United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-220 Oct. 1981
Project Summary
Data Base for Influent Heavy
Metals in Publicly Owned
Treatment Works
Roger A. Minear, Roy 0. Ball, and Richard L Church
Results are presented of a 2-year
study involving the identification and
assembly of a data base on influent
heavy metals in the publicly owned
treatment works (POTW's) of the
United States. The general character
of the data base is provided with
respect to associated descriptors
(among which are the percent of
industrial contribution, combined
sewers, and infiltration/inflow, the
sample frequency and type, and the
analytical method). Wastewater
treatment plant laboratories were
evaluated during the study and gen-
erally found to be satisfactory within
the framework of the evaluation
method. Of the 80,000 individual
items of data from 239 wastewater
treatment plants, a substantial data
base was generated for cadmium,
chromium, copper, nickel, lead, and
zinc. Extensive data (but reduced in
total volume) were obtained for silver,
arsenic, and mercury. Limited data
were obtained for beryllium, cobalt,
antimony, and selenium. Aluminum,
iron, and manganese data were re-
ceived as well. Median and mean
values (computed in varying manner)
were reported and compared. Gen-
erally, log normal distributions were
observed for all but the data extremes.
No associations could be demonstrated
between the median or mean values
for the composite data base and the
individual descriptors using Pearson
and Spearman* techniques. But iso-
lation of the low-percent industrial
waste category data from the parent
data base did show significant dif-
ferences for 6 of 7 metals (lead
showed no difference).
Additional data treatment proce-
dures have been applied to illustrate
future directions to be pursued with
the data that have been computerized
and supplied on tape with documenta-
tion to the Municipal Environmental
Research Laboratory in Cincinnati,
Ohio.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, 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
The heavy metals loading to publicly
owned treatment works (POTW's) is of
interest because of (a) the possible
inhibitory effect it has on the biological
treatment process, (b)the effluent levels
that can be achieved as a function of
influent concentration, and (c) the
practice of land disposal of waste sludge
where the total metal load to the
treatment plant is of concern. Efforts to
*Sokal, R.R., and Rohlf, F.J. Biometry. W.H.
Freeman and Co , San Francisco. 1969.
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limit metals in influents to POTW's in a
cost effective manner depend on devel-
opment of data on the contributions of
metals from various sources.
Though a number of general studies
and detailed investigations have been
conducted, the existing published
literature base is inadequate for making
a general assessment of the relative
importance of industrial, domestic, and
urban nonpoint contributions to the
total load of heavy metals to municipal
treatment systems. Influent metals data
have been published for only a small
number of plants. No basis exists for
judging the quality of the available data.
Detailed studies have been made for
several cities, but replication of such
studies at a number of cities would be
quite expensive. An alternative to this
approach is to examine the unpublished
and unconsolidated data base existing
in municipal records.
This study was undertaken by the
University of Tennessee to determine
the extent and character of this data
base, specifically with respect to the
influent concentrations of heavy metals.
Conducted in two phases, the study had
the following specific objectives:
1. To determine the extent and
character of the national data base
for influent metal concentrations
in POTW's.
2. To provide an indication of the
quality of the data base by means
of direct laboratory evaluation.
3. To obtain and computerize a
representative sampling of the
defined data base in conjunction
with an array of descriptors for the
data source.
4. To summarize the quantitative
character of the data base and
examine variations relative to the
array of descriptors obtained.
Phase I: Survey of Data
Sources
The first phase of the research project
was to determine the extent of the
POTW data base for influent heavy
metals on a national scale by conducting
a survey of federal, state, and municipal
agencies concerned with treatment of
wastewater. Regional offices of the U.S.
Environmental Protection Agency (EPA)
could offer little or no direct assistance
in determining which cities might have
data on influent metals. Visits to each
regional office did, however, afford a
rapid means of obtaining names of ap-
propriate state contacts.
These state contacts were in turn of
mixed value for completing the survey.
In most cases, considerable information
was obtained on cities that might be
performing analyses for heavy metals in
treatment plant influents, and the
names of city contacts were provided.
For a few states, state agency require-
ments for POTW's under certain cir-
cumstances included reporting of
influent heavy metals. On the other
hand, some states had no direct know-
ledge of such activities within the
municipal sector and were convinced
that such data did not exist.
Though communication with EPA and
state agency offices yielded a sizeable
number of cities to be contacted, it was
apparent that many cities had been
excluded from the list. The balance of
the city selection process was based on
population (as reported in the 1977
Rand McNally Road Atlas), as all cities
with populations greater than 25,000
were to be included. Some allowance
was made for states with few cities of
this size by lowering the population
cutoff to include major population
centers.
The information as to whether or not
the POTW measured heavy metals in
the plant influent was acquired by direct
telephone inquiry. In all, 900 cities were
contacted, of which 180 were contrib-
utors to POTW's in other cities. Based
on the Rand McNally data, these 900
cities represented a total population of
84.2 million, or 41.4% of the U.S.
population. When the appropriate
individual had been contacted, a yes/no
answer regarding measurements of
influent heavy metals was requested. If
an affirmative response was given,
further information was requested that
consisted of a list of the metals
analyzed, the frequency of measure-
ment, the sampling procedure, the
analytical method used, whether total
or soluble metals or both were deter-
mined, the type of treatment, and a
rough indication of how much industrial
waste was included in the plant flow.
