The URL can be used to link to this page

Home My WebLink AboutFRCC HEALTH CARE CAREERS CENTER - SPA180002 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTNovember 27, 2018 Wes Lamarque, P.E. City of Fort Collins Utilities – Stormwater Engineering 700 Wood Street Fort Collins, CO 80521 RE: Front Range Community College, Health Care Career Center – Preliminary Drainage Letter JVA Job No. 2996c Dear Wes: This letter has been prepared to summarize the drainage concept and proposed changes in impervious area associated with the site improvements for the Health Care Career Center (HCCC) project located at 4616 South Shields Street in the City of Fort Collins. This letter represents an addendum to the approved Master Drainage Study for the Front Range Community College Larimer Campus, dated May 22, 2014, prepared by Interwest Consulting Group. PROJECT DESCRIPTION The project site is an approximately 3.2 acre area in the northwest corner of the FRCC Larimer Campus located at the intersection of South Shields Street and West Harmony Road, in the City of Fort Collins, Colorado. The project site is currently undeveloped and generally consists of grassy open space with a few trees. The proposed site improvements include the construction of a new approximately 31,800 square foot multi-story building, plazas on the east & west sides and at the south entrance to the building, connections to existing walks, accessible routes and ramps, passenger drop off area and connection to existing parking area to the south. The existing undeveloped site overall imperviousness is 7.3%. The proposed improvements will increase the overall imperviousness to 47.4%. HISTORIC AND DEVELOPED RUNOFF Detention for runoff generated by the Front Range Community College (FRCC) Larimer Campus is provided in two existing detention ponds. A permanent detention pond is located at the northeast corner of the campus, at the intersection of Harmony Road and Starflower Drive. A temporary detention pond is located at the proposed location of the Health Care Career Center. The temporary pond was constructed in the interim condition before proper conveyance facilities were constructed to route runoff to the permanent pond. Now that the conveyance facilities are in place, this temporary pond may be removed with the proposed HCCC improvements. A study was performed in April 2018 by Crestone Consultants to analyze the impact of future development on the permanent detention pond. It was determined that the existing infrastructure and permanent detention pond have the capacity to capture and detain approximately 70,000 square feet of additional impervious area associated with construction of the HCCC and other future improvements. A copy of the study is included as an attachment to this letter. A map of the campus showing the location of the detention pond is included within the study. FRCC Health Care Career Center Preliminary Drainage Letter November 27, 2018 2 of 3 Runoff generated by the existing project site currently is conveyed to the permanent detention pond via a system of underground storm drains and grassy swales. A portion of the existing site is routed to the temporary detention pond and then conveyed to the permanent detention pond via the same system of underground storm drains and grassy swales. The temporary pond will be removed with the construction of the HCCC. The proposed site has been graded in an attempt to maintain historic flow patterns. Runoff from the proposed site will be captured via a system of inlets and underground storm and roof drains and released into the existing conveyance system which discharges into the permanent detention pond. The permanent detention pond releases runoff into a channel that runs parallel to Harmony Road. Below is a summary of the existing and proposed changes to impervious area. The newly added impervious area with the proposed HCCC improvements is less than the 70,000 square foot confirmed additional impervious area that the existing permanent detention pond can accommodate. IMPERVIOUS AREA SUMMARY TABLE Impervious Area (sf) Pervious Area (sf) Total Area (ac) % Impervious Existing 10,169 129,223 3.2 7.3% Proposed 66,112 73,280 3.2 47.4% ∆ +55,943 -55,943 - +40.1% Chapter 2 of the Urban Drainage and Flood Control District’s Urban Storm Drainage Criteria Manual Volume 3 (USDCM) provides guidelines for the selection of appropriate structural BMPs for a site that is to be developed or redeveloped. FRCC’s Health Care Career Center is best characterized as a “conventional redevelopment” with just over 1 acre of impervious area on the project site. The BMP decision tree for such sites is provided in Figure 2-2 of the USDCM. The site and surrounding vicinity are comprised primarily of hydrologic soil group Type C soils, per the NRCS soil survey. Permeable pavement and/or the use of a “green roof”, rain garden, or grass swales/buffers are the recommended runoff reduction practices for this scenario. The HCCC site design includes large areas of grass/vegetated buffers and swales that convey stormwater to local area inlets which will serve to treat storm runoff for a minimum of 75% of the added impervious area on