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HomeMy WebLinkAboutPLATTE RIVER POWER AUTHORITY CAMPUS - PDP - PDP170040 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1501 Academy Ct. Ste. 203 Fort Collins, Colorado 80524 (970) 530-4044 Preliminary Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO Prepared for: Platte River Power Authority 2000 East Horsetooth Road Fort Collins, CO 80525 November 14, 2017 Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO i U16014-DrainageReport-Preliminary.doc November 14, 2017 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Platte River Power Authority HQ Campus Fort Collins, Colorado Project Number: U16014 Dear Staff: United Civil Design Group, LLC. is pleased to submit this Preliminary Drainage Report for the Platte River Power Authority Headquarters Campus site in Fort Collins, Colorado. In general, this report serves to document the stormwater impacts associated with the proposed redevelopment of the existing campus. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Fort Collins Stormwater Criteria Manual (FCSCM). This report was prepared in compliance with technical criteria set forth in both the Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual and the Fort Collins Stormwater Criteria Manual. If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, United Civil Design Group Kevin Brazelton, PE Engineering Manager Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO ii U16014-DrainageReport-Preliminary.doc TABLE OF CONTENTS PAGE I. General Location and Description ........................................................................................... 1 A. Location ............................................................................................................................ 1 B. Description of Property ................................................................................................... 1 C. Description of Development............................................................................................ 2 II. Drainage Basins and Sub-Basins .............................................................................................. 3 A. Major Basin Description .................................................................................................. 3 B. Sub-Basin Description ...................................................................................................... 3 III. Drainage Design Criteria ......................................................................................................... 3 A. Regulations ...................................................................................................................... 3 B. Directly Connected Impervious Area (DCIA) ................................................................... 3 C. Development Criteria Reference and Constraints .......................................................... 4 D. Hydrological Criteria ........................................................................................................ 5 E. Hydraulic Criteria ............................................................................................................. 6 F. Floodplain Regulations .................................................................................................... 6 G. Modifications of Criteria .................................................................................................. 6 IV. Drainage Facility Design .......................................................................................................... 6 A. General Concept .............................................................................................................. 6 B. Specific Details ................................................................................................................. 9 V. Sediment/Erosion Control ..................................................................................................... 15 VI. Conclusions ........................................................................................................................... 15 A. Compliance with Standards ........................................................................................... 15 B. Drainage Concept .......................................................................................................... 15 C. Stormwater Quality ....................................................................................................... 15 VII. References ......................................................................................................................... 16 APPENDICES APPENDIX A – Hydrology Computations APPENDIX B – Detention and Water Quality Calculations APPENDIX C – Hydraulic Computations C.1 – Storm Pipe Calculations C.2 – Inlet Sizing Calculations (Reserved for Final Submittal) C.3 – Swale and Sidewalk Chase Calculations (Reserved for Final Submittal) C.3 – Riprap Sizing Calculations (Reserved for Final Submittal) APPENDIX D – Referenced Materials APPENDIX E – Drainage Exhibits Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO iii U16014-DrainageReport-Preliminary.doc VICINITY MAP Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 1 U16014-DrainageReport-Preliminary.doc I. General Location and Description A. Location The Platte River Power Authority Headquarters Campus (referred herein as ”the site” or “the Campus”) is a parcel of land situated in the Southeast Quarter of Section 30, Township 7 North, Range 68 West of the 6th Principal Meridian to the City of Fort Collins, Larimer County, Colorado. More specifically, the site is located at the northwest corner of Horsetooth Road and Timberline Road and is bounded by East Horsetooth Road to the south, Timberline Road to the east, existing commercial property and Danfield Court to the north, and Union Pacific Railroad right-of-way to the west. B. Description of Property The campus has an existing platted area of 16.7-acres and has acted as the headquarters for Platte River Power Authority since it was first constructed in the late 1970s. The following is a summary of the existing conditions: Ground Cover - The site currently exists as commercial property and is currently covered with various buildings, pavements and open areas. Grades – The majority of the site slopes towards one of three (3) drainage outfalls. In general, the slopes within each outfall basin range between 0 to 5 percent, with some landscaped berm areas reaching near 20%. Soil Type - According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey, the site consists of Nunn clay loam (Hydrologic Soil Group C). Utilities – The campus includes an extensive network of existing utilities including mains and services for water, sanitary sewer, natural gas, electric, telephone and data lines. These mains and services are located within the property limits of the campus along with mains located within the rights-of- ways for Horsetooth Road, Timberline Road and Danfield Court. Detention Ponds and Storm Sewer – The campus currently has three (3) drainage outfalls available to accept stormwater flows from the site. These include the existing wet pond which currently acts as an irrigation and stormwater retention facility for the campus, an existing 12-inch storm sewer located at the east side of the campus along Timberline Road, and the curb and gutter at the Danfield Court cul-de-sac. There are also two (2) other internal detention areas that drain to the 12-inch storm sewer outfall. The campus also has limited internal storm drains varying in size from 4-inch Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 2 U16014-DrainageReport-Preliminary.doc to 15-inch. Of note, there is an existing storm inlet and drain located on the north side of Horsetooth Road that collects stormwater from the roadway and conveys it into the existing wet pond on the south side of the property. This existing system will require to be maintained and/or replaced with the construction of the proposed project. Drainageways – No known externally owned drainageways currently exist within the proposed development limits. Irrigation - City records indicate that there is an existing irrigation pipe located along the southern property boundary, running from west to east. Only portions of this irrigation system have been found or identified with utility locates or site survey but from the information available it is believed that this system consists of a 20-inch concrete pipe that is located just north of the existing curb and gutter along Horsetooth Road. The existing onsite wet pond also serves as an irrigation system and is supplied by an existing irrigation well located on the campus. Floodplains – The campus is not located within either a City or FEMA floodplain. C. Description of Development The planned campus redevelopment is planned to be constructed phases. Ultimately, the campus redevelopment will consist of the following improvements: • The demolition of most of the existing buildings and much of the existing pavements throughout the campus. • The construction of seven (7) proposed commercial buildings including the main headquarters building and various other support buildings. • The construction of an internal roadway network with associated parking areas. • The construction of utilities in support of the campus including sanitary, water and storm drainage. • The construction of detention and water quality facilities located throughout the site with the main detention area located in the northeast portion of the site. • The reconfiguration and relining of the existing wet pond. