1. Estimation of Loadings for Nonpoint Sources and Stormwater
Jian Shen
Virginia Institute of Marine Science

2. Outline Example of the Baltimore Harbor TMDL
Proposed methods for the James River

3. Baltimore Harbor PCB TMDL
PCB sources
Nonpoint sources
Stormwater
Point sources

4. Approach for Loading Estimation
Based on Watershed modeling
Difficult to estimate loading (pollutant sources, background load)
Need data for model variation
Based on observations
Nonpoint sources
Use statistics method (regression)
Need more data (wet, dry, mean flow condition)
Stormwater
Use event mean concentration method
Use statistics method and landuse partition (urban vs. nonurban)
Point sources
Measurement
Water quality endpoint

5. Statistical Approach (Baltimore Example)
Loading = Concentration x Flow

6. Loading Results
B425

7. Non-point Source Loadings

8. Landuse Distribution of Baltimore Harbor Watershed

9. James River Landuse Distribution

10. Stormwater Loading
Regression results are used as baseline loading for the drainage basin
If there are identified contaminated sites, the loadings from the contaminated sites will be estimated and subtracted from the baseline loading
Estimate stormwater loading based on imperviousness of land
The areas regulated by the NPDES stormwater permits are represented by the urban land use associated with residential, commercial, open urban, industrial, and institutional land use classifications
The NPDES regulated Stormwater tPCB baseline load was estimated by multiplying the percentage of urban land use area of each impaired region by the total watershed baseline load.
Stormwater loading = % area of impervious landuse x Baseline loading

11. Point Source Loading Industrial Facility Wastewater Treatment
Facility Name
NPDES #
Outfall
Average
Flow (MGD)
Outfall Average Concentration (ng/L)
PCB
Loading
(g/day)
Constellation Power – Fort Smallwood Complex MD
255.50
0.389
0.376
ISG Sparrows Point LLC MD
31.04
1.008
0.118
Wastewater Treatment
Facility
NPDES
County
Concentration
(ng/L)
Design
Flow
(MGD)
Measured
Load
(g/day)
Cox Creek
WWTP MD
Anne
Arundel
2.152 15
10.81
0.09
Patapsco MD
Baltimore
4.182 73
57.92
0.92
Water column endpoint of tPCB concentration is used to compute TMDL loading
Endpoint (derived from fish tissue) = 0.27 ng/L

12. PCB Budget
Air flux is ng/m2/day, which agrees with the result of 350 ng/m2/day estimated from the observations (Bamford et al., 2002)
If assuming mean dissolved t-PCBs concentration is 0.5 ng/L and the air-water exchange is the only loss process for t-PCBs, the residence time of dissolved t-PCBs is ~ 9.5 days, which agrees with results of Bamford et al. (2002).
If assuming mean t-PCBs concentration is 3.96 ng/L, the residence time for t-PCBs is about 75 days (residence time is ~ days),

13. Proposed Method for James River
Event mean concentration method
Take as many sample as possible in one storm event and composite samples to measure mean concentration
Prefer two or more event measurements
Regression method (statistical method)
Take monthly or bimonthly samples
Preferred approach but lacking time and resources to utilize
Other methods ?

14. Event Mean Concentration
It needs to measure both PCB concentration and flow
It is difficult to catch peak flow
It varies with respect to storm intensity and duration and two or more events will be ideal
The advantage is that it can be used for similar landuse to obtain loadings
concentration
time
Flow
time

15. Calculate Loading Event Mean Concentration (EMC) concentration
ML = EMCL*RL*K  
Where:
ML = loading factor for land use L (lbs/ac/year)
EMCL= event mean concentration of runoff from land use L (mg/l); EMCL varies by land uses
RL= total average annual surface runoff from land use L (in/year)
K= a unit conversion constant (0.2266).
composite samples to obtain mean concentration