Monitoring And Modeling Of Chollas, Paleta, And Switzer Creeks For San Diego Bay Water Quality.pdf

Background:
San Diego Bay faces water quality challenges due to contaminated sediments and impaired benthic communities, particularly at creek mouths in urbanized watersheds. This study aimed to gather data for the Total Maximum Daily Load (TMDL) to address these issues.

Study Objective:
Identify pollutant loading from Chollas, Paleta, Switzer, and their respective forks to San Diego Bay and estimate relative contributions from various land uses.

Methods:
- Wet Weather Monitoring: Monitored flow and water quality during the 2005-06 wet season in all three watersheds.
- Modeling: Used two approaches: dynamic watershed model (LSPC, a recoded version of EPA's HSPF) for TSS, trace metals, and specific land use pollutants; empirical data analysis for non-land use related constituents like total PAHs, chlordane, and total PCBs.

Key Findings:

1. Flow and Water Quality:
- Paleta Creek had the highest flow weighted mean concentrations for most monitored constituents.
- Switzer Creek showed the highest concentration of total chlordane.
- TSS, trace metals, and total PAH concentrations varied significantly within and between storm events.

2. Model Validation:
- LSPC modeled flow with 84% accuracy.
- Water quality simulations were moderately successful, with over 70% of event mean concentrations matching measured values.

3. Pollutant Loading:
- Model simulations showed significant interannual variability in pollutant loads, influenced by rainfall.
- High and low density residential land uses contributed disproportionately to copper loading, despite their small areas.

4. Land Use Contributions:
- Approximately 46% of Chollas Creek's copper loading originated from high density residential, though this land use comprised only 11% of the watershed area.

Conclusion:
The study successfully addressed data gaps in pollutant loading to San Diego Bay and relative land use contributions, providing crucial information for TMDL development and restoration efforts.