Monitoring for Long-term Trends in San Diego County

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A monitoring program was designed with the San Diego County Co-permittees to:

Be adaptive and provide long-term trend information to predict short- and long-term impacts to receiving waters that result from changes in land use within each watershed

Provide data that can be analyzed to develop pollutant reduction strategies for those impacts.

A total of 10 mass loading stations covering 9 watersheds were monitored under this program.

Comparisons between watersheds were performed using several different statistical tools. Watersheds were compared both by examining constituents of concern (COC) concentrations across watersheds and by grouping similar watersheds by COC relationships. Statistical analysis for cross watershed comparison included scatterplot analysis, regression analysis, analysis of variance (ANOVA), multivariate cluster analysis, and multiple regression. The relationships between toxicity and COCs have been evaluated by threshold analysis, which is used to test relationships for COC with established thresholds.

These water quality assessment processes provide an iterative tool for watershed stakeholders to evaluate the conditions and improvements of watershed water quality through time.

INTRODUCTION

The County of San Diego, City of San Diego, the San Diego Unified Port District, and 17 other cities (collectively referred to as “Co-permittees”) are covered under a municipal National Pollutant Discharge Elimination System (NPDES) permit for discharge of runoff to waters of the United States. A monitoring program was designed with the Co-permittees to be adaptive and provide long-term trend information to predict short- and long-term impacts to receiving waters that result from changes in land use within each watershed, and to provide data that can be analyzed to develop pollutant reduction strategies for those impacts.

This monitoring program includes three elements: Mass Loading Station (MLS) Monitoring, Stream Bioassessment Monitoring, and Ambient Bay and Lagoon Monitoring. The main focus of this discussion will be the MLS monitoring program. A total of 10 mass loading stations covering 9 watersheds were monitored under this program. Some of these stations have been monitored for more than 10 years, and the results from this program will be discussed in this report.

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