United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development EPA/600/M-87/031 September 1987
ENVIRONMENTAL
RESEARCH BRIEF
Low-Cost/Low-Technology Aeration Techniques
For Removing Radon From Drinking Water
N.E. Kinner, C.E. Lessard , G.S. Schell, and K.R. Fox
ABSTRACT
Simple low-cost/low-technology aeration techniques were
investigated to determine their effectiveness in removing
radon from drinking water. The techniques consisted of
flow-through storage and minimal aeration in various
configurations, and were found to be effective in varying
degrees for the reduction of radon. These low-cost/low-
technology aeration techniques may be easily applied in
small communities.
INTRODUCTION
In an effort to assemble information concerning simple
treatment techniques for the removal of radon from drinking
water, the University of New Hampshire and the New
Hampshire Department of Environmental Services
(NHDES), through a U.S. EPA Cooperative Agreement,
evaluated low-cost/low-technology aeration treatment
techniques for radon removal. All the techniques involved
storage and/or storage with minimal aeration. These tests
included monitoring radon reduction in a distribution
system, radon release from an open air storage tank with
no mixing (still pool of water), radon reduction in a flow-
through reservoir system with various influent control
devices, and radon reduction in a flow-through reservoir
system with minimal bubble aeration.
DISTRIBUTION SYSTEM
The site selected to evaluate radon loss in a distribution
system was the Rolling Acres Trailer Park in Mont Vernon,
NH. The trailer park consists of 33 mobile homes served by
2 wells that are currently being treated using granular
activated carbon (GAG) to remove radon. The distribution
system consists of 3.8 cm (1.5 in.) to 5.1 cm (2 in.)
diameter pipe. Distances between sampling locations were
measured with a surveyor's tape (Figure 1). Samples were
taken in the evening from kitchen taps at 5 homes located
at various distances from the pump house. The first two
sets of samples were of GAC-treated water. During the
next two sampling periods, raw water was pumped directly
into the distribution system. The greatest reduction (18.8%)
in radon concentration occurred at the sampling point
furthest from the pump house (Table 1), but overall the
reductions observed were very low (0% to 10%).
The actual reduction of radon in a distribution system would
result from decay alone, so loss during distribution would
not be significant unless the distribution system was
extraordinarily long or the flow rate extremely slow. Small
reductions are anticipated in short systems, but the removal
rate would vary with water usage. Data were collected at
.Mont Vernon during periods of high flow and thus
represented a worst case senario.
OPEN-AIR STORAGE
A laboratory study at the University of New Hampshire
monitored radon reduction from a still pool of water. A
115-L (30-gal) plastic storage tank (Figure 2) was filled to
a depth of 68 cm (27 in.) with water containing radon.During
four individual runs, the radon concentration was monitored
for 5 to 6 days (Figure 3). Samples were taken at various
depths in the tank to determine if the radon concentration
varied with depth. No significant difference in radon
concentration was found within the tank.
High levels of radon removal (80% to 90%) were observed,
but 5 to 6 days of storage were necessary to achieve these
reductions. Theoretical reduction by radon decay alone
would be 67% over 6 days, thus open air storage
contributed to a greater reduction in radon removal than by
decay alone. A 24- and 48-hr average reduction rate of
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Figure 1. Mont Vernon Distribution System.
KO
^X.
\ona\
NAME
S I
MA
KO
CU
L A
APR
ROX . D I ST
'TO HOME
( FT)
1 6 9
1 1 4
328
7 2 1
1632
(METERS)
5 2
3 5
1 0 0
220
497
55'
BOX
497
/\cu
1
414' ^j
2371
°a
TABLE 1. Percent Radon Reduction in a Distribution System
Approximate Distance from Pump House, in (ft)
35 (1114)
52(169)
100 (328)
220 (721)
497 (1632)
Influent Radon (26,644 pCi/L
GAG, Treated)
Run 1
Run 2
Influent Radon (234,000
pCi/L, Untreated)
Run 3
Run 4
tt
2.1
10.8
7.3
4.1
9.2
11.8
15.6
18.8
7.5
* Radon concentration at sample point exceeded influent radoniconcentration.
# Sample data not available.
t Homeowner not available during sampling. j
30% and 50%, respectively, was observed. A snrjall
community that could store the water at atmospheric
pressure for several days could use this technique,
although extended storage may be impractical in miDst
cases.
FLOW-THROUGH RESERVOIR
A flow-through reservoir system (Figure 4) was
constructed in Derry, NH, to treat water supplied by the
Southern New Hampshire Water Supply Company. The
storage tank was designed to contain water to a depth of
0.6 m (2 tt) [total volume of 1.64 m3 (433 gal)], with variable
influent entry. The modes of influent entry studied weref 1)
entry at the bottom of the reservoir, 2) discharge 0.6 rrY (2
ft) above the reservoir level, 3) discharge 0.6 m (2 ft) above
the reservoir level with a spray attachment, and 4)
discharge 0.6 m (2 ft) above the reservoir level through a
venturi apparatus to add air to the stream. In addition to the
four tests with varied influent entry type, minimal bubble
aeration was added to entry types 1 and 2.
In the tests where minimal bubble aeration was used, a
laboratory-made bubbler was used. This bubbler was
constructed using 0.6-cm (1/4-in.) I.D. plastic tubing with
holes made at 10 cm (4 in.) intervals by puncturing the
tubing with a thumbtack. Four radial arms of 81 cm (32 in.)
length were placed in the bottom of the reservoir and air
was provided by a laboratory air pump [maximum capacity
0.3 m3/min (1.-1 ft3/min)]. The bubbles from the tubing
appeared to be approximately 1.5 cm (3/16 in.) in diameter
and were produced at an average rate of 2 to 3 per second
from each hole.