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 3 U16014-DrainageReport-Preliminary.doc II. Drainage Basins and Sub-Basins A. Major Basin Description The site is located within the Foothills drainage basin within the City of Fort Collins Master Drainage Plan. Stormwater from this basin adjacent to the site is collected within streets and storm sewer systems and ultimately discharged into the Fossil Creek Reservoir Inlet Ditch. B. Sub-Basin Description Historically, the property has been utilized as the main headquarters for Platte River Power Authority. The campus has grown over the decades but is currently largely developed containing a variety of existing buildings, utility infrastructure systems and open spaces. Stormwater from the campus is collected in one of three (3) basins that either convey water after detention to public infrastructure or retain the stormwater onsite. The proposed project will maintain the historic drainage patterns to the extent feasible, but will eliminate the stormwater retention aspect of the site and reroute that stormwater to the main detention facility to be provided on the site. III. Drainage Design Criteria A. Regulations The design criteria for this study are directly from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual and the Urban Storm Drainage Criteria Manuals Volumes 2, and 3 (referred to herein as USDCM). B. Directly Connected Impervious Area (DCIA) With the adoption of the USDCM, the City has also adopted the “Four Step Process” that is recommended in Volume 3 of the USDCM in selecting structural BMPs for the redeveloping urban areas. The following portions of this summary describe each step and how it has been utilized for this project: Step 1 – Employ Runoff Reduction Practices The objective of this step is to reduce runoff peaks and volumes and to employ the technique of “minimizing directly connected impervious areas” (MDCIA). This project accomplishes this by: • Routing the roof and pavement flows through bioswales, underground detention treatment/infiltration facilities and vegetated swales to increase time of concentration, promote infiltration and provide water quality. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 4 U16014-DrainageReport-Preliminary.doc Step 2 – Provide Water Quality Capture Volume (WQCV) The objective of providing WQCV is to reduce the sediment load and other pollutants that exit the site. For this project WQCV is provided within underground treatment facilities and a campus waterquality pond. Step 3 – Stabilize Drainageways The site is not adjacent or near a major drainageway; however, this project will pay stormwater development and stormwater utility fees which the City uses, in part, to maintain the stability of the City drainageway systems. Step 4 – Consider Need for Site Specific and Source Control BMPs Site specific and source control BMPs are generally considered for large industrial and commercial sites. The redevelopment of the existing campus will include multiple site specific and source controls, including: • Covered storage areas for vehicles and materials • A warehouse for materials storage • A vehicular maintenance building with appropriate internal waste collection systems • Dedicated maintenance personnel providing landscape maintenance and snow and ice management C. Development Criteria Reference and Constraints The campus has most recently been included within the Drainage Study entitled, “Platte River Power Authority Maintenance Facility”, prepared by RBD Engineering Consultants Inc., and dated March 1984. With the proposed complete redevelopment of the site and the age of the previous studies, this report relies very little on previous drainage information and studies prepared for the site. Four (4) drainage constraints for the campus have been identified and include the following: Existing Storm Outfall The existing 12-inch storm sewer outfall for the site conveys stormwater north down Timberline Road. Utilizing invert and hydraulic grade line information provided within the construction plans entitled, “Collindale Industrial Park Storm Sewer Extension”, prepared by Meline & Irelan Consulting Engineers and dated February 1995, the existing system has been analyzed to determine the maximum allowable release rate from the campus to this existing 12-inch outfall. Refer to Appendix C for the hydraulic analysis of the existing storm drain and Appendix D for the information used to create the hydraulic model. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 5 U16014-DrainageReport-Preliminary.doc Utilizing the mentioned information, it was determined that the release rate from the main detention area will be limited to 3.15 cfs. Danfield Court Outfall Storm sewer does not exist at the west end of Danfield Court; therefore, any drainage outfall at the north property line will be required to tie into the curb and gutter of the street or construct offsite storm sewer. The current design does not include offsite storm sewer and the elevation of the existing curb and gutter in relation to site grades limits the feasibility of providing a significant amount of detention or water quality. To limit the impact of these constraints, the design proposes to maintain the existing parking lot with its’ current parking lot detention system. Per information provided by City personnel, maintaining the existing parking lot and detention system will be acceptable with the condition that no new impervious area is added to this existing outfall and only minor improvements are made to the existing parking area. Horsetooth Road Drainage Approximately 1-acre of Horsetooth Road drains to an existing inlet located immediately west of the south entrance to the existing site. Drainage collected via the existing inlet is conveyed to the existing wet pond and retained onsite. The proposed design will alter the design of this existing system but will required to collect, treat, and convey the Horsetooth Road runoff through the proposed redeveloped campus. Existing Offsite Storm Sewer The existing property north of the main campus (formerly the “LSI property”) has existing storm sewer along the west and south perimeters of that property. Documentation of the design of these storm sewers is not available; therefore, it has been assumed that the offsite system has only been designed for the existing property and impervious areas that currently drain to the existing storm inlets. The proposed design will be required to limit the area draining to the offsite storm sewer system and ensure that existing flowrates to the system are not exceeded. D. Hydrological Criteria In accordance with the Fort Collins policy, a minor and major storm for the Fort Collins area is identified as the 2-year and 100-year storms, respectively. A major storm for the Fort Collins area has a recurrence interval of 100 years and has a peak intensity of 9.95 in/hr. These storms have been used as a basis for planning and system design. The peak flow rates for design points have been calculated based on the Rational Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 6 U16014-DrainageReport-Preliminary.doc Method as described in the USDCM with storm duration set equal to the time of concentration for each sub-basin. This method was used to analyze the developed runoff from the 2-year (minor) and the 100-year (major) storm events. The Rational Method is widely accepted for drainage design involving small drainage areas (less than 160 acres) and short time of concentrations. The Rational Method is ideal for storm sewer sizing and small detention pond sizing (for tributary areas no larger than 90 to 160 acres). Runoff coefficients were assumed based on impervious area and soil type and are given in Appendices. E. Hydraulic Criteria The redeveloped campus will convey runoff to the proposed pond(s) via swales, gutters, concrete pans, and pipes. The FCSCM and USDCM were referenced for all hydraulic calculations. In addition, the following computer programs were utilized: • Hydraflow Storm Sewers Extension for AutoCAD Civil 3D • Hydraflow Express Extension for AutoCAD Civil3D • UD-Inlet by UDFCD F. Floodplain Regulations The campus is not located within either a City or FEMA floodplain. G. Modifications of Criteria No modifications to the City drainage criteria or codes are being requested. IV. Drainage Facility Design A. General Concept The project includes the redevelopment of a vast majority of the existing campus including the headquarters (HQ) building, support buildings and supporting roadway, parking and utility infrastructure. In general, the site is being graded to maintain existing drainage patterns, where feasible, and will collect stormwater runoff via swales, pans and storm sewer and direct them to the proposed detention and water quality pond located at the east side of the site. The pond will discharge to the existing 12-inch storm sewer located along the west edge of Timberline Road. All referenced tables, charts, formulas, etc. are included in the Appendices. The area, time of concentration, and runoff of each proposed sub-basin is Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 7 U16014-DrainageReport-Preliminary.doc summarized in Appendix A. The project site was divided into multiple developed sub-basins as explained further below: Basin A Basin A consists of Basins A1-A13 which are designed to be collected via a series of swales, pans and storm drains that will discharge to the proposed detention pond at the east side of the property. Basin A will contain the majority of the proposed improvements and will ultimately consist of rooftop, sidewalk, roadway, and landscaped areas. Specifics to each sub- basin within Basin A include the following: Basin A1 consists of approximately 3.5 acres and includes the proposed detention pond and portions of the proposed paving improvements around the HQ building. Approximately 8,500 square feet (sf) of future building is also included within the hydrology and detention pond calculations. A pond outlet and emergency overflow will be provided at the northeast end of the pond that will both be directed towards Timberline Road. Refer to Appendix A for additional information. Basins A2-A5 consist of approximately 2.3 acres and includes a portion of the proposed HQ and the employee parking areas for the project north of HQ. These basins are collected with proposed storm sewer and conveyed to the proposed detention pond in Basin A1. Basins A6-A11 consist of approximately 3.0 acres and includes the maintenance yard facility north of HQ and the employee parking areas. These basins are collected with proposed storm sewer and conveyed to the proposed detention pond in Basin A1. Basin A12 consists of approximately 1.5 acres and includes minimal proposed improvements with this project. The area is planned for future expansion of an unknown type. For storm sewer calculations the basin has been assumed to have a percent imperviousness of 90%. Due to the unknown nature of the future improvements, Basin A12 will be required to provide detention, water quality and LID improvements either within Basin A12 or within Basin A1 with the future improvements. Refer to Appendix A for additional information. Basin A13 consists of approximately 0.25 acres and includes the southern portion of the HQ building. The basin will be collected with a proposed roof drain system and conveyed to the detention pond in Basin A1. