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HomeMy WebLinkAboutFile Documents.533 W Hallam St.0285.2018 (97).ARBK CITY OF ASPEN DRAINAGE MAINTENANCE PLAN 533 W HALLAM STREET ASPEN, CO 81611 I hereby affirm that this report and the accompanying maintenance plan for 244 Eastwood Drive, Aspen, Colorado was prepared under my direct supervision for the owners thereof in accordance with the provisions of the City of Aspen Urban Runoff Management Plan with proposed variances and exceptions listed thereto. I understand that it is the policy of the City of Aspen that the City of Aspen does not and will not assume liability for drainage facilities designed by others. Permit #: 0016-2020-BRES February 2, 2023 Rick Barth, P.E. 36749 Prepared by 118 West Sixth Street, Suite 200 Glenwood Springs, CO 81601 970.945.1004 970.945.5948 fax 533 W Hallam Street, Aspen, Colorado February 2, 2023 Drainage Report for Major Design i CITY OF ASPEN DRAINAGE MAINTENANCE PLAN 533 W HALLAM STREET ASPEN, CO 81611 REVIEWED BY RICK BARTH SGM Project # 2018-292.001 \\sgmfile1\projects\2019\2019-465-Eastwood244\001\E-Reports\SGM\Working Docs\Eastwood-Drainage-Report.docx 533 W Hallam Street, Aspen, Colorado February 2, 2023 Drainage Report for Major Design ii TABLE OF CONTENTS 1.0 Existing Site 3 1.1 Description of Existing Site 3 1.2 Description of Existing Drainage 3 2.0 Proposed Project 3 3.0 Maintenance 4 3.1 Pervious Pavers 4 3.2 Rain Garden 4 3.3 Additional Maintenance Resources 4 4.0 Conclusion 5 533 W Hallam Street, Aspen, Colorado February 2, 2023 Drainage Report for Major Design 3 1.0 Existing Site 1.1 Description of Existing Site The physical address of the project is 244 Eastwood Drive, Aspen, Colorado and it is located on parcel no. 2737-181-20-011. This parcel is approximately 0.36 acres and is owned by 244 Eastwood AH LLC. Current zoning of the property is moderate density residential (R-15B). The existing structures on the parcel are one house and a small shed. The project focuses on demolishing the house while preserving access, utilities, and most existing vegetation except for most trees on the southeastern property being removed. The existing house is 2064 square feet and has two stories with a garage. 1.2 Description of Existing Drainage Existing storm water runs off the existing house either as sheet flow or through gutters and downspouts. Topography of the site suggests that the existing drainage patterns flow from the northeast side of the property to the southwest side of the property. No existing storm water detention or treatment BMPs have been found on the site. There are no apparent erosive or runoff issues (gullies, channels, etc.). A soils report was performed for the site by Kumar & Associates on October 11, 2019 and a NRCS web soil survey. The results correlated and find the soil to be Type A with a moderate infiltration rate of 2 minutes per inch. There is no existing offsite runoff that enters the property as upstream flows are blocked by Eastwood Drive. The property will require detention beyond the water quality capture volume (WQCV). 2.0 Proposed Project The primary purpose of this project is to demolish the existing house and build a new residence. Other improvements include the addition of onsite snowmelt pavement and improving storm water runoff quality. The proposed project is considered a major project as defined by the COA Urban Runoff Management Plan (URMP) because more than 1000 square feet and 25% of the site will be disturbed. The proposed residential development with have a footprint of 2503 square feet and consist of a main level, basement, and upper level. Storm water quality improvements consist of 869 square feet of full-infiltration pervious pavers and 52.9 cubic feet of rain gardens. The full-infiltration pervious pavers will be located on the driveway. Rain gardens are located west, northwest, and southwest of the residence. 533 W Hallam Street, Aspen, Colorado February 2, 2023 Drainage Report for Major Design 4 3.0 Maintenance 3.1 Pervious Pavers The following maintenance recommendations were found in the Urban Drainage Flood Control District USDCM: Volume 3 Storm water Quality (page 6-15 to 6-17) and will be used as a guide for the maintenance of the proposed pervious pavers. An inspection of the condition and observation of infiltration should be completed annually. The pavers will lose infiltration capabilities over time and it is recommended to use ASTM C1707 Standard Test Method for Infiltration Rate of In Place Pervious Concrete to measure the infiltration rate of the pavers. A regenerative air or vacuumed sweeper should be used twice annually and after any significant site work, like landscaping, is done. However, the timing of vacuum sweeping is variable based on site conditions and biannual vacuuming may be more often than needed. Sand should never be applied to the pavers for snow removal as this will decrease the permeability of the pavers. The proposed pavers will have snowmelt capabilities, but if snow removal is necessary, mechanical snow removal should be done. If the surface of the paver system ever becomes completely clogged, remove and replacement of the first ½ to 1 inch of infill. The use of a push broom is recommended for the replacement of infill. 3.2 Rain Garden Annual inspection of the rain gardens should be taken to ensure that the material is not clogged and inhibiting drainage. Inspection after large storms should also be taken to ensure that the rain garden is draining as it should. Replacement and/or cleaning of the material should be performed when it is observed that the rain garden is performing less than optimally in its existing condition. Cleaning of the underdrain should be inspected annually and after large storms that could cause debris to clog the pipes. Cleanouts have been provided to facilitate this maintenance. 3.3 Additional Maintenance Resources The following maintenance recommendations were found in the Urban Drainage Flood Control District USDCM: Volume 3 Stormwater Quality (page 6-5 to 6-7) and will be used as a guide for the maintenance of the proposed facilities. Grass buffers and rain gardens should be inspected at least twice a year for cover and vehicle impacts. Trash and debris should be removed from the buffer at least twice a year. The buffer should be aerated once a year with holes of 2 inches in depth and no more than four inches apart. When aerating the buffer, sprinkler heads and shallow utilities should be marked to ensure they are not damaged. It is recommended to mow only when weeds need to be removed in the first 3 years. After the first 3 years the grass should be maintained at 6 inches or more in height. If grass buffers and rain gardens are no longer holding storm flows or are not draining in 24 hours, immediate maintenance is required. When drainage overflows to areas not intended to detain or convey flows immediate maintenance is required. Additional information on mowing the grass buffer is provided in Figure 1. Irrigation is recommended to maintain a healthy vegetation cover. In the early summer and fall, irrigation is typically needed less, but in July and August more irrigation is needed. If native grasses are used, irrigation should not be needed after establishment but could be useful during long dry periods. Although irrigation is necessary for the establishment of the grass buffer, overwatering could cause uneven growth which can inhibit the conveyance of runoff and should be avoided. Every 533 W Hallam Street, Aspen, Colorado February 2, 2023 Drainage Report for Major Design 5 year the irrigation system should be drained and blown out before the first winter freeze. The irrigation system should be inspected before reactivation in the spring. Fertilizers and herbicides should be used only on an as-needed basis, and it is recommended to use biodegradable nontoxic fertilizers and herbicides. The following maintenance recommendations were found in the City of Aspen URMP. Mowing recommendations for grass buffers or vegetated rain gardens that are included in the Urban Drainage Flood Control District USDCM: Volume 3 Stormwater Quality are provided in the figure below. 4.0 Conclusion The proposed BMPs (grass buffer, pervious pavers, and rain gardens) are expected to treat 100% of the required WQCV at the 244 Eastwood Drive project with room to spare. With proper maintenance and installation, these BMPs will meet the criteria outlined in the City of Aspen’s current Urban Runoff Management Plan.