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 (d) list:  Zn  Toxics (PCB)  Sampling data shows Zn is not a problem in Back River

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

Inventory of Data

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

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)

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

Watershed load Estimation Approach  3 methodologies considered: 1. Loads from potential source sites using the universal soil loss equation 2. Estimating loads on a subwatershed basis using flow data and average subwatershed PCB concentration 3. Estimating loads from TSS using SWMM

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

BACKTOX Model  3 different mass balances are represented 1. A water balance 2. A solids balance 3. Contaminants mass balances

BACKTOX Model Cont’d  It includes: 1. Hydrodynamic model – CH3D 2. Sediment transport model 3. Fate and transport model – Toxiwasp 4. Also included are sediment layers to account for sediment –water interactions.

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

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

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