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Stormwater Management report Stormwater Management Report for the proposed CWI Exit/Ramp Addition 37 Everts Ave, Queensbury, NY 12804 Warren County, New York Prepared For. Community, Work, & Independence Inc 37 Everts Ave Queensbury, NY 12804 Prepared By: VISION Engineering, LLC 206 Glen Street Suite 56 Glens Falls, New York 12801 June 15, 2018 Storm Water Management Report CWI - 37 Everts Ave, Qby ATTACHMENTS Drainage Design Summary NRCS Soil Information HydroCAD Hydrologic Models a. Post Development 100-Year Storm Event Calculations Storm Water Management Report CWI - 37 Everts Ave, Qby Section 1.0 1.1 Project Description The Applicant proposes to construct a small 348 square foot exit/ramp addition in the south-east corner of the existing developed parcel consisting of 4.73 acres of land located in Queensbury. The site is situated in a commercial light industrial development zone and lies south of the Duke Concrete Industrial Park on the west side of Everts Avenue. The existing parcel consists of developed land with approximately 38,398 square feet of building footprint and 69,145 square feet of impervious pavements. The developed portion of the parcel is surrounded by various landscaped/lawn areas with various forest/natural vegetation fringes. The periphery of the parcel is bound by commercial and residential properties, with exception of the west property line which parallels the Warren County Bikeway. The parcel will be accessed from an entrance drive on Everts Avenue via an easement. The project is zoning compliant and includes; an approximately 348 square foot exit/ramp addition, removal of four parking spaces and associated asphalt, and construction of sidewalk, landscaping, and storm water management features for the addition. 1.2 Purpose The purpose of this stormwater management report is to demonstrate stormwater compliance with the Town of Queensbury Stormwater Regulations and, when required, New York State Department of Environmental Conservation (NYSDEC) stormwater management requirements for coverage under NYSDEC SPDES General Permit for Stormwater Discharges from Construction Activity Permit No. GP-0-15-002 for the project site. This report provides the calculations and results of the drainage analysis for the proposed development demonstrating compliance with stormwater regulations applicable to the project with mitigation of runoff required for the newly created impervious areas proposed on the project site. Regarding the NYSDEC regulations applicable to land development activity, projects which plan land disturbance of an area greater than one acre, require coverage under the general permit which requires the preparation of a SWPPP and calculations for both runoff water quantity and quality. Since the project area (exit/ramp addition) is a mere 348 sf and will only disturb approximately 1500 square feet of land area, these permit coverage requirements and regulations do not apply. The applicable regulations for the local municipality regarding stormwater management are contained within Chapter 147 of the Town code and apply when projects propose to add or increase the impervious surfaces on the site. This allows for mitigation and management of the resulting runoff. Standard practice for site engineering typically includes analysis of runoff and proposed stormwater management systems to assess the 10-25 year storm events for device sizing and verification that the 100-year storm event can be fully attenuated safely without causing local flooding. Since this project is of such a small magnitude (relative to runoff Storm Water Management Report CWI - 37 Everts Ave, Qby concern) and results in a net reduction of impervious surfaces on the site, we propose to address stormwater management from a simplified approach. This results in the design of the planned stormwater management system from a more conservative methodology than required by the Town standards and ensures the 100-year storm event is fully attenuated on site for the proposed building addition. 1.3 Analysis Methodology This study was prepared using the Soil Conservation Service/National Resource Conservation Service's (SCS/NRCS) Method as contained in the USDA Soil Conservation Service Publication TR-55 "Urban Hydrology for Small Watersheds". The TR-55 method outlines procedures for calculating peak rates of runoff resulting from precipitation events to developing runoff hydrographs. The TR-55 procedure simulates a watershed using the drainage area, curve number (CN), and time of concentration (Tc) for each watershed or sub-area within the overall analysis area. The curve number is a land sensitive coefficient that dictates the relationship between total rainfall depth and direct storm runoff. Site data indicates well drained loamy sand soils exist on site (see soil data attached). Hydrologic curve numbers (CN) used to determine the runoff characteristics were assumed to be hydrologic soil group C soil type, with a CN of 98 for impervious surfaces to include pavements and buildings contributing to each planned stormwater device, and a CN of 39 for areas designated to be landscaped or lawn. The time of concentration is defined as the time for runoff to travel from the hydraulically most distant point of the watershed to a point of interest. Times of concentration (Tc) paths determined for post development subareas were used to compute the peak discharge from each area. As a result of the Tc analysis for each sub-area a minimum Tc of 6 minutes was used in the analysis as a result of the small project size. Sub- catchment areas CN numbers and Tc paths used for the project analysis are defined in the HydroCad Storm Water Modeling reports included in this report, when appropriate. A grading information is provided in the site design drawings which provides for adequate on- site collection and control of roof runoff. The site will be developed to ensure runoff within the planned project limits remain on site for proper control and mitigation without detriment to neighboring properties. Site testing was conducted to confirm the subgrade soils and in order to verify runoff management methods are suitable for use on the project site. Based upon site testing the subgrade consists of loamy sand with layers or areas of silt loam present in lower depths and elevations. This is further validated by information contained in the NRCS Saratoga County Soil Survey which maps the