Introduction-
There are three general types of aeration system presently available. They are Shallow Trayâ aeration, diffused bubble, and
re-spray units. This article will not address the re-spray technology because its removal efficiency is low compared
to Shallow Tray or diffused bubble and, therefore, has a more limited use.
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Rising bubbles created in a Shallow Trayâ system
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Both the Shallow Trayâ and
diffused bubble systems force air into the water. The air bubbles formed create a large surface area. This large
area makes it easy for the radon gas to escape from the water into the air. The air and the radon gas are then
vented through a stack to an area above the roof where it can be safely released. Both of these systems require
a repressurization pump to send the water to the house and at least one float switch to control a solenoid valve
that keeps the aeration tank full. The main differences between the two systems is the depth of water used and
the size of the openings in the aerator.
The Shallow Trayâ uses a tray that has 3/16” holes
through the bottom. The tray has solid vertical dividers that provide a path width of approximately 2”. Water is
sprayed onto the tray to a depth of 2”. The air passing up through the holes in the tray suspends the water on
the tray. At the end of the path the water drop into the bottom of the aeration unit where it can be pumped to
the house.
diffused bubble aeration works like an air stone in a fish tank. Air is forced through a series of small opening in what can best be described as a wand that extends into to the water
to a depth of 10” to 15”. The diffused bubble systems usually consist of a single tank with one or more baffles
to separate each aeration wand.
In deciding what to buy you should consider the answers to the following questions:
How much will the radon concentrations be reduced?
The contractor providing you with any type of water treatment equipment should be able to
provide you with a written performance warranty. This performance should not be just a statement about being free
from defects but a statement about the quality of the water that will be produced. Aeration system performance
can be modeled with computer programs to tell you what removal efficiency the system will provide. This information
should be provided in writing on a sheet that identifies the manufacturer as providing this information, the model
# of the unit, and conditions under which this performance can be expected. If the contractor is reluctant to
provide you with this information it probably is not available and the unit he is selling has not been thoroughly
tested.
Does the unit have an auxiliary fan?
Although the EPA does not have specific guidelines for radon water systems, it does require
that radon systems be maintained under negative pressure by placing a fan on the outside of the building. This
is done to prevent the high concentration of gas that is generated in the aeration tank from being forced back
into the building through any leak that may develop. Most aeration systems have a blower mounted on the unit that
pressurizes the system. Under these pressurized conditions, any leak would release high concentrations of radon gas into the home. To prevent this and to satisfy the EPA mitigation
standards the system needs to have an auxiliary fan on the outside of the building to maintain negative pressure
in the system.
What is the vent size?
The diffused bubble system uses a minimum of a 2” stack and the Shallow Tray system uses a
minimum of a 3” stack. The smaller the vent size the easier the installation, however, this is not the only consideration.
The stack should be sized so that the auxiliary fan can maintain negative pressure and that in cold climates
there is no possibility of freezing. The smaller stack sizes will allow the moisture generated in the vent
to create frost and ice that will restrict the flow. This along with the already small stack will create enough
restriction to prevent the auxiliary fan from maintaining negative pressure in the vent stack and aeration tank.
Make sure to ask your contractor how he will size the pipe and if the system will be checked for its ability to
maintain negative pressure.
Where will the vent be run?
The stacks for these systems must be installed so that they do not contain water traps. This
means the pipe must continually drain back to the aeration tank with no low spots that could hold or collect water
that would block the vent. There is also a limit on the length of pipe that can be run. This length is measured
as an equivalent length. The equivalent length will depend on the number of elbows as well as the length of straight
pipe that must be used to route the pipe out of the building. Your contractor should show you the route the
pipe will take, explain how it will be routed to prevent water traps and explain how he has calculated the equivalent
length of the vent stack.
What flow and pressure will be delivered to the house?
Make sure you understand what rate (gallons/min) and pressure the water will be delivered
to the house. Most of these systems are restricted to flows based on the removal rate that is required. The higher
the flow through the aeration system the lower the removal rate. Make sure the contractor is willing to put
in writing the flow and the pressure at which the water will be delivered.
What type of pump will be used?
Aeration systems increase the oxygen content of the water and therefore will oxidize any iron
that is dissolved in the water. This is why it is a good idea under some water conditions that the repressurization
pump not be made of cast iron. Check with your contractor to see if this is a problem for your water and if he
can provide an optional stainless steel pump.
What type of maintenance will be required?
Most manufactures recommend disinfection be done every six months. This requires the simple
addition of a measured amount of household bleach.
Unless careful attention is paid to water quality(hardness, iron, and manganese), the diffused bubble system will
require monitoring and cleaning of the aeration wands as they tend to foul easily. The larger holes in the Shallow
Trayâ system stay clean under
all but the most severe conditions.
Other than this it is recommended that once a year you have the unit inspected, its mechanical functions checked,
aeration tank cleaned and perform two water radon tests(treated and untreated at the same time). There may be air
filters and cartridge filters that need to be changed at the time of this service. Check with your contractor to
determine what your system will need.
How much will the electricity cost to operate the system?
Most of these systems will operate on anywhere for $40-$60 per year. Try this link http://www.awqinc.com/elec_consumption.html to learn how to calculate this for your needs
and electrical rates.
What about references and experience?
These systems should be installed by professionals to be sure they continue to operate efficiently
and quietly. Please be sure you get references and talk to references before hiring a contractor. A good contractor
is as important to the final result as is the choice of the right equipment.
Conclusion-
Please remember this is a lifetime investment. You will be creating a long term relationship
with the company that installs your unit. You need to feel comfortable with them and the equipment you choose.
A few extra dollars spent up front can save you many years of aggravation. The following list will help you keep
the important points in mind as you go through your decision process.
- Get the performance rating of the system.
- Be sure the system will maintain negative pressure.
- Make sure the vent stack is large enough.
- Find out where and how the vent stack will be run.
- Check to see how much water you will get.
- Make sure your contractor is experienced.
