Science of Water : Concepts and Applications

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All about Water 37 DEEP WELLS Deep wells are the usual source of groundwater for municipalities. Deep wells tap thick and extensive aquifers that are not subject to rapid fl uctuations in water (piezometric surface—the height to which water will rise in a tube penetrating a confi ned aquifer) level and that provide a large and uniform yield. Deep wells typically yield water of a more constant quality than shallow wells, although the quality is not necessarily better. Deep wells are constructed by a variety of techniques; we discuss two of these techniques (jetting and drilling) below. Jetted Wells Jetted well construction commonly employs a jetting pipe with a cutting tool. This type of well cannot be constructed in clay, hardpan, or where boulders are present. Jetted wells are not acceptable as a public water supply. Drilled Wells Drilled wells are usually the only type of well allowed for use in most public water supply systems. Several different methods of drilling are available; all of which are capable of drilling wells of extreme depth and diameter. Drilled wells are constructed using a drilling rig that creates a hole into which the casing is placed. Screens are installed at one or more levels when water-bearing formations are encountered. COMPONENTS OF A WELL The components that make up a well system include the well itself, the building and the pump, and the related piping system. In this section, we focus on the components that make up the well itself. Many of these components are shown in Figure 2.6. WELL CASING A well is a hole in the ground called the borehole. The hole is protected from collapse by placing a casing inside it. The well casing prevents the walls of the hole from collapsing and prevents contaminants (either surface or subsurface) from entering the water source. The casing also provides a column of stored water and housing for the pump mechanisms and pipes. Well casings constructed of steel or plastic material are acceptable. The well casing must extend a minimum of 12 in. above grade. GROUT To protect the aquifer from contamination, the casing is sealed to the borehole near the surface and near the bottom where it passes into the impermeable layer with grout. This sealing process keeps the well from being polluted by surface water and seals out water from water-bearing strata that have undesirable water quality. Sealing also protects the casing from external corrosion and restrains unstable soil and rock formations. Grout consists of near cement that is pumped into the annular space (it is completed within 48 h of well construction). It is pumped under continuous pressure starting at the bottom and progressing upward in one continuous operation. WELL PAD The well pad provides a ground seal around the casing. The pad is constructed of reinforced concrete 6 ft × 6 ft (6 in. thick) with the wellhead located in the middle. The well pad prevents contaminants from collecting around the well and seeping down into the ground along the casing.
38 The Science of Water: Concepts and Applications SANITARY SEAL To prevent contamination of the well, a sanitary seal is placed at the top of the casing. The type of seal varies depending upon the type of pump used. The sanitary seal contains openings for power and control wires, pump support cables, a drawdown gauge, discharge piping, pump shaft, and air vent, while providing a tight seal around them. WELL SCREEN Screens can be installed at the intake point(s) on the end of a well casing or on the end of the inner casing on gravel-packed well. These screens perform two functions: (1) supporting the borehole and (2) reducing the amount of sand that enters the casing and the pump. They are sized to allow the maximum amount of water while preventing the passage of sand/sediment/gravel. CASING VENT Top soil Water bearing sand Clay FIGURE 2.6 Components of a well. Casing vent 12 in. minimum Water bearing sand Casing Drop pipe Sanitary well seal Water table Cement grout formation seal Submersible pump Pump motor Drive shoe Screen Well pad The well casing must have a vent to allow air into the casing as the water level drops. The vent terminates 18 in. above the fl oor with a return bend pointing downward. The opening of the vent must be screened with no. 24 mesh of stainless steel to prevent entry of vermin and dust.
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Second Edition THE SCIENCE OF WATER
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Cover Image: Falling Spring at Fall
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Contents Preface ..................
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Contents ix Velocity Head .........
Page 12 and 13: Contents xi Specifi c Conductance .
Page 14 and 15: Contents xiii (5) Beetles (Order: C
Page 16 and 17: Contents xv Chlorine Residual Testi
Page 18: Contents xvii Water Filtration Calc
Page 22: To the Reader In reading this text,
Page 26 and 27: 1 Introduction When color photograp
Page 28 and 29: Introduction 3 On second look, we s
Page 30 and 31: Introduction 5 As mentioned earlier
Page 32 and 33: Introduction 7 This scream of lost
Page 34: Introduction 9 Metcalf & Eddy, Inc.
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Page 70 and 71: 3 Water Hydraulics Anyone who has t
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Page 76 and 77: Water Hydraulics 51 √ Important P
Page 78 and 79: Water Hydraulics 53 FIGURE 3.4 Thru
Page 80 and 81: Water Hydraulics 55 Example 3.8 Pro
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Page 84 and 85: Water Hydraulics 59 With regard to
Page 86 and 87: Water Hydraulics 61 or hydraulic gr
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Page 90 and 91: Water Hydraulics 65 √ Note: In de
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Page 94 and 95: Water Hydraulics 69 • • • •
Page 96 and 97: Water Hydraulics 71 The Darcy-Weisb
Page 98 and 99: Water Hydraulics 73 Of course, pipe
Page 100 and 101: Water Hydraulics 75 In this section
Page 102 and 103: Water Hydraulics 77 Slope (S) The s
Page 104 and 105: Water Hydraulics 79 and important c
Page 106 and 107: Water Hydraulics 81 and the depth o
Page 108 and 109: Water Hydraulics 83 TYPES OF DIFFER
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Water Hydraulics 87 Meter backpress
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Water Hydraulics 89 VELOCITY FLOWME
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Water Hydraulics 91 The positive-di
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Water Hydraulics 93 Solution: 1200g
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Water Hydraulics 95 Water and Waste
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100 The Science of Water: Concepts
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6 Water Ecology The subject of man
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Water Ecology 157 The environment i
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Water Ecology 159 FIGURE 6.2 Notone
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Water Ecology 161 H 2 O O 2 FIGURE
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Water Ecology 163 FeS FIGURE 6.6 Th
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Water Ecology 165 Algae FIGURE 6.8
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Water Ecology 167 2. Likewise, biom
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Water Ecology 169 Population densit
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Water Ecology 171 succession can be
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Water Ecology 173 dark winter month
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Water Ecology 175 In rain events wh
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Water Ecology 177 long profi le, cr
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Water Ecology 179 THE FLOODPLAIN A
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Water Ecology 181 It is important t
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Water Ecology 183 Specifi c Adaptat
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Water Ecology 185 serve to indicate
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Water Ecology 187 UNITS OF ORGANIZA
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Water Ecology 189 FIGURE 6.20 Stone
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Water Ecology 191 FIGURE 6.22 Midge
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Water Ecology 193 FIGURE 6.25 Riffl
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Water Ecology 195 They push their m
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Water Ecology 197 FIGURE 6.32 Damse
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Water Ecology 199 Darwin, C., 1998.
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10 Water Treatment Calculations Gup
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