the site for water quality prior to discharge into the public storm system. These features facilitate sedimentation and filtration while limiting erosion, accounting for both treatment and slowed release of the runoff in order to provide a higher degree of water quality, known as Low Impact Development (LID), as described in the USDCM. The proposed development of this site will serve to reduce water quality and quantity impacts to natural drainageways by decreasing the frequency, rate, duration, and volume of runoff. FRCC Health Care Career Center Preliminary Drainage Letter November 27, 2018 3 of 3 Erosion and Sediment Control During construction, temporary erosion and sediment control practices will be used to limit soil erosion and sediment discharge off the site. Please feel free to contact me to discuss any questions you may have. Sincerely, JVA, INCORPORATED By: ________________________________ Karen Brigman, CFM . Senior Project Engineer Enclosures: Reference Materials Schematic Grading Plan CC: Gwen Gilley, Hord Coplan Macht CRESTONE CONSULTANTS, LLC - 14145 West Warren Circle - Lakewood, CO - 80228 303 · 997 · 6113 - www · crestonellc · com - crestone@crestonellc.com April 23, 2018 Mr. Dennis DeRemer Director of Facilities – Larimer Campus Front Range Community College 4616 S. Shields Street Fort Collins, CO 80526 Re: Larimer Campus - Northwest Detention Pond Status Crestone Project No.: 13020 Dear Mr. DeRemer: Per your request on April 17, 2018, we’ve prepared this letter to identify the status of the existing detention pond located west of the Sunlight Peak (SP) building and north of the Observatory and Harmony Library Parking Lot at the northwest corner of the Larimer Campus. We’ve reviewed the following Master Drainage Studies for the Larimer Campus in the preparation of this letter: 1. Master Drainage Study – Front Range Community College Campus, prepared by Interwest Consulting Group, dated December 1, 2010 revised. (AKA 2010 Master Study) 2. Master Drainage Study – Front Range Community College Campus, prepared by Interwest Consulting Group, dated May 22, 2014. (AKA 2014 Master Study) A summary of the 2010 Master Study as it pertains to the subject detention pond has been provided as follows: 2010 Master Study Summary: The subject detention pond was constructed with the Harmony Library Parking Lot project in 2010/2011 to help mitigate any effects from the parking lot development on the existing storm sewer system. The 2010 Master Study identified the existing storm sewer system which the Harmony Library Park Lot is tributary to (i.e. Storm System 1) as being undersized. The subject detention pond is located within Basin A1 and is required to be installed to attenuate developed flows from the interim condition Basin A1 until improvements to the campus’ storm drainage conveyance and storage systems are constructed. Required storm drainage conveyance improvements include the construction of a new storm pipe (36”) located on the north side of the SP building which will convey the developed flows from Basin A1 east to the existing riprap channel adjacent to Harmony Road which outfalls to the campus’ North Detention Pond located at the northeast corner of the campus. Required storage improvements include increasing the North Detention Pond volume by raising the pond’s spillway elevation and providing additional pond excavation to account for the additional April 23, 2018 Dennis DeRemer; Front Range Community College – Northwest Detention Pond Status Page 2 imperviousness proposed throughout the campus and to provide additional water quality capture volume. Additionally, the 2010 Master Study includes modifying the North Detention Pond outlet structure to accommodate the additional water quality capture volume and detained volumes. Please refer to select excerpts and maps attached to this letter from the 2010 Master Study. In 2011, the storm drainage conveyance and storage systems identified in the 2010 Master Study were constructed. This includes the 36” storm pipe conveyance for Basin A1 as well as the North Detention Pond storage improvements and outlet structure modifications. A summary of the 2014 Master Study as it pertains to the subject detention pond has been provided as follows: 2014 Master Study Summary: The 2014 Master Study states, “In the current condition, Basin A1 drains to a temporary pond. This temporary pond drains north to the existing 36” RCP Storm System located to the northeast that conveys the flow east to the Northern Channel adjacent to Harmony Road at the northeast corner of the SP building and finally to the North Detention Pond. This temporary pond can be removed at any time, the existing storm pipes and swales are adequate to receive undetained water now and with future building. This entire basin will drain to the existing 36” RCP Storm System.” Please refer to select excerpts and maps attached to this letter from the 2014 Master Study. Based on the 2014 Master Study, all improvements which were required to be installed for the removal of the subject detention pond have been constructed and the subject detention pond may be removed at any time. Please Note - The 2014 Master