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Home My WebLink AboutMitchell Community College - Health Sciences Building - 6028-MCC Calc Book_Storm ENGINEERING CALCULATIONS FOR MITCHELL COMMUNITY COLLEGE HEALTH SCIENCES BUILDING Prepared by: LandDesign, Inc. 223 North Graham St. Calculations by: GR Checked by: MDM March 09, 2018 LandDesign PN: 1016028 TABLE OF CONTENTS PROJECT NARRATIVE EROSION CONTROL CALCULATIONS SEDIMENT TRAP AND SKIMMER SEDIMENT BASIN DESIGN 10-YR STORM SEWER REPORT STORM SEWER PLAN STORM SEWER PROFILE PIPE CAPACITY CALCULATIONS ABOVE GROUND SAND FILTER CALCULATIONS DESIGN CALCULATIONS HYDROCAD WATER QUALITY ANALYSIS HYDROCAD CHANNEL PROTECTION AND DETENTION ANALYSIS RIPRAP CALCULATIONS APPENDIX EXISTING CONDITIONS - WEB SOIL SURVEY - SITE LOCATION MAP - EXISITNG CONDITIONS SURVEY (IN PLAN SET) - USGS TOPO MAP - PROPERTY DATA AND DEED(S) PRE-DEVELOPMENT HYDROLOGY EXHIBIT POST-DEVELOPMENT HYDROLOGY EXHIBIT STORMWATER PERMIT APPLICATION BMP OPERATION AND MAINTENANCE AGREEMENT PROJECT NARRATIVE Stormwater Management Narrative Mitchell Community College Health Sciences Building 706 Cherry Street Statesville, NC, Iredell County INTRODUCTION LandDesign, Inc (LDI) has prepared a Stormwater Management package for the Mitchell Community College (MCC) Health Sciences Building on the campus of MCC in Statesville, North Carolina. Existing conditions of the project site include asphalt pavement , gravel, dense grasses and fallow bare soils. The proposed project is located within Statesville city limits on property owned by Mitchell Community College Endowment for Excellence, Tax IDs #473-64-9849, #4734-74-0876, #4734- 74-1947. Current zoning of the parcels is O+I-2 (office-institutional). Planned facilities associated with the Health Sciences Building include offices, classrooms, and lab rooms. CONSTRUCTION SEQUENCE 1. Verify approved erosion control plan is on site. 2. Flag the construction limits and mark any trees, wetlands, or existing structures noted to remain. 3. Set up an on-site pre-construction conference with erosion control inspector to discuss erosion control measures. Failure to schedule such conference 48 hours prior to any land-disturbing activity is a violation and is subject to fine. 4. Contractor to coordinate perimeter construction fencing with owner and submit fencing plan to owner for approval. 5. Install temporary construction entrance(s). 6. Install silt fence and any other measures required by the erosion control inspector. 7. Install skimmer sediment basin, temporary sediment traps, check dams and diversion ditches. (Phase I) 8. Notify NCDEQ inspector that erosion control measures are in place. 9. Obtain grading permit and/or perform any field revisions as required by inspector. 10. Remove existing utilities as shown on sheet C1.01 - Demolition Plan a. Power b. Gas line – coordinate with Piedmont Natural Gas c. Telecom Line d. Storm Drainage e. Light poles and underground electric. Contractor to coordinate with construction manager. 11. Upon removal of all utilities in conflict with proposed grading, the grading contractor wi ll verify that erosion control measures are in place and functioning prior to grubbing and mass grading operations. 