ND, not detected]

Well 

number

Compound 1 Compound 2 Compound 3

BQSiteMax

BQSiteSum

(rounded to 1 

significant 

figure)

Measured

concentration

(μg/L)

HH

benchmark

(μg/L)

BQ

Measured

concentration

(μg/L)

HH

benchmark

(μg/L)

BQ

Measured

concentration

(μg/L)

HH

benchmark

(μg/L)

BQ

1 0.06 2 0.03 0.03 3 0.01 0.08 40 0.002 0.03 0.04

2 ND 2 0 .06 3 .02 .02 40 .0005 .02 .02

3 ND 2 0 .006 3 .002 ND 40 0 .002 .002
Assessment of Ground-Water Quality in New Jersey 45

Figure 10. Cumulative distributions and ratios of maximum and summed Benchmark Quotient values for individual wells for

(a) pesticides, (b) VOCs, and (c) pesticides and VOCs with human-health benchmarks detected in public-supply, domestic, and 

monitoring wells in the Long Island-New Jesey Study Unit.

EXPLANATION EXPLANATION

BQSiteMax or BQSiteSum WELL TYPE BQSiteMax/BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

0

20

40

60

80

100

10-6 104 102 100 10-2 10-4

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

10-6

0

20

40

60

80

100

102 104 100 10-2 10-4

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

10-6

0

20

40

60

80

100

104 102 100 10-2 10-4

(a)

Pesticides

(c)

Pesticides

and VOCs

(b)

VOCs

0

0.2

0.4

0.6

0.8

1.0

PSW DW MW

When the cumulative percent is less than 100, contaminants with humanhealth benchmarks were detected in less than 100 percent of individual wells. 

BQSiteMax public-supply wells

BQSiteMax monitoring wells

BQSiteMax domestic wells 

BQSiteSum public-supply wells

BQSiteSum domestic wells 

BQSiteSum monitoring wells

25th percentile

75th percentile

Median

Minimum

Maximum

WELL TYPE

BQSiteMax/BQSiteSum

0

0.2

0.4

0.6

0.8

1.0

PSW DW MW

WELL TYPE

BQSiteMax/BQSiteSum

0

0.2

0.4

0.6

0.8

1.0

PSW DW MW

[BQ, Benchmark Quotient = ratio of measured concentration to human-health benchmark value; VOC, volatile organic compound; BQSiteMax = 

maximum BQ value in an individual well; BQSiteSum, sum of all BQ values in an individual well; PSW, public-supply well; DW, domestic well;

MW, monitoring well] 
46 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Occurrence of Multiple Contaminants 

by Aquifer and Land Use 

In this study, ground-water quality data were collected for 

multiple aquifers and land-use areas, in addition to multiple 

well types. Cumulative distribution plots of the domestic-well 

data, separated by aquifer, are presented in figure 11 for pesticide data, VOC data, and pesticide and VOC data combined. 

For pesticide and VOC data combined, 1 of 30 domestic wells 

in each of the Kirkwood-Cohansey aquifer system and the New 

England Physiographic Province had BQSiteMax values ≥ 1 (as 

a result of 1,2-dibromo-3-chloropropane and dieldrin exceedances, respectively), and 3 of 22 wells in the Piedmont Physiographic Province had BQSiteMax values ≥ 1 (as a result of two 

dieldrin and one TCE exceedances) (table 9; fig. 11). Results of 

analysis of variance on the ranked-transformed BQSiteMax 

values for pesticides and VOCs combined indicate that the 

BQSiteMax values were statistically similar for domestic-well 

samples from different aquifers (Kirkwood-Cohansey aquifer 

system and the New England and Piedmont Physiographic 

Provinces), at a 95-percent confidence level. Results of this statistical test were the same using BQSiteSum values. 

Cumulative distribution graphs of the shallow monitoringwell data, plotted as a function of land use, are presented for 

pesticide data (fig. 12a), VOC data (fig. 12b), and pesticide and 

VOC data combined (fig. 12c). Pesticides and VOCs with 

human-health benchmarks were detected in at least 70 percent 

of the individual shallow monitoring wells in most land uses 

(figs. 12a and 12b); the only exception is pesticides in shallow 

monitoring wells in the undeveloped land-use area (31 percent 

detection) (fig. 12a). No wells from the undeveloped land-use 

area had BQSiteMax or BQSiteSum values ≥ 1; the highest BQ 

value from an individual undeveloped land-use well was 0.02, 

a factor of 50 less than human-health benchmarks. No VOCs 

were detected at concentrations greater than human-health 

benchmarks in any of the individual shallow monitoring wells 

from any land-use area (fig. 12b). All of the exceedances of 

human-health benchmarks (that is, BQSiteMax ≥ 1) were the 

result of pesticide (dieldrin) detections in one agricultural well, 

two old-urban wells, and eight new-urban wells (table 9; 

figs. 12a and 12c). 

Results of analysis of variance on the ranked-transformed 

BQSiteMax values for pesticides and VOCs combined indicate 

that the BQSiteMax values were statistically different for samples from shallow monitoring wells in different land-use areas 

(agricultural, old urban, new urban, and undeveloped), at a 

95-percent confidence level. A comparison of the means of 

BQSiteMax values for each shallow monitoring well by landuse area using the Tukey test indicates that BQSiteMax values 

for wells in undeveloped land-use areas were significantly less 

than those for wells in new urban areas at a 95-percent confidence level. Results of these two statistical tests were the same 

using BQSiteSum values. Although figure 12c shows a pattern 

of consistently lower BQ values for shallow monitoring wells in 

the undeveloped land-use areas than those in other land-use 

areas, the Tukey test did not indicate that BQ values for wells in 

undeveloped areas were significantly different than for wells in 

agricultural or old urban areas at a 95-percent confidence level, 

perhaps because the sample sizes were too small to see significant differences between BQ values and because the distributions are similar.

