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HomeMy WebLinkAboutSW6220302_Design Calculations_20220812Gruber Mini -Mall, Ft. Bragg Project Number 0630-11-000004 Stormwater Narrative and Calculations Prepared By: uiVa lib -re Calibre Engineering, Inc PO BOX 4041 Wilmington, NC 28406 (P) 910-791-4441 Prepared For: Marshall -Waters -Woody Associates, INC 1736 E. Sunshine, Suite 311 Springfield, MO 65804 (P) 417-883-2720 (F) 417-883-0161 October 4, 2021 •�\4 CAR �% ��pQ`••�es3 '0�i��'. SEAL 025483 may'•, c�,�, � • g,V. /(-30-z F4V. 3-2z- zz -7 7 Z r- e- // - Z Z Narrative Protect Description This project is for the construction of a convenience store with gas pumps and adjoining restaurants located at the intersection of Gruber and Graves Street at the Ft. Bragg Military Base. Currently the site is vacant and stabilized with lawn grass. Existing topography is sloping heading South to North. The site is a redevelopment site and previously had barracks and parking onsite which were demolished years ago. No wetlands are located within the project limits. Improvements to the site will be the construction of a new building, gas pumps and parking/ drive areas. The site will have two connection points to existing roadways. One connection on Graves and one onto Gruber. The total project is approximately 4.93 acres with 3.08 acres of impervious being treated in a NCDEQ Stormwater BMP. Water and sewer utilities for the building will be provided by ASUS. Stormwater from the site will be collected via catch basins and trench grates and conveyed to an open infiltration basin designed to handle the 1.0" rain fall event. The infiltration basin is designed per chapter C-1 of NCDEQ Stormwater Design Manual. The outlet structure of the basin will connect to an existing stormwater collection system located in Graves Street. Stormwater from the site will drain to Tank Creek (C, 18-23-27) located in the Cape Fear River Basin. A portion of the project area for this site is located in the roadway of Gruber Street for the installation of a decel lane. The elevations and existing utilities make capturing and directing the water to the infiltration basin not feasible. Volume Runoff reduction calculations have been performed for the site based off the draft Version 1.0 May 2021 Technical Release 2 document. The infiltration basin has been oversized and the increase in volume is less that 10% so the decel lane can be left in an untreated condition. PROJECT DATA: Existing Site Data (within Project Area) Existing roadway 5,417 sf (0.12 acres) Existing sidewalk 702 sf (0.02 acres) Existing uplands 214,192 sf (4.92 acres) Total proposed project area 220,311 sf (5.06 acres) Existing Site Data (within Basin drainage delineation) Existing wetlands 0.0 sf (0.0 acres) Existing uplands 164,291 sf (3.77 acres) Total proposed basin area 164,291 sf (3.77 acres) Proposed BUA within Project Area: Proposed building 15,494 sf (0.35 acres) Proposed sidewalk/concrete pads 10,701 sf (0.25 acres) Proposed concrete drive aisles 106,765 sf (2.45 acres) Proposed Decel Lane 4,369 sf (0.10 acres) Total proposed impervious area 137,329 sf (3.15 acres) Proposed Site Data within Infiltration Basin Drainage Area: Proposed building Proposed sidewalk/concrete pads Proposed concrete drive aisles Total proposed BUA within DA to Basin: Soil Types Within Project Limits: Abbreviation M (See attached soils map) Type and Description Wagram 15,494 sf (0.35 acres) 9,548 sf (0.22 acres) 103,744 sf (2.38 acres 128,786 sf (2.96 acres) Hydrologic Group Area A 3.77 ac INFILTRATION BASIN CALCULATIONS BASIN 1 DETERMINE IMPERVIOUS PERCENTAGE area to basin = 164,291 sf buildings = 15,494 sf roads = 103,744 sf sidewalks = 9,548 sf future = sf rec = - sf total impervious surface = 128,786 sf total non -impervious surface = 35,505 sf percent imp. = 78.4 % 1.0" VOLUME DETERMINATION: Infiltration Basin 1 DETERMINE RUNOFF COEFFICIENT (Rv) I = 78.4 percent impervious Rv = ? (runoff coefficient, inches per inch) Rv= 0.05 + 0.009 (1) Rv = 0.76 in/in DETERMINE VOLUME design storm = 1 inch Rv = 0.76 in/in drainage area = 3.77 acres volume = ? volume = (design storm)(Rv)(drainage area) volume = 0.2 acre-ft volume = 10,401 cf of required storage volume MINIMUM SURFACE AREA: SA = FS X (DV X 12) / (K X T) 3.77 acres 0.36 acres 2.38 acres 0.22 acres - acres - acres 2.96 acres 0.82 acres SA ? = REQUIRED MIN. SURFACE AREA FS 2 =FACTOR OF SAFETY (MIN OF 2) DV 13,553 = DESIGN VOLUME (CF) K 0.99 =INFILTRATION RATE (IN/HR) T 72 = MAX DEWATERING TIME (72 HR) SA = 4,563 SF Surface area provided = 4,858 SF CALIBRE ENGINEERING PO BOX 4041 WILMINGTON, NC 28406 INFILTRATION BASIN STAGE -STORAGE TABLE: ELEVATION AREA (FT) (SF) 386 4,858 387 5,411 388 5,654 388.5 5,887 389 6,119 390 9,638 391 11,144 392 12,707 1.0" Volume provided at elev. 388.5 STAGE - DISCHARGE TABLE: infiltration rate (cfs) = 0.99 crest length of weir cut (ft) = 0.40 crest length of spillway (ft) = 20 ELEVATION INFILTRATION WEIR SPILLWAY (ft) (cfs) (cfs) (cfs) 386 0.00 0 387 0.99 388 0.99 - 389 0.99 0.47 390 0.99 2.42 391 0.99 5.22 - 392 0.99 8.64 21 DRAWDOWN TIME: T=(FSXDVX12)/(KXSA) SA 4,858 FS 2 DV 13,553 K 0.99 T 72 T = 67.6 hours INCREMENTAL VOLUME STORAGE (cf) (cf) 5,135 5,135 5,533 10,668 2,885 13,553 3,002 16,555 7,879 24,434 10,391 34,825 11,926 46,751 13,553 cf elevation of weir cut = 388.5 elevation of spillway = 391.5 TOTAL (cfs) 0 1 1 3 6 31 =REQUIRED MIN. SURFACE AREA =FACTOR OF SAFETY (MIN OF 2) = DESIGN VOLUME (CF) =INFILTRATION RATE (IN/HR) = MAX DEWATERING TIME (72 HR) CALIBRE ENGINEERING PO BOX 4041 WILMINGTON, NC 28406 Volume Reduction Calculations Step 1 Pre- Development Whole Project Area: Total project Area = 220,311 sf 5.06 acres Existing Impervious 6,119 sf 0.14 acres total impervious surface = 6,119 sf 0.14 acres total non -impervious surface = 214,192 sf 4.92 acres percent imp. = 2.8 % DETERMINE RUNOFF COEFFICIENT (Rv) I = 2.8 percent impervious Rv = ? (runoff coefficient, inches per inch) Rv= 0.05 + 0.009 (1) Rv = 0.08 in/in ARV =PjxRvxAx(P/12) ARV = ? Annual Runoff Volume Pi = 0.90 Fraction of Rainfall events that produce runoff (assumed 0.9) Rv = 0.08 Runoff Coefficient A = 220,311 Area of Intrest (square feet) P = 45.75 Average Annual Rainfall Amount (in inches) ARV = 60,475 CIF Step 2 POST- Development Whole Project Area Total Project Area = 220,311 sf 5.06 acres buildings = 15,494 sf 0.36 acres roads = 106,765 sf 2.45 acres sidewalks = 10,701 sf 0.25 acres Decel Lane = 4,369 sf 0.10 acres total impervious surface = 137,329 sf 3.15 acres total non -impervious surface = 82,982 sf 1.90 acres percent imp. = 62.3 % DETERMINE RUNOFF COEFFICIENT (Rv) I = 62.3 percent impervious Rv = ? (runoff coefficient, inches per inch) Rv= 0.05 + 0.009 (1) Rv= 0.61 in/in ARV =PjxRvxAx(P/12) ARV = ? Annual Runoff Volume Pi = 0.90 Fraction of Rainfall events that produce runoff (assumed 0.9) Rv = 0.61 Runoff Coefficient A = 220,311 Area of Intrest (square feet) P = 45.75 Average Annual Rainfall Amount (in inches) ARV = 461,125 CIF 4493 461,125 60,475 = 400,650 cf CALIBRE ENGINEERING PO BOX 4041 WILMINGTON, NC 28406 Step 3. a. DETERMINE INFILTRATION BASIN PERCENT SIZING area to basin = 164,291 sf 3.77 acres buildings = 15,494 sf 0.36 acres roads = 103,744 sf 2.38 acres sidewalks = 9,548 sf 0.22 acres future = sf - acres rec = - sf - acres total impervious surface = 128,786 sf 2.96 acres total non -impervious surface = 35,505 sf 0.82 acres percent imp. = 78.4 % DETERMINE RUNOFF COEFFICIENT (Rv) I = 78.4 percent impervious Rv = ? (runoff coefficient, inches per inch) Rv= 0.05 + 0.009 (1) Rv= 0.76 in/in DETERMINE VOLUME design storm = 1 inch Rv = 0.76 in/in drainage area = 3.77 acres volume = ? volume = (design storm)(Rv)(drainage area) volume = 0.2 acre-ft volume = 10,401 cf of required storage volume ii. DETERMINE TREATMENT VOLUME PROVIDED: Treatment Volume = 13,553 cf (reference Infiltration Basin Calculations) iii. DETERMINE PERCENT SIZING: %SCM Size = Treatment Volume / Required Volume %SCM Size = 130.3 % b. DETERMINE FATES OF RUNOFF ENTERING INFILTRATION BASIN: i. DETERMINE POST ARV OFTHE INFILTRATION BASIN DRAINAGE AREA ARV =PjxRvxAx(P/12)-Vrry ARV = ? Annual Runoff Volume Pi = 0.90 Fraction of Rainfall events that produce runoff (assumed 0.9) Rv = 0.76 Runoff Coefficient A = 164,291 Area of Intrest (square feet) P = 45.75 Average Annual Rainfall Amount (in inches) ARV = 428,430 CIF CALIBRE ENGINEERING PO BOX 4041 VVILMINGTON, NC 28406 ii. DETERMINE THE %ART Since Basin is oversized, information from Part C.1 of the SCM Credit Document will be used to determine the %ART for the infiltration system. This information is calculated using the following equation. y = 0.2231xA3 - 1.141xA2 + 1.9953x - 0.2332 X = 1.303 Percent Sizing of the SCM (expressed as decimal) y = ? %Annual Runoff Treated, %ART (expressed as a decimal) %ART = 0.923 92.3% iii. DETERMINE THE UNTREATED BYPASS VOLUME: % Untreated Bypass = 100%- %ART %Untreated Bypass = 7.7 % Untreated Bypass Volume = % Untreated Byass x ARV(to SCM) _ ARV (SCM) = 428,430 x 0.077 Untreated Bypass Volume = 32,989 cf iv. DETERMINE THE TREATED EFFLUENT VOLUME: From Table 2, the "effluent" value of an Infiltration Facility (per MDC) over HSG "A" is 0%. %Treated Effluent = %ART x (Effluent Value) = 92.3 x 0 = 0 v. DETERMINE THE ET&I VOLUME: From Table 2, the ET&I value of an