Tracers in Hydrology (Proceedings of the Yokohama Symposium, July 1993)
IAHSPubl.no. 215, 1993.
A HYDROGEOLOGICAL STUDY OF
GROUNDWATER POLLUTION BY
N. EGUSA & K. JINNO
Department of Civil Engineering(SUIKO), Faculty of Engineering,
Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812, Japan
K. NAKAMUTA & H. HIRONAKA
Institute of Public Health of Fukuoka City, Yoshizuka, Hakata-ku, Fukuoka 812,
Department of Civil Engineering, Faculty of Engineering, Fukuoka University,
Nanakuma, Jounan-ku, Fukuoka 814-01, Japan
Department of Environment Protection of Fukuoka City, Tenjin, Chuo-ku,
Fukuoka 810, Japan
ABSTRACT Groundwater pollution by chlorinated hydrocarbons has been
frequently reported in Japan since the 1980s, according to domestic surveys
conducted by the Japanese Environment Protection Agency and local
communities. The pollution by these chemicals will be discovered and
persist at many places for a longtime,because they are still widely used by
various industries. Despite the intensive surveys and discoveries of the
pollution, concrete counter measures for the recovery of water quality are
not yet sufficiently established due to various hydrogeological conditions,
technical hurdles, and limited funds for remediation. It is, therefore,
indispensable to examine the characteristics of the pollution in an aquifer,
so that appropriate and effective counter measures can be established. The
present paper examines (1) the location of pollutant source, (2) the areal
extent of the contamination, (3) the results of water-quality and
tetrachloroethylene vapor distribution from field surveys, (4) possible paths
of infiltration from the source into the aquifer, and (5) pollution of deep
Groundwater pollution by trichloroethylene(TCE) which leaked from a storage tank
occurred in Silicon Valley, USA, in 1981. This accident suggested that similar groundwater
pollution by chlorinated hydrocarbons (CHC) also could occur in Japan, because these
chemicals are widely used by various industries. In 1982, Japan Environment Protection
Agency (JEPA) surveyed the groundwater pollution in 15 major cities. More than 10% of
the wells surveyed were found to be polluted by either N03" and N0 2 \ TCE,
tetrachloroethylene (PCE), chloroform or 1.1.1-trichloroethane. The concentration of PCE
in 53 wells and TCE in 40 wells, 4 and 3% of 1,360 wells examined, respectively, exceeded
the guidelines of WHO. The results of the survey suggested that groundwater pollution by
CHC could spread throughout the country. JEPA also surveyed the drainage channel of the
factories close to the wells that exceeded the guidelines of WHO. PCE was detected in all
channels from 35 factories and TCE in 12 channels from 17 factories.
126 N. Egusa et al.
In 1983, JEPA examined intensively 71TCE and PCE polluted wells that exceeded the
guidelines in the previous survey. They found that 85 and 98% of the wells contained TCE
and PCE, and 64 and 96% out of them exceeded the guidelines for TCE and PCE, respec-
tively. Furthermore, 42 and 65% of the simultaneously surveyed wells that were close to
these polluted wells also contained TCE and PCE, respectively, and 11 and 25% of diem
exceeded the WHO guidelines. During the period from 1984 to 1988, a total of 26 000 wells
were surveyed in the local communities. According to the report by JEPA, 2.7 and 4.1% of
them exceeded the guidelines for TCE and PCE, respectively. Simultaneously, 8.0 and
11.9% of additionally measured wells close to the polluted wells also exceeded the guide-
lines for TCE and PCE, respectively.
Standards for waste disposal, based on n-Hexsan (detection limit of 2 and 0.5 |ig l"1 for
TCE and PCE, respectively), were set by JEPA at 300 and 100 \xg Tl, respectively. The law
enacted for drinking water also includes standards for TCE and PCE of 30 and 10 p.g l"1,
respectively. Because of the regulatory actions taken against the polluted groundwater
quality, it becomes indispensable not only to continue monitoring the pollution, but also to
establish a method of quantitative analyses so that appropriate counter measures against the
pollution can be made.
0 100 200 m
^— i ' Contour line of PCE (mg H)
Groundwater level (m)
FIG, 1 Isopleths of dissolved PCE in groundwater (1990.12 -1991.1).
