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HomeMy WebLinkAboutMaster Permit.701 Gibson Ave.0086-2021-BRES (2)701 Gibson Ave High Country Engineering, Inc. November 1, 2021 CITY OF ASPEN ENGINEERING COMMENTS AND RESPONSES (shown in bold text) Drainage Report 1. Soils report needs to be submitted for review. Update plans and report as necessary. A soils report has been included in the updated drainage report. 2. The Engineering Department has responded to drainage complaints from this area regarding Gibson Ave draining onto driveways, have these flows been analyzed and accommodated? The private property is responsible for protecting itself from ROW drainage. The Gibson Avenue ROW has been analyzed as an offsite basin using City of Aspen GIS data. A description and calculations for the basin can be found in the updated drainage report. Flows from Gibson Avenue will be better accommodated by the proposed sidewalk, curb and gutter. The driveway will have a beveled edge lip along the gutter flowline to prevent Gibson Ave runoff from entering the site. Should runoff overtop the beveled edge during large storm events, stormwater will have a flow path that will avoid structures and neighboring properties. 3. Revise the report to include the findings of the potholing. Potholing of water main is ongoing. Current findings can be find in the civil plans. 4. Provide capacity calculations for this system that confirm that detention requirements are met. Detention is being provided by three existing drywells onsite and are not to be disturbed. The scope of this project provides WQCV and drainage improvements for the new/disturbed impervious areas. Detention for the site has been improved by the installation of a bioretention pond that will capture runoff not previously detained or treated from the existing impervious areas. The drainage report has been updated to further describe the existing detention. 5. Include a description of the offsite basin. A description for offsite basins has been added to the drainage report. 6. The runoff ultimately reaches the drywells for detention, are there swales to ensure this runoff reaches the drywell? How is the flow pattern maintained to ensure detention is provided? The existing drywells are not within the scope of the proposed project, but detention provided by the existing drywells will not be decreased with the proposed work. One of the existing drywells has an area inlet that captures a portion of surface drainage under existing conditions, and the flow pattern to this inlet will not be changed to reduce the amount of runoff captured under proposed conditions. The grade surrounding the south side of the area inlet could be slightly raised to improve existing conditions, and are included in revisions to the proposed grading. The drainage report has been revised to further describe the existing drywells. 11/02/2021 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 7. The WQCV calculation is for the driveway, shouldn't this be 100% impervious? The appendix uses 0.26 for the calculation. The WQCV calculations have been revised to provide water quality for new impervious areas onsite and the improvements in the ROW. Impervious was calculated using the combined areas of onsite and offsite basins that are tributary to the bioretention pond. Please see drainage report for revised calculations and descriptions. 8. Mention of the riprap overflow should be included in the drainage report. The riprap overflow is mentioned in the revised drainage report. 9. Include maintenance for the rip rap overflow. Maintenance for the riprap overflow has been included in the revised drainage report. 10. The maintenance plan submitted for CO for this property shall be more robust. It should include a brief summary of how the site drains/functions, how to know if the system is failing, how to test for failure, and how to remedy any failures. This should be written in a way that a homeowner or landscaper will be able to follow. The maintenance plan submitted for CO will be written as described. 11. Label the offsite basin OS-1 on the map. Offsite basins are now labeled on the revised map shown on exhibit 3 of the drainage report. 12. Does the total area include the offsite basin? How is the new impervious area calculated? This value doesn't match what's in the drainage report. For effective impervious to apply, the impervious area should be disconnected via overland flow to the treatment BMP rather than hard piped. How is this applicable? Why is the new impervious area of 2165.7sf different than the impervious area of 1133sf used in the new impervious area WQCV calculation? Does the offsite basin drain through the rain garden? The total area and new impervious area values shown in the bioretention pond calculations have been revised to match the drainage report. Effective imperviousness was not applied to WQCV calculations, but was described by the language found in the URMP chart used for WQCV calculations. The bioretention pond calculations sheet and drainage report has been revised to more clearly demonstrate how values were found. An additional offsite basin has been delineated to show the area that may drain onsite only during larger storm events. One offsite basin will drain onsite during all storm events and will be treated by the rain garden Please see the updated drainage basin maps and drainage report. 13. Does this flow of 0.2 account for the driveway area and the offsite basin? How was this flow calculated to size the pipes and drains? The flowrate does account for the driveway area and offsite basin tributary and was used in the hydraulic calculations to size the drainage infrastructure. The flowrate has been increased with the addition of the sidewalk area, so the revised drainage report will show updated values. 