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HomeMy WebLinkAboutFile Documents.287 McSkimming Rd.0044.2018 (23).ARBK The permit processing time is stopped on this review and will not begin again until all issues from all review agencies are addressed and the corrections are approved for resubmittal. At that time, your resubmittal will re-placed in the queue with other permits being processed. To: Hailey Guglielmo Development Engineer, City of Aspen Phone 970/429-2751, Fax 970/920-5081 hailey.guglielmo@cityofaspen.com From: Sean Walmsley Roaring Fork Engineering 592 Highway 133 Carbondale, CO 81623 seanw@rfeng.biz (970) 340-4130 Richard Goulding Roaring Fork Engineering PO Box 9554 Aspen, CO 81612 richardg@rfeng.biz (970) 340-4130 287 McSkimming Rd. Permit Number: 0073.2017.ARBK August 18th, 2017 Included in this document are the comments and corrections made by the City of Aspen’s Engineering Department. In green, below each comment, is a written response to the comment from Roaring Fork Engineering. These responses explain the alterations to the proposed design for conformance to the state and local codes. Adjustments to the plans, calculations, and drainage report are all described in the responses. ENGINEERING REVIEW COMMENTS AND CORRECTIONS Survey 1. A surveyor’s certificate stating that the error of closure is less than 1/15,000 shall be added to the survey. The surveyor’s certificate has been updated to include this statement. 2. Please indicate the datum of the survey elevations. The survey’s vertical datum has been added (see note 9 of the survey). 3. Label all easements and add reference numbers as applicable. All easements crossing the parcel have been labeled and reception numbers have been included. 4. Please indicate if there are any natural hazards onsite and the floodplain designation. The floodplain designation has been included in note 10 and all natural hazards have been labeled (steep slopes). The permit processing time is stopped on this review and will not begin again until all issues from all review agencies are addressed and the corrections are approved for resubmittal. At that time, your resubmittal will re-placed in the queue with other permits being processed. 5. If there are service stub-outs already to the property please designate their location. Also indicate where the existing gas, electric, cable, etc. is located. The existing gas, electric, telephone and cable lines have been added to the survey, no service stub outs were found on site. Soils Report 1. Final approval will not be granted until percolation testing results are submitted for review. If the testing results differ from the design assumptions then the plans will need to be revised accordingly and resubmitted for review. HP Kumar completed a percolation test on July 10, 2017 the report for which has been included with this submittal. This test indicated a percolation rate of 4 minutes per inch. Excavation Stabilization Requirement 1. Submit an excavation and stabilization plan. Anywhere layback is planned show the extents of the layback at 1:1 slope. Ensure layback stays within property lines and does not impact trees or utilities. An excavation stabilization plan has been added to the civil set with layback shown at a 1:1 slope for the majority of the foundation excavation. A temporary shoring wall will be required along the west side of the house in order to avoid crossing the west property line and to protect the mature trees in this area. Adequate separation has been shown between the layback and the existing water line to the East and all trees that will remain on site. Utility Meters, Pedestals 1. There does not appear to be proper separation of trees, shrubs, etc. (landscaping) from the site utilities. Gas, electric, telephone, and the water service line are all located directly below proposed trees. Please revise. The planting plan has been updated to allow for space to route the utility service lines to the residence and all utilities have been adjusted to avoid conflicts with the updated planting plan (see sheet C-107) 2. The proposed landscaping plan located within the waterline easement cannot be accepted. All trees and shrubs shall be located a minimum of 10’ away from existing utilities. Refer to section 2.5.1 of the Engineering Design Standards. All proposed trees and shrubs have been moved 10’ or more off of the existing water line. 3. Provide 10’ separation between plantings and the main waterline in the ROW. All proposed trees and shrubs have been moved 10’ or more off of the main water line in the ROW. 4. Pothole the waterline within the easement. Show that with regrading for the swale, minimum cover of 7’ is still maintained. All disturbance has been moved 5’ or more off of the existing surveyed water line. Per our meeting with Hailey on June 12, 2017, we will not need to pothole the waterline now that we have moved all proposed grading 5 feet off of the waterline. Drainage Report and Plan The permit processing time is stopped on this review and will not begin again until all issues from all review agencies are addressed and the corrections are approved for resubmittal. At that time, your resubmittal will re-placed in the queue with other permits being processed. The drainage report and plan set is not in compliance with the City of Aspen Grading and Drainage Requirements for Major Design. The following items from the Checklist for Grading and Drainage Requirements for Major Design need to be included, addressed or discussed: DRAINAGE REPORT SHALL INCLUDE: 5. Page 4 of the Drainage Report (DR) states the infiltration rate of 5 minutes per inch is recommended. An onsite percolation test is required to verify the assumptions in the report and must be submitted to the City for review before approval. If the assumptions are found to be incorrect the design shall be changed. HP Kumar completed a percolation test on July 10, 2017. This test indicated a percolation rate of 4 minutes per inch. Section 1.1 and section 6.2.1 of the drainage report has been updated to reflect this. 6. The report needs to discuss the existing site easements and the storm water improvements that are being proposed within them. Any negative effects such as reduction in cover, access, etc. shall be considered and addressed. A discussion of the waterline easement has been included in section 1.5 of the drainage report. 7. Page 9 of the report indicates the flow will be release from the site at historic peak flow rate from the site, but no details are provided. The plans don’t adequately address how flows will be released at historic rates. Please explain and provide details showing how this will be accomplished. Show release orifice calculations. Show how pipe B surcharges to allow bypass flows at the end of the NE swale. Section 5.3 – Outlet Structure has been added to the drainage report. This section describes the function and calculation of the outlet pipe and associated orifice which functions to restrict the 100-year flow rate out of the drywell. A discussion of how offsite flows will bypass inlet-B1 has been added to section 5.1 8. The hydraulic grade line and pipe capacity table on page 15 indicates pipe DS is 5 inches in diameter. Please verify this is correct. This has been corrected to reflect the correct pipe size of 4 inches. 