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Home My WebLink AboutSW8041215_COMPLIANCE_20050124STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. SW(0412�5� DOC TYPE El CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE YYYYMMDD STORMWATER DIVISION CODING SHEET NCG PERMITS PERMIT NO. /v DOC TYPE ❑ HISTORICAL FILE ❑ MONITORING REPORTS DOC DATE ❑ YYYYMMDD Compliance Inspection Report Permit: SW8041215 Effective: 01/24/05 Expiration: Owner: Keith Andrews Builders, Inc. Project: Osprey Point Townhomes County: Pender New River Dr Region: Wilmington Surf City NC 28445 Contact Person: Keith Andrews Title: Phone: 910-791-9065 Directions to Project: From the intersection of US 17 & NC 50, east on 50 approx 5.3 miles to New River Drive (NC 210), turn left on New River Drive approx 0.8 mile, site on right. Type of Project: State Stormwater- High Density State Stormwater- Infiltration System Drain Areas: 1 - 2- 3- 4- On-Site Representative(s): Related Permits: Inspection Date: 04/0712011 Entry Time: 11:40 AM Primary Inspector: Angela K Hammers Secondary Inspector(s): Reason for Inspection: Other Permit Inspection Type: State Stormwater Facility Status: Q Compliant ■ Not Compliant Question Areas: a State Stormwater (See attachment summary) Exit Time: 12:10 PM Phone: 919-796-7215 Ext.7317 Inspection Type: Compliance Evaluation 4 Page: 1 Permit: SW8041215 Owner - Project: Keith Andrews Builders, Inc. Inspection Date: 04107/2011 Inspection Type: Compliance Evaluation Reason for Visit: Other Inspection Summary: The following deficiencies were noted during the inspection: 1. An engineers' certification of the stormwater system was not found in the file. 2. The vegetated filter and swales of the project were not observed. To bring this system into compliance, the following must be completed: 1. Submit an engineers' certification of the stormwater system to this office. 2. Verify the stormwater system is installed according to the approved plan — this can be done by the PE. (Vote: It was observed that 6 units have been constructed on New River Drive and 6 units have been constructed on Topsail Drive. File Review Yes No NA NE Is the permit active? ■ ❑ ❑ ❑ Signed copy of the Engineer's certification is in the file? ❑ 0 ❑ ❑ Signed copy of the Operation & Maintenance Agreement is in the file? ®❑ ❑ ❑ Copy of the recorded deed restrictions is in the file? ❑ ❑ ■ ❑ Comment: A copy of the engineers' certificate was not found in the DWQ file. SW Measures Yes No NA NE Are the SW measures constructed as per the approved plans? ❑ ■ ❑ ❑ Are the inlets located per the approved plans? Cl ❑ ❑ ■ Are the outlet structures located per the approved plans? Q ❑ ❑ 0 Comment: The vegetated filter on the north side of the project and the swales throughout the project were not observed. Page: 2 Swale Calculations Project: Osprey Point By: DKN Procedure: Adjust y until zav = zreq Where: Let: B = bottom width n = 0.03 y = trial depth A=By+My2 M=2.5 P = B + 2y(1+Mz 111 R=AIP z, = AR2'3 Use: n = .02 for earth lined n = .03 for mowed grass n = .05 for unwowed grass n = .013 for concrete lined Location Qio 5 zTe I B y A P R za„ VEL Vegetated Filter 1 Vegetated Filter 1 Vegetated Filter 2 3.24 3.96 3.96 0.0035 0.0035 0.0035 1.10 1.35 1.35 ## 3.5 6.5 2.5 0.47 0.38 0.60 2.17 6.00 8.54 5.74 0.36 0.33 0.42 1.10 1.35 1.35 1.49 1.40 1.64 ###### 2.82 2.41 ()i(- v1c 01c 'INFIL"i+RATION TRENCH ANALYSIS Y 1 Project # SW 8 0412151 Project Name Osprey Pt. Townhomes l Recvng Stream Intracoastal waterway Drainage Basin Cape Fear Site Area 1.7 acres Impervious Area Calculation Buildings Parking/Asphalt Concrete Total Volume/Storage Calculation Filename Date Reviewer *Classification Index # Drainage Area S:\WPDATA\WQS\INTRENCH\041215-1 06-Jan-05 P. Bartlett SA 23574 SF ✓ 0.54 Acres " outside the 575' AEC Rational Cc (list C after