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HomeMy WebLinkAboutDrainage Reports - 06/19/2025 March 12, 2025 Derek Lutz - Development Review City of Fort Collins Utilities – Stormwater Engineering 700 Wood Street Fort Collins, Colorado 80521 RE: City of Fort Collins – Banner Health Fort Collins Medical Campus, Neuro and Ortho Clinics Drainage Conformance Letter JVA Job No. 241220.CIV Dear Dan: JVA, Inc. has been contracted to provide civil engineering and design services for site improvements at Banner Health Fort Collins Medical Campus. The proposed project includes a new drop off zone and entry way into the clinic, an expansion to the existing parking lot, new accessible parking stalls, new concrete sidewalks, landscaping, and a reroute of the existing emergency fire access road. The approximate area of disturbance is 2.11 acres. Existing drainage patterns, as approved in the Final Drainage and Erosion Control Report on file with the City for Banner Health Medical Campus, Dated September 20, 2013, by Northern Engineering, will not be substantially altered. Banner Fort Collins Medical Campus is located at 4700 Lady Moon Drive, Fort Collins Colorado, 80528. The site is legally identified as Lot 1, Banner Health Medical Campus. The existing site is fully developed and contains buildings, parking lots, concrete walks, and access drives. The site is bound to the North by E Harmony Road, to the West by Lady Moon Drive, to the South by Le Fever Drive, and to the East by Cinquefoil Lane. The majority of the site storm runoff is directed to a storm drainage system which connects to an existing on-site detention pond. For the purpose of this study, analysis of the site has been limited to the proposed limits of work which lie majorly within historic basin 17 and partially within basins 13 and 18 from the previous drainage report. Site soils are classified by the Natural Resources Conservation Service as primarily Nunn Clay Loam with Hydrologic Soil Group Rating C. The site is located in a minimal flood hazard, Zone X, based on the latest FEMA Flood Insurance Rate Map Number 08069C0994F. The proposed improvements will be located on the Southwest portion of the site. Three existing drainage basins from the approved drainage report, basin 17 (4.01 acres), basin 13 (3.44 acres) and basin 18 (2.33 acres) will be disturbed to facilitate construction. Basin 17 is shown to be primarily overlot grading area with future parking area (that is proposed in this project) with a 100-year runoff coefficient and peak flow of 1.00 and 39.9 cfs, respectively. Basin 17 flows the South into the onsite storm system that gets directed to the detention pond in the Southeast corner of the site. Basin 13 is shown to be an overlot grading area with future building areas with a 100-year runoff coefficient and peak flow of 1.00 and 28.9 cfs. Basin 13 flows to the south into the existing