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Stormwater report STORMWATER MANAGEMENT REPORT Prepared for: Judkins Family Trust & William & Bonnie Thomas 15 & 9 Genista Drive Tax Map #'s 289.10-1-36 & 289.10-1-35 Town of Queensbury Warren County, New York Prepared by: Hutchins Engineering 169 Haviland Road Queensbury, NY 12804 January 15, 2018 i Project Description The project consists of the redevelopment of a 0.34-acre parcel for the Judkins Family Trust, in which the existing camp will be demolished and a new 3-bedroom home will be constructed, along with a new on-site wastewater system and well, landscaping, and stormwater management. Upon the 0.25-acre parcel owned by the Thomas', a shared driveway will be constructed to access the two subject parcels along with an enlarged parking area for their existing camp. The parcels are situated off of Genista Drive and have approximately 50 feet of lake frontage on Glen Lake in the Town of Queensbury, Warren County, New York. Total project disturbance upon both parcels totals approximately 17,500 square-feet. Existing Site Conditions Presently, the project sites each contain a camp, situated close to Glen Lake, with very steep slopes behind them. The parking areas above and behind the camps and steep slopes north of the drive/parking areas slope up to Genista Drive. The vacant portions of the site are moderately wooded consisting of a mixture of evergreen and deciduous trees and brush. The project site slopes east to west at 10-40%. Site soils are mapped as Hinckley Cobbly Sandy Loam, HSG-A. Field observations of exposed cut slopes revealed cobbly, bouldery coarse sands and gravel, typical of the Glen Lake area. Site slopes over the house site generally range from 5- 10% near the lake shore and 15-50% over the central and northerly portions of the site. Design Storm Events: 25-year, 24hr, Type-II distribution, 4.5" Existing Conditions Calculated Stormwater Runoff from the Site: Design Point 1 — Runoff to Lake over the Judkins' Parcel 25 -year design storm (4.5") 0.37 cfs 0.019 acre-feet Design Point 2— Runoff to Lake over the Thomas' Parcel 25 -year design storm (4.5") 0.21 cfs 0.014 acre-feet Proposed Stormwater Management For residential projects, the Town of Queesbury requires that 25-year design storm be evaluated in predeveloped vs. developed site conditions. Runoff from the reconstructed drive and parking areas and the adjacent upland portions will be conveyed via paved wing swales to a series of two 8-ft diameter x 4-ft deep drywells. Runoff from the roof area of the new home will be captured in roof gutters and will be piped to subsurface infiltration stone beds with Infiltrator Chambers. Runoff calculations have been prepared utilizing SCS TR-20 methodology and HydroCAD analysis software for 25-year Type-II simulated rainfall distributions. Criteria utilized in the analysis are summarized as follows: Design Storm Events: 25-year, 24hr, Type-II distribution, 4.5" Proposed Conditions Calculated Stormwater Runoff from the Site: Design Point 1 — Runoff to Lake over the Judkins' Parcel 25 - year design storm (4.5") 0.12 cfs 0.006 acre-feet Design Point 2— Runoff to Lake over the Thomas' Parcel 25 - year design storm (4.5") 0.00 cfs 0.002 acre-feet 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. Results The analyses show that the drywells and subsurface infiltration beds are of adequate capacity to manage calculated runoff from the proposed construction for the design storm event. Reductions in both runoff rate and volume are realized from the existing conditions for the 25-year design storms. Construction Phase Erosion Practices Practices to be implemented during construction for erosion and sediment control include silt fencing and temporary sediment traps in various portions of the total disturbed area. Silt fencing will be placed across slopes (on the contour) in all areas downgrade of disturbed areas. Temporary sediment traps will be utilized in areas where construction phase runoff concentrates. Temporary Erosion and Sediment Control Measures Erosion and sediment control measures will be incorporated into the construction of the project. These practices will comply with the New York State Department of Environmental Conservation publication entitled "New York State Standards and Specifications for Erosion and Sediment Control" (the blue book). The following temporary erosion and sediment control devices are to be utilized: Sediment Control Fence Silt Fence shall be used to control erosion from sheet flow on slopes not to exceed 1 on 3. Concentrated flows shall not be directed toward the silt fence. The silt fence must be installed parallel to the contour lines to eliminate drainage along the fence. Temporary Seeding Land that is stripped of vegetation will be seeded and planted as soon as possible. Any area that will remain cleared but not under construction for 14-days or longer will be seeded with a ryegrass mixture and mulched to stabilize soil until construction resumes. Temporary Diversion Swales Temporary diversion swales shall be constructed either to divert clean stormwater runoff from newly graded areas or to direct sediment laden runoff to a sediment trapping device. Dust Control Measures for dust control during construction shall be implemented as needed. Daily water sprays will be used during dry conditions. In addition to water sprays, temporary mulching, temporary seeding and covering stockpiles with tarps shall be implemented when necessary. Erosion Control Blanket Fabricated straw or biodegradable mesh blankets shall be utilized to protect and temporarily stabilize slopes of 1:3 or greater and applied to graded, topsoiled and seeded slopes. Blankets will be attached with staples or stakes in accordance with manufacturer's recommendations. Blankets will be maintained in place until permanent groundcover is firmly established. Control of Litter, Construction Debris and Construction Chemicals _ During the course of construction, the site shall be kept clear of debris and litter which could be transported by water or wind. This material shall be picked up daily and shall be stored in waste debris containers where it will be securely held. All petroleum products or other waste contaminants which are water soluble, or could be dispersed and transported by stormwater, shall be stored in covered containers and be regularly removed from the site and properly and legally disposed of. All petroleum or other hazardous materials shall be stored and handled in conformance with NYSDEC spill prevention and containment requirements. Sequence of Construction Prior to the start of construction, the contractor shall install the sediment control fence along the low side of each area to be disturbed to contain runoff from the construction site. Following the completion of all planting and the establishment of all grass areas, any collected sediment, rock check dams and sediment control fencing shall be removed. Any debris from the perimeter of the site shall be removed and all waste material shall be disposed of in a legal manner. Maintenance of Temporary Erosion & Sediment Control Devices The contractor shall inspect the sediment control fence weekly and after every rain event and remove trapped sediment and maintain the devices such that they are in good working order. Permanent Erosion Control All pervious areas shall be graded, topsoil installed and seeded or planted as soon as practical. Seed beds shall be mulched with straw and plant beds shall be mulched with pine bark mulch. Seeded areas on slopes over 1:3 shall be stabilized with erosion control netting as specified on the plans. Attachments • Soils Map • Subcatchment Map— Existing Model • Subcatchment Map— Proposed Model HydroCAQ - Existing Condition —Type-II 24 hr Rainfall = 4.5" (25-year) - Proposed Condition —Type-II 24 hr Rainfall = 4.5" (25-year) i Soils Map A r,.�.i:•� Nin inS ) i .ifs � Nx,ricdp J ■ ��1� r. i. 49 nh•u WIN— mp ��- ■Cu Ire 04d r Satr t'tr .,,Ad.,pti. �, 1 uw7�1F f HI 10 cab ndy loam,8 pa'cant rfo y ` 1 11 4s I r pt 'r Existing Conditions i i i r�I/ • / / \ �\ \\' J�f d'id .� �`�d ••may y � / 2 / 441 Val to" ` WO OV ---' j4C. 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