Grundfos A2 Water Engineering[1]

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Water Systems Engineering Manual

for Groundwater Supply and Special Applications

U.S.A.

GRUNDFOS Pumps Corporation 17100 West 118th Terrace

Canada

GRUNDFOS Canada Inc. 2941 Brighton Road

Mexico

Bombas GRUNDFOS de Mexico S.A. de C.V. Boulevard TLC No. 15 L-SP-TL-500 5/04 PRINTED IN USA

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1A Water Supply . . . 1-2

Sources, Quality, Quantity & Rights

1B Groundwater & Wells . . . 1-8

Supply, Hydraulics, Construction & Treatment

1C Water Quality & Treatment . . . 1-37

Drinking Water Regulations, Characteristics & Treatment

1D Water System Capacity Requirements . . . 1-59

Rural, Public and Irrigation Systems, Sizing

1E Pumping, Distribution and Storage . . . 1-81

Hydro-Pneumatic System

Grundfos

Engineering Manual for

Groundwater Supply and Special Applications

INTRODUCTION FOREWORD

This manual was developed to serve three (3) principal purposes:

1. To provide the water supply professional with a technical primer applicable to many of the various system considerations and issues associated with the development of a new or expansion of existing groundwater supply systems commonly encountered in the United States.

2. To provide a single source reference for commonly required information associated with the design of groundwater supply systems utilizing submersible pumping equipment and selective special applications 3. To acquaint the water supply professional with the use, application and advantages of Grundfos stainless steel

submersible pump and control products.

We have taken considerable time and care to make the presentation as convenient and easy to use as possible; however, we realize there is always room for improvement and invite comment. It is our sincere hope that the user finds this manual a useful reference tool in the design and construction of groundwater systems, and associated submersible pump products.

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A global business

With over 11,000 employees worldwide, and annual production of 10 million pump units per year, Grundfos is one of the world’s leading pump manufacturers. Over 60 Grundfos Companies around the globe help bring pumps to every corner of the world, supplying drinking water to Antarctic expeditions, irrigating Dutch tulips, monitoring groundwater beneath waste heaps in Germany, and air conditioning Egyptian hotels.

Efficient, sustainable products

Grundfos is constantly striving to make its products more user-friendly and reliable as well as energy-saving and efficient. Our pumps are equipped with ultra-modern electronics allowing output to be regulated according to current needs. This ensures convenience for the end-user, saves a great deal of energy and, in turn, benefits the environment.

Research and development

In order to maintain its market position, Grundfos takes customer research to heart when improving or developing

new products. Our Research and Development department makes use of the latest technology within the pump industry in search of new and better solutions for the design and function of our pump solutions.

Corporate values

The Grundfos Group is based on values such as sustainability, openness, trustworthiness, responsibility, and also on partnership with clients, suppliers and the whole of society around us, with a focus on humanity that concerns our own employees as well as the many millions who be-nefit from water that is procured, utilized and removed as wastewater with the help of Grundfos pumps.

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Grundfos North America

IT IS OUR MISSION – the basis of our existence – to

successfully develop, produce, and sell high quality

pumps and pumping systems worldwide, contributing

to a better quality of life and a healthier environment.

Fresno, California

Monterrey, Mexico Allentown, Pennsylvania Oakville, Canada Olathe, Kansas

● North American headquarters in Olathe, Kansas

● Manufacturing in Fresno, California

● Service, distribution and light assembly in Allentown, Pennsylvania

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Disclaimer

Considerable effort has been expended to insure the accuracy of the information presented in this manual and to the best of our knowledge, the information contained is accurate.

Grundfos, it’s dealers and distributors, and authors of and contributors to this manual assumes no liability or warranty whatsoever, expressed or implied, for the accuracy, completeness and/or reliability of such information contained herein. Final determination of the suitability of the information or products for the use contemplated is the sole responsibility of the user. We recommend that anyone intending to rely on the guidelines and

recommendations mentioned in this manual satisfy themselves as to the suitability, fitness for a particular purpose and compliance to all applicable safety and public health codes before implementation.

The format, presentation and a majority of the tabulated information is copyrighted by Grundfos. Manual materials may be copied for individual use only.

PRODUCT LINES Groundwater

Grundfos offers a wide range of “no lead” submersible pumps for domestic groundwater system applications. Built of rugged stainless steel and superior components, Grundfos submersibles are regarded as the toughest, most reliable pumps on the market.

Commercial/Industrial

Grundfos pumps provide a multitude of commercial uses, providing high capacity pumps for universities, hospitals, hotels and high-rise buildings. Grundfos is also well recognized for industrial applications including automotive plants, paper mills, food processing machinery, offshore platforms and reverse osmosis systems.

Plumbing and Heating

Grundfos offers a full line of circulators for hydronic, hot water, and solar energy applications. Currently there are more than 3 million Grundfos circulators systems in use throughout the world.

Sewage, Effluent and Sump Pumps

Grundfos offers a line of sewage, effluent and sump pumps for applications involving residential and light commercial sewage, septic system effluent and residential sump and waste water removal.

Environmental

Grundfos Redi-Flo submersible pumps are designed for environmental groundwater monitoring, sampling and clean-up operations.

Grundfos Pumps Corporation is one of the first U.S. pump manufacturers to be ISO 9001 certified for high quality standards throughout its entire product line. Advanced robotics fabrication, skilled applications engineers, CAD/CAM & Catia engineering, on-going educational training, and service and repair facilities all contribute to success at Grundfos.

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Grundfos

Engineering Manual for

Groundwater Supply and Special Applications

SECTION 1:

WATER SUPPLY PLANNING

1A WATER SUPPLY PLANNING FUNDAMENTALS

• Water Sources . . . 1-2 • Water Quality . . . 1-5 • Quantity of Water . . . 1-6 • Water Rights . . . 1-7

1B GROUNDWATER & WELLS

• Groundwater as a Water Supply Source . . . 1-8 • Groundwater Hydrology & Well Hydraulics . . . 1-11 • Well Design & Construction . . . 1-17 • Well Disinfection & Treatment . . . 1-34

1C WATER QUALITY & TREATMENT

• Drinking Water Regulations . . . 1-37 • Water Quality for Agriculture . . . 1-44 • Water Quality Characteristics . . . 1-45 • Water Treatment . . . 1-50

1D WATER SYSTEM CAPACITY REQUIREMENTS

• Residential / Domestic and Farm Systems . . . 1-59 • Public Water Systems . . . 1-65 • Agricultural and Turf Irrigation Systems . . . 1-69 • Curves for Sizing Domestic Water Demand . . . 1-74

1E PUMPING, DISTRIBUTION & STORAGE

• Pumping . . . 1-81 • Distribution . . . 1-87 • Storage . . . 1-89 • Hydro-Pneumatic Systems . . . 1-92

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1A WATER SUPPLY PLANNING FUNDAMENTALS

Planning a water-supply system begins with the identification of available water sources. The quality of water from those sources must then be investigated, as well as the quantity of water that each source can reliably supply. Finally, before a source can be selected and developed, the legal rights to the water from that source must be established.

