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Applications to Rezone, Area Variance, & Site Plan STORMWATER MANAGEMENT SUMMARY 1.0 PROJECT DESCRIPTION The project consists of the construction of a new parking addition to the north of the existing rear parking area of the Silo Restaurant & Gift Shop. The project proposed is to incorporate a residential parcel to the north into the existing parcel to accommodate overflow parking for the existing commercial facility. There is no proposed increase of the existing commercial use operating hours or facilities. Also associated with the project is demolition of the existing residential structure / accessory buildings, landscaped buffer and stormwater management. The parcels are a 0.32 acre developed existing residential lot and a 0.77 acre developed existing commercial lot. Project disturbance totals 0.33-acres. 2.0 EXISTING SITE CONDITIONS The project site is mostly on the existing residential parcel which has a driveway (west side), house, covered deck and a patio(east side) of the parcel, the central portion of the parcel is a slightly sloping (west to east) grassed lawn area which has a retaining wall running north-south along the east section and partially along the southwest corner of the south boundary. The runoff from the front half of the roof and driveway runs east to west and discharges to the town road, the rear house roof, covered deck and patio runoff flows to the east and is captured in the lawn area in a depression in the lawn along the retaining wall and infiltrates into the soils. The eastern most portion of the parcel is gravel and grassed area that has three accessory buildings. The runoff from this area flows to the southeast corner of the parcel and reaches an existing drywell on the commercial parcel. Site slopes generally range from 2-4% from the west to east. Site soils are mapped as Hinckley Cobbly Sandy Loam, HSG-A which are deep, well drained sandy soils on outwash plains. A deep soil test pit performed for a previous project encountered fine and medium sands. Existing Conditions Summary Total Project Site Area: 1.09 Acres (combined) Building & Porch Coverages: 9,010 SF Walks, Drives & Parking Areas: 28,780 SF Total Impervious: 43,285 SF Drainage design points The site is broken into four drainage design points. Design point 1 is the southern portion of the existing commercial use which flows from the northwest entrance to the southeast entrance and drains to an existing trench drain. Design point 2 is the north portion of the existing commercial use and the east portion of the residential parcel which flows to the east and collects in the existing drywell. Note that during the 50 yr storm the runoff from this area exceeds the capacity of the drywell and ponds in the existing parking area until it eventually infiltrates into the drywell soils. Design Point 3 is the central east portion of the residential lot which flows from the east half of the house roof to the lawn depression along the retaining wall. Design point 4 is the west side of the residential parcel which the west portion of the house roof and driveway runoff and discharge onto the Town Road. 3.0 PROPOSED DEVELOPMENT Proposed Conditions Summary Total Project Site Area: 1.09 Acres Building & Porch Coverages: 6,450 SF Asphalt Parking & Permeable Asphalt Parking Areas: 34573 SF Total Impervious: 41,023 SF Project Disturbance: 0.33 Acres 4.0 PROPOSED STORMWATER MANAGEMENT As this is a commercial project with soil disturbances not exceeding 1-acre, NYSDEC SPDES requirements for stormwater discharges from construction activities do not apply to the project. The Town of Queensbury requires that commercial projects must implement stormwater management practices designed to manage the 50-year design storm event. Runoff from the south portion of the parcel will not be modified as no disturbance in this area is proposed. Runoff from the new parking addition will be directed to a new catchbasin in the southeast corner of the new parking area and discharge into a new stormwater subsurface infiltration trench. The new trench will be a 20 ft by 41 ft stone trench with 15 Cultec XL330 chambers in 3 rows of 5 chambers. The existing drywell will be connected to the new catchbasin with 12” HDPE piping allowing the existing drywell to discharge into the new infiltration trench. The permeable pavement infiltration was not included as part of the stormwater calculations. Design points 3 will be eliminated as part of the proposed work as the new parking area will discharge directly into design point 2. Design point 4 will also be eliminated as the landscaped area and parking area will discharge runoff to design point 2. An infiltration rate of 100-inches per hour is utilized for the infiltration facilities. Runoff calculations have been prepared utilizing SCS TR-20 methodology and HydroCAD analysis software for the 50-year Type-II simulated rainfall distributions. Criteria utilized in the analysis are summarized as follows: The developed site has been modeled as a series of subcatchments (drainage areas) and ponds, as shown on the HydroCAD drainage diagram. Full results of stormwater runoff computations are attached to this report. 5.0 TOWN OF QUEENSBURY REQUIREMENTS The Town of Queensbury requires that for commercial projects, the 50-year design storm event be evaluated. Existing 50-year peak storm volume: 0.182 AF Developed 50-year peak storm volume: 0.172 AF Existing 50-year peak storm discharge: 3.57 CFS Developed 50-year peak storm discharge: 3.40 CFS The 50-year storm calculations show that the Town's requirements for commercial projects are met.