Saro Lee

Dae-Ha Lee

Soon Hak Choi

Won Young Kim

Seung-Gu Lee

As systematic approach to the dealing of groundwater pollution, DRASTIC system developed by U.S.EPA was introduced at Younggwang County in Korea. Hydrogeologic spatial databases for the system include information on topography, depth to water, net recharge, geological properties of vadose zone and aquifer. Using the databases and the DRASTIC system with GIS, regional groundwater pollution susceptibility of the study area was assessed and results were compiled on DRASTIC, PESTICIDE DRASTIC and MODIFIED DRASTIC maps. In MODIFIED DRASTIC map, the fracture density extracted from lineament maps were added to consider the preferential migration of contaminants through fractures. From the results of the study, a degree of groundwater pollution susceptibility through the study area could be interpreted easily.

Groundwater pollution susceptibility means the relative possibility of groundwater pollution under either point or non-point pollution application. The study area, Younggwang County in Korea, covers area about 460km² from 126。20' to 126。40' in latitude and from 35。10' to 35。27' in longitude. Efficient development and management of groundwater are needed in the study area because of increasing demand of groundwater and existence of various potential sources of groundwater pollution including agricultural activities, industrialization, and seawater intrusion. To analyze the regional groundwater pollution susceptibility in the study area, DRASTIC system (Aller et al., 1987) was applied. The DRASTIC system is standardized system of groundwater pollution susceptibility assessment by analyzing hydrogeologic factors. The DRASTIC system is widely used in Korea (Min, et al., 1996, Lee, et al, 1996).

DRASTIC system was developed by U.S.EPA in 1987 to assess relative groundwater pollution susceptibility using hydrogeologic factors. The system can be used for selection of well sites and waste disposal sites as preliminary screening tool, and land use planning for groundwater protection as basic data. In addition, it can be used for monitoring purpose and efficient allocation of resource for remediation. The system is not for local analysis but for regional (larger than 100 acres) analysis and is developed with assumption that a pollutant having the mobility of water introduced at the surface and carried towards the groundwater by infiltration. The hydrogeologic factors defined in the DRASTIC system are follows; D - Depth to water , R - net Recharge , A - Aquifer media , S - Soil media , T - Topography or slope , I - Impact of vadose zone media , C - hydraulic Conductivity. Each DRASTIC factor has been evaluated with respect to the other to determine the relative importance of each factor so that a relative weight ranging from 1 to 5 was assigned to each factor(Table 1). Again, the each factor was divided into either ranges or significant media types and a rating representing relative significance on pollution susceptibility was assigned to each range (Table 2). The DRASTIC system allows the user to determine a numerical value which shows an area of more likely to be susceptible to groundwater contamination relative to others. The higher the DRASTIC index, the greater the groundwater pollution susceptibility. There are two types of DRATSIC system. One is general DRASTIC system and the other is pesticide DRASTIC system. The pesticide DRASTIC system is designed to be used where the activity of concern is the application of pesticides to an area. The pesticide DRASTIC differs from general DRASTIC in the assignment of weights. The equation for determining the DRASTIC Index is: DRASTIC Index (Pollution susceptibility) = DrDw + RrRw + ArA + SrSw +TrTw + IrIw + CrCw (1) (r: rating, w: weight, D: depth to water, R: net Recharge, A: Aquifer media, S: Soil media, T: topography, I: Impact of vadose zone media, C : hydraulic Conductivity) The DRATIC Index has been computed, it is possible to identify areas which are

Table 1. Assigned weights for DRASTIC features.

Table 2. Ranges and ratings for DRASTIC factors.

Modified DRASTIC system is sum of DRASTIC system and lineament density. Lineament is numerous linear features of surface of land. However in this study, it only represents geological structures such as fractures and joints. The lineament is closely related to groundwater flow and contaminants migration resource so the higher lineament density values may mean the more potential groundwater contamination. Especially in Korea, most of the aquifers are developed in fractured rock so groundwater mainly moves through the fault and fracture. Therefore, by applying analysis of lineament density to the DRASTIC system, groundwater pollution susceptibility can be assessed more accurately.. Using the lineament database, lineament density is obtained by using photolineament factor value (Hardcastle, 1995). The method of photolineament factor value calculation is shown in Fig. 1. As considering lineament frequency, obtained lineament density is rated in detail. Then assigned range and rating were assigned to lineament density, considering lineament frequency and is overlaid with DRASTIC system. The weight of lineament density was assigned 5, the greatest value of DRATIC system weights, because of the importance of lineament density. So modified DRASTIC system index was calculated using formula (2)

