M1 AM Delaware River/Bay
Monday, 14 November 2005: 8:00 AM - 11:40 AM in Ballroom 1

(BIE-1117-828565) Dynamics of PCBs and Organic Carbon in the Delaware River Estuary.

Bierman, V.¹, Hinz, S.², Suk, N.³, Liao, S.³, Yagecic, J.³, Fikslin, T.³, ¹ Limno-Tech, Inc., Greensboro, NC, USA² Limno-Tech, Inc., Austin, TX, USA³ Delaware River Basin Commission, West Trenton, NJ, USA

ABSTRACT- A mass balance model was used to investigate PCB and organic carbon dynamics in the Delaware River Estuary, and to develop a Stage 1 TMDL for PCBs. External sources of PCBs include: non-point source runoff, point discharges, Delaware River at Trenton, Schuylkill River, runoff from contaminated sites, other tributaries, CSOs, and atmospheric deposition. Water column PCB concentrations are also influenced by legacy contamination in the sediments and by exchanges across external boundaries with the C&D Canal and Atlantic Ocean, and the air-water interface. The surface sediments are a net source of PCBs to the water column in the upper estuary and a net sink in the lower estuary. For the estuary as a whole there is net PCB flux from the water column to the surficial sediments, and net burial of PCBs from the surficial sediments to the deep sediments. Net volatilization of PCBs occurs throughout the estuary. Primary production accounts for 80 percent of total organic carbon loading. Most of the organic carbon from primary production decays to particulate detrital carbon in the water column. The fate pathways for particulate detrital carbon in the water column are approximately equal among decay, sedimentation and outflow to the Atlantic Ocean. Approximately half of sediment organic carbon decays due to diagenesis and the remainder is buried to the deep sediments. Water column PCB concentrations are currently several hundred times higher than the water quality criteria. Remediation of sediment PCBs is not necessary to achieve the water quality criteria because under long-term equilibrium TMDL conditions the sediments are a net sink for PCBs not a source. The significance of sediment PCBs is their influence on the response time of the estuary. Water column PCB concentrations could require 20-30 years to achieve the criteria even if all external PCB loadings were completely eliminated.

Key words: Model, PCBs, Carbon, Delaware