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Home My WebLink AboutFile Documents.506 E Main St.0054.2019 (12).ACBK PITKIN COUNTY COURTHOUSE 506 E MAIN STREET CITY OF ASPEN, COLORADO DRAINAGE REPORT August 2019 PREPARED FOR: CITY OF ASPEN ATTN: DEVELOPMENT ENGINEERING PHONE: 970-920-5080 PITKIN COUNTY ATTN: JODI SMITH, FACILITIES DIRECTOR PHONE: 970-920-5396 PREPARED BY: MARTIN/MARTIN, INC. 0101 FAWCETT ROAD, SUITE 260 P.O. BOX 8896 AVON, COLORADO 81620 PHONE: 970.926.6007 PRINCIPAL-IN-CHARGE: L. MARK LUNA, P.E. DESIGN ENGINEER: MASON A. TALKINGTON, P.E. M.M. DRAINAGE REPORT JOB # M17.1435 08/21/2019 Reviewed by Engineering 09/05/2019 1:15:37 PM "It should be known that this review shall not relieve the applicant of their responsibility to comply with the requirements of the City of Aspen. The review and approval by the City is offered only to assist the applicant's understanding of the applicable Engineering requirements." The issuance of a permit based on construction documents and other data shall not prevent the City of Aspen from requiring the correction of errors in the construction documents and other data. TABLE OF CONTENTS A. INTRODUCTION ........................................................................................................ 1 1. Location .................................................................................................................................................................. 1 2. Proposed Development ...................................................................................................................................... 2 B. HISTORIC DRAINAGE .............................................................................................. 2 1. Description of Property ...................................................................................................................................... 2 2. Overall Basin Description .................................................................................................................................. 3 C. DESIGN CRITERIA .................................................................................................... 4 1. List of References ................................................................................................................................................ 4 2. Hydrologic Criteria ............................................................................................................................................... 4 3. Hydraulic Criteria ................................................................................................................................................. 5 D. DRAINAGE PLAN ...................................................................................................... 5 1. General Concept ................................................................................................................................................... 5 2. Specific Details ..................................................................................................................................................... 5 E. CONCLUSION ............................................................................................................ 8 F. REFERENCES............................................................................................................ 8 Appendix A – Supporting Documents Appendix B – Hydrologic Computations & Water Quality Appendix C – Hydraulic Computations Appendix D - Drainage Maps 08/21/2019 P a g e | 1 A. Introduction The intent of this drainage report is to present an urban storm water management plan for conveying and treating excess storm runoff for the proposed Pitkin County Courthouse remodel herein known as the Site. As proposed, the drainage design shall capture and route the excess storm water where feasible to an existing inlet located North of the building where it will be conveyed to an existing CDS Hydrodynamic Separator unit and ultimately to System 2 within the City of Aspen’s Master Plan drainage network. No onsite detention is proposed as part of this project. This report follows the guidelines of and is in compliance with the City’s Urban Runoff Management Plan (URMP). 1. Location A. Adjacent Roadways and Developments The site is located within the City of Aspen, Pitkin County. The site is approximately 0.54 acres and is located within Section 7, Township 10 South, and Range 85 West of the Sixth Principal Meridian. The site is bordered to the west by N. Galena St. and to the south by Main Street also known as SH 82. North and East are the Pitkin County Jail Building and Pitkin County Courthouse Plaza Building. B. Vicinity Map 08/21/2019 P a g e | 2 2. Proposed Development A. Type of Development The courthouse building is proposed be remodeled with more than 50% of the interior demolished. The majority of the site area is to remain in the existing condition with the exception of an ADA ramp on the south side, a sidewalk and ADA ramp on the east side of the building, additional landscaping on the north side, and an egress stair landing on the north side of the building. B. Requested Variances There are no requested drainage variances for the site. B. Historic Drainage 1. Description of Property A. Property Conditions and Historic Drainage Pattern. The existing site is developed with the historic Pitkin County Courthouse facility, which was completed in the 1890’s and associated infrastructure improvements such as sidewalks and landscaping. The adjacent Pitkin County facilities were recently constructed, including a plaza area that is directly east of the building. The building has an existing roof drain system that collects the majority of the roof area. The drain system discharges into an existing 36” diameter drywell, where the water infiltrates into the soil strata. The landscape area north of the building drains overland to an inlet located in a sump condition and is noted as Design Point 4 in the drainage map. The landscape areas west, south and east of the building are accounted for in the previous site drainage report as being tributary to this inlet. The previous site drainage report was prepared by JVA and is attached to this report within the Appendix. In reviewing of the survey and conducting site visits, it has been determined that these landscape areas are not actually tributary to this inlet due to the existing site grades. The landscape area on the south side of the building, west of the entry appears to be relatively flat, with a very slight downward slope to the northwest where per the survey there appears to be a low point in the grass south of the existing pavers. This is a mostly 08/21/2019 P a g e | 3 vegetated landscape area and the minimal runoff generated from this area is anticipated to infiltrate into the ground. The landscape area on the south side of the building and east of the main entry appears to generally slope