&ERAJ technical BRIEF
www.epa.gov/research
Adherence of Chemical, Biological, and Radiological
Contaminants to Sediments Found in Water Storage
Tanks
INTRODUCTION [1,2]
Many large and small drinking water distribution systems store treated water in storage tanks.
The tanks serve as primary water sources or as reserves for emergency water use. Tanks also
help equalize water demand and maintain pressure in the distribution system.
Unless used frequently or cleaned regularly,
a substantial build-up of sediments can occur
in tanks. The sediments can contain material
that has sloughed off from corroded tank
linings or material brought into the tank from
the source water. Although rare, waterborne
illnesses have resulted from organisms
introduced into the tank when open vents,
hatches, or inadequate covers allow matter,
birds, or other animals to gain access.
The type and quantity of sediments varies
widely depending on many factors including
the amount of water passing through the
tank, the characteristics of the water, the
amount of mixing the water receives, and the
tank's maintenance schedule.
Sediment accumulation can impact water quality and potentially cause health concerns. Direct
monitoring of the tank water itself might not detect potential problems because chemicals or
microorganisms can adhere to sediments or biofilm (the communities of microorganisms
attached to a surface.)
In addition to the concerns about the impact of sediments on water quality, sediments can serve
as sinks for chemical, biological, or radiological agents if the distribution system becomes
contaminated. The presence of these contaminants on sediment materials would require special
decontamination and disposal practices following intentional or unintentional contamination
incidents.
-------
SEDIMENT ADHERENCE INVESTIGATION [2]
To help define the potential difficulties involved in remediating water tanks if they became
contaminated with CBR agents, the United States Environmental Protection Agency conducted
a study to determine the extent to which contaminants adhered to tank sediments. The study
involved donated sediment and drinking water samples collected from 25 tanks located in 12
different states. The tanks contained finished water that originated from both ground and
surface water sources.
The amounts collected and the characteristics of the sediments varied widely. Eight of the
samples contained enough water and sediment to use in the contaminant adherence study.
This study tested the adherence of four contaminants:
• Nonradioactive cesium (Cs-133), which acted as a surrogate for radioactive Cs-137
• Lindane, an organochlorine pesticide
• Escherichia coli (E. coli, strain K-12J
• Bacillus anthracis Sterne (BaS)
B. anthracis Sterne acted as non-virulent surrogate for pathogenic B. anthracis. E. coli is a
bacterium of interest to the drinking water community since it has been linked to disease
outbreaks. The K-12 strain used in this study is non-virulent.
The small range of pHs in the storage tank water made pH an unlikely significant variable;
however, for consistency, all the water used for adherence tests was adjusted to pH 7.5 and
8.5.
Researchers characterized the sediment samples by particle size, pH, total exchange capacity,
percent total organic carbon, and percent organic matter. Table 1 presents the basic properties
of the sediments.
Table 1. Characteristics of the Study Sediments Collected From Drinking Water Tanks
Drinking Water
Tank Location a
Alabama
Arizona
Arkansas
North Carolina
Ohiol
Ohio 4
Tennessee
Illinois
Particle Size
Clay%
2.73
7.35
3.91
7.63
1.36
1.68
0.4
41.68
Silt %
2.33
34.34
14.44
23.39
6.7
21.67
1.06
21.39
Sand %
94.94
58.31
81.65
68.98
91.94
76.65
98.54
36.93
PH
7.8
6.7
6.7
7.6
7.1
6.6
8.2
7.6
Total
Exchange
Capacity
(mmol/L/100g)
12.2
154.14
12.17
110.8
26.7
57.34
3
9.66
Total
Organic
Carbon %
0.42
9.42
2.78
3.11
0.25
2.09
0.42
1.69
Organic
Matter %
0.88
4.08
11.45
5.45
0.89
5.9
0.43
16.52
The location name was used to identify the sediment.
-------
RESULTS FOR CESIUM AND LINDANE [2]
Prior to beginning the adhesion study, researchers tested the sediments for background levels
of nonradioactive Cs-133 and lindane. Samples Alabama, Arizona, Arkansas, and Ohio 4
contained Cs-133 at levels ranging from 0.3 to 0.4 ug/kg. Researchers considered the
background concentrations too small to interfere with the adherence experiments results.
At the beginning of the adhesion study, researchers spiked the drinking water samples with Cs-
133 or lindane and adjusted to pH 7.5 and 8.5. They placed measured portions of the
sediments into centrifuge tubes and added the contaminated (i.e. spiked) water. They rotated
the tubes for 16 hours at room temperature (22 to 24 °C). Following the 16 hours of contact the
researchers tested the water and sediments and calculated percent adherence. Table 2
presents the results.
The average cesium adherence ranged from 5% to 88%. The average adherences for lindane
ranged from 7% to 88%. As expected, the small range in pH had no statistical significance in
adherence.
