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Alternative Title:Water Year 2022 - 2024 End of Study Technical Memorandum — District 3, 4, and 10 Trash Migration and Characterization Study Document [Title from Cover]
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Edition:Final Report
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Abstract:The overall goal of this study was to obtain information on trash generation and discharge from Significant Trash Generating Areas (STGAs) to determine the effectiveness of selected controls and demonstrate full trash capture efficiency. The study monitored eight STGAs with on-land visual trash assessments for general trash accumulation. In addition, the study installed temporary trash capture netting in the test sites to determine trash generation in stormwater drainage for 3 years. The study occurred over one summer for dry-weather monitoring and three winters after significant rainfall events (>0.5 inches in 24h). Although the study observed some trash accumulation fluctuations due to factors such as stormwater flows, trash removal, littering, wind transport, trash buildup in roadside vegetation, rain events did not significantly impact trash accumulations. In other words, STGAs were not cleaner or dirtier, post precipitation. The results also showed that 54% of the STGAs scored B ratings, using an inverse letter-grading system (i.e. an A and D ratings associated with low and high trash presence, respectively) indicating a moderate level of trash presence. In addition, the study observed the effectiveness of trash pickup and street sweeping maintenance activities. On average, trash volume generated at a rate of 0.04 – 0.9 gal/ac per event, or a corresponding annual trash generation rate of 2.3 to 41.6 gal/ac/yr in stormwater drainage areas. These data are among the first documented for trash discharged from various types of SGTAs within the Caltrans rights of way. The new data advances Caltrans and the State Water Board planning processes regarding the extent of effort for meeting Trash Provisions. The results further support Caltrans use of compliance resources with the National Pollutant Discharge Elimination System (NPDES) permit. The study finally demonstrates that not all observed trash in the right of way accumulates in stormwater drainage areas and waterways or necessarily infringes on permit conditions.
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