to identify the key sections of water well
specifications and briefly discuss their contents.
INTRODUCTION
Design and construction of water wells is a topic
unfamiliar to many, if not most mechanical engineers. As a
result, the task is often poorly handled or worse, ignored. This
rarely results in a well completed in the best interests of the
owner. Although the HVAC engineer may not always be
directly responsible for the design of the well, its
specification or construction management, it is, in the context
of a ground-source heat pump system, a critical part of the
mechanical design. Consequently, it is in the interest of the
HVAC design engineer to become familiar with the
terminology of water wells and the key specification issues
relating to their construction. The goal of this paper is not to
provide suggested specification text but to briefly discuss the
key sections found in a well specification document and
comment on the contents of each.
WATER WELL TYPES
The design of a water well and the preparation of the
construction documents related to it is a function of several
issues including the purpose (domestic, municipal, irrigation,
injection, etc.), capacity (low <10 gpm [0.6 L/s], medium 10 -
100 gpm [0.6 - 6.0 L/s], high >100 gpm [>6.0 L/s]), geology
penetrated (consolidated, unconsolidated, combination) and
construction method (mud rotary, air rotary, reverse
circulation, cable tool) (NWWA, 1975). Since this paper is
limited to wells serving commercial GWHP systems (normally
medium to high capacity, rotary constructed), the primary
influence on design and specification is the nature of the
geology penetrated in the process of construction.
Although, there are an infinite number of well
construction designs for a substantial part of the country, the
alternatives can be reduced to some variation on one of the
two basic designs as shown in Figures 1 and 2. Special
modifications to these basic designs can be made to
accommodate conditions such as artesian aquifers, injection
rather than production, corrosive water etc. The simplest well
is one completed in rock formations in which the water is
produced from fractures in the rock. In these wells,
sometimes called open-hole completions due to the nature of
GHC BULLETIN, MARCH 2001
the geology, no casing or screen is necessary to stabilize and
filter the aquifer materials adjacent to the well bore. Casing
is normally placed in the upper portion of the well for a short
distance to accommodate the installation of a surface seal.
Figure 1. Open-hole well completion.

Figure 2. Gravel envelope well.
25 Pumping Water Level
(changes with
pumping rate)
Pumping and static levels
measured from ground surface
Drawdown (changes with
pumping rate
Static Water Level
(non-pumping conditions)
Pump Housing
Casing
Production
Casing
Groundwater
Production
Zone
Screen
Perforated
Casing
Or Open Hole
(Well Intake)
Pump Bowl Assembly
(lineshaft type pump
shown)
Cone of Depression
develops around well
during pumping
Ground Level
Motor
Grout
Seal
The second type of well, completed in
unconsolidated materials (sand, gravel, clay, soil and mixtures
thereof) is more complex. In these applications the well is
completely lined with casing, screen and sometimes an
artificial filter or gravel pack. In unconsolidated settings,
the variation in the size of the aquifer materials results in the
need to adequately filter the water entering the well to control
the content of sand in the water produced. In some cases, a
screen alone, attached to the bottom of the casing, will provide
the necessary filtering of the water. In other cases, the screen
must be accompanied by an artificial filter or gravel pack
located between the screen and the borehole wall. This gravel
is sometimes only a formation stabilizer of relatively
uncomplicated description. For other situations, a more
carefully specified filter gravel must be used. The need for
accurate description of these components and their installation
results in a more voluminous specification document for these
wells compared to an open-hole well.
WATER WELL TERMINOLOGY
Prior to discussing the details of individual well
specifications sections, it is useful to review a few of the key
terms relating to water wells and their operation. Figure 3
includes many of these terms. In any well, under non-
pumping conditions, the level at which the water resides in the
well is known as the static water level. When the pump is
started, the water level will drop to a new level known as the
pumping level and this level is a function of the pumping rate.
The difference between the static water level and the pumping
level is referred to as the drawdown. Dividing the pumping
rate by the drawdown yields a value known as the specific
capacity with units of gpm/ft (lps/m). This value provides a
rough indication of the aquifer/well capacity to produce water.
The drawdown is the manifestation, at the well, of the cone
of depression which forms around the well in response to
pumping.
The lower portion of the well in the production zone
may be completed with only a borehole (in rock formations),
a screen or with a screen and artificial filter (gravel pack)
depending on the nature of the aquifer materials. Casing is
placed in the well to support the borehole and prevent
collapse, to accommodate the installation of a pump, or to
facilitate the placement of a seal. The diameter of the
innermost well casing (known as the pump housing casing)is
primarily a function of the size pump to be installed.
Submersible pumps, the type most often used in GWHP
systems due to their operation at 3600 rpm, often require one
size smaller casing than line shaft driven pumps which
normally operate at 1800 rpm or less. Other well casing is
sometimes installed in the upper portion of the well to
accommodate the installation of the surface seal. The surface
seal, often a cement grout, prevents surface water from
draining down between the casing and borehole into the
subsurface.
WELL SPECIFICATION ISSUES
There are several areas which should be addressed in
the course of preparing a specification for a water well and
26
Figure 3. Water well terminology.
Table 1 presents the most important of these. Some issues
relate only to certain types of wells or conditions, but this
table is a useful checklist for the specification process. There
are two approaches to the design and specification of a water
well. If there are other wells nearby producing from the same
formation and of approximately the same yield, the design of
a new well can be based upon the existing wells. This is an
acceptable practice assuming the existing wells operate
without problems. In other cases, the well design is
determined to a large extent by the geology and aquifers it
penetrates. A preliminary design can be developed, but it may
be necessary to modify this in the course of construction.
Table 1.
Key Water Well Specification Sections
(gravel pack well)
________________________________________________
Scope of Work Logs/Records Flow testing
Non-Technical Plumbness/Alignment Sterilization
Well Issues
Equipment
Casing
Abandonment
Requirements
Drilling Fluid Screen
Drilling Program Gravel
Formation Sampling Development

________________________________________________
GHC BULLETIN, MARCH 2001 For a well completed in a consolidated formation
(rock), the sections on screen, gravel and sometimes
development can be eliminated.
SCOPE OF WORK
This is the section in which a general description of
the work is provided. The scope at a minimum, includes the
type of drilling rig to be used, approximate depth and number
of wells along with the expected yield for production wells.
When available, the scope may also provide additional detail
on the general construction of the well in terms of casing size,
depth, screen type diameter, location and development
method. If a performance guarantee with respect to yield, or
specific capacity is required, this is also included in the scope
section (Roscoe Moss, 1985).
NON-TECHNICAL WELL ISSUES
Non-technical well issues (a phrase used in this paper
and not in the specification document) include items not
directly related to the technical details of construction.
Contractor qualifications, site description, noise control,
archeological discovery and facilities provided by owner are
normally covered as individual sections, but are grouped
together here for simplicity.
The contractor qualifications paragraph normally
includes a minimum experience requirement (number of wells
similar to the current project, and years in business) and a
licensing requirement. Details for a list of reference projects
may also be spelled out. The site description is especially
important, particularly if potential drillers are from outside the
area. A physical description of the site is provided along with
background on the geology/hydrogeology. If available, well
completion reports from nearby wells are a key part of this
information. Noise is normally addressed through the
specification of acceptable operating hours for drilling
operations. Facilities provided by the owner is one of the few
s p e c i f i c a t i o n i s s u e s a c t u a l l y r e q u e s t e d b y
contractorsparticularly in the