Modified DRASTIC index = DRASTIC index + (Distribution density rating x 5) (2)

Topographic, geologic and groundwater related data are collected through the study area. The data were constructed into spatial database using GIS for groundwater pollution susceptibility assessment. The database construction status is shown in Table 3

Table 3. GIS layers in Younggwang county

Topographic Map(1/50,000)

GIS database design and construction for each factor of study area are follows

Topographic database was constructed using 1:50,000 scale topographic map (contour interval : 20m). The database structure is shown in Table 4. This database has line attribute. By Converting the coverage to GRID format, height distribution map, slope map, aspect map, hillshaded map, surface water flow map and basin map were made. These are needed to detect overall topography and surface water flow

Table 4. Topographic database structure

Drainage database was constructed using 1:50,000 scale topographic map. The drainage database has line and point attributes. The line attribute represents river and stream and the polygon attribute represents reservoir, lake and large river. The drainage database structure is shown in Table 5 and Table 6.

Table 5. Drainage (line) database structure

Table 6. Drainage (polygon) database structure

Well database includes information about well and groundwater. Well inventory was made 6 times for 252 well sites. The data from the inventory are well location, owner, address, phone number, installation year, use, depth, diameter, static water table, survey date, depth to water level, temperate, pH, EC and TDS and they were constructed to spatial database using GIS. The well database has point attribute and the database structure is shown in Table 7.

Table 7. Well database structure

Geologic database was constructed using 1:50,000 scale geological map. Geologic database has polygon attribute and the structure is shown in Table 8.

Table 8. Geologic database structure

Soil database was constructed using 1: 25,000 scale detailed soil map. The database has polygon attribute and the structure is shown in Table 9.

Table 9. Soil database structure

Land use database has polygon attribute, and the structure is shown in Table 10. Land use database was constructed by converting from the result of image processing of LANDSAT TM image (1995.3.17) and used for water budget analysis.

Table 10. Land use database structure

Lineament database has line attribute, and the structure is shown in Table 11. The lineament database was obtained from the aerial photo interpretation and used for calculating lineament density

Table 11. Lineament database structure

Map, explanation, range and rating about hydrogeologic factors - Depth to water, net recharge, aquifer media, soil media, topography, hydraulic conductivity - are as follows.

Using the well database, depth to water was obtained and range and rating distribution of depth to water are shown Fig. 2 and Table 12.

Table 12. Range and rating of depth to water

The recharge to aquifer is infiltration of precipitation to aquifer. Precipitation data was extracted from meteorological station report. Runoff was calculated using SCS (Soil Conservation Service) method and evapotranspiration was calculated using estimated value by land use (Shin et al., 1995). So net recharge was calculated as precipitation minus runoff and evapotranspiration. The result of the spatial hydrological analysis using GIS is shown in Table 13. Range and rating distribution of net recharge are shown in Fig. 3 and Table 14.

Table 13. Runoff, evapotranspiration and infiltration for land use and soil type

Table 14. Range and rating of net recharge

Using the geological database, the information on aquifer media was obtained and range and rating distribution of aquifer media are shown Fig. 4 and Table 15.

Table 15. Range and rating of aquifer media

Metamorphic/igneous 

Using the soil database, soil media was obtained and range and rating distribution of soil media are shown in Fig. 5 and Table 16.

Table 16. Range and rating of soil media

Using the topographic database, topography was obtained and range and rating distribution of topography are shown in Fig. 6 and Table 17

Table 17. Range and rating of topography

Hydraulic conductivity data are not sufficient for mapping. So using the geological database, hydraulic conductivity was estimated and range and rating distribution of hydraulic conductivity are shown in Fig. 7 and Table 18.

Table 18. Range and rating of hydraulic conductivity

Using the lineament database, lineament density value was obtained by using photolineament factor value (Hardcastle, 1995) and range and rating distribution of lineament density value are shown in Fig. 8 and Table 19.

Table 19. Ranges and ratings of lineament density

The graphic user interface program was developed in the UNIX environment using AML (Arc Macro language) of ArcInfo software. The people who are not familiar to GIS can use the program easily and fast using user friendly graphic menu system. The program is composed of main menu and submenu. The main menu and its description are shown in Table 20.