Benefits of Applying Health-Based 

Screening Levels to Water-Quality 

Data

HBSL values increase the number of compounds with 

human-health benchmarks analyzed and detected in this study, 

thereby expanding the basis for interpreting contaminantoccurrence data in a human-health context. USEPA humanhealth benchmarks (that is, MCL, Lifetime HA, or RSD values) 

currently do not exist (as of August 2004) for 79 of the 182 

compounds analyzed in this study. New HBSL values were 

calculated for 39 of these 79 unregulated compounds, plus an 

additional 7 compounds for which updated toxicity data were 

available. The 46 new HBSL values for 37 pesticides and 9 

VOCs are provided in Appendix 2. New HBSL values increase 

the total number of analytes with human-health benchmarks 

from 103 of 182 compounds (57 percent) to 142 (78 percent) 

and the total number of detected compounds with human-health 

benchmarks from 65 of 97 compounds (67 percent) to 77 

(79 percent). Acceptable USEPA toxicity values are not available for the remaining 40 (out of the 79) analytes without existing human-health benchmarks; therefore, HBSL values could 

not be determined for these 40 analytes (10 pesticides and 

30 VOCs) (Appendix 3). 

Fourteen of the 46 compounds with new HBSL values 

were detected in this study, increasing the total number of 

detected unregulated compounds with human-health benchmarks from 24 of 56 compounds (43 percent) to 36 (64 percent) 

(fig. 3). Two of the 14 detected unregulated compounds with 

new HBSL values (carbaryl and diuron) have Lifetime HA 

values published by USEPA OW, but new HBSL ranges were 

calculated using updated toxicity data published by USEPA 

OPP. The Lifetime HA values for carbaryl and diuron published 

in 1988 are based on their USEPA OW cancer classifications as 

Group D carcinogens, indicating that they are not classifiable as 

to human carcinogenicity (U.S. Environmental Protection 

Agency, 2004). More recent toxicity data published by USEPA 

OPP indicates that carbaryl and diuron are “likely to be carcinogenic to humans” and “known/likely” carcinogens, respectively 

(U.S. Environmental Protection Agency, 2002c and 2003e). For 

comparison purposes, the figures and tables in this report that 

include carbaryl and diuron provide both their HBSL concentration ranges and Lifetime HA values. Carbaryl was not identified as a contaminant of potential human-health concern in 

any well type. Diuron was identified as a contaminant of potential human-health concern in domestic and monitoring wells 

(BQmax = 1) using the low end of the HBSL range (tables 5 and 

8), but it also would have been identified as a contaminant of 

potential human-health concern in these wells types using the 

Lifetime HA value (table 5). 
Benefits of Applying Health-Based Screening Levels to Water-Quality Data 47

Figure 11. Cumulative distributions of Benchmark Quotient values for (a) pesticides, (b) VOCs, and (c) pesticides and

VOCs with human-health benchmarks detected in individual domestic wells in the Kirkwood-Cohansey aquifer system,

and aquifers in the New England and Piedmont Physiographic Provinces in the Long Island-New Jersey Study Unit.

EXPLANATION

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

0

20

40

60

80

100

10-6 102 100 10-2 10-4

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

10-6

0

20

40

60

80

100

102 100 10-2 10-4

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

10-6

0

20

40

60

80

100

102 100 10-2 10-4

(a)

Pesticides

(c)

Pesticides

and VOCs

(b)

VOCs

When the cumulative percent is less than 100, contaminants with human-health benchmarks were detected in

less than 100 percent of individual wells. 

BQSiteMax Kirkwood-Cohansey aquifer system

BQSiteMax Piedmont Physiographic Province

BQSiteMax New England Physiographic Province 

BQSiteSum Kirkwood-Cohansey aquifer system

BQSiteSum New England Physiographic Province 

BQSiteSum Piedmont Physiographic Province

[BQ, Benchmark Quotient = ratio of measured concentration to human-health benchmark value; VOC, volatile organic compound;

BQSiteMax = maximum BQ value in an individual well; BQSiteSum, sum of all BQ values in an individual well] 
48 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Figure 12. Cumulative distributions of Benchmark Quotient values for (a) pesticides, (b) VOCs, and (c) pesticides and VOCs

with human-health benchmarks detected in individual shallow monitoring wells representing agriculture, old urban, new

urban, and undeveloped land uses in the Kirkwood-Cohansey aquifer system in the Long Island-New Jersey Study Unit.

EXPLANATION

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

0

20

40

60

80

100

10-6 102 102 100 10-2 10-4

10-6 102 102 100 10-2 10-4

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

0

20

40

60

80

100

BQSiteMax or BQSiteSum

CUMULATIVE PERCENT

OF WELLS WITH

BQ VALUES

0

20

40

60

80

100

(a)

Pesticides

(c)

Pesticides

and VOCs

(b)

VOCs

When the cumulative percent is less than 100, contaminants with human-health

benchmarks were detected in less than 100 percent of individual wells. 

BQSiteMax agricultural land use

BQSiteMax new urban land use

BQSiteMax old urban land use 

BQSiteSum agricultural land use

BQSiteSum old urban land use 

BQSiteSum new urban land use

BQSiteMax undeveloped land use BQSiteSum undeveloped land use

[BQ, Benchmark Quotient = ratio of measured concentration to human-health benchmark value; VOC, volatile organic compound;

BQSiteMax = maximum BQ value in an individual well; BQSiteSum, sum of all BQ values in an individual well] 

10-6 102 102 100 10-2 10-4
Benefits of Applying Health-Based Screening Levels to Water-Quality Data 49

Figure 13. Detection frequencies and Maximum Benchmark Quotient values for unregulated pesticides and VOCs with new HBSL 

values detected in (a) public-supply wells, (b) domestic wells, and (c) monitoring wells in the Long Island-New Jersey Study Unit.

(a)

Pesticides

(c)

Pesticides

and VOCs

(b)

VOCs

[BQmax, Maximum Benchmark Quotient = ratio of maximum detected concentration to human-health benchmark value; VOC, volatile organic

compound; HBSL, Health-Based Screening Level; 1,1,2-TCFA, 1,1,2-trichloro-1,2,2-trifluoroethane; EPTC, 5-ethyl dipropylthiocarbamate;

USEPA, U.S. Environmental Protection Agency; Lifetime HA, Lifetime Health Advisory; μg/L, micrograms per liter] 

EXPLANATION

Maximum Benchmark

 Quotient value = 1 

Maximum Benchmark

 Quotient value = 0.1 

Detection frequency =

 10 percent 

Public-supply wells

Domestic wells

Monitoring wells

*

**

MAXIMUM BENCHMARK QUOTIENT VALUE

DETECTION FREQUENCY, IN PERCENT

102 100 10-2 10-4 10-6 10-8

DETECTION FREQUENCY, IN PERCENT

102 100 10-2 10-4 10-6 10-8

DETECTION FREQUENCY, IN PERCENT

102 100 10-2 10-4 10-6 10-8

Carbaryl has a USEPA Lifetime HA value (700 μg/L); it also has a new HBSL range (40-4,000 μg/L) based

on updated toxicity data published by USEPA Office of Pesticide Programs. BQmax values for carbaryl

in this figure were calculated using an HBSL of 40 μg/L. 

