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HomeMy WebLinkAboutWPO202100068 Correspondence 2021-12-02EROSION AND SEDIMENT CONTROL NARRATIVE FOR NYSTROM DRIVEWAY November 29, 2021 LOCATION: TM 7-29A Albemarle County, Virginia OWNER: Jonathan Nystrom 12417 Grove Ave Richmond, Virginia 23220 PREPARED BY: Roudabush, Gale & Associates 999 Second Street Charlottesville, VA 22902 P: 434.977.0205 Total disturbed area = 0.94 acres �EALi '` OF G� O SSTtN E. RREENE a Lic. No. 55833 ° t0��R ll/Z�/�/ \G�c4� '"Li.SI()NAL Er Al. PROJECT DESCRIPTION: THIS PROJECT PROPOSES TO BUILD A DRIVEWAY ACCESS ACROSS TWO LIVE STREAMS WITH PREFABRICATED BRIDGES. THERE IS TO BE NO DISTURBANCE TO THE STREAM BED WITH THIS EROSION AND SEDIMENT CONTROL PLAN A2. EXISTING SITE CONDITIONS: THE CURRENT CONDITIONS OF THIS LOT CONSISTS OF APPROXIMATELY 30.57 ACRES OF VACANT LAND THAT CROSSES BUCK MOUNTAIN AND MUDDY CREEKS. APPROXIMATELY 17.60 ACRES OF THE PROPERTY IS IN THE 100-YR FLOOD PLAIN. THE DRIVEWAY WILL CROSS BOTH CREEKS AS SHOWN ON THE E&SC PLAN AND THE APPROVED FLOOD DEVELOPMENT PERMIT PROVIDED. B3. ADJACENT AREAS: THE RURAL LOT IS BOUND BY ADJACENT RURAL PROPERTIES ON THE NORTH AND EAST. THE PROPERTY IS BOUND TO THE SOUTH BY SHIFFLETTS MILL ROAD 134. SOIL DESCRIPTIONS: 17 - CRAIGSVILLE LOAM 0 TO 2 PERCENT SLOPES HYDROLOGIC SOIL GROUP A. FREQUENTLY FLOODED AND WELL DRAINED. STARTING AT SURFACE LAYER TO SUBSTRATUM, SOIL LAYERS CONSIST OF LOAM, VERY COBBLY SANDY LOAM, AND EXTREMELY COBBLY SANDY LOAM. WATER CAPACITY IS HIGH. SURFACE RUNOFF IS LOW. HAZARD OF EROSION IS MODERATE. 36D - HAYESVILLE LOAM 15 TO 25 PERCENT SLOPES HYDROLOGIC SOIL GROUP B. DEEP HILL SLOPES, SUMMITS AND CONVEX DOWN SLOPES WELL DRAINED. STARTING AT SURFACE LAYER TO SUBSTRATUM, SOIL LAYERS CONSIST OF LOAM, CLAY AND SANDY CLAY LOAM, PERMEABILITY AND WATER CAPACITY IS MODERATE. SURFACE RUNOFF IS HIGH. HAZARD OF EROSION IS MODERATE. 38C - HAYESVILL LOAM 7 TO 15 PERCENT SLOPES HYDROLOGIC SOIL GROUP B. GENTLE, HILL SLOPES, SUMMITS AND CONVEX DOWN SLOPES WELL DRAINED. STARTING AT SURFACE LAYER TO SUBSTRATUM, SOIL LAYERS CONSIST OF LOAM, CLAY LOAM AND SANDY CLAY LOAM, PERMEABILITY AND WATER CAPACITY IS MODERATE. SURFACE RUNOFF IS MEDIUM. HAZARD OF EROSION IS MODERATE. B5. CRITICAL AREAS: THE FLOODPLAIN AREA AND STREAM BANKS ARE CRITICAL AREAS. B6. EROSION AND SEDIMENT CONTROL MEASURES: UNLESS OTHERWISE INDICATED, ALL EROSION AND SEDIMENT CONTROL PRACTICES WILL BE CONSTRUCTED AND MAINTAINED ACCORDING TO THE MINIMUM STANDARDS AND