11/02/2021 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 Civil Plans 14. The Engineering Department requested HCE to review this turn to determine if improvements could be made to this blind curve. Was that analysis completed? What was the determination? The blind curve was discussed further with the Engineering Department after receiving these comments. The numerous existing trees offsite and south of the curve create the obstructions that limit sight distance. Development onsite cannot be made to improve the blind curve, and would be most feasibly done by removing trees on the adjoining property. Signage in the North Spring Street ROW before the curve could help drivers be more cautious of the conditions. 15. Per the landuse approvals, any existing encroachments that do not have an existing license will need to apply for a license through the Engineering Department. The new snowmelted driveway in the ROW shall be included in the revocable encroachment license application. Retaining walls are not permitted within the ROW. What are the alternatives to these walls? Snowmelted driveway areas within the ROW will be included in the revocable encroachment license. The retaining wall is existing and in an area that will not be disturbed with this project. The existing retaining wall maintains the existing grade surrounding nearby trees that would be disturbed by making changes to the existing retaining wall. 16. Has the testholing of the existing water main in the easement been completed? Submit this information for review. Testholing of the existing water main has been completed, but the water main was not discovered in any of the testholes. The City of Aspen Water Department came onsite during testhole excavation and confirmed the correct testhole locations. Information is provided in the updated site and grading plans on sheets C.1.001 and C.1.002. 17. Is the proposed paver driveway pervious or just non-pervious pavers? The existing water service line is placed below a snowmelted area. Please note that if this line requires maintenance/access in the future the repairs to the snowmelt system will be at the owner's expense. The snowmelt in the ROW is required to be on a separate zone from the snowmelt within private property. Please call this out on the plans. The proposed driveway has non-pervious pavers. The snowmelted driveway in the ROW will be on a separate zone and is called out in the revised site plan on sheet C.1.001. 18. These are construction documents, the potholing needs to be completed prior to permit issuance, the information gathered from the potholing should be included in the construction drawings. Information found while potholing the water main is now provided on the revised civil plans. See sheets C.1.001 and C.1.002. 19. Is the minimum 7' bury depth maintained on Unit A's water service line? The proposed grading will not reduce the bury depth of the existing water service line. 11/02/2021 Driveway is not pervious pavers. 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 20. Clarify this landscape timber wall is existing. Is this area within the scope of work? A permanent encroachment is required for this wall. The grading plan and site plan has been revised to clarify the landscape timber wall is existing. The timber is used for the driveway on the neighboring property on will not be part of the scope of this project. The proposed work near a small portion of the landscape timber is seeded low grow grasses, and the existing grades are to be maintained. See sheets C.1.001 and C.1.002. 21. These planters aren't treated as they discharge to the riprap overflow. Do they need to be treated? The planters are not mentioned in the drainage report nor is this second drain pipe. The planters do not capture any drainage from impervious areas and do not need to be treated. The pipe is only to prevent ponding and to provide better drainage for plantings. 22. This is a construction drawing civil set, this note should be updated to reflect the testholing results. The testholing results have been provided in the plans, and the note has been removed. 23. Since the interior remodel is only 9% of the structure per the SalesForce application and the exterior work impacts less than 25% of the lot, public improvements such as curb and gutter are not triggered. This property is responsible for protecting itself from street drainage. Since curb and gutter are not required at this time, has the private stormwater system been designed to accommodate the offsite drainage? The owner has decided to install sidewalk, curb and gutter despite not being required by work impacts. A beveled edge was used for the gutter flowline along the driveway to prevent offsite drainage. The stormwater system has been designed to accommodate the portion of the offsite drainage that will drain onsite during all storm events. Please see updated sheet C.1.002 and drainage report. 24. Has the soil type been confirmed with a geotech? Provide a soils report that complies with the checklist requirements in the URMP. A soils report has been completed and provided with the permit resubmittal. The soils report can also be found in the appendices of the drainage report. 25. How will the new driveway connect to the asphalt in Gibson Ave? Provide a detail. Gibson Ave is not in the sidewalk deferred zone. Ensure the proposed plan does not prohibit the installation of a sidewalk (grading, plantings, etc.) so that if/when the project scope of work on this property is large enough to trigger sidewalk installation or the City installs sidewalk, this design permits sidewalk and there are no impacts. Show the driveway slope complies with ADA slopes. The owner has decided to install a new sidewalk, curb and gutter along Gibson Avenue. The connection has been designed and shall be installed per City of Aspen Engineering standards. The driveway and sidewalk slopes have been design to meet the City of Aspen Engineering and ADA standards. See revised sheets C.1.002 and C.6.001. 