Water Sources

There are two principal sources suitable for use as a potable water supply; groundwater and surface water. In some instances, a water supply may use a combination of both sources. Both sources are part of, and renewed by the hydrologic cycle. Refer to Figure 1-1 for a graphical depiction of the Hydrologic Cycle.

Groundwater. Groundwater supplies are important sources of water supply which have a number of advantages

over surface supplies. They may require little or no treatment, have uniform temperature throughout the year, are cheaper than impounding reservoirs, and amounts of water available are more certain. They are relatively

unaffected by drought in the short term.

Groundwater is the portion of water that infiltrates the soil not utilized by plants (evapo-transpiration) or directly evaporated. This unused water eventually reaches the zone of saturation through the force of gravity. Water in the zone of saturation is referred to as “groundwater.” The upper surface of the zone saturation, if not confined by impermeable material, is called the water table. The saturated zone may be viewed as a huge natural reservoir whose capacity is the total volume of pores or openings in the rocks that are filled with water. Groundwater may be found in one continuous body or several separate strata.

The thickness in the zone of saturation varies from a few feet to many hundreds of feet. Factors that determine its thickness are: the local geology, the availability of pores or openings in the formations. Movement of water within the zone is a result of gradient changes as a result of natural or man made recharge and discharge. Formations or strata within the saturated zone from which ground water can be obtained for beneficial use are called “aquifers.” An aquifer is a water-saturated geologic unit that will yield water to wells or springs at a sufficient rate as to be a practical sources of water supply. Sand, gravel and sandstone aquifers provide the best aquifer media for high capacity water well construction.

Types of Wells. In the ordinary or water-table well the water rises to the height of the saturated material surrounding

it. There is no pressure other than atmospheric upon the water in the surrounding aquifer. An artesian well is one in which the water rises above the level at which it is encountered in the aquifer because of pressure in the confined water of the aquifer. A flowing well is an artesian well where the pressure raises the water above the casing head. Heavy draft upon the aquifer may so lower the hydraulic gradient that a flowing well will cease to flow. Figure 1-2 illustrates artesian conditions.

Pumping will cause a lowering of the water table near the well. If pumping continues at a rate that exceeds the rate of ground water recharge, a condition known as ground water mining occurs. Prolonged groundwater mining will increase pumping cost as the water level drops, change quality and can promote salt-water encroachment in coastal areas.

Springs: An opening in the ground surface form which ground water flows is a spring. Water may flow by force of

gravity (from water-table aquifers) or be forced out by artesian pressure. Springs constitute only a very small portion of groundwater supply sources.

Surface Water. Precipitation that does not enter the ground through infiltration or is not returned to the atmosphere by evaporation, flows over the ground surface and is classified as direct runoff. Direct runoff is water that moves over saturated or impermeable surfaces into stream channels, lakes or artificial storage sites. The dry-weather (base) flow is derived from groundwater or snowmelt. Runoff from ground surfaces may be collected in either natural or artificial reservoirs. A portion of the water stored in surface reservoirs is lost by evaporation and by infiltration to the groundwater.

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Figure 1-1: Schematic Diagram of the Hydrologic Cycle

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Potable Water Available in the United States. It is estimated that the earth contains 380 million cubic miles of

water. About 2.5% of this is fresh water and of this, 1.5 % is in the form of ice at the polar caps. Slightly less than 1% of all water therefore remains available to man for potable use. One percent sounds like a small amount, however, it represents a tremendous quantity, far outranking all other natural resources.

Water is not used up like other resources. By virtue of the hydrological cycle it is continually returned to its source. It has been estimated that ground waters in the United States have been depleted less than 1/4% of 1% in 500 years. Of all usable water available on earth, approximately 26% exists in the United States, 77% of which is contained in underground aquifers, 23% as surface water (21% in lakes and 2% in rivers and reservoirs).

Approximately 47% of the water presently used in the United States comes from surface water. The remaining 53% is taken from groundwater sources (source: USGS 1986 National Water Summary). The major groundwater regions of the continental United Sates are shown in Figure 1-3.

Figure 1-3: Groundwater Availability and Regions in the U.S.

Groundwater 77% Lakes 21% Rivers Reservoirs Groundwater 53% Surface Water 47%

Fresh Water Availability in the U.S Groundwater vs. Surface Water in the U.S.

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Water Quality

Precipitation in the form of rain, snow, hail or sleet contains very few impurities and virtually no bacteria. It may contain trace amounts of minerals, gases, and other substances as it forms and falls through the earth’s atmosphere. Once precipitation reaches the earth’s surface, however, mineral and organic substances, microorganisms, and other forms of pollution (which tend to lower water quality) enter the water.

When water runs over or through the ground surface, it may pick up soil particles. This is noticeable in the water as cloudiness, or “turbidity.” Water also picks up particles of organic matter and bacteria. As surface water seeps into the soil and through the underlying material to the water table, most suspended particles are filtered out. This natural filtration is partially effective in removing bacteria and other particulate materials; however, the chemical characteristics of the water may change and vary widely when it comes in contact with mineral deposits in the soil. The widespread use of synthetically produced chemical compounds; including pesticides, insecticides and solvents, has had a pronounced effect on water quality. Many of these materials are known to be toxic. Others have certain undesirable characteristics, which interfere with water use even when these materials are present in relatively small concentrations.

The Safe Drinking Water Act. When selecting a source as a water-supply for potable purposes, it is necessary to

carefully examine all water-quality factors that might adversely affect the intended use of the water source. As a minimum, the quality of the water must be such that it will meet (after treatment, if necessary) the standards established under the drinking water regulations of the Federal Safe Drinking Water Act (SDWA), as well as any additional state or local standards. When selecting a water source it is also important to consider other

characteristics, including the water’s palatability, its aesthetic quality and its potential for corrosion or scaling of pipes.

A detailed discussion of the SDWA and associated water quality issues are presented in Section 1C.

Treatment. In evaluating a source based on water quality, the availability and costs of water-treatment techniques

to remove undesirable constituents must be considered. Conventional water treatment techniques; such as aeration, sedimentation, coagulation/flocculation, filtration, softening, fluoridation, adsorption and disinfection have been used for decades to produce potable water for large municipal water systems. The same techniques can be used to produce water of potable quality for smaller systems. In addition, small package treatment units using membrane separation processes, primarily reverse-osmosis (RO), are commercially available. These units, although often uneconomical for large utilities, may be a viable alternative for a small system, especially for use with brackish ground water sources.

Water quality characteristics can be broken into four categories; physical, chemical, biological and radiological. Some of the treatment methods that a small utility might economically use to reduce objectionable contaminants to an acceptable level are discussed in Section 1C.

