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Home My WebLink AboutSW8041111_COMPLIANCE_20091013STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. swq g �r DOC TYPE ❑ CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE YYYYMMDD Compliance Inspection Report Permit: SW8041111 Effective: 11/24/04 Expiration: 11/24/14 Owner: Willa Properties, Inc_ Project: Lake Brewster County: New Hanover 501 Vallie Ln Region: Wilmington Wilmington NC 28405 Contact Person: Ardieth Lupton Title: Phone: 919-880-7630 Directions to Project: Type of Project: State Stormwater - HD - Detention Pond Drain Areas: 1 - (Mott Creek (Todds Creek)) (03-06-17) ( C;Sw) On -Site Representative(s): Related Permits: Inspection Dater 1011312009 Entry Time: 12:45 PM Exit Time: 01:30 PM Primary Inspector: Angela K Hammers Phone: 919-796-7215 Ext.7317 Secondary Inspector(s): Reason for Inspection: Follow-up Inspection Type: Complaint Permit Inspection Type: State Stormwater Facility Status: 0 Compliant ® Not Compliant Question Areas: ® State Stormwater (See attachment summary) Page: 1 Permit: SW8041111 Owner - Project: Willa Properties, Inc. Inspection Date: 1011312009 Inspection Type: Complaint Reason for Visit: Follow-up Inspection Summary: Please submit the changes to the stormwater permit in regards to the addition of the ditch to the stormwater system and submit pond calculations to DWQ. Additionally, please verify the depth of the forebay. Thank you for your efforts. If you have questions, please contact DWQ at 910-796-7215. Operation and Maintenance Yes No NA NE Are the 5W measures being maintained and operated as per the permit requirements? ■ ❑ ❑ ❑ Are the SW BMP inspection and maintenance records complete and available for review or provided to DWQ ❑ ❑ ❑ ■ upon request? Comment: The vegetative maintenance of the ditch and pond are acceptable. Other Permit Conditions Yes No NA NE Is the site compliant with other conditions of the permit? Comment: The changes to the currently approved stormwater permit have not yet been received by DWQ regarding the pond calculations and addition of the ditch to the stormwater system. Other WO Issues Is the site compliant with other water quality issues as noted during the inspection? Comment: Access to the outlet structure and forebay have been created. ®❑ ❑ ❑ Page: 2 Compliance Inspection Report Permit: SW8041111 Effective: 11/24/04 Expiration: 11/24/14 Owner: Willa Properties. Inc. Project: Lake Brewster County: New Hanover 501 Vailie Ln Region: Wilmington Wilmington NC 28405 Contact Person: Ardieth Lupton Title: Phone: 919-880-7630 Directions to Project: Type of Project: State Stormwater - HD - Detention Pond Drain Areas: 1 - (Mott Creek (Todds Creek)) (03-06-17) ( C;Sw) On -Site Representative(s): Related Permits: Inspection Date: 06/19/2009 Entry Time: 09:45 AM Primary Inspector: Angela K Hammers Secondary Inspector(s): Reason for Inspection: Complaint Permit Inspection Type: State Stormwater Facility Status: ❑ Compliant ® Not Compliant Question Areas: ■ State Stormwater (See attachment summary) Exit Time: 10A5 AM Inspection Type: Complaint Phone: 919-796-7215 Ext.7317 Page: 1 Permit: SW8041111 Owner - Project: Willa Properties, Inc. Inspection Date: 06/19/2009 Inspection Type: Complaint Inspection Summary: The following deficiency was noted during an inspection and file reveiw: Reason for Visit: Complaint 1. The drainage ditch between Lake Brewster and Sycamore Grove Subdivisions appears to be utilized by Sycamore Grove as stormwater drainage system to the pond at Lake Brewster. This is not shown on the approved plan for Lake Brewster. To bring this permit into compliance, please complete the following: 1. Submit a plan of action to modify the permit to show the drainage routed through the ditch to the Lake Brewster detention pond forebay. File Review Is the permit active? Signed copy of the Engineer's certification is in the file? Signed copy of the Operation & Maintenance Agreement is in the file? Copy of the recorded:deed restrictions is in the file? Comment: SW Measures Are the SW measures