United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/050  Aug. 1985
Project Summary
Determination  of  Toxic
Chemicals  in  Effluent from
Household  Septic Tanks

Foppe B. DeWalle, David A. Kalman, Donald Norman, and Gary Plews
  The presence of volatile organics was
evaluated in raw domestic sewage that
was generated in a subdivision and
treated by a large 5-year-old commuar-
nity septic tank from which the solids
had been pumped just before this
study. Analyses showed the presence
of priority pollutants in the raw
sewage. Essentially no removal of
these compounds occurred during the
2-day detention in the septic tank. The
priority pollutants generally showed
higher levels during the weekend, prob-
ably reflecting leisure activities and use
of related chemicals (paint thinners,
grease removers, toilet bowl cleaners,
etc.). Most of the other volatile com-
pounds were hydrocarbons, and their
removal by the septic tank generally de-
creased with increasing molecular
weight.  Several organosulfur com-
pounds showed substantial increase as
a result of anaerobic degradation pro-
cesses in the septic tank.
  This Project Summary was devel-
oped by EPA's Water Engineering Re-
search 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
  Onsite disposal of sewage is widely
practiced in  rural areas and urban
fringes, but it has received relatively lit-
tle attention from regulatory agencies
or research institutes. For example, little
comprehensive information is currently
available to document  successes and
failures of onsite disposal systems and
the resulting health implications. In the
State of Washington, the census noted
403,910 septic tanks  or cesspools and
14,464 other individual systems such as
aerobic units  or ponds. Such systems
represented 34.7% of all housing units.
A current survey in the State of Wash-
ington also indicates the presence of
more than 500  large onsite  systems
serving hospitals, schools, restaurants,
and subdivisions.  Because the septic
tank effluent is directly returned to the
soil through infiltration into the subsur-
face drainfield, considerable public
health concern exists over groundwater
contamination and pollution of drinking
water wells.  A  recent study showed
such widespread contamination  in
major parts of central Pierce County
south of Tacoma.
  In previously published studies, only
the efficiency of the septic tank with re-
spect to BOD, SS, and grease removal
was evaluated; the trace organics pres-
ent in  domestic  sewage  and in septic
tank effluent were not measured. The
present study was conducted to collect
such data. The aim was to measure the
presence of volatile priority pollutants
in domestic sewage as it entered a large
community septic tank  system. The
study also evaluated the removal  of
these compounds in the anaerobic sep-
tic tank by analyzing effluent samples
collected from the distribution box.

Materials and Methods
  This study used a community septic
tank serving 97 homes in the Oakbrook
6 subdivision located  south of Tacoma,

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Pierce County, Washington. The homes
are located on four streets served by a
200-mm (8-in.) gravity sewer that dis-
charges into a wetwell. A 10.1-L/s (160
gpm) submersible centrifugal  pump
transports the waste to the septic tank.
The unit contains 84,935 L (22,440 gal)
liquid volume in  the first compartment
and 42,468 L (11,220 gal) in the second
compartment. The raw sewage sample
was collected through  the  manhole
from  the  inlet-T before the sewage
mixed with the contents of the first com-
partment.  The effluent sample was col-
lected from the distribution box located
4.57 m  (15 ft) downstream  from the
effluent-T.

  The sewage was collected with an all
glass and teflon, custom-made sampler.
The sewage was  drawn by suction
through a 0.5-in. telfon intake line with a
100-ml glass syringe. When the syringe
was in the drawn position,  a  teflon
solenoid valve closed the intake line and
opened the discharge line. When the sy-
ringe content  was subsequently  dis-
placed, it flowed  through the discharge
line to a collection device with a floating
plunger to prevent losses of volatile or-
ganics. The septic tank effluent was col-
lected using a similar sampler that drew
from below the liquid surface in the dis-
tribution box. The samples were col-
lected as  24-hr  composites  during a
7-day continuous period.