11/02/2021 Soil Type B 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 26. Max allowable slope per Engineering Standards is 3:1, existing slopes greater than 3:1 are permitted, no new slopes greater than 3:1 are permitted without a written variance request. Clarify this note that the steeper slopes are existing only. The note on sheet C.1.002 has been clarified that the steeper slopes are existing only. 27. Include the bioretention pond in the legend. The bioretention pond has been included in legend of civil plans. 28. Per presubmittal meetings, no stairs were permitted in the easement. How will these be installed so that access to the water main isn't prevented or impacted? Provide a detail and call out where the detail is located. The stairs were removed by landscape architects in the revised plans. 29. What does this line represent? The lines represented pipes entering the drywells. The pipes were not located and are not involved in the scope of this project; therefore, the lines have been removed from the plans. Information regarding the existing pipe inverts are still shown in the drywell callouts. 30. The riprap overflow is not permitted as an encroachment in the water main easement. The riprap overflow has been discussed further with the City of Aspen Engineering Department and will be allowed. The riprap will not be intrusive and is easily removed. The riprap will also prevent erosion in the waterline easement. The civil plans have been updated to provide more riprap information and details. Please see revised sheets C.1.002 and C.6.001. 31. The trench drain and storm pipe connection is right above the water main. What is the vertical separation? How can this design be modified to minimize the encroachment of private storm infrastructure in the water main easement? Per the easement language, encroachments are not permitted. The storm infrastructure encroachment shall be minimized. The encroachment has been minimized by shortening the trench drain so the trench drain grate, channel and storm pipe connection are outside of the water main easement. Please see revised sheet C.1.002. 32. What does this line represent? The lines represented pipes entering the drywells. The pipes were not located and are not involved in the scope of this project; therefore, the lines have been removed from the plans. Information regarding the existing pipe inverts are still shown in the drywell callouts. 33. Show the water service line connecting to the main line in Gibson Ave. The civil site plan has been revised to more clearly show water service connections. Please see revised sheet C.1.001. 11/02/2021 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 34. Is there an agreement that permits work to occur outside of the property boundary? Provide the agreement if there is one. The work outside the property boundary is within a landscape area subject to right of Unit C owner for landscaping design and installation, as shown in the Hill House Condominium Plat. 35. All "boulders" placed in the easement need to be set so they can easily be removed. Call this out on the civil sheets and the landscape sheets. Civil sheets have been revised to callout boulders within the easement to be set for easy removal. 36. The driveway in the water main easement is not permitted to be snowmelted. The driveway is permitted to encroach in the easement however it is not permitted to be snowmelted and is recommended to be asphalt or concrete, easier to remove if/when the line needs to be accessed. The snowmelted driveway will modify the frost depth for the water main. Revise the plan. The frost depth may be impacted by the heat tape along the stormwater pipe to the rain garden, depending on the testholing results, will the storm drain need insulation? Snowmelt is no longer proposed for the area of the driveway that is within the water main easement. Storm drain insulation is called out in the revised grading plan. See sheet C.1.002. 37. Is the utility easement 15 or 20'? A landuse approval condition was to increase the easement width to comply with COA Water Distribution Standards. The necessary width is 25'. Please provide a formalized easement for review and signatures. Two utility easements have been recorded at different dates. Easement exhibits for a 25’ wide utility easement have been provided for review. 38. Where does the water main connect to the main in Gibson? Show this connection. The updated site plan shows the water main connection to the main in Gibson Avenue. See sheet C.1.001. Landscape: Please see comment responses from landscape architect. Survey: 39. The survey must be tied to two COA monuments per the survey checklist in the Engineering Standards. The survey has been revised to have ties to two COA monuments. 40. Improvements are proposed outside the property line, is this in an easement? The survey needs to extend 5' beyond the disturbance area per the Engineering Standards. The work outside the property boundary is within a landscape area subject to right of Unit C owner for landscaping design and installation, per the Hill House Condominium Plat. The survey is now showing improvements on the neighboring property. A small section that is 5’ 11/02/2021 701 Gibson Ave High Country Engineering, Inc. November 1, 2021 beyond the disturbance has limited survey data for contours, and 2020 City of Aspen GIS contour data has been added to this section and noted. 41. Include the recording number for the encroachment. Recording number for the encroachment has been added to the survey. 42. Confirm all easements shown in this document been shown on the survey. All easements shown in this document have been shown on the survey. 43. Surveyor's certificate shall state that the error of closure is less than 1:15,000. Include Surveyor's certificate in compliance with the Engineering Standards survey checklist. The surveyor’s certificate has been updated to state the error of closure. 44. Show the width of the easement through the extent of the property. All utilities shall be shown on the survey - show the water main on the survey. Call out size and material. The width of the easement is now shown through the extent of the property. All utilities are shown on the survey, including the water main with related information. 11/02/2021