Infiltration Facility (per MDC) over HSG "A" is 100%. %ET&I = %ART X (ET&I VALUE) 0.923 X 100 = 92.3% ET&I VOLUME = %ET&I x ARV(SCM) 0.923 x 428.430 = 395.441 cf Step 4 DETERMINE THE POST-DEV. ANNUAL RUNOFF VOLUME (INCLUDING SCM VOLUME REDUCTION) 461,125 395,441 = 65,684 cf Step 5 DEMONSTRATE COMPLIANCE WITH RUNOFF VOLUME MATCH 65,684 60,475 = 5,209 cf 5,209 / 60,475 = 8.61 % VOLUME IS LESS THAN 10% INCREASE THEREFORE SITE IS IN COMPLIANCE CALIBRE ENGINEERING PO BOX 4041 WILMINGTON, NC 28406 Hydrograph Summary Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Hyd. No. Hydrograph type (origin) Peak flow (cfs) Time interval (min) Time to Peak (min) Hyd. volume (cult) Inflow hyd(s) Maximum elevation (ft) Total strge used (cuft) Hydrograph Description 1 SCS Runoff 0.000 2 n/a 0 ------ ------ ------ Pre-Dev 2 SCS Runoff 7.090 2 724 21,189 ------ ------ ------ Post-Dev 3 Reservoir 0.108 2 956 1,721 2 388.69 14,700 Routed basin.gpw Return Period: 1 Year Thursday, 08 / 11 / 2022 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Hyd. No. 1 Pre-Dev Hydrograph type = SCS Runoff Peak discharge = 0.000 cfs Storm frequency = 1 yrs Time to peak = n/a Time interval = 2 min Hyd. volume = 0 cuft Drainage area = 3.770 ac Curve number = 39 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 3.07 in Distribution = Type III Storm duration = 24 hrs Shape factor = 484 Q (Cfs) 0.10 0.09 on e: 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 00 Pre-Dev Hyd. No. 1 -- 1 Year Q (Cfs) 0.10 0.09 0.07 0.06 0.05 0.04 0.03 0.02 0.01 - 0 00 0 20 40 60 80 100 120 — Hyd No. 1 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Hyd. No. 2 Post-Dev Hydrograph type = SCS Runoff Peak discharge Storm frequency = 1 yrs Time to peak Time interval = 2 min Hyd. volume Drainage area = 3.780 ac Curve number Basin Slope = 0.0 % Hydraulic length Tc method = User Time of conc. (Tc) Total precip. = 3.07 in Distribution Storm duration = 24 hrs Shape factor Composite (Area/CN) = [(2.960 x 98) + (0.820 x 39)] / 3.780 Q (Cfs) 8.00 ME 4.00 2.00 0.00 0 120 240 360 — Hyd No. 2 Post-Dev Hyd. No. 2 -- 1 Year 480 600 720 840 Thursday, 08 / 11 / 2022 = 7.090 cfs = 724 min = 21,189 cuft = 85* = 0 ft = 5.00 min = Type III = 484 Q (Cfs) 8.00 Me] 4.00 2.00 0.00 960 1080 1200 1320 1440 1560 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Hyd. No. 3 Routed Hydrograph type = Reservoir Peak discharge = 0.108 cfs Storm frequency = 1 yrs Time to peak = 956 min Time interval = 2 min Hyd. volume = 1,721 cuft Inflow hyd. No. = 2 - Post-Dev Max. Elevation = 388.69 ft Reservoir name = Infil Basin Max. Storage = 14,700 cuft Storage Indication method used. Exfiltration extracted from Outflow Q (cfs) 8.00 ME 4.00 2.00 0.00 0 120 240 — Hyd No. 3 Routed Hyd. No. 3 -- 1 Year 360 480 600 720 840 960 1080 1200 1320 Hyd No. 2 Total storage used = 14,700 cuft Q (cfs) 8.00 4.00 2.00 0.00 1440 Time (min) Hydrograph Summary Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Hyd. No. Hydrograph type (origin) Peak flow (cfs) Time interval (min) Time to Peak (min) Hyd. volume (cult) Inflow hyd(s) Maximum elevation (ft) Total strge used (cuft) Hydrograph Description 1 SCS Runoff 0.321 2 742 3,817 ------ ------ ------ Pre-Dev 2 SCS Runoff 15.98 2 724 48,585 ------ ------ ------ Post-Dev 3 Reservoir 2.524 2 750 26,815 2 390.03 24,680 Routed basin.gpw Return Period: 10 Year Thursday, 08 / 11 / 2022 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Hyd. No. 1 Pre-Dev Hydrograph type = SCS Runoff Peak discharge = 0.321 cfs Storm frequency = 10 yrs Time to peak = 742 min Time interval = 2 min Hyd. volume = 3,817 cuft Drainage area = 3.770 ac Curve number = 39 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 5.44 in Distribution = Type III Storm duration = 24 hrs Shape factor = 484 Q (Cfs) 0.50 0.45 lox, no 0.35 0.30 0.25 0.20 0.15 Pre-Dev Hyd. No. 1 -- 10 Year 1 1 �1 •1 �:I •11 1 :�1 ••1 /:/ // Me, I1 •/ Q (Cfs) 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Hyd. No. 2 Post-Dev Hydrograph type = SCS Runoff Peak discharge = 15.98 cfs Storm frequency = 10 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 48,585 cuft Drainage area = 3.780 ac Curve number = 85* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 5.44 in Distribution = Type III Storm duration = 24 hrs Shape factor = 484 Composite (Area/CN) = [(2.960 x 98) + (0.820 x 39)] / 3.780 Q (Cfs) 18.00 15.00 12.00 •M .M 3.00 a�ais Post-Dev Hyd. No. 2 -- 10 Year Q (Cfs) 18.00 15.00 12.00 • wo] 3.