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 8 U16014-DrainageReport-Preliminary.doc Basin B Basin B includes Basins B1-B2 which consist of approximately 1.9 acres south of HQ and will include the proposed visitor parking area and landscaping. The basins are designed to be collected via a bioswale and storm drain that will discharge to the proposed detention pond in Basin A1. Approximately 11,000 (sf) of future paving is also included within the hydrology and detention pond calculations to accommodate for future visitor parking on the west end of Basin B2. Refer to Appendix A for additional information. Basin C Basin C includes Basin C1 which consists of approximately 1.2 acres south HQ and primarily includes the proposed wet pond and landscaping. Detention will be provided for Basin C1 over the permanent water surface of the proposed wet pond. A pond outlet and emergency overflow will be provided at the east end of the pond that will both be directed towards Basin A1. Offsite Basins The site includes five (5) existing offsite basins that are being maintained with the proposed redevelopment. Specifics to each offsite basin include the following: Basin OS1 consists of approximately 0.7 acres of onsite property that drains offsite towards the north and east ultimately draining to Timberline Road. The area of this basin has increased from historic conditions but due to the removal of pavement area within the basin the percent-imperviousness has been reduced. Ultimately, the runoff generated from this basin has increased slightly with the proposed conditions (approximately 0.5 cfs in the 100-year event); however, the additional flow is not anticipated to negatively impact the street capacity of Timberline Road or downstream infrastructure. Basin OS2 consists of approximately 1.2 acres of Horsetooth Road and onsite property that drain to an existing inlet located just west of the Horsetooth Road entrance into the property. Drainage from this inlet is currently conveyed into the existing wet pond located south of HQ. The redevelopment is raising the permanent water surface of the wet pond by approximately 3-feet; therefore, Basin OS2 will be collected with a proposed storm drain system and routed around the proposed wet pond to the detention pond in Basin A1 where flows from the basin will be treated and detained prior to being released from the pond. Basin OS3 consists of approximately 0.4 acres of onsite property that drains offsite to the adjacent commercial property east and north of the redevelopment (formerly the “LSI property”). This basin was originally Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 9 U16014-DrainageReport-Preliminary.doc owned by, and was designed to drain towards, the offsite property but has been recently purchased by Platte River Power Authority. In the existing conditions Basin OS3 includes approximately 2.2 acres or property. The proposed redevelopment alters the drainage patterns to minimize the size of Basin OS3; and therefore, the amount of drainage that flows offsite. Much of the existing basin is now included within the onsite Basins A7-A11. Refer to the Drainage Plans and Appendix A for additional information. Basin OS4 consists of approximately 1.3 acres of onsite property that drains to Danfield Court. The basin currently exists as a parking lot that includes a small amount of parking lot detention prior to being released to Danfield Court. This existing parking lot is remaining largely unmodified with the proposed redevelopment; therefore, per communications with City personnel, no drainage improvements are being made to the basin. Basins OS5 consists of approximately 0.5 acres of landscaped area that historically drains west offsite and onto Union Pacific Railroad property. The proposed redevelopment is proposing to maintain the existing drainage patterns, size and percent imperviousness of this basin. B. Specific Details Detention The proposed redevelopment includes two (2) extended detention ponds for the proposed improvements. These ponds are located within Basins A1 and C1 and are shown within this report as Pond A and Pond C. Pond A includes detention and waterquality for all of Basins A, B and OS2. The release rate from the pond is limited by the existing 12-inch storm sewer outfall for the site which conveys stormwater north down Timberline Road. As previously mentioned, the release rate from Pond A was determined to be 3.15 cfs by analyzing the existing 12-inch storm sewer system. Refer to Appendices C and D for additional information. Also, note that neither detention or water quality are provided for the future conditions of basin A12. Due to the unknown nature of the future improvements, Basin A12 will be required to provide detention, water quality and LID improvements either within Basin A12 or within Basin A1 with the future improvements. Refer to Appendix A for additional information. A pond outlet structure and emergency overflow will be provided at the northeast end of the pond that will both be directed towards Timberline Road. Pond C includes only Basin C1 and will provide detention over the permanent water surface of the proposed wet pond. The pond is designed Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 10 U16014-DrainageReport-Preliminary.doc to require less than 6-inches of ponding from the permanent water surface to the 100-year water surface. A pond outlet and emergency overflow will be provided at the east end of the pond that will both be directed towards Basin A1. A summary of both detention ponds are as follows: Pond Designation Detention Volume Required (ac-ft) Detention Volume Provided (ac-ft) 100-year WSEL Pond Release Rate (cfs) WQCV Required (ac-ft) WQCV Provided (ac-ft) Water Quality WSEL Top of Pond Elevation Pond A 2.77 2.88 4952.00 3.15 0.26 0.30 4949.60 4953.00 Pond C 0.32 0.35 4955.50 0.50 0.02 0.02 4955.05 4956.50 Stormwater Quality Several long-term stormwater quality measures have been selected for the site that will provide treatment of stormwater prior to it being discharged from the site. For this project the following measures have been included: Grass Swales - The soft bottom/overbank areas of the swales allow for infiltration to occur as well as including a flow path across a vegetated surface slowing the conveyance rate of storm water runoff while also removing sediment and other pollutants. These have been utilized to convey and treat stormwater prior to entering the storm sewer systems or Pond A. Grass Open Areas/Buffers – Grass open areas and/or grass buffers allow for infiltration to occur as well as including a flow path across a vegetated surface slowing the conveyance rate of storm water runoff while also removing sediment and other pollutants. These have been utilized to convey and treat stormwater prior to entering the storm sewer systems or Ponds A and C. Bioswales – Bioswales remove sediment and pollution from stormwater runoff via infiltration through an engineered sand media. This slows the conveyance rate of storm water runoff, reduces runoff and provides a flow path across a vegetated surface. These have been utilized to convey and treat stormwater prior to entering the storm sewer system and Pond A. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 11 U16014-DrainageReport-Preliminary.doc utilized to collect, store and treat storm water runoff prior to it entering Pond A. Wet Pond – A wet pond provides water quality by acting as a permanent sedimentation basin which collects and stores the runoff prior to discharging to the pond outlet structure. This removes sediment from the flows entirely which settle to the bottom of the pond. The existing onsite wet pond is being redeveloped as part of this project and will collect and treat only those areas that drain immediately to the wet pond itself. Extended Detention Basin – Extended detention basins, in conjunction with the use of a waterquality plate, collect, store and slowly release minor storm events. This allows runoff to pond, infiltrate into the grass bottom of the pond, and settle out particulates prior to being discharged from the site. An extended detention basin has been selected as a highly effective last treatment option prior to discharging runoff from the site. Low Impact Development (LID) In December of 2015, Fort Collins City Council adopted the revised Low Impact Development (LID) policy and criteria which requires developments within City limits to meet certain enhanced stormwater treatment requirements in addition to more standard treatment techniques. The proposed development will be required to meet the newly adopted LID criteria which requires the following: • Treat no less than 75% of any newly added impervious area using one or a combination of LID techniques. • Treat no less than 50% of any newly added impervious area using one or a combination of LID techniques when at least 25% of any newly added pavement is provided with permeable pavement. The following measures are being implemented with this proposed development: Underground Detention – Basins A3-A11 (with 144,320 sf of proposed impervious area) will be routed through an underground detention system located north of HQ. The underground detention system will have an overall volume of approximately 3,900 cubic feet which exceeds the minimum design requirements for the area. Refer to Appendix B for additional information. Bioswales – Basins B1-B2 (with 28,300 sf of proposed impervious area) will be routed through a bioswale (with a surface area of 3,035 sf). Basin B-2 will include future parking area of approximately 11,000 sf. Once the future parking area is constructed, the bioswale will also require extension Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 12 U16014-DrainageReport-Preliminary.doc to provide LID treatment of the future parking lot expansion. With future construction, the bioswale within Basins B1 and B2 will treat approximately 39,260 sf of impervious area. Wet Pond – Basin C1 (with 5,730 sf of proposed impervious area) will drain directly into the wet pond within the basin. The wet pond will act as a permanent sedimentation basin and will remove sediment and pollution from storm water runoff prior to releasing it downstream. Future LID Treatment – At the end of construction, Basin A12 will be left as open space but is planned for future expansion. With the future development of the basin, it is estimated that a minimum of 17,500 sf of future impervious area will require to be treated to maintain a total treatment for the campus of 75%. In total, the development is proposing to collect and treat 206,809 sf (75%) of the overall 277,324 sf of impervious area developed (including both proposed and future developments) with this project. In addition, the site is also being designed with other various open landscaped areas and vegetated swales and buffers to provide additional water quality in addition to the areas being treated with LID techniques. Standard Operating Procedures (SOPs) In order for physical stormwater Best Management Practices (BMPs) to be effective, proper maintenance is essential. Maintenance includes both routinely scheduled activities, as well as non-routine repairs that may be required after large storms, or as a result of other unforeseen problems. Standard Operating Procedures should clearly identify BMP maintenance responsibility. BMP maintenance is typically the responsibility of the entity owning the BMP. Identifying who is responsible for maintenance of BMPs and ensuring that an adequate budget is allocated for maintenance is critical to the long-term success of BMPs. Maintenance responsibility may be assigned either publicly or privately. For this project, the privately owned BMPs including vegetative swales and bioswales, underground detention, and the extended detention pond are to be maintained by the property owner. Storm Sewers Multiple storm sewer systems are being proposed with the redevelopment of the campus that include storm sewer mains, roof drains and underdrains. All storm sewer on the property is expected to be private. The system that collects and conveys the public storm water from Horsetooth Road will be Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 13 U16014-DrainageReport-Preliminary.doc included within a drainage easement. Due to the complexities of the proposed site and constraints of the existing site, it is currently anticipated that all storm sewer mains and roof drains will be sized to accommodate the 100-year storm event. Further sizing and hydraulic information will be provided during Final Compliance design. Wet Pond As previously mentioned, the existing wet pond on the site is also being redeveloped/reconfigured with the project. As part of the reconfiguration, the following design elements are being provided: • A 12-foot depth is being provided in the pond to allow for increased water quality and to allow for the use of a geothermal mechanical system for HQ. Related to these elements, the elevation difference between the finished floor of HQ and the permanent water surface of the pond has been minimized to accommodate a deeper pond while minimizing the impacts to existing groundwater. The existing pond sits approximately 6-feet below the existing building. The current design has set the proposed permanent lake water surface 3-feet below the proposed finished floor. • The amount of surface drainage conveyed to the pond is being minimized to limit the amount of storage required above the permanent water surface due to storm runoff. • The pond is being provided with an emergency overflow and outlet. Currently the pond does not have an emergency overflow or any means of draining the lake other than through irrigation. The proposed design has located both an emergency overflow and outlet structure on the east side of the lake. Phasing As mentioned previously, the redevelopment of the campus will be accomplished in phases due to the requirement that the existing Engineering/Operations (E/O) and Headquarters (HQ) buildings remain fully operational during the construction of the proposed HQ building. Only when the proposed HQ is fully operational and in use will the existing E/O and HQ buildings be demolished. Due to this, it is currently expected that two major phases of construction will be required. The initial phase of construction will construct much of the proposed drainage infrastructure apart from the southern portion of Pond A as this is where the existing HQ building is located. The final phase of construction will construct the remainder of Pond A. Through initial communication with City personnel, it is currently anticipated that the Stormwater Department will issue a full CO for the proposed HQ building with an escrow provision as required. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 14 U16014-DrainageReport-Preliminary.doc Drainage Summaries The following is a basin summary table for existing and proposed conditions: Existing Basins Basin Design Pt. Area %I Runoff Coefficients Peak Discharge acre C2 C100 Q 2 Q100 cfs cfs EX1 EX1 3.75 48.6% 0.59 0.74 5.14 22.42 EX2 EX2 2.38 32.3% 0.47 0.59 2.23 9.73 EX3 EX3 2.19 80.4% 0.83 1.00 5.16 21.75 EX4 EX4 2.33 18.9% 0.38 0.48 1.88 8.20 EX5 EX5 1.35 12.5% 0.32 0.40 0.91 3.98 OS-1 OS-1 0.31 20.5% 0.38 0.47 0.27 1.17 OS-2A OS-2A 0.33 26.6% 0.43 0.54 0.38 1.65 OS-2B OS-2B 0.97 77.0% 0.80 1.00 1.94 8.47 OS-3 OS-3 2.21 20.1% 0.38 0.48 1.62 7.09 OS-4 OS-4 1.29 73.3% 0.76 0.95 2.17 9.47 OS-5 OS-5 0.54 2.0% 0.25 0.31 0.30 1.31 Totals 22.00 95.25 Proposed Basins Basin Design Pt. Area Area Runoff Coefficients Peak Discharge acre acre C2 C100 Q 2 Q100 cfs cfs A-1 A-1 3.46 17.5% 0.37 0.46 2.82 12.32 A-2 A-2 0.94 0.81 0.82 1.00 1.85 7.85 A-3 A-3 0.37 0.90 0.95 1.00 1.01 3.71 A-4 A-4 0.58 0.91 0.90 1.00 1.16 4.48 A-5 A-5 0.40 0.85 0.84 1.00 0.96 3.96 A-6 A-6 0.31 0.65 0.75 0.94 0.58 2.54 A-7 A-7 0.32 0.53 0.66 0.82 0.45 1.96 A-8 A-8 0.10 0.72 0.81 1.00 0.22 0.95 A-9 A-9 0.71 0.90 0.95 1.00 1.94 7.11 A-10 A-10 0.86 0.72 0.80 1.00 1.48 6.39 A-11 A-11 0.65 0.26 0.44 0.55 0.71 3.12 A-12 A-12 1.53 0.02 0.25 0.31 1.02 4.45 A-12 (Future) A-12 (Future) 1.53 0.90 0.88 1.00 3.60 14.25 A-13 A-13 0.26 0.90 0.95 1.00 0.72 2.63 B-1 B-1 0.46 0.51 0.62 0.78 0.61 2.66 B-2 B-2 1.43 0.46 0.57 0.71 1.88 8.21 C-1 C-1 1.19 0.12 0.33 0.41 1.04 4.52 OS-1 OS-1 0.68 0.02 0.25 0.31 0.39 1.70 OS-2A OS-2A 0.21 0.41 0.54 0.68 0.30 1.29 Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 15 U16014-DrainageReport-Preliminary.doc V. Sediment/Erosion Control Erosion control, both temporary and permanent, is a vital part of any development project. For this project, the site disturbance will be over 1-acre; therefore, a comprehensive Erosion Control Report will be completed under a separate cover during the Final Compliance phase of the project. The Erosion Control Report will be utilized for site construction activities and will be prepared in accordance with City and Colorado Department of Public Health and Environment requirements. VI. Conclusions A. Compliance with Standards Storm drainage designs for the Platte River Power Authority Headquarters campus have typically followed the guidelines provided by the Fort Collins Stormwater Criteria Manual and/or the Urban Storm Drainage Criteria Manual. In addition, the site drainage has been designed to meet City requirements in terms of detention, waterquality and Low Impact Development standards. B. Drainage Concept The drainage system has been designed to convey the runoff to the designated design points and the existing public infrastructure in an effective, safe manner. No negative impacts are anticipated to the City of Fort Collins Master Drainage Plan or to downstream properties or infrastructure due to the proposed improvements. C. Stormwater Quality Several long-term stormwater quality measures have been selected for the site that will provide treatment of stormwater prior it to being discharged from the site. For this site this includes grass swales, grass open areas/buffers, a bioswale, underground detention and an extended detention basin. Drainage Report Platte River Power Authority HQ Campus Fort Collins, CO 16 U16014-DrainageReport-Preliminary.doc VII. References 1. Fort Collins Stormwater Criteria Manual, City of Fort Collins, as adopted in 2011. 2. Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Inc., Denver, Colorado, Revised April 2008. 3. Larimer County Urban Area Street Standards, Larimer County, Colorado, Repealed and Reenacted, Effective April 1, 2007. 4. Geotechnical Engineering Report – PRPA New Headquarters Campus, Terracon Consultants, Inc., October 30, 2017. 5. Storm Drainage Study for Platte River Power Authority Maintenance Facility, RBD Engineering Consultants, March 1984. 6. Collindale Industrial Park Storm Sewer Extension Construction Plans, Meline & Irelan, Inc., Revised May 1995. 7. Collindale Industrial Park Construction Plans, James H. Stewart & Associates, Revised October 1978. 