Groundwater Pollution by Tetrachloroethylene 127
In this paper, a detailed hydrogeological background of the aquifer and the flowpaths,
where the serious groundwater pollution by PCE occurs, is presented. Examining the
results of the field survey, a possible in situ remediation for the polluted soil, gas, and water
in the unsaturated and saturated zones of the aquifer are discussed. The present case study
provides a means for understanding the behavior of PCE in natural groundwater flow sys-
tems and information on how to design an in situ remediation for the polluted groundwater.
Outline of field survey
Groundwater pollution by PCE was detected by the preliminary survey carried out by the
local community in 1984, where a certain domestic well contained 0.21 mg l"1 of PCE
which exceeded the tentative guideline. In 1988, another survey of the same area was con-
ducted and PCE of 23 mg l"1 was detected at the well of a certain laundry. Because of this
high concentration of PCE dissolved in the groundwater, the local community surveyed as
many of the wells around the suspected laundry as possible. Meanwhile, the factories which
might use PCE in this area were checked and several domestic wells were regularly moni-
tored. As a result of the survey, the suspected laundry wasfinallyidentified as the source
of the pollution. In 1991, the survey for volatile PCE and the content of PCE in the soil was
conducted to investigate the behavior of PCE and develop effective counter measures.
Areal extent of polluted groundwater by PCE
In Fig. 1, PCE isopleths, based on the results of the well water surveys, are shown. Well 1
is the pumping well for the laundry. The concentrations exceed water quality standards for
drinking water from this well to approximately 400 m down gradient. The extent of the pol-
lution in the laterally is narrower than that in the direction of groundwaterflowas the result
of the groundwater recharge from the west and east boundaries. In Fig. 2, the temporal vari-
ations in tlie PCE concentration for several wells that exceed drinking water standards are
shown. The temporal variation in the PCE concentration for each well should be affected
by the change in the groundwater flow caused by hydrological fluctuations and groundwa-
ter use among other factors. However, the variations seem to be small. Consequently, high
PCE concentrations persist for long periods.
10 1 Well
Ï 10° -• 3
E -o 5
89/1 90/1 91/1 92/1
FIG. 2 Temporal variations of the PCE concentration in groundwater.
128 N. Egusa et al.
drying machine I _ ~ • . < .• .
I / ° Point of first survey
• Point of second survey
S Boring point
10 15 m
FIG. 3 Sampling sites for PCE in soil gas at the laundry.
Soil-gas surveys were conducted to identify the source of PCE infiltration from the ground
surface to the unsaturated zone. In Fig. 3, the large solid circles are the sites selected for the
initial soil-gas survey and small solid circles are the sites of the second survey. The con-
centration of PCE gas in the soil was measured at 80 cm below land surface by a detector
tube in the first survey. In the second survey, the area around the laundry was sectioned into
a 3 m grid for sampling. The sites at which the concentration of PCE gas exceeded 1000 fig
l"1 were A4, A7, A10, D4, D10, A28, and A34 (Fig. 3). Two of the laundries driers were
adjacent to sites A4, A7, D4, A10, and D10. Sites A28 and A34 were in the sludge yard.
The concentration of PCE gas at 80 cm was measured by n-Hexan method in the sec-
ond soil-gas survey. Areas of high PCE gas concentrations from the first survey were sec-
Groundwater Pollution by Tetrachloroethylene
drying macnine drying machine
> sludge yard sludge yard
Contour line of PCE gas concentration Oil i"1)
FIG. 4 Distribution of PCE gas concentrations.
tioned into a 2 m grid for additional sampling. In Fig. 4, the PCE concentrations at A34
were very high. While, the concentration of PCE gas at A28 (the sludge yard) was less, be-
cause 8.21 raw PCE and 4 m^ of polluted soil was removed, when raw PCE was discovered
at the depth from 30 cm to 80 cm below the ground surface in the first survey.
Finally, the possible sources where the concentration of PCE gas was extremely high
were identified at the places of the drying machines and the sludge yard. Therefore, the
cracks in the concrete foundation for the drying machines and the sludge yard, should allow
the infiltration of the raw PCE.
FIG. 5 Vertical distribution ofPCE content in the soil at A3, All, and Cll.