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 Hyd No. 2 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Hyd. No. 3 Routed Hydrograph type = Reservoir Peak discharge = 2.524 cfs Storm frequency = 10 yrs Time to peak = 750 min Time interval = 2 min Hyd. volume = 26,815 cuft Inflow hyd. No. = 2 - Post-Dev Max. Elevation = 390.03 ft Reservoir name = Infil Basin Max. Storage = 24,680 cuft Storage Indication method used. Exfiltration extracted from Outflow Q (cfs) 18.00 15.00 12.00 M ME 3.00 M Routed Hyd. No. 3 -- 10 Year 120 240 360 480 600 720 Hyd No. 3 Hyd No. 2 Q (cfs) 18.00 15.00 12.00 CM 0.00 840 960 1080 1200 1320 1440 1560 Time (min) Total storage used = 24,680 cuft Pond Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Thursday, 08 / 11 / 2022 Pond No. 1 - Infil Basin Pond Data Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 386.00 ft Stage / Storage Table Stage (ft) Elevation (ft) Contour area (sgft) Incr. Storage (cult) Total storage (cult) 0.00 386.00 4,858 0 0 1.00 387.00 5,411 5,132 5,132 2.00 388.00 5,654 5,532 10,663 3.00 389.00 6,119 5,884 16,547 4.00 390.00 9,638 7,811 24,359 5.00 391.00 11,144 10,381 34,740 6.00 392.00 12,707 11,916 46,655 Culvert / Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in) = 15.00 Inactive 0.00 0.00 Crest Len (ft) = 4.00 0.40 20.00 0.00 Span (in) = 15.00 0.00 0.00 0.00 Crest El. (ft) = 390.60 388.50 391.50 0.00 No. Barrels = 1 1 0 0 Weir Coeff. = 3.33 3.33 2.60 3.33 Invert El. (ft) = 386.00 0.00 0.00 0.00 Weir Type = 1 Rect Broad --- Length (ft) = 74.00 0.00 0.00 0.00 Multi -Stage = Yes Yes No No Slope (%) = 0.90 0.00 0.00 n/a N-Value = .013 .013 .013 n/a Orifice Coeff. = 0.60 0.60 0.60 0.60 Exfil.(in/hr) = 0.990 (by Contour) Multi -Stage = n/a Yes No No TW Elev. (ft) = 0.00 Stage (ft) 6.00 6'x11IH 4.00 3.00 PAIIH m Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s) Stage / Discharge 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00 27.00 30.00 Total Q Elev (ft) 392.00 W15911I6, 390.00 389.00 [d:%I11I6, 387.00 1 386.00 33.00 Discharge (cfs) [ME =07 ffTqWTMq 1,7M III�Iil III pill 11111,11111111 1111111 I� III r,1111111 III 1 11 1111 ''111 IN CB1 1 Outfall 2 CB2 3 OB3 4 C134 CB8 5 1135 7 CB6 CB7 Project File: SW—BRANCH—l.stm Number of lines: 8 Date: 8/11/2022 Storm Sewers v12.00 Page 1 Station Len Drng Area Rnoff Area x C Tc Rain Total Cap Vel Pipe Invert Elev HGL Elev Grnd / Rim Elev Line ID coeff (1) flow full Line To Incr Total Incr Total Inlet Syst Size Slope Dn Up Dn Up Dn Up Line (ft) (ac) (ac) (C) (min) (min) (in/hr) (cfs) (cfs) (ft1s) (in) 00 (ft) 00 (ft) (ft) 00 I End 34.000 0.27 1.63 0.95 0.26 1.55 5.0 8.2 6.9 10.70 1735 5.70 24 0.59 390.00 390.20 391.14 391.37 394.40 395.30 OUTFALL TO CB 2 1 82.000 0.14 1.36 0.95 0.13 1.29 5.0 7.7 7.0 9.10 15.80 5.00 24 0.49 390.20 390.60 391.37 391.68 395.30 395.00 CB1 TO CB2 3 2 102.000 0.16 1.22 0.95 0.15 1.16 5.0 7.3 7.1 8.28 6.58 4.69 18 0.39 390.60 391.00 392.29 392.92 395.00 395.90 CB2 TO CB3 4 3 94.000 0.11 1.06 0.95 0.10 1.01 5.0 6.9 7.3 7.31 6.85 4.14 18 0.43 391.00 391.40 393.10 393.55 395.90 395.90 CB3 TO CB4 5 4 101.000 0.00 0.65 0.00 0.00 0.62 0.0 6.5 7A 4.57 4.98 3.72 15 0.59 391.40 392.00 393.95 394.46 395.90 399.10 CB4 TO JB5 6 5 133.000 0.35 0.65 0.95 0.33 0.62 5.0 5.9 7.6 4.68 3.96 3.82 15 0.38 392.00 392.50 394.67 395.37 399.10 395.90 JB5 TO CB6 7 6 101.000 0.30 0.30 0.95 0.29 0.29 5.0 5.0 7.9 2.25 4.54 1.84 15 0.50 392.50 393.00 395.48 395.60 395.90 395.90 CB6 TO CB7 8 4 53.000 0.30 0.30 0.95 0.29 0.29 5.0 5.0 7.9 2.25 6.87 1.84 15 1.13 391.40 392.00 393.95 394.01 395.90 396.10 CB4 TO CB8 Project File: SW-BRANCH-l.stm Number of lines: 8 Run Date: 8/11/2022 NOTES:Intensity = 78.63 / (Inlet time + 12.40) 1 0.80; Return period =Yrs. 10 c = cir e = ellip b = box Storm Sewers 02.00 IIIIII!IIIIIIIIIIIII 111111riplill 111111111�11111 r,1111111 III I 1 1111111 ''111 11111 pil, Outfall 1 Cgq 2 TRENCH C t Cg9 2 T' B10 3 4) CB1 I CB12 Project File: SW—BRANCH-2.stm Number of lines: 5 Date: 8/11/2022 Storm Sewers v12.00 Page 1 Station Len Drng Area Rnoff Area x C Tc Rain Total Cap Vel Pipe Invert Elev HGL Elev Grnd / Rim Elev Line ID coeff (1) flow full Line To Incr Total Incr Total Inlet Syst Size Slope Dn Up Dn Up Dn Up Line (ft) (ac) (ac) (C) (min) (min) (in/hr) (cfs) (cfs) (ft1s) (in) 00 (ft) 00 (ft) (ft) 00 I End 40.000 0.10 1.15 0.95 0.10 1.09 5.0 6.8 7.3 7.96 19.59 2.53 24 0.75 387.00 387.30 390.03 390.08 392.00 392.20 OUTFALL TO CB 2 1 62.000 0.16 0.98 0.95 0.15 0.93 5.0 6.4 7.4 6.92 24.03 2.20 24 1.13 387.30 388.00 390.21 390.27 392.20 391.90 CB9 TO CB1 0 3 2 90.000 0.38 0.82 0.95 0.36 0.78 5.0 5.9 7.6 5.90 15.65 4.21 18 2.22 388.00 390.00 390.36 390.94 391.90 393.60 CB1 0 TO CB1 1 4 3 105.000 0.44 0.44 0.95 0.42 0.42 5.0 5.0 7.9 3.30 16.84 3.49 18 2.57 390.00 392.70 390.94 393.39 393.60 396.10 CB1 1 TO CB1 2 5 1 37758 0.07 0.07 0.95 0.07 0.07 5.0 5.0 7.9 0.53 0.34 2.68 6 0.26 389.50 