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Figure 2. Laboratory Setup for Atmospheric Loss During
Storage (No Flow).
L-27IN.
TOP PORT
MIDDLE PORT
VOL = 115-L130-GALI
BOTTOM PORT
Flow controllers were installed in the influent stream to
control the flow to 1.1 L/min (0.3 gpm), 2.2 L/min (0.6 gpm),
and 3.2 L/min (0.9 gpm). This controlled flow resulted in
theoretical detention times of 24, 12, and 8 hr. The nozzle
attachment used a garden hose spray nozzle adjusted to
give a spray of approximately 15 cm (6 in.) diameter at the
water surface [0.6 m (2 ft) from the nozzle end]. At the low
flow of 1.1 L/min (0.3 gpm), a fine spray could not be
achieved, and thus data are not available for those
conditions.
Good removals of radon were achieved in all test
combinations (Figures 5, 6, and 7) except for the bottom
entry tests. The bottom entry tests provided the minimum
water disturbance of any of the tests and thus the lowest,
removal rate. In fact, the radon removals observed in the
bottom entry tests were only slightly better than would be
expected by radon decay alone.
In all cases where the water was allowed to fall (or was
sprayed) to the reservoir surface, or where minimal bubble
aeration was added, high radon removal rates were
observed. A minimum removal of nearly 50% was seen with
the shortest detention time and simple influent free fall.
Higher removals (80% to 95%) resulted with longer
detention times and supplemental aeration (Figures 5, 6,
and 7). The data collected in this phase of the study
showed that simple aeration can be very effective for radon
reduction and might be easily applied in small communities.
A laboratory venturi was attached to the influent line of the
storage reservoir (Figure 4). The venturi pulled ambient air
into the water stream, and measurements were made to
determine if the additional air would help to remove radon.
The water was then allowed to free fall 0.6 m (2 ft) to the
surface of the tank at the 3 flow rates of 0.9 L/min (0.24
gpm), 2.2 L/min (0.6 gpm), and 3.0 L/min (0.8 gpm). The
venturi addition increased the radon removal over free fall
alone by a range of 5% to 12%, except at the longest
detention time [0.9 L/min (0.24 gpm)]. In this case, the
radon removal with the venturi was 10% less than by free
,fall alone. The flow rates may have been too low to
generate good venturi action (aeration), thus better
removals were not observed in all the venturi runs.
SUMMARY
Simple low-technology/low-cost aeration treatment
techniques are capable of lowering the radon concentration
in drinking water. Removal percentages of 60% to 87% can
be achieved with only 9 hr of retention time and simple
aeration. Better than 95% removal was observed with
aeration applied during 30 hr of storage. Storage for 30 hr
and the addition of minimal aeration should be within the
operational capability of a small community. Larger scale
testing of the simple aeration technique may be completed
under the existing cooperative agreement with the NHDES.
The data presented here are a qualitative description of
some simple laboratory and field tests to remove radon.
Further investigations are necessary to better understand
the simple technologies and the options available to small
communities.
THE AUTHORS
This low-cost/low-technology aeration study was
conducted by Dr. Nancy Kinner, Ms. Carol Lessard, and
Ms. Gretchen Schell of the University of New Hampshire,
funded under Cooperative Agreement CR812602 with the
New Hampshire Department of Environmental Services.
The data shown here and the information presented here
were compiled by Kinner, Lessard, and Schell (Department
of Civil Engineering, University of New Hampshire, Durham,
NH 03824) and will be finalized as a project report under
U.S. EPA Cooperative Agreement CR812602. K.R. Fox,
the EPA Project Officer, is with the Water Engineering
Research Laboratory, Cincinnati, Ohio.
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Figure 3. Radon Loss During Open-Air Storage.
100
0
\ THEORETICAL RADON DECAY
!
RADON CONCENTRATION AT TIME ZERO
(44,000-87,000 pCi/L) |
50
100
150
ELAPSED TIME (hr)
200
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Figure 4. Pilot Scale Atmospheric Tank, Deny, NH.
2 FT ABOVE WATER LEVEL
T
BAFFLE
EFFLUENT
1 FT
EFFLUENT TROUGH
INFLUENT HOSE
SOURCE
Figure 5. Radon Removal at Deny, NH (3.3 L/min (0.9 gpm) 8 hr Detention Time).
3
100-,
0
o
LU
s
o
Q
80-
60-
40-
20-
maximum removal
observed in test
minimum removal
observed in test
removal by decay alone
TREATMENT
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Figure 6. Radon Removal at Derry, NH (2.2 L/min (0.6 gpm) 12 hr Detention Time)
8
§
O
Q
<
o:
100-1
80-
60-
40-
20-
0J
^?£r
maximium removal
observed in test
minimum removal
observed in test
removal by decay alone
TREATMENT
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Figure 7. Radon Removal at Derry, NH (0.9 L/min (0.24 gpm) 30 hr Detention Time).
maximum removal
observed in test
O
a;
UJ
Q_
O
O
100-1
80-
60-
40-
20H
0J
minimum removal
observed in test
removal by decay alone
TREATMENT
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United States
Environmental Protection
Agency
Center for Environmental Research
Information i
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/M-87/031
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