Abstract

 A 1997 sediment-dredging project resulted in the removal of approximately 27,000 cubic yards of PCB-contaminated sediments (maximum concentration 49,000 PPM) from the Raisin River near Monroe, Michigan. The remedial work at the site was completed in October 1997. In 2001, the USEPA's Great Lakes National Program Office collected sediment samples to evaluate the extent of recovery in the vicinity of the removal area. Sampling consisted of collecting 19 sediment cores and seven (7) surficial Ponar grab samples. Core samples were collected using a Rossfelder vibrocorer outfitted with lexan core tubes. Core samples were cut into discrete sub-sections and analyzed for sediment chemistry including: PCB congeners and aroclors (EPA Method 8082B) and total organic carbon (Method 9060). Ponar grab samples were and analyzed for sediment chemistry [PCBs, SVOCs (Method 8270C), heavy metals (Method 6020, 6010, and 7471A), total organic carbon, acid volatile sulfides (Method 6020M) , simultaneously extracted metals, grain size (ASTM-D422)], whole sediment toxicity [28-day Hyalella azteca (EPA/600/R-99/064, Method 100.4) and 10-day Chironomus tentans ( Method 100.2)], and Lumbriculus variegatus bioaccumulation testing (Method 100.3).
Levels of PCBs concentrations in sediments in the removal area and downstream depositional zones were significantly higher than upstream concentrations, both in surface sediments (max. PCB concentration >200 PPM), and deeper sediments (max. PCB concentration >300 PPM). However, it is unclear whether the contamination is due to sloughing of contaminated sediments that were outside the removal area, or residual contamination from the removal activities.
Whole sediment bioaccumulation testing indicated that bioaccumulation of PCBs by L. variegatus was up to 100 times higher in the removal area than at an upstream reference site. Toxicity results indicate reduced survival or growth at three locations (upstream, in, and downstream of the removal area), but there is no clear evidence indicating the cause of this reduced survival.