USGS

Water-Quality Changes and Organic-Carbon Characterization During Recharge with Recycled Water at a Research Basin in Montebello Forebay, Los Angeles County, California, 1991-1996

By Roy A. Schroeder

 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03-4146

Sacramento, California 2003

Prepared in cooperation with the

Water Replenishment District of Southern California




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Abstract

    During the early 1990s, the U.S. Geological Survey (USGS) investigated water-quality changes that occur in treated municipal wastewater (recycled water) at a small research basin constructed in the Montebello Forebay of the Central Ground-Water Basin in south-central Los Angeles County. The instrumented research basin is located on a 1/2-acre site at the upgradient end of the San Gabriel River Coastal Spreading Grounds where recharge has been augmented using recycled water since 1961. The facility was used to measure attenuation in selected constituents as recycled water delivered to the basin percolates downward and moves laterally beneath the basin. Attenuation in aqueous concentration was found to range from 20 to 60 percent for total dissolved nitrogen and was about one-third for dissolved organic carbon (DOC). Isotopic data confirmed permanent loss of nitrogen by denitrification. Detailed investigations showed that there were no large differences in the loss of various components of the DOC at the structural or compound level, although surfactants and their metabolites were abundant and did persist in the subsurface. The DOC of wastewater origin was found to have a lower trihalomethane (THM) formation potential upon chlorination than does organic matter of natural origin from most surface-water sources.

    The organization of this report into 12 topical chapters, and the report's relation to additional USGS publications from this study, is noted in a preface.

CONTENTS

Preface

Abstract

Part I

Chapter 1:Introduction

Purpose and Scope

Acknowledgments

Chapter 2: Research Basin Construction and Instrumentation

Chapter 3: Geologic and Hydrologic Settings

Lithology

Vertical Hydraulic Conductivity

Horizontal Hydraulic Conductivity

Hydraulic Conditions During the Recharge Experiments

Chapter 4: Microbiological Changes During Recharge

Methods

Bacterial Distributions in Cores

Total and Fecal Coliform in Water

Nitrogen-Transforming Bacteria in Water

Chapter 5: Changes in Common Chemical Constituents During Recharge

Methods for Common Chemical Constituents

Chemical Attenuation During Recharge

Mixing and Displacement During Recharge

Nitrogen

Organic Carbon

Zinc

Arsenic

Chemical and Isotopic Evidence for Denitrifiction

Other Possible Mechanisms for Nitrogen Removal

Volatization

Ion Exchange

Sorption

Relative Importance of Oxygen and Nitrate as Electron Acceptors

Part II

Chapter 6: Hierarchal Approach to Organic Matter Characterization

Chapter 7: Isoloation and Characterization of Colloids

Sampling and Methods

Colloid Isolation Procedures

Analytical Methods

Results and Discussion

Colloid Concentration and Changes in Elemental Composition

Nuclear Magnetic Resonance Sepectrometry

Chapter 8: Characterization of Dissolved Organic Matter by Concentration, Fractionation, and Molecular Weight Determinations

Methods

Sample Collection and Field Processing

Analytical Methods

Total and Dissolved Organic and Inorganic Carbon Concentration

Dissolved Organic Carbon Fractionation

Dissolved Organic Carbon Molecular-Weight Characterization

Results and Discussion

First Recharge Experiment

Organic Carbon Concentration

Dissolved Organic Carbon Fractionation

Second Recharge Experiment

Organic Carbon Concentration

Molecular Weight of Dissolved Organic Carbon

Dissolved Organic Carbon Fractionation

Third Recharge Experiment

Organic Carbon Concentration

Molecular Weight of Dissolved Organic Carbon

Dissolved Organic Carbon Fractionation

Chapter 9: Characterization of Dissolved Organic Matter by Infrared and Ultraviolet/Visible Spectrometry

Fractionation and Isolation Methods

Spectral Characterizations

Ultraviolet/Visible Spectrometry

Chapter 10: Characgerization of Dissolved Organic Matter by Nuclear Magnetic Resonance (NMR) Spectrometry

Sampling

Results

Chapter 11: Distributions of Halogenated Organic Compounds

Methods

Results

Chapter 12: Specific Organic Contaminants

Sampling

Analytical Methods

Methylene Blue Active Substances

Anionic Surfactants

Caffeine

Volatile Organic Compounds

Results

April 1994 Sampling

Methylene Blue Active Substances

Linear Alkylbenzene Sulfonate

Caffeine

September 1994 Sampling

Linear Alkylbenzene Sulfonate

Caffeine

Volatile Organic Compounds

References Cited

Appendixes


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