Groundwater Recharge and Wells

A Guide to Aquifer Storage Recovery

R. David G. Pyne

• Publisher: CRC Press
• Year: 2017
• Topic: Technology & Engineering
• eBook ISBN:
  9781351443869
• Subtopic: Hydrology
• Index: Technology & Engineering

Understanding the issues that have been encountered at other sites, and the steps that have led to successful resolution of these issues, can provide great help to those considering, planning, or implementing new groundwater recharge projects. Recent technical advances and operational experience have demonstrated that well recharge is a feasible and cost effective method of artificially recharging natural aquifers. This practical guide reviews the technical constraints and issues that have been addressed and resolved through research and experience at many sites. The book presents aquifer storage recovery (ASR) technology and traces its evolution over the past 25 years in the United States. Procedures for groundwater recharge are presented, and selected case studies are examined. Drinking water quality standards and conversion factors are provided in the appendix for easy reference.

CHAPTER 1

Introduction

Slowly they wind athwart the wild,

And while young Day his anthem swells,

Sad falls upon my yearning ear

The tinkling of the Camel-bells.

The Kasidah of Haji Abdu El-Yezdi

Sir Richard Burton

1.1 WATER MANAGEMENT: A GLOBAL CHALLENGE

We are many travelers in a land that has limited water resources, and the distance and direction to the next oasis are not well known. However, the camel knows the way and will guide us. By storing water when and where it is available, the camel is an appropriate symbol for a world in which the incessant increase in demand for water is challenging our ability to meet this demand.

Water resources must be managed more efficiently and wisely if we are to sustain the needs of a growing world population. The signs are all around us, for those willing to see:

• Groundwater supplies 97% of the water used in Saudi Arabia, yet water levels are declining at such a rate that groundwater reserves will soon be exhausted, probably within 20 to 50 years.

• About two-thirds of India is underlain by basalt aquifers that supply water to hand dug wells for domestic and agricultural use. Increasing withdrawals are causing these wells to dry up in many areas, creating the need for deep well pumping equipment and accelerating the rate of water level decline.

• Groundwater withdrawals in the Denver Basin of Colorado in the U.S. have caused water levels to decline from near land surface to a depth of almost 275 m (900 ft).

• Wells supplying growing populations in many coastal areas have been lost to saltwater intrusion directly attributable to increasing groundwater withdrawals.

• Loss of wetlands and natural areas to urban development and agricultural production is accelerating the rates of storm runoff and erosion in many countries, creating pronounced increases in the intensity of flooding and droughts in downstream areas, and reducing natural recharge to aquifers.

• In Beijing, China, water levels have been dropping about 1 to 2 m per year and about one-third of the wells have reportedly gone dry [1].

• With a 1992 population of 56 million, Egypt has a renewable water supply averaging only about 82 LPC/day (22 GPC/day). The population of Egypt is doubling about every 28 years [2].

At the time of Christ, world population has been estimated to have been approximately 300 million people [3]. It required 1700 years for the population to double to slightly over 600 million people. By about 1860, a span of 160 years, it had doubled again to 1.2 billion. The population reached 2.4 billion by about 1945, doubling within 85 years. It had doubled again to 4.8 billion by about 1984, 39 years, and is expected to double again by the end of the century, another 16 years. Annual population growth rates for the period 1980 to 1988 averaged about 1.7% worldwide, within a range of 0.3% for Europe to 2.8% for Africa.

Per capita water demands have tended to rise, associated with standards of living that have improved in many parts of the world. However, per capita water supplies have fallen rapidly, associated with increasing population growth. The widening difference between per capita demand and supply represents a growing potential for problems and a growing challenge for water managers. Figure 1.1 shows the estimated annual world water use between 1900 and 2000. During this period, water use has increased almost ten times to over 5000 km³/year [4].

Global water supplies are generally believed to be constant. About 40,000 km³/year constitutes the world’s renewable freshwater supply [5].

Figure 1.1 Estimated annual world water use, total and by sector, 1900–2000. From Shiklomanov, I. A., Global Water Resources, Nature and Resources, Vol. 26, No. 3, 1990. With permission.

It is apparent that water is being utilized more intensively to meet the growing needs of the global population. Examples include flood control and channelization projects, levees and pumping stations, dams, reservoirs, regional irrigation systems, and water transmission pipelines.

These types of major regional water supply facilities were first constructed over 2500 years ago to irrigate the region of Mesopotamia around the Tigris and Euphrates rivers, including such cities as Babylon, Nineveh, and Ur. They have become quite common throughout the world during this century.

Even more intensive water management measures have been implemented relatively recently in a few areas to meet local needs. Some of these include pumped storage projects to meet peak power requirements, deep injection wells to dispose of wastewater and to form salinity intrusion barriers, desalination of brackish water and seawater, reclaimed water irrigation systems, increasingly sophisticated treatment plants to treat water and wastewater to potable standards, and artificial recharge facilities to replenish aquifers.

Artificial recharge is therefore but one of many tools available to achieve more efficient utilization of limited available water supplies. Improvements in artificial recharge technology in recent years have reduced the cost of water supply facilities expansion substantially. As a result, future use of this technology is expected to accelerate.

