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HomeMy WebLinkAboutFile Documents.905 Chatfield Rd.0111.2018 (65).ARBK MAINTENANCE AND OPERATION PLAN FOR 905 CHATFIELD ROAD, LOT 4, WEST ASPEN SUBDIVISION CITY OF ASPEN, COUNTY OF PITKIN, STATE OF COLORADO HCE PROJECT #: 2171653.00 Reviewed by Engineering 02/17/2021 11:19:56 AM "It should be known that this review shall not relieve the applicant of their responsibility to comply with the requirements of the City of Aspen. The review and approval by the City is offered only to assist the applicant's understanding of the applicable Engineering requirements." The issuance of a permit based on construction documents and other data shall not prevent the City of Aspen from requiring the correction of errors in the construction documents and other data. A. Introduction As part of the Certification of Occupancy, the following maintenance plan has been prepared for 905 Chatfield Road, (Lot 4, West Aspen Subdivision) City of Aspen, Colorado. B. Site Description and Drainage Pattern The proposed site is approximately 15,005 square feet (0.34 acres). The west property line adjoins the Harvey Subdivision, while the east property line adjoins the Chatfield ROW near the intersection of Homestake Drive and Chatfield Road. The south property line adjoins Lot 3 of the West Aspen Subdivision, while the north property line adjoins Lot 5 of the West Aspen Subdivision. The construction called for the removal of an existing residence, concrete walkways, a driveway with a detached garage and a hot tub. The proposed development consisted of the construction of a single-family residence, concrete and sand set paver walkways, a driveway with an attached garage, terraces and a spa. There are several existing trees on the site which have been noted on the existing conditions survey. The trees remaining on the site were protected from the proposed construction activities per the City Foresters recommendations during construction. The remaining portions of the site are mainly covered in gardens and sod/grass outside of the above mentioned hardscapes. The storm water on the existing site flows from the east side of the property to the west side of the property. A small portion of the storm water flows from the south property line to the north. The storm water from the south and the majority of storm water from the east are captured by area inlets and a trench drain. This drainage is conveyed to the water quality and detention vaults located west of the residence via storm pipes. The remaining eastern portion of storm water enters a swale that conveys drainage north and into a bioretention pond. The bioretention pond is drained by a perforated underdrain pipe beneath the filter media, and has a concrete weir for the pond to overflow into a swale. Both the underdrain and the swale discharge to rip-rap located at the northwest corner of the site. The historic release locations remain with the constructed changes to the site. C. Site BMP Maintenance The following Best Management Practices (BMPs) shall be implemented to prolong the life of the storm water infrastructure and to assure that the drainage facilities are functioning properly. Below is a list of BMPs that shall be implemented after construction. Refer to the As-Built plan created by High Country Engineering for locations of the drainage facilities. 1. Mowing, trimming, and weed control shall be performed on a regular basis throughout the growing season. Mowing shall keep the grass to a length of no longer than six inches. Trimmings shall be picked up and removed from the mowed area or a bagging system shall be used. A mulching lawnmower may also be used. 2. All drainage facilities shall be inspected for damages on an annual basis. If structures are damaged to a point that they cannot function properly, then the structure must be replaced. 3. Leaves and debris shall be removed from the roof drainage system in the spring, after snow melt and in the fall once the trees have lost their leaves to prevent clogging. If the roof gutter system and drain pipes are functioning properly, water will not back up in the gutters and overtop them. Storm water shall drain to the water quality tank or bioretention pond, where most runoff will percolate into the soils. The roof drains and pipes shall be cleaned by using a brush system or a hose to flush out the debris. The storm pipes and roof drains may need to be jetted with a high pressure water system to remove any clogged debris. The area drains must also be inspected to make sure debris has not accumulated. These may require water jetting to adequately clean these lines. 4. Area inlets will be inspected in the spring and after major storm events for debris and cleaned as needed. 5. Swales should be kept mowed or raked smooth and must not be filled with dirt or debris. 6. Roof drains to drain in the direction of onsite grass swales, and yard area inlets or patio inlets. 7. The bioretention pond will need to be inspected and maintained quarterly to make sure that the reservoirs have not become clogged and that the reservoirs are functioning properly. Minimum inspection and maintenance requirements include the following: a. Inspect detention area to determine if the sandy growth media is allowing acceptable infiltration. b. Debris and liter removal from detention area to minimize clogging of the sand media shall occur routinely. c. Occasional mowing of grasses and weed removal to limit unwanted vegetation. Maintain irrigated turf grass as 2 to 4 inches tall and non- irrigated native turf grasses at 4 to 6 inches. d. Routinely evaluate the bioretention pond drain-down time does not exceed 12 hours. If the time is exceeding the maximum - inspect the underdrain pipe, grow media and landscaping layer for clogging. e. The sandy loam turf and landscaping layer will clog with time as materials accumulate on it. This layer will need to be removed and replaced to rehabilitate infiltration rates, along with all turf and other vegetation growing on the surface. This will need to be done every 5 to 15 years, depending on infiltration rates needed to drain the WQCV in 12-hours or less. The maintenance may need to be done more frequently if exfiltration rates are too low to achieve this goal. f. Remove any debris or material clogging the perforated underdrain pipe using the pipe cleanout located on the pond surface. Jet the pipe clear with a high pressure water system, if necessary. 