Sanitary Survey. A sanitary survey is important in the development of a new water supply and is often a

regulatory requirement for permit. The sanitary survey should be made in conjunction with the collection of initial engineering data covering the development of a given source and its capacity to meet existing and future needs. The sanitary survey should include the detection of all health hazards and the assessment of there present and future importance. Only persons trained and competent in public health and familiar with water supply engineering should conduct the sanitary survey. In the case of an existing supply, the survey should be made at a frequency compatible with the control of the health hazards and the maintenance of good sanitary quality, or as required by the governing regulatory agency. A general outline of the issues/ factors that should be investigated or considered in a ground water sanitary survey is listed as follows:

A. Character of local geology and slope of ground surface.

B. Nature of soil and underlying porous strata - whether clay, sand, gravel, rock (especially porous limestone); coarseness of sand or gravel; thickness of water-bearing stratum, depth to water table; location, log and construction details of local wells in use and abandoned.

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C. Slope (gradient) of water table.

D. Extent of drainage area likely to contribute water to the supply. E. Nature, distance and direction of local pollution sources.

F. Possibility of surface-drainage water entering the supply and of wells becoming flooded, methods of protection. G. Methods used for protecting the supply of pollution by means of sewage treatment, waste disposal, etc.

H. Water quality data collected from test wells or permanently constructed monitoring wells constructed in advance of production wells.

I. Well construction: 1. Total depth of well..

2. Casing - diameter, wall thickness, material and length from surface.

3. Screen or perforations - diameter, material, construction, locations and lengths.

4. Formation seal - material (cement, sand, bentonite, etc.), depth intervals, annular thickness and method of placement.

J. Protection of well head - presence of sanitary well seal, casing height above ground, floor or flood level, protection of well vent, protection of well from erosion and animals.

K. Pumphouse construction (floors, drains, etc.), capacity of pumps, drawdown when pumps are in operation. L. Availability of an unsafe supply, usable in place of normal supply, hence involving danger to the public health. M. Disinfection - equipment, supervision, test kits or other types of laboratory control..

Note: Not all the items listed are pertinent to any one supply.

Quantity of Water

An important step in selecting a suitable water-supply source is determining the demand that will be placed on it. The four principal issues that must be addressed in conjunction with determining system water quantity needs are usage, flow, pressure and storage.

Usage (consumption). The quantity of water must be established to determine the adequacy of the source to

meet demand; as well as establishing infrastructure requirements. The quantity of water required to be supplied by a system is most easily calculated when the ultimate or end use is known. Quantity requirements are normally estimated based on average daily usage (consumption) and is expressed in gallons per day (gpd) or gallons per capita per day (gpcd) depending on the size of the system.

Metering can significantly reduce consumption within a system. Surveys of public water systems, which have went from a flat rate charge to individually metered services, have reduced system wide

consumption by as much as 50%. The usage rate generally will increase slightly with time after meters have been installed.

Flow. Flow requirements must be determined to insure the adequacy of the system to deliver the required

amount of water on demand. The first step in calculating flow requirement is to estimate the average daily consumption, which is discussed above under the heading of “Usage”. The average daily consumption can then be translated to a average instantaneous daily flow value, most often referred to as average demand or average flow, usually expressed in gallons per minute (gpm). The peak demand rate (peak flow) can then be estimated by multiplying the average flow by the appropriate correction factors. The peak flow requirements can be ten times greater than the average daily flow. Knowledge of the average and peak flow requirements in a system is critical for developing system infrastructure such as; pipe lines, pumping equipment, buffer storage, treatment, etc.

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Pressure. For ordinary service, the typical delivery pressure ranges from 20 to 40 psi. The discharge pressure at

the well head (discharge of the pump) is often 10 to 20 psi greater than system pressure to over come friction losses within the system. Optimum system pressure requirements are a function of topography, fire protection needs, building height, etc. The availability of water under pressure stimulates its use. Increasing pressure from 25 psi to 45 psi can encourage a increase water use of up to 30%.

Storage. Storage is required to equalize pumping rates over the day, to equalize supply and demand over a

long period of high consumption, and to furnish water for such emergency and seasonal usage such as fire fighting and landscape irrigation.

The issues discussed above under the general heading of “Quantity of Water” are most applicable to public water systems. Technical issues associated with estimating usage, flow, pressure and storage requirements for several of the most common water system categories are detailed in Section 1D “Water System Capacity Requirements”. Special considerations, such as landscape irrigation and fire protection are addressed within the context of each water system category (system type) presented in Section 1D.

Water Usage in the United States. On average, the United States uses 80 to 100 gallons of drinking water per

person per day. Of the “drinking water” supplied by public water systems, only a small portion is actually used for drinking. A majority of residential water consumers use water for such purposes as: sanitation, cooking, cleaning and landscape irrigation.

The typical daily residential water use profile is described as follows: • Lowest rate of use - 11:30 p.m. to 5:00 a.m.

• Sharp rise/high use - 5:00 a.m. to noon. (Peak hourly use from 7:00 a.m. to 8:00 a.m.) • Moderate use - noon to 5:00 p.m. (Lull around 3:00 p.m.)

• Increasing evening use - 5:00 p.m. to 11:00 p.m. (Second minor peak from 6:00 p.m. to 8:00 p.m.)

A typical family of four on a public water supply uses about 350 gpd. In contrast, a typical household that gets its water from a private well or cistern uses about 200 gpd for a family of four. The commonly accepted value for individual water usage for rural/domestic populations is 100 gpd per person. Public water systems typically used a design values ranging from 125 to 175 gpd per person (175 gpd avg.) Major factors which affect consumption are metering, climate and delivery pressure.

Commercial and industrial businesses may also place heavy demands on public water supplies. In most water supply systems, the predominant number of user connections are residences, but the few connections to nonresidential customers may account for a significant portion of the system-wide water use. Of the total annual U.S. water use; it is estimated 10% is consumed by residential use, with the remainder being consumed by Industry and Agriculture.

Rights to the Use of Water

The right to use surface or groundwater for domestic use, irrigation, or other purposes varies between states. Some water rights stem from ownership of the land bordering or overlying the source, while others are acquired by a performance of certain acts required by law.

The three basic types of water rights are:

• Riparian - Rights that are acquired together with title to the land bordering or overlying the water source. • Appropriative - Rights that are acquired by following a specific legal procedure, usually involving diverting

unclaimed water and putting it to use.

• Prescriptive - Rights that are acquired by diverting and putting to use, for a period, and under the conditions specified by statute, water to which other parties may or may not have prior claims.

When there is any question regarding the right to the use of water, the utility owner should consult the appropriate state authority and clearly establish the rights to its use.

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1B GROUNDWATER & WELLS

Groundwater as a Water-Supply Source

Rock Types and Geology. About 98% of the earth’s crust is composed of 8 chemical elements. Two of the eight elements, oxygen and silicon (silica Si 02), compose 75% of the crust. Most of the elements of the earth’s crust have combined with one or more other elements form compounds called minerals. The minerals generally exist in mixtures to form rocks.