soils for this location as Raynham silt loam and Wareham loamy sands. Each of these soil categories is poorly drained with shallow groundwater likely present within 1-2 feet below grade if not at the surface. A test hole was completed to a depth of approximately four feet below grade using an auger and confirmed a groundwater depth of 42- inches below the finished grade in the vicinity of the planned building addition (due to the presence of fill). An infiltration test was also conducted (in native soil beneath existing fill material) to determine the capacity of the existing site soils for design purposes. The field Storm Water Management Report CWI - 37 Everts Ave, Qby verified infiltrative capacity near the bottom of proposed infiltration/storage devices was determined to be approximately 24 inches per hour. Due to the small size and nature of the project, the analysis was limited to confirming the suitability of the planned stormwater device to fully attenuate the 100-year design storm event without surface flooding or allowing runoff to discharge off-site. The building addition roof runoff will be directly conveyed to a storage device consisting of a subsurface stone basin. Since the asphalt parking area will be reduced to accommodate the addition, the existing onsite drainage system will continue to mitigate surface runoff from the developed property. With the planned stormwater management system for the addition capable of handling the 100-year storm event it is compliant with Town regulations regarding mitigation of runoff volumes and rates using the simplified procedure applied, and there would be no need to further evaluate the storm water management system. Stormwater calculations assessing the stormwater management system analytically for post-development runoff volumes and rates were performed utilizing SCS TR-20 and TR-55 methodology incorporated into HydroCad Storm Water Modeling Software for Type II storm events. The Type II rainfall amount used for the 100-year 24 hour storm duration was 6.0- inches of rainfall. 1.4 Analysis Results The building roof runoff is considered "clean" and can be directly conveyed to and stored/infiltrated into the subsurface. The runoff produced from the proposed 348 sf building addition is conveyed via a roof scupper to a subsurface stone storage and infiltration basin. This results in 100% mitigation of the roof runoff for the addition, for all storm events up through and including the 100-year design storm event, being captured, stored, and conveyed to the proposed storage/infiltration device without flooding or overflowing. The stone storage and infiltration basin was designed as follows; - the bottom of the device is a minimum two feet separation from groundwater - a verified soil infiltration rate of 24-inches per hour was utilized in the calculations - the stone basin consists of 40% voids - the basin utilizes an overflow/channel conveyed to an existing detention area to accommodate extreme conditions 1.5 Operations and Maintenance Plan To ensure continuous and effective operation of the Stormwater Management practices, scheduled inspections and maintenance of the implemented practices will be required periodically by the project Owner. These requirements are outlined on site plan drawings/details. Section 2.0 Erosion and Sediment Control Practices 2.1 Erosion and sediment control practices are proposed to be implemented for the project and are shown on the site plans. Details have been provided for various erosion and sediment Storm Water Management Report CWI - 37 Everts Ave, Qby control practices, and the site operator is responsible to ensure their proper installation and implementation. The following temporary erosion and sediment measures will be utilized for this site: Sediment Control Fence: Silt fence shall be used to control erosion from sheet flow on slopes not to exceed 3 on 1. 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 10 days or longer will be seeded with a ryegrass mixture and mulched to stabilize soil until construction resumes. Stabilized Construction Entrance: Entrance roads will be protected by installation of a crushed stone blanket for cleaning construction vehicle wheels. Blankets shall be placed at any intersection of a construction road with a paved or publicly owned road. Stabilized construction entrances shall be installed as necessary. Stockpiles: Soil stockpiles shall be placed in a convenient and designated location to prevent interference with ongoing site operations. Stockpiles shall be protected with surrounding silt fence to prevent migration of stockpiled materials. When materials are deemed unusable or stockpiles contain more material than is needed for the site work proposed, excess and unusable material shall be removed off site and legally disposed of. 2.2 The Contractor shall inspect the sediment control fence, construction entrance, inlet protection measures, and stockpiles weekly and after every rain event and remove trapped sediment and maintain the devices in good working order for the duration of site disturbance. The site operator shall inspect and evaluate the erosion and sediment control procedures at least once weekly. Deficiencies in protection measures shall be corrected, or an alternative or additional device shall be utilized, when necessary to further mitigate erosion or sedimentation of runoff. 2.3 All disturbed areas shall be final graded, topsoiled, and seeded or planted as soon as practical. Seed beds shall be mulched with straw or hydro-mulch with tackifier and plant beds shall be mulched with bark mulch. Water seeded area to promote dense establishment of ground cover. 2.4 Maintenance of stormwater management practices is integral to the continued satisfactory function of the devices to provide the required treatment and flow attenuation as designed. Sediment shall be removed once yearly or after 50 % of the total capacity of the device(s) has been lost (i.e. for catch basin sumps). Corrective measures shall be implemented immediately for deficient conditions found to exist which impact the drainage system. Site plan drawings and details provide additional maintenance requirements for each device. z z iD o 096L6Lb 096L6Lb O Z6Lb OZEEV O66L6Lb O88L6Lb 098L6Lb O Z6Lb OZ8L6Lb W (1) O N O) tb qug d tb q� tb qo� tb � y + 0 Z �• U) ¢g� • U) O > U 4 m U) Q u�i o c o Now '. z A In Ln v cn x 8 8 G- 0 g g � N O' N N ra ai � C C in o. 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