downward to the north along the east side of the building. There is an existing inlet located immediately east of the proposed ramp entry at the northeast corner of the building and it is anticipated that runoff generated from this landscape area makes its way to the existing inlet. It is understood through conversations with Aspen Engineering that this inlet most likely ties into the existing drainage system of the Courthouse Plaza Building and is ultimately routed north to an existing water quality unit. There is a plaza located on the east side of the east landscape area. The recent construction in this area installed several drains that we anticipate are also routed through the Courthouse Plaza Building addition, north to an existing water quality unit. Soil data for the proposed site was obtained from the USDA Natural Resources Conservation Service’s Web Soil Survey. The Web Soil Survey characterizes the on-site soils as Hydrologic Soils Group B. Runoff in these types of soils is medium to rapid with the erosion hazard ranging from moderate to high. Refer to Appendix A for a soils classification map. The Site is located within Zone X, as referenced from the FEMA Flood Insurance Rate Map (08097C0204 C) dated June 4 1987. The FEMA map legend defines “Zone X” as “Areas determined to be outside the 0.2% annual chance floodplain.” 2. Overall Basin Description A. Off-Site Basins There are no off-site basins tributary to the site. The sidewalk surrounding the Site drains away to the adjacent roadways. B. Major Drainageways There are no major drainage ways that are adjacent to the site or that are directly impacted by the proposed Site Development. 08/21/2019 P a g e | 4 C. Outfalls Downstream from Property Design Point 4 is the inlet north of the building where the site is accounted for. Flows to this location are not anticipated to exceed what was calculated in previous reports. C. Design Criteria 1. List of References Various reports, studies and criteria were reviewed and used for the development of the drainage approach and analysis for the Site. The following is a summary of the references used for the preparation of this Report. These documents are also listed in Section F, References at the end of this Report. 1. Web Soil Survey, Natural Resources Conservation Service, United States Department of Agriculture, Available at http://websoilsurvey.nrcs.usda.gov 2. Aspen’s Urban Runoff Management Program (URMP), City of Aspen, Latest Revision. 3. Pitkin County Courthouse Plaza Building Addition Drainage Report; JVA; dated December 19, 2016 4. Pitkin County Courthouse Plaza Building Addition Drainage Report Temporary Sally Port Supplement to Drainage Report; JVA; dated October 14, 2016 5. Urban Drainage and Flood Control District (UDFCD) Drainage Criteria Manual, Volumes 1, 2, and 3, November 2010, with latest revisions. 2. Hydrologic Criteria The hydrologic criteria and calculations methods used for the preparation of this Report are per the City of Aspen Urban Runoff Management Plan (URMP) and supplemented with UDFCD Drainage Criteria Manuals where applicable. A. Rainfall/Runoff: The Rational Method was used to calculate peak runoff rates for the 2-year, 5-year, 10- year, and 100-year storm events. Time of concentration was calculated using equations in Section 3.4.3 of the URMP. Rainfall intensity was calculated using Equation 2-1 of the URMP. The P1 values were taken from the Table 2.2 of the URMP. A value of 0.77 inches was used for the 10-year P1, and a value of 1.23 was used for the 100-year P1. Composite impervious and runoff coefficients were developed for the proposed property based on Figure 3.2, 3.3, and 3.4 of the URMP. 08/21/2019 P a g e | 5 B. Design Frequencies: This report considers the 10-year storm the minor event and the 100-year storm the major event. All storm sewers and inlets are designed for the major storm event. 3. Hydraulic Criteria Full flow pipe capacity was analyzed using Bentley FlowMaster V8i (SELECT series 1). D. Drainage Plan 1. General Concept A. Drainage Concept The general concept for the Site safely and efficiently conveys flows generated from the property to the respective discharge points. A roof drain line will convey flows from the roof area to the inlet north of the building. B. Major Conveyance Elements There are no major drainage ways that are adjacent to the site or is directly impacted by the Site Development. 2. Specific Details A. Proposed Drainage Concept The previous JVA report assigned the Pitkin County Courthouse area to Sub-basin D. This overall basin area delineation remains consistent between the previous report and this report. The area is further subdivided in this report into 4 sub-basins, D.1, D.2, D.3 and D.4. The site composite impervious area is 42.9% which is slightly less than the previous site drainage report which anticipated a site imperviousness of 46.5%. Sub-basin D.1 drains overland north to an existing inlet at Design Point 4. Sub-basin D.2 is the roof area that will be piped to this inlet. The combined flow of these basins is 1.21 cfs for the 100-year storm event. The calculated flow rate for these two sub-basins is less than the 1.29 cfs identified in the JVA report. 08/21/2019 P a g e | 6 Sub-Basin D.3 is comprised of the area south of the main south entry and the landscape area to the west. The runoff from this area is likely to remain small and mostly infiltrate into the ground in landscape areas. There are also permeable pavers proposed within this basin that will be placed at the landing to a lower level entry and that will replace existing stamped concrete from the Main Street sidewalk to the bottom of the main stair entry. The permeable paver area will allow runoff to infiltrate through the pavers and drainage course and filter material beneath and will not be collected by the existing inlet noted above. Sub-Basin D.4 is area south and east of the building and as noted previously, is not anticipated to be tributary to Design Point 4 due to the current site grades. This basin appears tributary to the drain system within the plaza and subsequently drains to a water quality unit north of the Courthouse Plaza building. B. Water Quality Water Quality treatment for Sub-basins D.1 and D.2 will occur within the existing Contech CDS2015-4 unit that is directly downstream of the inlet at Design Point 4. This stormwater unit was installed as part of a previous project, as designed by JVA. The approved JVA report is included in the appendix of this report and identifies the maintenance plan for the existing water quality unit. In the previously approved site drainage report prepared by JVA, a WQCV of 196cf was identified for the basin tributary to the water quality unit per the URMP WQCV Equation within Section 8.4. The WQCV for this project has been calculated to be 133 cf, which is approximately 1/3 less than the WQCV that was anticipated per the JVA drainage report. Calculations for the WQCV are