United States
Environmental Protection
Agency
Risk Reduction Engineering
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-90/047 Dec. 1990
Project Summary
Radon Removal Using
Point-of-Entry Water Treatment
Techniques
Nancy E. Kinner, James P. Malley, Jr., and Jonathan A. Clement
The report summarized here presents
the results of a 1 yr evaluation of radon
removal using polnt-of-entry (POE)
granular activated carbon (GAC) ad-
sorption with and without ion exchange
pretreatment, diffused bubble aeration,
and bubble plate aeration. The full report
discusses each of the treatment alterna-
tives with respect to their radon removal
efficiency, potential problems (i.e., waste
disposal, radiation exposure, equipment
malfunctions, intermedia pollution), and
economics.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
Is fully documented In a separate report
of the same title (see Project Report
ordering Information at back).
Introduction
In a recent status report, the U.S. Envi-
ronmental Protection Agency (EPA) indi-
cated that it is considering setting the
Maximum Contaminant Level (MCL) for ra-
don-222 (hereafter referenced as radon in
the text) in the range 200 to 2,000 pCi/L
Several studies on the distribution of radon
in groundwater supplies in the United States
indicate that there will be a large number of
private water supplies with activities in that
range. Although an EPA regulation for ra-
don would not apply to privately owned
wells, states normally adopt Federal regula-
tions and apply them to these water sup-
plies. Private supplies exceeding the radon
regulations will require POE treatment.
The purpose of this EPA Cooperative
Agreement was to evaluate the performance
of POE GAC and diffused bubble and
bubble plate aeration systems while treat-
ing a groundwater supply containing radon.
In this study, direct comparisons could be
made among the individual POE systems
because they were operated in a parallel
flow configuration, each receiving the same
influent water from an abandoned, small-
community groundwater supply. All systems
treated 1.02 m3/day of water applied in a
pattern designed to simulate daily demand
for a POE system. Each of the treatment
systems was evaluated with respect to three
primary factors: radon removal efficiency,
potential problems (i.e., waste disposal,
radiation exposure, equipment malfunctions,
intermedia pollution), and economics over a
1 yr period of operation.
Separate POE GAC systems were oper-
ated with and without ion exchange pre-
treatment and were monitored for changes
in radon removal, radiation emissions, and
general water quality parameters (e.g., pH,
alkalinity, iron, manganese, turbidity, micro-
bial numbers, and nonpurgeable dissolved
organic carbon [NPDOC]). In addition, sev-
eral special monitoring events were con-
ducted on the GAC systems to assess the
effect on performance of daily variations in
water flowrate and raw water quality and
backwashing. The ion exchange and GAC
units were also cored after 1 yr of operation
to determine if iron, manganese, microor-
ganisms, or radionuclides (any or all of
them) were accumulating within the bed.
The POE diffused bubble and bubble plate
aeration systems were monitored for radon
Printed on Recycled Paper
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removal, general water quality parameters,
and radon off-gas emissions.
Analytical Methods
Standard Methods for the Examination of
Water and Wastewater and EPA methods
were used to determine radon; gamma/
beta emissions, the activity of total uranium,
radium-226, and lead-210; microbial num-
bers; pH; temperature; turbidity; iron; and
manganese. The University of New Hamp-
shire and the State of New Hampshire con-
ducted the analyses; when commercial
equipment was used, it was calibrated ac-
cording to the manufacturer's instructions.
Air monitoring using alpha track detectors
was conducted outside the building housing
the treatment units. The detectors were
analyzed by Terradex Corp.* (Glenwood,
IL) after approximately 4 mo exposure.
GAC POE Systems
The GAC units were designed by Lowry
Engineering (Unity, ME), and both con-
tained approximately 0.05 m3of Barrieby
Cheney (Columbus, OH) Type 1002 acti-
vated carbon. Both GAC units were pre-
ceded by pleated paper sediment filters
designed to remove particulates from the
raw water. An ion exchange unit containing
approximately 0.04 m3 of a strong cationic
resin was installed between the sediment
filter and the second GAC unit. The ion
exchanger, which was regenerated every 2
wk, was designed to remove iron and man-
ganese from the raw water before it entered
the GAC.