onsite City of Fort Collins Approved Plans Approved by: Date: Wes Lamarque 06/19/2025 Banner Health Fort Collins Medical Campus Drainage Conformance Letter March 12, 2025 2 of 4 storm system that gets directed to the detention pond in the Southeast corner of the site. Basin 18 is shown to be an overlot grading area with future parking and building areas with a 100 -year runoff coefficient and peak flow of 1.00 and 23.2 cfs. Basin 18 flows to the east into the existing onsite storm system that gets directed to the detention pond in the Southeast corner of the site. The drainage patterns are proposed to match the historic and proposed conditions shown in the previous drainage report. Trying to match historic basins as best available from the previous report, we analyzed the impervious and runoff from each basin, although basin areas did not match exactly with the previous report. Each basin in the original report was designed with an imperviousness of 90% for future conditions, and the basins analyzed in these improvements are less than 90%, and each have decreasing runoff, even with the emergency gravel drive being considered the same impervious as concrete. See below for table comparing the historic basins and proposed with these improvements, showing that the current drainage report is being met. See attached calculations and drainage figure included with this letter. PLANNED VS PROPOSED RUNOFF COMPARISON SUMMARY TABLE BASIN DESIGN POINT PLANNED AREA (ACRES) PROPOSED AREA (ACRES) PLANNED IMPERV (%) PROPOSED IMPERV (%) PLANNED 2- YR RUNOFF (CFS) PROPOSED 2-YR RUNOFF (CFS) PLANNED 100-YR RUNOFF (CFS) PROPOSED 100-YR RUNOFF (CFS) 17 17 4.01 4.27 90% 64.4% 9.70 3.97 39.90 20.38 13 13 3.44 3.34 90% 50.4% 6.80 2.85 28.90 17.81 18 18 2.33 2.34 90% 21.8% 5.70 1.00 23.20 13.32 In the new developed condition, Basin 17 consists of the drop off zone, concrete sidewalks, parking lot expansion, and landscaping. The 100-year runoff coefficient and peak flow are to be nearly the same as shown in the original report due to the report accounting for these new improvements in the original design. Basin 13 consists of the rerouted emergency fire access road and Basin 18 will consist of some minor grading. The 100-year runoff coefficient and peak flow are to be less than as shown in the original report due to the improvements already being accounted for in the future condition. The developed basins have been designed to follow the historic drainage patterns. The design for the proposed improvements meet the City requirements, the impervious and runoff meet the original drainage report intent, and the proposed development will not impact neighboring or downstream property owners. Please contact us if you have any questions regarding this submission. Sincerely, JVA, INCORPORATED By: __________________________ Eric J. Kohnen, P.E. Senior Project Engineer Banner Health Fort Collins Medical Campus Drainage Conformance Letter March 12, 2025 3 of 4 REFERENCES 1. Final Drainage and Erosion Control Report, Banner Health Medical Campus, Dated September 20, 2013, Northern Engineering 2. Flood Insurance Rate Maps, FEMA Map Service Center. Panel 08069C0994F, December 19, 2006. 