389.60 390.21 390.45 392.20 391.50 CB1 TO TRENCH Project File: SW-BRANCH-2.stm Number of lines: 5 Run Date: 8/11/2022 NOTES:Intensity = 78.63 / (Inlet time + 12.40) 1 0.80; Return period =Yrs. 10 ; c = cir e = ellip b = box Storm Sewers 02.00 Outfall 1 JB14 Project File: SW_BRANCH_3.stm Number of lines: 1 Date: 8/11/2022 Storm Sewers v12.00 Page 1 Station Len (ft) Drng Area Rnoff coeff (C) Area x C Tc Rain (1) (in/hr) Total flow (cfs) Cap full (cfs) Vel (ft1s) Pipe Invert Elev HGL Elev Grnd / Rim Elev Line ID Line To Line Incr (ac) Total (ac) Incr Total Inlet (min) Syst (min) Size (in) Slope Dn 00 Up (ft) Dn 00 Up (ft) Dn (ft) Up 00 I End 75.000 0.36 0.36 0.95 0.34 0.34 5.0 5.0 7.9 2.70 9.72 5.45 15 2.27 390.00 391.70 390.45 392.36 395.70 396.70 OUTFALL TO JB1 Project File: SW—BRANCH-3.stm Number of lines: 1 Run Date: 8/11/2022 NOTES:Intensity = 78.63 / (Inlet time + 12.40) 1 0.80; Return period =Yrs. 10 ; c = cir e = ellip b = box Storm Sewers 02.00 VELOCITY CONTROL FOR PIPE OUTFALL: CB1 OUTFALL - 24" PIPE OUTFALL: Qpeak = 10.7 cfs from 24 " pipe (see sheet C131) Q=VA V= Q/A = 10.7 / 3.14 = 3.4 ft/sec From chart 8.06b, Q = 10.7 cfs d= 24" d50 = 0.20 ft or 2.4 ", use 4 " La = 9 ft 3d = 6.0 ft W=d+La= 11 ft dmax =1.5xd50= 6" apron thickness = 1.5 x dmax = 9 " apron dimensions: min. stone size = 4 inches min. apron thickness = 9 inches apron length = 9 ft width of apron at pipe outlet = 6 ft width of apron at end of apron = 11 ft C139 OUTFALL - 24" PIPE OUTFALL: Qpeak = 7.96 cfs from 24 " pipe (see sheet C131) Q=VA V= Q/A = 7.96 / 3.14 = 2.5 ft/sec From chart 8.06b, Q = 7.96 cfs d= 24" d50 = 0.20 ft or 2.4 ", use 4 " La = 9 ft 3d = 6.0 ft W=d+La= 11 ft dmax =1.5xd50= 6" apron thickness = 1.5 x dmax = 9 " apron dimensions: min. stone size = 4 inches min. apron thickness = 9 inches apron length = 9 ft width of apron at pipe outlet = 6 ft width of apron at end of apron = 11 ft CALIBRE PO BOX 4041 WILMINGTON, NC 28406 JB14 OUTFALL - 15" PIPE OUTFALL Qpeak = 2.7 cfs from 15 " pipe (see sheet C131) Q=VA V= Q/A = 2.7 / 1.23 = 2.2 ft/sec From chart 8.06b, Q = 2.7 cfs d= 15" d50 = 0.20 ft or 2.4 ", use 4 " La = 9 ft 3d = 3.8 ft W=d+La= 10.25ft dmax=1.5xd50= 6" apron thickness = 1.5 x dmax = 9 " apron dimensions: min. stone size = 4 inches min. apron thickness = 9 inches apron length = 9 ft width of apron at pipe outlet = 4 ft width of apron at end of apron = 10.3 ft CALIBRE PO BOX 4041 WILMINGTON, NC 28406 Geotechnical, Environmental, and Materials Engineers August 31, 2021 Marshall -Waters -Woody Associates, Inc. 1736 East Sunshine Street Springfield, MO 65804 610 Spring Branch Road Dunn, NC 28334 Phone: (910) 292-2085 www.BuildingAndEarth.com Attention: Mr. Mark Cummins, Project Architect Subject: Letter of Transmittal for Soil Science and Infiltration Report for Erosion Control and Site Drainage Calculations Gruber Mini -Mall Fort Bragg, North Carolina Building & Earth Project No: RD210506 Mr. Cummins: As requested, Building & Earth Sciences, LLP is pleased to present the results of the field testing and observations for the above stated project site located on Gruber Road at Fort Bragg, North Carolina. Scope of Service The intent of our testing and field work was to observe and document the soil profile and the groundwater conditions that will affect and influence the drainage rate of the proposed storm water basins at the locations provided by our client. SHWT determination was performed for two (2) locations within one storm basin. Infiltration tests were also performed at these locations. Boring locations SHWT-01 and SHWT-02 are shown on the attached boring location plan. The controlling parameters for the design of infiltration basins are the depth to evidence of Seasonal High Water Table (SHWT), and the saturated (stabilized) permeability of the soils that should be expected in the floor and berms of the basin. Any restrictive horizons within the soil profile could substantially affect the drainage capacity of the basin. In order to determine the depth to SHWT, Mr. Mike Eaker, a North Carolina Licensed Soil Scientist with Southeastern Soil & Environmental Associates, Inc., under contract tc Birmingham, AL • Auburn, AL • Huntsville, AL • Montgomery, AL - Columbus, GA • Louisville, KY • New Orleans, LA • Raleigh, NC • Dunn, NC • Jacksonville, NC • Springdale, AR • Little Rock, AR • Ft. Smith, AR • Tulsa, OK • Oklahoma City, OK • DFW Metroplex, TX• Virginia Beach, VA Gruber Mini Mall, Fort Bragg, North Carolina Project No.: RD210506: August 31, 2021 Building & Earth Sciences, has assisted with the field work and reporting for this work. Mr. Eaker's report details the procedures used in his field evaluation, the