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HomeMy WebLinkAboutC_VEK_Aberdeen_Townhomes_On_Hold_Letter_200110 January 10, 2020 Nicole Mecum Encompass Engineering & Surveying 165 NE Juniper St, Suite 201 Issaquah, WA 98027 SUBJECT: "On Hold" Notice VEK on Aberdeen Townhomes Plat, LUA19-000280, ECF, MOD, PP, SA-H Dear Ms. Mecum The Planning Division of the City of Renton accepted the above master application for review on December 3, 2019. During our review, staff has determined that additional information is necessary in order to proceed further. The following information will need to be submitted before April 8, 2020, so that we may continue the review of the above subject application: 1. A Preliminary Drainage Plan and Technical Information Report (TIR), dated October 31, 2019, was submitted by Encompass Engineering and Surveying with the Land Use Application. Based on the City of Renton’s flow control map, the site falls within the Peak Rate Flow Control area matching Existing Site Conditions and is within the East Lake Washington – Renton Drainage Basin. The development is subject to Full Drainage Review in accordance with the 2017 Renton Surface Water Design Manual (RSWDM). All nine core requirements and the six special requirements must be discussed in the Technical Information Report. The following stormwater improvements are required and shall be discussed within the TIR: a. There are regulated slope, erosion hazard, and landslide areas found within the western side of the property. Due to the steep slopes downstream of the project, the project lies within a flood problem flow control standard area (see section 1.2.3.1 (4) of the 2017 RSWDM). Therefore, unless a flow control exemption is identified, and if stormwater will be discharged to the steep slope area, then the project must match the Flow Duration of pre-developed rates for Existing Site Conditions from 50% of the 2-year up to the full 50- year flow, and match Existing Site Conditions for the 2-, 10-, and 100-Year Peaks. Based on the preliminary design, the facility meets this standard. Update Section 4 of the TIR to include discussion of how this standard is being met (currently states that only the peak flow rate standard is being met). Additionally, update the TIR and detention tank design to include a minimum 0.5-foot sediment storage and minimum 0.5-foot freeboard. b. Continuous modeling did not include flows from the steep forested area on the western portion of the site to the natural discharge location. In order for these flows to be excluded from the point of compliance analysis, per Section 1.2 (A) of the 2017 RSWDM (Peak Rate Flow Control Target Surfaces part 2): “…the extent of new pervious surface : Nicole Mecum Page 2 of 4 January 10, 2020 shall be assumed to be the entire lot area, except the assumed impervious portion and any portion in which native conditions are preserved by covenant, tract, or easement”. The final plat shall place the forested area in permanent and protected open space/critical areas tract or easement or the facility redesigned to attenuate these flows at the point of compliance. Update the preliminary plans and report indicating if the forested area will be placed in permanent open space or provide updated calculations including this area. c. Appropriate flow control BMPs are be required to help mitigate the new runoff created by this development. The preliminary drainage plan indicates that the proposed development is considered a “small subdivision”, however, due to the nature of the development being multi-family with individual lots being created out of multi-family building sharing common walls the project is more in order with the “large lot” BMP requirements as specified in section 1.2.9.2.2 of the 2017 RSWDM. Due to steep slope, landslide and erosion hazard areas being located onsite, full dispersion, full infiltration, limited dispersion, limited infiltration, bioretention and permeable pavement are all infeasible. Specifically, section 1.2.9.2.2 (5) of the 2017 RSWDM states: “The buildable portion of the site/lot is the total area of the site/lot minus any critical areas and minus 200 ft. buffer areas from a steep slope hazard, landslide hazard, or erosion hazard area”. For the applicability of BMP’s, the 200 ft. buffer encompasses the entire site, therefore, per definition, there are no onsite buildable areas subject to BMP’s and the project is exempt from meeting Core Requirement #9. Update the preliminary TIR to include a discussion of how this project is not subject to the BMP requirement as described above. d. Optional BMP’s may be utilized to reduce the size of the flow control facility, however, any