Diffused Bubble POE System
The diffused bubble unit, designed by
Lowry Engineering (Unity, ME), consisted
of three small tanks in series, each contain-
ing a diff user attached to a common header.
The diffusers had variably spaced 0.64-
mm-diameter holes. Water was pumped
from the third compartment of the unit to a
hydropneumatic tank. A timer connected to
the blower was set to ensure that air flow
continued 10 min after cessation of water
flow. The exhaust, collected at the top of the
unit, was vented outside the building.
Bubble Plate Aeration System
The bubble plate aeration unit was de-
signed by North East Environmental Prod-
ucts (West Lebanon, NH). Raw water en-
tered the unit directly from the well and was
distributed by a spiral diffuser into a 7.6-cm-
wide, 270-cm-long channel. The bottom of
the channel was perforated by 4.8-rnm-
diameter holes spaced 1.9 cm apart. During
operation, air was forced up through these
holes, and this caused the water column to
rise to a height of 17 cm. At the end of the
channel, water flowed over a weir into a
holding tank; from there, it was pumped to a
hydropneumatic pressure tank. A timer
connected to the air bbwer was set to
ensure that air flow continued for 1 min after
cessation of water flow. Exhaust, collected
from the top of the bubble plate chamber,
was vented outside the building.
Sampling Events
All systems were started in January 1989,
and data collection was completed in Janu-
ary 1990. Approximately 1,022 L of water
was distributed to each unit every day in one
30-min and six 18-min intervals at aflowrate
of approximately 7.6 L/min. All units were
monitored daily for the first 3 days. The GAC
units were monitored every 3 to 4 days for
the first month, weekly for the next 5 mo,
and biweekly thereafter. The aeration units
were monitored for the first 6 mo and bi-
weekly thereafter.
During the loading rate studies, the
flowrate to the GAC systems was between
7.6 and 20 L/min or the total daily through-
put was changed from 1,022 L to 1,890 L, or
both. The GAC units were also backwashed
after 11 mo of operation using a water
flowrate of approximately 7.6 l_/min for 15
min.
Data Analysis
All data were analyzed using Student's t
tests at a values of 0.01,0.05, and 0.10. The
most rigorous a value of the three at which
the stated trends occurred was reported for
each data set tested.
Results and Discussion
The raw water characteristics at the test
site are summarized in Table 1.
Table 1. Raw Water Characteristics
Constituent
Granular Activated Carbon
The sediment filters and ion exchange
unit did not remove any detectable amount
of radon from the water (a - 0.05). The ac-
tivity in the effluent (Figure 1) was negligible
for several days and then increased rapidly
to an average of 881 ± 662 pCi/L for the
GAC without pretreatment and 660 ± 204
pCi/L for the GAC with pretreatment; this
activity continued for 4 mo. During the re-
maining 8 mo of operation, the effluent
quality from both GAC units gradually de-
creased from a radon removal efficiency of
99.7% to between 79% and 85%. The radon
mass loading applied to the GAC units was
generally within the range expected and
was least variable during the end of the
study when radon removal decreased the
most. Though the decrease in radon efflu-
ent quality started at approximately the same
time that the NPDOC breakthrough oc-
curred, the correlation between NPDOC
and radon removal was not strong. Nor
could the decreased efficiency be totally
attributed to iron accumulation within the
bed because both GAC units showed the
same trend with respect to radon removal,
although they received greatly different iron
loading.
Though the radon removal profile within
the GAC units could not be determined
directly, gamma emissions measurements
were examined to determine where the
zone of radon removal was occurring.
Gamma radiation is emitted during the de-
cay of bismuth-214 and polonium-214, which
are short-lived progeny of radon. Hence,
gamma emissions are highest where the
greatest radon removal is occurring. Ini-
tially, the greatest gamma emissions oc-
curred at the top of both GAC beds, but
during the middle and end of the study, an
equal or greater amount of emissions came
from the mid-depth of the units (Figure 2).