Study identifies conveyance and storage capacity allowances provided by the existing storm drainage system for future identified planned improvement areas. The study also identifies triggers for future improvements to the storm drainage conveyance and storage systems, including improvements for North Detention Pond. We recommend that Front Range Community College provide a complete copy of the 2014 Master Study to all perspective designers for their review and use in preparing their respective designs of future improvements throughout the Larimer Campus. Should you have any questions, please feel free to call me at your convenience at (303) 997-6113. Sincerely, Crestone Consultants, LLC Joseph M. Erjavec, P.E. Principal Attachment(s) Attachment A – 2010 Master Study Select pages from Master Drainage Study ‐ Front Range Community College Campus, prepared by Interwest Consulting Group, dated December 1, 2010 revised Attachment B – 2014 Master Study Select pages from Master Drainage Study ‐ Front Range Community College Campus, prepared by Interwest Consulting Group, dated May 22, 2014 MASTER DRAINAGE STUDY Front Range Community College Campus Prepared for: Front Range Community College 4616 S Shields St Fort Collins, Colorado 80526 Prepared by: Interwest Consulting Group 1218 West Ash, Suite C Windsor, Colorado 80550 (970) 674-3300 May 22, 2014 Job Number 1124-086-00 6 the current peak runoff from the site to the pond is about 178.4 cfs. The existing pond, based on a current topographic survey, has 3.1 Ac-ft of storage (not including water quality capture volume). The 100-yr water surface elevation is at elevation 5063.8’ and spillway is at elevation 5063.9’. With today’s pond size and the historic 100-year release rate of 42 cfs, 0 cfs would spill over the spillway to the drainage channel adjacent to the Coventry Subdivision. Please refer to Appendix D for the North Detention Pond calculations. The South Detention Pond is located in the southeast portion of the campus adjacent the Clarendon Hills and Coventry Subdivisions. This pond treats water quality and detains flow from the newest parking lot. The pond releases to the Southern channel that directs flow to the North Detention Pond. The South Detention Pond releases 0.6 cfs and is a negligible impact to the overall release from the North Pond. 5. DRAINAGE FACILITY DESIGN 5.1 Specific Flow Routing A summary of the drainage patterns within each basin is provided in the following paragraphs. The Master Drainage Plan Current Condition map is located in the back pocket of this study. Basins A and A1 include the northwest portion of the site. These basins contain portions of HL, BP and RP buildings and all of SP and CP buildings. With current conditions, basins A and A1 consist of 8.0 acres. Basin A is 3.8 acres and flow from this basin enters Storm System 1 and is conveyed east to the North Detention Pond. Basin A1 is 4.2 acres and is the area west of the SP building, consists of a parking lot and has space for an additional impervious area in the future. Once an improvement adding hard surface is completed, it will then be considered completely built out. For the purposes of this report, basin A1 will be considered in its current condition. In the current condition, basin A1 drains to a temporary pond. This temporary pond drains north to the existing 36” RCP Storm System located to the northeast that conveys the flow east to the Northern Channel adjacent to Harmony Road at the northeast corner of the SP building and finally to the 7 North Detention Pond. This temporary pond can be removed at any time, the existing storm pipes and swales are adequate to receive undetained water now and with future building. This entire basin will drain to the existing 36” RCP Storm System. Basin B is 3.2 acres and includes the center portion of the site. This basin includes portions of buildings BP, RP, LP and MA. Flows from this basin enter existing Storm System 2 and are conveyed east to the North Detention Pond. Basin C is 14.3 acres and includes the student parking lots located in the center of the site. Flows in this area will be routed east in existing Storm System 3 to the North Detention Pond. Basin D is a total of 5.5 acres and consists of the south central portion of the site. It consists of parking lots and the existing Southern Channel. This basin drains north via curb cut and inlet in the parking lot to the existing grass lined Southern Channel located between the existing student parking lots. Culverts are sized to pass this flow and the additional offsite flow from the Westbury Pond and Shields under the two drive aisles that access the parking lot. Basin E is 4.2 acres and is located in the east portion of the site. The majority of this basin is a parking lot. Flow from this basin sheets to the northeast and into the existing North Detention Pond. If an addition of a building does occur in the future, it will occur in the existing parking lot and will include removal of pavement and will not affect the overall site imperviousness of this basin. Basin F is 6.7 acres and consists of the northeast portion of the site and includes the Northern Channel and the North