Admin Order 58-12-14 - Laserfiche WebLink

Home Browse Search

SECTION 4 water Quality Eualuatiou that would allow for expansion of the initial rain gardens to accommodate the total volume of runoff was determined. As the addition of ROW would also result in the addition of contributing area and runoff to the rain gardens, an iterative sizing process was conducted until the size of the rain gardens would also handle the increases in runoff associated with the expanding ROW. The results of this process and the associated increases in ROW width are summarized in Table 4 -1 below for each of the six options. As a result of this evaluation process and attempts to minimize the required ROW width, Concepts #2, #4, and #6 were selected for potential future implementation. Concepts #1, #3, and #5 were eliminated from further consideration for the following reasons: Concept #1 — This ROW option was eliminated, as providing sidewalk directly adjacent to the street is not optimal from a safety standpoint. Concept #3 — This ROW option was eliminated due to the significant amount of additional ROW width that would be required to accommodate a rain garden that would be large enough to manage the runoff from the ROW during the 5 -year event. Concept #5 — This ROW option was also eliminated due to the significant amount of additional ROW that would be required. Final renderings of the three selected local street concepts (both plan views and cross - section views) including the required ROW widths are provided in Figures 4 -5 through 4 -10. CP Al -15 -UIC includes the development of street -side rain gardens, and it was selected to address drywell decommissioning for the drywell cluster south of Horn Lane. This project will provide water quality benefits in terms of preventing a significant increase in pollutant loads and hydrologic impacts that would be associated with decommissioning of drywells and routing discharges to surface waters. It should be noted that, while these street -side rain garden concept options for local street improvements were developed to address UIC decommissioning needs, these options are envisioned to be employed for various circumstances beyond UIC - related projects. Implementing the street -side rain garden concepts will require first making some changes to the City's Local Street Plan under a separate process subsequent to completion of the River Road Santa Clara Basin Plan. A decision flowchart was developed as part of this basin planning process, to illustrate the approach to managing stormwater runoff from sites, and where the street -side rain garden approach could be employed. In the broad sense, the approach to managing stormwater runoff from a site, and the potential application of the street -side rain garden concept options, will depend on whether a project is public or private, whether it is for an arterial or collector street, and whether it is for infill or new development. A decision flow chart for the project planning phase, to show where the new local street concepts could be employed, is provided in Figure 4 -11. During the conceptual development of CP Al -15 -UIC, for decommissioning drywells south of Horn Lane, a timeline mandate for decommissioning was not known. It was assumed that UIC decommissioning could occur over a decades -long timeframe that could allow for decommissioning to occur in association with street improvements in annexed areas. The Department of Environmental Quality (DEQ) has more recently indicated that decommissioning 0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 4 -14