Fresh Water and Watersheds

Yeqiao Wang, Yeqiao Wang

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9780429804830
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Environmental Conservation & Protection
• Index: Biological Sciences

Authored by world-class scientists and scholars, The Handbook of Natural Resources, Second Edition, is an excellent reference for understanding the consequences of changing natural resources to the degradation of ecological integrity and the sustainability of life. Based on the content of the bestselling and CHOICE-awarded Encyclopedia of Natural Resources, this new edition demonstrates the major challenges that the society is facing for the sustainability of all well-being on the planet Earth. The experience, evidence, methods, and models used in studying natural resources are presented in six stand-alone volumes, arranged along the main systems of land, water, and air. It reviews state-of-the-art knowledge, highlights advances made in different areas, and provides guidance for the appropriate use of remote sensing and geospatial data with field-based measurements in the study of natural resources.

Volume 4, Fresh Water and Watersheds, covers fresh water and watersheds, their health and conservation, protection, and management. Organized for ease of reference, it provides fundamental information on groundwater storage, water quality, supply and balance, and water resource vulnerability. New in this edition are discussions on water footprint assessment, water surface dynamics, and water management on a global scale. Understanding the conditions of watersheds is crucial for restoring areas with degraded water quality as well as protecting healthy waters from emerging problems. This volume demonstrates the key processes, methods, and models used through several practical case studies from around the world.

Written in an easy-to-reference manner, The Handbook of Natural Resources, Second Edition, as individual volumes or as a complete set, is an essential reading for anyone looking for a deeper understanding of the science and management of natural resources. Public and private libraries, educational and research institutions, scientists, scholars, and resource managers will benefit enormously from this set. Individual volumes and chapters can also be used in a wide variety of both graduate and undergraduate courses in environmental science and natural science at different levels and disciplines, such as biology, geography, earth system science, and ecology.

II

Water Management

17

Groundwater Contamination

Introduction

Types of Contaminants

Sources of Contamination

Effect of Climate

Transport of Contaminants

Fate of Contaminants

References

Charles W. Fetter

Oshkosh

Introduction

Contamination can be defined as the presence of a biological or chemical agent in groundwater in such a concentration that it renders water unfit for a particular use.^[1] Agricultural uses of water include domestic drinking water, stock watering, and irrigation. Water that is contaminated for purposes of drinking might be perfectly suitable for use in irrigation.

Contaminants can be from both anthropogenic and natural sources, for example, arsenic. Arsenic found in groundwater in northeastern Wisconsin comes from a naturally occurring mineral, arsenopyrite, present in aquifer. Arsenic has also become a contaminant in groundwater due to use its use in agriculture as a pesticide as well as industrial sites where arsenic was used as a wood preservative.^[1] The drinking water standard for arsenic in the United States for many years was 50 μg/L (micrograms per liter). However, in May 2000 the U.S. Environmental Protection Agency reviewed the standard and it was lowered to 10 μg/L.

Types of Contaminants

Groundwater contaminants fall into two broad categories, biological and chemical. Biological contaminants include bacteria, viruses, and protozoa. Chemical contaminants can be classified as organic or inorganic. Organic chemicals are based on a framework of carbon and hydrogen atoms. Inorganic compounds include all other chemicals, although some will have carbon present in an inorganic form, such as carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻).

Organic chemicals include fuels and most pesticides. Fuels such as gasoline and diesel are composed of hundreds of different organic chemicals in varying proportions depending upon the source, and their composition will vary depending upon the season. Fuels do not mix with groundwater, rather if present in the ground they will float on the water table. They are sometimes referred to as Light Non-Aqueous Phase Liquid (LNAPL) as they are less dense than water. However, some of the chemicals that comprise gasoline and diesel will separate from fuel into a dissolved form in the groundwater. The most soluble of these chemicals are benzene, toluene, ethylbenzene, and xylenes. They are referred to by acronym BTEX.^[2] Some organic pesticides may be soluble in water as they may be mixed with water prior to application to a field.

Inorganic chemicals found in groundwater are salts that dissociate into cations and anions when in contact with water. The cations include heavy metals such as iron, lead, manganese, cadmium, chromium, zinc, and mercury. The anions include nitrate (NO₃⁻), nitrite (NO₂⁻), sulfate (SO₄²⁻), fluoride (F⁻), chloride (Cl⁻), arsenate (AsO₄³⁻) and arsenite (AsO₃³⁻).

Sources of Contamination

Sources of contamination can be divided into point sources and non-point sources. As the name implies, point sources can be traced to a very specific location. An example of a point source might be a septic tank, a landfill, or a pesticide mixing area. Non-point sources are dispersed across the landscape. Fertilizer and pesticides applied to fields are examples of non-point sources.

Human and animal wastes are sources of potential groundwater contamination due to the presence of bacteria and viruses as well as nitrogen compounds. One chemical compound frequently found in groundwater in rural areas is nitrate. This can come from cesspools and septic tanks, barnyards, manure spread as fertilizer, and chemical fertilizers. Nitrate and nitrite in drinking water in excess of 10 mg/L (milligrams per liter) as nitrogen have been implicated in infant methemoglobinemia or “blue baby syndrome.” Another salt found in animal waste is chloride. This will impart a salty taste in drinking water if present in amounts in excess of 250 mg/L.

Pesticides are also a potential source of groundwater contamination. They can be found concentrated in areas where pesticides are mixed or equipment is washed. Likewise pesticides can be a non-point source of contamination when they are spread on a field. For example, atrazine has been found in groundwater in Wisconsin as a result of use on corn crops. Not only can pesticides occur in the environment, but breakdown products called metabolites can also occur in groundwater.

When water is used for irrigation, some will evaporate. This will concentrate the soluble salts in the remaining water, which will drain down to the water table. As a result, toxic salts may build up in the soil and groundwater. This situation has developed in some areas of California with selenium.

Fuels used on the farm can leak from underground storage tanks resulting in the formation of a pool of LNAPL on the water table below the tank and dissolved BTEX chemicals in the groundwater. The federal drinking water standard for benzene in the United States is 5 μg/L. In some states the groundwater standard is even lower, 1 μg/L.

Chemicals used for degreasing equipment can also contaminate groundwater if improperly disposed.^[3] Many degreasers contain chlorinated organic compounds such as trichloroethylene (TCE) and 1,1,1-trichlorethane (TCA). These liquids are denser than water and mix poorly with water. They are referred to by acronym DNAPL. If disposed into the environment, for example by spilling on soil, they can migrate vertically to the water table and then sink below the water table into the underlying aquifers. These compounds are sparingly soluble in water, but even small amounts are dangerous. The federal drinking water standard for trichloroethylene in the United States is 5 μg/L. In some states the groundwater standard is even lower, 1 μg/L.

Chemicals used in wood preservatives are also potential groundwater contaminants. These include creosote and CCA (copper, chromium, arsenic). Treated wood itself wou...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Table of Contents
• Preface
• About The Handbook of Natural Resources
• Acknowledgments
• Aims and Scope
• Editor
• Contributors
• SECTION I Fresh Water and Hydrology
• SECTION II Water Management
• SECTION III Water and Watershed Monitoring
• Index