8. Underground water quality and detention vaults must be inspected and maintained quarterly to remove sediment and debris that is washed into them. Minimum inspection and maintenance requirements include the following: a. Sand filter areas shall conform to URMP & UDFCD standards. b. Closely manage sediment loads on drainage facilities to prevent high sediment concentrations from clogging the drainage systems, especially the underground vaults. c. Runoff from areas with pollutants that have the potential to contaminate groundwater should not be captured or treated in the underground vaults. d. Inspect underground water quality vault and detention vault quarterly and after every storm exceeding 0.25 inches. e. Periodically remove sediment and debris that accumulates in the underground vaults and upstream drainage facilities. f. At minimum, once per year the top 3 inches of the sand surface in the water quality vault should be scarified. g. Routinely evaluate the drain-down time of the underground water quality and detention vaults to ensure the maximum time of 24 hours is not being exceeded. If drain-down times are exceeding the maximum, drain the underground vaults via pumping and clean out the percolation areas. The sand and gravel in the percolation areas will need to be cleaned or removed if stormwater is not percolating. If slow drainage persists, gravel from the detention vault will need to be removed and replaced to return the gravel depth to 6 inches. Sand filter removal in the water quality vault will consist of removing the top 3 inches of sand from the sand filter. After a second removal, backfill with 6 inches of new sand to return the sand depth to 18 inches. Replacement of the sand bed will be required, if no construction activities take place in the tributary watershed, every 2 to 5 years depending on observed drain times, namely when it takes more than 12 hours to empty 3-foot deep pool, otherwise more often. Minimum sand depth is 15 inches. Monitor the percolation rate in each vault as a preemptive measure to detect changes in performance. h. Dispose of sediment, debris/trash, and any other waste material removed from the underground vaults at suitable disposal sites and in compliance with local, state, and federal waste regulations. The owners of the property will be responsible for the maintenance and upkeep of the drainage facilities. The property owner shall dispose of sediment and any other waste material removed from a reservoir at suitable disposal sites and in compliance with local, state, and federal waste regulations. D. Proper Function of Best Management Practices The proposed water quality and detention tanks will need to be inspected quarterly, as well as after large storm events, to assure that it is accepting all flow directed to it and to assure that it is functioning properly. If the water quality and detention vaults are functioning properly, storm water will collect and percolate into the gravel and sand filter material along the bottom of the vaults. Water should not be visible within 24 hours after a minor storm event. As described above, the sand and gravel may require cleaning or replacement if percolation rates have reduced significantly over time. Bioretention (also known as porous landscape detention) BMPs function by capturing runoff and releasing it over an extended period of time (typically 12 hours for Aspen). This allows time for sedimentation and contact with vegetation for biological treatment. The proposed bioretention pond will need to be inspected annually, as well as after large storm events, to assure that it is accepting all flow directed to it and to assure that it is functioning properly. If the facility is functioning properly, storm water will infiltrate into the material along the bottom of the basin. In order to maintain drain-down times, runoff will enter a perforated underdrain pipe beneath the pond growing media. Water from a storm event should not be visible within 12 hours after a minor storm event. If water remains present in the bioretention area after small/minor storm events, inspect the underdrain pipe for clogging. The surface of the bioretention basin may need to be scarified. A heavy toothed rake may be used scarify the surface as a first choice. A garden tiller may be used if raking does not promote greater percolation rates into the infiltration media. If neither method promotes adequate seepage of storm water in to the filter media, then the growing media and filter material shall be removed and replaced with the proposed materials. The removed material shall be disposed of in a City of Aspen approved location such as the landfill. The drainage swales capture and convey overland flows to area inlets or the bioretention pond. Stormwater should flow through the landscape without causing sogginess or erosion. Debris and rubbish will need to be removed from the swales to prevent floatables flushing downstream, clogging and maintain the capacity established in the drainage study. E. Record Keeping The above BMP plan shall prolong the lifespan of the storm water drainage facilities. The operation and maintenance of the storm water facilities shall be in compliance with the City of Aspen’s Urban Runoff Management Plan (URMP). If the owner cannot perform the routine facility checks discussed above, then they shall hire someone that can perform the duties in order to comply with the City of Aspen’s URMP. All inspections and any maintenance performed on the drainage facilities shall be recorded in inspection and maintenance logs and made readily available for review by the City of Aspen upon their request.