SPECIFICATIONS AS SET FORTH IN THE VIRGINIA EROSION AND SEDIMENT CONTROL HANDBOOK, LATEST EDITION. THE MINIMUM STANDARDS OF THE VIRGINIA EROSION AND SEDIMENT CONTROL REGULATIONS SHALL BE ADHERED TO UNLESS OTHERWISE WAIVED OR APPROVED BY VARIANCE. TEMPORARY CONSTRUCTION ENTRANCE (CE) - 3.02 A CONSTRUCTION ENTRANCE SHALL BE PROVIDED AT THE ENTRANCE OF THE PROJECT SITE TO PROVIDE A MEANS OF REMOVING SEDIMENT FROM THE TIRES OF CONSTRUCTION VEHICLES LEAVING THE WORK SITE. THE CONTRACTOR SHALL REMOVE ANY MUD FROM THE EXISTING ROAD SURFACE BY MEANS OF SWEEPING AND SHOVELING, IN THE EVENT THE WASH AREA IS NOT ADEQUATE IN SEDIMENT REMOVAL. SEDIMENT -LADEN RUNOFF IS TO BE DIRECTED TOWARDS THE SEDIMENT BASIN. SILT FENCE (SF) - 3.05 SILT FENCING WILL BE INSTALLED AS A FIRST STEP IN CONSTRUCTION ACTIVITIES. LOCATION AND DETAILS ARE SHOWN ON THE PLANS. B7. PERMANENT AND TEMPORARY STABILIZATION: PERMANENT SEEDING - 3.32 (OPTIONAL) A PERENNIAL VEGETATIVE COVERING SHALL BE ESTABLISHED ON DISTURBED AREAS WITHIN 7 DAYS OF BEING BROUGHT TO FINAL GRADE ON AREAS NOT OTHERWISE PROTECTED. SELECTION OF THE SEED MIXTURE SHALL DEPEND ON THE TIME OF YEAR IT IS TO BE APPLIED ACCORDING TO THE PERMANENT SEED SCHEDULE AS SHOWN ON THE DRAWING. SEEDED AREAS SHALL BE LIMED WHEN NECESSARY, AT RATE OF 2 TONS PER ACRES, AND FERTILIZED AT A RATE OF 1,000 LBS. PER ACRE OF 10-20-10 (10 LBS. PER 1,000 SQUARE FEET) OR EQUIVALENT. USE A MIXTURE OF KENTUCKY 31 FESCUE (108 LBS), RED TOP GRASS (2 LBS), ANNUAL RYE (20 LBS) AND CROWN VETCH (20 LBS) OR OTHER APPROVED PERMANENT SEEDING MIXTURE IN SPECIFICATION 3.32. B8. SOIL STOCKPILES AND BORROW AREAS IT IS NOT ANTICIPATE TO BE ANY SOIL STOCKPILE OR BORROW AREAS FOR THIS PLAN. B9. OFF -SITE AREAS: ANY EXCESS MATERIAL GENERATED AS PART OF THIS PROJECT SHALL BE STORED OR SPREAD WITHIN THE APPROVED LAND DISTURBANCE AREA OR IN AN AREA APPROVED BY THE COUNTY OF ALBEMARLE COMMUNITY DEVELOPMENT DEPARTMENT. 1310. STORM WATER MANAGEMENT: Not applicable, less than 1 acre od disturbance 611. MAINTENANCE SCHEDULE: IN GENERAL, ALL EROSION AND SEDIMENT CONTROL MEASURES SHALL BE CHECKED DAILY AND AFTER EACH SIGNIFICANT RAINFALL. THE FOLLOWING ITEMS WILL BE CHECKED IN PARTICULAR: 2 THE CONSTRUCTION ENTRANCE SHALL BE CHECKED DAILY FOR SOIL BUILDUP. IF THE ENTRANCE BECOMES CLOGGED WITH SOIL AND FAILS TO PREVENT THE TRANSPORTATION OF SOIL ONTO THE ROADWAY, ADDITIONAL STONE, REPLACEMENT OF STONE, OR A WASH -RACK MAY BE REQUIRED. 