Diuron has a USEPA Lifetime HA (10 μg/L). Diuron also has a new HBSL range (2-200 μg/L) based on

updated toxicity data published by USEPA Office of Pesticide Programs. BQmax values for diuron in

this figure were calculated using an HBSL of 2 μg/L.

Isopropylbenzene

Carbaryl*

1,1,2-TCFA

1,1,2-TCFA

EPTC Diuron**

Carbaryl*

Ethyl ether

Acetone Benfluralin

Napropamide

Isopropylbenzene

Isopropylbenzene

& Napropamide

Carbon disulfide

Carbon disulfide

Pendimethalin Diuron**

Linuron

Norflurazon

Carbaryl*

Acetone

Acetochlor

Linuron

Ethyl ether

40

30

20

10

0

40

30

20

10

0

40

30

20

10

0
50 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

The other 12 detected compounds that have new HBSL 

values were detected at concentrations ranging from 30- to 12-

million-fold less than HBSL values (BQmax < 0.1) in all three 

well types (fig. 13) and, therefore, were not identified as being 

contaminants of potential human-health concern in any well 

type. Before HBSL values were calculated, these 12 compounds would have been detected, but their occurrence could 

not have been interpreted in a human-health context using 

USEPA drinking-water standards and guidelines. Twelve of the 

14 detected unregulated compounds with new HBSL values 

were detected in public-supply and (or) domestic wells, and all 

but diuron have BQmax values less than 0.1 (fig. 13a and 13b). 

Because these water resources are used as drinking-water supplies, it is particularly valuable to explain the occurrence of 

these contaminants in a human-health context.

In this report, measured concentrations of pesticides and 

VOCs are normalized to human-health benchmarks (MCL and 

HBSL values). It is common to present distributions of measured concentration data as in figures 4 and 5; however, the distributions of measured concentration data relative to humanhealth benchmarks have infrequently been presented as in figures 6-13. These types of figures allow for human-health related 

comparisons between compounds, well types, sampling 

regions, and land use. These types of figures can be created 

without HBSL values, instead using only USEPA drinkingwater standards and guidelines as benchmarks. The addition of 

HBSL values, however, allows for the comparison of groundwater quality data in a human-health context for a larger suite of 

contaminants than those that have existing drinking-water standards and guidelines. 

Additionally, HBSL values are scientifically defensible 

human-health benchmarks that provide a useful threshold for 

determining when measured contaminant concentrations in raw 

water approach or exceed concentrations that are relevant to 

human health. HBSL values can be used to assist with groundwater quality monitoring efforts and be used as planning tools 

to help (1) identify water resources with contaminant concentrations of potential human-health concern, (2) identify locations for future water-supply development, and (3) prioritize 

which contaminants detected at a site or in a study area are of 

potential human-health concern and may merit further study, 

monitoring, toxicity testing, regulation, or source control. 

Summary

The primary objective of this report is to demonstrate the 

use of the Health-Based Screening Level (HBSL) approach as a 

tool for communicating water-quality data in a human-health 

context. A retrospective analysis of water-quality data was performed using ground-water quality data collected as part of the 

work conducted by the U.S. Geological Survey National WaterQuality Assessment (NAWQA) Program in the Long IslandNew Jersey (LINJ) Coastal Drainages Study Unit. Another 

important objective of this report is to provide guidance on the 

use and interpretation of HBSL values and other human-health 

benchmarks in the analyses of water-quality data in other study 

areas. This guidance is intended primarily for USGS personnel 

conducting state- or local-scale water-quality studies; however, 

it can also be applied more generally by other agencies or organizations to facilitate the interpretation of water-quality data in 

a human-health context. 

Ground-water samples were collected from 30 public-supply, 82 domestic, and 108 monitoring wells in New Jersey (3 

wells in New York), and were analyzed for 97 pesticides and 85 

volatile organic compounds (VOCs) during 1996-98. U.S. 

Environmental Protection Agency (USEPA) drinking-water 

standards or guidelines do not exist for 79 of these 182 compounds. Nonetheless, acceptable USEPA toxicity values are 

available for 39 of the 79 compounds; new HBSL values were 

calculated for these 39 unregulated compounds (that is, compounds without drinking-water standards) plus an additional 7 

unregulated compounds for which updated toxicity data were 

available. Fourteen of these 46 compounds with new HBSL values were detected in the LINJ Study Unit. HBSL values were 

calculated using USEPA toxicity values and USEPA Office of 

Water methodologies. The use of HBSL values, in addition to 

USEPA standards and guidelines, increased the total number of 

pesticides and VOCs with human-health benchmarks analyzed 

in the study from 103 to 142 out of 182 compounds, a 

21-percent increase. 

Benchmark Quotient (BQ) values, defined as the ratio of 

the measured concentration of a detected contaminant to its 

Maximum Contaminant Level (MCL) value (for a regulated 

compound) or to its HBSL value (for an unregulated compound), were calculated for all detected pesticides and VOCs. 

Pesticides and VOCs were identified as being of potential 

human-health concern if their maximum detected concentrations in any well type were within a factor of 10 of their humanhealth benchmarks (that is, BQmax 0.1). Most (57 of 77) 

detected pesticides and VOCs with human-health benchmarks 

were detected at concentrations well below these levels 

(BQmax < 0.1), including 13 of the 14 detected compounds 

with new HBSL values. Twenty contaminants (6 pesticides and 

14 VOCs) were identified as being of potential human-health 

concern in the study area because they had BQmax values 

greater than or equal to 0.1 for at least one well type. Four patterns of the occurrence of these 20 contaminants emerged.

1. Four contaminants—dieldrin, 1,2-dibromoethane, tetrachloroethylene, and trichloroethylene—were (1) measured in concentrations that met or exceeded humanhealth benchmarks and (2) frequently detected (that is, 

detected in more than 10 percent of samples) in raw 

(untreated) ground water that is used as drinking water 

(that is, public-supply wells and (or) domestic wells) and, 

therefore, are particularly relevant to human health. 

2. Three contaminants—dinoseb, diuron, and 1,2-dibromo3-chloropropane—were measured in concentrations that 

met or exceeded human-health benchmarks in 

monitoring and (or) domestic wells, but were not 

frequently detected in any well type. 
Acknowledgments 51

3. Nine contaminants—atrazine, simazine, benzene, 1,1-

dichloroethane, 1,1-dichloroethene, cis-1,2-

dichloroethylene, 1,2-dichloropropane, methyl tert-butyl 

ether, and trichloromethane—were detected in measured 

concentrations that were less than, but within a factor of 

10 of human-health benchmarks in at least one well type, 

and were frequently detected in public-supply or 

domestic wells. 