included in the Appendix. Additionally, we reached out to Contech to confirm the treatment flow rate provided by the CDS unit installed at this site would be adequate to accommodate the proposed water quality flow, which we generally equate to the 2-year storm event. The 2-year storm event generates a combined flow of 0.33 cfs for basins D.1 and D.2. The treatment flow rate capacity of the existing CDS unit is 0.70 cfs. Finally, we asked Contech to confirm that the CDS unit can remove the minimum particle size at the minimum efficiency rate as required per Section 8.4 of the URMP, which is 60- micron particles and larger at greater than 90% efficiency rate of removal. Contech did not 08/21/2019 P a g e | 7 have testing for 60-micron particle removal, however, they did have testing for 50-micron and 75-micron particle sizes and provided efficiency removal rates for those particle sizes. The information provided in the Appendix shows that based on the site tributary area, C- value and flow rate that efficiency removal rate is 89.1% and 92.4% for 50-micron and 75- micron particle sizes, respectively. For the range of particle size and removal efficiency rate provided, we can interpolate that 60-micron particles would be removed at approximately 90.4% efficiency, which meets the minimum criteria of greater than 90%. Water quality for Sub-basin D.3 occurs due to infiltration of the southern landscape area, infiltration into the permeable paver systems and the eastern area being tributary to the plaza system, which as noted previously, is tributary to a water quality unit filtration system that is north of the Courthouse Plaza building. Calculations identifying available detention volume for the permeable paver system have been provided in the Appendix. An Inspection and Maintenance Manual has been prepared for this project and should be used by Pitkin County staff as a minimum guideline to implement inspection and maintenance for the existing and proposed water quality elements onsite. C. Storm Sewer System The roof drain system and the ADA ramp drain at the northeast corner of the building are the only storm systems proposed on site. The 8” roof drain system has a capacity of 1.57 cfs which is greater than the 0.79 cfs 100-year flow rate, and the capacity of the existing 8” corrugated plastic pipe has been calculated to be 1.91 cfs, which is greater than the combined Sub-Basin D.1 and D.2 flows of 1.21 cfs. The ADA ramp is covered by building roof, so we do not anticipate more than minor nuisance flows during windy snow or rain storms to be captured by this storm sewer. The capacity of the 4” storm line is 0.39 cfs which is greater than what we would anticipate to be generated by this isolated area for the 100-year storm event of 0.03 cfs 08/21/2019 P a g e | 8 E. Conclusion The proposed drainage plan is to provide safe and efficient conveyance of flows through the property in compliance with adjacent/previous studies. As proposed, the drainage design captures and routes the excess storm water where feasible to an existing inlet located North of the building. Stormwater runoff will be treated by an existing water quality unit located downstream from the inlet. The remainder of the site not tributary to the inlet will have water quality addressed by either infiltration into the soil strata, porous pavers, or other existing water quality units. The remodel of the Pitkin County Courthouse is not anticipated to impose adverse effects on the adjacent developments as described within this report. F. References 1. Web Soil Survey, Natural Resources Conservation Service, United States Department of Agriculture, Available at http://websoilsurvey.nrcs.usda.gov 2. Aspen’s Urban Runoff Management Program (URMP), City of Aspen, Latest Revision. 3. Pitkin County Courthouse Plaza Building Addition Drainage Report; JVA; dated December 19, 2016 4. Pitkin County Courthouse Plaza Building Addition Drainage Report Temporary Sally Port Supplement to Drainage Report; JVA; dated October 14, 2016 5. Urban Drainage and Flood Control District (UDFCD) Drainage Criteria Manual, Volumes 1, 2, and 3, November 2010, with latest revisions. 08/21/2019 Appendix A Supporting Documents 08/21/2019 Hydrologic Soil Group—Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties (PITKIN COUNTY COURTHOUSE) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/11/2019 Page 1 of 4 43 3 9 4 5 0 43 3 9 4 7 0 43 3 9 4 9 0 43 3 9 5 1 0 43 3 9 5 3 0 43 3 9 5 5 0 43 3 9 5 7 0 43 3 9 5 9 0 43 3 9 4 5 0 43 3 9 4 7 0 43 3 9 4 9 0 43 3 9 5 1 0 43 3 9 5 3 0 43 3 9 5 5 0 43 3 9 5 7 0 43 3 9 5 9 0 342990 343010 343030 343050 343070 343090 343110 342990 343010 343030 343050 343070 343090 39° 11' 29'' N 10 6 ° 4 9 ' 5 ' ' W 39° 11' 29'' N 10 6 ° 4 9 ' 0 ' ' W 39° 11' 24'' N 10 6 ° 4 9 ' 5 ' ' W 39° 11' 24'' N 10 6 ° 4 9 ' 0 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 35 70 140 210 Feet 0 10 20 40 60 Meters Map Scale: 1:781 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. 08/21/2019 MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties Survey Area Data: Version 9, 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: Data not available. 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—Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties (PITKIN COUNTY COURTHOUSE) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/11/2019 Page 2 of 4 08/21/2019 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 107 Uracca, moist-Mergel complex, 1 to 6 percent slopes, extremely s B 3.2 100.0% Totals for Area of Interest 3.2 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Hydrologic Soil Group—Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties PITKIN COUNTY COURTHOUSE Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/11/2019 Page 3 of 408/21/2019 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties PITKIN COUNTY COURTHOUSE Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/11/2019 Page 4 of 408/21/2019 site location 08/21/2019 December 19, 2016 City of Aspen Engineering Department City Hall 130 S. Galena Aspen, CO 81601 RE: Pitkin County Courthouse Plaza Building Addition Drainage Report JVA Job No. 2402c Dear Engineering Staff: The following revised Drainage Report and attached drainage map have been prepared for the Pitkin County Courthouse Plaza Building Addition Project at 530 E. Main Street in Aspen, Colorado. The drainage report and drainage map have been produced in accordance with the City of Aspen’s “Urban Runoff Management Plan” and comply with provisions thereof. It is our understanding that the information provided herein meets all requirements of the City of Aspen’s Grading and Drainage Requirements for Major Design. Please contact us if you have any questions regarding this submission. Sincerely, JVA, Inc. _____________________________ Gregory Schroeder, P.E. Project Manager 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report i TABLE OF CONTENTS SECTION 1 – INTRODUCTION ..................................................................................................... 