Vertical distribution of PCE content in the soil
At A3, All, and Cll where the high concentration of PCE gas were detected during the
first survey, the content of PCE in the soil is measured to a depth of 3 m from the ground
surface. Also, the concentration of PCE dissolved in the groundwater was measured. These
results are shown in Fig. 5 and Table 1. The content of PCE in the soil is extremely high
130 N. Egusa et al.
from 50 to 100 cm below land surface. However, the PCE content a these sites decreases
with depth and the decrease is attributed to stagnation of the PCE- rich water in the silt and
finer sand layer. The concentration of PCE dissolved in the groundwater at Al 1 (Table 1)
is almost equal to the saturated concentration of PCE in water(150 mg l"1), which suggests
that the groundwater at this point should be saturated with PCE. Whereas the concentration
of PCE dissolved in die groundwater at the point of C11 is much less than the saturated con-
centration of PCE. This is due to a fact that the content of PCE in the soil at Al 1 exceeds
1000 mg kg"1 at any depth, while the content of PCE in the soil at CI 1 is 2100 mg kg"1 only
at 65 cm below ground surface. In contrast, the content of PCE in the soil close to the
groundwater table, for example, is less 91 or 16 mg kg"1. In other word, when the content
of PCE close to groundwater table is high, the concentration of PCE dissolved in the
groundwater is nearly equal to the saturated concentration, because PCE can dissolve in the
groundwater. When the content of PCE close to the groundwater table is low, the concen-
tration of PCE dissolved in groundwater is low, because PCE cannot dissolve in the
groundwater. At the pumping well, the high concentration of PCE of about 30 mg l"1 in the
groundwater was found at depths between 15 to 25 m in the groundwater, it can be inferred
that raw PCE will be contained in the soil layer.
TABLE 1 Concentration of PCE dissolved in the groundwater.
Sampling site Sampling Depth Concentration (mg l"1)
All Groundwater table 160
Cll Groundwater table 7.6
Pumping well Depth -5 m 5.4
Depth, 10 m 8.9
Depth, 15 m 28
Depth, 20 m 36
Depth, 25 m 37
A similar survey was conducted at several sites of B3 and B11 where the dry machines
were located, B33 the sludge yard, and three otfier points B13, B20 and B45. These results
of the survey are shown in Fig.6. The content of PCE in the soil is quite high at 2 and 5 m
below the ground surface at the points of B3 and B11.
BEHAVIOR OF PCE IN SOIL
It is necessary to understand the behavior of PCE in soil to evaluate recovery methods. Be-
cause the viscosity of PCE is much less and the density is larger than those of water, PCE
can infiltrate easily into the unsaturated zone and reach the groundwater table. Due to the
buoyancy of water, PCE tends to stagnate at the groundwater table. When the porosity is
large, PCE will infiltrate deeper if the gravitational force on the raw PCE is larger than the
capillary force. In contrast, PCE will remain as blobs where the porosity is small. The blobs
or streaks of PCE which are not retained in soil will finally reach the bottom of an aquifer
and will stratify on the bottom. Volatilization and dissolution also occurs while PCE infil-
trates into unsaturated and saturated zones depending on the properties of PCE and soil
Groundwater Pollution by Tetrachloroethylene 131
-10 mil 1 ..
10l 101 102 103 10* 10-
0.0 0.1 0.2 0.3 0.4 0.5
FIG. 6 Vertical distribution ofPCE content in the soil at B3, Bll, andB20.
such as surface tension, organic carbon content, and soil water content. Details of the PCE
transport are given by Schwille (1988). Therefore, PCE can exist as raw PCE, entrained
blobs, volatile PCE, and dissolved PCE in both the unsaturated and saturated zones.
Because the dissolved PCE is directly transported by groundwater flow, the pollution can
132 N. Egusa et al.
Based on the above discussion, the following classification of PCE behavior in the
saturated zone constrains the development of a numerical model and remedial actions:
(a) If the fraction of PCE to the porosity in the soil is nearly equal to the porosity, then the
pore space is completely filled with raw PCE in saturated zone. In contrast, PCE either
in the dissolved or raw phases or both can exist in the saturated zone when the fraction
of PCE is less than the porosity.
(b) In the latter case, if the concentration of PCE which is calculated assuming that no raw
PCE exists exceeds the saturated concentration, 150 mg f1 for PCE, then the pore
space should be filled by both the dissolved and raw PCE.
