Water Quality Data

Analysis and Interpretation

Arthur Hounslow

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351404891
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Gestion de l'environnement

Water Quality Data emphasizes the interpretation of a water analysis or a group of analyses, with major applications on ground-water pollution or contaminant transport. A companion computer program aids in obtaining accurate, reproducible results, and alleviates some of the drudgery involved in water chemistry calculations.
The text is divided into nine chapters and includes computer programs applicable to all the main concepts presented. After introducing the fundamental aspects of water chemistry, the book focuses on the interpretation of water chemical data. The interrelationships between the various aspects of geochemistry and between chemistry and geology are discussed. The book describes the origin and interpretation of the major elements, and some minor ones, that affect water quality.
Readers are introduced to the elementary thermodynamics necessary to understand the use and results from water equilibrium computer programs. The book includes a detailed overview of organic chemistry and identifies the simpler and environmentally important organic chemicals. Methods are given to estimate the distribution of organic chemicals in the environment. The author fully explains all accompanying computer programs and presents this complex topic in a style that is interesting and easy to grasp for anyone.

CHAPTER 1

Introduction

Introduction

This text covers two somewhat different fields of water chemistry, namely, inorganic water geochemistry and organic geochemistry. When dealing with problems of environmental pollution it is necessary to integrate both of these areas if a solution to pollution problems is to be successful.

Whereas the background water quality is primarily one of inorganic geochemistry, many pollution problems arise from the manufacture of organic compounds and the use of trace metals in industrial processes. Considerable research, in what has been called organic geochemistry, has been conducted in areas relating to the origin of petroleum. It has included topics such as water washing and microbiological degradation of crude oil. Pressing environmental problems now center about the leakage of petroleum refinery products from underground storage tanks, the measurement of the fraction dissolved in water from nonaqueous phases, and the rate of microbiological degradation. In the past, considerable work has been conducted relative to the discovery of metalliferous ore deposits by using geochemical prospecting methods. Now the emphasis is on the transport and fate of a variety of toxic trace metals from known sources.

Some aspects of the various approaches to water chemistry will be discussed below. Several terms used to describe the study of geochemistry from a holistic viewpoint include Environmental Geochemistry, a Canadian term; Landscape Geochemistry, a Russian term; and Geochemical Ecology.

Geochemical Spheres

Geochemists have used the term geochemical spheres to describe the various parts of the earth being studied. They include the lithosphère (rocks), pedosphere (soils), biosphere (living organisms), atmosphere (air), hydrosphere (water), and anthroposphere (man’s effect on the other spheres), Figure 1.1. The main processes occurring in these various spheres include the hydrologie cycle, which describes the distribution of water on the planet, and the rock cycle, which describes the distribution of rocks. In addition, when studying pollutant transport and fate, other aspects of the system and the various interactions between the various spheres must be considered. Minerals dissolve and contribute to water quality, as do several common gases—CO₂, which affects the pH of water, and H₂S and O₂, which often determine the redox of water. The texture and rock type determine the porosity and permeability of the rocks and hence their aquifer characteristics. The presence and amount of clay minerals, amorphous oxides, and natural organic matter exert a strong influence on the mobility or retardation of both trace metals and synthetic organic pollutants in the groundwater system. The microbiological population affects the biodegradation of synthetic organics, as well as catalyzes many of the redox reactions. These interactions are shown diagrammatically in Figure 1.2.

Figure 1.1 Geochemical spheres.

Lithosphere

Rocks have been examined from various aspects in order to determine the mobility of various chemical elements in them. During the 1940s to 1960s, intensive work was conducted in trying to establish metallogenic provinces. These efforts were hampered by relatively poor analytical precision of trace metal analysis. The most common technique employed was optical emission spectroscopy, a time-consuming and very demanding procedure. This technique has been superseded by modern rapid and inexpensive instrumental methods.

Exploration geochemistry has been concerned with the origin of ore deposits, particularly base metals in the 1960s and uranium in the 1970s. The primary aim is the determination of the mobility of metals in order to determine the source of the metals. Soils were examined for underlying mineralization. Stream sediments were examined by selective screening, preferential dissolution, and heavy liquid separations. These allowed the examination of heavy minerals, adsorbed metals, clays, and coatings.

