The remediation of Lake Jarnsjon: Project implementation

The remediation of Lake Jarnsjon in Eman was carried out during the period 1993-1994. PCB-contaminated sediments were dredged, dewatered and disposed of in a landfill. In order to reduce the spreading of suspended solids and PCB to the watercourse, a suction dredger constructed specially for dredgin g with minimal spread of suspended solids was used. In addition, dredging o f the most contaminated part of the lake was carried out within a protectiv e geotextile screen. An extensive environmental monitoring program, running throughout the operation, showed that the spread of suspended solids and P CB during dredging was limited. Monitoring of PCB also showed that the use of geotextile screens considerably reduced the exposure of the river water to PCB. Dewatering was carried out with filter presses and the surplus wate r was returned to Jarnsjon after cleaning by flocculation, flotation and se dimentation. The landfill was covered with 1.2 m sand and gravel from the s ite. No external hydraulic barriers were constructed. Instead, the relative ly low permeability of the fine-grained and low-contaminated sediments in t he topmost meter of the disposed sediments was considered sufficient, also taking into account the low mobility of PCB from deposited sediments, as me asured in the pilot study. Thus, calculated leakage from the landfill is sm all compared to the remaining transport of PCB in the river. During the fir st years of monitoring after construction, only minor leakage has been dete cted from the landfill.