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U.S. GEOLOGICAL SURVEY

Open-File Report 01-327


Occurrence and Distribution of Selected Contaminants in Public Drinking-Water Supplies in the Surficial Aquifer in Delaware

By Matthew J. Ferrari

 

Abstract

Water samples were collected from August through November 2000 from 30 randomly selected public drinking-water supply wells screened in the unconfined aquifer in Delaware, and analyzed to assess the occurrence and distribution of selected pesticide compounds, volatile organic compounds, major inorganic ions, and nutrients. Water from a subset of 10 wells was sampled and analyzed for radium and radon. The average age of ground water entering the well screens in all the wells was determined to be generally less than 20 years.

 

Low concentrations of pesticide compounds and volatile organic compounds were detected throughout the State of Delaware, with several compounds often detected in each water sample. Pesticide and metabolite (pesticide degradation products) concentrations were generally less than 1 microgram per liter, and were detected in samples from 27 of 30 wells. Of the 45 pesticides and 13 metabolites analyzed, 19 compounds (13 pesticides and 6 metabolites) were detected in at least 1 of the 30 samples. Desethylatrazine, alachlor ethane sulfonic acid, metolachlor ethane sulfonic acid, metolachlor, and atrazine were the most frequently detected pesticide compounds, and were present in at least half the samples. None of the pesticide detections was above the U.S. Environmental Protection Agency’s Primary Maximum Contaminant Levels or Health Advisories. Volatile organic compounds also were present at low concentrations (generally less than 1 microgram per liter) in samples from all 30 wells. Of the 85 volatile organic compounds analyzed, 34 compounds were detected in at least 1 of the 30 samples. Chloroform, tetrachloroethene, and methyl tert-butyl ether were the most frequently detected volatile organic compounds, and were found in at least half the samples. None of the volatile organic compound detections was above U.S. Environmental Protection Agency’s Primary Maximum Contaminant Levels or Health Advisories.

 

A few samples contained compounds with concentrations above the U.S. Environmental Protection Agency’s Primary Maximum Contaminant Levels or Secondary Maximum Contaminant Levels for inorganic compounds and radionuclides. One sample out of 30 contained a concentration of nitrite plus nitrate above the U.S. Environmental Protection Agency’s Primary Maximum Contaminant Level of 10 milligrams per liter as nitrogen. Iron and manganese concentrations above the U.S. Environmental Protection Agency’s Secondary Maximum Contaminant Levels were found in 7 of 30 ground-water samples, most of them from Sussex County. In the 10 wells sampled for radionuclides, only one sample had detectable levels of radium-224 and -226, and another sample contained detectable levels of radium- 228; both of these samples also had detectable gross-alpha and gross-beta activities. None of these activities were above the U.S. Environmental Protection Agency’s Primary Maximum Contaminant Levels or Secondary Maximum Contaminant Levels. Radon was detected in all 10 samples, but was above the current U.S. Environmental Protection Agency’s proposed Primary Maximum Contaminant Level of 300 picocuries per liter in only one sample.

Contents

Abstract

Introduction

Purpose and scope

Acknowledgments

Methods of study

Sampling network design

Sampling collection and analysis

Quality-control sampling

Age dating

Occurrence and distribution of selected contaminants in public drinking-water supplies in the surficial aquifer

Pesticides and metabolites

Volatile organic compounds

Inorganic compounds

Radium and radon

Summary

References cited

Appendixes

Figures

1-2. Maps showing:

1. Location of sampled public-supply wells screened in the unconfined aquifer in Delaware

2. Location of selection cells and public-supply wells screened in the unconfined aquifer in Delaware

3. Map showing pesticide and metabolite detections at each sampling location of public-supply wells screened in the unconfined aquifer in Delaware

 

4. Graph showing pesticides and metabolites detected in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

5. Boxplot showing concentrations of selected pesticides and associated metabolites in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

6. Map showing volatile organic compound detections at each sampling location of public-supply wells screened in the unconfined aquifer in Delaware

 

7. Graph showing volatile organic compounds detected in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

8-9. Maps showing:

8. Location of detections above the U.S. Environmental Protection Agency Primary or Secondary Maximum Contaminant Levels for major ions and nutrients in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

9. Location of public-supply wells in Delaware screened in the unconfined aquifer and sampled public-supply wells screened in the unconfined aquifer in Delaware for radiochemistry

 

Tables

1. Well construction data for sampled public-supply wells screened in the unconfined aquifer in Delaware and modeled ages of ground-water samples

 

2. Pesticides and metabolites measured in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

3. Summary statistics for pesticides and metabolites detected in ground-water samples from

public-supply wells screened in the unconfined aquifer in Delaware, and comparisons to

U.S. Environmental Protection Agency Primary Maximum Contaminant Levels and Health Advisories

 

4. Volatile organic compounds measured in ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware

 

5. Summary statistics for volatile organic compounds detected in ground-water samples from

public-supply wells screened in the unconfined aquifer in Delaware, and comparisons to

U.S. Environmental Protection Agency Primary Maximum Contaminant Levels and Health Advisories

 

6. Summary statistics for selected field parameters, major ions, and nutrients for ground-water samples from public-supply wells screened in the unconfined aquifer in Delaware, and comparisons to U.S. Environmental Protection Agency Primary and Secondary Maximum Contaminant Levels

 

7. Radiochemical activities for ground-water samples from public-supply wells screened in the

unconfined aquifer in Delaware and comparisons to U.S. Environmental Protection Agency Primary Maximum Contaminant Levels

Appendixes

A. Hydrologic data for the Delaware Source Water Assessment Program unconfined aquifer well network—Site information, well construction data, and modeled ages of ground-water samples

 

B. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Field parameters

 

C. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Major inorganic compounds

 

D. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Nutrients

 

E. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Pesticides

 

F. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer

well network—Pesticide metabolites

G. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Volatile organic compounds

 

H. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Radium and radon

 

I. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Age dating:

Ia. Sulfur hexafluoride data.

Ib. Dissolved gas data

 

J. Ground-water quality data for the Delaware Source Water Assessment Program unconfined aquifer well network—Quality-control data:

Ja. Major inorganic compounds

Jb. Nutrients

Jc. Pesticides

Jd. Pesticide metabolites

Je. Volatile organic compounds

Jf. Radionuclides


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For more information about USGS activities in Maryland, Delaware and the District of Columbia contact:

 

Director
MD-DE-DC Water Science Center
U.S. Geological Survey
8987 Yellow Brick Road
Baltimore, MD 21237
Telephone: (410) 238-4200
Fax: (410) 238-4210

 

or access the USGS Water Resources of Maryland, Delaware, and District of Columbia home page at:  http://md.water.usgs.gov/.



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