The rocks that form the earth’s crust are divided into three classes:

1. Igneous. Rocks that are derived from magma deep in the earth. They include granite and other coarsely crystalline rocks, dense igneous rocks such as basalt and other lava rocks occur in dikes and sills.

2. Sedimentary. Rocks that consist of chemical precipitates and rock fragments deposited by water, ice, or wind. These include deposits of gravel, sand, silt, clay, and the hardened derivatives of these-conglomerates, sandstone, siltstone, shale, limestone, gypsum and salt.

3. Metamorphic. Rocks that are derived from both igneous and sedimentary rocks through considerable alternation by heat and pressure at great depths. These include gneiss. schist, quartzite, slate, and marble.

The pores, joints, and crevices of the rocks in the zone of saturation are generally filled with water. Although the openings in these rocks are usually small, the total amount of water that can be stored in the subsurface reservoirs of the rock formations is large. The most productive aquifers are deposits of clean, coarse sand and gravel; coarse, porous sand stone; cavernous limestone; and broken lava rock. Some limestone, however, is very dense and unproductive. Most of the igneous and metamorphic rocks are hard, dense, and of low permeability, and generally yield small quantities of water. Among the most unproductive formations are the silts and clays. The openings in these materials are too small to yield water, and the formations are structurally too weak to maintain large openings under pressure. Compact materials near the surface, with open joints similar to crevices in rock, may yield small amounts of water.

Formation and deposition of the various rock types can be further classified in terms of geologic time period. The time period in which the various formation deposits were made often identify the characteristic of the groundwater (Aquifer) system. Generally, younger rocks are better aquifer’s than older materials.

Groundwater and Quality. Water movement within a ground water basin is caused by gradient changes. Gradient changes are primarily a result of recharge (inflow), stemming from precipitation infiltration and discharge (outflow) as a result of pumping. The quantity of water that can be removed from a ground water basin, without depleting storage, is referred to as the basin yield.

Proper development of a groundwater source requires careful consideration of the hydrological and geological conditions of the area. Information about the geology and hydrology of an area may be available in publication of the US Geological Survey or from other federal and state agencies. The National Water Well Association may also offer assistance.

Sanitary Quality of Groundwater: When water seeps through overlying material to the water table, particles in suspension, including microrganisms, may be removed. The extent of removal depends on the thickness and character of the overlying material. Clay or hardpan provides the most effective natural filtration of ground water. Silt and sand also provide good filtration if it is fine enough and in thick enough layers. The bacterial quality of the water also improves during storage in the aquifer because storage conditions are usually unfavorable for bacterial survival.

Groundwater found in unconsolidated formations (sand, clay, and gravel) and protected by similar materials from pollution sources is more likely to be safer than water coming from consolidated formations (limestone, fractured rock, lava, etc.).

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In areas where human waste are deposited in septic tanks, cesspools, or pit privies, the bacteria in the liquid

effluents from such installations may enter shallow aquifers. Sewage effluents have been known to enter directly into water-bearing formations by way of abandoned wells or soil-absorption systems. In such areas, the threat of

contamination may be reduced by proper well construction-locating the well father from the source of contamination. The direction of groundwater flow usually approximates that of surface flow, and it is always desirable to locate a well so that the normal movement of ground water flow carries the contaminate away from the well.

Chemical and Physical Quality of Groundwater. The mineral content of groundwater reflects the type of

formation which it moves through. Generally, groundwater in arid regions is harder and more mineralized than water in regions of high annual rainfall. Deeper aquifers are more likely to contain higher concentrations of minerals in solution because the water has had more time to dissolve the mineral rocks. For any groundwater region there is a depth below which salty water, or brine, is almost certain to be found. This depth varies from one region to another.

Some substances found naturally in groundwater, while not necessarily harmful, may cause a disagreeable taste or undesirable properties to the water. Magnesium sulfate (Epsom salt), sodium sulfate (Glauber’s salt), and sodium chloride (common table salt) are a few of these. Iron and manganese are commonly found in groundwater. Regular users of water containing relatively high concentrations of these substances commonly become accustomed to the water and consider it good tasting.

Concentrations of chlorides and nitrates that are unusually high generally indicate sewage pollution.

Temperature. The temperature of groundwater remains nearly constant throughout the year. Water from very

shallow sources (less than 50 ft [15m] deep) may vary in temperature from one season to another, but water from deeper zones remain relatively constant – about the same as the average annual surface air temperature. Beyond about 100 ft (30 m), the temperature of ground water increases steadily at the rate of about 1°F (5/9°C) for each 100 ft. (30m) of depth. In volcanic regions, this rate of increase may be much greater.

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Distances to Sources of Contamination. All groundwater sources should be located a safe distance from sources

of contamination. In cases where sources are severely limited, groundwater that might become contaminated may be considered for a water supply if treatment is provided. All water sources should be placed a safe distance from potential contamination with consideration to the direction of water movement. A determination of a safe distance should be based on specific local factors and addressed in the “Sanitary Survey” phase. Table 1-1 is a guide for determining safe distances.

Table 1-1: Guide for Determining Location of Water Source From Contamination Source

Formation Minimum Acceptable distance from Well to Source of Contamination

Favorable 50 ft (15 m). Lesser distances only with health department approval following

(unconsolidated) comprehensive sanitary survey of proposed site and immediate surroundings.

Unknown 50 ft (15 m) only after comprehensive geological survey of the site and its surroundings has

established, to the satisfaction of the health agency, that favorable formations do exist.

Poor Safe distances can be established only following both the comprehensive geological and

(consolidated) comprehensive sanitary surveys. These surveys also permit determining the direction in

which a well may be located with respect to sources of contamination. In no case should the acceptable distance be less than 50 ft (15 m)

Development of a Groundwater Supply. The type of groundwater development to be undertaken depends on

the geological formations and hydrological characteristics of the water-bearing formation. Development of ground water falls into two main categories:

1. Development by wells 2. Development from springs

a. Nonartesian or water table a. Gravity

b. Artesian b. Artesian

Note: Development of springs is outside the scope of this manual.

Nonartesian wells penetrate formations in which groundwater is found under water table conditions. Pumping from

the well withdrawls water, lowering the water table in the vicinity of the well, as a result of the artificially created pressure differences.

Artesian wells penetrate aquifers in which the ground water is found under hydrostatic pressure. Such a condition

occurs in an aquifer that is confined beneath an impermeable layer of material at an elevation lower than that of the intake area of the aquifer. When the water level in the well stands above the top of the aquifer, the well is

described as artesian. A well that yields water by artesian pressure at the ground surface is a flowing artesian well.

Preparation of Ground Surface at Well Site. A properly constructed well should prevent surface water from entering

a ground water source to the same degree as does the undisturbed overlying geologic formation. The top of the well must be constructed so that no foreign matter or surface water can enter. The well site should be properly drained and adequately protected against erosion, flooding, damage and contamination. Surface drainage should be diverted away from the well.

Well Yields. The amount of water that can be pumped from any well depends on the character of the aquifer and the construction of the well. In general, doubling the diameter of a well increases its yield only about 10 percent. The casing diameter is generally selected to provide enough room for proper installation of the pump.

