New Jersey Water Science Center

Water-Quality Constituents, Dissolved-Organic-Carbon Fractions, and Disinfection By-Product Formation in Water from Community Water-Supply Wells in New Jersey, 1998-99

Prepared in cooperation with the N.J. Department of Environmental Protection

By Jessica A. Hopple, Julia L. Barringer, and Janece Koleis

Scientific Investigations Report 2006-5260


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Abstract

Water samples were collected from 20 community water-supply wells in New Jersey to assess the chemical quality of the water before and after chlorination, to characterize the types of organic carbon present, and to determine the disinfection by-product formation potential. Water from the selected wells previously had been shown to contain concentrations of dissolved organic carbon (DOC) that were greater than 0.2 mg/L. Of the selected wells, five are completed in unconfined (or semi-confined) glacial-sediment aquifers of the Piedmont and Highlands (New England) Physiographic Provinces, five are completed in unconfined bedrock aquifers of the Piedmont Physiographic Province, and ten are completed in unconsolidated sediments of the Coastal Plain Physiographic Province. Four of the ten wells in the Coastal Plain are completed in confined parts of the aquifers; the other six are in unconfined aquifers.

One or more volatile organic compounds (VOCs) were detected in untreated water from all of the 16 wells in unconfined aquifers, some at concentrations greater than maximum contaminant levels. Those compounds detected included aliphatic compounds such as trichloroethylene and 1,1,1-trichloroethane, aromatic compounds such as benzene, the trihalomethane compound, chloroform, and the gasoline additive methyl tert-butyl ether (MTBE).

Concentrations of sodium and chloride in water from one well in a bedrock aquifer and sulfate in water from another exceeded New Jersey secondary standards for drinking water. The source of the sulfate was geologic materials, but the sodium and chloride probably were derived from human inputs.

DOC fractions were separated by passing water samples through XAD resin columns to determine hydrophobic fractions from hydrophilic fractions. Concentrations of hydrophobic acids were slightly lower than those of combined hydrophilic acids, neutral compounds, and low molecular weight compounds in most samples.

Water samples from the 20 wells were adjusted to a pH of 7, dosed with sodium hypochlorite, and incubated for 168 hours (seven days) at 25 °C to form disinfection by-products (DBPs). Concentrations of the DBPs—trihalomethanes, haloacetic acids, haloacetonitriles, and chlorate—were measured. Concentrations of these compounds, with few exceptions, were higher in water from Coastal Plain wells than from wells in glacial and bedrock aquifers.

The organic-carbon fractions were dosed with sodium hypochlorite, incubated for 168 hours at 25 °C, and analyzed for trihalomethanes, haloacetic acids, haloacetonitriles, and chlorate. Concentrations of trihalomethanes and haloacetic acids were higher in most of the hydrophobic organic-acid fractions than in the hydrophilic fractions, with the highest concentrations in samples from Coastal Plain aquifers. Traces of haloacetonitriles were measured, mostly in the hydrophilic fraction.

The aromaticity of the precursor DOC, as estimated by measurements of the absorbance of ultraviolet light at 254 nanometers, apparently is a factor in the DBP formation potentials determined, as aromaticity was greater in the samples that developed high concentrations of DBPs. VOCs may have contributed to the organic carbon present in some of the samples, but much of the DOC present in water from the 20 wells appeared to be natural in origin. The sediments of the Coastal Plain aquifers, in particular, contain substantial amounts of organic matter, which contribute ammonia, organic nitrogen, and aromatic DOC compounds to the ground water. Thus, the geologic characteristics of the aquifers appear to be a major factor in the potential for ground water to form DBPs when chlorinated.


Contents

Abstract

Introduction

Background

Purpose and Scope

Description of Study Area

Water Use and Land Use

Previous Investigations of Ground-Water Quality in New Jersey

Sources of Water-Quality Constituents and Characteristics

Volatile Organic Compounds

Nutrients

Major and Minor Ions, Trace Elements, and pH

Organic Carbon

Methods of Investigation

Well Selection

Collection and Processing of Samples

Analysis of Samples

Water-Quality Constituents

Organic Carbon Fractionation

Disinfection By-Product Formation

Carbon Fraction Preparation for Determination of Disinfection By-Product Formation

Ultraviolet Absorbance Measurements

Quality Assurance Program

Quality of Source Water to Community Water-Supply Wells

Volatile Organic Compounds

Nutrients

Major and Minor Ions, Trace Elements, and pH

Organic Carbon

Dissolved Organic Carbon Fractions and Disinfection By-Products

Organic Carbon Fractions

Disinfection By-Products

Sources

Formation of Disinfection By-Products During the Laboratory Incubation Study

Formation of Disinfection By-Products in Dissolved-Organic-Carbon Fractions

Laboratory Determined Formation Rates of Disinfection By-Products in Treated Water from Community Water-Supply Wells

Differences in Disinfection By-Product Formation Potential in Water from Different Aquifer Types

Possible Bias in Disinfection By-Product Data

Relations Among Disinfection By-Product Formation Potentials

Origins of Selected Chemical Characteristics and Constituents and Their Effects on

Disinfection By-Product Formation Potential

Dissolved Organic Carbon

Bromide

Iron, Manganese, and Ammonia

Indicators of Disinfection By-Product Formation Potential

Summary and Conclusions

Acknowledgments

References Cited

Appendix 1. Quality-assurance data (blanks, replicates, and related environmental samples) for 1) water samples and 2) chlorinated water samples from community water-supply wells, New Jersey, 1998-99

Appendix 2. Constituent concentrations in, and characteristics of, water samples from 20 community water-supply wells, New Jersey, 1998-99

Appendix 3. Concentrations of disinfection by-products formed in chlorinated water from seven selected community water-supply wells in New Jersey, 1998-99, during three periods of incubation


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