COMPLETE SCHOOL PROJECT TOPICS & MATERIALS :
CHAPTERS: Chapter 1-5
|
DOC FORMAT: MS WORD/PDF
|
PRICE: ₦5,000
CHAPTER ONE
INTRODUCTION/LITERATURE REVIEW
The problem of environmental pollution due to toxic metals has begun to cause concern now in most major metropolitan cities. The toxic heavy metals entering the ecosystem may lead to geoaccumulation, bioaccumulation and biomagnification. Heavy metals like Fe, Cu, Zn, Ni and other trace elements are important for proper functioning of biological systems and their deficiency or excess could lead to a number of disorders (Ward, 1995). Food chain contamination by heavy metals has become a burning issue in recent years because of their potential accumulation in biosystems through contaminated water, soil and air. Therefore, a better understanding of heavy metal sources, their accumulation in the soil and the effect of their presence in water and soil on plant systems seem to be particularly important issues of present-day research on risk assessments (Rajesh et al., 2004). The main sources of heavy metals to vegetable crops are their growth media (soil, air, nutrient solutions) from which these are taken up by the roots or foliage (Ward, 1995).
Most of our water resources are gradually becoming polluted due to the addition of foreign materials from the surroundings. These include organic matter of plant and animal origin, land surface washing, and industrial and sewage effluents (Karnataka State Pollution Control Board, 2002). Rapid urbanization and industrialization with improper environmental planning often lead to discharge of industrial and sewage effluents into lakes. The lakes have a complex and fragile ecosystem, as they do not have selfcleaning ability and therefore readily accumulate pollutants. Bellandur Lake, the largest one in Bangalore urban area, recently attracted a lot of public attention because of the formation of froth during rainy season due to chemicals (soaps, detergents, etc.) and biosurfactants. For the last few decades, the treated, partially treated and untreated wastewater has been discharged to this lake and the lake water is being used for farming purposes (Pruss et al., 2002).
Individual rural homeowners are often responsible for providing and protecting their own water supplies. Where safety of these sources is concerned, no “short-cuts” can be taken. Protecting the quality of individual water supplies is a combination of controlling land use around the supplies and using proper water treatment techniques where necessary. Rural homeowners must assume responsibility for protecting their families from contaminated drinking water. Assistance in this regard can be obtained from a number of agencies (Ward, 1995). Local health authorities can answer questions relating to applicable local regulations; health hazards posed by contaminated water, and suggested procedures for sampling and analyzing drinking water for contaminants. In some cases, local health officials will analyze individuals‟ water samples for common pollutants at no cost or for a nominal charge. Complete well water analysis is the homeowner‟s responsibility and is not free. State regulatory agencies charged with water resource management can answer questions regarding water use. They usually also have information regarding the availability and suitability of water sources in the State. Such agencies usually administer safety regulations for dams as well (Ward, 1995).
1.2 Water, Water Wells, and Water Contamination
1.2.1 Understanding the Hydrologic Cycle
Water is constantly moving. As rain or snow (precipitation) falls to earth, some of it collects to form lakes, streams, and other bodies of water. The remaining water enters the soil in a process called infiltration. Some of this water evaporates back into the air and some is used by growing plants. The remainder seeps d o w n w a rd through the soil, until it accumulates at some depth and becomes groundwater (Wright et al., 2004).
Downward movement of water thro u g h the soil is percolation. This water eventually makes its way into a zone of soil where the space around each soil particle is completely filled with water (saturated). Water in this space is called groundwater, and its upper boundary is called the water table. Groundwater is located in underground formations called aquifers at various depths beneath the ground surface, and is generally available for human use. It can move laterally as groundwater flow to replenish surface water supplies. Groundwater constantly moves through the soil and reappears on the lowland surface as lakes, streams, swamps, or streams (Ward, 1995).
Although water is in constant motion, it seems to be stored in lakes, bays, oceans, and glaciers, as well as in underground supplies as discussed below, because the rate of movement in these vast bodies is relatively slow. Surface waters constantly evaporate into the air and produce clouds and later precipitation. Thus, water changes constantly from precipitation, to surface water, to groundwater, back to surface water, to atmospheric moisture, and back to rain or snow. This cycle of water movement is called the hydrologic cycle (Wright et al., 2004).
Fig. 1.1: The hydrologic cycle (Wright et al., 2004).