A more effective way of increasing well capacity is by drilling deeper into the aquifer. Consideration of the inlet portion of the well structure (screen, perforations, slots) is also important in determining the yield of a well in a sand or gravel formation. The amount of open area in the screened or perforated portion exposed to the aquifer is critical. Wells completed in consolidated formations are usually of open-hole construction.

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It is rarely possible to accurately predict the yield of a well before it is completed. Knowledge can be gained from studying the geology of the area and results obtained from other wells constructed in the vicinity. This information is helpful in selecting the location and type of well most likely to be successful. The information can also provide an indication of the yield to expect.

A common way to describe the yield of a well is to express its discharge capacity in relation to its drawdown. This relationship is called the “specific capacity of the well” and is expressed in gallons per minute per foot of drawdown. The specific capacity may range from less than 1 gpm/ft of drawdown for a low yield well to several 100 gpm/ft for high yield wells.

Groundwater Hydrology and Well Hydraulics

Porosity. Not all of the water contained in unconsolidated sand and gravel aquifers (water-bearing formation) can

be used. The amount of water which can be taken out of an aquifer depends upon the porosity of this water-bearing formation.

Porosity is a term describing the amount of open space between sand grains in an underground aquifer (Figure 15 -diagram A). The term “absolute porosity” is the total amount of water that can be held in a given volume of the aquifer. Of the total amount of water held in an aquifer, only a portion of it is “free water” available for use. It is this free water which can be used promptly, that determines the useable porosity of the formation. The useable “bound water” is trapped (held) in the form of a thin film wetting the sides of the particles of sand (Figure 1-5 - diagram B). The more uniform the grains of sand are in size, the higher the porosity and yield from a well. A fine uniform sand will often produce more water than a coarse, mixed sand and gravel.

Permeability and Transmissibility.

The terms permeability and

transmissibility are used to describe the ability of an aquifer (or water bearing fomation) to allow water to pass through it. The drawing in Figure 1-6 shows a sand and gravel water bearing formation and the arrows indicate the water flow.

Permeability is a measure of the flow of

water, in gallons per day, which will take place across opposite faces of a one foot cube (P) under a differential head of one foot of water. Transmissibility is the average permeability of a section (T) of the entire aquifer at a given location multiplied by the thickness of the aquifer.

Figure 1-5: Porosity of a Water - Bearing Formation

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Cone of Depression. When a well is pumped, the water level in the well falls below the water level out in the

aquifer, creating a gradient which immediately creates a flow into the well from all directions. As a result, the free water surface in the aquifer takes the shape of an inverted cone or curved funnel. This cone is appropriately called the “cone of depression”.

If the material of the aquifer transmits water easily, the cone is flat and wide spread. If it transmits poorly, the cone will be steep. The cone does not have a fixed shape and becomes deeper and flatter as the well is pumped. The science of aquifer hydraulics has been built around the shape and behavior of this cone. Cone of depression issues are graphically illustrated in Figure 1-13 - diagram A & B.

Seasonal Water Level Changes. A hydrograph is a record of water levels over a period of time. To obtain a

hydrograph on ground water, a recorder is installed in an observation well which is not directly affected by pumping. The water level in the observation well fluctuates with the seasons of the year. Water levels will be fairly constant during the winter months and a sharp rise in the water level is generally noted in the spring season, followed by a slow decline through summer and fall. The range of seasonal variations may be as great as five to ten feet and has a marked effect on the yield in shallow wells.

Hydrographs on artesian wells show interesting effects. Changes in barometric pressure may cause a foot or more change in water level. Earthquake tremors temporarily affect levels and can be detected by sensitive hydrograph instrumentation. Pumping data obtained during the spring should be adjusted to allow for the normal decline in water levels typically observed in the fall. The collection of such hydrographic data on local ground and surface water sources is often available form the Federal and State Geological Surveys.

Figure 1-7: Seasonal Water Level Changes

Well Efficiency and Overpumping. The concept of pumped well efficiency was first presented by Jacob in 1947.

Basically, “well efficiency” is defined as the formation loss (the head loss required to produce flow) divided by the total drawdown observed in the well. This quotient is expressed as a percentage and is typically calculated based on data compiled from a step - drawdown pump test.

Figure 1-8 represents a simplified sketch illustrating the well efficiency concept. Since groundwater flow through porous medial is laminar in nature, the head loss required to produce the flow through the aquifer is directly proportional (linear) to the well discharge.

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Construction and maintenance parameters to be considered in order to maximize well efficiency are: 1. Well screen aperture size (as large as

possible consistent with gravel pack formation material retention).

2. Screen entrance velocity (3.5 fps or less, assuming at the design flow rate- 50% plugging of the available screen open area -effective area of opening).

3. Well development (well development should be conducted immediately after completion and should be continued until there is no change in specific capacity/well yield). 4. In areas where wells are subject to plugging,

as a result of incrustation and/or fouling, chemical treatment should be performed periodically to maintain acceptable well performance.

In general, open hole completions in

consolidated formations are more efficient than screened completions in unconsolidated formations assuming complete development. High efficiency does not insure higher specific capacity, as wells completed in unconsolidated formation usually have a higher specific capacity than consolidated formations.

Overpumping (pumping the well in excess of the design rate) will result in decreased well efficiency. Adverse

affects associated with overpumping are:

• Increased risk of dry run (pump-off) and/or cascading water which may damage pumping equipment. • Increased risk of developing a sand problem, which can damage the well and pump.

• Decrease in water quality as a result of adverse gradient changes (salt water intrusion, pull in of pollutants, silt fouling, etc.)

• Increase incrustation potential. Deep drawdown increases oxygen exposure (oxidation) and can lead to plugging of both the well and pump. Incrustation is a function of the presence of detrimental micro-organisms and specific water quality conditions.

Careful analysis of pump test data should be made to insure pumping equipment is sized properly to avoid

overpumping. Pumping to storage over a longer period of time and/or the construction of multiple wells to provide the required system demand can be used to reduce over pumping.

Figure 1-8: Well and Formation Loss in a Pumped Well

Pumping Water

Level

Static Water Level

Well Loss Formation Loss Flow

Figure 1-9: Overpumping Illustration

0 100 200 300 400 500 600 700 800 900 1000 gpm

Static Water Level

Acceptable Gradient (ft/gpm) Increasing Gradient

40

10

Acceptable Well Load

Overpumping

Formation Loss 55

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Well Spacing and Interference. The location of water wells in relation to one another becomes critical where:

1. The land is limited for large spacing between wells.

2. There is a high concentration of wells in the immediate vicinity. 3. A high yield well field is planned.

4. The aquifer has a low permeability and/or nearby boundaries, or when recharge is at great distance. When determining well spacing requirements, it is necessary to have some idea of the shape and extent of the “cone of influence”. The cone of influence is defined as the slope of the hydraulic gradient or water surface away from a pumping well. Figure 1-13 diagram C illustrates “cone of influence” affect relative to well spacing. By determining the “cone of influence” of adjacent wells the effect of the overlapping curves can be determined, and a decision made to allow a large overlap or keep the overlap small. The cone of influence is normally determined by an aquifer pumping test. This involves measuring flows and draw- downs in the pumping well and observation wells located a distance away from the pumping well. In some highly permeable formations, wells of 2000 gpm capacity could be spaced 200’ apart, as opposed to a low permeability formation 50 gpm wells might be spaced up to 1000’ apart.