8. Natural Resources Conservation Service Web Soil Survey at websoilsurvey.nrcs.usda.gov/app APPENDIX A Hydrology Computations Runoff Coefficients and % Impervious Platte River Power Authority Campus, Fort Collins, CO Basin Design Pt. Composite NRCS Soil Total Total Roof (1) Asphalt Concrete (1) Gravel (1) Lawns (1) Imperviousness Type C 2 C100 %I = 90% %I = 100% %I = 90% %I =40% %I=2% (%I) acres sf sf sf sf sf sf EX1 EX1 3.75 163,553 19,370 51,627 8,627 2,670 81,259 48.6% C/D 0.59 0.74 EX2 EX2 2.38 103,485 2,883 22,033 7,506 1,767 69,296 32.3% C/D 0.47 0.59 EX3 EX3 2.19 95,233 17,683 54,408 6,104 1,029 16,009 80.4% C/D 0.83 1.00 EX4 EX4 2.33 101,325 9,012 5,208 4,316 810 81,979 18.9% C/D 0.38 0.48 EX5 EX5 1.35 58,652 16,194 42,458 12.5% C/D 0.32 0.40 OS-1 OS-1 0.31 13,409 928 343 3,331 8,807 20.5% C/D 0.38 0.47 OS-2A OS-2A 0.33 14,302 2,539 1,177 10,586 26.6% C/D 0.43 0.54 OS-2B OS-2B 0.97 42,132 26,583 6,282 9,267 77.0% C/D 0.80 1.00 OS-3 OS-3 2.21 96,344 14,084 4,110 78,150 20.1% C/D 0.38 0.48 OS-4 OS-4 1.29 56,148 38,984 2,061 15,103 73.3% C/D 0.76 0.95 OS-5 OS-5 0.54 23,668 23,668 2.0% C/D 0.25 0.31 17.64 768,253 48,948 216,394 40,526 25,801 436,584 41.1% C/D 0.54 0.67 Notes: (1) Recommended % Imperviousness Values from USDCM Vol 1 - Ch 5 - Table RO-3. Increased Lawns from 0% to 2% Impervious. (2) Runoff C is based on %I, UDFCD Eq RO-7 and correction factors in Table RO-4. Composite Runoff Coefficients Areas (2) Existing Basins Existing Total Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Runoff Coefficients and % Impervious Platte River Power Authority Campus, Fort Collins, CO Existing Basins Basin Design Pt. Composite NRCS Soil Total Total Roof (1) Asphalt Concrete (1) Gravel (1) Lawns (1) Imperviousness Type C 2 C100 acres sf %I = 90% %I = 100% %I = 90% %I =40% %I=2% (%I) sf sf sf sf sf A-1 A-1 3.46 150,739 11,029 8,701 5,865 - 125,144 17.5% C/D 0.37 0.46 A-2 A-2 0.94 40,805 - 26,691 6,712 - 7,403 80.6% C/D 0.82 1.00 A-3 A-3 0.37 16,242 16,242 - - - - 90.0% C/D 0.95 1.00 A-4 A-4 0.58 25,276 2,825 16,621 4,116 - 1,714 90.6% C/D 0.90 1.00 A-5 A-5 0.40 17,344 - 13,831 905 - 2,608 84.7% C/D 0.84 1.00 A-6 A-6 0.31 13,391 117 - 9,482 - 3,791 65.1% C/D 0.75 0.94 A-7 A-7 0.32 14,010 6,334 - 1,841 - 5,835 53.4% C/D 0.66 0.82 A-8 A-8 0.10 4,429 - 3,539 - 889 72.3% C/D 0.81 1.00 A-9 A-9 0.71 31,121 5,826 - 25,295 - (0) 90.0% C/D 0.95 1.00 A-10 A-10 0.86 37,508 5,872 - 23,853 - 7,783 71.7% C/D 0.80 1.00 A-11 A-11 0.65 28,184 7,569 - - - 20,615 25.6% C/D 0.44 0.55 A-12 A-12 1.53 66,694 - - - - 66,694 2.0% C/D 0.25 0.31 A-12 (Future) A-12 (Future) 1.53 66,694 - 60,000 - - 6,694 90.2% C/D 0.88 1.00 A-13 A-13 0.26 11,517 11,517 - - - - 90.0% C/D 0.95 1.00 A-TOTAL A-TOTAL 10.50 457,259 67,332 65,845 81,608 - 242,474 44.8% C/D 0.58 0.72 B-1 B-1 0.46 20,135 - 5,907 4,744 - 9,484 51.5% C/D 0.62 0.78 B-2 B-2 1.43 62,469 - 25,335 3,277 - 33,857 46.4% C/D 0.57 0.71 B-TOTAL B-TOTAL 1.90 82,604 - 31,242 8,021 - 43,341 47.6% C/D 0.58 0.73 C-1 C-1 1.19 51,708 - - 5,726 - 45,982 11.7% C/D 0.33 0.41 C-TOTAL C-TOTAL 1.19 51,708 - - 5,726 - 45,982 11.7% C/D 0.33 0.41 OS-1 OS-1 0.68 29,533 29,533 2.0% C/D 0.25 0.31 OS-2A OS-2A 0.21 8,940 2,539 1,177 5,224 41.4% C/D 0.54 0.68 OS-2B OS-2B 0.97 42,132 26,583 6,282 9,267 77.0% C/D 0.80 1.00 OS-3 OS-3 0.41 17,716 6,871 1,027 9,818 45.1% C/D 0.56 0.70 OS-4 OS-4 1.26 54,693 38,984 2,061 13,648 75.2% C/D 0.78 0.97 OS-5 OS-5 0.54 23,668 23,668 2.0% C/D 0.25 0.31 OS-TOTAL OS-TOTAL 4.06 176,682 - 74,977 10,547 - 91,158 48.8% C/D 0.59 0.74 17.64 768,253 67,332 172,063 105,902 - 422,955 43.8% C/D 0.56 0.71 Notes: (1) Recommended % Imperviousness Values from USDCM Vol 1 - Ch 5 - Table RO-3. Increased Lawns from 0% to 2% Impervious. (2) Runoff C is based on %I, UDFCD Eq RO-7 and correction factors in Table RO-4. (3) Basin A-1 includes approximately 8,500 sf of future building. Basin B-2 includes approximately 11,000 sf of future parking area. (4) Basin A-12 (Future) is included for storm sewer sizing only and is not included within "A-TOTAL" above. Detention and LID requirements will be required within Basin A-12 with future development. Proposed Total Proposed Basins Areas Composite Runoff Coefficients (2) Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Time of Concentration Platte River Power Authority Campus, Fort Collins, CO Basin Design Pt. Area Initial Ground C5 (1) Length Slope t i (2) Length Slope C v Velocity (3) tt (4) Check t c? Total Length t c (5) acres Type ft % min ft % fps min min Urban? ft min min EX1 EX1 3.75 Lawn 0.09 35 3.8% 6.9 390 2.3% 20 3.0 2.1 9.1 Yes 425 12 9.1 EX2 EX2 2.38 Lawn 0.09 275 0.6% 35.8 190 1.0% 7 0.7 4.5 40.3 Yes 465 13 12.6 EX3 EX3 2.19 Paved 0.90 20 1.2% 1.5 415 1.0% 20 2.0 3.5 5.0 Yes 435 12 5.0 EX4 EX4 2.33 Lawn 0.09 50 1.0% 12.9 205 1.1% 7 0.7 4.7 17.5 Yes 255 11 11.4 EX5 EX5 1.35 Lawn 0.09 105 1.1% 18.1 130 0.1% 7 0.2 9.3 27.4 Yes 235 11 11.3 OS-1 OS-1 0.31 Lawn 0.09 70 4.4% 9.4 20 4.6% 20 4.3 0.1 9.4 Yes 90 11 9.4 OS-2A OS-2A 0.33 Lawn 0.09 30 5.9% 5.6 60 1.2% 20 2.2 0.5 6.0 Yes 90 11 6.0 OS-2B OS-2B 0.97 Paved 0.90 50 2.0% 2.0 490 0.7% 20 1.6 5.1 7.1 Yes 540 13 7.1 OS-3 OS-3 2.21 Lawn 0.09 30 10.0% 4.7 610 0.4% 7 0.4 23.0 27.6 Yes 640 14 13.6 OS-4 OS-4 1.29 Lawn 0.09 60 5.0% 8.3 250 1.1% 20 2.1 2.0 10.3 Yes 310 12 10.3 OS-5 OS-5 0.54 Lawn 0.09 30 10.0% 4.7 200 0.7% 7 0.6 5.7 10.4 Yes 230 11 10.4 Notes: (1) C5 based initial ground type and Table RO-5 (2)ti = [0.395(1.1-C5)L1/2]/S1/3, S= slope in %, L=length of overland flow (400' max) (3)V=CvS0.5, S=watercourse slope in ft/ft, UDFCD Equation RO-4 (4)tt=L/(V*60 sec/min) (5)tc check (for urban or developed areas only) = total length/180 + 10 (6)min tc = 5 min Existing Basins ti+t t Final tc (6) Initial Overland Flow Time (t tc Check for Urbanized Basins i) Travel/Channelized Time of Flow (tt ) Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Time of Concentration Platte River Power Authority Campus, Fort Collins, CO Existing Basins Basin Design Pt. Area Initial Ground C5 (1) Length Slope t i (2) Length Slope C v Velocity (3) tt (4) Check t c? Total Length t c (5) acres Type ft % min ft % fps min min Urban? ft min min A-1 A-1 3.46 Paved 0.90 235 1.5% 4.8 465 0.5% 20 1.4 5.5 10.3 Yes 700 14 10.3 A-2 A-2 0.94 Lawn 0.09 10 2.0% 4.6 305 0.5% 20 1.4 3.6 8.2 Yes 315 12 8.2 A-3 A-3 0.37 Roof 0.73 50 12.5% 2.1 15 30.0% 20 11.0 0.0 2.1 Yes 65 10 5.0 A-4 A-4 0.58 Lawn 0.09 36 2.0% 8.7 242 2.0% 20 2.8 1.4 10.1 Yes 278 12 10.1 A-5 A-5 0.40 Paved 0.90 50 2.0% 2.0 133 1.5% 20 2.4 0.9 2.9 Yes 183 11 5.0 A-6 A-6 0.31 Lawn 0.09 17 2.0% 6.0 123 2.0% 20 2.8 0.7 6.7 Yes 140 11 6.7 A-7 A-7 0.32 Lawn 0.09 47 1.5% 10.9 200 1.0% 15 1.5 2.2 13.2 Yes 247 11 11.4 A-8 A-8 0.10 Lawn 0.09 15 2.0% 5.6 50 2.0% 20 2.8 0.3 5.9 Yes 65 10 5.9 A-9 A-9 0.71 Roof 0.73 25 12.5% 1.5 210 0.5% 20 1.4 2.5 3.9 Yes 235 11 5.0 A-10 A-10 0.86 Lawn 0.09 63 4.0% 9.2 200 1.5% 20 2.4 1.4 10.5 Yes 263 11 10.5 A-11 A-11 0.65 Lawn 0.09 20 7.0% 4.3 190 0.5% 15 1.1 3.0 7.3 Yes 210 11 7.3 A-12 A-12 1.53 Lawn 0.09 10 2.0% 4.6 205 2.0% 20 2.8 1.2 5.8 Yes 215 11 5.8 A-12 (Future) A-12 (Future) 1.53 Lawn 0.09 10 2.0% 4.6 205 2.0% 20 2.8 1.2 5.8 Yes 215 11 5.8 A-13 A-13 0.26 Roof 0.73 72 12.5% 2.5 15 30.0% 20 11.0 0.0 2.5 Yes 87 10 5.0 A-TOTAL A-TOTAL 10.50 Lawn 0.09 51 1.5% 11.4 985 0.4% 20 1.3 13.0 24.4 Yes 1036 16 15.8 B-1 B-1 0.46 Lawn 0.09 70 2.0% 12.1 40 2.0% 20 2.8 0.2 12.4 Yes 110 11 10.6 B-2 B-2 1.43 Lawn 0.09 50 25.0% 4.5 290 0.5% 15 1.1 4.6 9.0 Yes 340 12 9.0 B-TOTAL B-TOTAL 1.90 Lawn 0.09 50 25.0% 4.5 1350 0.3% 20 1.0 22.5 27.0 Yes 1400 18 17.8 C-1 C-1 1.19 Lawn 0.09 16 2.0% 5.8 75 10.0% 15 4.7 0.3 6.1 Yes 91 11 6.1 C-TOTAL C-TOTAL 1.19 Roof 0.09 16 2.0% 5.8 75 10.0% 15 4.7 0.3 6.1 Yes 91 11 6.1 OS-1 OS-1 0.68 Lawn 0.09 70 4.4% 9.4 20 4.6% 20 4.3 0.1 9.4 Yes 90 11 9.4 OS-2A OS-2A 0.21 Lawn 0.09 30 5.9% 5.6 60 1.2% 20 2.2 0.5 6.0 Yes 90 11 6.0 Rational Method Peak Runoff Platte River Power Authority Campus, Fort Collins, CO Basin Design Pt. Area Final acre tc (6) C 2 C5 C100 I 2 I5 I100 Q 2 Q5 Q100 min in/hr in/hr in/hr cfs cfs cfs EX1 EX1 3.75 9 0.59 0.59 0.74 2.30 3.26 8.03 5.14 7.28 22.42 EX2 EX2 2.38 13 0.47 0.47 0.59 1.98 2.79 6.92 2.23 3.14 9.73 EX3 EX3 2.19 5 0.83 0.83 1.00 2.85 3.97 9.95 5.16 7.18 21.75 EX4 EX4 2.33 11 0.38 0.38 0.48 2.13 2.98 7.42 1.88 2.64 8.20 EX5 EX5 1.35 11 0.32 0.32 0.40 2.13 2.98 7.42 0.91 1.28 3.98 OS-1 OS-1 0.31 9 0.38 0.38 0.47 2.30 3.26 8.03 0.27 0.38 1.17 OS-2A OS-2A 0.33 6 0.43 0.43 0.54 2.67 3.79 9.31 0.38 0.54 1.65 OS-2B OS-2B 0.97 7 0.80 0.80 1.00 2.52 3.61 8.80 1.94 2.78 8.47 OS-3 OS-3 2.21 14 0.38 0.38 0.48 1.92 2.70 6.71 1.62 2.28 7.09 OS-4 OS-4 1.29 10 0.76 0.76 0.95 2.21 3.08 7.72 2.17 3.02 9.47 OS-5 OS-5 0.54 10 0.25 0.25 0.31 2.21 3.08 7.72 0.30 0.42 1.31 22.00 68.54 95.25 Existing Basins Totals Runoff Coefficients Rainfall Intensity Peak Discharge Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Rational Method Peak Runoff Platte River Power Authority Campus, Fort Collins, CO Existing Basins Basin Design Pt. Area Final acre tc (6) C 2 C5 C100 I 2 I5 I100 Q 2 Q5 Q100 min in/hr in/hr in/hr cfs cfs cfs A-1 A-1 3.46 10.0 0.37 0.37 0.46 2.21 3.08 7.72 2.82 3.93 12.32 A-2 A-2 0.94 8.0 0.82 0.82 1.00 2.40 3.44 8.38 1.85 2.65 7.85 A-3 A-3 0.37 5.0 0.95 0.95 1.00 2.85 3.97 9.95 1.01 1.41 3.71 A-4 A-4 0.58 10.0 0.90 0.90 1.00 2.21 3.08 7.72 1.16 1.61 4.48 A-5 A-5 0.40 5.0 0.84 0.84 1.00 2.85 3.97 9.95 0.96 1.34 3.96 A-6 A-6 0.31 7.0 0.75 0.75 0.94 2.52 3.61 8.80 0.58 0.84 2.54 A-7 A-7 0.32 11.0 0.66 0.66 0.82 2.13 2.98 7.42 0.45 0.63 1.96 A-8 A-8 0.10 6.0 0.81 0.81 1.00 2.67 3.79 9.31 0.22 0.31 0.95 A-9 A-9 0.71 5.0 0.95 0.95 1.00 2.85 3.97 9.95 1.93 2.69 7.11 A-10 A-10 0.86 11.0 0.80 0.80 1.00 2.13 2.98 7.42 1.48 2.07 6.39 A-11 A-11 0.65 7.0 0.44 0.44 0.55 2.52 3.61 8.80 0.71 1.02 3.12 A-12 A-12 1.53 6.0 0.25 0.25 0.31 2.67 3.79 9.31 1.02 1.45 4.45 A-12 (Future) A-12 (Future) 1.53 6.0 0.88 0.88 1.00 2.67 3.79 9.31 3.60 5.11 14.25 A-13 A-13 0.26 5.0 0.95 0.95 1.00 2.85 3.97 9.95 0.72 1.00 2.63 A-TOTAL A-TOTAL 10.50 16.0 0.58 0.58 0.72 1.81 2.53 6.30 11.00 15.35 47.85 B-1 B-1 0.46 11.0 0.62 0.62 0.78 2.13 2.98 7.42 0.61 0.86 2.66 B-2 B-2 1.43 9.0 0.57 0.57 0.71 2.30 3.26 8.03 1.88 2.67 8.21 B-TOTAL