1.2.2 Surface and Groundwater Supplies
What Is Surface Water? Surface supplies of water are quite familiar to most of us. They include rivers and streams, ponds and lakes (reservoirs), and cisterns or other controlled catchments. For purposes of this discussion, streams are also considered surface supplies although, strictly speaking, streams originate from groundwater and occur where the water table intersects the land surface. Each of these sources has different characteristics. Ponds and lakes occur where nature has created an obstruction to the normal flow of surface runoff or where a natural waterholding depression has formed. People can also create such supplies by building dams. Controlled catchments are areas from which nearly 100 percent of precipitation is collected as run off. Rooftops are the most easily recognized type of controlled catchment. However, larger areas of land can be manipulated to maximize run off and subsequent collection (for example, by paving with concrete or asphalt). Streams and seeps occur at the land surface where water from underground sources appears. Because streams appear at the ground surface,
they must be treated differently than groundwater to adequately protect their quality (Clasen and Bastable, 2003).
What Is Groundwater? Groundwater, water that lies hidden beneath the earth‟s surface, is an important resource. Although it makes up only 4 percent of the total amount of water on earth, it constitutes 95 percent of the fresh water that is suitable for human consumption (Wright et al., 2004).
Groundwater and the way it moves is not as easy to understand or visualize as surface water simply because we cannot see it. People often imagine that groundwater exists in vast buried lakes and rivers. However, only in certain soluble deposits, such as limestone, do water-filled cavern s or channels resemble underground lakes and rivers. Unfortunately, the “hidden” nature of groundwater has resulted in a “out of sight, out of mind” sentiment and therefore contributed to its being considered out of danger. We now know that this is not so; too many cases of groundwater pollution are known. Groundwater occurs beneath the earth‟s surface in geologic formations called aquifers. In aquifers, all the spaces around individual soil particles and cracks within rocks are completely filled with water. Aquifers can be relatively small in area or they can stretch for several thousand s q u a re miles. Aquifers vary in thickness from a few feet to several thousand feet. Unconfined aquifers have no impermeable layers overlaying them and usually a re found close to the surface of the land. As shown in Figure 1.2, precipitation percolates through the soil until it reaches the unconfined aquifer‟s upper boundary, the water table. Only a very small portion of the water ever filters down to the confined aquifers. Unconfined aquifers, due to their proximity to people‟s activities on the soil surface, and the fact that the soil material above them transmits water readily, are especially susceptible to pollution. A confined aquifer is bounded on the top and bottom by relatively impermeable layers of clay or solid rock through which only very small amounts of water can pass. Precipitation can enter these deeper aquifers directly through regions called recharge areas where an aquifer is exposed to the earth‟s surface (Fig. 1.2). In the Coastal Plains especially, several aquifers might overlie each other (Wright et al., 2004).
Fig. 1.2: Confined and unconfined aquifers. (Wright et al., 2004).
Only about 1 inch of this precipitation ever reaches the deeper aquifers. Most groundwater is later returned to the surface as base flow; that is, water discharged continuously into perennially flowing streams. Within an aquifer, groundwater travels along fractures in the rock, through the pores in sand and gravel, or along chananels carved out of soluble rock, such as limestone. The direction and rate of this movement are very diff e rent from that of surface water. Whereas surface water moves at the rate of tens or even hundreds of feet per minute, groundwater moves at the rate of inches per day or less. Once water enters an aquifer, it can remain there for centuries. Therefore, if contaminated, it might take aquifers just as long to cleanse themselves naturally. Though the soil above aquifers might filter some materials transported by percolating water, these substances can continue to be leached if they are not degraded in the soil by microbial and/or chemical processes.