Table 20. Main menu

The steps of study shown Fig. 9 were (1) data collection about study area (2) database construction using the collect data (3) extraction of hydrogeologic factors from the database and (4) overlay analysis of the factors. The impact of vadose zone is excluded because of data insufficiency. The result values from the formula (1) are as follows; the minimum DRASTIC index is 52 and maximum DRASTIC index is 141, the minimum Pesticide DRASTIC index is 61 and maximum DRASTIC index is 187 and the minimum Modified DRASTIC index is 52 and maximum Modified DRASTIC index is 141. The DRASTIC index is combined to 55-97, 98-102, 103-110, 111-120 and 121-141, Pesticide DRASTIC index is combined to 66-118, 119-124, 125-140, 141-150 and 151-187, and Modified DRASTIC index is combined to 66-118, 119-124, 125-140, 141-150 and 151-187 to map the results shown in Fig. 10, Fig. 11 and Fig.12 with consideration of area.

Regional groundwater pollution susceptibility was analyzed accurately, quickly and easily using DRASTIC system and GIS. To apply the DRASTIC system, topography, drainage, well, geology, soil, land use and lineament databases were designed and constructed. Using the database, hydrogeologic factors such as depth to water, net recharge, aquifer media, soil media, slope, hydraulic conductivity and lineament density were extracted. Then DRASTIC and Pesticide DRASTIC were applied to the Younggwang County in Korea. Modified DRASTIC was developed and applied to consider groundwater flow and contaminants transport through fractures. The Modified DRASTIC system is a sum of DRASTIC system and lineament density designed for fractured aquifer. Groundwater pollution susceptibility assessment is necessary for systematic management and protection of groundwater resources in the study area. Information of non-point and point sources of potential pollutants including population, livestock, pesticide usage, industries will be needed for the vulnerability analysis of groundwater pollution.

Kenneth C. Hardcastle, 1995, Photolineament factor: a new computer-aided method for remotely sensing the degree to which bedrock is fractured, Photogrammetric Engineering & Remote Sensing, Vol. 61, No. 6 p.739-747.

Lee,S.R., Kim,Y.J., 1996, Groundwater pollution potential and risk analysis using GIS,, Journal of Geographic Information System Association of Korea, Vol.4, No. 1, p.1-11.

Linda Aller, Truman Bennett, Jay H. Lehr, Rebecca J.Petty, and Glen Hackett, 1987, DRASTIC: A Standardized system for evaluating groundwater pollution potential using hydrogeologic settings. National Water Well Association, EPA-600/ 2-87-035.

Min, K. D., Lee, Y.H., Lee, S. R.,Kim,Y.J.,Han,J.S., 1996, Groundwater pollution potential analysis using GIS and graphic user interface development , Journal of the Korean Society of Groundwater Environment, Vol. 3, No. 2, p.101-109

Shin, S.C., Sawamoto, M, Kim,C.H., 1995, Evapotranspiration estimation using NOAA-AVHRR data, Journal of Korea Water Resources Association, Vol. 28. No. 1. P.71-79.

Saro Lee

Korea Institute of Geology, Mining & Materials(KIGAM), 30 Kajung-dong, Yusug-ku, Taejon, Korea, 305-350, Tel. 82-42-868-3057, FAX.82-42-861-9719, E-mail:leesaro@rock25t.kigam.re.kr

Dae-Ha Lee

Korea Institute of Geology, Mining & Materials(KIGAM), 30 Kajung-dong, Yusug-ku, Taejon, Korea, 305-350, Tel. 82-42-868-3078, FAX.82-42-861-9719, E-mail:renee@rock25t.kigam.re.kr

Soon Hak Choi

Korea Institute of Geology, Mining & Materials(KIGAM), 30 Kajung-dong, Yusug-ku, Taejon, Korea, 305-350, Tel. 82-42-868-3025, FAX.82-42-861-9719

Won Young Kim

Korea Institute of Geology, Mining & Materials(KIGAM), 30 Kajung-dong, Yusug-ku, Taejon, Korea, 305-350, Tel. 82-42-868-3345, FAX.82-42-861-9719

Seung-Gu Lee

Korea Institute of Geology, Mining & Materials(KIGAM), 30 Kajung-dong, Yusug-ku, Taejon, Korea, 305-350, Tel. 82-42-868-3376, FAX.82-42-861-9719, E-mail:sgl@rock25t.kigam.re.kr