1 GENERAL LOCATION AND DESCRIPTION ................................................................................ 1 PROPOSED PROJECT ............................................................................................................ 1 SECTION 2 – EXISTING SITE INFORMATION ................................................................................... 2 EXISTING SITE DESCRIPTION ................................................................................................... 2 EXISTING SITE DRAINAGE AND EXISTING FACILITIES .................................................................. 2 SECTION 3 – PROPOSED (DEVELOPED) SITE INFORMATION .......................................................... 4 DRAINAGE DESIGN CRITERIA ................................................................................................ 4 HYDROLOGIC METHOD AND DESIGN STORM FREQUENCIES .................................................... 4 PROPOSED SITE BASINS ........................................................................................................ 4 RUNOFF AND STORMWATER QUALITY ENHANCEMENT/DETENTION FACILITIES ............................. 5 SECTION 4 – CONCLUSIONS ..................................................................................................... 7 SECTION 5 – REFERENCES ......................................................................................................... 8 APPENDIX A – SITE MAPS SITE VICINITY MAP FEMA FIRMETTE FIGURE 1 – HISTORIC DRAINAGE MAP FIGURE 2 – DEVELOPED DRAINAGE MAP APPENDIX B – HYDRAULIC CALCULATIONS APPENDIX C – DRAINAGE LETTER FOR BASIN D, DATED 10/14/2016 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 1 SECTION 1 – INTRODUCTION GENERAL LOCATION AND DESCRIPTION Pitkin County proposes to construct an addition to the Courthouse Plaza Building lot 1, Pitkin County Center Subdivision and a portion of Block 92 City of Aspen, and portion of Block 10, East Aspen Addition. The 1.590-acre site is located in section 7, Township 10 South, Range 84 West, of the 6th P.M., City of Aspen, Pitkin County, State of Colorado. The subject property is fully developed and is the site of the Pitkin County Courthouse, Pitkin County Jail Building, Veteran’s Plaza, the aforementioned Courthouse Plaza Building, and associated parking and vehicular circulation infrastructure. The primary purpose of this drainage report is to address the proposed runoff information and to address water quality enhancement facilities at the proposed development. Reference is made to the attached “Figure 1 – Grading and Drainage Map.” PROPOSED PROJECT The proposed project will consist of removing the parking lot that is located between the Pitkin County Jail Building and the Courthouse Plaza building in order to construct an 8,932 sf (building footprint), three-story addition to the Courthouse Plaza Building. To support this building addition existing utilities, including domestic water, sanitary sewer, natural gas, electric, fiber optic, telephone and cable, will be removed and rerouted. An access drive from Galena Plaza will also be constructed to serve as a private access to a temporary sally port for the Jail Building during construction. The drive will also serve as a permanent fire lane to serve the proposed building addition and the other buildings on site. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 2 SECTION 2 – HISTORIC DRAINAGE MAJOR DRAINAGE BASIN DESCRIPTION The site is located in the Roaring Fork River Basin. Specifically, the site is within the System 2 Drainage Basin as delineated in the City of Aspen Master Drainage Plan. According to the FEMA Flood Insurance Rate Map Panel Number 08097 C0204 C, dated June 4, 1987, the site is located in Zone X which is designated as being outside of the 100-year floodplain area. Copies of the referenced flood map that depict the site location are included in the Appendix. SITE DRAINAGE AND EXISTING FACILITIES The existing site is entirely developed. As previously mentioned, the subject property is the site of the Pitkin County Courthouse, Pitkin County Jail Building, Veteran’s Plaza, and the Courthouse Plaza Building. There are also two parking areas, an access drive, and sidewalks/pedestrian paths throughout the site. The site is bound by Rio Grande Place to the north, Main Street to the south, Galena Plaza on the west, and the Aspen Police Department parcel to the east. Overall, the site slopes from an approximate elevation of 7913 at the south property line along Main Street to an elevation of approximately 7890 along the north property line along Rio Grande Place. There are no significant offsite flows entering the site. The site has several storm drainage improvements. Runoff from the roof of the County Courthouse is discharged to the adjacent landscaped areas directly from the roof or by gutter down spouts. A series of area inlets then collect storm water from the surface. The routing of these inlets is largely unknown due to the lack of available design and as-built information. Such is the case throughout the majority of site. Storm water is collected by roof drains on the Courthouse Plaza building. The existing discharge point is also unknown. Information gathered from design plans indicates that the majority of runoff from the roof of the Jail Building is collected and routed to an existing dry well onsite. The exact location and size of the drywell is unknown at this time. Attempts to locate the existing dry well onsite have been unsuccessful. Run off from the perimeter of the roof of the Jail building is discharged to adjacent landscaped areas directly from the roof edge or by gutter downspouts. There is an existing 2’ x 2’ area drainage inlet (designated as Inlet-1 on Figure 1) in the plaza area to the north of the Courthouse and West of the Jail Building. Inlet-1 captures surface run off from the adjacent sidewalks, landscaped areas including the west portion of Veteran’s plaza, as well as runoff from the adjacent roofs and roof down spouts. There are multiple pipes discharging into the box of Inlet-1. The orientation of these discharge pipes suggests that they are likely roof drain or area drain connections from the Courthouse and Jail Buildings. Due to the lack of available design/as-built information and survey attempts, the actual locations and origins of these pipes have not been verified. The west portion of Veteran’s Plaza and the landscaped areas to south and west of the 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 3 Courthouse sheet flow to small gravel and earthen swale that direct these flows towards Inlet-1. Storm water captured by Inlet-1 is routed underground (pipe size and exact location/routing unknown) and is discharged directly to Rio Grande Place through a culvert of unknown size that is mostly buried by overgrown vegetation and sedimentation. The