by Rick Stryker
Water from the tap or showerhead is something many of us take for granted.
Until, of course, it’s not there on demand. Because of their inherent
remoteness, camps and conference centers are particularly vulnerable to
the problems caused by a water outage. Most camp facilities’ staff have
a basic understanding of their particular system, but may not be especially
well versed on how small changes in the system can have far reaching effects.
Similarly, many executives and owners are asked to make decisions about
their systems without really understanding how the choices can affect
operations in the long run.
Let’s look at several of the basic design and operating parameters for
small water systems including estimated daily demand, the sources, and
types of supplies and methods for supplying pressure.
How much do we need?
Most states have adopted conservative design figures between forty and
eighty gallons per day per person at resident camps for estimating both
the required fresh water supply volume as well as the volume of wastewater
expected to require treatment. In most areas, if your organization can
provide historical water usage, those “real” figures can be used when
designing new components of either system. For those reasons, we strongly
recommend that all water systems be metered and monitored. Without site-specific
data, we normally assume conservatively that each person will consume
eighty gallons per day. This usage includes bathing, food preparation,
and regular consumption. For example, if your camp capacity is 300, we
would estimate your average daily demand at 300 people X 80 gallons per
person = 24,000 gallons per day.
Water Supply
There are two facets of this issue to be considered. Either a camp’s water
comes from a public source such as a village or town by way of a water
supply line or it is self-sufficient, relying on sources within its own
boundaries. Both sources have issues with which the camp or conference
center executive must grapple.
Public supply
This is a mixed bag of benefits and shortcomings. On the plus side, the
customer is typically not required to monitor the quality of the water
nor is it required to submit the water for tests. In today’s climate of
government paperwork, this freedom can certainly be a blessing. There
is also the added benefit of being connected to a proverbial “endless
supply.” Anyone who has been at camp when the well “went dry” or the well
pump died can certainly appreciate this!
For the camp that is being approached (or in some cases, has been directed)
to connect to a public supply network, there are often concerns about
whether the amount charged is commensurate with the volume actually used.
In some cases, the camp has negotiated a flat fee for which it receives
water for its operating season.
In light of recent drought conditions in many regions, this type of arrangement
has become increasingly rare. For the organizations that still operate
this way, we suggest that the days are numbered. At the very least, the
camp should expect to see fairly large increases in the fee. This is the
method by which the seller of the water will encourage conservation measures.
Most users of public water are metered, with the customer paying a regular
fee per thousand gallons of water used.
Private supply
Historically, surface water has been available for water supplies. However
with the increased population in surrounding areas, surface waters are
more and more contaminated with pollutants and bacteria. Even in remote
areas, the most pristine appearing water likely contains cysts and pathogens
generated by wildlife. Without advanced and very expensive treatment,
this water does not meet potability standards of most state health departments.
In fact, most wells whose construction does not physically prevent the
entry of surface water runoff are not considered acceptable sources.
Operating a “nontransient, community water supply” has certain monitoring
requirements, which are imposed by state health agencies and enforced/monitored
by local ones. This normally involves very basic periodic sampling for
indicator organisms such as coliforms. Systems which operate under the
influence of surface waters (as described above) often have additional
testing requirements to ascertain whether other contaminants have entered
the well.
Today, most camps’ water supplies are underground in the form of wells.
The depth and construction of these sources varies by subsurface geology,
but in general, the operating principles are the same. A hole is either
drilled or dug through the surface layers of earth until a water bearing
layer (or strata) is encountered. The amount of water that enters the
hole will be dependent on the size of the hole, the physical size of the
“underground pond” (or aquifer), and the characteristics of the material
through which the water flows.
Water In = Water Out
It’s important to consider that this describes the property of the well
known as “specific capacity.” We have encountered several facilities where
a larger well pump was perceived as a solution to a water supply shortage.
The capacity of the well can only be determined by performing a test known
as a “drawdown,” or “pumping test.” Typically, a fairly high capacity
pump is temporarily installed in the well and is connected to a water
flow meter at the top of the well. As water is drawn from the well, the
depth from the top of the well casing to the water level is measured at
regular time intervals. The rate at which the water is pumped out is adjusted
until the water level in the well does not fall further from one measurement
to the next, indicating that water is being removed from the well at the
same rate as it is flowing in. This test is conducted over a fairly long
time period, twenty-four hours or more. When the pump is turned off at
the end of the test, measurements are taken and recorded to determine
the rate at which the well “recovers” from being pumped. This data is
used to determine how much water is physically available from that particular
well, and to set the depth at which the final pump should be set. For
smaller wells (typically single family residences), the well driller skips
this step and uses equipment on the drilling rig and makes a best guess.
For a large organization with a similarly large water demand, however,
this is a particularly important procedure and should not be skipped.
