History of the Site
The Yongkang groundwater contamination site is located in the Shan-Yongkang District of Tainan City, Taiwan. It is a complex site with two sources of contamination and a large contaminated area of more than 6 hectares.
The main contaminants include primary products such as tetrachloroethylene, trichloroethylene, 1,1,2-trichloroethane, and their associated degradation products cis-1,2-DCE, VC, 1,1-DCE, 1,2-DCA, etc.
As the site is a coastal sedimentary stratum, the geological conditions vary greatly between high and low permeability layers, containing layers of silt, sand, sandy clay and clay, with permeability coefficients ranging from 1.5x10-3 to 5x10-5 cm/s.
The site was found to be contaminated in 2001, but the actual date of contamination is not known. It is believed that a factory used organic solvents containing chlorine in the 1970s.
Remediation Strategy
Due to the large area of the site, including private land (factories, open space) and roads, comprehensive pollution improvement requires huge funds. In order to effectively manage the site pollution, administrative control measures and pollution improvement are adopted in parallel. In the first phase, pollution source improvement and high pollution interception will be carried out to achieve the pollution reduction and interception objectives and to reduce the health risk of the people downstream.
Remediation Methods
The site was treated using a precision remediation concept consisting of intelligent characterization, precision infiltration, and rapid monitoring. The intelligent characterization survey is a high resolution survey combining contamination, hydrogeology and water chemistry; the precision infiltration is a double plug infiltration method (as shown below) with one infiltration point every 33-50 cm. Rapid monitoring is the use of cross-hole geo-resistance detection to assess the reagent transfer during the filling process (as shown in Figure 4), in order to adjust the reagent filling operation and achieve efficient remediation.
Results
After 1.5 years of improvement, the results are shown in the graph below. The concentration of various pollutants in Area B is already below the government control standard, the concentration of pollutants downstream of the pollution interception zone in Area A is showing a decreasing trend, and the pollutant reduction target in Area C has also been achieved.