3. NRCC Hydrologic Soil Group Map, Data Acquired 1/16/2025 Banner Health Fort Collins Medical Campus Drainage Conformance Letter March 12, 2025 4 of 4 APPENDIX 1 4908.95 CP BANNER N=1432931.95 E=3137756.32 2 4912.36 CP E.R. N=1433537.87 E=3136991.71 3 4910.66 CP HEALTH N=1432813.60 E=3137339.06 4 4912.97 CP MEDICAL N=1433297.20 E=3137303.22 5 4914.19 CP CENTER N=1433144.81 E=3136850.67 RD CC CCCC CCCC CCCC CCCC CCCC CCCC CCCC CCCC CCCC CCCC CCCC RDRD FOFO EB CC CC CCCC CCCC CC CCE EB FO FO EBEBW EB EB EB EB FO EB W EB E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E EE E E E E E E FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO E E E E E E E E E E E E FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO E E E E E E E E E E E E FO FO FO FO FO FO FO FO SMH 11651 RIM = 4910.33 INV. N = 4904.65 (4" PVC) INV. E = 4904.41 (6" PVC) SMH 11822 RIM = 4912.05 INV. E = 4901.89 (6" PVC) INV. W = 4901.84 (6" PVC) INV. S = 4901.73 (8" PVC) SMH 12340 RIM = 4907.12 INV. N = 4898.14 (8" PVC) INV. S = 4898.12 (8" PVC) STUB, OR CLOGGED INV. E = 4897.87 (8" PVC) DMH 12337 RIM = 4908.25 INV. N = 4904.62 (15" RCP) INV. W = 4903.37 (36" RCP) INV. E = 4903.35 (36" RCP) DMH 12288 RIM = 4909.66 INV.W = 4902.91 (36" RCP) INV.SE = 4902.85 (42" RCP) INV. NE = 4902.85 (30" RCP) INLET 12700 GRATE = 4908.1 INV. SW = 4903.51 (30" RCP) SMH 12695 RIM = 4910.88 INV. N = 4900.87 (4" PVC) INV. N = 4896.32 (4" PVC) INV. W = 4896.10 (8" PVC) INV. E = 4895.94 (8" PVC) INLET 12677 RIM = 4909.83 INV. NW = 4904.83 (15" RCP) DMH 12705 RIM = 4911.58 INV. E = 4906.20 (6" PVC) INV. S = 4905.35 (15" RCP) INV. N = 4905.35 (15" RCP) INLET 12710 GRATE = 4911.3 INV. S = 4906.39 (15" RCP) PIPE INV. = 4903.82 (36" RCP WITH FES) PIPE TOP FES = 4903.32 (15" RCP) END FES ELEV. = 4901.63 PIPE TOP FES = 4906.76 (42" RCP WITH FES)END FES ELEV. = 4902.53 PIPE TOP FES = 4904.95 (24" RCP WITH FES)END FES ELEV. = 4902.52 PIPE TOP FES = 4905.66 (24" RCP WITH FES)END FES ELEV. = 4903.24 PIPE INV. = 4907.80 (8" PVC) PIPE INV. = 4908.15 (8" PVC) SMH 12690 RIM = 4912.05 GREASE TRAP SMH 12691 RIM = 4912.06 GREASE TRAP FOUND #4 REBAR WITH BLUE PLASTIC CAP LS 38470 FOUND #4 REBAR FOUND #5 REBAR WITH BROKEN YELLOW PLASTIC CAP LS 37963 "JR ENG." FOUND #4 REBAR WITH BLUE PLASTIC CAP LS XXX64 FOUND MAG NAIL WITH BRASS TAG LS 38470 "NE" RIM = 4909.39 NUT = 4903.08RIM = 4909.53 NUT = 4902.80RIM = 4909.70 FILLED WITH DIRT NUT / TOP DIRT = 4908.79 RIM = 4908.32 TOP NUT EXTENSION = 4907.10 BOTTOM = 4902.82 RIM = 4909.92 NUT = 4904.82 RIM = 4909.79 NUT = 4904.78 RIM = 4910.87 NUT = 4906.03 PIPE ON WALL INV. = 4914.48 (6" PVC) PIPE