4. Four contaminants—heptachlor epoxide, chloroethylene, 

1,2-dichloroethane, and methylene chloride—were 

detected in measured concentrations that were less than, 

but within a factor of 10 of human-health benchmarks in 

monitoring or domestic wells, but were not frequently 

detected in any well type. 

Eighteen of the 20 contaminants of potential human-health 

concern had Minimum Reporting Level (MRL) values less than 

their MCL or HBSL values for all well types, which permitted 

quantitation of these contaminants at concentrations that are relevant to human health. In contrast, 1,2-dibromo-3-chloropropane and 1,2-dibromoethane had MRL values greater than their 

MCL values in at least one well type, indicating the possibility 

that these two contaminants may be present, but not detected, in 

some samples at concentrations that are relevant to human 

health. In addition to the 20 contaminants of potential humanhealth concern identified in this study, deethylatrazine (a degradation product of the herbicides atrazine and propazine) is noteworthy because it was frequently detected in all well types, but 

it has no human-health benchmark for comparison with 

detected concentrations. 

The detection frequencies of pesticides and VOCs generally were higher for public-supply well samples than for domestic-well samples. More contaminants were detected at concentrations within a factor of 10 of human-health benchmarks in 

samples from domestic wells (10 contaminants) than from public-supply wells (7 contaminants). Because water from domestic wells typically is consumed directly (that is, without treatment), this is an important finding and indicates that additional 

monitoring may be warranted for domestic wells. 

Because multiple contaminants (53 to 75 pesticides plus 

VOCs) were detected in each type of well, initial efforts were 

undertaken to examine the occurrence of multiple contaminants 

in individual wells in relation to their respective human-health 

benchmarks. At least one pesticide or VOC with a humanhealth benchmark was detected in 208 of 220 (95 percent) individual wells. BQ values were calculated for detected compounds with human-health benchmarks in each well, and these 

values were used to determine the maximum BQ value 

(BQSiteMax) and the sum of all BQ values (BQSiteSum) 

for each individual well. In all wells, the median ratio of 

BQSiteMax to BQSiteSum values was approximately 1 for pesticides, and ranged from 0.77 for public-supply wells to 0.94 for 

domestic wells for VOCs, indicating that the BQSiteMax value 

makes up the majority of the sum. In other words, in this data 

set, the summed BQ value for all contaminants detected in a 

well was not substantially greater than the BQ value for the 

individual compound whose measured concentration in that 

well was highest relative to its human-health benchmark.

When the ground-water data were evaluated by individual 

well, BQSiteMax and BQSiteSum values were statistically 

greater (95-percent confidence level) for public-supply wells 

than for domestic and monitoring wells, likely because publicsupply wells had the largest percentage of individual wells with 

pesticide or VOC concentrations that exceeded their humanhealth benchmarks. Although more contaminants were detected 

at concentrations with BQmax ≥ 0.1 in samples from domestic 

wells than from public-supply wells, BQSiteMax and BQSiteSum values were significantly lower (95-percent confidence 

level) for individual domestic wells than for individual publicsupply and monitoring wells likely because (1) fewer domestic 

wells contained pesticides or VOCs detected at concentrations 

greater than human-health benchmarks than public-supply or 

monitoring wells, and (2) more domestic wells had no detections of compounds with human-health benchmarks than public-supply or monitoring wells. 

The HBSL approach is an effective tool for placing waterquality data in a human-health context. As part of this pilot 

effort: (1) HBSL values increased the number of analyzed and 

detected compounds with human-health benchmarks; (2) guidance was provided on the use of HBSL values in the interpretation of water-quality data in a human-health context; (3) most 

detected contaminants were not identified as being of potential 

human-health concern, including 13 of the 14 contaminants 

with new HBSL values; and (4) contaminants of potential 

human-health concern that were identified were evaluated in 

the context of several factors, including the magnitude of BQ 

values, detection frequency, well type, and use of water.

Acknowledgments

The authors gratefully acknowledge the essential contributions of William G. Wilber, USGS NAWQA National Synthesis Coordinator, and John S. Zogorski, Chief of the USGS VOC

National Synthesis Project, who spearheaded this pilot effort. 

The authors also acknowledge the collaboration and cooperation provided by individuals in several USEPA offices in the 

development of HBSL values, particularly Joyce Donohue from 

USEPA OW and Catherine Eiden from USEPA OPP, who were 

instrumental in HBSL development for compounds with multiple USEPA cancer classifications or toxicity values. Additionally, the authors thank Richard C. Hertzberg from USEPA ORD 

for his technical review of the “Health-Based Comparison of 

Wells with Multiple Contaminants” section. The authors are 

grateful to Mark Ayers, former LINJ Study-Unit Chief, for 

helping to develop collaborative relationships between USGS, 

NJDEP, and OHSU. The authors also acknowledge and thank 

Gregory C. Delzer, Michael J. Focazio, and Eric F. Vowinkel of 

USGS for their insightful technical reviews of this report. 

Finally, the authors thank Ruth M. Larkins who edited this 

report, and Ella Decker and Connie Ross who prepared this 

report for publication. 
52 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

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U.S. Environmental Protection Agency, 2003c, Code of Federal 

Regulations, title 40 - Protection of environment, chapter 1 - 

Environmental Protection Agency, subchapter E - Pesticide 

programs, part 159 - Statements of policies and interpretations, subpart D—reporting requirements for risk/benefit 

information: Washington, D.C., National Archives and 

Records Administration, 40 CFR 159, July 1, 2003, 

http://www.gpoaccess.gov/ecfr/index.html.

U.S. Environmental Protection Agency, 2003d, Framework for 

cumulative risk assessment: Washington, D.C., U.S. Environmental Protection Agency, Risk Assessment Forum, 

EPA/630/P-02/001F, May 2003, 109 p.

U.S. Environmental Protection Agency, 2003e, Interim reregistration eligibility decision for carbaryl, list A, case 0080: 

Washington D.C., U.S. Environmental Protection Agency, 

Office of Prevention, Pesticides and Toxic Substances, 

June 30, 2003, 160 p., 

http://www.epa.gov/oppsrrd1/REDs/carbaryl_ired.pdf.

U.S. Environmental Protection Agency, 2004, 2004 Edition of 

the drinking water standards and health advisories: Washington, D.C., U.S. Environmental Protection Agency, Office 

of Water, EPA 822-R-04-005, Winter 2004, 20 p., 

http://www.epa.gov/waterscience/drinking/standards/

dwstandards.pdf.