9. Please provide drainage swale design calculations. A calculation of the capacity of the eastern drainage swale at its narrowest point (near the corner of the patio) has been added to the appendix of the drainage report showing that the swale has adequate capacity to convey the 100-year peak flow rate from the offsite and onsite basins. Similar calculations have been performed for the driveway swales and can be found in the appendix. 10. Please provide rip rap design calculations. Show the 7.74 cfs of offsite runoff is safely dissipated down the slope. Section 5.4 – Rip Rap Sizing, has been added to the drainage report to discuss the method used to size Rip-rap and the calculations have been added to the appendix of the report. 11. Demonstrate runoff velocity does not exceed 7 ft/sec down the slope from offsite flow. A discussion of this calculation has been included in section 5.4 and the calculation itself has been included in the appendix. The calculation shows that the flowrate down the slope is 4.93 ft/s. 12. Please provide a discussion about the drainage path of the water once it leaves the site. Verify there are no negative impacts to the retaining wall downhill. The permit processing time is stopped on this review and will not begin again until all issues from all review agencies are addressed and the corrections are approved for resubmittal. At that time, your resubmittal will re-placed in the queue with other permits being processed. A discussion of the drainage once it leaves the site has been included in section 1.4. The drainage reports for improvements made to Skimming Lane and 189 Skimming Lane were referenced as these reports had analyzed this site as part of their offsite analyses. A level spreader has been added to disperse the runoff from the site. This sheet flow will match the historic pattern and protect the retaining wall downhill. DRAINAGE PLANS SHALL INCLUDE: 1. The site benchmark and tie to the City of Aspen survey monuments needs to be added to the plans. These are depicted on the existing conditions page (C-101) 2. It appears some improvements will be made in the utility easements. Please indicate if these improvements are allowed and provide documentation. Per our meeting with Hailey on June 12, 2017, the section of patio that extends into the easement will be acceptable as it is 13’ off of the surveyed water line. The drainage swale being proposed in the easement was also discussed and will be acceptable as it does not reduce cover over the water line. 3. Sheet C-110 (utility plan that is overlaid with the proposed landscaping) shows multiple locations where landscaping is being planted directly on top of existing and proposed utilities and in proposed easements. Utilities such as the water main need to be clear of such landscaping conflicts. Please revise. The landscaping plan has been updated to move proposed planting, shrubs and trees off of the water line. All utility services have been routed around proposed trees. 4. All road/saw cuts shall be in conformance with the City of Aspen standards. Road saw cuts have been adjusted to be perpendicular to the flow of traffic, bringing them into conformance with the City of Aspen standards. 5. All storm inlets don’t appear to have sumps to help collect and direct water. Please revise or add more spot elevations. Inlet-A1 and A4 will be revised to include a 0.5’ sump depth as they were intended to have (see sheet C-109 for these revisions). All inlets are located in low points, the spot elevations have been added and updated to make this clear. 6. Not all of the swale cross sections show the water surface elevations. Please revise. Water surface elevations have been added to all swale cross sections and the calculations have been included in the appendix of the drainage report. 7. Provide a cross section of the east swale. Show water surface elevation. Show infiltration is 10’ away from the waterline. This cross section is shown on sheet C-109 (in the bottom right corner) and the 100-year storm water surface elevation is included. A PVC liner has been added to a portion of the swale on the east side to ensure that infiltration does not occur within 10 feet of the existing water line (see sheets C-102 and C-108 for the full extent of the liner) The permit processing time is stopped on this review and will not begin again until all issues from all review agencies are addressed and the corrections are approved for resubmittal. At that time, your resubmittal will re-placed in the queue with other permits being processed. 8. The eastern swale is shown to collect both offsite and onsite flow. Describe in more detail how the onsite flow and bypass flows are separated. Include in the discussion the times of concentration. Verify the onsite WQCV will pass through the inlet before the offsite runoff. A discussion of this has been added to section 5.1 of the drainage report. 9. The water sewer and storm trench detail on sheet C-501 should show aggregate base course for the road and not just native material. This detail has been updated on sheet C-501 10. Please show the flow path leaving the development ending at a major drainage way and ensure it does not negatively affect downstream properties on its way to the final outfall point. This flow path has been added to sheet C-103. 11. Slopes on the site exceed 30%. A point discharge is being applied to this steep slope. Per Section 6.3.3 the site requires a slope stability study. The study shall take into account the runoff channelized down the slope at both the swale and drywell locations. HP Geotech completed this study and this has been included with this submittal. The release from the drywell will no longer be channelized as a level spreader has been proposed to promote sheet flow. 12. Due to the steep slope, provide slope protection at the foundation drywell outlet. Rip-Rap has been added at this outlet. Construction Management and Erosion Control Plan The construction management plan is reviewed under a separate review process. Please contact Tony Kornasiewicz (970) 309-8424 with any questions regarding the CMP requirements and contact Aaron Reed at (970) 429-2782 with any questions regarding the Erosion Control Plan requirements. Once the standards of the Urban Runoff Management Plan standards and requirements are met, the Development Engineer can sign off on the requested permit. If you have any questions or concerns about any of the items shown, please feel free to contact me. IMPORTANT: The City of Aspen Engineering Department is requiring that all stormwater BMP’s be inspected throughout the construction process to ensure BMP’s are installed per the approved plans. Please contact Hailey Guglielmo at (970) 429-2751 48 hrs prior to construction of each stormwater BMP. Sincerely, Sean Walmsley, EI Roaring Fork Engineering 970-340-4130