3. SILT FENCE SHALL BE INSPECTED IMMEDIATELY AFTER EACH RAINFALL AND AT LEAST DAILY DURING PROLONGED RAINFALL. CLOSE ATTENTION SHALL BE PAID TO THE REPAIR OF DAMAGED SILT FENCE RESULTING FROM END RUNS AND UNDERCUTTING. SHOULD THE FABRIC ON A SILT FENCE DECOMPOSE OR BECOME INEFFECTIVE PRIOR TO THE END OF THE EXPECTED USABLE LIFE AND THE BARRIER STILL BE NECESSARY, THE FABRIC SHALL BE REPLACED PROMPTLY. SEDIMENT DEPOSITS SHOULD BE REMOVED AFTER EACH STORM EVENT. THEY MUST BE REMOVED WHEN DEPOSITS REACH APPROXIMATELY ONE-HALF THE HEIGHT OF THE BARRIER. ANY SEDIMENT DEPOSITS REMAINING IN PLACE AFTER THE SILT FENCE IS NO LONGER REQUIRED SHALL BE DRESSED TO CONFORM WITH THE EXISTING GRADE, PREPARED, AND SEEDED. 4. 4.STORMWATER CONVEYANCE CHANNELS (WHERE APPLICABLE): 4.1. GRASS LINED CHANNELS - DURING THE INITIAL ESTABLISHMENT, GRASS LINED CHANNELS SHOULD BE REPAIRED IMMEDIATELY AND RE- ESTABLISHED IF NECESSARY. AFTER GRASS HAS BECOME ESTABLISHED, THE CHANNEL SHOULD BE CHECKED PERIODICALLY TO DETERMINE IF THE GRASS IS WITHSTANDING FLOW VELOCITIES WITHOUT DAMAGE. IF THE CHANNEL IS TO BE MOWED, IT SHOULD BE DONE IN A MANNER THAT IT WILL NOT DAMAGE THE GRASS. 4.2. RIPRAP-LINED CHANNELS - RIPRAP LINED CHANNELS SHOULD BE CHECKED PERIODICALLY TO ENSURE THE SCOUR IS NOT OCCURRING BENEATH FABRIC UNDERLINING OF THE RIPRAP LAYER. THE CHANNEL SHOULD ALSO BE CHECKED TO DETERMINE THE STONES ARE NOT DISLODGED BY LARGE FLOWS. 4.3. IF SEDIMENT IS DEPOSITED IN A GRASS -LINED CHANNEL, IT SHOULD BE REMOVED PROMPTLY TO PREVENT DAMAGE TO THE GRASS. SEDIMENT DEPOSITED IN A RIPRAP CHANNEL SHOULD BE REMOVED WHEN IT REDUCES THE CAPACITY OF THE CHANNEL. 5. 5ALL SEEDED AREAS WILL BE CHECKED REGULARLY TO ENSURE THAT A GOOD STAND IS MAINTAINED. AREAS SHOULD BE FERTILIZED AND RE- SEEDED AS NEEDED. IN THE EVENT THAT THE APPLIED SEEDING FAILS TO TAKE HOLD, BLANKET MATTING SHALL BE PLACED IN APPROPRIATE AREAS DEEMED NECESSARY BY THE ENGINEER OR EROSION CONTROL A CONSTRUCTION SEQUENCE 1. PRIOR TO ANY LAND DISTURBANCE, CONTRACTOR TO HAVE SURVEYOR FLAG CLEARING LIMITS. NO CLEARING OR GRADING IS ALLOWED OUTSIDE OF LIMITS. PERMANENT SEEDING SHALL BE APPLIED TO AREAS WHERE FINAL GRADE IS REACHED. 2. INSTALL CONSTRUCTION ENTRANCE TO GAIN ACCESS TO THE SITE. INSTALL SILT FENCE, AS INDICATED ON THE PLANS, ENSURE THAT SILT FENCE IS PLACED 1 FOOT ON THE DOWNHILL SIDE OF ALL SILL AND OR ABUTMENTS SO THERE IS AS LITTLE EARTH MOVING ACTIVITIES ALONG THE STREAM BANK AS POSSIBLE. NO STREAM DISTURBANCES SHALL OCCUR WITH THIS EROSION & SEDIMENT CONTROL PLAN. 3. BUILD THE STORMWATER CONVEYANCE CHANNEL AS SHOWN ON SHEET 3. 