U.S. Geological Survey, 1999, Pesticides analyzed in NAWQA 

samples—use, chemical analyses, and water-quality criteria: 

U.S. Geological Survey, Pesticide National Synthesis 

Project, updated August 20, 1999, accessed May 28, 2004, at 

URL http://ca.water.usgs.gov/pnsp/anstrat/.

Vogue, P.A., Kerle, E.A., and Jenkins, J.J., 1994, Oregon State 

University extension pesticide properties database: National 

Pesticide Information Center, updated July 24, 1994, 

accessed August 4, 2002, at URL 

http://npic.orst.edu/ppdmove.htm.

Vowinkel, E.F., Clawges, R.M., Buxton, D.E., Stedfast, D.A., 

and Louis, J.B., 1996, Vulnerability of public drinking water 

supplies in New Jersey to pesticides: U.S. Geological Survey 

Fact Sheet FS-165-96, 2 p., 

http://nj.usgs.gov/publications/FS/fs-165-96.pdf.

Ware, G.G., 1989, The pesticide book: New York, W. H. 

Freeman and Company, 386 p.

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—Determination of pesticides in 

water by Carbopak-B solid-phase extraction and high-performance liquid chromatography: U.S. Geological Survey 

Open-File Report 96-216, 42 p., http://nwql.usgs.gov/Public/

pubs/OFR96-216/OFR96-216.html.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water-Quality Laboratory—Determination 

of pesticides in water by C-18 solid-phase extraction and 

capillary-column gas chromatography/mass spectrometry 

with selected-ion monitoring: U.S. Geological Survey OpenFile Report 95-181, 49 p.

Zogorski, J.S., Morduchowitz, A., Baehr, A.L., Bauman, B.J., 

Conrad, D.L., Drew, R.T., Korte, N.E., Lapham, W.W., 

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and water quality, Interagency assessment of oxygenated 

fuels, ch. 2: Washington, D.C., Office of Science and Technology Policy, Executive Office of the President, p. 2-1 - 

2-80.
Glossary 55

Glossary

Benchmark Quotient (BQ) Ratio of the measured 

concentration of a detected contaminant to its Maximum 

Contaminant Level (MCL) value (for a regulated compound) 

or to its Health-Based Screening Level (HBSL) value (for an 

unregulated compound).

• BQmax Ratio of the maximum detected 

concentration of a contaminant in a given well type to 

its MCL or HBSL value. 

• BQmed-det Ratio of the median of detected 

concentrations of a contaminant in a given well type to 

its MCL or HBSL value.

• BQmed-all Ratio of the median of all samples 

(including non-detections) of a contaminant in a given 

well type to its MCL or HBSL value.

• BQSiteMax Maximum of Benchmark Quotient 

values for detected contaminants in a given individual 

well.

• BQSiteSum Sum of all Benchmark Quotient values 

for detected contaminants in a given individual well.

Contaminants of Potential Human-Health Concern As 

used in this report, contaminants with maximum detected 

concentrations within a factor of 10 of applicable humanhealth benchmarks (that is, Maximum Benchmark Quotients 

(BQmax) greater than or equal to 0.1) for any well type. 

Drinking-Water Guideline As used in this report, threshold 

concentrations that have no regulatory status, but are issued in 

an advisory capacity by the U.S. Environmental Protection 

Agency (USEPA) or state agencies.

Drinking-Water Standard As used in this report, threshold 

concentrations that are legally enforceable by the USEPA or 

state agencies.

Frequently Detected Compound As used in this report, a 

compound that is detected in at least 10 percent of samples 

from any given well type.

Health-Based Screening Level (HBSL) Estimates of 

benchmark concentrations (for noncarcinogens) or 

concentration ranges (for carcinogens) of contaminants in 

water that (1) may be of potential human-health concern; 

(2) can be used as threshold values against which measured 

concentrations of contaminants in ambient water samples can 

be compared; and (3) are consistent with USEPA Office of 

Water methodologies for setting drinking-water Lifetime 

Health Advisory and Risk-Specific Dose values (Toccalino and 

others, 2003; U.S. Environmental Protection Agency, 1988, 

1993).

Human-Health Benchmarks As used in this report, a 

variety of drinking-water standards, guidelines, and threshold 

concentrations. These include USEPA and New Jersey 

Department of Environmental Protection (NJDEP) MCL 

values, USEPA Lifetime Health Advisory and Risk-Specific 

Dose values, NJDEP Ground Water Quality Criteria and 

Interim-Specific Ground Water Quality Criteria, and HBSL 

values developed collaboratively by the U.S. Geological 

Survey, USEPA, NJDEP, and Oregon Health & Science 

University.

Lifetime Health Advisory (Lifetime HA) The 

concentration of a chemical in drinking water that is not 

expected to cause any adverse noncarcinogenic effects over a 

lifetime of exposure (70 years). The Lifetime HA is based on 

exposure of a 70-kilogram adult consuming 2 liters of water 

per day, and assumes that only a portion (generally 20 percent) 

of the total exposure to a contaminant is from drinking water 

(U.S. Environmental Protection Agency, 1993 and 2004). A 

drinking-water guideline value issued by USEPA.

New HBSL As used in this report, HBSL values calculated 

for unregulated contaminants that (1) have no existing USEPA 

drinking-water guideline values or (2) have more recent 

USEPA toxicity data than that used to calculate existing 

USEPA drinking-water guideline values, resulting in different 

benchmark values.

Reference Dose (RfD) An estimate (with an uncertainty of 

perhaps one order of magnitude) of the daily exposure that is 

likely to be without appreciable risk of deleterious health 

effects in the human population (including sensitive 

subgroups) over an individual's lifetime (70 years) (U.S. 

Environmental Protection Agency, 1989b). 

Regulated Compounds As used in this report, compounds 

with Federal and (or) state (specifically New Jersey) drinkingwater standards. 

Risk-Specific Dose (RSD) The drinking-water concentration 

associated with a specified cancer risk level (typically 1 in 

10,000, 1 in 100,000, or 1 in 1,000,000), under certain 

exposure conditions: consumption of 2 liters per day of 

drinking water by a 70-kilogram body weight individual over a 

lifetime (70 years) (U.S. Environmental Protection Agency, 

1993). A drinking-water guideline value issued by USEPA.

Slope Factor (SF) The cancer potency estimate for a 

compound as derived from the slope of the dose-response 

(carcinogenicity) data extrapolated to zero using an appropriate 

mathematical model (U.S. Environmental Protection Agency, 

1989a,1993). 