results of the soil observations, the depth to seasonal high groundwater, and the depth to observed water at each test location. Mr. Eaker's report is included with this report. Summary of Field Observations and Testing To determine the parameters that the Civil Designer will need to design the basins, the SHWT was determined at each boring location. Once the SHWT was determined, infiltration testing was performed at the elevation provided by our client. While onsite, our representative communicated our results with Mr. Bill Roark, PE. The results of our testing are summarized below. Ground Surface Elevation (ft) 393.6 393.8 Bottom of Basin Elevation (ft) 386.0 386.0 Depth to Observed SHWT (in) SHWT Elevation (ft) Depth to Groundwater (in) 65 124 388.2 383.5 NE* NE Groundwater Elevation (ft) NE NE CCHP Elevation (ft) Ksat (in/hour) 384.0 384.0 4.06 0.99 * NE — Not Encountered Statement of Design Method. Test Method and Limitations The flow of the near surface soils has been approximated using the concepts presented in Bernoulli's Equation for steady state flow and Darcy's Law for fluid flow through a porous media. Additionally, our Ksat values were calculated using the Glover solution which is dependent on soil saturation, the geometry of the bore hole, and the hydraulic head. To develop our recommendations, Building & Earth has measured/calculated the saturated flow rate (Ksat) for the soils at the site using accepted test methods and equipment. Ultimately, the drainage of the basins will be a function of the saturated flow rate of the soils, the surface area of the basin geometry, and the pressure differential (hydraulic head) induced by the storm water levels in the drainage structure. In order to determine the appropriate Ksat for the soils in each basin, a small diameter bore hole was advanced to a pre -determined depth of interest. At this depth, a BUILDING & EARTH 1 0 ■ Gruber Mini Mall, Fort Bragg, North Carolina Project No.: RD210506: August 31, 2021 constant head (pressure) was established and maintained. Once our measurements approached a stabilized flow rate, our test was terminated. The recommendations in this report are limited by several geologic considerations. The primary limitation is that geologic formations are variable in nature. The soils in the Fort Bragg are subject to perched water conditions, artesian conditions, and layers of undulating low permeability clay seams and layers. All of these geologic conditions have an effect on the steady state flow of groundwater. To the extent possible we have identified the material types that will impact the flow of groundwater, and have provided our professional opinion regarding the depth (elevation) to evidence of SHWT. Although Building & Earth has not provided an exhaustive survey of all of the soil deposits at the site, it is our opinion that we have properly and adequately characterized the site with regard to flow from the storm water basins that are planned for this development. Closing If you need further information, or if we can provide additional service, please do not hesitate to contact us. Respectfully Submitted, Building & Earth Scie $ K t A. Miller, P.E. Geotechnical Engineer NIA Attachments: Soil Scientist Report for Soil Profile and SHWT, and CCHP Testing Results Page 13 Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax (910) 822-4540 Email mike@southeasternsoil.com August 17, 2021 Mr. Bangnhi Pham Building and Earth, LLP 610 Spring Branch Road Dunn, NC 28334 Re: Seasonal High -Water Table determination for proposed stormwater treatment/retention area, Gruber Mini -Mall, Gruber Road, Fort Bragg, North Carolina Dear Mr. Pham, An evaluation of soil properties has been conducted at your request on a portion of the aforementioned property. The purpose of the investigation was to determine Seasonal High - Water Table depths (SHWT) based on soil profiles. Soils at the proposed basin site are most similar to the Wagram soil series (see attached boring logs). Two (2) soil borings were advanced to 8.0 or more feet below the soil surface. Seasonal High -Water Table (SHWT) as determined by evidence of colors of chroma 2 or less (and/or concentrations of high redox mottles) was encountered at depths of 65 and 124 inches below the ground surface (see chart attached). It should be noted that the reported SHWT does not necessarily reflect the elevation of static groundwater at the time of testing (due to variations in groundwater recharge rates, weekly and/or annual rainfall, drought conditions or other factors). The data presented in this report are limited by a number of considerations. The primary consideration is that