4. UPON FINAL STABILIZATION AND WITH THE APPROVAL OF THE E&SC INSPOECTOR EXTERIOR MEASURES MAY BE REMOVED. NOTE: IT SHALL BE THE CONTRACTOR OR OWNERS' RESPONSIBILITY TO ADHERE TO REQUESTS FROM THE COUNTY'S E&S INSPECTOR TO ADD OR MODIFY E&S MEASURES DURING CONSTRUCTION. B. MINIMUM STANDARDS (MS): 1. PERMANENT OR TEMPORARY SOIL STABILIZATION SHALL BE APPLIED TO DENUDED AREAS WITHIN SEVEN DAYS AFTER FINAL GRADE IS REACHED ON ANY PORTION OF THE SITE. TEMPORARY SOIL STABILIZATION SHALL BE APPLIED WITHIN SEVEN DAYS TO DENUDED AREAS THAT MAY NOT BE AT FINAL GRADE BUT WILL REMAIN DORMANT FOR LONGER THAN 14 DAYS. PERMANENT STABILIZATION SHALL BE APPLIED TO AREAS THAT ARE TO BE LEFT DORMANT FOR MORE THAN ONE YEAR. 2. DURING CONSTRUCTION OF THE PROJECT, SOIL STOCK PILES AND BORROW AREAS SHALL BE STABILIZED OR PROTECTED WITH SEDIMENT TRAPPING MEASURES. THE APPLICANT IS RESPONSIBLE FOR THE TEMPORARY PROTECTION AND PERMANENT STABILIZATION OF ALL SOIL STOCKPILES ON SITE AS WELL AS BORROW AREAS AND SOIL INTENTIONALLY TRANSPORTED FROM THE PROJECT SITE. 3. A PERMANENT VEGETATIVE COVER SHALL BE ESTABLISHED ON DENUDED AREAS NOT OTHERWISE PERMANENTLY STABILIZED. PERMANENT VEGETATION SHALL NOT BE CONSIDERED ESTABLISHED UNTIL A GROUND COVER IS ACHIEVED THAT IS UNIFORM, MATURE ENOUGH TO SURVIVE AND WILL INHIBIT EROSION. 4. SEDIMENT BASINS AND TRAPS, PERIMETER DIKES, SEDIMENT BARRIERS AND OTHER MEASURES INTENDED TO TRAP SEDIMENT SHALL BE CONSTRUCTED AS A FIRST STEP IN ANY LAND -DISTURBING ACTIVITY AND SHALL BE MADE FUNCTIONAL BEFORE UPSLOPE LAND DISTURBANCE TAKES PLACE. 5. STABILIZATION MEASURES SHALL BE APPLIED TO EARTHEN STRUCTURES SUCH AS DAMS, DIKES AND DIVERSIONS IMMEDIATELY AFTER INSTALLATION. 6. SEDIMENT TRAPS AND SEDIMENT BASINS SHALL BE DESIGNED AND CONSTRUCTED BASED UPON THE TOTAL DRAINAGE AREA TO BE SERVED BY THE TRAP OR BASIN. A. THE MINIMUM STORAGE CAPACITY OF A SEDIMENT TRAP SHALL BE 134 CUBIC YARDS PER ACRE OF DRAINAGE AREA AND THE TRAP SHALL ONLY CONTROL DRAINAGE AREAS LESS THAN THREE ACRES. B. SURFACE RUNOFF FROM DISTURBED AREAS THAT IS COMPRISED OF FLOW FROM DRAINAGE AREAS GREATER THAN OR EQUAL TO THREE ACRES SHALL BE CONTROLLED BY A SEDIMENT BASIN. THE MINIMUM STORAGE CAPACITY OF A SEDIMENT BASIN SHALL BE 134 CUBIC YARDS PER ACRE OF DRAINAGE AREA. THE OUTFALL SYSTEM SHALL, AT A MINIMUM, MAINTAIN THE STRUCTURAL INTEGRITY OF THE BASIN DURING A 25-YEAR STORM OF 24- HOUR DURATION. RUNOFF COEFFICIENTS USED IN RUNOFF CALCULATIONS SHALL CORRESPOND TO A BARE EARTH CONDITION OR THOSE CONDITIONS EXPECTED TO EXIST WHILE THE SEDIMENT BASIN IS UTILIZED. 