ON WALL INV. = 4914.42 (6" PVC) PIPE ON WALL INV. = 4914.51 (4" PVC) SIGN: "FIRE LANE" SIGN: "FIRE LANE" SIGN: "FIRE LANE" SIGN: STAFF / PHYSICIAN PARKING SIGN: PHYSICIAN PARKING ONLY SIGN: PHYSICIAN PARKING ONLY ← EMERGENCY CALL BOX SIGN: "RESERVED PARKING" SIGN: "FIRE ACCESS ONLY" SIGN: "FIRE ACCESS ONLY" SIGN: RED DOTS, TYP. SIGN: "ANYTIME" MONUMENT SIGN: HOSPITAL DIRECTIONS FF = 4913.33 TOC @ THRESHOLD FF = 4913.42 TOC @ DOOR FF = 4913.42 TOC @ DOOR LIGHTS ON BOLLARDS, TYP. LIGHT POLE ON 2' CONCRETE BASE, TYP. LIGHT POLE ON 2' CONCRETE BASE, TYP. ROCK ROCK CRUSHER FINES SHRUBS SHRUBS ROCK SHRUBS ROCK SHRUBS ROCK SHRUBS ROCK ROCK IIII IIIIIIII III I IIII IIII IIII IIII IIII IIII IIII IIII IIII IIII ET IIII IIII SIGN: NO PARKING INLET 12355 RIM = 4909.58 INV. SE = 4904.38 (15" RCP) INV. NE = 4901.99 (15" RCP) EMERGENCY CALL BOX RIM= 4909.60 RIM = 4909.71 NUT = 4906.25 LE FE V E R D R I V E LA D Y M O O N D R I V E (R . O . W . W I D T H V A R I E S ) FIRE DEPT. ACCESS ROAD 1.7'3.6' 1.3' 1.9' 3.6'27.5'0.5'13.6'2.2' 11 6 . 2 ' 23.7' 4. 9 ' 29.8'4. 2 ' 26.4'1.4'12.1' 92 . 6 ' 215.5' 12 6 . 5 ' 30.0' CENTURY LINK FIBER CONNEXION FIBER FORT COLLINS ELECTRIC XCEL GAS FORT COLLINS WATER FORT COLLINS WATER FORT COLLINS WATER FORT COLLINS WATER FORT COLLINS ELECTRIC COMCAST FIBER XCEL GAS PRIVATE ELECTRIC PRIVATE ELECTRIC PRIVATE ELECTRIC PRIVATE ELECTRIC PRIVATE ELECTRIC CIN Q U E F O I L L A N E TIMBERWOOD DRIVE (R.O.W. WIDTH VARIES) PRIVATE ACCESS ROAD SUBJECT PARCEL 1,170,323 SQ. FT. 26.867 ACRES XCEL GAS FORT COLLINS ELECTRIC CENTURY LINK FIBER CONNEXION FIBER COMCAST FIBER SUBJECT PARCEL 1,170,323 SQ. FT. 26.867 ACRES E E E E E E ROCK DE V E L O P E D D R A I N A G E M A P FIG 1 RE V I S I O N D E S C R I P T I O N D' W N DE S ' D DA T E NO . DESIGNED BY: DRAWN BY: CHECKED BY: JOB #: DATE: © JVA, INC. BA N N E R H E A L T H FO R T C O L L I N S M E D I C A L C A M P U S NE U R O A N D O R T H O C L I N I C S SHEET NO. 241220.CIV MARCH 2025 KJC JLT EJK JVA, Inc.1319 Spruce Street www.jvajva.com Boulder, CO 80302 303.444.1951 Boulder ● Fort Collins ● Winter Park Glenwood Springs ● Denver JVA Incorporated Job Name: Banner FCMC 1319 Spruce Street Job Number: 241220.civ Boulder, CO 80302 Date: 3/12/25 Ph: (303) 444 1951 By: EJK Banner FCMC Composite Runoff Coefficient Calculations Municipality: Fort_Collins Impervious Values: MHFD Runoff Coefficients: MHFD Formulae Basin Design Data I (%) = 95% 95% 95% 20%I (%) Area (sf) Area (sf) Area (sf) Area (sf) Basin Name Soil Type Design Point Streets Paved Concrete Drives/Wa lks Roof Landscapi ng ATotal (sf) ATotal (ac) Imp (%)C2 C5 C10 C100 17A C/D 17A 59,408 14,545 22,836 96,789 2.22 77.3% 0.62 0.67 0.70 0.80 17B C/D 17B 24,663 10,153 44,584 79,400 1.82 52.9% 0.41 0.47 0.52 0.70 17C C/D 17C 1,277 8,453 9,730 0.22 29.8% 0.21 0.28 0.35 0.61 13 C/D 13 16,415 42,525 86,710 145,650 3.34 50.4% 0.39 0.45 0.50 0.69 18 