each BUA) 10302 1 7446 1 695 / 1 ✓V o o A43, /o Impervious_ 78.2/0 If Rational Method is used, place a 1 in this box Required Design Storm RV 1f-1'uiii e t a Stti ire Provided Pipe Diameter Length Of a Single run of Pipe Number of Pipe Runs in Trench Storage In Piping Total Storage in Piping Cross -Sectional Area Of Pipe Runs Length Of Trench Width Of Trench Height Of Trench Cross -Sectional Area Of Trench Voids Volume, 40% Trench Volume per linear foot Minimum Trench length required VT&al Volume Provided Elevation Of Bottom Of Trench Elevation Of SHWT pugrWkr'Overflow Elevation Exfiltration Rate / Drawdown Reported Hydraulic Conductivity Bottom Surface Area .. .. .. ............ iDkdd� #i:Qv tn' , ime 25 YEAR 24 HOUR STORM NIA Intensity, i = .33 inches / hour Qr-CiA= Qp through the bottom of the basin= Cc- 0.83 1.5 in 0.75 NTCF ✓ Pipe Size 1 Pipe Size 2 2 Feet 152 Feet / 3 1433 Cubic Feet € € A438 ' Cubic Feet 9.425 152 Feet 9 Feet 2.5 Feet 22.50 SF 7g5': CF Cubic Feet Feet Cubic Feet I_ :. 2228 0.15 CFS 0.1900 CFS 4.6 Mean Sea Level --" 2.6 Mean Sea Level./ 7.1 Mean Sea Level &,"" .4 0 • L_ 0.5 Cubic Feet Per Hour Per Sq Ft 1368 Square Feet €3s5€ hours Must be > Qr 10 YEAR 10 MIN HIGH INTENSITY EVENT Intensity, i = 6.3 inches / hour Volume for 10 yr. 10 min. event = 1689.48 CIF < 2228 CF a._ I`NFIL-rikATION TRENCH ANALYSIS Filename: S:IWPDATAIWQSIINTRENCH1041215-2 Project # SW8 041215-2 (�9 ' Date 06-Jan-05 Project Name Osprey Pt. Townhome� Reviewer P. Bartlett Recvng Stream Intracoastal waterway *Classification SA Drainage Basin Cape Fear Index # / Site Area 1.7 acres Drainage Area 12019 SF ✓ 0.28 Acres * outside the 575' AEC Impervious Area Calculation Rational Cc (list C after each BUA) Buildings 3777 1 Parking/Asphalt 7166 1 Concrete 300 1 Total `1143. / ✓ % Impervious= 93.5% Volume/Storage Calculation / If Rational Method is used, place a 1 in this box J Cc: 0.95 Required Design Storm 1.5 in RV 0.89 ✓ ............... ulurietoStae €i34t} CF Provided Pipe Diameter Length Of a Single run of Pipe Number of Pipe Runs in Trench Storage In Piping Total Storage in Piping Cross -Sectional Area Of Pipe Runs Length Of Trench Width Of Trench Height Of Trench Cross -Sectional Area Of Trench Voids Volume, 40% Trench Volume per linear foot Minimum Trench length required Total Volume Provided Elevation Of Bottom Of Trench Elevation Of SHWT Overflow Elevation Exfiltration Rate / Drawdown Reported Hydraulic Conductivity Bottom Surface Area 'Dri3wdow�ri�"me 25 YEAR 24 HOUR STORM N/A intensity, i = .33 inches / hour Qr=CiA= Qp through the bottom of the basin= Pipe Size 1 1 Pipe Size 2 4.6 Mean Sea Level 2.6 Mean Sea Level 7.42 Mean Sea Level 0.5 Cubic Feet Per Hour Per Sq Ft 768 Square Feet hours 0.09 CFS 0.1067 CFS Must be > Qr 10 YEAR 10 MIN HIGH INTENSITY EVENT Intensity, i = 6.3 inches / hour Volume for 10 yr. 10 min. event = 989.10 CF < 1343 CF INFILTRATION TRENCH ANALYSIS Filename: S:\WPDATA\WQS\INTRENCH\041215-3 Project # SW 8 041215-3 0 J L Date Project Name Osprey Pt. Townhomes ✓J Reviewer Recvng Stream Intracoastal waterway *Classification Drainage Basin Cape Fear Index # Site Area 1.7 acres Drainage Area outside the 575' AEC Impervious Area Calculation 06-Jan-05 P. Bartlett SA 12268 SF 0.28 Acres Rational Cc (list C after each BUA) Buildings 3777 1 Parking/Asphalt 7487 1 Concrete 342 1 Total 1'160.6 % Impervious- Volume/Storage Calculation If Rational Method is used, place a 1 in this box Required Provided Design Storm RV :VoluinetoS#ore Pipe Diameter Length Of a Single run of Pipe Number of Pipe Runs in Trench Storage In Piping Total Storage in Piping Cross -Sectional Area Of Pipe Runs Length Of Trench Width Of Trench Height Of Trench Cross -Sectional Area Of Trench Voids Volume, 40% Trench Volume per linear foot Minimum Trench length required Total Volume Provided Elevation Of