Contaminant Stratigraphy of the Ballville Reservoir, Sandusky River, NW Ohio: Implications for Dam Removal

摘要

The Ballville Dam (Sandusky River) is one of the major structures in the Lake Erie watershed, impounding 1.7 million m3 of water and sediment. Removal of the dam would open ＞ 40 km of suitable upstream habitat for aquatic species, but there are concerns about contaminated sediment in the reservoir. In cooperation with the Ohio EPA, sediment cores were evaluated for 18 metals and 138 organic contaminants. Geochronology was provided by ~(137)Cs and ~(210)Pb, recognition of historical flood horizons, and stratigraphic correlation to 14 previously dated cores. Seven metals (A l, As, Cr, Fe, Ni, Pb, Zn) exceeded Threshold Effect Levels (TEL) and four others (Cd, Cu, Hg, Mn) were close. Only Fe exceeded the Probable Effect Levels (PEL) although Al, As and Ni were close. Most metal concentrations were uniform throughout the cores (when normalized for Al content), with the exception of upward increases in Cr and Se, and downward increases in Mn. DDT residues (DDD and DDE) exceeded PEL values between 50-125 cm in the cores (corresponding to mid-1940s to late-1970s). Total petroleum hydrocarbons (C_(15) to C_(24)) showed moderate levels (1-9 mg/kg) of petroleum pollution. Finally, PAH concentrations reach TEL values only below the redox zone (pre-1950) in the sediments. Possibly this is an historical archive of a 757,000-liter toluene spill reported in 1988 on the Sandusky River upstream of the reservoir. Removal of the dam would require dredging or release downstream of 0.35 million m~3 of sediment to re-establish the channel of the Sandusky River. Sediment contamination in the Ballville reservoir involves concentrations less than or equal to those in existing Lake Erie sediment, and the effects would be diluted by mixing with downstream or nearshore Lake Erie sediments.