location of this discharge point is indicated as Outfall-1 on Figure 1. Run off from the parking areas and vehicular access drive sheet flow across the paved parking areas and collect in the curb and gutter of the access drive. The curb and gutter directs this run off toward the north through valley pans and eventually discharges directly to the curb and gutter in Rio Grande Place. A drainage analysis was performed to determine existing runoff from the total site area as well as the overall imperviousness of the site. The existing drainage basins and runoff paths on the existing drainage map were delineated using all available information and on the ground observations. The site consists of six minor drainage basins, two of which are the roof areas of the Jail Building and Courthouse Plaza Building. Drainage Basin H1 consists of the Courthouse building, landscaped areas surrounding the Courthouse Building, the west portion of Veteran’s Plaza, and the plaza area to the north of the Courthouse building. Basin H1 collects at Inlet-1 and discharges through a culvert onto Rio Grande Place as described above. Drainage Basin H2 consists of the onsite portion of the paved pedestrian path that connects Galena Plaza to Rio Grande Place and the onsite landscaped area directly to the east and west of the path. Basin 2H sheet flows runoff directly to Rio Grande Place. Drainage Basin H3 consists of the landscaped area to the west and north of the Jail Building as well as the sidewalks and paved parking area north of the Jail Building. Basin H3 discharges into the curb and gutter of the access drive that connects to Rio Grande Place. Drainage Basin H4 consists of the east portion of Veteran’s Plaza and the paved parking area and access drive to the north of the Courthouse Plaza Building. Drainage Basin H4 discharges runoff into the curb and gutter of the access drive connecting to Rio Grande Place. The roof of the Jail Building is shown as an independent basin, H5, since available design drawings show that the building’s roof drains direct storm runoff to an onsite drywell. However, as previously mentioned, the location and size of this dry well is unknown at this time. Similarly, the roof of the Courthouse Plaza Building is shown as an independent basin, H6, since a roof drain system is in place. Details of the existing outfall of this roof drain system is unknown. The combined peak runoff for Basins H1, H2, H3, and H4, which all discharge to Rio Grande Place was determined to be 1.5 cfs and 3.17 cfs for the 10-year and 100-year events respectively. The peak runoff for the Jail Building, Basin JB-H into the dry well was determined to be 0.83 cfs and 1.52 cfs for the 10-year and 100-year events respectively. The peak runoff for the Courthouse Plaza Building, Basin CHP-H, was determined to be 0.29 cfs and 0.53 cfs for the 10- year and 100-year events respectively. The approximate imperviousness of the site was determined to be 64.4%. Details for these calculations can be found in Appendix B of this report. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 4 SECTION 2 – PROPOSED (DEVELOPED) DRAINAGE DRAINAGE DESIGN CRITERIA The proposed private storm drainage facilities for the project are designed to comply with the City of Aspen “Urban Runoff Management Plan – A Guide to Stormwater Management in the City of Aspen” Revised December 2014 Edition (URMP). HYDROLOGIC METHOD AND DESIGN STORM FREQUENCIES The Rational Method (Q=CIA) was used to determine the storm runoff (Q) from the areas tributary to the new storm system, with composite runoff coefficients (C) and contributing areas (A) given for design points in sub-basins. The runoff coefficients for various land usages were obtained derived using tables from the UDFCD Urban Storm Drainage Criteria Manual Volume 1 as outlined in Section 3.4.2 of the URMP. Intensity-Duration-Frequency Values were determined using Table 2.2 of the URMP and the calculated Time of Concentration (Tc). PROPOSED SITE BASINS As shown on the attached Figure 2 – Proposed Drainage Basins, the entire site was analyzed to determine the proposed runoff from the redeveloped site area. The proposed site was divided into seven basins with no significant offsite drainage entering the site as in historic conditions. Drainage Basin A consists the Courthouse Plaza Building, including the new addition. The roof drain conveyance system to the existing CHP building will be rerouted along with the roof drains for the building addition. This roof drain conveyance system will discharge directly into the water quality sand filter basins located underground in the parking area to the north of the jail building. Drainage Basin B consists of the east portion of Veteran’s Plaza and the paved courtyard entrance to the CHP. A small area drain will collect surface runoff from this basin. This area drain will be routed under the building and will tie in with the roof drain conveyance system to discharge into the sand filter basins. A low point has been graded into the plaza to provide an overflow point to eliminate the possibility of stormwater flooding the new addition. Drainage Basin C consists of the access drive to north of the building addition as well as the paved areas between the Jail Building and the CHP. Runoff from this basin collects in the curb and gutter of the access drive and is directed to a combination curb inlet along the west curb line of the drive. This inlet routes runoff to the water quality sand filter basins. Drainage Basin D generally consists of the same area as Existing Drainage Basin H1; the Courthouse building, landscaped areas surrounding the Courthouse Building, the west portion of 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 5 Veteran’s Plaza, and the plaza area to the north of the Courthouse building which will now include a fire lane and temporary sally port. Drainage Inlet 1 will be reset to match the new elevation of the fire lane/temporary sally port access drive. The routing of the storm drain pipes connected to this inlet will not be modified with this project. Additional details regarding this approach are provided in the following section. Drainage Basin E coincides with existing Drainage Basin JB-H and consists of the Pitkin County Jail Building. The exact location of the dry well to which runoff is currently routed to will be verified during construction. The current design approach assumes that the existing drywell does not meet current water quality standards. Therefore, the dry well will be removed and storm runoff will be rerouted to the water quality sand filter basins. If the existing drywell is found to be adequately sized to meet current standards and there is an adequate bypass, it will be serviced and will remain in place. Drainage Basin F coincides with existing Drainage Basin H2. There will be no modifications to this basin resulting from this project. Drainage Basin G coincides with existing Drainage Basin H3. There