  The volatile organics were removed
from the aqueous sample with a purge
and trap method. A modified Hewlett/
Packard 7675A* purge and trap sampler
was used to purge 10 ml of liquid with
nitrogen gas at a  rate of 20 ml/min. The
volatile organics that were stripped
from the liquid were subsequently ab-
sorbed when the  nitrogen passed
through a  Tenax  GC trap. The trap was
subsequently heated,  and the volatile
organics were backflushed and trapped
in the initial 0.5-m portion of a  30-m
fused silica WCOT  column  with an
SE-54 stationary  phase chilled by liquid
nitrogen. After removal of the cryotrap
and flash  heating  of the column, the
volatiles were separated in the gas chro-
matograph and detected by mass spec-
trometry.  A computer library system
containing spectra of 30,000 com-
pounds was used for a spectral compar-
ison with each detected compound.
"Mention of trade names or commercial products
 does not constitute endorsement or recommenda-
 tion for use.
Results and Discussion

Flow Measurements
  Flow data were obtained both from
the water usage records of the  Lake-
wood Water District Company and from
measurements  in the wetwell.  The
water usage  data show a baseline of
58.7 L/min (15.5 gpm), which  usage
triples to 219.5 L/min (58 gpm) during
the summer months because of exten-
sive usage. The frequency distribution
of the flow rates shows several maxima
corresponding to usage in a household
with 1, 2, 3,4, 5, 6, or 7 persons, respec-
tively. The  median  household with 3.2
persons uses 897 L/day (237 gal/day).
The usage ranges from 329.3 L/ person
per day (87 gal/  person per day) for a
one-person household to 242.2 L/ per-
son per day (64 gal/ person per day) for
a seven-person household.
  The flow measurement at the wetwell
consisted of  determining the interval
between sequenced  pump  switch-on
times. The flow rate during the day was
calculated with the holdup volume in
the wetwell. The average  calculated
flow was 44.7 L/min (11.8 gpm), which is
24% less than that calculated with the
usage data. This discrepancy indicates
that about a quarter of the used water
does not reach the septic tank and is lost
through evaporation (clothes  dryer,
plant evapotranspiration, sewer leaks,
etc.). The highest discharge rates and
the  highest standard deviation were
noted around 9 p.m.

Presence of Trace Organics
  The efficiency  of the volatile organic
analysis (VOA) using the purge and trap
unit was evaluated  using surrogate
compounds  spiked  at 20 ppb  in the
liquid  before purging. The results
show a median recovery of 91% for
bromochloromethane, 90% for 1,4-
dichlorobutane,  and  82% for De-
benzene (Figure 1). However, the stand-
ard deviations were substantial  at this
tow concentration level.
  The organics were measured in the
samples during an intensive, week-long
monitoring followed  by six  additional
samplings, the last of which occurred
on  January 23,  1982. The  results are
summarized in Table 1 and indicate that
dichloromethane was found in all sam-
ples. Toluene followed  in frequency of
detection. These two compounds were
also found in the water collected from
the 125-ft-deep  monitoring  well adja-
cent to the drainfield. The analysis dur-
ing the week-long monitoring was initi-
 200
 750
01

  50
 20 iig/L Spiking Level

— o Bromochloromethane
  A 1,4-Dichlorobutane
  a D6-Benzene
         JO
              30   50  70
                       90
                                  98
    Percentage of Samples with Less Than
         Corresponding Recovery

Figure 1.   Normal frequency distribution of
          surrogate recovery.

ated on Monday, September 22, and it
was terminated on Sunday, September
28, 1980. The  volatile organic fraction
typically contained 40 to 50 compounds
at a concentration >1 ppb, but only five
were identified as priority pollutants.
   Toluene was the most prevalent
among the priority pollutants, with an
average concentration  of 34.6 (xg/L in
the raw sewage and 38.8 u-g/L in the ef-
fluent. The toluene, which originates
from cleaning  solvents and paint  thin-
ners, reached  its maximum concentra-
tion of 47.8 p-g/L in the influent on Fri-
day, and 56.9 |xg/L in  the  effluent on
Sunday. The  shift in the maximum
toluene concentration by 2 days may be
a  result of the detention  time, which
was estimated at approximately 2 days.
   Dichloromethane, which  likely origi-
nated from chlorinated tapwater, was
present in the next highest concentra-
tion (9 M-9/U and also showed its highest
level on Sunday. No lag  was detected
between effluent and influent, however.
Chloroform showed its maximum con-
centration (5 u.g/L) in the influent on Sat-
urday, and the effluent showed a sec-
ond maximum on Sunday (0.8 (Jtg/L),
representing  a 1-day shift. Tetrachlo

