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BACKRIVER TMDL PROJECT

BACKRIVER TMDL PROJECT. Technical Outreach Prepared by MDE/TARSA Prepared for the Baltimore Harbor Stakeholder Advisory Group September 10, 2002. Maryland 303(d) list identification:. The impairing substances on the 1998 303(d) list: Zn Toxics (PCB)

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BACKRIVER TMDL PROJECT

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  1. BACKRIVER TMDL PROJECT Technical Outreach Prepared by MDE/TARSA Prepared for theBaltimore Harbor Stakeholder Advisory Group September 10, 2002

  2. Maryland 303(d) list identification: The impairing substances on the 1998 303(d) list: • Zn • Toxics (PCB) • Sampling data shows Zn is not a problem in Back River

  3. Data Assessment • Data used include: • Physiographic data: describe the physical conditions of the watershed • Environmental Monitoring Data: identify potential pollutant sources and their contribution, and in-stream water quality monitoring data

  4. Inventory of Data

  5. General Trend for Monitoring to Estimate Loads Timing: Winter – wet and dry (Water and Sediment) Spring – wet and dry (Water and Sediment) Sampling for: • Storm Water Outfall/In-stream (NPDES) • Point Source Outfall/In-stream (DMR) • Stream Water Quality Data (mainstem & tributaries) • Boundaries • Sediment – Sediment Quality Triad (toxics) • Cross Section/Longitudinal

  6. General Trend for Monitoring to Estimate Loads Number of samples • At least 1+1(QA/QC) samples per site, per event Substance list • Water column sample • Total, Dissolved, POC, DOC, TSS • Sediment Concentration • Total, Dissolved, AVS, SEM, foc • Sediment Toxicity/Benthic (toxics)

  7. Modeling PCBs • The model and approach to develop the TMDL is influenced by the sources of impairment and type of impairment (PCB). • We looked outside traditional sources of water quality data as a new way to tackle a TMDL for potential “legacy pollutants” • There are no obvious point or nonpoint sources of the contaminant under the Clean Water Act

  8. Watershed load Estimation Approach • 3 methodologies considered: • Loads from potential source sites using the universal soil loss equation • Estimating loads on a subwatershed basis using flow data and average subwatershed PCB concentration • Estimating loads from TSS using SWMM

  9. Toxic Modeling Framework for PCB Framework Under Consideration: • BACKTOX model developed by UVA (on-going project) • Bioaccumulation approach • Biota-Sediment Accumulation Factor

  10. BACKTOX Model • 3 different mass balances are represented • A water balance • A solids balance • Contaminants mass balances

  11. BACKTOX Model Cont’d • It includes: • Hydrodynamic model – CH3D • Sediment transport model • Fate and transport model – Toxiwasp • Also included are sediment layers to account for sediment –water interactions.

  12. BACKTOX Model Cont’d • Linkages: • Linkage to incorporate the hydrodynamic and sediment transport model results into the fate and transport model • Linking the watershed model to the fate and transport model

  13. Bioaccumulation approach • Fish tissue levels are compared to the sediment criteria using Biota-Sediment Accumulation Factor (BSAF) • Tissue level= Sediment conc. *BSAF*unit conversion • Endpoint is based on risk-based PCB fish tissue consumption advisory

  14. TMDL Status • Watershed Assessment (Source/Data Assessment) – Completed • Nonpoint/point source loads – in progress • Endpoint (BSAF) – in progress • Hydrodynamic/Sediment Transport Modeling – at final stage • Linkage – in progress • Toxic model – in progress

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