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