Unregulated Compounds As used in this report, 

compounds without Federal and (or) state (specifically New 

Jersey) drinking-water standards. Note that a compound that is 

unregulated in drinking water (federally, under the Safe 

Drinking Water Act) may be regulated in other contexts and 

under other statutes.

Appendixes
58 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Appendix 1. U.S. Environmental Protection Agency and New Jersey MCL values (current as of August 2004) for

regulated pesticides and VOCs analyzed in ground-water samples from the Long Island-New Jersey Study Unit. 

[MCL, Maximum Contaminant Level; VOC, volatile organic compound; CASRN, Chemical Abstracts Service Registry Number; USEPA, 

U.S. Environmental Protection Agency; μg/L, micrograms per liter; NJ, New Jersey; LINJ, Long Island-New Jersey Study Unit]

Compound CASRN USEPA MCL1

(μg/L)

NJ MCL2

(μg/L) Detected in LINJ

Pesticides

Alachlor 15972-60-8 2 2 yes

Aldicarb 116-06-3 3 3 no

Aldicarb sulfone 1646-88-4 3 3 no

Aldicarb sulfoxide 1646-87-3 4 4 yes

Atrazine 1912-24-9 3 3 yes

Carbofuran 156-36-6 40 40 yes

Chlordane, technical 12789-03-6 2 .5 yes

2,4-dichlorophenoxyacetic acid (2,4-D) 94-75-7 70 70 yes

Dinoseb 88-85-7 7 7 yes

Endrin 72-20-8 2 2 no

Heptachlor 76-44-8 .4 .4 no

Heptachlor epoxide 1024-57-3 .2 .2 yes

Lindane 58-89-9 .2 .2 yes

Methoxychlor 72-43-5 40 40 no

Oxamyl 23135-22-0 200 200 no

Picloram 1918-02-1 500 500 yes

Simazine 122-34-9 4 4 yes

Toxaphene 8001-35-2 3 3 no

2-(2,4,5-trichlorophenoxy) propionic 

acid (2,4,5-TP)

93-72-1 50 50 yes

VOCs

Benzene 71-43-2 5 1 yes

Bromodichloromethane 75-27-4 80 80 yes

Bromoform 75-25-2 80 80 yes

Chlorobenzene 108-90-7 100 50 yes

Chlorodibromomethane 124-48-1 80 80 yes

Chloroethylene 75-01-4 2 2 yes

1,2-Dibromo-3-chloropropane 96-12-8 .2 .2 yes

1,2-Dibromoethane 106-93-4 .05 .05 yes

1,2-Dichlorobenzene 95-50-1 600 600 yes

1,3-Dichlorobenzene 541-73-1 NAV 600 yes

1,4-Dichlorobenzene 106-46-7 75 75 yes
Appendix 1 59

VOCs—Continued

1,1-Dichloroethane 75-34-3 NAV 50 yes

1,2-Dichloroethane 107-06-2 5 2 yes

1,1-Dichloroethene 75-35-4 7 2 yes

cis-1,2-Dichloroethylene 156-59-2 70 70 yes

trans-1,2-Dichloroethylene 156-60-5 100 100 yes

1,2-Dichloropropane 78-87-5 5 5 yes

Ethylbenzene 100-41-4 700 700 yes

Methyl tert-butyl ether 1634-04-4 NAV 70 yes

Methylene chloride 75-09-2 5 3 yes

Naphthalene 91-20-3 NAV 300 yes

Styrene 100-42-5 100 100 yes

1,1,2,2-Tetrachloroethane 79-34-5 NAV 1 no

Tetrachloroethylene 127-18-4 5 1 yes

Tetrachloromethane 56-23-5 5 2 yes

Toluene 108-88-3 1,000 1,000 yes

1,2,4-Trichlorobenzene 120-82-1 70 9 no

1,1,1-Trichloroethane 71-55-6 200 30 yes

1,1,2-Trichloroethane 79-00-5 5 3 no

Trichloroethylene 79-01-6 5 1 yes

Trichloromethane 67-66-3 80 80 yes

Xylenes (sum of isomers)3 1330-20-7 10,000 1,000 yes

1U.S. Environmental Protection Agency, 2003a and 2004.

2New Jersey Department of Environmental Protection, 2000.

3Sum of Xylenes = m- & p-xylene (CASRN 108-38-3 & 106-42-3) + o-xylene (CASRN 95-47-6). 

Appendix 1. U.S. Environmental Protection Agency and New Jersey MCL values (current as of August 2004) for

regulated pesticides and VOCs analyzed in ground-water samples from the Long Island-New Jersey Study Unit. —Continued

[MCL, Maximum Contaminant Level; VOC, volatile organic compound; CASRN, Chemical Abstracts Service Registry Number; USEPA, 

U.S. Environmental Protection Agency; μg/L, micrograms per liter; NJ, New Jersey; LINJ, Long Island-New Jersey Study Unit]

Compound CASRN USEPA MCL1

(μg/L)

NJ MCL2

(μg/L) Detected in LINJ
60 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Appendix 2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs analyzed in ground-water samples from the 

Long Island-New Jersey Study Unit.

[HBSL, Health-Based Screening Level; VOC, volatile organic compound; CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; 

LINJ, Long Island-New Jersey Study Unit; USEPA, U.S. Environmental Protection Agency; RSD, Risk-Specific Dose; OPP, Office of Pesticide Programs 

(USEPA); q1*, cancer potency factor; IRIS, Integrated Risk Information System; SF, oral slope factor; Lifetime HA, Lifetime Health Advisory; RfD, oral 

reference dose; HEAST, Health Effects Assessment Summary Tables (USEPA); OW, Office of Water (USEPA)]

Compound CASRN

HBSL value

or range1

(μg/L)

Basis for HBSL

(see Toccalino and others, 2003, for

details on the HBSL approach)

New

HBSL2

Detected in

LINJ

Pesticides

Acetochlor 34256-82-1 2 to 200 RSD approach using OPP q1* yes yes

Acifluorfen3 50594-66-6 90 Lifetime HA approach using IRIS RfD yes no

Aldrin 309-00-2 0.002 to 0.2 RSD approach using IRIS SF no no

Azinphos-methyl 86-50-0 10 Lifetime HA approach using OPP RfD yes no

Benfluralin 1861-40-1 2,000 Lifetime HA approach using IRIS RfD yes yes

Bentazon 25057-89-0 200 Lifetime HA value no yes

Bromacil 314-40-9 90 Lifetime HA value no no

Bromoxynil 1689-84-5 10 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes no