BMP’s utilizing dispersion or infiltration techniques (i.e. permeable pavement, limited dispersion, or bioretention) will require the use of underdrains and/or interceptor trenches to collect the runoff and route it to the detention system. Update preliminary TIR if any BMP’s are being included for facility sizing credits. e. The final design and Technical Information Report shall take into account all provisions of Core Requirement #1 (Discharge at Natural Location). Specifically, section 1.2.1 (2) states that: “IF a proposed project, or any natural discharge area within a project, is located within a Landslide Hazard Drainage Area and drains over the erodible soils of a landslide hazard with slopes steeper than 15%, THEN a tightline system must be provided through the landslide hazard to an acceptable discharge point…”. The preliminary TIR identifies that an HDPE tightline over the steep slope will discharge into the onsite drainage way (which is still located on slopes above 15% within the erosion and landslide area), however, additional analysis and mitigation is required to show that the decrease in runoff volume and energy dissipation fully meets Core Requirement #1. At a minimum, the tightline must extend to John’s Creek where the slopes are less than 15% and the other nearby properties discharge to. Alternatively, section 1.2.1 (2) provides an exception where CED can approve an alternative system based on geotechnical evaluation/recommendation where the developed conditions runoff volume from the natural discharge area is less than 50% of the existing conditions runoff volume. Update the preliminary plans and TIR to reflect how Core Requirement #1 is being met. If the alternative exception is being proposed, provide a drainage modification request with all applicable geotechnical and engineering justifications and recommendations provided. Nicole Mecum Page 3 of 4 January 10, 2020 f. Per RMC 4-3-050 (G)(2) steep slope and landslide hazard buffers shall be established by the geotechnical engineer. Section 4.6.6 of the Geotechnical Report states: “The proposed townhomes have been designed to step down with the existing topography and the majority of the development is on the least sensitive area of the site. Three townhomes are proposed on top of the slope outside of the sensitive slopes and setback from the slope. Based on the results of our subsurface explorations and slope stability analysis, the proposal will not increase the threat of the geological hazard to adjacent or abutting properties beyond predevelopment conditions; and will not adversely impact other critical areas; and the proposed development can be safely accommodated on the site”, however, the report references a previous site plan which shows the proposed buildings set back considerably further than the current site plan and does not take into account the drainage structures and retaining wall which is located on and around the steep slope. Prior to land-use approval, the geotechnical engineer shall provide a quantitative analysis of the steep slope and landslide hazard area and provide set-back based on the recommendations for the updated site plan and facilities being proposed closer than identified in the report. Additionally, a 15’ building set-back line (BSBL) will be required from the edge of the buffer, including the case that the buffer is determined to be 0’. Building, retaining walls and subsurface drainage structures shall not be located within the buffer or BSBL. Update the preliminary plans, geotechnical report and TIR to include any changes resulting in the buffer and BSBL and relocating facilities and/or buildings outside of this area. g. The final technical information report shall include the “bypass” area in the point of compliance analysis since the conveyance system located within Aberdeen Ave NE converges at the site’s point of compliance at the southwest corner (John’s Creek) less than ¼ mile downstream. Based on the preliminary design, the bypass area was included in the facility sizing calculation. See comments 1a and 1b. Update the level one downstream analysis to include this downstream drainage system to the point where the flows converge at the western portion of the site. 2. The development is required to provide enhanced water quality treatment prior to discharge. Project water quality treatment will consist of conveyance to a Biopod system prior to connection to the proposed detention tank. a. Presettling shall be being provided per Sections 6.1.1 and 6.5.1 of the 2017 RSWDM. Update the plans and TIR to include all relevant design and calculations for presettling prior to entering biopod system. If the manufacturer’s system