will be no modifications to this basin besides the disturbance during construction in that area needed to install the sand filter basins. RUNOFF AND STORMWATER QUALITY ENHANCEMENT/DETENTION FACILITIES Since the entire site has a direct conveyance to System 2 of the City of Aspens Master Drainage Plan without adverse impacts on upstream, surrounding, or downstream properties and facilities, storm water detention is not required or provided. Water quality enhancement will be provided for Drainage Basins A, B, D and E. Drainage Basin D is discussed in the attached letter dated 10/14/2016 and included in the Appendix of this report. The letter was submitted for a separate permit that details the Sally Port improvements made within this basin including the dedicated water quality feature to treat runoff, per direction of Pitkin County. Drainage Basins F and G have not been included in the water quality enhancement since this project will not modify these basins in any way. Moreover, this area is also planned to be redeveloped in the near future and a water quality enhancement feature will be provided at that time. Water quality enhancement is provided by dual water quality sand filter basins. The basins captures and provides treatment for the water quality capture volume of Basins A, B, C, and E as outlined above. They have been designed according to the criteria of the Typical Underground Sand Filter as detailed in the Urban Runoff Management Plan. The previous design consisted of a single sand filter vault located in the alley to the east of the jail building. Due to site access and construction limitations, the treatment system was relocated to the parking area north of the jail building and redesigned as a two-unit system with twin vaults working in parallel. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 6 Discharge from the treated drainage basins enters Vault 1 on the southwest corner of the structure. An equalizing pipe connects the wet pools/sedimentation chambers of Vaults 1 and 2. The top of the equalizing pipe is set at the same elevation as the top of the primary chambers. This insures that the water level in the two vaults will equalize prior to entering the filtration chamber. The outlet chambers are also connected by an equalizing pipe in order to provide a single, combined discharge point for the system. The calculated water quality capture volume being for the treated basins is 564.8 cubic feet. The basins are designed for a treatment volume of 577.5 cubic feet. Moreover, the volume captured in the wet pools/sedimentation chambers of the two units is 540 cubic feet which exceeds the volume required by URMP (0.3*WQCV = 169 cubic feet). The oversized sedimentation champers provide additional treatment capacity by the unit since more runoff can be contained in the vaults before the water level in the units reaches the overflow weirs. The basin calculations for runoff and water quality are provided in Appendix B of this report. The water quality sand filter basins each include an overflow weir which provides a by-bass for storm runoff in excess of the water quality capture volume. The bypass for this system has been designed to convey run off from the 100-year storm event per the Urban Runoff Management Plan. The discharge from the WQ basins is routed to the proposed public storm drain main extension being designed by SGM Engineers for the City of Aspen. The main extension runs in Rio Grande starting near the existing inlet in the north side of the Street just east of Mill Street. The extension runs to the east and terminates at the curb entrance of the project site in Rio Grande. The extension will serve this project, as well as the adjacent Police Department, which is currently being designed for redevelopment. The capacity of the extension is sized for both projects, as well as additional capacity per the City’s direction. MAINTENANCE Pitkin County staff will maintain the sand filter structure per the following requirements: Required Action Maintenance Objective Frequency of Action Inspection Monitor water level and accumulation of sediments in chambers. Quarterly and following all rainfall events >0.25 inches. Scarify filter surface Scarify top 3 inches by raking the filter’s surface. Once per year or when needed to promote drainage. Sand filter removal Remove the top 3 inches of sand from the sand filter. After a second removal, backfill with 6 inches of new sand to return the sand depth to 18 inches. Minimum sand depth is 15 inches. If no construction activities take place in the tributary watershed, every 2 to 5 years depending on observed drain times, namely when it takes more than 12 hours to empty 3-foot deep pool. Otherwise more often. Pitkin County’s facilities staff will keep records of all maintenance performed including action(s) taken and dates. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 7 SECTION 3 – CONCLUSIONS All storm water flows from the existing buildings, the Courthouse Plaza building addition, plaza areas, and access drive improvements will be captured and conveyed to new or existing storm sewer systems or public right of way. Water quality enhancement features will be implemented for Drainage Basins A, B, C and E to provide water quality capture volume treatment prior to being discharged into the City’s storm infrastructure. Water quality features will be provided for the remainder of the site at the time that it is redeveloped. Detention storage will not be provided since the site has a direct conveyance to the City of Aspens storm drainage infrastructure, and is not required per the URMP. The recommendations of this report are in conformance with all applicable storm drainage regulations. Calculations, a vicinity map, and other reference materials used are attached in the Appendix. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Project – Preliminary Drainage Report 8 SECTION 4 – REFERENCES 1. “Urban Runoff Management Plan – A Guide to Stormwater Management in the City of Aspen”, City of Aspen, Revised December 2014 Edition 2. “Urban Storm Drainage Criteria Manual,” Urban Drainage and Flood Control District, Revised Edition 2008. 