From Fig. 7 obtained from soil analysis, PCE at 2 m depth at B3 and Bll should be in a
raw state stagnating around the groundwater table, 1.6 m below the ground surface. PCE at
65 cm at site B33 can exist as raw PCE in the unsaturated zone, because raw PCE was also
found between 30 to 80 cm at A28, where polluted soil was previously removed. The low
permeable layer around the depth of 65 cm could be the reason why raw PCE exists there.
At the depth of 5 m below the groundwater table of the points of B3 and Bll where the
high content of PCE in the soil is observed, raw PCE which used to be located around the
groundwater table without extraction of water should be transported downward due to draw
down of groundwater table by pumping up of the water. PCE at the other points should be
either volatile or dissolved in the unsaturated and saturated zones, and be transported by
convection and dispersion in gaseous or aqueous phases.
RECOVERY OF POLLUTED GROUNDWATER
Based on the analyses of the soil gas and liquid phase of PCE for the measured data, it could
be evident that raw PCE infiltrated from the foundation of the drying machines and the
sludge yard into the unsaturated zone and either stagnated partly near the ground surface or
reached the groundwater table. Then raw PCE reached the groundwater table might migrate
downward due to draw down of groundwater table by the pumping well of the laundry.
Some of raw PCE migrated further and stratified on the less pervious fractured granite.
While raw PCE descends, the dissolved or volatile PCE should be transported by convec-
tion and dispersion in the aqueous or gaseous phase. On the other hand, the captured PCE
as blob in the pore space of both unsaturated and saturated zone should remain until it di-
minishes. The discussions herein would be important for designing the in situ remediation.
Since the extent of raw PCE above the groundwater table has been clarified as it is illustrat-
ed in Fig.7, several countermeasures need to be considered.
For the captured PCE in the unsaturated soil, possible methods to reduce the content
of PCE, would be to remove the polluted soil completely and to vacuum out PCE gas. The
polluted soil could be removed if the pollution is limited to shallow depths. On the other
hand, it will be necessary to vacuum out PCE gas if the pollution takes place at the deeper
unsaturated zone. In this case, stagnated PCE above the groundwater table can be simulta-
For PCE in deep in the saturated zone near the drying machines, pumping of highly
polluted water should be necessary. The pumping well at the laundry can be used for this
purpose. De watering of groundwater table may cause an additional transport of PCE down-
ward as suggested by the numerical simulation by Egusa et al. (1992) and by some reports
for the field remediations. Considering the situations of the present case, it seems that re-
moval of the polluted soil in the unsaturated zone, vacuuming of volatile PCE and abstrac-
tion of the polluted groundwater in the laundry need to be carried out simultaneously
Groundwater Pollution by Tetrachloroethylene
B3 B11B13 B20 ,surface layer ground surlace B4S
:|weathered granite (sand):j:
,volatiled r\jc duu ut;>i>uiveu r v c
yvuictliieu PCE and dissolved PCE
1B13 B20 J ...B£3 B
•„„.l ~ '
hlntis and dissolved PCE
FIG. 7 Illustration ofpossible phases of PCE in the unsaturated and satu-
rated zones, (a) Geological structure of the aquifer, (b) Distribution of PCE
(Nakasugi, 1992). A numerical modeling with various boundary conditions will be indis-
pensable in order to evaluate an effective counter measures.
The behavior of PCE in the unsaturated and saturated zones could be understood based on
the results of the field survey. And also an available information for establishing effective
countermeasures was obtained. The authors will evaluate the migration of PCE in different
phases through the unsaturated and saturated zones and establish an effective countermea-
sure by the numerical simulation.
Egusa, N., Jinno, K., Momii, K. & Sumi, E. (1992). Characteristics of infiltration of trichloroethylene
from the natural river bed to groundwater. Proceedings of hydraulic engineering. JSCE.
36:391-396 (in Japanese).
134 N. Egusa et al.
Nakasugi, O. (1992) Groundwater pollution and Countermeasures. Proceedings of the Second Sym-
posium on Groundwater Pollution and Its Management, 282-287 (In Japanese).
Schwille, F. (1988) Dense chlorinated solvents. Lewis Publishers, USA.