Admin Order 58-12-14 - Laserfiche WebLink

Home Browse Search

upper Al system) that are predicted by the model for the larger contributing area under existing (2006) conditions, and exacerbated by future development. Topic; Pollutant Estimates Pollutant load estimates are not based upon basin - specific water quality data. Question use of TSS as an indicator. Question assumption regarding contribution of runoff from decommissioned UICs. [SC -101, [RR -111 Although there is limited data on water quality in the Basin, the pollutant load estimates point to the need to address expected increases in pollutants from added impervious surfaces, and provide a means by which pollutant estimates can be compared between basins and contrasted between existing and future build -out conditions. Estimating pollutant loads helps in identifying locations for water quality capital projects. For example, RRSC -2, Water Quality Facilities for High Source Areas, includes specific high pollutant source locations for water quality retrofit facilities. The pollutant load estimates also support the implementation of Stormwater Development Standards and support continuation of the other complimentary best management practices conducted in the City and County's stormwater programs. Estimating pollutant loads from runoff being surfaced by decommissioning drywells supports the strategy for decommissioning drywells via rain gardens or pipe connections with pre- treatment, so as not to adversely affect downstream surface water quality. With regards to the use of total suspended solids (TSS) as an indicator of pollutant, TSS was used in the basin plans as a surrogate for the suite of pollutants typically associated with stormwater (specifically, sediment, nutrients, heavy metals). This is a common approach, utilized by other large municipalities in the state of Oregon. The TSS amounts are approximations based upon pollutant loading data used by the Phase I municipalities in Oregon. Estimates assume no water quality BMPs for future development. Estimates assume all runoff from decommissioned drywells will be transferred untreated to surface waters. [RR -101, [SC -111 Agree. The pollutant load estimates are based upon pollutant loading concentrations used by Phase I municipalities in Oregon, and the comment is correct in that the loadings assume no water quality BMPs. The pollutant load estimates were generated for illustrative and comparative purposes (e.g. identifying high pollutant source areas within a basin, comparing basin loads), and staff thought it important to use the same approach as for the other stormwater basins completed in 2002. The City is collaborating with other Phase I municipalities and professionals across the country to compile and utilize effectiveness data for stormwater management facilities so as to better estimate pollutant loadings from urban areas utilizing these facilities. RR -SC Stormwater Basin Plan Comments Pg.16 of 17