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Table 1. Occurrence of Volatiles in Septic Tank Samples
Percent of Samples in which Compound was Present
Compound
Dichloromethane
Chloroform

Trichlorofluoromethane

Bromomethane
1, 1,2-Trichloroethane
Trichloroethane
1, 1, 1 -Trichloroethane

1,3- Trichloropropene

Benzene
Chlorobenzene
Toluene
Ethylbenzene
Tap
n=2
WO
0

0

0
0
0
0

0

0
0
0
0
Influent
n=13
WO
62

0

0
0
8
0

8

0
0
85
15
Effluent
n = 13
100
62

0

15
8
8
8

0

IS
0
85
23
Scum
n=2
WO
0

50

100
8
50
0

0

100
0
50
100
Sludge
n=2
WO
0

0

50
0
0
0

0

50
50
0
WO
Well
n = 1
100
0

0

0
0
0
0

0

0
0
100
0
presence of a thick scum layer and dur-
ing subsurface drainage and migration.
Some biodegradation of several organ-
osulfurs and hydrocarbons is likely to
occur during soil migration, especially
since aerobic conditions generally pre-
vail. However, the chlorinated organics
and most of the branched or cyclic hy-
drocarbons are less likely to be de-
graded by bacterial action and are ex-
pected to migrate considerable dis-
tances in the soil. A related study noted
substantial migration of low-molecular-
weight chlorinated solvents away from
a landfill in Delaware.
The full report was submitted in fulfill-
ment of Grant No. R806102 by the Uni-
versity of Washington under the spon-
sorship of the U.S. Environmental
Protection Agency.




roethene was generally low during the
week, but it reached  a  maximum  on
Monday  (8 p,g/L in the influent and 1
|j,g/L in the effluent).  Benzene was de-
tected only on Wednesday.
  A log-normal frequency distribution
graph  of the aromatic  compounds
showed the presence of benzene only in
the scum and sludge layer. Although
benzene  was not detected in the influ-
ent, it was detected on two occasions in
the effluent, possibly as a result of dis-
charged solids from the scum or sludge
layer. Toluene showed no removal in
the septic tank and very little accumula-
tion in the scum and sludge layer. Low
removals were also noted for the chlori-
nated compounds.
  The generally low removals  of the
volatile organics was  further reflected
by the similarity of the  reconstructed
total ion current of the volatile organics
in the influent and effluent of the septic
tank. A tabulation of the 48 compounds
(Table 2) shows that the majority are
hydrocarbons, including  both aliphatic
and cyclic structures. Several com-
pounds reflect the presence of anaero-
bic degradation processes occurring in
the sewer line or septic tank. High con-
centrations were noted for 2-propanone,
2-ethyl-4-methyl-1-pentanol,  and  4-
methyl-2-propyl-1-pentanol—all likely
originating from anaerobic decomposi-
tion processes. Large increases were
 ilso noted for several biogenic organ-
osulfur compounds such as carbon di-
sulfide, methanethiol (methylmercap-
tan), dimethyl disulfide, and dimethyl
trisulfide. The largest increase was
noted for methanethiol. Small increases
were noted for compounds with larger
molecular weights, probably reflecting
the greater difficulty with which bacte-
ria  generate these larger compounds.
The low-molecular-weight  alkylated
benzenes  show a significant removal,
probably  because of biodegradation;
but the results show no removal for
higher-molecular-weight compounds.
The hydrocarbons showed the .highest
removals at  intermediate  molecular
weight and lower removals at larger
molecular weights, probably because of
reduced  volatilization. The increase
noted for several of the low-molecular-
weight hydrocarbons may be a result of
their formation as intermediates in the
breakdown of larger-molecular-weight
hydrocarbons.