Detention Pond. It also contains the MP and FB buildings. Basin G is 5.2 acres and is located in the southwest portion of the campus. This basin includes the southern parking lot and is north of the irrigation ditch and is considered the Southwest Parking Lot Expansion. The basin drains via a self-contained storm system to a detention and water quality pond located in the southeast portion of the campus adjacent the Clarendon Hills and Coventry Subdivisions. The pond detains this basin’s 100-year event to historic 2-year flows and is sized to also handle runoff from a future phase of 8 parking area. The total 100-year developed release rate for the Southwest Parking Lot Expansion is slightly over the 10-year historic runoff. Construction of a parking lot and South Detention Pond in this basin is currently underway (2014). Design of this area is included in JVA Consulting Engineers, “FRCC Larimer Campus—South Parking Lot (Phase I & II) Final Drainage Letter”, dated January 12, 2014 in Appendix E of this document. Because of the detention provided in Basin G, this acreage is not included in the North Detention Pond volume calculations. 5.2 Proposed Improvements The current conditions of the portions of the site draining to the existing North Detention Pond include 41.9 acres at 61% imperviousness. The existing pond, based on a current topographic survey, has 3.1 ac-ft of storage (not including water quality capture volume). The required water quality capture volume is 1.0 ac-ft and is achieved at elevation 5061.8’ based on the as-built shots of the water quality outlet structure. With today’s pond size and the historic 100-year release rate of 42 cfs, the 100-yr water surface elevation is at elevation 5063.8’ and spillway is at elevation 5063.9’. The entire site is detained and 0 cfs spills over the spillway to the drainage channel adjacent to the Coventry Subdivision. Currently, the pond has capacity for 70,000 square feet of additional impervious area allowing for Future Impervious Areas A and B to be completed without needing to upgrade the North Detention Pond or water quality outlet structure. These improvements equate to the 41.9 acres having 65% imperviousness. With these conditions, the required water quality capture volume will be 1.1 ac-ft at elevation 5061.8’. With today’s pond size and the historic 100-year release rate of 42 cfs, the 100-year water surface and spillway elevation will be at elevation 5063.9’. Please refer to Appendix D for pond calculations. Please refer to the Master Drainage Plan Current Conditions map located in the back pocket for two delineated areas where future impervious areas could be located. Area A is located in the northwest corner of the site within Basin A1. Area B is in Basin F and is located in the flat area adjacent to the Mount Antero Building. If changes to the 41.9 acres that drain to the North Detention Pond cause a percent imperviousness to be greater than 65%, the pond must be reanalyzed using EPA SWMM 5.0 software and a new water quality and detention volume must be calculated. Changes Hydrologic Soil Group—Larimer County Area, Colorado (FRCC HCCC) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/27/2018 Page 1 of 4 4485700 4485720 4485740 4485760 4485780 4485800 4485820 4485840 4485860 4485700 4485720 4485740 4485760 4485780 4485800 4485820 4485840 4485860 491870 491890 491910 491930 491950 491970 491990 491870 491890 491910 491930 491950 491970 491990 40° 31' 24'' N 105° 5' 45'' W 40° 31' 24'' N 105° 5' 40'' W 40° 31' 18'' N 105° 5' 45'' W 40° 31' 18'' N 105° 5' 40'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 40 80 160 240 Feet 0 10 20 40 60 Meters Map Scale: 1:893 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 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 3 Altvan-Satanta loams, 0 to 3 percent slopes B 0.0 1.4% 4 Altvan-Satanta loams, 3 to 9 percent slopes B 0.4 14.4% 74 Nunn clay loam, 1 to 3 percent slopes C 0.8 29.5% 75 Nunn clay loam, 3 to 5 percent slopes C 1.0 37.3% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 0.5 17.4% Totals for Area of Interest 2.7 100.0% Hydrologic Soil Group—Larimer County Area, Colorado FRCC HCCC Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/27/2018 Page 3 of 4 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 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado FRCC HCCC Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/27/2018 Page 4 of 4 213 Linden Street, Suite 200 Fort Collins, CO 80524 970.225.9099 www.jvajva.com JVA, Inc. Boulder ● Fort Collins ● Winter Park Glenwood Springs ● Denver CONSULTANT: ISSUE: OWNER: PROJECT: DRAWING INFORMATION: PROJECT NO: SHEET TITLE: 1 2 3 4 5 6 A B C D E 1 2 3 4 5 6 P 303.607.0977 www.hcm2.com 1331 Nineteenth Street Denver, CO. 80202 hord|coplan|macht FRONT RANGE COMMUNITY COLLEGE FRCC Health Care Career Center 218214.00 4616 S. Shields St. Fort Collins, CO 80526 11/28/18 Schematic Design Package C1.0 GRADING & DRAINAGE PLAN of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Sep 20, 2015—Oct 21, 2017 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 (FRCC HCCC) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/27/2018 Page 2 of 4