Groundwater Mining. Excessive pumping of an aquifer or water-bearing formation is called “groundwater

mining”. Groundwater mining occurs when the quantity of water annually pumped out of a given aquifer exceeds the quantity recharged into the aquifer. Prolong groundwater mining will result in a declining water tables and can create serious long term water supply problems, as well as increasing the cost of pumping. In certain areas, surface subsidence can occur as the water bearing formation is de-watered.

The overproduction (overdraft pumping) from a well can only be maintained until the water in storage has been “mined out”. Pumping level on the well will continue to fall until it reaches the bottom of the well, at which time production cannot exceed the natural recharge rate. Overpumping and overdraft pumping are not directly relate; overpumping applies to exceeding the well design capacity, where as overdraft pumping refers to the long term depletion of aquifer storage.

A remedy for groundwater mining is to space wells further apart to capture only the groundwater which is escaping from various water supply sources such as rivers, streams and lakes. In some areas, the deficiency is being made up by artificial recharge from surface water sources, as they become available. In arid regions such as the southwestern states, where pumpage far exceeds available recharge, there is no easy solution short of reduced pumping from the aquifer.

Figure 1-10: Ground Water Mining

Flow 1970 1980 1990 (Water Level) Clay

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Artificial Recharge. When the groundwater level in an area drops at an excessive rate, it is a sign that

groundwater mining is occurring. In some cases it is possible to make up this shortage with surface water. If the aquifer is shallow, it may be possible to artificially recharge the aquifer by ponding or shallow recharge pits. If the aquifer is relatively deep and confined between with impervious materials, recharge wells may be required.

Artificial recharge is commonly practiced in many arid regions. Increased usage of this practice is recommended in areas where the groundwater supply is being depleted. Successful use of this method requires a careful study and analysis.

Figure 1-11: Artificial Recharge

Surface Water _{Recharge Ponding} Well Water Supply

Sand & Gravel

Clay

Well

Dewatering. A dewatering system is typically used to lower (depress) water levels for the purposes of construction

of sub surface structures, changing aquifer flow gradient for the purposes pollutant recovery and to counter buoyancy forces which can dislodge (float out) underground structures subjected to high water table.

Shallow Dewatering for construction purposes is typically accomplished through the insertion of 2” diameter well

points at depths and spacings ranging from 10’ - 25’ and 20’ - 25’ respectively. The well points are typically plumbed into a central collection header system, using a single large pump equipped with a auxiliary vacuum pump, to “dewater” each well through a riser pipe by suction lift.

Deep Dewatering (25’ and greater), generally require the use of individual pumps which must be controlled based

on water level within the well. Submersible pumps are typically used for this purposes, as they are ideally suited as a result of there compact design and high capacity. Control (water level maintenance) is accomplished using a variety of methods ranging from throttling valves, to on - off controls, to direct acting variable speed control or a combination of one or more of these techniques.

Figure 1-12: Typical Shallow Well Dewatering System

Note: Mutual interference between 2 or more wells depresses the water table for

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Water Well Hydraulics. When a well is pumped, the level of the water table in the vicinity of the well will be

lowered (Figure 1-13 A). This lowering, or drawdown, causes the water level to take the shape of an inverted cone called a cone of depression. This cone, with the well at the apex, is measured in terms of the difference between the static water level and the pumping level. At increasing distances from the well, drawdown decreases until the slope of the cone merges with the static water table. The distance from this point to the well is called the radius of influence. The character of the aquifer-artesian or water table-and the physical characteristics of the formation that affect the shape of the cone include thickness, lateral extent, size and grading of sand or gravel.

The radius of influence is not constant and continuously expands with continued pumping. At a given pumping rate, the shape of the cone of depression depends on the characteristics of the water-bearing formation. Shallow wide cones will form in highly permeable aquifers composed of coarse sand or gravel. Steep and narrow cones will form in less permeable aquifer. As the pumping rate increases, the drawdown increases and consequently the slope of the cone steepens. In a material of low permeability such as fine sand or sandy clay, the drawdown will be greater and the radius of influence less than for the same pumpage from very coarse gravel (Figure 1-13).

When the cones of depression overlap, the local water table will be lowered (Figure 1-13). An increase in pumping lifts is required to obtain water from the interior portion of the group of wells. Wider distribution of wells over the groundwater basin will reduce the cost of pumping and allow the development of more water.

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Figure 1-13: Pumping Effects on Aquifers

Discharge Ground Surface

Static Water Table

Cone of Depression for Lesser Pumping Rate Cone of Depression for

Greater Pumping Rate

Radius of Influence Draw-Down A. Effect of Pumping on Cone of Depression Discharge Ground Surface Static Water Table

Cone of Depression Radius of Influence Fine Sand Draw-Down Discharge Ground Surface Static Water Table

Cone of Depression Radius of Influence Coarse Gravel Draw-Down B. Effect of Aquifer Material on Cone of Depression Discharge B Discharge Aquifer A

Cone created by pumping wells A andB

Cone created by pumping wel

l A

Static Water Table

C. Effect of Overlapping Field of Influence Pumped Wells

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Well Design & Construction

Well Specifications. High capacity water wells are usually constructed by contract, so it is advisable that careful

specifications be written to insure a satisfactory well. Before specifications are written there should be considerable investigation made by the system operator or owner. Some estimates and investigation should be made of the well size and capacity by way of the methods outlined in this manual.

The drilling of a test hole as part of the geophysical investigation process is recommended in order to specify in advance the well completion requirements (casing, screen, gravel pack, etc.). In areas where high capacity water well completions are not always assured, a test well may be necessary – in addition to a test hole – to properly assess the suitability of the well location. A sanitary survey investigation as described in Section 1C should be conducted in conjunction with the initial investigation. The contract technical specification for a production water well should address the following issues.

1. Design Targets. An estimate of the anticipated well capacity in gpm, depth and diameter must be established in order to develop preliminary well design parameters, select drilling equipment and infrastructure planning. 2. Construction Method. The drilling and completion method should be specified based on the type of water

bearing formation in which the well completion is to be made.

3. Casing. The type, weight, material, diameter and wall thickness of the casing should be specified, as well as accessory item requirements.

4. Screen. The screen type, diameter, wall thickness, aperture size, etc.

Note: Screen selection and installation intervals are normally based on geophysical investigative work performed in conjunction with test hole work,

5. Gravel Pack. Gradation and installation interval to be specified when applicable. 6. Annular Seals. Grout/cement mix and application interval to be specified.

