backriver tmdl project
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BACKRIVER TMDL PROJECT
Technical OutreachPrepared by
MDE/TARSA
Prepared for theBaltimore Harbor Stakeholder Advisory Group
September 10, 2002
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
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 DataData Category Description Data Source(s)
Land Use (1997) Maryland Department of Planning
Stream Reach Coverage (RFA2060003)
U.S. EPA BASINS
Watershed Physiographic Data
Weather Information National Climatic Data Center
NPDES Data
MDE
Discharge Monitoring Report Data
MDE
303(d) Listed Waters MDE
Environmental Monitoring Data
Water Quality Monitoring Data EPA STORET, Superfund, USGS, MDE
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 samplesAt 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
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