7. CUT AND FILL SLOPES SHALL BE DESIGNED AND CONSTRUCTED IN A MANNER THAT WILL MINIMIZE EROSION. SLOPES THAT ARE FOUND TO BE ERODING EXCESSIVELY WITHIN ONE YEAR OF PERMANENT STABILIZATION SHALL BE PROVIDED WITH ADDITIONAL SLOPE STABILIZING MEASURES UNTIL THE PROBLEM IS CORRECTED. 8. CONCENTRATED RUNOFF SHALL NOT FLOW DOWN CUT OR FILL SLOPES UNLESS CONTAINED WITHIN AN ADEQUATE TEMPORARY OR PERMANENT CHANNEL, FLUME OR SLOPE DRAIN STRUCTURE. 9. WHENEVER WATER SEEPS FROM A SLOPE FACE, ADEQUATE DRAINAGE OR OTHER PROTECTION SHALL BE PROVIDED. 10. ALL STORM SEWER INLETS THAT ARE MADE OPERABLE DURING CONSTRUCTION SHALL BE PROTECTED SO THAT SEDIMENT -LADEN WATER CANNOT ENTER THE CONVEYANCE SYSTEM WITHOUT FIRST BEING FILTERED OR OTHERWISE TREATED TO REMOVE SEDIMENT. 11. BEFORE NEWLY CONSTRUCTED STORMWATER CONVEYANCE CHANNELS OR PIPES ARE MADE OPERATIONAL, ADEQUATE OUTLET PROTECTION AND ANY REQUIRED TEMPORARY OR PERMANENT CHANNEL LINING SHALL BE INSTALLED IN BOTH THE CONVEYANCE CHANNEL AND RECEIVING CHANNEL. 12. WHEN WORK IN A LIVE WATERCOURSE IS PERFORMED, PRECAUTIONS SHALL BE TAKEN TO MINIMIZE ENCROACHMENT, CONTROL SEDIMENT TRANSPORT AND STABILIZE THE WORK AREA TO THE GREATEST EXTENT POSSIBLE DURING CONSTRUCTION. NONERODIBLE MATERIAL SHALL BE USED FOR THE CONSTRUCTION OF CAUSEWAYS AND COFFERDAMS. EARTHEN FILL MAY BE USED FOR THESE STRUCTURES IF ARMORED BY NONERODIBLE COVER MATERIALS. 13. WHEN A LIVE WATERCOURSE MUST BE CROSSED BY CONSTRUCTION VEHICLES MORE THAN TWICE IN ANY SIX-MONTH PERIOD, A TEMPORARY VEHICULAR STREAM CROSSING CONSTRUCTED OF NONERODIBLE MATERIAL SHALL BE PROVIDED. 14. ALL APPLICABLE FEDERAL, STATE AND LOCAL REQUIREMENTS PERTAINING TO WORKING IN OR CROSSING LIVE WATERCOURSES SHALL BE MET. 15. THE BED AND BANKS OF A WATERCOURSE SHALL BE STABILIZED IMMEDIATELY AFTER WORK IN THE WATERCOURSE IS COMPLETED. 16. UNDERGROUND UTILITY LINES SHALL BE INSTALLED IN ACCORDANCE WITH THE FOLLOWING STANDARDS IN ADDITION TO OTHER APPLICABLE CRITERIA: A. NO MORE THAN 500 LINEAR FEET OF TRENCH MAY BE OPENED AT ONE TIME. B. EXCAVATED MATERIAL SHALL BE PLACED ON THE UPHILL SIDE OF TRENCHES. C. EFFLUENT FROM DEWATERING OPERATIONS SHALL BE FILTERED OR PASSED THROUGH AN APPROVED SEDIMENT TRAPPING DEVICE, OR BOTH, AND DISCHARGED IN A MANNER THAT DOES NOT ADVERSELY AFFECT FLOWING STREAMS OR OFF -SITE PROPERTY. D. MATERIAL USED FOR BACKFILLING TRENCHES SHALL BE PROPERLY COMPACTED IN ORDER TO