Identification of the governing water quality criteria is an essential step in the TMDL process. For the Delaware Estuary, available water quality criteria for PCBs include human health criteria for carcinogenic and systemic effects, wildlife criteria, and both freshwater and marine
acute and chronic aquatic life criteria. Recent actions are causing regulatory agencies to update their current human health water quality criteria for PCBs. These actions include: 1) the change in the cancer potency factor for total PCBs reported in EPA's Integrated Risk Information System,
and 2) the issuance of a revised methodology for deriving ambient water quality criteria for the protection of human health in the fall of 2000. The latter methodology also includes several new recommendations on the fish consumption rate to be used in criteria development, and the use of
a bioaccumulation factor (BAF) rather than a bioconcentration factor (BCF). A subcommittee of the Delaware River Basin Commission's Toxic Advisory Committee was tasked with developing revised human health criteria for four zones of the Delaware Estuary. Existing criteria for the estuary
are 44.4 pg/l for Zones 2 and 3, 44.8 pg/l for Zones 4 and the upper portion of Zone 5, and 7.9 pg/l for the lower portion of Zone 5. The lower criterion in Zone 5 is due to a higher fish consumption rate being used while only Zones 2 and 3 are designated as a drinking water source.
Values for five factors were needed to develop the revised criteria. Three of the factors used EPA-recommended default values. These three factors were 1) risk-specific dose (2.0 mg/kg-day at a risk level of 10-6), 2) body weight (70 KG), and 3) drinking water intake (2 liters/day).
Site-specific data was needed to develop appropriate values for the other two factors: fish consumption at each trophic level, and BAF at each trophic level. Site-specific data for fish consumption in Zone 5 and Delaware Bay indicated an average consumption rate for all species of 17.46 grams
per day. This value is remarkably close to the national default value of 17.5 grams per day. Field studies were conducted to provide PCB congener data on fish tissue concentrations of PCBs in species representative of trophic level 3 (channel catfish) and trophic level 4 (white perch). Ambient
water concentrations of PCB congeners and organic carbon were also determined using low level sampling and analytical techniques for use in calculating the BAF in the new methodology. Data on the percent lipid of consumed fish were also determined from routine monitoring conducted by state
agencies and the Commission since 1990. Data on the proportion of each trophic level consumed was assumed to be 50% based upon data from all zones that indicated roughly equal proportions for the two trophic levels. Use of these data with the new EPA methodology results in a single criterion
value of 16.0 pg/L. A probabilistic approach was also used to assess the impact of the uncertainty of the values used in the methodology. This analysis indicated that the median criterion value was close to that obtained using the deterministic approach, and that the interquartile range
(25th percentile to the 75th percentile) fell between 6.2 pg/L to 49.7 pg/L. The final criterion selected will provide a uniform TMDL target throughout the estuary and eliminate the current sharp transition within the estuary.
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