New Jersey Water Science Center
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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.
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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