B-TOTAL 1.90 18.0 0.58 0.58 0.73 1.70 2.38 5.92 1.88 2.63 8.18 C-1 C-1 1.19 6.0 0.33 0.33 0.41 2.67 3.79 9.31 1.04 1.47 4.52 C-TOTAL C-TOTAL 1.19 6.0 0.33 0.33 0.41 2.67 3.79 9.31 1.04 1.47 4.52 OS-1 OS-1 0.68 9.0 0.25 0.25 0.31 2.30 3.26 8.03 0.39 0.55 1.70 OS-2A OS-2A 0.21 6.0 0.54 0.54 0.68 2.67 3.79 9.31 0.30 0.42 1.29 OS-2B OS-2B 0.97 7.0 0.80 0.80 1.00 2.52 3.61 8.80 1.94 2.78 8.47 OS-3 OS-3 0.41 12.0 0.56 0.56 0.70 2.05 2.89 7.16 0.47 0.66 2.05 OS-4 OS-4 1.26 10.0 0.78 0.78 0.97 2.21 3.08 7.72 2.15 3.00 9.39 OS-5 OS-5 0.54 10.0 0.25 0.25 0.31 2.21 3.08 7.72 0.30 0.42 1.31 Totals 23.99 33.78 101.08 Proposed Basins Runoff Coefficients Rainfall Intensity Peak Discharge Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm APPENDIX B Detention and Water Quality Calculations Dention Pond Volume (FAA Method) Platte River Power Authority Campus, Fort Collins, CO POND ID: POND A 100 Year Storm Into Detention Facility Area = 590,935 square feet Area = 13.57 acres C 100 = 0.74 Q 100 = 56.02 cfs Release Rate Out of Pond Q OUT = 3.15 cfs Unit Flow = 0.23 cfs/acre T C = 15.8 minutes Notes: 1. Release Rate limited by the existing 12" outfall capacity in Timberline Road. 2. Pond area includes all of Basins A, B and OS-2 but excludes "Basin A-12 (Future)". Detention Volume Calculations Rainfall Rainfall Inflow Rate Inflow Volume Adjustment Factor Average Outflow Volume Required Duration (T) Intensity (I) Qin= ∑C100*Area*I Vi=(Qin*T*60) Factor Outflow Rate Vo=Qav*T *60 Storage Volume m= 0.5(1 + Tc/T) Qav = m*Qout Vs=Vi-Vo min in/hr cfs ft 3 cfs ft 3 ft 3 5 9.95 100.3 30,081 1.00 3.15 945 29,136 10 7.72 77.8 46,678 1.00 3.15 1,890 44,788 15 6.52 65.7 59,134 1.00 3.15 2,835 56,299 20 5.60 56.4 67,719 0.89 2.82 3,379 64,341 25 4.98 50.2 75,277 0.82 2.57 3,851 71,426 30 4.52 45.5 81,989 0.76 2.40 4,324 77,665 35 4.08 41.1 86,342 0.73 2.28 4,796 81,546 40 3.74 37.7 90,454 0.70 2.20 5,269 85,185 45 3.46 34.9 94,142 0.68 2.13 5,741 88,401 50 3.23 32.5 97,649 0.66 2.07 6,214 91,435 55 3.03 30.5 100,763 0.64 2.03 6,686 94,077 60 2.86 28.8 103,756 0.63 1.99 7,159 96,597 70 2.59 26.1 109,621 0.61 1.93 8,104 101,517 80 2.38 24.0 115,123 0.60 1.89 9,049 106,074 90 2.21 22.3 120,263 0.59 1.85 9,994 110,269 100 2.06 20.8 124,555 0.58 1.82 10,939 113,617 110 1.94 19.5 129,030 0.57 1.80 11,884 117,146 120 1.84 18.5 133,504 0.57 1.78 12,829 120,675 Required Detention Volume V 100 = 120,675 cubic feet V 100 = 2.77 acre-ft Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Dention Pond Volume (FAA Method) Platte River Power Authority Campus, Fort Collins, CO POND ID: POND C 100 Year Storm Into Detention Facility Area = 51,708 square feet Area = 1.19 acres C 100 = 1.00 Q 100 = 4.52 cfs Release Rate Out of Pond Q OUT = 0.50 cfs Unit Flow = 0.42 cfs/acre T C = 6.1 minutes Notes: 1. Release Rate limited to maximize detention volume but keep maximum ponding to less than 6". 2. For Pond C Calculations, C100 has been assumed to be 1.00 assuming that the pond water surface is at the maximum elevation and all water that falls on the wet pond will pass through the outlet . Detention Volume Calculations Rainfall Rainfall Inflow Rate Inflow Volume Adjustment Factor Average Outflow Volume Required Duration (T) Intensity (I) Qin= ∑C100*Area*I Vi=(Qin*T*60) Factor Outflow Rate Vo=Qav*T *60 Storage Volume m= 0.5(1 + Tc/T) Qav = m*Qout Vs=Vi-Vo min in/hr cfs ft 3 cfs ft 3 ft 3 5 9.95 11.8 3,543 1.00 0.50 150 3,393 10 7.72 9.2 5,498 0.80 0.40 241 5,257 15 6.52 7.7 6,966 0.70 0.35 316 6,650 20 5.60 6.6 7,977 0.65 0.33 391 7,586 25 4.98 5.9 8,867 0.62 0.31 466 8,401 30 4.52 5.4 9,658 0.60 0.30 541 9,117 35 4.08 4.8 10,171 0.59 0.29 616 9,555 40 3.74 4.4 10,655 0.58 0.29 691 9,964 45 3.46 4.1 11,089 0.57 0.28 766 10,323 50 3.23 3.8 11,503 0.56 0.28 841 10,662 55 3.03 3.6 11,869 0.56 0.28 916 10,953 60 2.86 3.4 12,222 0.55 0.28 991 11,231 70 2.59 3.1 12,913 0.54 0.27 1,141 11,772 80 2.38 2.8 13,561 0.54 0.27 1,291 12,270 90 2.21 2.6 14,166 0.53 0.27 1,441 12,725 100 2.06 2.4 14,672 0.53 0.27 1,591 13,081 110 1.94 2.3 15,199 0.53 0.26 1,741 13,458 120 1.84 2.2 15,726 0.53 0.26 1,891 13,835 Required Detention Volume V 100 = 13,835 cubic feet V 100 = 0.32 acre-ft Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Water Quality Platte River Power Authority Campus, Fort Collins, CO Required Onsite Water Quality Capture Volume Basin Area Area Imperviousness Watershed WQCV* (Extended Detention) (sf) (acres) (%) (inches) (cf) A-TOTAL 457,259 10.497 72% 0.29 13,080 B-TOTAL 82,604 1.896 73% 0.29 2,383 C-TOTAL 51,708 1.187 41% 0.18 943 TOTAL REQUIRED 591,571 13.581 70% 0.27 16,183 Less WQ Provided by Underground Detention 3,895 Less WQ Provided in Wet Pond 943 Total WQ Provided in Pond A 11,346 * based on 40 hr storage and additional 20% for extended detention Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Water Quality - Low Impact Development Platte River Power Authority Campus, Fort Collins, CO Required Onsite Water Quality Capture Volume For Underground Detention Basin Area Area Imperviousness Watershed WQCV* (Extended Detention) (sf) (acres) (%) (inches) (cf) Basin A South - Underground Detention LID A-3 16,242 0.37 90% 0.321 435 A-4 25,276 0.58 91% 0.325 685 A-5 17,344 0.40 85% 0.288 417 A-12 66,694 1.53 2% 0.012 67 125,555 2.88 43% 0.149 1,564 Basin A North - Underground Detention LID A-6 13,391 0.31 65% 0.204 227 A-7 14,010 0.32 53% 0.172 201 A-8 4,429 0.10 72% 0.229 84 A-9 31,121 0.71 90% 0.321 833 A-10 37,508 0.86 72% 0.226 708 A-11 28,184 0.65 26% 0.110 258 128,642 2.95 63% 0.198 2,127 Total To Underground Detention 3,691 * Based on 12 hr storage forunderground detention ** Basin A-12 Future will be required to provide LID treatment at time of future development. Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Dention Pond Volume (FAA Method) Platte River Power Authority Campus, Fort Collins, CO POND ID: Basin A South - Underground Detention LID WQ Basin Characateristics Area = 125,555 square feet Area = 2.88 acres C 2 = 0.48 Q in = 2.07 cfs WQ Release Rate Determined from Number of Chambers and Chamber Release Rate Q OUT = 0.52 cfs Unit Flow = 0.18 cfs/acre T C = 15.8 minutes Notes: 1. Release rate out of pond based on number of chambers multiplied by release rate per chamber. 2. Rainfall intensities approximated as one-half the 2-yr peak runoff rate. 3. C2 utilized for water quality event detention calculation. Detention Volume Calculations Rainfall Rainfall Inflow Rate Inflow Volume Adjustment Factor Average Outflow Volume Required Duration (T) Intensity (I) Qin= ∑C100*Area*I Vi=(Qin*T*60) Factor Outflow Rate Vo=Qav*T *60 Storage Volume m= 0.5(1 + Tc/T) Qav = m*Qout Vs=Vi-Vo min in/hr cfs ft 3 cfs ft 3 ft 3 5 1.425 2.0 591 1.00 0.52 156 436 10 1.105 1.5 917 1.00 0.52 311 606 15 0.935 1.3 1,164 1.00 0.52 467 697 20 0.805 1.1 1,336 0.89 0.46 557 780 25 0.715 1.0 1,484 0.82 0.42 634 849 30 0.650 0.9 1,619 0.76 0.40 712 906 35 0.585 0.8 1,700 0.73 0.38 790 910 40 0.535 0.7 1,776 0.70 0.36 868 909 45 0.495 0.7 1,849 0.68 0.35 946 903 50 0.460 0.6 1,909 0.66 0.34 1,024 886 55 0.435 0.6 1,986 0.64 0.33 1,101 885 60 0.410 0.6 2,042 0.63 0.33 1,179 863 65 0.385 0.5 2,077 0.62 0.32 1,257 820 70 0.365 0.5 2,121 0.61 0.32 1,335 786 75 0.345 0.5 2,148 0.61 0.31 1,413 735 80 0.330 0.5 2,192 0.60 0.31 1,491 701 85 0.315 0.4 2,223 0.59 0.31 1,568 654 90 0.305 0.4 2,279 0.59 0.30 1,646 632 95 0.290 0.4 2,287 0.58 0.30 1,724 563 100 0.280 0.4 2,324 0.58 0.30 1,802 522 105 0.270 0.4 2,353 0.58 0.30 1,880 474 110 0.260 0.4 2,374 0.57 0.30 1,958 417 115 0.255 0.4 2,434 0.57 0.29 2,035 399 120 0.245 0.3 2,441 0.57 0.29 2,113 327 Required Detention Volume V 100 = 910 cubic feet V 100 = 0.02 acre-ft Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Dention Pond Volume (FAA Method) Platte River Power Authority Campus, Fort Collins, CO POND ID: Basin A North - Underground Detention LID WQ Basin Characateristics Area = 128,642 square feet Area = 2.95 acres C 2 = 0.67 Q in = 2.69 cfs WQ Release Rate Determined from Number of Chambers and Chamber Release Rate Q OUT = 0.71 cfs Unit Flow = 0.24 cfs/acre T C = 15.8 minutes Notes: 1. Release rate out of pond based on number of chambers multiplied by release rate per chamber. 2. Rainfall intensities approximated as one-half the 2-yr peak runoff rate. 3. C2 utilized for water quality event detention calculation. Detention Volume Calculations Rainfall Rainfall Inflow Rate Inflow Volume Adjustment Factor Average Outflow Volume Required Duration (T) Intensity (I) Qin= ∑C100*Area*I Vi=(Qin*T*60) Factor Outflow Rate Vo=Qav*T *60 Storage Volume m= 0.5(1 + Tc/T) Qav = m*Qout Vs=Vi-Vo min in/hr cfs ft 3 cfs ft 3 ft 3 5 1.425 2.8 846 1.00 0.71 212 634 10 1.105 2.2 1,312 1.00 0.71 425 887 15 0.935 1.9 1,665 1.00 0.71 637 1,028 20 0.805 1.6 1,911 0.89 0.63 759 1,152 25 0.715 1.4 2,122 0.82 0.58 865 1,257 30 0.650 1.3 2,315 0.76 0.54 971 1,344 35 0.585 1.2 2,431 0.73 0.51 1,077 1,353 40 0.535 1.1 2,541 0.70 0.49 1,184 1,357 45 0.495 1.0 2,644 0.68 0.48 1,290 1,355 50 0.460 0.9 2,731 0.66 0.47 1,396 1,335 55 0.435 0.9 2,840 0.64 0.46 1,502 1,338 60 0.410 0.8 2,920 0.63 0.45 1,608 1,312 65 0.385 0.8 2,971 0.62 0.44 1,714 1,257 70 0.365 0.7 3,033 0.61 0.43 1,820 1,213 75 0.345 0.7 3,072 0.61 0.43 1,926 1,145 80 0.330 0.7 3,134 0.60 0.42 2,033 1,102 85 0.315 0.6 3,179 0.59 0.42 2,139 1,040 90 0.305 0.6 3,259 0.59 0.42 2,245 1,014 95 0.290 0.6 3,271 0.58 0.41 2,351 920 100 0.280 0.6 3,324 0.58 0.41 2,457 867 105 0.270 0.5 3,366 0.58 0.41 2,563 802 110 0.260 0.5 3,395 0.57 0.40 2,669 726 115 0.255 0.5 3,481 0.57 0.40 2,776 706 120 0.245 0.5 3,490 0.57 0.40 2,882 609 Required Detention Volume V 100 = 1,357 cubic feet V 100 = 0.03 acre-ft Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Underground Detention Platte River Power Authority Campus, Fort Collins, CO Required Underground Detention/WQ Volume Chamber Total Required Detention/ Chamber Chamber Unit Chamber *Installed Min. Min. Min. Req'd Design No. of Provided Provided Total ID Detention/WQ WQ Type Release Rate c Unit Chamber Unit No. of WQ Isolator Row Control i Chambers WQ Isolator Installed Volume a Inflow b Volume d Volume inc. Chambers f Release Volume by Provided Release Row System Aggregate e Rate g FAA Method h Rate j Volume k Volume l (cf) (cfs) (cfs) (cf) (cf) (sf) (cfs) (cf) (cfs) (cf) (cf) Basin A South 1564 2.07 SC-740 0.024 45.90 74.90 21.00 0.50 910 WQCV 22 0.52 1,010 1,648 Basin A North 2127 2.69 SC-740 0.024 45.90 74.90 29.00 0.68 1,357 WQCV 30 0.71 1,377 2,247 TOTAL 3691 4.76 SC-740 0.024 45.90 74.90 50.00 1.18 2,267 WQCV 52 1.23 2,387 3,895 *Volume assumes minimum aggregate depth below chamber. a. Total required WQCV calculated per 12-hr drain time. b. WQ inflow is approximated as one-half the 2-yr peak runoff rate. c. Release rate per chamber, limited by flow through geotextile with accumulated sediment. d. Volume within chamber only, not accounting for void spaces in surrounding aggregate. The Isolator Row(s) are sized per this unit volume. e. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit. The total system WQCV is sized per this unit volume. f. Number of chambers required to provide full WQCV within total installed system, including aggregate. g. Release rate per chamber times number of chambers. This is used at the 'outlet control' for the FAA calculations. h. Minimum 'chamber-only' volume to ensure dirty water is fully contained within Isolator Row. i. Determines whether the design is controlled by the Isolator Row volume or WQCV. j. Release rate per chamber times number of chambers provided. This is the approximate controlled discharge from the WQ event. k. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume. l. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required 12-hr WQCV. Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm Low Impact Development Summary Platte River Power Authority Campus, Fort Collins, CO Basin Proposed Impervious Area LID Treatment Area Treated % of Site Treated (sf) (acres) (sf) (%) A-1 25,596 None (1) - 0% A-2 33,402 None - 0% A-3 16,242 Underground Detention 16,242 6% A-4 23,562 Underground Detention 23,562 8% A-5 14,736 Underground Detention 14,736 5% A-6 9,600 Underground Detention 9,600 3% A-7 8,175 Underground Detention 8,175 3% A-8 3,539 Underground Detention 3,539 1% A-9 31,121 Underground Detention 31,121 11% A-10 29,725 Underground Detention 29,725 11% A-11 7,569 Underground Detention 7,569 3% A-12 (Future) 17,500 Future LID Treatment (2) 17,500 6% A-13 11,517 None - 0% B-1 10,651 Bioswale 10,651 4% B-2 28,612 Bioswale (3) 28,612 10% C-1 5,726 Wet Pond 5,726 2% Total Site 277,273 206,758 75% (1) Basin A-1 includes approximately 8,500 sf of future building area not being treated (2) Minimum required future LID treatment for basin A-12 (3) Basin B-2 includes 11,000 sf of future treated area by the future extension of the proposed bioswale Low Impact Development (LID) Treated Areas Calculations by: KRB Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm APPENDIX C Hydraulic Calculations APPENDIX D Referenced Materials United States Department of Agriculture A product of the National Cooperative Soil Survey, a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local participants Custom Soil Resource Report for Larimer County Area, Colorado Platte River Power Authority Natural Resources Conservation Service February 23, 2017 9 Custom Soil Resource Report Soil Map 4486900 4487100 4487300 4487500 4487700 4487900 4488100 4488300 4488500 4486900 4487100 4487300 4487500 4487700 4487900 4488100 4488300 4488500 495900 496100 496300 496500 496700 496900 497100 495900 496100 496300 496500 496700 496900 497100 40° 32' 50'' N 105° 2' 55'' W 40° 32' 50'' N 105° 1' 59'' W 40° 31' 54'' N 105° 2' 55'' W 40° 31' 54'' N 105° 1' 59'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 400 800 1600 2400 Feet 0 100 200 400 600 Meters Map Scale: 1:8,480 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. Map Unit Legend Larimer County Area, Colorado (CO644) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 6 Aquepts, ponded 3.5 1.0% 34 Fort Collins loam, 0 to 1 percent slopes 8.6 2.4% 35 Fort Collins loam, 0 to 3 percent slopes 4.2 1.2% 36 Fort Collins loam, 3 to 5 percent slopes 5.7 1.6% 73 Nunn clay loam, 0 to 1 percent slopes 180.2 50.8% 74 Nunn clay loam, 1 to 3 percent slopes 131.4 37.1% 75 Nunn clay loam, 3 to 5 percent slopes 13.3 3.8% 76 Nunn clay loam, wet, 1 to 3 percent slopes 7.6 2.2% Totals for Area of Interest 354.6 100.0% Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit. A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils. Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a Custom Soil Resource Report 11 73—Nunn clay loam, 0 to 1 percent slopes Map Unit Setting National map unit symbol: 2tlng Elevation: 4,100 to 5,700 feet Mean annual precipitation: 14 to 15 inches Mean annual air temperature: 48 to 52 degrees F Frost-free period: 135 to 152 days Farmland classification: Prime farmland if irrigated Map Unit Composition Nunn and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Nunn Setting Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Pleistocene aged alluvium and/or eolian deposits Typical profile Ap - 0 to 6 inches: clay loam Bt1 - 6 to 10 inches: clay loam Bt2 - 10 to 26 inches: clay loam Btk - 26 to 31 inches: clay loam Bk1 - 31 to 47 inches: loam Bk2 - 47 to 80 inches: loam Properties and qualities Slope: 0 to 1 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 7 percent Salinity, maximum in profile: Nonsaline (0.1 to 1.0 mmhos/cm) Sodium adsorption ratio, maximum in profile: 0.5 Available water storage in profile: High (about 9.1 inches) Interpretive groups Land capability classification (irrigated): 3e Land capability classification (nonirrigated): 4e Custom Soil Resource Report 18 Hydrologic Soil Group: C Ecological site: Clayey Plains (R067BY042CO) Hydric soil rating: No Minor Components Heldt Percent of map unit: 10 percent Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Ecological site: Clayey Plains (R067BY042CO) Hydric soil rating: No Wages Percent of map unit: 5 percent Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Ecological site: Loamy Plains (R067BY002CO) Hydric soil rating: No 74—Nunn clay loam, 1 to 3 percent slopes Map Unit Setting National map unit symbol: 2tlpl Elevation: 3,900 to 5,840 feet Mean annual precipitation: 13 to 17 inches Mean annual air temperature: 50 to 54 degrees F Frost-free period: 135 to 160 days Farmland classification: Prime farmland if irrigated Map Unit Composition Nunn and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Nunn Setting Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Pleistocene aged alluvium and/or eolian deposits Typical profile Ap - 0 to 9 inches: clay loam Bt - 9 to 13 inches: clay loam Custom Soil Resource Report 19 Btk - 13 to 25 inches: clay loam Bk1 - 25 to 38 inches: clay loam Bk2 - 38 to 80 inches: clay loam Properties and qualities Slope: 1 to 3 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 7 percent Salinity, maximum in profile: Nonsaline to very slightly saline (0.1 to 2.0 mmhos/cm) Sodium adsorption ratio, maximum in profile: 0.5 Available water storage in profile: High (about 9.9 inches) Interpretive groups Land capability classification (irrigated): 2e Land capability classification (nonirrigated): 3e Hydrologic Soil Group: C Ecological site: Clayey Plains (R067BY042CO) Hydric soil rating: No Minor Components Heldt Percent of map unit: 10 percent Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Ecological site: Clayey Plains (R067BY042CO) Hydric soil rating: No Satanta Percent of map unit: 5 percent Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Ecological site: Loamy Plains (R067BY002CO) Hydric soil rating: No 75—Nunn clay loam, 3 to 5 percent slopes Map Unit Setting National map unit symbol: 2tlpm Custom Soil Resource Report 20 Table—Hydrologic Soil Group (Platte River Power Authority) Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 6 Aquepts, ponded A/D 3.5 1.0% 34 Fort Collins loam, 0 to 1 percent slopes B 8.6 2.4% 35 Fort Collins loam, 0 to 3 percent slopes C 4.2 1.2% 36 Fort Collins loam, 3 to 5 percent slopes B 5.7 1.6% 73 Nunn clay loam, 0 to 1 percent slopes C 180.2 50.8% 74 Nunn clay loam, 1 to 3 percent slopes C 131.4 37.1% 75 Nunn clay loam, 3 to 5 percent slopes C 13.3 3.8% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 7.6 2.2% Totals for Area of Interest 354.6 100.0% Rating Options—Hydrologic Soil Group (Platte River Power Authority) Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Custom Soil Resource Report 28 References American Association of State Highway and Transportation Officials (AASHTO). 2004. Standard specifications for transportation materials and methods of sampling and testing. 24th edition. American Society for Testing and Materials (ASTM). 2005. Standard classification of soils for engineering purposes. ASTM Standard D2487-00. Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of wetlands and deep-water habitats of the United States. U.S. Fish and Wildlife Service FWS/OBS-79/31. Federal Register. July 13, 1994. Changes in hydric soils of the United States. Federal Register. September 18, 2002. Hydric soils of the United States. Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric soils in the United States. National Research Council. 1995. Wetlands: Characteristics and boundaries. Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service. U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/ nrcs/detail/national/soils/?cid=nrcs142p2_054262 Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. 