The URL can be used to link to this page

Home My WebLink About20051920 Ver 2_Stormwater Info_20070605~ ®AVIS-MARTIN-POV1/ELL & ASS®CIATES, INC. ENGINEERING LAND PLANNING SURVEYING 6415 Old Plank Road, High Point, NC 27265 - (336) 886-4821 • Fax (336) 886-4458 • www.dmp-inc.com Cynthia Van Der Wiele 401 Oversight/Express Review Permitting Unit 2321 Crabtree Boulevard Suite 250 Raleigh, NC 27604 Dear Ms. Van Der Wiele: June 1, 2007 RE: Marvin Ridge Middle and High School DMP Job No. E3768 DWQ EXP No. OS-1920 Q~~~oe~~ JUN 5 2001 OEiVR _ WATER C~ALI'i'Y ~nAiVDS AND STO,R~rAJER BRANCH Thank you for the review dated April 18, 2007 of the storm water management plan for Marvin Ridge Middle and High School. Your comments are listed below with our response in italics. Enclosed are three copies. The 401 Water Quality Certification issue don November 30, 2005 noted that along with the requirements contained in the Water Quality Certifications (GC3374 and GC 3402 which correspond to NW12 and NW39) you were required to comply with additional conditions contained in the written approval letter. Condition Number 1 states: "...The storm water management .facilities must be designed to treat the runoff from the entire project unless otherwise explicitly approved by the Division of Water Quality." You have only provided storm water management for two of the five drainage areas you have on this project. A. Please provide storm water management for the other three drainage areas. B. Please provide all worksheets and calculations for the other three drainage areas. C. Please provide a signed and notarized operation and maintenance agreement that includes all storm water management facilities on this project. During the review process Mr. Eddie MacEldowney with Davis-Martin-Powell and Associates met on site with the DWQ ~°ep~°esentative from the Mooresville Regional Office, Mr. Barry Love, to discuss the wetland impacts and to discuss the requirements of the storm water management plan that Mr. Love indicated would be required. Mr. Love indicated that the two largest ac^ea of impe~°vious material (i. e. the high school sticdent paJ°king lot and the parking lots and drives north of the proposed school buildings), will be ~°equired to have some sort of water quality devices. Water quality devices were designed for these two main areas (Drainage Basins 2 and 3). The remaining basins (DT^ainage Basin #1, 4 and 5) can be excused fi^om the storm water management plan as stated in Condition 1. Please explicitly excuse the requirements for storm water management from the i^emaining basins (Drainage Basins 1, 4, and 5) due to the following reasons for each basin. Drainage Basin #1 nearly 12.6 acres and encompasses mainly the football stadium. The basin is bordered by Crane Road on the west, Waxhaw Mal"VlTZ Road on the south, and an 18 "Sanitary Sewer Outfall/Pump Station for Union County Public Worizs and the property line on the east. Thes^e is no room for any device without encroaching into the right of way of Waxhaw Marvin Road, encT^oaching into the Union County Public Worlcs utility easement or onto someone else property. North of the football field drains into the storm water device for Drainage Basin #2. Prior to the school being consti^ucted, the area was cultivated farm land. The ricnoff fi^om the cultivated land was approximately 31.3 cfs. The post development runoff is 30.5 cfs. The reduction in runoff is approximately 2.56%. Therefore no storm water management plan was designed since the runoff was being reduced. Calculations supporting this are enclosed. Please excuse Drainage Basin #1 fi^om the required storm water management due to site constraints and an overall runoff reduction from pre and post development flows. Drainage Basin #4 is 9.1 acres with approximately 6.1 % impervious coverage. This drainage area is 93.9% grass and 6.1 % gravel. The gravel is part of the access drive to the baseball and softball field which are part of Drainage Basin #S. Prior to the school being constructed, the area was cultivated farm land. The J^unoff from the cultivated land was approximately 22.6cfs. The post development runoff is 12.92 cfs. The reduction in runoff is approximately 42.8%. Therefore no storm water management plan was designed since the runoff was being reduced. Calculatio~as supporting this are enclosed. Please excuse Drainage Basin #4 from the required storm water management due to the large percent i^eduction in pT^e and post development flows. Di^ainage Basin #S is approximately 14.3 acres with 0.40 acr^es of impervious coves^age. The impervious areas for Drainage Basin #S is the walks to the spectator area and the concrete around the portable bleachers. As with Drainage Basin #4, prioT^ to the school being constT^ucted, Area #S was mainly cultivated farm land. The runoff fi^om the cultivated land was approximately 35.5 cfs. The post development f^unoff is 17.26 cfs. The i^eduction in runoff is approximately 51.4%. Therefore no stoi^m water manageme~Zt plan was designed since the runoff was being reduced. Calculations supporting this are also enclosed. Please excuse Drainage Basin #S from the required stoT^m. water manageme~zt due to the large percent reduction in pre and post development flows. The s^equested infoi^mation for the Di^ainage Basins 1, 4 and S (BMP Worksheets and an Operation and Maintenance Agreement) are not included due to storm water management being achieved by changing the site conditions from cultivated agricultural land to established lawns (athletic fields) type at^eas. 2. The length to width ratio of the two wet ponds provided in your plans appears to be under 3:1; DWQ has concerns about short-circuiting of the pond treatment systems. Due to site constraints such as roads, established athletic fields, sanitary sewer easements and .flood plain location, incT~easing the length from the inlet into the pond to the outlet of the pond to have a 3:1 length to width ratio is unable to be done. Gabion walls are placed to increase the length to get it closer to the 3:1 ratio. Revised worl~sheets ai°e not included since the design information of the pond has not changed. All elevations and storage volumes remain the same. All revised or additional calculations are enclosed. Thank you once again for your review of the project. If you have any more questions, please let us know. Eddie MacEldowney and I would be available to sit down and talk with you about your concerns. Sincerely, Davis-Martin-Powell and Associates y uffey, Cc: File Tony Wentz Client ~~ ~~ " rc~~~ w~ ~ ~~w Computed By - Job No. F~ ~ ~~~ dm /h./~J,-, ~j tt1/ Date p Project Description 1~/~~V/~ ~C i?'>E~~" /~~ ~ / 1~1 Checked By _ (Revised, Superseded, and Yoid Calculations Must Be Clearly Identified, Initialed, and Dated by the Responsible Individual) Calculations For ,5~1~/~7 wQ~~-- //14~./.-'l~f,°J~~i~IT Date DAVIS-MARTIN-POWELL 8r ASSOCIATES, INC. 218 GATEWOOD AVE., SUITE 102, HIGH POINT, NC 27262 Page of Client - Job No. F_. ~71n~ dm ~~~,~~ ~,~~~~~ ~~s ~- ~~ -p Project Description Calculations For %Ci~Y!"1 G~.1;AW v- v/ ~` ~1~ ~~?~'~~ DAVIS-MARTIN-POWELL & SSOCIATES, INC. 218 GATEWOOD AVE., SUITE 102, HIGH POINT, NC 27282 Computed By Date Checked By Date Page of (Revised, Superseded, and Yoid Calculations Must Be Clearly Identifeed, Initialed, and Dated by the Responsible Individual)