Butylate 2008-41-5 400 Lifetime HA value no yes

Carbaryl4 63-25-2 40 to 4,000 RSD approach using OPP q1* yes yes

Chloramben 133904 100 Lifetime HA value no no

Chlorothalonil5 1897-45-6 5 to 500 RSD approach using OPP q1* yes no

Chlorpyrifos 2921-88-2 20 Lifetime HA value no no

Clopyralid 1702-17-6 4,000 Lifetime HA approach using OPP RfD yes no

Cyanazine 21725-46-2 1 Lifetime HA value no yes

Dacthal 1861-32-1 70 Lifetime HA value no yes

2,4-Dichlorophenoxybutyric 

acid (2,4-DB)

94-82-6 60 Lifetime HA approach using IRIS RfD yes no

p,p'-Dichlorodiphenyldichloroethane (p,p'-DDD)72-54-8 0.1 to 10 RSD approach using IRIS SF no no

p,p'-Dichlorodiphenyldichloroethylene (p,p'-DDE)72-55-9 0.1 to 10 RSD approach using IRIS SF no yes

p,p'-Dichlorodiphenyltrichloroethane (p,p'-DDT)50-29-3 0.1 to 10 RSD approach using IRIS SF no no

Diazinon 333-41-5 .6 Lifetime HA value no no

Dicamba 1918-00-9 200 Lifetime HA value no yes

Dichlobenil 1194-65-6 9 Lifetime HA approach for Group C

carcinogens using OPP RfD

yes no

Dichlorprop 120-36-5 40 Lifetime HA approach using OPP RfD yes no

Dieldrin 60-57-1 0.002 to 0.2 RSD approach using IRIS SF no yes

Disulfoton 298-04-4 .3 Lifetime HA value no no

Diuron6 330-54-1 2 to 200 RSD approach using OPP q1* yes yes
Appendix 2 61

Appendix 2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs analyzed in ground-water samples from the 

Long Island-New Jersey Study Unit.—Continued

Compound CASRN

HBSL value

or range1

(μg/L)

Basis for HBSL

(see Toccalino and others, 2003, for

details on the HBSL approach)

New

HBSL2

Detected in

LINJ

Pesticides—Continued

Endosulfan 115-29-7 40 Lifetime HA approach using IRIS RfD yes no

5-Ethyl dipropylthiocarbamate (EPTC)759-94-4 200 Lifetime HA approach using IRIS RfD yes yes

Esfenvalerate 66230-04-4 100 Lifetime HA approach using OPP RfD yes no

Ethalfluralin 55283-68-6 30 Lifetime HA approach for Group C

carcinogens using OPP RfD

yes no

Ethoprophos 13194-48-4 1 to 100 RSD approach using OPP q1* yes no

Fluometuron 2164-17-2 90 Lifetime HA value no yes

Fonofos 944-22-9 10 Lifetime HA value no no

alpha-Hexachlorocyclohexane (alpha-HCH) 319-84-6 0.006 to 0.6 RSD approach using IRIS SF no no

Linuron 330-55-2 1 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes yes

Malathion 121-75-5 100 Lifetime HA value no no

2-Methyl-4-chlorophenoxyacetic acid (MCPA)94-74-6 4 Lifetime HA value no no

4-(2-Methyl-4-chlorophenoxy) butyric acid (MCPB)94-81-5 70 Lifetime HA approach using IRIS RfD yes no

Methiocarb 2032-65-7 40 Lifetime HA approach using OPP RfD yes no

Methomyl 16752-77-5 200 Lifetime HA value no yes

Metolachlor 51218-45-2 100 Lifetime HA value no yes

Metribuzin 21087-64-9 200 Lifetime HA value no yes

Mirex 2385-85-5 1 Lifetime HA approach using IRIS RfD yes no

Molinate 2212-67-1 1 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes no

Napropamide 15299-99-7 700 Lifetime HA approach using IRIS RfD yes yes

Norflurazon 27314-13-2 30 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes yes

Oryzalin 19044-88-3 40 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes no

Parathion 56-38-2 .02 Lifetime HA approach for Group C

carcinogens using OPP RfD

yes no

Parathion-methyl 298-00-0 2 Lifetime HA value no no

Pebulate 1114-71-2 50 Lifetime HA approach using OPP RfD yes no
62 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Pesticides—Continued

Pendimethalin 40487-42-1 30 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes yes

Phorate 298-02-2 4 Lifetime HA approach using OPP RfD yes no

Prometon 1610-18-0 100 Lifetime HA value no yes

Propachlor7 1918-16-7 1 to 100 RSD approach using OPP q1* yes no

Propanil 709-98-8 4 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes no

Propargite 2312-35-8 0.2 to 20 RSD approach using OPP q1* yes no

Propham 122-42-9 100 Lifetime HA value no no

Propoxur8 114-26-1 9 to 900 RSD approach using OPP q1* yes no

Propyzamide9 23950-58-5 2 to 200 RSD approach using OPP q1* yes no

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T)93-76-5 70 Lifetime HA value no no

Tebuthiuron 34014-18-1 500 Lifetime HA value no yes

Terbacil 5902-51-2 90 Lifetime HA value no yes

Terbufos 13071-79-9 .9 Lifetime HA value no no

Thiobencarb 28249-77-6 70 Lifetime HA approach using IRIS RfD yes no

Triallate 2303-17-5 9 Lifetime HA approach for Group C

carcinogens using IRIS RfD

yes no

Triclopyr 55335-06-3 400 Lifetime HA approach using OPP RfD yes no

Trifluralin 1582-09-8 5 Lifetime HA value no yes

VOCs

Acetone 67-64-1 6,000 Lifetime HA approach using IRIS RfD yes yes

Acrylonitrile 107-13-1 0.06 to 6 RSD approach using IRIS SF no no

Bromochloromethane 74-97-5 90 Lifetime HA value no no

Bromomethane 74-83-9 10 Lifetime HA value no no

Carbon disulfide 75-15-0 700 Lifetime HA approach using IRIS RfD yes yes

1-Chloro-2-methylbenzene 95-49-8 100 Lifetime HA value no yes

4-Chlorotoluene 106-43-4 100 Lifetime HA value no no

Dichlorodifluoromethane 75-71-8 1,000 Lifetime HA value no yes

Ethyl ether 60-29-7 1,000 Lifetime HA approach using IRIS RfD yes yes

Ethyl methacrylate 97-63-2 600 Lifetime HA approach using HEAST RfD yes no

Appendix 2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs analyzed in ground-water samples from the 

Long Island-New Jersey Study Unit.—Continued

Compound CASRN

HBSL value

or range1

(μg/L)

