ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
359 
This suggests that the arsenic in shallow groundwater may 
come from the recharge of surface water due to precipitation. 
3.2 ARSENIC LEVEL IN DEEP GROUNDWATER 
The deep groundwater is the water from the lower aquifer, 
normally from depth 15m to 50m in study area. The map of 
total arsenic level in deep groundwater was also interpolated. 
The area with arsenic level higher than 50 ppb is 7,057,125 m 2 
that occupies 83.93% of the total interpolated. On the other 
hand, the area with arsenic level lower than 50 ppb is 
1,351,475 m 2 , stands for 16.07%. This showed the 
contamination situation in deep groundwater was very severe. 
The mean value of total arsenic was 0.26 ppm, 5.2 times 
higher than limit. These maps also showed the highest arsenic 
zone with the highest value 4.01 ppm. (Fig. 3) 
The map in Fig. 3 shows the hot spots to be mostly in the 
vicinity of foot hill concentrator, where huge amount of mining 
waste were dumped along the river bank. The sample with the 
highest arsenic level is also observed at this site. The other 
sample sites with higher arsenic level were located among the 
center of study area, where waste dump sites are present. 
Comparing with the shallow groundwater arsenic level, this 
map shows a larger area with arsenic level higher than 50 ppb. 
In order to testify the relationship between the mining waste 
sites and arsenic level in deep groundwater, a correlation test 
shows a slightly correlative relationship between the distance 
to mining and waste sites and the arsenic level in deep 
groundwater (R=-0.661, P<0.05, Table 2). This result suggests 
that the pollution mechanism in varied aquifer may be different. 
3.3 ARSENIC LEVEL IN SOIL 
The total arsenic concentration (soil elution) in surface soil 
(30cm underground) was displayed in Fig. 4. The area with 
elution arsenic level higher than 50 ppb was 2,694,675 m 2 , 
occupied 32.05%. While the area with elution arsenic level 
lower than 50ppb was 5,713,925 m 2 , the percentage is 67.95% 
in total area. The mean arsenic elution level was 87.83 ppb, 
with the highest value 1570ppb. Provided the surface soil in 
study area is 1-2 meters deep (average 1.5meter), the total 
contaminated soil would add up to 4,042,012.5 m 3 . Due to the 
lack of arsenic standard in soil, it was hard to say whether it 
was polluted or not, so, the elution arsenic level was only used 
as reference. Correlation test between surface soil elution 
arsenic level with distance to mining and waste site show a 
very strong significance within 300 meters range(R=-1,Table 
3). However, from the source to 1,000 meters range, a less 
significance was observed(R=-0.636, P<0.05, Table 3). This 
strongly suggests that the mining and waste sites are the 
major pollution source for surface soil arsenic pollution. 
3.4 ARSENISM PATIENTS’ DISTRIBUTION AND 
GEOLOGICAL FEATURES 
Arsenism patients’ distribution map was displayed in Fig.5. On 
this map, it is hard to see the relation between mining and 
waste sites with the location of patients’ occurring. But, after 
overlay of surface soil type, arsenic level in groundwater, 
arsenic level in surface soil, it shows that the patients appear 
only at the area with sandy surface soil and arsenic level in 
shallow or deep groundwater above 50ppb, arsenic in soil 
elution above 50 ppb. The arsenic level in shallow and deep 
groundwater within the zone of arsenism patient is significantly 
higher than outside zone, while the difference of arsenic level 
in surface soil elution inside or outside the patients’ zone is not 
significant (Table 4). This indicates the major pathway of 
arsenism is through drinking water, while the inhalation and 
ingestion of soil dust may be less important. 
3.5 DYNAMIC CHANGES OF ARSENIC LEVEL IN 
SHALLOW GROUNDWATER IN DRY AND RAINY SEASON 
In order to observe the arsenic pollution situation between dry 
and rainy season, the interpolated map of arsenic level in 
shallow groundwater in both seasons was compared. In dry 
season, the mean arsenic level is 1.06 ppm with the highest 
value 13 ppm. The area with arsenic level higher than 50 ppb 
is 8,372,075 m 2 occupies 99.57% of the total interpolated area. 
Comparing with rainy season, the polluted area increases by 
2,291,625 m 2 . The reason why the arsenic pollution extends 
from rainy season to dry season is supposed as: in rainy 
season, the recharge of groundwater from precipitation is 
huge, at the mean time, arsenic amount flushed into surface 
runoff and eventually into groundwater increase 
simultaneously. But, due to the huge volume of groundwater, 
the mean arsenic level in groundwater is relatively low. While 
in the dry season, recharge to groundwater is low and 
évapotranspiration became huge. This results in the relatively 
higher arsenic level in groundwater. The extension of arsenic 
containing aquifer area is contributed to the dispersion of 
groundwater along its flow direction. Considering the arsenic- 
increasing location of groundwater, it is found that most of 
such locations are at the eastern part of study area where is a 
plain area and the groundwater flow velocity is slow. But the 
clearer mechanism of pollution extension is far more complex 
than this, which needs further study later. 
3.6 ARSENIC LEVEL IN SURFACE WATER 
40 river water samples and 5 pond water samples were taken 
for the measurement of total arsenic. The arsenic level In river 
water is from 0.02 to 0.62 ppm, mean value 0.11 ppm, pond 
arsenic from 0.04 to1.1 ppm, mean value 0.33ppm. Because 
the exchange between river and groundwater, river may 
interfere the groundwater arsenic concentration in some 
extent. Table 5 shows that within 600 meters, groundwater 
arsenic is decreasing significantly with the increasing of 
distance to river. 
4. CONCLUSIONS 
The arsenic pollution situation in Ron Phibun district, Nakhorn 
Si Thammarat Province was depicted with GIS help. The 
groundwater arsenic concentrations had a large distribution 
ranging from 0 to 64 ppm throughout the study area. The 
mappings of the groundwater arsenic concentrations in study 
area showed that groundwater arsenic concentrations tend to 
be higher in the vicinity of mining waste and dump sites than 
the other parts. These were approved to be the arsenic 
pollution sources in study area. Taking into consideration of all 
measured environmental media, shallow groundwater, deep 
groundwater, the pollution situation was rather severe based 
on the WHO recommended drinking water limit (0.05mg/L). 
Due to the lack of standard of soil arsenic and background 
arsenic value in study area, the arsenic level of soil elution in 
this study is only of reference for arsenic contamination. The 
GIS database could be used for the local government to guide 
the action for arsenic alleviating, monitoring of arsenic level, 
provide support for decision-making. As to the severity of 
arsenic pollution in groundwater, it is strongly suggested that 
the groundwater should be treated efficiently to lower the 
arsenic level in it. Mining waste and dump as well as the 
contaminated soil should also be removed out in order to get 
rid of the pollution sources. Alternative drinking water must be 
found because of the current high arsenic content in 
groundwater. 
5. ACKNOWLEDGES 
The authors gratefully acknowledge the ERTCTThailand for 
providing data on arsenic level in surface and groundwater, 
soil and geological information. We thank the STAR/AIT 
program for providing GIS process facilities 
6. REFERENCES 
Ahmadul Hassan and Timothy Martin, Spatial information 
systems for arsenic mitigation programs( International 
conference on arsenic pollution of ground water in 
Bangladesh: causes, effects and remedies, Abstracts Date: 8-