provides presettling, indicate how the requirement is being met using the manufacturer’s design criteria and any applicable calculations in sizing of the facility. b. Per section 6.2.1 (Water Quality Design Flows and Treatment Volumes) 2017 RSWDM the on-line facility will have a modified water quality flow modeling rate (ratio k) of 1.88 based on the 2-yr isopluvial of 1.95” (linear interpolation of Table 6.2.1.A). Based on the WWHM On-Line facility target flow of 0.0369 cfs, Qwq = kQ or 0.0694 cfs. This will need to be the number that is submitted to the manufacturer for sizing of the facility. Update the plans and TIR with the revised water quality facility design, including manufacturer’s data sheets based on the updated water quality flow. Ensure to note to the manufacturer during the sizing that the enhanced water quality treatment menu is being met as their calculations will take this into account for a decrease in media filtration rate. Nicole Mecum Page 4 of 4 January 10, 2020 https://oldcastleinfrastructure.com/wp- content/uploads/2018/10/Stormwater_Treatment_Design_Assistance_Form_Infra.pdf c. A maintenance access road is required to the stormwater facilities in the proposed storm tract/easement and shall be in accordance with the design requirements outlined in the RSWDM. Update the plans and TIR to include this access road. 3. The Critical Area Report submitted with the project application identified a wetland on the project site. The Critical Area Report does not delineate or classify the on-site wetland. Please provide a Wetland Assessment consistent with the requirements of RMC 4-8-120D.23. 4. The Critical Area Report submitted with the project application identified an unclassified stream on the project site. Per RMC 4-8-120D. 19, if the site contains an unclassified stream, a qualified biologist shall provide a proposed classification of the stream(s) based on RMC 4-3-050G7, Streams and Lakes, and a rationale for the proposed rating. Please revise the stream study to comply with all Standard Stream Study requirements per RMC 4-8-120D.19, including evaluation of impacts from proposed improvements. 5. Include critical area buffers, and buffer setbacks, on plan sets. 6. Per RMC 4-2-110D.20, an additional ten feet (10') of maximum wall plate height and an additional story for a residential dwelling structure may be obtained through the provision of additional amenities such as additional recreation facilities, underground parking, and additional landscaped open space areas; as determined through the site development plan review process and depending on the compatibility of the proposed buildings with adjacent or abutting existing residential development. Please provide a full description of proposed additional amenities. As part of your description, differentiate between code- required open space and amenities, and the additional amenities you are proposing for this project. At this time, your project has been placed “on hold” pending receipt of the requested information. The maximum time for resubmittal shall be within ninety (90) days of this notice. Please contact me at (425) 430-7312 if you have any questions. Sincerely, Angelea Weihs Associate Planner cc: Nord West Properties, LLC/ Owner(s) Enclosures: Civil Engineering Memo DEPARTMENT OF COMMUNITY & ECONOMIC DEVELOPMENT M E M O R A N D U M DATE: January 2, 2020 TO: Angelea Weihs, Planner FROM: Michael Sippo, Civil Plan Reviewer SUBJECT: Utility and Transportation Corrections Required for the VEK on Aberdeen Townhomes Plat Land Use Approval 957 Aberdeen Ave NE, Renton, WA 98056 LUA19-000280 I have reviewed the application for the V.E.K. on Aberdeen Townhomes Plat at 957 Aberdeen Ave NE (APN 311990-0066) and have the following required correction comments on the Land Use Application in regards to utilities and transportation: CODE REQUIREMENTS SURFACE WATER 1. A Preliminary Drainage Plan and Technical Information Report (TIR), dated October 31, 2019, was submitted by Encompass Engineering and Surveying with the Land Use Application. Based on the City of Renton’s flow control map, the site falls within the Peak Rate Flow Control area matching Existing Site Conditions and is within the East Lake Washington – Renton Drainage Basin. The development is subject to Full Drainage Review in accordance with the 2017 Renton Surface Water Design Manual (RSWDM). All nine core requirements and the six special requirements must be discussed in the Technical Information Report. The following stormwater improvements are required and shall be discussed within the TIR: a. There are regulated slope, erosion hazard, and landslide areas found within the western side of the property. Due