In agriculture, trace nutrients have been of major concern. For example, the need of Co for the well being of sheep in Australia in the 1940s, and toxic elements, such as Se—a small amount is essential, whereas too much is toxic.

Since the 1970s, pollution abatement and the transport and fate of synthetic organic chemicals has been of major interest. This has involved the determination of where the pollutants are going. Another topic on which the foregoing depends has been called subsurface characterization, that is, the study of constituents adsorbing and retarding the movement of pollutants. The compounds primarily involved in these processes are natural organic materials, amorphous hydroxides and oxides, and clay minerals.

Figure 1.2 Groundwater chemistry.

Groundwater geochemical research involving the lithosphère includes studies of concretions such as gypsum, barite, chert, and agate; red beds; opal and turquoise deposits; uranium deposits, particularly roll fronts; dolomitization; and caliche formation.

The present emphasis on the lithosphère is the release of toxic trace elements during the mining, processing, and beneficiation of the multitude of elements used in our industrial society.

Hydrosphere

Water quality data have been collected for many years by the U.S. Geological Survey, as well as state surveys and individual water districts, and more recently by the U.S. Environmental Protection Agency. Surface water sample data dominate. Samples from streams and lakes are easier and much less expensive to collect than groundwater samples. Wells are expensive to install, although springs and seeps allow inexpensive sampling of groundwater in some areas. Streams can also be used to extract groundwater quality data by the mathematical separation of groundwater and surface water components using hydrograph separation techniques.

A major concern with water quality is human health and disease. Cancer may result from excessive Cd, Ni, and Pb. The study of potential carcinogens involves massive data collection and interpretation. Cardiovascular disease is also of great interest, and this involves the study of Ca, Mg, and water softening. Urolithiasis, that is, the occurrence of kidney stones, because of the build-up of Ca oxalate and Ca phosphate is also of continuing interest. The hydrosphere contains the drinking water of the world. Therefore, the primary interest is to keep drinking water supplies free of toxic contaminants, whether they be heavy metals or trace amounts of toxic organic contaminants. In addition to the detection and attenuation of these compounds, the major concern is in the determination of their mobility.

Atmosphere

Changes in the atmospheric composition of the earth can effect the climate of the earth directly. Excess CO₂ may increase its temperature via the greenhouse effect. Chlorofluorocar-bons are important in ozone depletion, and hence, ultraviolet radiation onto the surface of the earth. Air pollution also results from CO, SO₂, NO₂, CO₂, and hydrocarbons, which produce peroxy acyl nitrate the main ingredient of smog. Atmospheric gases also affect water quality in a number of ways. Oxygen is a dominant redox buffer, and CO₂ affects the pH-buffering capacity. N₂ and the nitrogen cycle are also important redox variables. Acid rain results primarily from SO₃ and SO₂ produced by smelting and coal-fired furnaces, as well as some contributions from nitrogen oxides.

Biosphere

Organic chemistry is the chemistry of carbon. During the history of the earth carbon has occurred in the various geochemical spheres. It is present in the atmosphere as CO₂, CO, and CH₄, in the lithosphère as carbon (graphite or diamond), carbonates (RCO₃), and as coal, petroleum, oil shale, and soil organic matter (SOM); in the hydrosphere as H₂CO₃, HCO₃⁻, and CO₃²⁻ and in the biosphere as lipids, carbohydrates, and proteins. A diagrammatic representation of the carbon cycle is shown in Figure 1.3. The ultimate source of organic compounds is the biosphere, specifically plants. They are formed by the process of photosynthesis by using the energy of the sun. The opposite reaction is respiration (Figure 1.4).

plants+CO2+H2O+energyphotosynthesis→←respirationsimplesugars+O2

Figure 1.3 Carbon cycle.

The bottom line is that the energy for the biosphere comes from the sun. The concept of a nuclear winter is that if there is no sun, then there is no life. Organic compounds are stored solar energy and may be divided pragmatically into renewable resources or biomass, such as wood, or as nonrenewable fossil fuels, such as oil shale, petroleum, or coal.

Two methods of geochemical prospecting using biosphere materials have been used. These are geobotany, or exploration using indicator plants, particularly for Ag, Au, Cu, Sn, and U. Trace metal...