constructed as per the approved plans? Are the inlets located per the approved plans? Are the outlet structures located per the approved plans? Yes No NA NE ■ ❑ ❑ ❑ ■ ❑ 0 0 ■❑❑❑ ■ ❑ ❑ ❑ Comment: The drainage ditch between Lake Brewster and Sycamore Grove Subdivisions appears to be utilized by Sycamore Grove as stormwater drainage system to the pond at Lake Brewster. This is not shown on the approved plan for Lake Brewster. Operation and Maintenance Yes No NA NE Are the SW measures being maintained and operated as per the permit requirements? ■ ❑ fl ❑ Are the SW SMP inspection and maintenance records complete and available for review or provided to DWQ ❑ ❑ ❑ ❑ upon request? Comment: All ditches were observed at a 3:1 slope or flatter and were stable. Other Permit Conditions Yes No NA NE Is the site compliant with other conditions of the permit? n ❑ f_I Comment: Other WQ Issues Yes No NA NE Is the site compliant with other water quality issues as noted during the inspection? 171 fl ❑ ■ Comment: Page: 2 WET DETENTION POND ANALYSIS FILE NAME: PROJECT #' SW8 041111 PROJECT NAME: Lake Brewster Subdivision S\WQS\POND\041 11 1.WK1 REVIEWER: L. Lewis DATE: 16-Nov-04 Receiving Stream: Motts Creek Class: C SW Drainage Basin: Cape Fear Index No. Site Area 47.40 acres square feet Area in Acres 36.06 Drainage Area 1. 1.1:.��--5'7.08.06:...... . IMPERVIOUS AREAS Rational C 137 lots @4050 per lot 554850.00 square feet Parking/Road 187860.00 square feet SW 25560.00 square feet Future square feet square feet square feet 2 TOTAL ..7 0ilsquare feet Rational Cc= 0.10 SURFACE AREA CALCULATION % IMPERVIOUS 48.91% SA/DA Ratio 2.63% Des. Depth 6 Req. SA 41384 sf TSS: 90 Prov. SA �": 92075sf 'I VOLUME CALCULATION * place a "'I" in the box if Rational is used Rational ?* Des. Storm h inc es Rv= 0.490 Bottom 0 msl Perm. Pool .. ................... msl Design Pool 6.7 msl Storage met @elev 6.68 msl Req. Volume ........ ..cf Vol. Prov. at DP ............ . ........ .1 7. cf ORIFICE CALCULATION FOREBAY Perm. Pool Volume= 176715 Req. Forebay Volume= 35343 Provided Volume= 39750.00 Percent= Elevation 6.00 6.70 Area 92075.00 96232.00 Inc. Vol. 65907.45 Acc. Vol. 0.00 65907.45 Avg. Head = 0.27 ft Q2 Area = 21.51 sq. inches Flow Q2, cfs 0.371 cfs Q5 Area = 8.60 sq. inches Flow Q5, cfs 0.149 cfs Orifice Area 12-57 sq. inches No. of Orifices .. ... = Q 0.217 cfs Diameter, inches .. weir H x W in x PIP Drawdown days Surface Area @DP = 96232 sq.ft. Falling Head Drawdown = 4.3 days COMMENTS Surface Area , Volume and Orifice are within Design Guidelines Detention Pond Calculations Lake Brewster Detention Pond 1 Drainage Area=36.06 ac Impervious Area=17.63 ac % Impervious=49% Existing pond 10-15' deep, but use 7.5' for calculations. Pond to be 7.5' deep with 90% TSS removal; from chart SA/DA=0.015 �1 CARpj� ESSInN',V SEAL 19915 Minimum surface area required at permanent pool=(0.015)(36.06 ac)(43,560 sf/ac) = Minimum required volume: Rv 0.05 + 0.009(49)=0.49 Volume=(l'712" per ft)(0.49)(36.06 ac)(43,560 sf)=_ 44- Surface Area provided at Permanent Pool (El. 6.00)=92,075 sf (> 23,562 sf required) 64,140 cf storage required (64,140 cf/92,075 sf)=0.70' Use 0.70' Set elevation of temporary pool at 6.70 Surface area at 6.70 = 96.232 sf Volume Provided = ((92,075 sf+ 96,232 sf)/2)(0.70')=65,907 of (> 64,140 of required) Required Volume of Permanent Pool=(23,562 sf x 7.5')=176,715 of (since ex. pond larger than required) Forebay Volume Required = 0.2(176,715 cf) = 343 cf Forebay Volume Provided: Elevation (ft) Areas Inc. Vol. (cfl Total Volume (cf) 2 8,270 0 0 3 9,077 8,674 8,674 4 9,916 9,497 18,171 5 10.783 10,350 28,521 6 11,674 1 1,229 39,750 Orifice Sizing: Q2=64,140 cf / (2 days)(86,400 seconds/day) = 0.37 cfs Q5-64,140 cf / (5 days)(86,400 seconds/day) — 0.15 cfs Choose 4" orifice: Average head = (0.70'—'/z(4"112" per foot))/2=0.27' Area of orifice=0.09 ft2 (> 35,343 cf required) RECEIVED NOV 16 2004 DW PRoa # SW IYU ¢1 I 1 Q=CnA(2gh)"2 —(0.61)(0.09 sf)[(2)(32.2 fps)(0.27')]112 Q=0.023 cfs Betwcen 0.15 cfs & 0.37 cfs so drawdown between 2 & 5 days as required