to the steep slopes downstream of the project, the project lies within a flood problem flow control standard area (see section 1.2.3.1 (4) of the 2017 RSWDM). Therefore, unless a flow control exemption is identified, and if stormwater will be discharged to the steep slope area, then the project must match the Flow Duration of pre-developed rates for Existing Site Conditions from 50% of the 2-year up to the full 50-year flow, and match Existing Site Conditions for the 2-, 10-, and 100-Year Peaks. Based on the preliminary design, the facility meets this standard. Update Section 4 of the TIR to include discussion of how this standard is being met (currently states that only the peak flow rate standard is being met). Additionally, update TIR and detention tank design to include a minimum 0.5’ sediment storage and minimum 0.5’ freeboard. b. Continuous modeling did not include flows from the steep forested area on the western portion of the site to the natural discharge location. In order for these flows to be excluded from the point of compliance analysis, per Section 1.2 (A) of VEK on Aberdeen Townhomes Required Utility and Transportation Corrections – LUA19-000280 Page 2 of 4 the 2017 RSWDM (Peak Rate Flow Control Target Surfaces part 2): “…the extent of new pervious surface shall be assumed to be the entire lot area, except the assumed impervious portion and any portion in which native conditions are preserved by covenant, tract, or easement”. The final plat shall place the forested area in permanent and protected open space/critical areas tract or easement or the facility redesigned to attenuate these flows at the point of compliance. Update the preliminary plans and report indicating if the forested area will be placed in permanent open space or provide updated calculations including this area. c. Appropriate flow control BMPs are be required to help mitigate the new runoff created by this development. The preliminary drainage plan indicates that the proposed development is considered a “small subdivision”, however, due to the nature of the development being multi-family with individual lots being created out of multi-family building sharing common walls the project is more in order with the “large lot” BMP requirements as specified in section 1.2.9.2.2 of the 2017 RSWDM. Due to steep slope, landslide and erosion hazard areas being located onsite, full dispersion, full infiltration, limited dispersion, limited infiltration, bioretention and permeable pavement are all infeasible. Specifically, section 1.2.9.2.2 (5) of the 2017 RSWDM states: “The buildable portion of the site/lot is the total area of the site/lot minus any critical areas and minus 200 ft. buffer areas from a steep slope hazard, landslide hazard, or erosion hazard area”. For the applicability of BMP’s, the 200 ft. buffer encompasses the entire site, therefore, per definition, there are no onsite buildable areas subject to BMP’s and the project is exempt from meeting Core Requirement #9. Update the preliminary TIR to include a discussion of how this project is not subject to the BMP requirement as described above. d. Optional BMP’s may be utilized to reduce the size of the flow control facility, however, any BMP’s utilizing dispersion or infiltration techniques (i.e. permeable pavement, limited dispersion, or bioretention) will require the use of underdrains and/or interceptor trenches to collect the runoff and route it to the detention system. Update preliminary TIR if any BMP’s are being included for facility sizing credits. e. The final design and Technical Information Report shall take into account all provisions of Core Requirement #1 (Discharge at Natural Location). Specifically, section 1.2.1 (2) states that: “IF a proposed project, or any natural discharge area within a project, is located within a Landslide Hazard Drainage Area and drains over the erodible soils of a landslide hazard with slopes steeper than 15%, THEN a tightline system must be provided through the landslide hazard to an acceptable discharge point…”. The preliminary TIR identifies that an HDPE tightline over the steep slope will discharge into the onsite drainage way (which is still located on slopes above 15% within the erosion and landslide area), however, additional analysis and mitigation is required to show that the decrease in runoff volume and energy dissipation fully meets Core Requirement #1. At a minimum, the tightline must extend to John’s Creek where the slopes are less than 15% and the other nearby properties discharge to. Alternatively, section 1.2.1 (2) provides an exception where CED can approve an alternative system based on geotechnical evaluation/recommendation