08/21/2019 APPENDIX A – SITE MAPS 08/21/2019 Regional Vicinity Map Local Vicinity Map 08/21/2019 SITE 08/21/2019 APPENDIX B – HYDRAULIC CALCULATIONS 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg Historic Runoff Coefficient & Time of Concentration Calculations Location: Aspen CA = KA + (1.31i3 - 1.44i2 + 1.135i + 0.12) Minor Design Storm: 10 Major Design Storm: 100 CCD = KCD + (0.858i3 - 0.786i2 + 0.774i + 0.04) Soil Type: B CB = (CA + CCD)/2 Basin Design Data I (%) = 100% 90% 90% 40% 10% 25% 2% 2%I (%)tc Comp tc Final Basin Name Design Point Apaved streets (sf) Adrives/co nc (sf) Aroof (sf) Agravel (sf) Aplygnd (sf) Aart. turf (sf) Alscape (B soil) (sf) Alscape (C/D soil) (sf) ATotal (sf) ATotal (ac) Imp (%)C2 C5 C10 C100 Upper most Length (ft) Slope (%) ti (min) Length (ft) Slope (%)Type of Land Surface Cv Velocity (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc=(L/180)+ 10 (min.) Min tc H1 H1 3,932 6,997 12,272 23,201 0.53 43.5% 0.25 0.31 0.37 0.50 220 2.7%15.3 Paved areas & shallow paved swales 20 0.0 0.0 15.3 220 11.2 11.2 H2 H2 2,399 2,414 4,813 0.11 45.9% 0.27 0.33 0.38 0.51 255 7.2%11.7 Paved areas & shallow paved swales 20 0.0 0.0 11.7 255 11.4 11.4 H3 H3 2,164 175 1,946 4,285 0.10 55.1% 0.33 0.38 0.43 0.54 74 14.9%4.6 56 7.1% Paved areas & shallow paved swales 20 5.3 0.2 4.8 130 10.7 5.0 H4 H4 12,130 2,354 5,158 19,642 0.45 73.1% 0.49 0.52 0.56 0.64 105 1.9%8.8 209 6.7% Paved areas & shallow paved swales 20 5.2 0.7 9.5 314 11.7 9.5 JB-H H5 12,903 12,903 0.30 90.0% 0.71 0.73 0.75 0.81 44 2.0%3.6 Paved areas & shallow paved swales 20 0.0 0.0 3.6 44 10.2 5.0 CHP-H H6 4475 4,475 0.10 90.0% 0.71 0.73 0.75 0.81 23 2.0%2.6 Paved areas & shallow paved swales 20 0.0 0.0 2.6 23 10.1 5.0 TOTAL SITE 14,294 8,860 24,375 0 0 0 21,790 0 69,319 1.59 64.4% 0.40 0.44 0.49 0.59 Basin Name Design Point Time of Conc (tc) C2 C5 C10 C100 2 5 10 100 ATotal (sf) ATotal (ac) Q2 Q5 Q10 Q100 H1 H1 11.2 0.25 0.31 0.37 0.50 1.44 2.07 2.60 4.42 23,201 0.53 0.19 0.35 0.52 1.19 H2 H2 11.4 0.27 0.33 0.38 0.51 1.43 2.06 2.58 4.39 4,813 0.11 0.04 0.07 0.11 0.25 H3 H3 5.0 0.33 0.38 0.43 0.54 2.06 2.98 3.72 6.32 4,285 0.10 0.07 0.11 0.16 0.34 H4 H4 9.5 0.49 0.52 0.56 0.64 1.57 2.25 2.82 4.80 19,642 0.45 0.34 0.53 0.71 1.39 JB-H H5 5.0 0.71 0.73 0.75 0.81 2.06 2.98 3.72 6.32 12,903 0.30 0.43 0.64 0.83 1.52 CHP-H H6 5.0 0.71 0.73 0.75 0.81 2.06 2.98 3.72 6.32 4,475 0.10 0.15 0.22 0.29 0.53 TOTAL SITE 69,319 1.59 1.23 1.92 2.62 5.21 Initial Overland Time (ti) Travel Time (tt) tt=Length/(Velocity x 60) tc Urbanized Check ON Runoff Coeff's Rainfall Intensities (in/hr)Area Flow Rates (cfs) Runoff Coeff's 2402c - Rational Calculations Historic 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg Composite Runoff Coefficient Calculations Location: Aspen Minor Design Storm: 10 Major Design Storm: 100 CA = KA + (1.31i^3 - 1.44i^2 + 1.135i + 0.12) Soil Type: B CCD = KCD + (0.858i^3 - 0.786i^2 + 0.774i + 0.04) CB = (CA + CCD)/2 Basin Design Data I (%) = 100% 90% 90% 40% 10% 25% 2% 2%I (%) Basin Name Design Point Apaved streets (sf) Adrives/c onc (sf) Aroof (sf) Agravel (sf) Aplygnd (sf) Aart. turf (sf) Alscape (B soil) (sf) Alscape (C/D soil) (sf) ATotal (sf) ATotal (ac) Imp (%)C2 C5 C10 C100 A 1 13,637 13,637 0.31 90.0% 0.71 0.73 0.75 0.81 B 2 3,063 1,858 4,921 0.11 56.8% 0.34 0.39 0.44 0.55 C 3 2,620 2,090 462 5,172 0.12 87.2% 0.66 0.69 0.72 0.78 D 4 5,183 6,997 11,407 23,587 0.54 46.5% 0.27 0.33 0.39 0.51 E 5 12,903 12,903 0.30 90.0% 0.71 0.73 0.75 0.81 F 6 2,399 2,414 4,813 0.11 45.9% 0.27 0.33 0.38 0.51 G 7 2,164 175 1,946 4,285 0.10 55.1% 0.33 0.38 0.43 0.54 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 TOTAL SITE 4,784 12,910 33,537 0 0 0 18,087 0 69,318 1.59 67.7% 0.43 0.47 0.51 0.61 Runoff Coeff's 2402c - Rational Calculations Developed C 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg Time of Concentration Calculations Location: Aspen Minor Design Storm: 10 Major Design Storm: 100 Soil Type: B Sub-Basin Data tc Comp tc Final Basin Name Design Point ATotal (ac)C5 Upper most Length (ft) Slope (%) ti (min) Length (ft)Slope (%) Type of Land Surface Cv Velocity (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc=(L/180)+ 10 (min) Min tc A 1 0.31 0.73 61 2.0%4.2 Paved areas & shallow paved swales 20 0.0 0.0 4.2 61 10.3 5.0 B 2 0.11 0.39 73 1.4%9.9 Paved areas & shallow paved swales 20 0.0 0.0 9.9 73 10.4 9.9 C 3 0.12 0.69 118 8.6%4.0 51 2.0% Paved areas & shallow paved swales 20 2.8 0.3 4.3 169 10.9 5.0 D 4 0.54 0.33 220 2.7%15.0 Paved areas & shallow paved swales 20 0.0 0.0 15.0 220 11.2 11.2 E 5 0.30 0.73 44 2.0%3.6 Paved areas & shallow paved swales 20 0.0 0.0 3.6 44 10.2 5.0 F 6 0.11 0.33 255 7.2%11.7 Paved areas & shallow paved swales 20 0.0 0.0 11.7 255 11.4 11.4 G 7 0.10 0.38 74 14.9%4.6 56 7.1% Paved areas & shallow paved swales 20 5.3 0.2 4.8 130 10.7 5.0 0 0 0.00 Paved areas & shallow paved swales 20 0 10.0 0 0 0.00 Paved areas & shallow paved swales 20 0 10.0 Initial Overland Time (ti)Travel Time (tt) tt=Length/(Velocity x 60) tc Urbanized Check ON 2402c - Rational Calculations Developed Tc 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg Developed Storm Runoff Calculations Design Storm : 100 Year Point Hour Rainfall (P1) : 1.23 B a s i n N a m e D e s i g n P o i n t A r e a ( a c ) R u n o f f C o e f f t c ( m i n ) C * A ( a c ) I ( i n / h r ) Q ( c f s ) T o t a l t c ( m i n ) S C* A ( a c ) I ( i n / h r ) Q ( c f s ) I n l e t T y p e Q i n t e r c e p t e d Q c a r r y o v e r Q b y p a s s P i p e S i z e ( i n ) or e q u i v a l e n t P i p e M a t e r i a l S l o p e ( % ) P i p e F l o w (c f s ) M a x P i p e Ca p a c i t y ( c f s ) L e n g t h ( f t ) V e l o c i t y ( f p s ) t t ( m i n ) To t a l T i m e (m i n ) N o t e s A 1 0.31 0.81 5.00 0.25 6.32 1.60 9.90 0.32 6.32 1.99 Roof Conveyance System 1.99 - - 12 in PVC 2.0% 2.3 7.0 60 2.9 0.34 10.24 A+B B 2 0.11 0.55 9.90 0.06 4.66 0.29 9.90 0.06 4.66 0.29 12" Area Drain 0.29 - - 6 in PVC 2.0% 0.3 1.1 20 1.5 0.23 10.13 C 3 0.12 0.78 5.00 0.09 6.32 0.58 5.00 0.33 6.32 2.10 Combination Curb Inlet 0.58 - - 12 in PVC 2.0% 2.1 7.0 47 2.7 0.29 5.29 C+E D 4 0.54 0.51 11.20 0.28 4.42 1.23 11.20 0.28 4.42 1.23 Existing 2'x2' Area Inlet 1.23 - -Existing E 5 0.30 0.81 5.00 0.24 6.32 1.52 5.00 0.24 6.32 1.52 Roof Conveyance System 1.52 - - 8 in PVC 2.0% 1.5 2.4 15 4.3 0.06 5.06 F 6 0.11 0.51 11.40 0.06 4.39 0.25 11.40 0.06 4.39 0.25 Sheet Flow Discharge 0.25 - - G 7 0.10 0.54 5.00 0.05 6.32 0.34 5.00 0.05 6.32 0.34 Sheet Flow Discharge 0.34 - - Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 2402c - Rational Calculations Q100 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg Developed Storm Runoff Calculations Design Storm : 10 Year Point Hour Rainfall (P1) : 0.77 B a s i n N a m e D e s i g n P o i n t A r e a ( a c ) R u n o f f C o e f f t c ( m i n ) C * A ( a c ) I ( i n / h r ) Q ( c f s ) T o t a l t c ( m i n ) S C* A ( a c ) I ( i n / h r ) Q ( c f s ) I n l e t T y p e Q i n t e r c e p t e d Q c a r r y o v e r Q b y p a s s P i p e S i z e ( i n ) or e q u i v a l e n t P i p e M a t e r i a l S l o p e ( % ) P i p e F l o w (c f s ) M a x P i p e Ca p a c i t y ( c f s ) L e n g t h ( f t ) V e l o c i t y ( f p s ) t t ( m i n ) To t a l T i m e (m i n ) N o t e s A 1 0.31 0.75 5.00 0.24 3.72 0.88 5.00 0.24 3.72 0.88 Roof Conveyance System 12 in PVC 2.0%0.9 7.0 60 1.1 0.89 5.89 A+B B 2 0.11 0.44 9.90 0.05 2.74 0.14 9.90 0.05 2.74 0.14 12" Area Drain 0.14 - -6 in PVC 2.0%0.1 1.1 20 0.7 0.48 10.38 C 3 0.12 0.72 5.00 0.08 3.72 0.32 5.00 0.08 3.72 0.32 Combination Curb Inlet 0.32 - -12 in PVC 2.0%0.3 7.0 47 0.4 1.95 6.95 C+E D 4 0.54 0.39 11.20 0.21 2.60 0.55 11.20 0.21 2.60 0.55 Existing 2'x2' Area Inlet 0.55 - -Existing E 5 0.30 0.75 5.00 0.22 3.72 