Concentration*
Radon
pH
Temperature
Alkalinity
Calcium
Turbidity
Microbial Numbers
NPDOC-
Total Iron
Soluble Iron
Total Manganese
Soluble Manganese
Uranium
Radium
35,620 ±6,
6.24 ± 0.19
11.8±2.5°C
34 ± 19 mg/L as CaCO3
15.5± 1.15 mg/L
1.04±0.94NTU
30,400 ± 29,500 CFU/100mL
1.30 ±0.28 mg/L
0.40 ±0.27 mg/L
0.32 ±0.22 mg/L
0.36 ±0.22 mg/L
0.35 ±0.11 mg/L
14.4 ±6.5 mg/L
3.5±2.4pCi/L
*Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
'Mean ± Standard Deviation.
•NPDOC = Nonpurgeable Dissolved Organic Carbon.
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GAC
m GAC with Ion Exchange
A GAC
m GAC with Ion Exchange
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 1. Effluent radon activities for the GAC systems for the first 4 months (a) and for the entire study
(b). (Note the scale difference.)
These data indicated that the zone of radon
removal was moving slowly down the beds.
Because of the relatively low cost of pur-
chasing 0.03 to 0.08 m3 of GAC, POE units
usually contain a large amount of excess
carbon that dampens potential overloads to
the system and probably prolongs the life of
the unit.
The lead-210 retention data (based on
analysis of GAC core samples) and the
gamma emissions data indicated that radon
removal was occurring deeper within the
GAC without pretreatment. This phenom-
enon appeared to be related to iron loading/
accumulation in the bed. The effluent from
the GAC without pretreatment contained no
detectable iron (0.06 mg/L), whereas the
GAC with pretreatment received no detect-
able iron loading because the ion exchange
unit preceded it. The iron data from the
coring experiment of this unit showed that
there was a significant accumulation (a «
0.01) of iron precipitates (13.5 g/kg dry
weight GAC) in the top of the GAC bed as
compared with the GAC with pretreatment.
During visual inspection of the GAC in the
unit without pretreatment, a crust of orange-
brown precipitate was observed in the top
15.2 cm of the bed. It is possible that the iron
precipitation in the GAC impeded radon
sorption by fouling the GAC surface or
causing short circuiting (channeling) of wa-
ter in the top of the bed. As a result, the
radon removal front appeared to be moving
further down the bed in the GAC without
pretreatment, so that the volume of excess
carbon available for polishing was reduced.
Increases in loading rates to both GAC
units resulted in increased radon activity in
the effluent, especially for the GAC without
pretreatment. The data indicated that, over
time, the ability of GAC to dampen mass
loading variations may be reduced.
Backwashing did not change the radon re-
moval observed in either GAC unit nor did it
affect gamma profiles or any of the other
water quality parameters monitored. There
was a small, temporary decrease in effluent
quality immediately after backwashing was
completed, as is typically observed in
granular media systems.
Gamma emissions measurements were
taken 1.5 m away from the GAC tanks
(Figure 3) and were within 80% to 100% of
the values predicted using the Carbdose
2.0 model developed by B. Keene and S.
Rydell (USEPARegion I; Boston, MA; 1989).
At the end of the study, the GAC with
pretreatment was placed in the center of a
61-cm-diameter plastic tank filled with wa-
ter. The data indicated that the water jacket
attenuated the gamma radiation by 14% to
17% at a distance 30.5 cm away from the
GAC unit.
Uranium was removed from the water as
it passed through the GAC without pretreat-
ment (80% ± 32% removal), the ion ex-
changer (73% ± 23%), and GAC with pre-
treatment (35% ± 39%). At a raw water pH
of 6.03 ± 0.34, the predominant uranium
species is the neutral uranyl carbonate
complex, UO2CO3, which should be
adsorbed by the GAC. There was good
agreement between the coring data and the
uranium removal based on measurements
of the treated water. According to the draft
"EPA Guidelines for Disposal of Drinking
Water Treatment Plant Residues Contain-
ing Naturally Occurring Radionuclides,"the
GAC would fall into the range 30 to 300 pCi/
g and, therefore, could be placed in a stabi-
lized landfill. The ion exchange resin would
not require specialized treatment (approxi-
mately 14 pCi/g) with respect to uranium.