Conclusions
  The present study has important im-
plications for assessing the environ-
mental impact of septic tanks. Since lit-
tle  removal  of the  volatile priority
pollutants occurs, these compounds
will be discharged through the subsur-
face drainfield  and  may  enter the
groundwater.  Volatilization is a removal
mechanism in the septic tank, but this
mechanism will not be effective in the

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Table 2. Volatile Compounds Found in Septic Tank (Sunday)
ng/L in
Volatile Compounds Scan Influent
Methane, dichlorodifluoro
Methanethiol
2-Propanone
Methane, thiobis
Unknown hydrocarbon
Carbon disulfide + dichloromethane
Cj hydrocarbon
Hexane, 3-methyl
Heptane
Disulfide, dimethyl
Benzene, methyl
Hexane, 2,5-dimethyl
Heptane, 3-methyl
Cyclohexane, 1,3-dimethyl, cis
Cyclohexane, 1,3-dimethyl, trans
Cyclohexane, 1-ethyl-2-methyl
Heptane, 2,4-dimethyl
C;0 cyclic hydrocarbon
Pentane, 2,2,3,4-tetramethyl
Trisulfide, dimethyl
Heptane, 6,6-dimethyl-2-methylene
Hexane, 2,2,5,5-tetramethyl
Branched C10 hydrocarbon
Nonene, 4,6,8-tri methyl
Hexane, 3,3,4-trimethyl
Hexane, 2,4-dimethyl
Benzene, 1,4-dichloro
Pentane, 2,2,3-trimethyl
Cw cyclic hydrocarbon
Benzene, 1-methyl-4 (1-methylethyl)
Heptane, 2,2,4,6,6-pentamethyl
Cyclohexane, 1-methyl-4-{ 1-methylethyl)
Cjo hydrocarbon
Hexane, 2,2,5-trimethyl
Hexane, 3,3-dimethyl
Hexane, 2,2,3-trimethyl
1,4-cyclohexadiene,
l-methyl-411-methylethyl)
Butane 2,2,3-trimethyl
1-pentanol, 2-ethyl-4-methyl
Pentane, 2,3,4-trimethyl
Pentane, 2,2,4,4-tetramethyl
Cyclohexane, 1-methyl-4-(1-methylethylidene
1 pentanol, 4-methyl-2-propyl
Hexane 2,2,3-trimethyl
Cyclohexane (1-methylethyl)
Bicycloheptane 3,7,7-trimethyl
Heptane, 5-ethyl-2-methyl
Benzene, 1,2,3-trichloro
Total '
1380
—
7407
7475
1419
1422
1536
1558
1612
1754
1842
1843
1875
1883
1890
1971
2009
—
2947
2960
2997
3000
3044
3074
3091
3124
3149
3157
3179
3211
3221
3229
3238
3240
3252
3326

3346
3349
3367
3408
3415
3453
3500
3583
—
3650
3717
—

0.64
<0.7
78.2
23.0
2.0
4.2
73.0
8.1
6.2
11.6
74.4
14.9
5.3
5.3
1.2
1.0
15.3
<0.7
9.7
11.4
6.2
8.0
3.7
3.4
3.2
8.3
16.7
2.5
7.2
15.4
17.1
126
3.6
7.2
38.7
45.8

3.9
3.9
21.2
11.9
4.0
9.2
13.5
5.9
<0.7
5.3
5.7
<0.7
623
Scan
—
7395
1410
1418
1421
1424
1527
—
—
7729
7825
—
—
—
—
—
—
2770
—
2947
—
—
—
—
—
—
3734
—
3768
3205
3272
3227
—
3237
3242
3378

—
—
3362
3402
3470
3449
3497
3579
3606
3652
3714
3745

\j.g/L in
Effluent
<0.7
128
70.3
84.4
4.2
10.0
13.6
<0.7
<0.7
29.7
16.7
<0.7
<0.7
<0.7
<0.7
<0.7
<0.7
3.3
<0.7
72.7
<0.7
<0.7
<0.7
<0.7
<0.7
<0.7
77.5
<0.7
25.7
77.6
7.2
707
<0.7
75.5
27.7
24.7

<0.7
<0.7
73.6
7.6
7.8
75.7
70.0
3.4
7.9
47.6
37.7
2.7
793

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      Foppe B. DeWalle, David A. Kalman. and Donald Norman are with University of
        Washington, Seattle. WA 98195; and Gary Plews is with Department of Social
        and Health Services, Olympia, WA 98504.
      Ronald F. Lewis is the EPA Project Officer (see below).
      The complete report, entitled "Determination of Toxic Chemicals in Effluent from
        Household Septic Tanks," (Order No. PB 85-196 798/AS; Cost: $8.50. 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:
             Water Engineering Research Laboratory
             U.S. Environmental Protection Agency
             Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300

EPA/600/S2-85/050
             US  6
             L I =• s?

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