ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
as well as the health impact assessment from arsenic in the 
polluted site. 
2. MATERIALS AND METHODS 
2.1 SITE SELECTION AND CHARACTERIZATION 
Ron Phibun is a district at Nakhorn Si Thammarat Province, 
which locates on the southern part at peninsular Thailand. This 
area was selected as a study area because the arsenic 
contamination was the most serious ever reported in Thailand. 
Extensive mining of tin and associated minerals has been 
done throughout the region for almost 100 years. The 
occurrence of keratosis and hyperpigmentation was known for 
long time in the region. The skin manifestation of chronic 
arsenic poisoning was first highlighted in 1987 in Ron Phibun 
district. Clinical survey during 1987-1988 showed that more 
than 1,000 people between age from 4 months to 85 years 
were affected (Munehiro, et al. 1998). The district situates 
between longitude 99°45’-100°00’ E and latitude 8°00’-8°15’ N. 
The district is on east side of Ron Na Mountain having 
elevation of 70m above mean sea level (Fig. 1). The elevation 
Figure 1 : The study area in Nakhorn Si 
Thammarat province, Thailand 
of surface area is decreased from west to east. The studied 
zone was chosen between longitude 99°50’-99°52’E and 
latitude 8°10’-8°12’N with total area of 14 km 2 (4X3.5km). 
2.2 OLD MINING SITES AND WASTE SITES 
Ten major mining sites, i.e. Yin In Soy, Mai Horn, Sang Son, 
Ngan Chan, Saijai, Nan Khaw, Ban Thai, Na Mun Mu, Sang 
Sak, Nan Moo, locate on the western hill side of study area at 
elevation from 150m to 500m. They are the former tin mining 
factories, but closed at present. However, there are large 
amounts of mining wastes along each mining location within 
that area. 6 waste sites: the foothill concentrator, town 
concentrator, reclaimed site 32C and 32L, old and new waste 
dumps are still present in this area. All these old mine sites 
were carefully identified using an altimeter and GPS. For the 
waste dump sites, their locations were also identified on an 
edited map. 
2.3 WATER AND SOIL SAMPLING 
Water and soil samples from arsenic polluted area were 
sampled in dry and rainy season providing that variation of 
season on arsenic concentration changes would take into 
account. Auger drilling technique was used to take soil and 
groundwater sample. The auger stations were at 141m 
intervals, 50 stations/km 2 (361 auger holes were drilled). Two 
soil samples were collected from each auger well at 30cm 
depth and 1m depth. Water samples were collected from the 
bottom of each hole wherever water was found. 
Total arsenic level in 361 auger water samples was analyzed 
by HG-AAS method in ERTC laboratory. 722 soil elution was 
used to represent the soil total arsenic situation. 40 rivers 
water samples, 5 pond water samples, 102 deep wells and 
107 shallow wells were also sampled to measure the total 
arsenic level by HG-AAS method. All the sampling sites were 
located by GPS. 
2.4 GIS PROCESS 
ArcView version 3.1 program was used for the GIS process, 
the steps are as follows: 
-Processing of maps 
• The digitization of general topography (the map with 
scale of 1:2,000 was edited from a well-organized set of 
aerial photograph taken in 1995), the distribution of 
arsenism patients, surface soil types, mining and waste 
sites. 
• Interpolated map of arsenic level in soil and ground water 
following input of locations and arsenic value for each 
sample site. The total interpolated area is 8,408,600m 2 . 
• Input of location of ponds, river sample sites into the map. 
-Input of attributes for each digital theme, including arsenic 
values of soil and water for each auger point, deep and 
shallow wells. 
-Query and analysis between arsenic level and mining sites, 
location of patients’ distribution. 
3. RESULTS AND DISCUSSIONS 
3.1 ARSENIC LEVEL IN SHALLOW GROUNDWATER 
The shallow groundwater in study area is the water from the 
first aquifer above 10-meter depth. This is the major source of 
drinking water for local population. The shallow groundwater 
arsenic concentrations were mapped as an interpolated grid 
surface to create a visual representation of the concentration 
gradients throughout the study area. The interpolation was 
performed on the groundwater arsenic concentration point 
theme. The interpolated grid map was adjusted to represent 
hot spots above the current 50 ppb limit for arsenic. The area 
with arsenic level higher than 50 ppb is 6,080,450m 2 that 
occupies 72.31% of the total interpolated. On the other hand, 
the area with arsenic level lower than 50 ppb is 2,328,150 m 2 , 
stands for 27.69%. This showed the contamination situation in 
shallow groundwater was very severe. The mean value of total 
arsenic was 0.53 ppm, 10.6 times higher than limit. These 
maps also showed the highest arsenic zone with the highest 
value 64 ppm. (Fig. 2) 
The map in Fig. 2 shows the hot spots to be mostly in the 
vicinity of 6 waste dump sites. The region with the largest hot 
spot is the western part of study area where huge amount of 
mining waste was disposed along the river bank, the site of 
foothill concentrator. This indicates obviously that all these 
mining and dump waste location may be the pollution source in 
this area. In order to testify the relationship between the mining 
waste sites and arsenic level in shallow groundwater, a 
correlation test shows that the farther the shallow groundwater 
sample to mining and waste site, the lower the arsenic 
concentration in groundwater (R=-0.827, P<0.01, Table 1).