Bottom Of Trench Elevation Of SHWT Overflow Elevation Exfltration Rate / Drawdown Reported Hydraulic Conductivity Bottom Surface Area Draw wn: Ti'rrie 25 YEAR 24 HOUR STORM NIA Intensity, i = .33 inches / hour Qr=CiA= Qp through the bottom of the basin= Cc: 0.96 94.6% 1.5 in 0.90 Pipe Size 1 Pipe Size 2 2 Feet 132 Feet 2 829 Cubic Feet 829 Cubic Feet 6.283 132 Feet 6 Feet 2.8 Feet 16.80 SF 55 € CIF Cubic Feet Feet Cubic Feet 104R 385 0.09 CFS 0.1100 CFS 4.6 Mean Sea Level 2.6 Mean Sea Level 7.42 Mean Sea Level 0.5 Cubic Feet Per Hour Per Sq Ft 792 Square Feet hours Must be > Or 10 YEAR 10 MIN HIGH INTENSITY EVENT Intensity, i = 6.3 inches / hour Volume for 10 yr. 10 min. event = 1018.62 CIF < 1385 CIF `INFILTRATION TRENCH ANALYSIS Filename: S:\WPDATA\WQS\INTRENCH1041215-4 Project # SW8 041215-4 0,' Date Project Name Osprey Pt. Townhomes Reviewer Recvng Stream Intracoastal waterway *Classification Drainage Basin Cape Fear Index # Site Area 1.7 acres Drainage Area Impervious Area Calculation * outside the 575'AEC 06-Jan-05 P. Bartlett SA 26122 SF 0.60 Acres Rational Cc (list C after each BLIA) Buildings 10515 1 Parking/Asphalt 4861 1 Concrete 701 1 Total '126 % Impervious= Volume/Storage Calculation If Rational Method is used, place a 1 in this box Required Provided Design Storm RV :Vol u,m:etQ Store Pipe Diameter Length Of a Single run of Pipe Number of Pipe Runs in Trench Storage In Piping Total Storage in Piping Cross -Sectional Area Of Pipe Runs Length Of Trench Width Of Trench Height Of Trench Cross -Sectional Area Of Trench Voids Volume, 40% Trench Volume per linear foot Minimum Trench length required Total Volume Provided Elevation Of Bottom Of Trench Elevation Of SHWT Overflow Elevation Exfiltra tion Rate / Dra wdo wn Reported Hydraulic Conductivity Bottom Surface Area rAw wn,::, Ime 25 YEAR 24 HOUR STORM N/A Intensity, i = .33 inches / hour Qr= C i A = Qp through the bottom of the basin= Cc: 0.69 61.5% 1,5 in 0.60 F v11 C Pipe Size 1 Pipe Size 2 2 Feet 135 Feet 3 1272 Cubic Feet -272:; ,.. Cubic Feet 9,425 135 Feet 9 Feet 2.5 Feet 22.50 SF ....... ....... ............ :657 978:7 0.14 CFS 0.1688 CFS CIF Cubic Feet Feet Cubic Feet 4.6 Mean Sea Level 2.6 Mean Sea Level V/� 7.1 Mean Sea Level 0.5 Cubic Feet Per Hour Per Sq Ft 1215 Square Feet, - hours Must be > Qr 10 YEAR 10 MIN HIGH INTENSITY EVENT Intensity, i = 6.3 inches / hour Volume for 10 yr. 10 min. event = 1569.45 CF < 1978 CIF Design Calculations Infiltration System for Osprey Point Townhomes December 22, 2004 1. Proiect Description •r*rr�t��ierrrrrr CA EAL _ 814` _ r'rr,111161Zz1 1 The project consists of construction of residentialTownh6meS : and associated sitework on a 1.70 acre tract located on N.C. Hwy. 210 in Surf City near its intersection with Shell Drive. 2. Design Requirements Project will be designed in accordance with NC Administrative Code Section 15A NCAC 21-1.1000 — Stormwater Management (hereinafter "Regulations". Due to density, the project is considered "high density development ". Runoff in excess of the design volume must flow overland through a vegetative filter. 3. Impervious Surface Areas & Design Volume In accordance with Section .1008(c)(1), the required design volume is computed as follows: Using Schuler "Simple Method": Rv = 0.05 + 0.009(1) where I - Percent Impervious Design Volume = Desig/n Rainfall (1.5")) x Rv x Drainage Area Area 1 Area 2 Area a Area 4 Existing 6,034 -0- -0- 6,229 - Buildings 3,268 3,277 3,277 3,286 (Streets -0- -0- -0- -0- Parking 7,446 7,166 7,487 4,861 Sidewalk 695 300 342 761 � Other -0- -0- -0- -0- Reserve 1000 500 500 1,000 AA TOTAL 18,443 sf 11,243 sf 11,606 sf v sf— Drain Area - 23,574 sf 12,019 sf 12,268 sf 26,122 sf % Impervious 78.23% 93.54% 94.60% 61.55% Rv .7541 '8919 .9014 .6039 Req'd Volume 2,222 cf 1,340 of 1,382 cf 1,972 cf y 4. System Configuration