Basis for HBSL

(see Toccalino and others, 2003, for

details on the HBSL approach)

New

HBSL2

Detected in

LINJ
Appendix 2 63

VOCs—Continued

Hexachlorobutadiene 87-68-3 1 Lifetime HA value no no

Hexachloroethane 67-72-1 1 Lifetime HA value no no

Isopropylbenzene 98-82-8 700 Lifetime HA approach using IRIS RfD yes yes

Methyl acrylate 96-33-3 200 Lifetime HA approach using HEAST RfD yes no

Methyl acrylonitrile 126-98-7 .7 Lifetime HA approach using IRIS RfD yes no

Methyl chloride 74-87-3 30 Lifetime HA value no yes

Methyl ethyl ketone 78-93-3 4,000 Lifetime HA value no yes

Methyl methacrylate 80-62-6 10,000 Lifetime HA approach using IRIS RfD yes no

1,1,1,2-Tetrachloroethane 630-20-6 70 Lifetime HA value no yes

1,1,2-Trichloro-1,2,2-

trifluoroethane

76-13-1 200,000 Lifetime HA approach using IRIS RfD yes yes

Trichlorofluoromethane 75-69-4 2,000 Lifetime HA value no yes

1,2,3-Trichloropropane 96-18-4 40 Lifetime HA value no yes

1HBSL range corresponds to a 10-6 to 10-4 cancer risk range for unregulated carcinogens.

2Unregulated compounds with new HBSLs do not currently (as of August 2004) have USEPA Lifetime HA or RSD values, except as noted. Unregulated 

compounds that do not have new HBSLs have previously published USEPA Lifetime HA values or USEPA RSD values from IRIS or OW. 

3Based on sodium acifluorfen, CASRN 62476-59-9. Sodium acifluorfen has a USEPA OW 10-4 RSD value (100 μg/L). Sodium acifluorfen also has a new 

HBSL value (90 μg/L) based on an updated cancer classification published by USEPA OPP and toxicity data published by IRIS.

4Carbaryl has a USEPA Lifetime HA value (700 μg/L). Carbaryl also has a new HBSL range (40-4,000 μg/L) based on updated toxicity data published by 

USEPA OPP.

5Chlorothalonil has a USEPA OW 10-4 RSD value (150 μg/L). Chlorothalonil also has a new HBSL range (5-500 μg/L) based on updated toxicity data 

published by USEPA OPP.

6Diuron has a USEPA Lifetime HA (10 μg/L). Diuron also has a new HBSL range (2-200 μg/L) based on updated toxicity data published by USEPA OPP.

7

Propachlor has a USEPA Lifetime HA (90 μg/L). Propachlor also has a new HBSL range (1-100 μg/L) based on updated toxicity data published by USEPA 

OPP.

8

Propoxur has a USEPA Lifetime HA (3 μg/L). Propoxur also has a new HBSL range (9-900 μg/L) based on updated toxicity data published by USEPA OPP.

9Propyzamide has a USEPA Lifetime HA (50 μg/L). Propyzamide also has a new HBSL range (2-200 μg/L) based on updated toxicity data published by 

USEPA OPP.

Appendix 2. HBSL values (current as of August 2004) for unregulated pesticides and VOCs analyzed in ground-water samples from the 

Long Island-New Jersey Study Unit.—Continued

Compound CASRN

HBSL value

or range1

(μg/L)

Basis for HBSL

(see Toccalino and others, 2003, for

details on the HBSL approach)

New

HBSL2

Detected in

LINJ
64 Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort

Appendix 3. Unregulated pesticides and VOCs analyzed for in ground-water samples

from the Long Island-New Jersey Study Unit that have no human-health benchmarks

(as of August 2004). 

[VOC, volatile organic compound; USEPA, U.S. Environmental Protection Agency; CASRN, Chemical

Abstracts Service Registry Number; LINJ, Long Island-New Jersey Study Unit]

Compound CASRN Detected in LINJ

Pesticides

Dacthal monoacid 887-54-7 no

Deethylatrazine 6190-65-4 yes

2,6-Diethylaniline 579-66-8 no

4,6-Dinitro-2-methylphenol 534-52-1 no

Fenuron 101-42-8 yes

3-Hydroxycarbofuran 16655-82-6 no

1-Naphthol 90-15-3 no

Neburon 555-37-3 no

cis-Permethrin 54774-45-7 no

Perthane 72-56-0 no

VOCs

Bromobenzene 108-86-1 yes

Bromoethene 593-60-2 no

n-Butylbenzene 104-51-8 yes

sec-Butylbenzene 135-98-8 yes

tert-Butylbenzene 98-06-6 yes

Chloroethane 75-00-3 yes

3-Chloropropene 107-05-1 no

Dibromomethane 74-95-3 yes

trans-1,4-Dichloro-2-butene 110-57-6 no

1,3-Dichloropropane 142-28-9 yes

2,2-Dichloropropane 594-20-7 no

1,1-Dichloropropene 563-58-6 no

cis-1,3-Dichloropropene 10061-01-5 no

trans-1,3-Dichloropropene 10061-02-6 no

Diisopropylether 108-20-3 yes

Ethyl tert-butyl ether 637-92-3 no

1-Ethyl-2-methylbenzene 611-14-3 yes

2-Hexanone 591-78-6 no

Methyl iodide 74-88-4 yes

4-Methyl-2-pentanone 108-10-1 no

1-Methyl-4-isopropylbenzene 99-87-6 yes

tert-Pentyl methyl ether 994-05-8 yes

n-Propylbenzene 103-65-1 yes

Tetrahydrofuran 109-99-9 yes

1,2,3,4-Tetramethylbenzene 488-23-3 yes

1,2,3,5-Tetramethylbenzene 527-53-7 no

1,2,3-Trichlorobenzene 87-61-6 no

1,2,3-Trimethylbenzene 526-73-8 yes

1,2,4-Trimethylbenzene 95-63-6 yes

1,3,5-Trimethylbenzene 108-67-8 yes
This publication is available online at URL

 http://pubs.water.usgs.gov/sir20045174

Prepared for the National Water-Quality Assessment Program,

 by the Oregon Health & Science University

Text layout by Ella M. Decker.

Graphics by Connie J. Ross.

Information regarding the National Water-Quality Assessment

 Program is available at URLs:

 http://water.usgs.gov/nawqa/

 http://sd.water.usgs.gov/nawqa/vocns/

 http://water.usgs.gov/nawqa/pesticides/
Toccalino and others —Application of Health-Based Screening Levels to Ground-Water Quality Data in a State-Scale Pilot Effort—SIR 2004-5174

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