MINIMIZE EROSION AND PROMOTE STABILIZATION. E. RESTABILIZATION SHALL BE ACCOMPLISHED IN ACCORDANCE WITH THIS CHAPTER. F. APPLICABLE SAFETY REQUIREMENTS SHALL BE COMPLIED WITH, 17. WHERE CONSTRUCTION VEHICLE ACCESS ROUTES INTERSECT PAVED OR PUBLIC ROADS, PROVISIONS SHALL BE MADE TO MINIMIZE THE TRANSPORT OF SEDIMENT BY VEHICULAR TRACKING ONTO THE PAVED SURFACE. WHERE SEDIMENT IS TRANSPORTED ONTO A PAVED OR PUBLIC ROAD SURFACE, THE ROAD SURFACE SHALL BE CLEANED THOROUGHLY AT THE END OF EACH DAY. 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. THIS PROVISION SHALL APPLY TO INDIVIDUAL DEVELOPMENT LOTS AS WELL AS TO LARGER LAND -DISTURBING ACTIVITIES. 18. ALL TEMPORARY EROSION AND SEDIMENT CONTROL MEASURES SHALL BE REMOVED WITHIN 30 DAYS AFTER FINAL SITE STABILIZATION OR AFTER THE TEMPORARY MEASURES ARE NO LONGER NEEDED, UNLESS OTHERWISE AUTHORIZED BY THE VESCP AUTHORITY. TRAPPED SEDIMENT AND THE DISTURBED SOIL AREAS RESULTING FROM THE DISPOSITION OF TEMPORARY MEASURES SHALL BE PERMANENTLY STABILIZED TO PREVENT FURTHER EROSION AND SEDIMENTATION. 19. PROPERTIES AND WATERWAYS DOWNSTREAM FROM DEVELOPMENT SITES SHALL BE PROTECTED FROM SEDIMENT DEPOSITION, EROSION AND DAMAGE DUE TO INCREASES IN VOLUME, VELOCITY AND PEAK FLOW RATE OF STORMWATER RUNOFF FOR THE STATED FREQUENCY STORM OF 24-HOUR DURATION IN ACCORDANCE WITH THE FOLLOWING STANDARDS AND CRITERIA. STREAM RESTORATION AND RELOCATION PROJECTS THAT INCORPORATE NATURAL CHANNEL DESIGN CONCEPTS ARE NOT MAN-MADE CHANNELS AND SHALL BE EXEMPT FROM ANY FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS FOR NATURAL OR MAN-MADE CHANNELS: A. CONCENTRATED STORMWATER RUNOFF LEAVING A DEVELOPMENT SITE SHALL BE DISCHARGED DIRECTLY INTO AN ADEQUATE NATURAL OR MAN- MADE RECEIVING CHANNEL, PIPE OR STORM SEWER SYSTEM. FOR THOSE SITES WHERE RUNOFF IS DISCHARGED INTO A PIPE OR PIPE SYSTEM, DOWNSTREAM STABILITY ANALYSES AT THE OUTFALL OF THE PIPE OR PIPE SYSTEM SHALL BE PERFORMED. B. ADEQUACY OF ALL CHANNELS AND PIPES SHALL BE VERIFIED IN THE FOLLOWING MANNER: (1) THE APPLICANT SHALL DEMONSTRATE THAT THE TOTAL DRAINAGE AREA TO THE POINT OF ANALYSIS WITHIN THE CHANNEL IS 100 TIMES GREATER THAN THE CONTRIBUTING DRAINAGE AREA OF THE PROJECT IN QUESTION, OR (2) (A) NATURAL CHANNELS SHALL BE ANALYZED BY THE USE OF A TWO-YEAR STORM TO VERIFY THAT STORMWATER WILL NOT OVERTOP CHANNEL BANKS NOR CAUSE EROSION OF CHANNEL BED OR BANKS: (B) ALL PREVIOUSLY CONSTRUCTED MAN-MADE CHANNELS SHALL BE ANALYZED BY THE USE OF A 10-YEAR STORM TO VERIFY THAT