C/D 18 2,441 99,279 101,720 2.34 21.8% 0.15 0.21 0.29 0.57 Basin 17 Total 84,071 25,975 0 75,873 185,919 4.27 64.4% 0.90 1.03 1.16 1.60 TOTAL SITE 84,071 44,831 42,525 261,862 433,289 9.95 49.7%0.63 0.73 0.84 1.20 Runoff Coefficients 241220.civ JVA Civil Rational Calculations Basin Data Page 1 of 4 JVA Incorporated Job Name: Banner FCMC 1319 Spruce Street Job Number: 241220.civ Boulder, CO 80302 Date: 3/12/25 Ph: (303) 444 1951 By: EJK Municipality: Fort_Collins Banner FCMC Time of Concentration Calculations Municipality: Fort_Collins Impervious Values: MHFD Runoff Coefficients: MHFD Formulae Sub-Basin Data tc Comp tc Final Basin Name Design Point ATotal (ac)C5 Length (ft)Slope (%) ti (min)Length (ft) Slope (%) Type of Land Surface Cv Velocity (fps) tt (min) Time of Conc ti + tt = tc Channelized Length (ft) Channelized Slope (ft/ft)tregional tc or tregional 17A 17A 2.22 0.67 265 1.79%10.7 75 0.89%Paved areas & shallow paved swales 20 1.9 0.7 11.4 75 0.009 13.5 11.4 17B 17B 1.82 0.47 86 1.92%8.7 613 0.60%Paved areas & shallow paved swales 20 1.6 6.6 15.2 613 0.006 25.0 15.2 17C 17C 0.22 0.28 72 2.35%9.6 Paved areas & shallow paved swales 20 0.0 0.0 9.6 0 0.000 N/A 9.6 13 13 3.34 0.45 70 1.00%10.0 Paved areas & shallow paved swales 20 0.0 0.0 10.0 0 0.000 N/A 10.0 18 18 2.34 0.21 9.5 1.00%5.0 Paved areas & shallow paved swales 20 0.0 0.0 5.0 0 0.000 N/A 5.0 Initial Overland Time (ti) MHFD Eq 6-3 Channelized Travel Time (tt) MHFD Eq 6-4 Regional Check (tregional) MHFD Eq 6-5 241220.civ JVA Civil Rational Calculations Basin Data Page 2 of 4 JVA Incorporated Job Name: Banner FCMC 1319 Spruce Street Job Number: 241220.civ Boulder, CO 80302 Date: 3/12/25 Ph: (303) 444 1951 By: EJK Banner FCMC Developed Storm Runoff Calculations Design Storm : 100 Year Point Hour Rainfall (P1) : 2.87 B a s i n N a m e D e s i g n P o i n t A r e a ( a c ) C 1 0 0 t c ( m i n ) C * A ( a c ) I ( i n / h r ) Q ( c f s ) T o t a l t c ( m i n ) S C* A ( a c ) I ( i n / h r ) Q ( c f s ) I n l e t T y p e Q i n t e r c e p t e d Q c a r r y o v e r Q b y p a s s P i p e S i z e ( i n ) or e q u i v a l e n t P i p e M a t e r i a l S l o p e ( % ) P i p e F l o w (c f s ) M a x P i p e Ca p a c i t y ( c f s ) L e n g t h ( f t ) V e l o c i t y ( f p s ) t t ( m i n ) To t a l T i m e (m i n ) N o t e s 17A 17A 2.22 0.80 11.4 1.78 7.34 13.05 11.36 1.78 7.34 13.05 Combo 18 in RCP 1.5%13.1 13.8 35 7.3 0.08 11.44 17B 17B 1.82 0.70 15.2 1.28 6.48 8.27 15.25 1.28 6.48 8.27 Combo 18 in RCP 1.5%8.3 13.8 34 7.6 0.07 15.32 Downstream of Proposed Manhole 15.32 3.05 6.45 19.71 36 in RCP 0.5%19.7 50.7 108 6.2 0.29 15.61 17C 17C 0.22 0.61 9.6 0.14 7.84 1.06 9.62 0.14 7.84 1.06 Area Drain 15 in RCP 0.5%1.1 4.9 349 3.0 1.95 11.57 Total Basin 17 (Downstream of Existing Manhole)15.61 3.19 6.39 20.38 36 in RCP 0.5%20.4 50.7 6.3 0.00 15.61 13 13 3.34 0.69 10.0 2.31 7.72 17.81 10.04 2.31 7.72 17.81 18 18 