The core program includes the collection and analysis of stormwater runoff during three storm events at 10 MLSs. Samples are analyzed for chemical constituents, biological indicators, and toxicity to bioassay test organisms. In addition to flow, rainfall for each MLS is recorded for each of the three monitored storm events. Rainfall distributions and totals are calculated by interpolating between rainfall amounts from available National Weather Service, San Diego County, and MLS rain gauges.
Statistical tools are used to make comparisons between watersheds. Statistical analyses for cross watershed comparison include scatterplot analysis, regression analysis, analysis of variance (ANOVA), and multivariate cluster analysis. The relationships between toxicity and constituents of concern (COCs) are evaluated using two statistical tools. The first method uses a multiple regression model to correlate changes in toxicity to changes in COC levels in the water. A second method, threshold analysis, is used to test relationships for COC with established thresholds.
In addition to monitoring, predicted pollutant loads and event mean concentrations (EMCs) expected from MLSs are calculated using a spreadsheet model. The model provides a comparison of anticipated results based upon land uses to measured results at MLSs during storm events.
These monitoring and assessment tools provide the basis for water quality assessments and processes for watershed stakeholders to evaluate the conditions and improvements of watershed water quality through time.