and Infiltration Time Cross Sectional Areas and volumes of infiltration trenches is calculated as follows: Trench Area (cross sectional) = Trench Height x Trench Width Pipe Area (cross sectional) = Pipe Area x Number of Pipes Voids Area (cross sectional) = (Trench Area - Pipe Area) x .40 (void ratio) Unit Volume = Pipe Area * Voids Area Length Required = Req'd Volume / Unit Volume System Volume = Length Provided x Unit Volume Actual storage volume is required to infiltrate completely within 5 days. The Land & Soils Evaluation (copy attached) indicates that existing sail conductivity is as high as 20 in/hr. Assuming conservatively that existing soils have a minimum hydraulic conductivity of 6.0 in/hr, infiltration rate is computed as follows: Infiltration Rate = Hydraulic Conductivity x Basin Bottom Surface Area where: Bottom Surface Area = Trench Width x Length Provided Draw Down Time is then calculated: Draw Down Time = Actual Volume / infiltration Rate System 1 System 2 System 3 System 4 Trench Height (ft) 2.5 used 2.8 used 2.8 used 2.5 used Trench Width (ft) 9 6 6 9 Trench Area(sf) 22.5 16.8 16.8 22.5 Pipe Area (sf) 9.42 6.28 6.28 9.42 Voids Area (so 5.23 4.21 4.21 5.23 Unit Volume (cf/ft) 14.7 10.5 10.5 14.7 Length Required (ft) 151.7 127.7 / 131.7 134.6 Length Provided (11) 152 128 �/ 132 135 System Volume (cf) 2234.4 1344.0 1386.0 1984.5 Bottom Area (sf) 1368 768 792 1215 Infiltration Rate (cf/hr) 684.0 384.0 396.0 607.5 Draw Down Time (hr) 3.3 3.5 3.5 3.3 Project: Osprey Point By: DKN Procedure: Adjust y until z, = zry Where: B = bottom width y = trial depth A=By+My2 P = B + 2y(1 +M�12 R=AIP z.=AR' Use: n = .02 for earth lined n = .03 for mowed grass n = .05 for unwowed grass n = .013 for concrete lined Swale Calculations Let: n = 0.03 M = 2. I Location Q10 S zr B-F y A P R ze„ VEL Vegetated Filter 1 Vegetated Filter 1 Vegetated Filter 2 3.24 3.96 3.96 0.0035 0.0035 0.0035 1.10 1.35 1.35 # # 3.5 7 3 0.47 0.36 0.56 2.17 6.00 8,96 6.00 0.36 0.32 0.41 #t fift 1.10 1.35 1.35 WINNOW 1.49 1.38 1.61 �# 2,88 2.45 ## # Stormwater Treatment & Erosion Control Narrative Osprey Point Townhomes Keith Andrews Builders, Inc. proposes to construct a residential townhome development on a 1.70 acre tract located near the intersection of NC 210 and Shell Drive in Surf City, Pender County. The site has been previously developed as a mobile home park, however, all structures were removed in early 2004. Since removal of mobile homes, six (6) townhome units have been constructed along Topsail Drive and six (6) units are presently under construction along New River Drive. The project is to be designed and constructed in accordance with NC Division of Environmental Management Stormwater Management- Rules (15A NCAC 2H.1000). Section .1005(2)(b). The proposed project is "High Density" (i.e., percent impervious > 25%). Division of Water Quality requires that the first 1.5" of rainfall be treated in an infiltration system. The project site is located approximately 0.1 mile from the Intracoastal Waterway (SA:HQW) in the Cape Fear Basin, however, the site does not have a defined drainage outlet. Existing site topography is gently sloping (0 — 2%) with highest areas toward center of tract. Topography suggests that precipitation currently infiltrates into the sandy soils or sheet flows onto adjacent street right-of-way. Soils are Medium to Coarse Sands (see attached soils evaluation) which have hydraulic conductivities ranging from 10 — 20 in/hr. Proposed grading activities will be limited to installation of building pads and sloping parking areas as minimally required for drainage. The site will be drained to one of four (4) proposed infiltration systems. Any excess stormwater which does not infiltrate will exit the site via one of two provided vegetated filters discharging to adjacent street right-of-way.