The URL can be used to link to this page

Home My WebLink AboutWPO201300050 Assessment - Environmental 2013-07-10 EROSION&SEDIMENT CONTROL NARRATIVE Stormwater Management Improvements County of Albemarle-Western Albemarle High School,Crozet Virginia PROJECT DESCRIPTION AND MS-19 This purpose of this project is to construct stormwater management improvements for the WAHS campus. These improvements include a new Bioretention Filter,new drainage utilities,and a small area of drainage channel stabilization. Approximately 0.60 acres,including on-site and off-site areas, will be disturbed during construction. The existing receiving channel is currently inadequate due to pre-existing site drainage conditions. There is no increase of impervious surfaces with this project. The proposed Storm Water Management facility will totally capture both the 10-yr and 100-yr storm volumes and release it slowly (over a 24-36 hour period) through the Biofilter under-drain system. The Biofilter will reduce the peak storm volumes in the existing drainage channel and reduce erosion. EXISTING SITE CONDITIONS The topographic and existing conditions on the site are depicted on the accompanying plans. The site currently consists of grass and wooded open spaces. A storage trailer will be removed. ADJACENT AREAS The project area is located behind the School and adjacent to the driver's education course. The site does not directly abut any adjacent properties. OFF-SITE AREAS No off-site areas are anticipated or shown on the plans. SOILS No soil testing was performed nor was a soils report prepared for this project. CRITICAL AREAS There are no critical areas on site. EROSION AND SEDIMENT CONTROL MEASURES The contractor shall provide,construct and maintain erosion and sediment control measures as shown on the Erosion Control Plan and in accordance with the Virginia Department of Transportation,and the County of Albemarle. All vegetative and structural erosion and sediment control practices shall be constructed and maintained according to the minimum standards and specifications of the Virginia Erosion and Sediment Control Handbook. Permanent or temporary soil stabilization shall be applied to denuded areas within seven(7) days after final grade is reached on any portion of the site. Temporary soil stabilization shall be applied within seven (7) days to denuded areas that may not be at final grade but will remain dormant (undisturbed) for longer than 30 days. Permanent stabilization shall be applied to areas that are to be left dormant for more than one year. Soil stabilization refers to measures that protect soil from the erosive forces of raindrop impact and flowing water. Applicable practices include vegetative establishment,mulching,and the early application of gravel base on areas to be stone. Soil stabilization measures should be selected to be appropriate for the time of the year, site conditions,and estimated duration of use. Sediment basins ANHOLD ASSOCIATES August 12, 2013 1 EROSION&SEDIMENT CONTROL NARRATIVE Stormwater Management Improvements County of Albemarle-Western Albemarle High School,Crozet Virginia and traps,perimeter dikes,sediment barriers and other measures intended to retain sediment shall be constructed as a first step in any land-disturbing activity and be make functional before up slope land disturbance takes place. Stabilization measures shall be applied to any earthen structures such as dams, dikes and diversions immediately after installation. The following structural practices will be implemented according to the requirements set forth by the Virginia Erosion and Sediment Control Manual. a) Temporary Stone Construction Entrance (3.02) -Due to the small areas and accessibility issues,the existing entrance road is proposed as the construction entrance.Where construction vehicle access routes intersect paved public roads or paved private access areas,provisions shall be made to minimize the transport of sediment by vehicular tracking onto the paved surface. Where sediment is transported onto an adjacent private or public road surface,the road shall be cleaned thoroughly. Sediment shall be removed from the roads by shoveling or sweeping and transported to a sediment control disposal area. Street washing shall be allowed only after sediment is removed in this manner. b) Silt Fence (3.05) -A temporary sediment barrier constructed of posts,filter fabric and in some cases,a wire support fence,placed across or at the toe of a slope or in a minor drainage way to intercept and detain sediment and decrease flow velocities from drainage areas of limited size; applicable where sheet and rill erosion or small concentrated flows may be a problem. Maximum effective life is six(6) months. c) Outlet Protection(3.18) structurally lined aprons or other acceptable energy dissipating devices placed at the outlets of pipes or paved channel sections. To prevent scour at stormwater outlets,to protect the outlet structure,and to minimize the potential for downstream erosion by reducing the velocity and energy of concentrated stormwater flows. d) Stormwater Conveyance Channel (3.17)-A permanent, designed waterway,shaped, sized, and lined with appropriate vegetation or structural material used to safely convey Stormwater runoff within or away from developing areas. e) Topsoiling(3.30) -Methods of preserving and using the surface layer of undisturbed soil, often enriched in organic matter,in order to obtain a more desirable planting and growth medium. f) Temporary Seeding (3.31) -Establishment of temporary vegetative cover by planting rapidly growing annual plant seed on rough-graded areas. g) Permanent Seeding(3.32) -The establishment of perennial vegetative cover on disturbed areas by planting seed. h) Tree Preservation&Protection(3.38) Protection of desirable trees from mechanical and other injury during land disturbing and construction activity. ANHOLD ASSOCIATES August 12,2013 2 EROSION&SEDIMENT CONTROL NARRATIVE Stormwater Management Improvements County of Albemarle-Western Albemarle High School,Crozet Virginia PERMANENT STABILIZATION All areas disturbed by construction will be stabilized with permanent sodding,gravel or pavement immediately following finish-grading operations. All sod will be approved by the"Virginia Crop Improvement Association", Blacksburg Virginia. Specification for fertilizer are FS 0-F-241C,Type 1 solid form;Grade A or B;recommended for grass, with one hundred (100) percent of the elements derived from organic sources of the following properties: a) Nitrogen 12.0% b) Phosphoric Acid 8.0% c) Soluble Potash 8.0% With at least fifty (50) percent of the nitrogen from a non-water soluble organic source. The following measures shall be incorporated during fertilization: a) Apply fertilizer at a rate of 1000 lbs/acre. b) Apply lime at a rate of 2000 lbs/acre. c) Apply additives after smooth raking of topsoil. d) Till fertilizer into upper two (2) inches of topsoil. e) Water as necessary to aid germination and dissipation of soil additives. STORMWATER RUNOFF CONSIDERATIONS Stormwater Water Management and BMP improvements will be prepared for this project. CALCULATIONS Stormwater Report is attached. MANAGEMENT STRATEGIES a) Construction will be sequenced so that grading operations can begin and end as quickly as possible. b) Use existing road as construction entrance. Mud and debris shall be removed from all construction vehicles and equipment before leaving the site. c) Install silt fence and curb inlet protection controls as a first step in grading per the plan. MAINTENANCE All erosion and sediment control measures must be maintained and repaired immediately to insure continued performance of their intended functions as stated in the latest edition of the Virginia Erosion&Sediment Control Handbook. In general,all erosion and sediment control measures will be checked daily and after each significant rainfall event. All seeded and sodded areas will be checked regularly to ensure that a good stand is maintained. Areas will be fertilized,reseeded,and re-sodded as required (See project specifications). DISPOSITION OF TEMPORARY MEASURES ANHOLD ASSOCIATES August 12,2013 3 EROSION&SEDIMENT CONTROL NARRATIVE Stormwater Management Improvements County of Albemarle-Western Albemarle High School,Crozet Virginia All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization is achieved or after the temporary measures are no longer needed unless otherwise authorized by the County Erosion Control Officer. Trapped sediment and other disturbed soil areas resulting from the disposition of temporary measures shall be permanently stabilized to prevent further erosion and sedimentation. ANHOLD ASSOCIATES August 12,2013 4