Table 2. Average Adherence to Sediments for Cesium-133 and Lindane at pH 7.5 and 8.5
Sediment
Alabama
Arizona
Arkansas
North Carolina
Ohiol
Ohio 4
Tennessee
Illinois a
pH
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
Cesium
Average %
Adherence
38
32
58
57
88
82
20
21
67
60
28
11
5
9
20
Cesium
%SD
5
6
6
6
3
2
1
2
5
8
6
5
5
1
11
Lindane
Average %
Adherence
37
31
86
83
41
43
40
27
87
88
39
44
7
7
27
Lindane
%SD
1
6
2
1
2
10
7
12
0
0
3
2
1
2
3
' Sample size was insufficient to also run tests at pH 8.5.
RESULTS FOR E. COL/AND B. ANTHRACIS STERNE [2]
Prior to beginning the adherence study, researchers determined that the sediments contained
no viable background concentrations of E. coli or BaS.
At the beginning of the adherence study, researchers spiked drinking water samples with E. coli
or BaS at relatively high densities of aboutIO6 colony forming units per ml and adjusted to pH
7.5 and 8.5. They placed measured portions of the sediments in centrifuge tubes and added the
contaminated water and rotated the tubes for 6 hours at 2 to 8 °C.
-------
Following the 6 hours of contact, researchers used tryptic soy agar enumeration to determine
the concentration of organisms in the sediments.
Researchers did not sterilize the samples and soy agar is a non-specific culture media, so the
non-diluted rinse from several of the sediment samples produced flora colonies when plated.
The colonies did not, however, demonstrate morphologies consistent with E. coli or BaS. With
each adherence experiment, researchers also rotated a sediment sample with uncontaminated
tank water and plated the resulting solution at a tenfold dilution. These dilutions produced no
growth of E. coli, BaS, or any other background microorganism.
Table 3 presents the adherence results for E. coli and BaS.
All adherences for E. coli were greater than 50% except for the pH 8.5 Ohio 1 (27%) and pH 7.5
(42%) Illinois samples. All BaS samples had average adherences greater than 90%, except the
Tennessee (86% at pH 7.5 and 82% at pH 8.5) and North Carolina samples (31% at pH 7.5 and
49% at pH 8.5).
Overall, pH differences in the contaminated drinking water were within the experimental
uncertainty of the measurements, thus no significant differences could be observed. However,
the E. coli adherence in the Ohio 1 sample showed a significant difference between pH 7.5 and
8.5; and the BaS adherence in the North Carolina sample showed a significant difference
between pH 7.5 and 8.5.
Table 3. Average Adherence to Sediments for E. coli and B. anthracis Sterne at pH 7.5
and 8.5
Sediment
Alabama
Arizona
Arkansas
North Carolina
Ohiol
Ohio 4
Tennessee
Illinois a
pH
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
8.5
7.5
E. coli
Average % Adherence
76
72
79
77
100
99
66
78
72
27
85
88
54
54
42
E. coli
A%A
4
27
17
18
20
121
39
21
36
3
27
28
6
2
18
3. anthracis Sterne
Average % Adherence
91
92
98
98
100
100
31
49
93
99
99
99
86
82
98
3. anthracis
Sterne
A%A
32
13
17
15
18
22
5
9
72
28
23
33
11
20
33
NOTE. — A% A = combined experimental uncertainty.
a Sample size was insufficient to also run tests at pH 8.5
-------
CONCLUSIONS [2]
Experimental conditions optimized the amount of contact between the sediments and
contaminated drinking water through centrifugation (cesium and lindane) and settling (E. coli
and BaS), so that potential adherence could be observed. In a water storage tank, the degree of
contact will depend on conditions in the tank, as well as characteristics of the contaminants and
the sediments.
In general, the biological contaminants adhered more readily than the chemical contaminants.
Overall, pH differences in the contaminated drinking water were often within the experimental
uncertainty of the measurements, thus no significant differences could be observed.
The results of this investigation suggest that when sediment is present, chemical and biological
contaminants may adhere to the sediment.
CONTACT INFORMATION
For more information, visit the EPA Web site at www.epa.gov/nhsrc.
Technical Contact: Jeff Szabo (szabo.jeff@epa.gov)
General Feedback/Questions: Kathy Nickel (nickel.kathy@epa.gov)
REFERENCES
[1] U.S. EPA. 2002. Finished Water Storage Facilities. (Total Coliform Rule, Distribution
System Issue Paper.) Washington DC: US EPA, Office of Water.
[2] U.S. EPA. 2014. The Impact of Chemical, Biological, and Radiological Contaminated
Sediments on Flushing and Decontamination of Drinking Water Storage Facilities. Washington,
D.C.: U.S. Environmental Protection Agency.
U.S. EPA's Homeland Security Research Program (HSRP) develops products based on scientific
research and technology evaluations. Our products and expertise are widely used in preventing,
preparing for, and recovering from public health and environmental emergencies that arise from
terrorist attacks or natural disasters. Our research and products address biological, radiological, or
chemical contaminants that could affect indoor areas, outdoor areas, or water infrastructure. HSRP
provides these products, technical assistance, and expertise to support EPA's roles and
responsibilities under the National Response Framework, statutory requirements, and Homeland
Security Presidential Directives.
EPA/600/S-14/224
September 2014
------- |