In the investigation conducted by the EPA (Environmental Protection Administration) in 2015, the concentration of heavy metal lead (Pb), copper (Cu), zinc (Zn) and chromium (Cr) in the soil of Jianguo Section land serial no. 549, 552 and 552-2, and Minan Section land serial no. 325, 431, and 442, had exceeded the soil pollution control standard of edible crop farmland. Therefore, Department of Environmental Protection New Taipei City Government conducted the “Thorough Investigation Project of Soil Pollution Control Site near Tan-Di Ditch, Xinzhuang Dist., New Taipei City” to clarify the range and the source of the pollutants.
In this project, soil samples were taken in 17 spots, and the depths were down to 8 meters beneath the ground surface. The surface (0-15 cm) and subsurface (15-30 cm) samples were directly analyzed, whereas the deeper samples were first screened by the XRF, and those with higher values were selected to be analyzed by standard methods. The results indicated that the concentration of Cr, Cu, Pb and Zn in the soil samples had exceeded the soil pollution control standard, and the concentration of cadmium (Cd) and nickel (Ni) had exceeded the soil pollution monitoring standard. Calculations demonstrated that the pollution had its largest range in surface and subsurface soil, the contaminants were down to 7 meters beneath the ground surface, and the volumes of polluted soil were estimated to be 20,450 m3 (equal to 30,674 tons multiplied by soil density of 1.5 ton/m3).
On the basis of the results mentioned above and several related documents, 3 factors were considered to be the origin of the pollution in these lands: 1) the low terrain of Tan-Di Ditch area might had led to flooding before the watercourse was improved, which might cause the sediments containing heavy metal to accrete on neighboring areas; 2) the contaminated sediments dredged up from the Tan-Di Ditch might had been backfilled to these lands by the landlords or farmers; 3) other polluted sites and enterprises in neighboring areas.
Soil excavation method with clean soil backfilled is recommended to remediate the contaminated soil in these lands, and the expenditure is about NT. 427,902,300 on a rough estimation.