2nd edition. Natural Resources Conservation Service, U.S. Department of Agriculture Handbook 436. http:// www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577 Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of Agriculture, Natural Resources Conservation Service. http:// www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580 Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and Delaware Department of Natural Resources and Environmental Control, Wetlands Section. United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of Engineers wetlands delineation manual. Waterways Experiment Station Technical Report Y-87-1. United States Department of Agriculture, Natural Resources Conservation Service. National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ home/?cid=nrcs142p2_053374 United States Department of Agriculture, Natural Resources Conservation Service. National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/ detail/national/landuse/rangepasture/?cid=stelprdb1043084 29 United States Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/ nrcs/detail/soils/scientists/?cid=nrcs142p2_054242 United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land resource regions and major land resource areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/? cid=nrcs142p2_053624 United States Department of Agriculture, Soil Conservation Service. 1961. Land capability classification. U.S. Department of Agriculture Handbook 210. http:// www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf Custom Soil Resource Report 30 This unofficial copy was downloaded on Nov-02-2016 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA This unofficial copy was downloaded on Nov-02-2016 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA This unofficial copy was downloaded on Nov-02-2016 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA APPENDIX E Drainage Exhibits SOUTHEAST CORNER S30, T.7N., R68W 50' RIGHT-OF-WAY R.O.W. WIDTH VARIES ACCESS EASEMENT WIDTH VARIES 60' RIGHT-OF-WAY 107.5' RIGHT-OF-WAY 50' RIGHT-OF-WAY R.O.W. WIDTH VARIES 2.21 1.29 2.38 3.75 2.33 1.35 2.19 0.31 0.33 0.97 0.54 EX1 EX4 OS1 EX2 EX3 EX5 OS2a OS3 OS4 OS2b OS5 EAST HORSETOOTH ROAD SOUTH TIMBERLINE ROAD DANFIELD COURT UNION PACIFIC RAILROAD OFFSITE PROPERTY OWNED BY: 2001 DANFIELD LLC EXISTING E/O BUILDING EXISTING HQ EXISTING WORKOUT SPACE EXISTING MICROWAVE BUILDING EXISTING POOL CAR GARAGE EXISTING CARPENTER SHOP EXISTING POND EXISTING DETENTION EXISTING DETENTION EXISTING DETENTION EXISTING STORM DRAINING HORSETOOTH ROAD EXISTING STORM SOUTHEAST CORNER S30, T.7N., R68W 50' RIGHT-OF-WAY R.O.W. WIDTH VARIES 60' RIGHT-OF-WAY 107.5' RIGHT-OF-WAY 50' RIGHT-OF-WAY R.O.W. WIDTH VARIES A1 C1 OS1 OS2a OS3 OS4 OS2b A2 A3 A13 B1 B2 A5 A4 A6 A7 A9 A10 A11 A8 0.41 1.26 3.46 1.19 0.68 0.21 0.97 0.37 0.26 0.94 0.46 1.43 0.40 0.58 A12 1.53 0.31 0.86 0.71 0.32 0.65 0.10 0.54 OS5 DETENTION POND DETENTION POND POND OUTLET STRUCTURE POND OUTLET STRUCTURE EAST HORSETOOTH ROAD SOUTH TIMBERLINE ROAD DANFIELD COURT UNION PACIFIC RAILROAD OFFSITE PROPERTY OWNED BY: 2001 DANFIELD LLC HQ BUILDING MICROWAVE BUILDING MAINTENANCE SHOP / TRUCK WASH POOL CAR WAREHOUSE SUBSTATION GARAGE FLEET PARKING GARAGE A PROPOSED POND EXISTING E&O BUILDING EXISTING HEADQUARTERS FLEET PARKING GARAGE B BIOSWALE W/ UNDERDRAIN POTENTIAL FUTURE PARKING AREA POTENTIAL FUTURE BIOSWALE UNDERGROUND DETENTION EXISTING STORM DRAINING BASIN OS3 PLATTE RIVER POWER AUTHORITY 11/14/17 U16014 1" = 60' 1" = N/A PLATTE RIVER POWER AUTHORITY HQ NORTH 11/8/2017 10:51:06 AM P:\U16014 - PRPA CAMPUS\CADD\CP\CX.XX_PROPOSED DRAINAGE PLAN.DWG CX.XX_PROPOSED DRAINAGE PLAN KRB NKS C6.00 26 DRAINAGE PLAN 0 60' 120' SCALE: 1" = 60' 30' PREPARED FOR: JOB NUMBER SHEET NUMBER OF SHEETS DATE SUBMITTED: The engineer preparing these plans will not be responsible for, or liable for, unauthorized changes to or uses of these plans. All changes to the plans must be in writing and must be approved by the preparer of these plans. NO. BY DATE CAUTION REVISIONS: VERTICAL: HORIZONTAL: SCALE PRELIMINARY PLANS NOT FOR CONSTRUCTION 1501 Academy Ct. Ste. 203 Fort Collins, CO 80524 (970) 530-4044 www.unitedcivil.com Civil Engineering & Consulting PROJ. MGR: DRAWING NAME: PATH: DATE: TIME: DESIGNER: UNITED CIVIL Design Group LLC NOTES 1. EXISTING UNDERGROUND AND OVERHEAD PUBLIC AND PRIVATE UTILITIES AS SHOWN ARE INDICATED ACCORDING TO THE BEST INFORMATION AVAILABLE TO THE ENGINEER. 2. VEGETATIVE SWALES, BIOSWALES, UNDERGROUND DETENTION AND THE WATERQUALITY AND DETENTION POND SHALL BE MAINTAINED BY THE PROPERTY OWNER AND FOLLOW APPLICABLE STANDARD OPERATING PROCEDURES AS SHOWN IN DEVELOPMENT AGREEMENT. 5124 5124 PROPOSED 1' CONTOUR EXISTING 1' CONTOUR STORM SEWER STORM INLET LEGEND EXISTING CURB & GUTTER PROPOSED CURB & GUTTER PROPOSED FLOWLINE LIMITS OF DISTURBANCE EXISTING PROPERTY LINE EXISTING R.O.W LINE EXISTING EASEMENT BASIN BOUNDARY SWALE SECTION D-101 XXXX BASIN DESIGNATION BASIN AREA (ACRE) 2 - YR RUNOFF COEFF. 100 - YR RUNOFF COEFF. DESIGN POINT FLOW DIRECTION 5125 5125 PROPOSED 5' CONTOUR EXISTING 5' CONTOUR A A DRAINAGE SUMMARY POND SUMMARY LOW IMPACT DEVELOPMENT TREATMENT SUMMARY Basin Proposed Impervious Area LID Treatment Area Treated % of Site Treated (sf) (acres) (sf) (%) A-1 25,596 None 0 0% A-2 33,402 None 0 0% A-3 16,242 Underground Detention 16,242 6% A-4 23,562 Underground Detention 23,562 8% A-5 14,736 Underground Detention 14,736 5% A-6 9,600 Underground Detention 9,600 3% A-7 8,175 Underground Detention 8,175 3% A-8 3,539 Underground Detention 3,539 1% A-9 31,121 Underground Detention 31,121 11% A-10 29,725 Underground Detention 29,725 11% A-11 7,569 Underground Detention 7,569 3% A-12 (Future) 17,500 Future LID Treatment 17,500 6% A-13 11,517 None 0 0% B-1 10,651 Bioswale 10,651 4% B-2 28,612 Bioswale 28,612 10% C-1 5,726 Wet Pond 5,726 2% Total Site 277,273 206,758 75% Proposed Basins Basin Area %I C2 C100 Q2 Q100 (acre) (cfs) (cfs) A-1 3.46 18% 0.37 0.46 2.82 12.32 A-2 0.94 81% 0.82 1.00 1.85 7.85 A-3 0.37 90% 0.95 1.00 1.01 3.71 A-4 0.58 91% 0.90 1.00 1.16 4.48 A-5 0.40 85% 0.84 1.00 0.96 3.96 A-6 0.31 65% 0.75 0.94 0.58 2.54 A-7 0.32 53% 0.66 0.82 0.45 1.96 A-8 0.10 72% 0.81 1.00 0.22 0.95 A-9 0.71 90% 0.95 1.00 1.94 7.11 A-10 0.86 72% 0.80 1.00 1.48 6.39 A-11 0.65 26% 0.44 0.55 0.71 3.12 A-12 1.53 2% 0.25 0.31 1.02 4.45 A-13 0.26 90% 0.95 1.00 0.72 2.63 A-TOTAL 10.50 45% 0.58 0.72 11.00 47.85 B-1 0.46 51% 0.62 0.78 0.61 2.66 B-2 1.43 46% 0.57 0.71 1.88 8.21 B-TOTAL 1.90 48% 0.58 0.73 1.88 8.18 C-1 1.19 12% 0.33 0.41 1.04 4.52 C-TOTAL 1.19 12% 0.33 0.41 1.04 4.52 OS-1 0.68 2% 0.25 0.31 0.39 1.70 OS-2A 0.21 41% 0.54 0.68 0.30 1.29 OS-2B 0.97 77% 0.80 1.00 1.94 8.47 OS-3 0.41 45% 0.56 0.70 0.47 2.05 OS-4 1.26 75% 0.78 0.97 2.15 9.39 OS-5 0.54 2% 0.25 0.31 0.30 1.31 Pond A Pond C WQCV REQUIRED 0.26 AC-FT 0.02 AC-FT WQCV PROVIDED 0.30 AC-FT 0.02 AC-FT DETENTION VOLUME REQUIRED 2.77 AC-FT 0.32 AC-FT DETENTION VOLUME PROVIDED 2.88 AC-FT 0.35 AC-FT WQCV WATER SURFACE ELEVATION 4949.60 4955.05 100-YEAR WATER SURFACE ELEVATION 4,952.00 4,955.50 TOP OF POND ELEVATION 4,953.00 4,956.50 DRAINING BASIN OS3 PLATTE RIVER POWER AUTHORITY 11/14/17 U16014 1" = 60' 1" = N/A PLATTE RIVER POWER AUTHORITY HQ NORTH 11/8/2017 10:11:32 AM P:\U16014 - PRPA CAMPUS\CADD\CP\CX.XX_EXISTING DRAINAGE PLAN.DWG CX.XX_EXISTING DRAINAGE PLAN KRB NKS EX-DR 1 EXISTING DRAINAGE PLAN 0 60' 120' SCALE: 1" = 60' 30' PREPARED FOR: JOB NUMBER SHEET NUMBER OF SHEETS DATE SUBMITTED: The engineer preparing these plans will not be responsible for, or liable for, unauthorized changes to or uses of these plans. All changes to the plans must be in writing and must be approved by the preparer of these plans. NO. BY DATE CAUTION REVISIONS: VERTICAL: HORIZONTAL: SCALE PRELIMINARY PLANS NOT FOR CONSTRUCTION 1501 Academy Ct. Ste. 203 Fort Collins, CO 80524 (970) 530-4044 www.unitedcivil.com Civil Engineering & Consulting PROJ. MGR: DRAWING NAME: PATH: DATE: TIME: DESIGNER: UNITED CIVIL Design Group LLC NOTES 1. EXISTING UNDERGROUND AND OVERHEAD PUBLIC AND PRIVATE UTILITIES AS SHOWN ARE INDICATED ACCORDING TO THE BEST INFORMATION AVAILABLE TO THE ENGINEER. 2. VEGETATIVE SWALES, BIOSWALES, UNDERGROUND DETENTION AND THE WATERQUALITY AND DETENTION POND SHALL BE MAINTAINED BY THE PROPERTY OWNER AND FOLLOW APPLICABLE STANDARD OPERATING PROCEDURES AS SHOWN IN DEVELOPMENT AGREEMENT. 5124 5124 PROPOSED 1' CONTOUR EXISTING 1' CONTOUR STORM SEWER STORM INLET LEGEND EXISTING CURB & GUTTER PROPOSED CURB & GUTTER PROPOSED FLOWLINE LIMITS OF DISTURBANCE EXISTING PROPERTY LINE EXISTING R.O.W LINE EXISTING EASEMENT BASIN BOUNDARY SWALE SECTION D-101 XXXX BASIN DESIGNATION BASIN AREA (ACRE) 2 - YR RUNOFF COEFF. 100 - YR RUNOFF COEFF. DESIGN POINT FLOW DIRECTION 5125 5125 PROPOSED 5' CONTOUR EXISTING 5' CONTOUR A A DRAINAGE SUMMARY Existing Basins Basin Area %I C2 C100 Q 2 Q100 (acre) (cfs) (cfs) EX1 3.75 49% 0.59 0.74 5.14 22.42 EX2 2.38 32% 0.47 0.59 2.23 9.73 EX3 2.19 80% 0.83 1.00 5.16 21.75 EX4 2.33 19% 0.38 0.48 1.88 8.20 EX5 1.35 12% 0.32 0.40 0.91 3.98 OS-1 0.31 20% 0.38 0.47 0.27 1.17 OS-2A 0.33 27% 0.43 0.54 0.38 1.65 OS-2B 0.97 77% 0.80 1.00 1.94 8.47 OS-3 2.21 20% 0.38 0.48 1.62 7.09 OS-4 1.29 73% 0.76 0.95 2.17 9.47 OS-5 0.54 2% 0.25 0.31 0.30 1.31 OS-2B OS-2B 0.97 Paved 0.90 50 2.0% 2.0 490 0.7% 20 1.6 5.1 7.1 Yes 540 13 7.1 OS-3 OS-3 0.41 Lawn 0.09 140 1.5% 18.9 165 0.7% 20 1.7 1.6 20.5 Yes 305 12 11.7 OS-4 OS-4 1.26 Lawn 0.09 60 5.0% 8.3 250 1.1% 20 2.1 2.0 10.3 Yes 310 12 10.3 OS-5 OS-5 0.54 Lawn 0.09 30 10.0% 4.7 200 0.7% 7 0.6 5.7 10.4 Yes 230 11 10.4 Notes: (1) C5 based initial ground type and Table RO-5 (2)ti = [0.395(1.1-C5)L1/2]/S1/3, S= slope in %, L=length of overland flow (400' max) (3)V=CvS0.5, S=watercourse slope in ft/ft, UDFCD Equation RO-4 (4)tt=L/(V*60 sec/min) (5)tc check (for urban or developed areas only) = total length/180 + 10 (6)min tc = 5 min Proposed Basins Initial Overland Flow Time (ti) Travel/Channelized Time of Flow (t t) ti +tt t c Check for Urbanized Basins Final tc (6) Date: 11/7/2017 P:\U16014 - PRPA Campus\Reports\Drainage\Calculations\U16014-Drain Calcs.xlsm OS-2B OS-2B 0.97 0.77 0.80 1.00 1.94 8.47 OS-3 OS-3 0.41 0.45 0.56 0.70 0.47 2.05 OS-4 OS-4 1.26 0.75 0.78 0.97 2.15 9.39 OS-5 OS-5 0.54 0.02 0.25 0.31 0.30 1.31 Totals 68.21 101.08 Underground Detention – Underground detention diverts storm water runoff during the water quality event and detains the flows underground. This provides for the removal of sediment and other pollutants from the runoff while also promoting infiltration. Underground detention has been