Page 147 - Water and wastewater engineering

4-2 WATER AND WASTEWATER ENGINEERING

4-1 INTRODUCTION

The design of a well field and/or individual wells begins after the completion of the evaluation
of the groundwater source to establish that a safe yield is available to meet the demand and that
water quality standards can be met. These issues were discussed in Chapter 2. The design must
provide for protection of the well from contamination, and it must conform to the hydraulic and
hydrogeologic constraints of the aquifer.

4-2 DESIGN ELEMENTS

The key requirements of wells are that they are:

• Located in an aquifer that has adequate long-term capacity (see Chapter 2 for a detailed
discussion).
• Protected from contamination.

• Reliable.
• Of adequate size and/or number to provide the required quantity of water.
• Located to obtain the best quality water.
• Not located where they will cause an adverse resource impact.

Protection from Contamination
A significant effort is made to protect wells from contamination because of their vulnerability to
numerous sources of contamination. Aquifers lack the inherent protection of replenishment that
is afforded to surface water supplies. Unlike surface waters that are replenished in hours, days,
weeks, or even years, contaminated groundwater may only be replenished over geologic time
scales—lifetimes in the shortest instances and centuries in most cases.

Reliability
Reliability is an essential requirement of groundwater supplies. The water supply system ceases
to function when the well system fails. Small systems are particularly vulnerable because they
typically have only a few wells.

Capacity
Unlike surface water systems, well systems may be expanded relatively inexpensively as com-
munities grow. However, the ability of the aquifer to yield adequate water is not infinite. The
geologic structure of the aquifer limits both the total quantity of water and the rate at which it can
be withdrawn.

Quality
All groundwater is not equal in quality. Contact with geologic minerals guarantees an abundance
of chemical constituents in the water. While most groundwater may be treated to meet water