2.34 0.57 5.0 1.34 9.95 13.32 5.01 1.34 9.95 13.32 Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 241220.civ JVA Civil Rational Calculations Q100 Page 3 of 4 JVA Incorporated Job Name: Banner FCMC 1319 Spruce Street Job Number: 241220.civ Boulder, CO 80302 Date: 3/12/25 Ph: (303) 444 1951 By: EJK Banner FCMC Developed Storm Runoff Calculations Design Storm : 2 Year Point Hour Rainfall (P1) : 0.86 B a s i n N a m e D e s i g n P o i n t A r e a ( a c ) C 2 t c ( m i n ) C * A ( a c ) I ( i n / h r ) Q ( c f s ) T o t a l t c ( m i n ) S C* A ( a c ) I ( i n / h r ) Q ( c f s ) I n l e t T y p e Q i n t e r c e p t e d Q c a r r y o v e r Q b y p a s s P i p e S i z e ( i n ) or e q u i v a l e n t P i p e M a t e r i a l S l o p e ( % ) P i p e F l o w (c f s ) M a x P i p e Ca p a c i t y ( c f s ) L e n g t h ( f t ) V e l o c i t y ( f p s ) t t ( m i n ) To t a l T i m e (m i n ) N o t e s 17A 17A 2.22 0.62 11.36 1.39 2.11 2.92 11.36 1.39 2.11 2.92 18 in RCP 1.5% 2.9 13.8 35 5.8 0.10 11.46 17B 17B 1.82 0.41 15.25 0.74 1.86 1.38 15.25 0.74 1.86 1.38 18 in RCP 1.5% 1.4 13.8 34 4.6 0.12 15.37 Downstream of Proposed Manhole 15.37 2.13 1.85 3.95 36 in RCP 0.5% 3.9 50.7 108 3.9 0.46 15.83 17C 17C 0.22 0.21 9.62 0.05 2.25 0.11 9.62 0.05 2.25 0.11 15 in RCP 0.5% 0.1 4.9 349 1.5 3.85 13.47 Total Basin 17 (Downstream of Existing Manhole)15.83 2.18 1.82 3.97 36 in RCP 0.5% 4.0 50.7 3.9 0.00 15.83 13 13 3.34 0.39 10.04 1.29 2.21 2.85 10.04 1.29 2.21 2.85 18 18 2.34 0.15 5.01 0.35 2.85 1.00 5.01 0.35 2.85 1.00 Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 241220.civ JVA Civil Rational Calculations Qminor Page 4 of 4 Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/16/2025 Page 1 of 4 44 8 5 3 7 0 44 8 5 4 3 0 44 8 5 4 9 0 44 8 5 5 5 0 44 8 5 6 1 0 44 8 5 6 7 0 44 8 5 7 3 0 44 8 5 7 9 0 44 8 5 8 5 0 44 8 5 3 7 0 44 8 5 4 3 0 44 8 5 4 9 0 44 8 5 5 5 0 44 8 5 6 1 0 44 8 5 6 7 0 44 8 5 7 3 0 44 8 5 7 9 0 44 8 5 8 5 0 499050 499110 499170 499230 499290 499350 499410 499050 499110 499170 499230 499290 499350 499410 40° 31' 24'' N 10 5 ° 0 ' 4 1 ' ' W 40° 31' 24'' N 10 5 ° 0 ' 2 4 ' ' W 40° 31' 7'' N 10 5 ° 0 ' 4 1 ' ' W 40° 31' 7'' N 10 5 ° 0 ' 2 4 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 100 200 400 600 Feet 0 35 70 140 210 Meters Map Scale: 1:2,540 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 19, Aug 29, 2024 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 2, 2021—Aug 25, 2021 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/16/2025 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 73 Nunn clay loam, 0 to 1 percent slopes C 8.0 29.8% 74 Nunn clay loam, 1 to 3 percent slopes C 18.9 70.2% Totals for Area of Interest 26.9 100.0% 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 Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/16/2025 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/16/2025 Page 4 of 4