12. Upon stabilization of all upstream area, muck out skimmer sediment basin and convert to an above ground sand filter. Remove temporary sediment trap and all unstable sediment, and smooth area to blend with adjoining areas. Stabilize properly. SITE UTILITIES All site utilities to serve the building are privately controlled by Mitchell Community College with the exception of natural gas which is owned by Piedmont Natural Gas. Water, sewer, electric and telecom service are all available to the site. WATER SERVICE Water service to the building will be provided from one 3” domestic tap and one 6” fire line tap into the water main on Cherry Street. Separate backflow devices will be used and where required separate meters. All domestic water will be metered for internal tracking. SANITARY SEWER SERVICE The Health Sciences Building waste will discharge into an existing 8” gravity sewer main line. The sanitary main will connect to larger lines which eventually connect to Third Creek or Fourth Creek Waste Water Treatment Plants STORMWATER SYSTEM Proposed drainage intends to maintain the existing runoff by utilizing an above ground sand filter to mitigate storm water impacts and detain the 2-yr and 10-yr, 24-hr storms. SITE GEOLOGY The project site contains asphalt, gravel, and dense grasses. Preliminary geotechnical analysis of the site encountered residuum, lean clay, and sandy silt. Residual soil was found below the surficial materials at each test location. SITE PREPARATION AND GRADING The placement of the building and the establishment of a finished floor elevation are based off of Cherry Street. Minor adjustments to the final FFE considered ADA accessibility, pedestrian movements and delivery truck access. SAND FILTER CALCULATIONS Project Name:Mitchell Community CollegeProject Number:1016028Design Requirements:85% TSS RemovalGiven Information:Land Use: InstitutionalDrainage Area to Facility (Acres): 1.48 NCDENR (Maximum 5 Acres)Meck. County (Maximum 10 Ac for a Surface Filter)Meck. County (Maximum 2 Ac for a Perimeter Filter)Meck. County (Maximum 5 Ac for an Underground Filter)Impervious Area (Acres): 0.7Percent Impervious: 47.3%Soil Type: CgCSoil Group: BCurve Number (CN) Pre: 87Curve Number (CN) Post: 79Time of Concentration Pre (hour): 0.210Time of Concentration Post (hour): 0.083Design Storm Rainfall Depth (in): 1.0 (Typically 1")Detention Time (Day): 1.66 Meck. County:2 days - 85% TSS & 70% TP (Optimal Efficiency)1 day - 70% TSS & 35% TP (Standard Efficiency)2 days - 85% TSS & 0% TP (TSS - Only Efficiency)NCDENR1.66 daysCoefficient of Permeability for the Sand Filter Bed: 1.75 inches/hourWatershed:Yadkin-Southeast Catawba - 85% TSS & 70% TPEfficiency:NCDENR Step 1: Compute the water quality volume (WQV). WQV (Ft3) = (RV / 1) X (AD / 1) X (43,560 Ft2 / 1 Acre) X (RD / 1) X (1 Ft / 12 in) WQVAdj (Ft3) = (0.75) WQV Where: WQV = Water Quality Volume (Ft 3) WQVAdj = Adjusted Water Quality Volume (Ft3) AD = Drainage Area to Sand Filter (acres). Max. 5 acres. RV = Volumetric Runoff Coefficient = 0.05 + 0.9 (% Impervious) RD = Design Storm Rainfall Depth (in). Typically 1.0". Percent Impervious = 47% AD =1.48 acres RD = 1.0 in RV = 0.48 WQV = 2,556 Ft3 WQVAdj =1,917 Ft3 Sand Filter Design (NCDENR - 2007) Project Name: Mitchell Community College Job Number: 1016028 Step 2: Determine the maximum head on the sand filter and sedimentation basin. ha (ft) = hMaxFilter / 2 hMaxFilter (Ft) = (WQV Adj) / (AS + Af) AS (Ft2) = -(Q0 / w) x (ln (1 - E)) Af (Ft2) = (WQV x dF) / (k x t x (hA + dF)) Q (Ft3/Sec) = k x (1 Day / 86,400 Sec) x (Af) x ((ha + dF) / dF) Where: ha = Average Head (Ft) hMaxFilter = Maximum Head on the Sand Filter (Ft) AS = Surface Area of the Sedimentation Basin (Ft2) Af = Surface Area of the Sand Filter Bed (Ft2) Q0 = Average Rate of Outflow From Sedimentation Chamber (Ft3 / sec.) = WQV / 86,400 E = Trap Efficiency of the Chamber = 0.9 w = Settling Velocity of Particle (Ft/sec) (Assume Particle Diameter of 20 microns = 0.0004 Ft/sec) dF = Depth of Sand Filter Bed (Ft) (Minimum of 1.5 Ft) k = Coefficient of Permeability for the Sand Filter Bed = 3.5 Ft/day t = Time Required to Drain the WQV through the Sand Filter Bed (day). Q = Sand Filter Infiltration Rate at hMaxFilter (Ft3/Sec). (Darcy's Law) For maximum heads between 2 and 6 feet, the following combinations of variables will work: (Ideal situation AS = Af) hMaxFilter WQVAdj AS + Af (Ft)(Ft3) (Ft 2) 2 1,917 959 3 1,917 639 4 1,917 479 5 1,917 383 6 1,917 320 Area available for sand filter = 639 Ft2 hMaxFilter =3 Ft ha = 1.5 Ft Minimum AS =170 Ft2 dF =2.0 Ft k = 3.5 Ft/day t = 1.66 day Minimum Af =251 Ft2 Min. required area for sand filter = 421 Ft2 TRUE Af =320 Ft2 AS =320 Ft2 hMaxFilter =3.0 Ft ha = 1.5 Ft Q = 0.023 Ft3/Sec Step 3: Ensure that the Water Quality Volume is Contained. (Af + AS) x hMaxFilter ≥WQVAdj 1,920 Ft3 ≥1,917 Ft3 TRUE Step 4: Additional Design Requirements. For underground sand filters, provide at least 5 feet of clearance between the surface of the sand filter and the bottom of the roof of the underground structure to facilitate cleaning and maintenance. Step 5: Calculate Surface Area and Underdrain Requirements Q (Ft3/Sec) = k x (1 Day / 86,400 Sec) x (Af) x ((ha + dF) / dF) Where: ha = Average Head (Ft) hMaxFilter = Maximum Head on the Sand Filter (Ft) (Maximum of 2.0 Ft) Af = Surface Area of the Sand Filter Bed (Ft2) AS = Surface Area of the Sedimentation Basin (Ft2) Cd = Sediment Chamber Depth (Ft) dF = Depth of Sand Filter Bed (Ft) (Minimum of 2.0 Ft) k = Coefficient of Permeability for the Sand Filter Bed = 3.5 Ft/day QMaxFilter = Sand Filter Infiltration Rate at hMaxFilter (Ft3/Sec). (Darcy's Law) Q0 = Sand Filter Infiltration Rate at Top of Sand (Ft3/Sec). (Darcy's Law) Required Af =251 Ft2 Provided Af = 300 Ft2 Required As =170 Ft2 Provided As = 2400 Ft2 Required Cd =0.3 Ft Provided Cd =3 Ft QMaxFilter =0.021 Ft3/Sec Q0 =0.000 Ft3/Sec Number of Underdrain Rows Required = 1 (Maximum Spacing = 10 Ft) Total Length of Underdrain = 33 Ft Number of Underdrain Perforations = 256 Holes 50% of Perforations = 128 Holes Area of One Perforation = 0.00077 Ft2 Capacity of One Hole = 0.0058 Ft3/Sec Total Capacity of Perforations = 0.74 Ft3/Sec Check: 0.74 Ft3/Sec > 0.021 Ft3/Sec :. GOOD Capacity of 6" PVC Underdrain at 0.50% Slope = 0.39 Ft3/Sec Assume 50% Clogging = 0.20 Ft3/Sec Check: 0.20 Ft3/Sec > 0.021 Ft3/Sec :. GOOD RIPRAP CALCULATIONS Structure Name:HW-(107)Diameter 18 in 1.5 ftQ 5.18 cfsd500.3 feet 3.6 indmax5.40 inchesLa10 feetW 11.5 feetThickness 8.1 inchesW@outlet 4.5 feetClass B16Round tonearest 1/4 ft Structure Name:BMP OUTFALL-1Diameter 18 in 1.5 ftQ 7.03 cfsd500.3 feet 3.6 indmax5.40 inchesLa10 feetW 11.5 feetThickness 8.1 inchesW@outlet 4.5 feetClass B16Round tonearest 1/4 ft PROJECT LOCATION PROJECT SITE