A small amount of radium removal was
detected through the GAC without pretreat-
ment, whereas the GAC with pretreatment
did not receive any detectable input of ra-
dium (<0.10 pCi/L) because it was pre-
ceded by the cationic exchange resin. The
coring data also indicated that little radium
was retained by the GAC, which was ex-
pected because radium is extremely
hydrophillic. Based on the draft EPA guide-
lines, the GAC from both units could be
disposed of without specialized treatment
with respect to radium because it contained
<3 pCi/g. The ion exchange resin, even
after regeneration, would require disposal
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I 1 1-—I \ 1 1 1
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Jan Feb Mar Apr May Jun
Aug Sep Oct Nov Dec
Figure 2. Gamma emissions measurements taken on the unit's surface at various depths for the GA C
without pretreatment (a) and the GAC with pretreatment (b).
in a stabilized landfill because it retained
between 10 and 22 pCi/g of radium.
The GAC retained 65 to 445 pCi/g of lead-
210; this falls in the draft EPA guidelines
range of 30 to 2,000 pCi/g and requires
disposal in a stabilized landfill. Lead- 210
was not retained by the ion exchange unit;
this was not surprising because the unit did
not remove radon from the raw water.
In addition, the ion exchange resin was
contaminated with many other radionuclides
probably retained from the raw water or
removed by adsorption or ion exchange
reactions occurring with other solid phases
(e.g., Fe(OH)3, MgCO3) or organic matter.
The water exiting the ion exchange unit
during brine regeneration contained sub-
stantial (102 to 103 pCi/L) amounts of ura-
nium and radium. Disposal of this slurry
should be carefully evaluated to determine
the appropriateness of any disposal alter-
native.
Aeration Systems
The diffused bubble unit consistently pro-
duced effluents with radon activities <200
pCi/L (Figure 4), even when the airflowrate
was restricted because the diffusers be-
came encrusted with iron precipitates. Re-
moval efficiencies of >99% were expected
because the influent radon activity was not
exceptionally high, the airwater (A:W) ratio
was large (approximately 119:1), and the
bubble size was relatively small.
The bubble plate unit (Figure 4) also
produced a very high quality effluent (>99%
radon removal), except on a few occasions
when the unit experienced mechanical
problems (e.g., solenoid valve and pump
failure) and when the air intake filter for the
bbwer was clogged (August-December).
The A:W ratio for the bubble plate unit was
also very high (approximately 156:1).
The pH of the effluents from both aeration
units (diffused bubble - 7.3 ± 0.4; bubble
plate m 7.2 ± 0.4) were not significantly
different from each other (
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0.40
0.30--
0.20 --
0.10--
0.00
O O GAC
• • GAC with Ion Exchange
Background
Figure 3.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Gamma emissions measurements for the GAC systems taken 1.5 m away from the units'
surfaces.
O
Q.
O Diffused Bubble
Bubble Plate
Jan Feb Mar
Nov Dec
May Jun Jul
Time (months)
Figure 4. Effluent radon activities for the diffused bubble and bubble plate aeration units.
financing POE costs) payback period. All
cost figures were updated to first quarter
1990 dollars using the ENR Construction
Cost Index (CCI). The 1967 base year CCI
index for first quarter 1990 is 435.
The cost estimates presented in the re-
port are intended to give a general indica-
tion of the economics of the POE radon
removal technologies studied. Specific
treatment requirements will vary from site
to site and may not be accurately reflected
by the systems or assumptions used in the
economic analysis.
Based on adesignflowof 1.02 m3/day,the
production costs for GAC without and with
ion exchange pretreatment were $9.317
1,000 gal and $12.25/1,000 gal, respec-
tively. If the GAC required disposal as a low
level radioactive waste, the costs would
increase to $9.88/1,000 gal and $13.40/
1,000 gal, respectively. These costs would
be lower if the GAC and ion exchange resin
could be disposed of in a stabilized landfill.
Total production cost estimates for the
diffused bubble and bubble plate aeration
systems were $22.58/1,000 gal and $26.74/
1,000 gal, respectively. The major discrep-
ancy between the costs of the two aeration
systems resulted from the differential in the
retail price of the equipment. (The costs of
the aeration units did not include any spe-
cial off-gas treatment or auxiliary blowers
but did include piping the radon vent above
the roof line).
The production costs for the POE radon
removal systems are high when compared
with public water supplies because (a) there
is no economy of scale and (b) it is assumed
individual homeowners will be purchasing
single POE units with short-term home eq-
uity bans unlike utilities that could purchase
large quantities of POE units for a service
area with a long-term loan. Therefore, there
will not be a quantity discount on the POE
equipmentforthe individual well water sup-
plies nor a long amortization period.