soil formations can be highly variable. The soils found on this site can be subject to inclusions of other soil types, perched water, artesian conditions and/or layers of undulating low permeability clay seams. These and other soil conditions can have an effect on the steady state of groundwater flow. To the extent possible, we have identified the soil types that will impact the flow of groundwater, and have provided a professional opinion as to the depth of SHWT. Sincerely, Mike Eaker NC Licensed Soil Scientist 41030 SOIUSITE EVALUATION • SOIL PHYSICAL ANALYSIS • LAND USE/SUBDIVISION PLANNING • WETLANDS GROUNDWATER DRAINAGE/MOUNDING • SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax(910) 822-4540 Email mike@southeasternsoil.com SHWT depths, Gruber Mini -Mall, Gruber Road, Fort Bragg, North Carolina BORING SHWT_DEPTH (inches) Observed Water inches SHWT-01 65 None SHWT-02 124 None SOIL/SITE EVALUATION - SOIL PHYSICAL ANALYSIS - LAND USE/SUBDIVISION PLANNING - WETLANDS GROUNDWATER DRAINAGE/MOUNDING - SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax (91 D) 822-4540 Email mike@southeasternsoif.com Soil Boring Log (Boring SHWT-01), Gruber Mini -Mall, Gruber Road, Fort Bragg, NC This map unit consists of well drained soils that formed in loamy sediment on uplands. Slope ranged from 1 to 2 percent. 0 to 30 inches mixed sand and clay fill material (some construction debris noted). Bt - 30 to 47 inches; yellowish red (5YR 5/6) sandy loam; weak fine subangular blocky structure; very friable; gradual wavy boundary. BC - 47 to 65 inches; strong brown (7.5YR 5/8) loamy sand; weak fine granular structure; very friable; gradual wavy boundary. C - 65 to 96 inches; mixed mottled pale brown (2.5Y 7/3) and light gray (2.5Y 7/2) coarse sand; many fine yellowish brown (10YR 5l$) mottles; very friable. SHWT @ 65 inches (2.5Y 7/2) SOIL/SlTE EVALUATION • SOIL PHYSICAL ANALYSIS • LAND USE/SUBDIVISION PLANNING • WETLANDS GROUNDWATER DRAINAGE/MOUNDING - SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax (91 D) 822-4540 Email mike@southeasternsoil.com Soil Boring Log (Boring SI WT-02), Gruber Mini -Mall, Gruber Road, Fort Bragg, NC This map unit consists of well drained soils that formed in loamy sediment on uplands. Slope ranged from 1 to 2 percent. 0 to 61 inches mixed sand and clay fill material (some construction debris noted). Bt - 61 to 92 inches; red (2.5YR 4/8) sandy clay loam; weak fine subangular blocky structure; firm; gradual wavy boundary. BC - 92 to 124 inches; yellowish red (5YR 5/8) sandy loam; weak fine granular structure; very friable; gradual wavy boundary. C - 124 to 136 inches; yellowish red (5YR 5/8) sandy loam; many medium prominent light gray (IOYR 7/2) mottles; very friable. SHWT @ 124 inches (IOYR 7/2) SOIUSITE EVALUATION - SOIL PHY&CAL ANALYSIS - LAND USE/SUBDIVISION PLANNING - WETLANDS GROUNDWATER DRAINAGE/MOUNDING - SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax (910) 822-4540 Email mike@southeasternsoil.com SHWT depths, Gruber Mini -Mall, Gruber Road, Fort Bragg, North Carolina BORING SHWT-01 SHWT-02 SHWT-03 SHWT DEPTH „(inches) 65 124 125 Observed Water (inches) None None None SOWSITE EVALUATION • SOIL PHYSICAL ANALYSIS • LAND USE/SUBDIVISION PLANNING • WETLANDS GROUNDWATER DRAINAGE/MOUNDING-, • SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN Southeastern Soil & Environmental Associates, Inc. P.O. Box 9321 Fayetteville, NC 28311 Phone/Fax (910) 822-4540 Email mike@southeasternsoil.com Soil Boring Log (Boring SHWT-03), Gruber Mini -Mall, Gruber Road, Fort Bragg, NC This map unit consists of well drained that formed in loamy sediment on uplands. Slope ranged from 1 to 2 percent. 0 to 60 inches mixed sand and clay fill material (some construction debris noted). Bt — 60 to 74 inches; yellowish red (5YR 5/8) sandy clay loam; weak fine subangular blocky structure; firm; sticky, plastic; few fine and medium roots; gradual wavy boundary. BC - 74 to 87 inches; brownish yellow (10YR 6/8) sandy clay loam; weak fine subangular blocky structure; firm; slightly sticky, slightly plastic; gradual wavy boundary. C1 - 87 to 109 inches; light yellowish brown (2.5YR 6/4) loamy sand; very friable; massive structure; gradual wavy boundary. C2 - 109 to 125 inches; yellowish brown (1 OYR 5/8) loamy sand; very friable; massive structure; gradual wavy boundary. C3 - 125 to 135 inches; mottled brownish yellow (1 OYR 6/8), light gray (10YR 7/1) and red 10R 4/6) coarse sand; very friable; massive structure. SHWT @ 125 inches (I OYR 7/1) SOIUSITE EVALUATION - SOIL PHYSICAL ANALYSIS - LAND USE/SUBDIVISION PLANNING - WETLANDS GROUNDWATER DRAINAGE/MOUNDING - SURFACE/SUBSURFACE WASTE TREATMENT