1.2 ASR: A NEW WATER MANAGEMENT TOOL

Interest in artificial recharge has strengthened in recent years, in response to declining groundwater levels, increased vulnerability of surface water supplies to contamination, environmental opposition to increased reliance upon surface water supplies, and many other reasons. Conventional artificial recharge methods have included surface infiltration systems and injection wells, both of which have technical constraints that have tended to limit their widespread implementation.

Surface recharge systems work well in situations where soils are permeable from ground surface to the water table and where adequate land area is available at reasonable cost to accommodate the recharge facilities. Solids that accumulate at the surface are periodically removed following a series of wet-dry cycles that maintain the long-term infiltration rate. Where low permeability soils are present between ground surface and the water table, or where land availability at reasonable cost is limited, surface recharge may not be viable.

Injection wells tend to plug, requiring periodic redevelopment to maintain their capacity. Since they are usually not equipped with pumps, this is achieved by redeveloping the well using a temporary pump or an air line, assuming the degree of plugging is slight. However, if plugging has been allowed to deteriorate to the point that this is inadequate to clear the well, then it is necessary to use physical scrubbing, acidification, jetting, surging, pumping, disinfection, and other more intensive methods to restore capacity.

Both surface recharge and injection well systems have been utilized to achieve the single limited objective of getting water into the ground. Since the quality of water required for injection well systems to minimize plugging generally has to be much better than that required for surface recharge systems, injection wells have generally been perceived as a higher cost recharge alternative, to be considered only at such time as all possible alternatives for surface recharge have been proven non-feasible or too costly. As a result, there have been relatively few applications of injection well technology to achieve artificial recharge objectives.

The author proposes a broader vision of artificial recharge, one in which the objective is not only to get water into the ground, but also to recover it for a beneficial use at the same location. A key element of this broader vision is that the storage zone may contain native water of poor or brackish quality, in addition to freshwater zones previously considered for recharge. With this broader vision and dual-purpose approach, recharge is accomplished with one or more wells, and the same wells are used for recovery of the stored water. Pumps provided in the wells to enable recovery are also used periodically to redevelop the wells, thereby maintaining their injection capacity. Such dual-purpose wells are called aquifer storage recovery or ASR wells.

This slight shift in approach radically alters the economics of artificial recharge, and is therefore altering the direction of its future development. In particular, operating experience has shown that if water is treated to a level that will avoid rapid plugging of the well, such as meeting potable drinking water standards, the water may be stored and recovered from the well, generally without the need for retreatment other than disinfection. This is true for freshwater storage zones and also for brackish water zones. For potable and other higher quality water uses, the option exists to use the same facilities for both recharge and recovery, without the need for retreatment other than disinfection. For lower quality water uses such as irrigation, the same advantage may possibly apply; however, greater care will be needed to avoid well plugging and also to avoid aquifer contamination (see Chapter 8, Future Directions).

With surface recharge systems, recovery of the water at the same site would require additional cost for construction of wells, for piping and pumps, and perhaps for construction of the associated treatment facilities to meet water quality requirements prior to the ultimate use. Where both surface and well recharge are feasible, well recharge may therefore tend to be more cost-effective in situations where a need exists for the recovered water at the recharge site and where treatment of the water would be required anyway. As discussed subsequently in this chapter, there are many applications that meet this description.

In situations where surface recharge is not feasible, ASR wells will tend to be cost-effective relative to systems that rely upon separate injection and recovery wells, due to the lesser costs of construction and operation for dual-purpose ASR wells. Probably the only applications where single-purpose injection wells are preferable are those where it is desired to maximize blending between stored water and native groundwater, and where aquifer hydraulics or recharge water quality are such that plugging is not an operating constraint. Even in situations where it is desired to use the aquifer to convey water from the point of injection to a distant point of recovery, providing a pump in the well will usually be less costly as a means of maintaining injection capacity than periodically removing all injection piping and redeveloping the well.

The ASR concept therefore represents a significant new development in how we manage water. First and foremost it is an idea, or change in thinking, about how to approach artificial recharge. However, it is also a new technology. The technology is usually not complicated; however, experience suggests that there are several technical and other elements unique to ASR that, if understood, can lead to a successful and cost-effective operation. Similarly, neglecting these elements may contribute to system failure due to plugging, improper well design or operation, poor location, geochemical problems, inappropriate regulatory actions, and other consequences.

Figure 1.2 Groundwater recharge.

1.3 WHAT IS ASR?

Aquifer Storage Recovery may be defined as the storage of water in a suitable aquifer through a well during times when water is available, and recovery of the water from the same well during times when it is needed. The con...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Acknowledgments
• List of Figures
• Chapter 1 Introduction
• Chapter 2 ASR Program Development
• Chapter 3 Design of ASR Systems
• Chapter 4 Selected ASR Technical Issues
• Chapter 5 Geochemistry
• Chapter 6 Selected ASR Non-Technical Issues
• Chapter 7 Alternative ASR Applications
• Chapter 8 Future Directions
• Chapter 9 Selected Case Studies
• References
• Appendices
• Index