Conclusions and
Recommendations
Of the three systems evaluated, the GAC
requires the least owner maintenance, is
the easiest to operate, and is the least
expensive with respect to capital and op-
eration and maintenance costs, even if bw
level radioactive waste disposal is required.
Neither GAC system, however, consistently
produced effluent radon activities in the
range of the proposed MCL (200 to 2,000
pCi/L). The data indicate that the only con-
dition where POE GAC systems could pro-
duce effluent in this range would be if the
influent activity were low, requiring <80%
removal. Other researchers have shown
that when the influent radon activity is bw
(i.e., <5,000 pCi/L), the gamma emissions
from the GAC units would yield acceptable
levels of exposure dose.
It appears that retention of iron precipi-
tates could shorten the life of the GAC with
respect to radon removal and make it more
susceptible to changes in loading. In appli-
cations where iron and manganese con-
centrations are high, ion exchange pretreat-
ment may be essential. This presents prob-
lems, however, because the resin becomes
contaminated with long lived radionuclides
and the heavily contaminated regenerant
brine and backwash water may require
special disposal. In cases where frequent
backwash ing of the GAC and use of a
sediment filter can limit accumulation of
particulates and metal precipitates in the
GAC bed, ion exchange pretreatment should
be avoided.
One of the ancillary problems associated
with GAC treatment is the retention of longer
lived radionuclides in quantities that dictate
the carbon must be disposed of in a special
manner. Even if the quantities of the bnger
lived radionuclides, such as radium, are bw
in the raw water, lead-210 will always accu-
mulate in a GAC unit retaining radon. A
more thorough evaluation must be made to
determine whether the benefits of GAC are
outweighed by the problems associated
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with specialized handling and disposal, when
the raw water radon activity is low.
Both the bubble plate and diffused bubble
POE units were very efficient (>99%) at
removing radon from the water, even when
it was present at relatively high levels.
Therefore, these units should be able to
meet an MCL of 200 to 2,000 pCi/L over a
wide range of loadings, primarily because
of the high A:W ratios used.
Of the several problems with aeration,
iron oxidation is the most prominent. Even
at tow iron concentrations, precipitates can
form and accumulate in the units, or be
released in pulses to the residence when
the unit is started to meet demand, or both.
Iron treatment will probably be required to
avoid these problems. In the diffused bubble
unit, pretreatment may be necessary to
prevent the diffusers from clogging. If ton
exchange pretreatment is used, however,
the problems associated with radionuclide
retention would have to be addressed. Post
treatment of iron precipitates using sand
filtration has been used, but a thorough
investigation of these units in POE applica-
tions should be performed before their
widespread installation.
In addition to having higher capital and
operation and maintenance costs than POE
GAC systems, the aeration units are more
prone to operational problems because they
have more mechanical parts. As a result,
frequent maintenance will be essential to
the proper operation of the aeration units.
Proper venting of the off-gas from the units
will require discharge above the roofline of
the home.
Elevated levels of bacteria (up to 200,000
CFU/100 ml.) were periodically obtained in
the effluent from all of the POE units tested.
Depending on EPA and state regulations, it
may be necessary to disinfect the treated
water before consumption. Finally, because
radon cannot be readily detected by the
senses, there is a potential for it to be
reintroduced into the water supply if a POE
unit fails without the residents being aware
of the problem. Therefore, frequent moni-
toring of the effluent from any of the POE
units should be stressed to the homeowner.
Thef ull report was submitted in fulfillment
of Cooperative Agreement CR-812602 by
the University of New Hampshire Environ-
mental Research Group under the sponsor-
ship of the U.S. Environmental Protection
Agency.
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Nancy E. Kinner, James P. Malley, Jr., and Jonathan A. Clement are with the Univer-
sity of New Hampshire Environmental Research Group, Durham, NH 03824..
Kim R. Fox is the EPA Project Officer (see below).
The complete report, entitled "Radon Removal Using Point-of-Entry Water Treatment
Techniques," (Order No. PB91-102 020/AS; Cost: $23.00 subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
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