SYSTEMS, EVALUATION & DESIGN C� 1 Meastern -,, - [-�1101 11 %_ Wes, P.O. Box 9321 E1993500 E19937pp E1993800 Phone/Fax (910) 822-4540 Email mike@southeasternsoil.com N5011 N50100 f�o"4 P M ` s X�n rrf � a 7o r rr� N50090 f j D� Npit N50080 !O. N50070 Soil Boring Location, Gruber Mini -Mali Fort Bragg, NC US State Plane 1983 Scale 1:1,000 GRUBER.SSF North Carolina 3200 NAD 1983 (Conus) N 0 125.0 7/8/2022 GPS Path£nderoOfce Feet Owplrimble. C. SOIL/SITE EVALUATION • SOiL PHYSICAL ANALYSIS • LAND USE/SUBDIVISION PLANNING • WETLANDS GROUNDWATER DRAINAGEWOUNDiNG • SURFACE/SUBSURFACE WASTF TREATMENT SYSTEMS, EVALUATION & DESIGN s `S- O � v+ -i Hip 160 pR;'aa Na52 no ! Ra s'=���2 l o���2N� � �Y4 � ill 212 �>�`p�3R� ��$ mz> 3i���g��= mgo�g $ a � ag�� aca�A s��s lip; g nb �g>�:R a�a�ya m z w 4' -��aSz� y -, �� -u ��ymA�'�� � �W qq S�"� A ��o�um��$ �_ -- �" 1�bo�oF�� _ ��mRA IM � n gmz m o 4 Q' c'�� pipy soil 1a�zi �iri n �� �z o"' miziaaqu a9.°i m r�a�nYsz,n Sn raua�.�„ mn%�uz.'•' As. Hy �6~mga L"cri �g F'+ eg o lout 1 1. ��ay-gyp 1m1mg rmnz -� " �ma o��a25'r ,,, p m g aR os A4�'mmPQg�m�g��o�� A 4�a�pp�$ o --- ' z 1 wzm- PC- I 9 ®�®mR- V� \ N ■ x - - .. j , N 1r7�mYell V. LF ^. Z �nfrica��c��v ,�yr31_.• t r' z� HM �w GRAVES STREET + � W' g�m IN. "wg RgKrS� s RR !1R g2€➢�m���N��ss����o��RFa� s �s a� �9§��t8 ;-mass! am ga n�mR W! g.g022 op 1ig B N �0 = 0 om gg b Z, ; 4 C z a O z- a m D F€ce ' i' Ok E© SOLICITATION SET 3 JUNE 2021 Geotechnical, Environmental, and Materials Engineers Project Name: Gruber Mini Mall SWHT Client Name: Marshall Waters Woody Associates Technician: M. Lumokin Test Constants Liquid Used: Municipal Water Test Location: SHWT-01 Project Number: RD210506 Report Number: 1 of Date: 8/31 /2021 Depth of Water Table: >90" Constants: Capacity Liquid Containers setting Rate cm'/cm Sight Tube 1 L 1 On Storage Tube 5L n5S.000 Flow rate used Water Temp (IF): Depth of Observed Water 105 Hole Diameter: 2 rr or NA inches 3 inches Start Saturation: 12:01 Water Head: 7.5 inches Hole Radius: 1.500 Hole Depth: 120 inches I-est Vata Date Time Elapsed Time (hrs) 0 Total Flow Readings Flow Kate in3/hr Conductivity Remarks: Weather conditions, etc. Reading Flow cm3 Ksat In/hr 1 S 8/31 12 :01 0.02 0.02 26.0 105 105 384.45 1.62 E 8/31 12:02 25.0 2 S 8/31 12 :02 0.02 0.03 25.0 105 262.5 961.12 4.06 E 8/31 12:03 22.5 3 S 8/31 12 :03 0.02 0.05 22.5 105 262.5 961.12 4.06 E 8/31 12:04 20.0 4 S 12/3 12 :04 0.02 0.07 20.0 105 262.5 961.12 4.06 E 12/3 12:05 17.5 5 S 12/3 12 :05 0.02 0.08 17.5 105 262.5 961.12 4.06 E 12/3 12:06 15.0 6 S 12/3 12 :06 0.02 0.10 15.0 105 262.5 961.12 4.06 E 12/3 12:07 12.5 7 S E 8 S E 9 S E 10 S E 11 S E 12 S E 13 S E 14 S Stabilized Ksat'n/hr 4.06 SHWT-01 Geotechnical, Environmental, and Materials Engineers Project Name: Gruber Mini Mall SWHT Client Name: Marshall Waters Woody Associates Technician: M. Lumokin Test Constants Liquid Used: Municipal Water Test Location: SHWT-02 Project Number: RD210506 Report Number: 2 of Date: 8/31 /2021 Depth of Water Table: >90" Constants: Capacity Liquid Containers setting Rate cm'/cm Sight Tube 1 L 1 On Storage Tube 5L n5S.000 Flow rate used Water Temp (IF): Depth of Observed Water 105 Hole Diameter: 2 rr or NA inches 3 inches Start Saturation: 12:30 Water Head: 8 inches Hole Radius: 1.500 Hole Depth: 96 inches Test a a MEN Elapsed Time (hrs) A I Total Flow Readings Flow Kate in'/hr Conductivity Auger Refusal at 8.0ft Hydrologic Soil Group —Cumberland County, North Carolina (Gruber Mini Mall) 680120 680160 6m" 680240 680280 p of I 4 e r � r _ Soil Map may not �e val1. at this scale. $. 35° T 28" N 680120 680160 680200 680240 3 Map Scale: 1:1,580 if printed on A portrait (8.5" x 11") sheet Meters N 0 20 40 80 120 Feet 0 50 100 200 300 A Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zane 17N WGS84 ust)A Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey 680280 680320 6-1 35° 7' 38" N —T — 35° 7' 28" N 680320 3 5/23/2021 Page 1 of 4 Hydrologic Soil Group —Cumberland County, North Carolina Gruber Mini Mall Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI WgB Wagram-Urban land complex, 0 to 8 percent slopes A 5.5 100.0% Totals for Area of Interest 5.5 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long -duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink -swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition uSDA Natural Resources Web Soil Survey 5/23/2021 Conservation Service National Cooperative Soil Survey Page 3 of 4 8°58' 159 M ILS 1-T 20 MILS UTM GRID AND 2019 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET OVERHILLS, NC 2019 1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 C L I F D A L E, NC FEET 2019