Natural water quality in the Coastal Plain aquifers is generally good, but varies with the type of aquifer material. Some elevation in dissolved mineral content (hardness) is always present, but is elevated in formations derived from fossilized material and limestone. The content of total dissolved solids in Coastal Plain groundwater varies widely, making some groundwater too bitter to drink. Although iron content is generally low, it can be very high in localized areas. Fractured bedrock formations present unique problems in both locating and protecting groundwater. Because fractures occur randomly and are generally discontinuous, it is very difficult to predict where adequate supplies of groundwater will be located. Yet, in certain areas, fractures can extend to the soil surface, providing a direct conduit through which pollutants can enter the aquifer. Such problems are prevalent in limestone areas where percolating water has dissolved the limestone, forming caverns underground and, sometimes, sinkholes at the ground surface. Though the cavernous channels can be productive aquifers from a quantity standpoint, they are susceptible to pollution from materials that can enter sinkholes with run off, or be placed there intentionally by people. Unfortunately, it is still possible to find sinkholes being used as private garbage dumps. Many contaminants exist that cannot be smelled, seen, or tasted. Some of these substances are believed to be health hazards in very low concentrations, sometimes at levels of a few parts per billion. (One part per billion would be equivalent to one ounce dissolved in a pool of water the size of a football field and 27 feet deep.) Although it might be technologically feasible in some cases to pump and treat contaminated groundwater to remove a pollutant, such a solution could take many years and a great deal of money. Unfortunately, it sometimes takes years to discover that groundwater has become polluted by contamination. All of these facts make it imperative to recognize the importance of groundwater to society, and to understand what it is, how it moves, and how to protect it. Clearly, the wisest and most economical approach is prevention and protection, rather than treatment (Trevett et al., 2005).
1.2.3 How are Surface and Groundwater Related?
Groundwater and surface water are intimately connected. Water in streams and lakes is, in most cases, directly linked to groundwater. For example, the surface of water flowing in most streams is actually a continuation of the water table (Figure 1.1). During drought periods, groundwater moves out of the aquifer and into the s t ream to supplement stream flow. During floods, water can flow from the stream into the surrounding aquifer. Hence, at times, streams have the potential to pollute groundwater and, at other times, groundwater can pollute surface water (Wright et al., 2004).
1.2.4 Water Utilization
Municipal water supplies meet Federal, State, and local guidelines. These requirements vary somewhat both with the size of the municipality and the region. Approximately 50 percent of the State‟s drinking water is supplied by municipalities. Most of the water on the Eastern Shore and much of the water to many rural homes is supplied by groundwater. If you are on an individual well or one that supplies only a few homes, you are pro b ably responsible for your own water quality. Since you more than likely obtain your water from a well, the following is a discussion of how groundwater is delivered (Lokhande and Kelkar, 1999).
1.2.5 Water Well Components
A well consists of two main elements. One element is the hole, or bore, through which water flows upward to the pump intake. This bore is commonly lined with a pipe or casing. The second element is the intake section where water enters the well. The intake usually is a screen at the bottom of the casing in a sand stratum, or it can be the open bore hole in a rock formation (Wright et al., 2004).
1.2.5.1 Well Casing
A drilled or driven well in unconsolidated material (such as sands, gravels, and unstable clays) must have a permanent well casing the full depth of the well, and a well screen. In unconsolidated material, soil usually packs tightly against the casing, providing a good seal. W h e re rock or other stable material overlays water-bearing sand or gravel, the upper part of the well must be sealed artificially on the outside of the casing to prevent contaminated water from moving through this upper layer along the outside of the pipe and down into the aquifer. Sealing usually is done with grout (a cement mix) or other sealants. Steel pipe has been used extensively for well casing even in soils or waters that are somewhat corrosive. Where abnormally corrosive conditions exist, a casing material of corrosion – resistant metal, such as brass or stainless steel, might be used. Plastic pipe can be used for well casings, but only when special methods can be employed to install the pipe without structural damage (Shivashankara et al., 1999).
1.2.5.2 Well Screen
A well screen fitted to the bottom of the casing allows water to enter the well freely, but prevents the entrance of coarse sand. The selection of the screen material usually is based on the cost of the material and the chemical character of the water. In some instances, where the waterbearing strata contain fine sands or silts, the well can be gravel-packed. The gravel pack acts as a primary filter and is held in place by the screen. Without the gravel pack the bottom of the bore hole would erode and cave in, while continually passing sand and silt to the pump (Wright et al., 2004).
1.2.5.3 Well Termination
The upper end of the casing pipe of the well can terminate on a pump house floor, platform, or soil surface. The casing should extend at least 8 inches above this surface. The entrance of any pump pipes, cable, air lines, or other device into the well casing must be effectively sealed with an approved sealing device to maintain well sanitation. Where the pump is mounted directly over the well, a sanitary well seal should be used. If the pump is offset from the well, the seal should consist of a watertight expandable seal that fits into the casing and at the same time seals the drop pipes, cables, and air line. If the pump is offset from the casing with pipes buried below the soil surface, a sealing device, called a pitless adapter, is used. In this case, the top of the casing still projects above the soil level and is fitted with a protective cap (Clesceri, 1998).