STORMWATER WILL NOT OVERTOP ITS BANKS AND BY THE USE OF A TWO-YEAR STORM TO DEMONSTRATE THAT STORMWATER WILL NOT CAUSE EROSION OF CHANNEL BED OR BANKS; AND (C) PIPES AND STORM SEWER SYSTEMS SHALL BE ANALYZED BY THE USE OF A 10-YEAR STORM TO VERIFY THAT STORMWATER WILL BE CONTAINED WITHIN THE PIPE OR SYSTEM. C. IF EXISTING NATURAL RECEIVING CHANNELS OR PREVIOUSLY CONSTRUCTED MAN-MADE CHANNELS OR PIPES ARE NOT ADEQUATE, THE APPLICANT SHALL: (1) IMPROVE THE CHANNELS TO A CONDITION WHERE A 10-YEAR STORM WILL NOT OVERTOP THE BANKS AND A TWO-YEAR STORM WILL NOT CAUSE EROSION TO THE CHANNEL, THE BED, OR THE BANKS, (2) IMPROVE THE PIPE OR PIPE SYSTEM TO A CONDITION WHERE THE 10-YEAR STORM IS CONTAINED WITHIN THE APPURTENANCES, (3) DEVELOP A SITE DESIGN THAT WILL NOT CAUSE THE PRE -DEVELOPMENT PEAK RUNOFF RATE FROM A TWO-YEAR STORM TO INCREASE WHEN RUNOFF OUTFALLS INTO A NATURAL CHANNEL OR WILL NOT CAUSE THE PRE - DEVELOPMENT PEAK RUNOFF RATE FROM A 10-YEAR STORM TO INCREASE WHEN RUNOFF OUTFALLS INTO A MAN-MADE CHANNEL, OR (4) PROVIDE A COMBINATION OF CHANNEL IMPROVEMENT, STORMWATER DETENTION OR OTHER MEASURES WHICH IS SATISFACTORY TO THE VESCP AUTHORITY TO PREVENT DOWNSTREAM EROSION. 7 D. THE APPLICANT SHALL PROVIDE EVIDENCE OF PERMISSION TO MAKE THE IMPROVEMENTS. E. ALL HYDROLOGIC ANALYSES SHALL BE BASED ON THE EXISTING WATERSHED CHARACTERISTICS AND THE ULTIMATE DEVELOPMENT CONDITION OF THE SUBJECT PROJECT. F. IF THE APPLICANT CHOOSES AN OPTION THAT INCLUDES STORMWATER DETENTION, HE SHALL OBTAIN APPROVAL FROM THE VESCP OF A PLAN FOR MAINTENANCE OF THE DETENTION FACILITIES. THE PLAN SHALL SET FORTH THE MAINTENANCE REQUIREMENTS OF THE FACILITY AND THE PERSON RESPONSIBLE FOR PERFORMING THE MAINTENANCE. G. OUTFALL FROM A DETENTION FACILITY SHALL BE DISCHARGED TO A RECEIVING CHANNEL, AND ENERGY DISSIPATORS SHALL BE PLACED AT THE OUTFALL OF ALL DETENTION FACILITIES AS NECESSARY TO PROVIDE A STABILIZED TRANSITION FROM THE FACILITY TO THE RECEIVING CHANNEL. H. ALL ON -SITE CHANNELS MUST BE VERIFIED TO BE ADEQUATE. I. INCREASED VOLUMES OF SHEET FLOWS THAT MAY CAUSE EROSION OR SEDIMENTATION ON ADJACENT PROPERTY SHALL BE DIVERTED TO A STABLE OUTLET, ADEQUATE CHANNEL, PIPE OR PIPE SYSTEM, OR TO A DETENTION FACILITY. J. IN APPLYING THESE STORMWATER MANAGEMENT CRITERIA, INDIVIDUAL LOTS OR PARCELS IN A RESIDENTIAL, COMMERCIAL OR INDUSTRIAL DEVELOPMENT SHALL NOT BE CONSIDERED TO BE SEPARATE DEVELOPMENT PROJECTS. INSTEAD, THE DEVELOPMENT, AS A WHOLE, SHALL BE CONSIDERED TO BE A SINGLE DEVELOPMENT