It’s important to note that most regulating agencies will not permit
a well to be operated continuously. For calculations and permitting, the
well is typically assumed to be operating only 12 hours a day and recovering
for 12 hours. Keep this in mind when considering whether a certain well
has sufficient capacity to supply your organization. Using our example
earlier, our average daily demand is 24,000 gallons. Your well(s) should
be capable of supplying that amount in 12 hours or 24,000 gallons/12 hours
= 2,000 gallons per hour. Dividing that by 60 (2,000 gallons per hour/60
minutes per hour = 33.3 gallons per minute. Therefore, your well would
need a specific capacity of about 34 gallons per minute to meet the estimated
demand.
As a final point on wells, if your records do not indicate the capacity
of your wells, or if the tests are more than ten years old, you may want
to have the tests run. Aquifers and their behavior change over time as
do the characteristics of the well. In bedrock wells, the cracks which
supply the water can fill with sediment, reducing the water available
to the well pump. In screened wells (found in gravelly or sandy soils),
the well screens which hold the hole open can become clogged with biomass,
silt or corrosion, also reducing the net capacity of the well. Finally,
development of the properties surrounding camp can be tapping into the
same aquifer as the one from which your well draws. This testing also
provides a great opportunity to inspect your well pump for wear of its
moving parts as well as the electrical system.
Under Pressure
More than just a great classic Rock hit, this is the property user’s
notice first about your water system. If it takes several minutes to fill
a bucket of water or a washing machine, the system operator is likely
to hear about it. There are only a few methods to supply pressure to a
system.
The first and simplest method of supplying pressure is gravity. The well
pump moves the water from underground to a storage tank whose height has
been set to deliver a regular, reliable system pressure. For each 1 pound
of pressure required, the water needs to be raised about 0.4’. Put another
way, raising the water 1’ increases the pressure 2.31 pounds per square
inch (psi). Average system pressure range at a faucet or showerhead should
be between 30 and 50 psi.
This means that the lowest water level above the highest faucet has to
be at least 30 * 0.43 = 12.9¢ above the highest faucet.
The upper end of the operating range is calculated the same way: 50 *
0.43 = 21.5¢ above the highest faucet.
Another way of looking at this is that the fluctuating height of the
water in the tank (“operating range”) is about 21.5¢ – 12.9¢
= 8.6 feet.
A pressure sensitive switch turns the well pump on when the pressure
falls below the 30 psi and turns the pump off when the pressure reaches
50 psi.
You can see, then, that by combining sufficient storage (about one day’s
supply) with a tank at the right elevation, the system can operate without
electricity or the pump for a period of time with no interruption in service.
Looking back at our example, we could estimate a cylindrical tank size
as follows:
- 24,000 gallons / 7.48 gallons per cubic foot = 3,210 cubic feet
- Volume of a cylindrical tank is calculated by V = p(r2)h
- 3,210 = 3.14 x (r2) x 8.6¢
- Solving for r yields a minimum tank radius of 10.9¢, or a diameter
of about 22¢.
There is a second way that pressure can be supplied to the network, and
it uses a principle with which we’re all familiar: the aerosol can. This
system is referred to as “hydro-pneumatic.” Again, a pump moves water
into a system connected to a closed tank that contains air at a certain
pressure. A pressure switch again turns the pump on and off as the pressure
reaches certain preset levels. This system has the advantage of replacing
physical height with air pressure, so giant columns of water aren’t required.
However, the main disadvantage is that air, being highly compressible,
takes up the majority of the space in the tanks. In fact, the effective
storage of most hydro tanks is about 18 percent of the total volume.
Using our same 24,000 gallon example, and assuming that we get the 18
percent storage, we would calculate that the required hydropneumatic storage
tank would have a total volume of 24,000 / 0.18 = 133,333 gallons! You
can see that storage of a day’s supply in hydro tanks is not very common,
so most often, the tanks are very undersized for the application. The
frequent off/on cycles of the well pump to repressurize the system significantly
shortens its service life.
The third way to supply pressure to a network is through a pump which
runs constantly, often referred to as a jockey pump. Most often, this
pressurizing method is for extraordinary circumstances such as accommodating
fire demand at a hydrant. While it is possible to supply normal operating
pressure for a small system, its absolute dependence on electricity makes
it a fairly unattractive option.
The simplest water supply and storage systems can be extraordinarily
complex. But when compared to the potential liability and inconvenience
of a contaminated system or interrupted service, the investment in doing
it right the first time is really very small. In our next installment,
we will discuss some of the other aspects of water systems including water
and system disinfection, taste and odor, network configurations, and the
effect of friction in water systems.
Originally published in the 2002 September/October
issue of Camping Magazine. |