Phase II: Data Collection
The second phase of the research was
to obtain actual data from all cities
willing to provide it. Because of varia-
tions in the amount of data available
from each city and physical limitations
in the anticipated computer coding of
the data, requests for data were based
on the frequency of analysis, as follows:
Frequency No. of Years of
of Analysis Data Requested
S 50/yr 1
>10but<50 2
g10/yr 4 (or what was
available)
In conjunction with this phase of the
project, a means of evaluating the
laboratories was devised, and a signifi-
cant percentage of the cities supplying
data were visited and their laboratory
facilities and operating procedures
were rated. The rating method was
based partly on a method developed for
EPA use in evaluating environmental
monitoring laboratories. The rating
criteria were grouped into three parts:
(1) personnel and external and internal
controls, (2) laboratory space and
facilities, and (3) general information
about the laboratory. The first two parts
were used while interviewing laboratory
personnel and inspecting the facilities,
and the third section was used after the
visit. All analyses were kept confidential,
and the scores have been used only for
the purpose of characterizing the data
set. Of the 85 cities rated, 53 had scores
above 60 (but of a possible 100) and did
not have any critical responses that
would cast doubt on the validity of,
laboratory measurements being per-l
formed. The laboratory rating forms
used for the metal analysis laboratories,
with critical response items noted, were
reproduced as Appendix B of the project
report.
Computer formatting and entry of the
data were undertaken, resulting in
generation of a master computer file of
data and other descriptors of the data
base, including the laboratory rating
scores. Cities were coded by number to
maintain some degree of anonymity, but
general geographic location and pop-
ulation data are contained in the
computer data base. The full report
provides the data base characteristics
and an examination of relationships to
specific descriptors or lack thereof.
Data Base Characteristics
The dominant metals represented in
the data base were cadmium, chromium
(total), copper, nickel, lead, and zinc—all
with more than 200 plants making
influent measurements. Silver, arsenic,
iron, mercury, and manganese repre-
sented an intermediate group, with
aluminum, cobalt, and selenium showing
much lower numbers of plants perform-
ing the analyses. A
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The dominant treatment plant type Table 1.
making influent measurements of
metals was an activated sludge plant.
Weekly sampling was the most common,
with monthly sampling a close second,
daily sampling a close third. By far the
greatest number of plants made mea-
surements on a 24-hour composite
sample. Flow-proportioned sampling
was the most common practice.
By far the dominant analytical method
was atomic absorption spectrophotom-
etry. Most of the data represented
analyses conducted at the treatment
plant or at a central municipal laboratory
rather than by commercial laboratories.
The percent of industrial flow con-
tributions were predominantly in the
10% to 39% range, but with appreciable
representation in both higher and lower
categories. Roughly half of the plants
reported no combined sewers.
Data Analysis
Table 1 summarizes information that
was received from 239 treatment plants
and entered into the computer. Data
supplied were usually in the form of
copied laboratory records and contained
entries for zero concentrations or less
than a particular value. For some
•metals, the combination of less-than or
ero values was high. Notably, arsenic,
cadmium, and selenium had 42,41, and
44 percent of the values reported in this
fashion. Zinc and copper, on the other
hand, were reported mostly as discrete
values with only 2% and 8% of the
values reported as zero or less than,
respectively.
Mean and median values of metal
concentrations were calculated in a
number of ways, using different process-
ing of less-than and zero values.
Weighted mean and median values,
which considered the number of obser-
vations at each plant, were also calcu-
lated. Median values were generally
lower than mean values (Figure 1).
Concentration ranges for each metal
extended over 2 to 4 orders of magni-
tude.
Overall, the individual plant mean and
median metal concentration data tend
to fit a log normal distribution. Figure 2
shows the relationship for median
cadmium concentrations. The curved
lines provide the 99% confidence
interval boundaries.
Though no association could be
determined between the percent of
industrial effluent and metal concentra-
tions in POTW influents, sufficient data Figure 1.
were available to determine that cities
Summary of Data Base on Heavy Metals from 239 Wastewater
Treatment Plant Influents
Number of Observations
Concentration, mg/L
Metal
Ag
Al
As
B
Ba
Be
Cd
Co
Cr
Cu
Fe
Hg
Mn
Mo
Ni
Pb
Sb
Se
Sn
Sr
Ti
V
Zn
Total
Observations
1,696
857
1.140
101
441
- 777
8,937
323
1 1,362
12.351
8.558
2,698
2,302
22
9,461
7,521
155
592
6
85
4
125
11,341
80,214
Number
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Concentration, mg/l
Range of individual concentrations reported and unweighted median
and mean concentrations for metals on the priority pollutant list.
-------
99.39 —i
99.95
99.9
99.
90.
70.
50.
30.
10.
1.
0.1
0.05 =
0.01
i KM rim i i 11 inn i i i nun i iiiiini
0.0001 0.001 0.01 0.1 1.0
Log Concentration CO (mg/IJ
Figure 2. Log probability plot for reported median cadmium concentrations.
with less than 4% industrial contribution
had significantly lower levels of cadmium,
chromium, copper, mercury, nickel, and
zinc. Only lead concentrations were not
significantly different for the two
populations.
Statistical evaluation of the data
showed seasonal variations in metal
concentrations, with mean concentra-
tions from 5% to 20% greater in the fall
than in the spring.
A general conclusion was that more
detailed time series information on
weather conditions (related to inflow
and infiltration), industrial profiles
(including pretreatment data), and other
descriptors for cities with large data
bases would be needed to elucidate
better associations between the com-
posite data base and the descriptors
evaluated in this report.
The full report was submitted in
fulfillment of Grant No. R805606-01 by
the University of Tennessee under
sponsorship of the U.S. Environmental
Protection Agency.
-------
Roger A. Minear, Roy O. Ball, and Richard L Church were formerly with the
Department of Civil Engineering, University of Tennessee, Knoxville, TN
37916.
Sidney A. Hannah is the EPA Project Officer (see below).
The complete report, entitled "Data Base for Influent Heavy Metals in Publicly
0 wned Treatment Works," (Order No. PB 82-108168; Cost: $21.50. 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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