PROJECT. HYDROLOGIC PARAMETERS THAT REFLECT THE ULTIMATE DEVELOPMENT CONDITION SHALL BE USED IN ALL ENGINEERING CALCULATIONS. K. ALL MEASURES USED TO PROTECT PROPERTIES AND WATERWAYS SHALL BE EMPLOYED IN A MANNER WHICH MINIMIZES IMPACTS ON THE PHYSICAL, CHEMICAL AND BIOLOGICAL INTEGRITY OF RIVERS, STREAMS AND OTHER WATERS OF THE STATE. L. ANY PLAN APPROVED PRIOR TO JULY 1, 2014, THAT PROVIDES FOR STORMWATER MANAGEMENT THAT ADDRESSES ANY FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS FOR NATURAL OR MAN-MADE CHANNELS SHALL SATISFY THE FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS FOR NATURAL OR MAN-MADE CHANNELS IF THE PRACTICES ARE DESIGNED TO (1) DETAIN THE WATER QUALITY VOLUME AND TO RELEASE IT OVER 48 HOURS; (II) DETAIN AND RELEASE OVER A 24-HOUR PERIOD THE EXPECTED RAINFALL RESULTING FROM THE ONE YEAR, 24-HOUR STORM; AND (III) REDUCE THE ALLOWABLE PEAK FLOW RATE RESULTING FROM THE 1.5, 2, AND 10-YEAR, 24- HOUR STORMS TO A LEVEL THAT IS LESS THAN OR EQUAL TO THE PEAK FLOW RATE FROM THE SITE ASSUMING IT WAS IN A GOOD FORESTED CONDITION, ACHIEVED THROUGH MULTIPLICATION OF THE FORESTED PEAK FLOW RATE BY A REDUCTION FACTOR THAT IS EQUAL TO THE RUNOFF VOLUME FROM THE SITE WHEN IT WAS IN A GOOD FORESTED CONDITION DIVIDED BY THE RUNOFF VOLUME FROM THE SITE IN ITS PROPOSED CONDITION, AND SHALL BE EXEMPT FROM ANY FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS FOR NATURAL OR MAN-MADE CHANNELS AS DEFINED IN ANY REGULATIONS PROMULGATED PURSUANT TO § 62.1-44.15:54 OR 62.1-44.15:65 OF THE ACT. M. FOR PLANS APPROVED ON AND AFTER JULY 1, 2014, THE FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS OF § 62.1-44.15:52 A OF THE ACT AND THIS SUBSECTION SHALL BE SATISFIED BY COMPLIANCE WITH WATER QUANTITY REQUIREMENTS IN THE STORMWATER MANAGEMENT ACT (§ 62.1- 44.15:24 ET SEQ. OF THE CODE OF VIRGINIA) AND ATTENDANT REGULATIONS, UNLESS SUCH LAND -DISTURBING ACTIVITIES (1) ARE IN ACCORDANCE WITH PROVISIONS FOR TIME LIMITS ON APPLICABILITY OF APPROVED DESIGN CRITERIA IN 9VAC25-870-47 OR GRANDFATHERING IN 9VAC25-870-48 OF THE VIRGINIA STORMWATER MANAGEMENT PROGRAM (VSMP) REGULATION, IN WHICH CASE THE FLOW RATE CAPACITY AND VELOCITY REQUIREMENTS OF § 62.1-44.15:52 A OF THE ACT SHALL APPLY, OR (II) ARE EXEMPT PURSUANT TO § 62.1-44.15:34 C 7 OF THE ACT. N. COMPLIANCE WITH THE WATER QUANTITY MINIMUM STANDARDS SET OUT IN 9VAC25-870-66 OF THE VIRGINIA STORMWATER MANAGEMENT PROGRAM (VSMP) REGULATION SHALL BE DEEMED TO SATISFY THE REQUIREMENTS OF THIS SUBDIVISION 19.