where the developed conditions runoff volume from the natural discharge area is less than 50% of the VEK on Aberdeen Townhomes Required Utility and Transportation Corrections – LUA19-000280 Page 3 of 4 existing conditions runoff volume. Update the preliminary plans and TIR to reflect how Core Requirement #1 is being met. If the alternative exception is being proposed, provide a drainage modification request with all applicable geotechnical and engineering justifications and recommendations provided. f. Per RMC 4-3-050 (G)(2) steep slope and landslide hazard buffers shall be established by the geotechnical engineer. Section 4.6.6 of the Geotechnical Report states: “The proposed townhomes have been designed to step down with the existing topography and the majority of the development is on the least sensitive area of the site. Three townhomes are proposed on top of the slope outside of the sensitive slopes and setback from the slope. Based on the results of our subsurface explorations and slope stability analysis, the proposal will not increase the threat of the geological hazard to adjacent or abutting properties beyond predevelopment conditions; and will not adversely impact other critical areas; and the proposed development can be safely accommodated on the site”, however, the report references a previous site plan which shows the proposed buildings set back considerably further than the current site plan and does not take into account the drainage structures and retaining wall which is located on and around the steep slope. Prior to land-use approval, the geotechnical engineer shall provide a quantitative analysis of the steep slope and landslide hazard area and provide set-back based on the recommendations for the updated site plan and facilities being proposed closer than identified in the report. Additionally, a 15’ building set-back line (BSBL) will be required from the edge of the buffer, including the case that the buffer is determined to be 0’. Building, retaining walls and subsurface drainage structures shall not be located within the buffer or BSBL. Update the preliminary plans, geotechnical report and TIR to include any changes resulting in the buffer and BSBL and relocating facilities and/or buildings outside of this area. g. The final technical information report shall include the “bypass” area in the point of compliance analysis since the conveyance system located within Aberdeen Ave NE converges at the site’s point of compliance at the southwest corner (John’s Creek) less than ¼ mile downstream. Based on the preliminary design, the bypass area was included in the facility sizing calculation. See comments 1a and 1b. Update the level one downstream analysis to include this downstream drainage system to the point where the flows converge at the western portion of the site. 2. The development is required to provide enhanced water quality treatment prior to discharge. Project water quality treatment will consist of conveyance to a Biopod system prior to connection to the proposed detention tank. a. Presettling shall be being provided per Sections 6.1.1 and 6.5.1 of the 2017 RSWDM. Update the plans and TIR to include all relevant design and calculations for presettling prior to entering biopod system. If the manufacturer’s system provides presettling, indicate how the requirement is being met using the manufacturer’s design criteria and any applicable calculations in sizing of the facility. b. Per section 6.2.1 (Water Quality Design Flows and Treatment Volumes) 2017 RSWDM the on-line facility will have a modified water quality flow modeling rate (ratio k) of 1.88 based on the 2-yr isopluvial of 1.95” (linear interpolation of Table 6.2.1.A). Based on the WWHM On-Line facility target flow of 0.0369 cfs, Qwq = VEK on Aberdeen Townhomes Required Utility and Transportation Corrections – LUA19-000280 Page 4 of 4 kQ or 0.0694 cfs. This will need to be the number that is submitted to the manufacturer for sizing of the facility. Update the plans and TIR with the revised water quality facility design, including manufacturer’s data sheets based on the updated water quality flow. Ensure to note to the manufacturer during the sizing that the enhanced water quality treatment menu is being met as their calculations will take this into account for a decrease in media filtration rate. https://oldcastleinfrastructure.com/wp- content/uploads/2018/10/Stormwater_Treatment_Design_Assistance_Form_I nfra.pdf c. A maintenance access road is required to the stormwater facilities in the proposed storm tract/easement and shall be in accordance with the design requirements outlined in the RSWDM. Update the plans and TIR to include this access road.