7. Development & Testing. Development and testing criteria should be clearly specified. In general, development should be continued until no increase in well specific capacity (yield) is noted and the sand specification is met. Pump performance testing should be conducted for 8-72 hours (minimum of 8 hours) after development. 8. Sand Content. A typical sand specification for a new water well is: “sand content not to exceed 5 ppm (mg/ l),

15 minutes after the start of pumping”. A properly designed and developed well should easily maintain the sand content level substantially below 1 ppm.

9. Alignment. In general, the well should not vary from the vertical (drift) in excess of 3” per 100’ of casing length (ie. 6” @ 200’ is permissible). Proper alignment of the well should be guaranteed and a test of alignment required.

10. Sanitary. Sanitary requirements should be recognized by closing the top of the well so that no surface water can enter. The casing of the well should extend at least 6” (150 mm) and preferably 12” (300 mm) above the finished grade. In areas subject to flooding, the well casing should extent 24” (600 mm) above the 100 year flood level. The well should be cleaned of all debris, lubricants and mud. Disinfection of the well must be performed.

All documents and records to be maintained, and submitted by the contractor should be clearly specified in the contract documents (logs, casing and screen materials, aperture size, gravel analysis, etc.). Reliable local contractors and consultants can provide valuable advice and design assistance in the development of a water well supply source. The American Water Well Association (AWWA) standard A100-84 for water wells, contains sample contract language and various design aids.

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Types of Wells. Wells are constructed using a variety of methods such as; dug, bored, driven, jetted or drilled.

Table 1-2 summarizes the suitability of the various well construction methods for a specific application and geologic formation. High capacity water wells are typically drilled using either the percussion (cable tool) or rotary (direct or reverse) drilling technique and/or combination of both.

High Capacity Water Well Drilling Methods. As previously mentioned, the two most common methods of drilling

high capacity water wells are the cable tool and rotary drilling techniques. These techniques, as they relate to drilling and completion (casing and screen) are presented below.

Cable Tool. In the cable tool (percussion) drilling method, the borehole is drilled by the pulverizing action of

a reciprocating steel bit suspended from the drilling rig by a wire cable. As the bit strikes the bottom of the hole, the formation is crushed, creating cuttings which are removed by balling. If the formation is loose and unconsolidated, the casing must be forced into the hole periodically to prevent caving.

Several procedures are available for completing wells drilled by the cable tool method. If casing is installed as the hole is drilled, it may be perforated by down-the-hole tools, forming a screen opposite the

water-producing formations. With most methods of down-the-hole perforating, a small aperture cannot be formed nor can the aperture size be precisely controlled. Consequently, finer-grained aquifers must be avoided. In general practice, the cable tool method lends itself more to drilling coarser, harder formations. Cable tool well diameters and depths range from 8” to 18” and 100’ to 1000’ respectively.

Small diameter wells for domestic purposes, drilled in tight - consolidated formations, can be constructed using the cable tools or down-the-hole air hammers. These wells often only need a surface conductor casing installed through the unconsolidated over-burden. Water is produced from the open hole. In some cases, a protective casing is installed to the depth of the pump.

Rotary. The use of the direct rotary and reverse circulation rotary drilling methods are the dominate method

of construction of higher capacity production water wells. Both rotary methods can be used to construct gravel envelope wells in unconsolidated formations. Typical rotary drilled well completions in unconsolidated and consolidated formations are illustrated in Figure 1-14.

Direct Rotary. In the direct rotary method, a rotating bit under controlled loading is applied to the formation.

Drilling fluid (water with additives-mud, is used to provide weight and viscosity) is pumped down the drill pipe, through the bit, and circulates up the hole carrying the cuttings, which are separated and removed at the surface. Usually the finished borehole is drilled in two or more stages. A smaller pilot bore is drilled first, then reamed to a diameter 6 to 12 inches greater than that of the casing and screen. The screen is selected and designed according to information gained through analysis of the cuttings, formation and electric logs. The casing string (blank pipe & screen) is generally installed in a continuous operation. Selected gravel is placed in the annular space adjacent to the screen, between the casing and enlarged hole to stabilize the formation and provide a filter against fine sand or silt. The annular space between the borehole and blank filled with cement grout. Well diameters and depths range form 4” to 24” and 100’ to 3000’ respectively.

Reverse Rotary. The reverse circulation rotary method varies from the direct rotary method in three major

respects. The circulating fluid flows down the hole and up the drill pipe. Drilling fluid hydrostatic pressure against the formation maintains the wall of the borehole from caving both systems, usually no additives are mixed with the circulating water (drilling fluid). The reverse circulation procedures, the hole is normally drilled in one pass without staging. Well completion (blank casing, screen, gravel placement and grout) are installed in the same manner as the direct rotary process.

Equipment requirements differ in that drill pipe diameters range from 6” to 10” and a high capacity suction lift pump is normally used to create the “reverse” flow. A compressor is required for deep well applications to induce reverse flow via air lift pumping action. The reverse rotary method is particularly applicable to unconsolidated formations, where large diameter-high capacity well construction is required. Well diameters and depths generally range from 18” to 42” and 100’ to 1500’ respectively.

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Air Rotary. The air rotary method is similar to the rotary hydraulic method in that the same type of drilling

machine and tools may be used. The principal difference is that air rather than mud or water is used as the drilling fluid. In place of the conventional mud pump to circulate the fluids, air compressors are used. The air rotary method is best suited for consolidated formation, and is especially popular in regions where limestone is the principle water source. The air rotary method requires that air be supplied at pressures from 100-250 psi. To effect removal of the cuttings, rising velocities of at least 3000 fpm are necessary. Penetration rates of 20-30 fph in hard rock are common with air rotary methods.

Table 1-2: Suitability of Well Construction Methods to Different Geological Conditions

Characteristics Dug Bored Driven Jetted

Range of practical depths 0-50 ft. 0-100 ft. 0-50 ft. 0-100 ft.

(general order of magnitude) (0-15 m) (0-30 m) (0-15 m) (0-30 m)

Diameter 3-20 ft. 2-30 in. 1 1/4-2 in. 2-12 in.

(1-6 m) (51-762 mm) (32-51 mm) (51-305 mm)

Type of geologic formation:

Clay Yes Yes Yes Yes

Silt Yes Yes Yes Yes

Sand Yes Yes Yes Yes

Gravel Yes Yes Fine 1/4-in (6-mm)

pea gravel

Cemented gravel Yes No No No

Boulders Yes Yes, if less than No No

well diameter

Sandstone Yes, if soft Yes, if soft Thin layers only No

Limestone and/or fractured and/or fractured No No

Dense igneous rock No No No No

Drilled

Rotary

Characteristics Percussion Direct Reverse Air

Range of practical depths 0-1000 ft. 0-3000 ft. 0-1500 ft. 0-750 ft.

(general order of magnitude) (0-305 m) (0-610 m) (0-455 m) (0-229 m)

Diameter 4-18 in. 4-24 in. 18-42 in. 4-10 in.

(102-457 mm) 102-610 mm) (305-762 mm) (102-254 mm)

Type of geologic formation:

Clay Yes Yes Yes No

Silt Yes Yes Yes No

Sand Yes Yes Yes No

Gravel Yes Yes Yes No

Cemented gravel Yes Yes (Difficult) No

Boulders Yes, when in (Difficult) (Difficult) No

firm bedding

Sandstone Yes Yes No Yes

Limestone Yes Yes No Yes

Dense igneous rock Yes Yes No Yes

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Drilling Method Selection Factors. Many factors are considered in selection of drilling method and well design.

Among them are depth, diameter, hardness of formation, presence of fine-grained aquifers that need a gravel envelope filter, accessibility of site to equipment and availability of the quantity of water required for drilling. Rotary drilling construction - particularly reverse rotary, requires large amounts of water. In some areas, gravel envelope wells permit the production of greater quantities of water than non-gravel envelope wells, but this is not always the case. Many high efficiency water wells are being constructed today by the cable tool method.

The diameter of a well should be selected only after a careful consideration of all factors such as the desired yield; the type of well construction; the type of pumping equipment to be used; the physical character of the water bearing formation; etc. The ability to produce sand-free water from water-bearing sands is related to the diameter of the well. A larger well diameter coupled with screen open area will decrease the velocity of the water as it enters the well. Decreased velocity reduces the possibility of pumping fine sand.

Sanitary Construction of Wells. Although there are different types of wells and construction methods, there are

basic sanitary aspects that apply to all. The broad issues are described as follows:

• The annular space outside the casing should be filled with a watertight cement grout or suitable impermeable material form the surface to the deepest level of excavation or as deep as necessary to prevent entry of contaminated water, whether from surface runoff or other aquifers.

• For artensian aquifer, the casing should be sealed into the overlying impermeable formations so as to retain the artesian pressure.

• When a water-bearing formation containing water of poor quality is penetrated, the formation should be sealed off to prevent infiltration of water into the well and aquifer.

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Figure 1-14: Typical Rotary Drilled Well Completions

Discharge

Sanitary Well Seal

Connection to Source of Power Plug Air Vent Ground Surface Sloped to Drain Away from Well

Top Soil

Artesian Pressure Surface or Piezometer Surface Clay Cement Grout Formation Seal Dynamic (Pumping) Water Level Submersible Pump Taper Section Screen

Water Bearing Sand

A. Unconsolidated Formation

Outer Casing Drill Hole Diameter for Cemented Casing Cement Grout Inner Casing Drill Hole Through Soft Formation Caving Formation Cased Out Pumping Unit Maximum Dia. Open Hole Hole Diameter on Bottom B. Consolidated Formation

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• A sanitary well seal with an approved vent should be installed at the top of the well casing to prevent entrance of contaminated water or other objectionable material. The well seal should be installed per the appropriate

regulatory requirements. A pitless adapter and cap assembly should be used in situation where applicable. For large-diameter shallow wells, it is difficult to provide a sanitary well seal to the depth normally required by most regulatory authorities. A typical surface completion consisting of a reinforced concrete slab, overlapping the casing and sealed to it with a flexible sealant or rubber gasket are normally used to affect a sanitary seal. The annular space between the casing and bore hole should first be filled with suitable grouting or sealing materials before surface completion.

Well Completion Considerations. The well size and completion method depends upon four principal issues:

1. The type of water bearing formation.

a. Consolidated formations - limestones, sandstones, granites, etc.

b. Unconsolidated formations - alluvial, glacial, sand and gravel deposits, etc.

2. The permeability of the water bearing formation. (The ability of the formation to yield water). 3. Design capacity of the well.

4. The type of deep well pump to be utilized. High capacity submersible pumps may require a larger diameter than turbine pumps to facilitate power cable installation; although alignment may be less critical.

Type of water bearing formation

a. Wells drilled into consolidated formation are normally more expensive and deeper than shallow

unconsolidated wells, the diameter is normally kept as small as possible in line with the diameter of pump to be used. Normally, a minimum of 2” is allowed between the pump end/ bowl and the casing, and 3”

between the casing and borehole.

b. In unconsolidated formations, the screen diameter may depend upon the bowl /pump diameter but may be increased to:

1. Reduce the entrance velocity through the screen.

2. Increase the screen opening area for longer life if mineral deposition from the ground water is a problem. 3. A minimum of 8” is added to the screen diameter for the gravel wall diameter (4” annulus). A 12” increase

(6” annulus) is recommended; however, larger annular clearance may improve well performance. Note: Typical guidelines for screen and gravel pack selection are overviewed in Section 1B.

Permeability of the Formation

Increasing the well borehole diameter in a consolidated formation will increase the yield somewhat, depending on how many additional crevices are encountered by the increased diameter. In unconsolidated formations it is often wise to increase the well diameter in formations with low permeability so that the maximum flow can be obtained. The higher the permeability the less the well diameter will increase the specific capacity (well yield).

Design Capacity

Local knowledge from existing well completions, local hydrology and geology studies can be used to estimate well yield and estimate pump size. The pump chamber casing diameter can be determined by estimating the maximum pump unit diameter (based on well yield) by adding at least 2” the minimum pump diameter, 3” is recommended for ease of installation of submersible units casing diameter vs pump/motor size are listed in Table 1-4.

Downhole Logs and Geophysical Investigative Methods. Numerous instruments and techniques are available for

special investigations of sub-surface and groundwater conditions. Logging equipment can be lowered into a well via wireline, measurements and other data are recorded at the surface by electrical means. Several of the most

commonly used logging techniques used in the water supply industry are presented as follows:

1. Electric log: (single point, short normal - 16” and long normal - 64”): Used in uncased fluid filled boreholes and are typically used for; identification of lithologic (sand, clay, etc.), determine high and low permeability zones, and casing depth in cased hole applications

2. Caliper log: Measures hole diameter at any depth; useful to locate large casing breaks, determine of size and position of casing and liners, location of caving formations (shales, cavernous limestone, etc.), determination of the effectiveness of “shooting” for well development and/or enlarging diameter, etc.

Grundfos A2 Water Engineering[1]

Water Systems Engineering Manual

for Groundwater Supply and Special Applications

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TABLE OF CONTENTS

Grundfos

Engineering Manual for

Groundwater Supply and Special Applications

A global business

Grundfos North America

IT IS OUR MISSION – the basis of our existence – to

successfully develop, produce, and sell high quality

pumps and pumping systems worldwide, contributing

to a better quality of life and a healthier environment.

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North American headquarters in Olathe, Kansas

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Manufacturing in Fresno, California

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Service, distribution and light assembly in Allentown, Pennsylvania

Grundfos

Engineering Manual for

Groundwater Supply and Special Applications

SECTION 1:

WATER SUPPLY PLANNING

1A WATER SUPPLY PLANNING FUNDAMENTALS

1B GROUNDWATER & WELLS