0.83 5.00 0.22 3.72 0.83 Roof Conveyance System 8 in PVC 2.0%0.8 2.4 15 2.4 0.11 5.11 F 6 0.11 0.38 11.40 0.04 2.58 0.11 11.40 0.04 2.58 0.11 Sheet Flow Discharge G 7 0.10 0.43 5.00 0.04 3.72 0.16 5.00 0.04 3.72 0.16 Sheet Flow Discharge Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 2402c - Rational Calculations Q Minor 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM FLOW CALCULATIONS - GRATE INLET SUMP CONDITION (Reference: Urban Drainage and Flood Control District Drainage Criteria Manual, 2001, V.1, Section 3.3.6) (Note: Spreadsheet assumes orifice condition for fully developed flow.) INLET TYPE:BASIN: Orifice Equation:Q = Cd*Ao*(2gH)^0.5 K = Clogging Coefficent value for multiple inlets Adjust Ao (open area) due to clogging as follows: N Grate 1 1 Effective Area Opening Ae = (1-C) Ao, where:2 1.5 C = K * Co / N 3 1.75 N = Number of Inlets 4 1.88 Co = Single Inlet Clogging Factor:5 1.94 Co(grate) = 0.5 (50% clogging) 6 1.97 7 1.98 8 1.99 Number of inlets:N =1 Inlet Dimensions and Effective Open Area: Grate Opening:Ao(g) =0.38 ft^2 Total Ao(g) = 0.38 ft^2 K = 1.00 C = K*Co/N = 0.50 Ae(g) = (1-C)Ao = 0.19 ft^2 Allowable depth:H =2.0 in = 0.1666667 ft Constants:g = 32.20 ft/s^2 Cd = 0.67 Flow Calculations: Grate Flow:Q = Cd * Ae(g) * (2g*H)^0.5 Qg= 0.42 CFS Total Intercepted Flow with 1 inlet(s) and an allowable depth of 2 inches is 0.4 cfs Required Flow (Q 10 ) = 0.14 cfs Bypass = 0.0 cfs Required Flow (Q 100 ) = 0.29 cfs Bypass = 0.0 cfs B12" Area Drain 2402c - Rational Calculations Basin B Inlet 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM FLOW CALCULATIONS - COMBINATION INLET SUMP CONDITION (Reference: Urban Drainage and Flood Control District Drainage Criteria Manual, 2001, V.1, Section 3.3.6) (Note: Spreadsheet assumes orifice condition for fully developed flow. Vertical curb opening only.) INLET TYPE:Single Combination Inlet BASIN: Orifice Equation:Q = Cd*Ao*(2gH)^0.5 K = Clogging Coefficent value for multiple inlets Adjust Ao (open area) due to clogging as follows:N Grate Curb 1 1 1 Effective Area Opening Ae = (1-C) Ao, where:2 1.5 1.25 C = K * Co / N 3 1.75 1.31 N = Number of Inlets 4 1.88 1.33 Co = Single Inlet Clogging Factor:5 1.94 1.33 Co(grate) = 0.5 (50% clogging) 6 1.97 1.33 Co(curb opening) = 0.1 (10% clogging) 7 1.98 1.33 8 1.99 1.33 Number of inlets:N =1 Inlet Dimensions and Effective Open Area: Grate Opening:Ao(g) =2.32 ft^2 (per inlet) Total Ao(g) = 2.32 ft^2 (total, all inlets) K = 1.00 C = K*Co/N = 0.50 Ae(g) = (1-C)Ao = 1.16 ft^2 Curb Opening:length (l) =36 in = 3.00 ft (per inlet) height (h) =6 in = 0.50 ft Total Ao(c) = 1.50 ft^2 (total, all inlets) K = 1.00 C = K*Co/N = 0.10 Ae(c) = (1-C)Ao = 1.35 ft2 Allowable depth:H =6.0 in = 0.5 ft Constants:g = 32.20 ft/s^2 Cd = 0.67 Flow Calculations: Grate Flow:Q = Cd * Ae(g) * (2g*H)^0.5 Qg= 4.41 CFS Curb Flow:Q = Cd * Ae(c) * (2g*D)^0.5 D = H - h/2 = 0.25 Qc= 3.63 CFS Total Intercepted Flow with 1 inlets and an allowable depth of 6 inches is 8.0 cfs Required Flow (Q 10 ) = 0.32 cfs Bypass = 0.0 cfs Required Flow (Q 100 ) = 0.58 cfs Bypass = 0.0 cfs C 2402c - Rational Calculations Basin C Inlet 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM FLOW CALCULATIONS - GRATE INLET SUMP CONDITION (Reference: Urban Drainage and Flood Control District Drainage Criteria Manual, 2001, V.1, Section 3.3.6) (Note: Spreadsheet assumes orifice condition for fully developed flow.) INLET TYPE:BASIN: Orifice Equation:Q = Cd*Ao*(2gH)^0.5 K = Clogging Coefficent value for multiple inlets Adjust Ao (open area) due to clogging as follows: N Grate 1 1 Effective Area Opening Ae = (1-C) Ao, where:2 1.5 C = K * Co / N 3 1.75 N = Number of Inlets 4 1.88 Co = Single Inlet Clogging Factor:5 1.94 Co(grate) = 0.5 (50% clogging) 6 1.97 7 1.98 8 1.99 Number of inlets:N =1 Inlet Dimensions and Effective Open Area: Grate Opening:Ao(g) =2.1 ft^2 Total Ao(g) = 2.10 ft^2 K = 1.00 C = K*Co/N = 0.50 Ae(g) = (1-C)Ao = 1.05 ft^2 Allowable depth:H =2.0 in = 0.1666667 ft Constants:g = 32.20 ft/s^2 Cd = 0.67 Flow Calculations: Grate Flow:Q = Cd * Ae(g) * (2g*H)^0.5 Qg= 2.30 CFS Total Intercepted Flow with 1 inlet(s) and an allowable depth of 2 inches is 2.3 cfs Required Flow (Q 10 ) = 0.55 cfs Bypass = 0.0 cfs Required Flow (Q 100 ) = 1.23 cfs Bypass = 0.0 cfs 2'x2' Inlet D 2402c - Rational Calculations Basin D Exist Inlet 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 7/1/16 Ph: (970) 404 3100 By: RMM WATER QUALITY CAPTURE VOLUME Water Quality Enhancement Provided For Basins A, B, C, & E Basin Name Area (ac.)Imperviousness I*A Basin A 0.31 0.90 0.28 Basin B* 0.11 0.49 0.06 Basin C 0.12 0.87 0.10 Basin E 0.30 0.90 0.27 TOTAL 0.84 0.84 - *Basin B includes a tree reduction to impervious area per Section 8.4.1, URMP as outlined below Impervious area: 3,063.0 Tree Canopy Area: 2,564.0 Decid. Reduction (.15): 384.6 Effect. Imp. Area: 2,678.4 Eff. Imperviousness 0.49 ## WQCV (watershed-inches) = 0.185 Total WQ Area (sf) = 36,633 WQCV (cu. Ft.)=564.8 (Reference: "Urban Runoff Management Plan – A Guide to Stormwater Management in the City of Aspen”, City of Aspen, Revised December 2014 Edition) 2402c - Rational Calculations WQCV 08/21/2019 APPENDIX C – BASIN D DRAINAGE LETTER 08/21/2019 October 14, 2016 City of Aspen Engineering Department City Hall 130 S. Galena Aspen, CO 81601 RE: Pitkin County Courthouse Plaza Building Addition Temporary Sally Port Supplement to Drainage Report JVA Job No. 2402c Dear Engineering Staff: This letter serves to supplement the drainage report dated July 1, 2016 as submitted for the above mentioned project. In the original report, on page 3, the existing drainage basin H1 consists of the existing Pitkin County Courthouse (PCCH), surrounding landscaped areas, the west portion of Veteran’s Plaza, and the plaza area north of the courthouse building. Drainage basin H1 presently collects at Inlet-1 and discharges into an existing culvert to the north. The temporary sally port is shown in this submission, and consists of an asphalt or similar path that will be a shared fire access, as well as an ADA accessible route to the PCCH. Due to the construction of the new Courthouse Plaza Building Addition (CPBA), the existing sally port in the Pitkin County Jail Building (PCJB) will be blocked, and the location north of the PCCH will serve this temporary location, until the CHPA is constructed, as the permanent sally port is located within this parking structure. In the July 1 drainage report, Basin H1, has a 100-year runoff of 1.19CFS, and as a developed Basin D, has a 100-year runoff of 1.23CFS. As a result of the sally port improvements, a new value for the developed 100-year runoff will be 1.29 CFS. (see attached “Revised Developed Storm Runoff Calculations”). Calculations for inlet and pipe capacities have also been included. Additionally, the Water Quality Capture Volume (WQCV) for Basin D was not included in the original drainage report, due to the inclusion of the sally port as mentioned above. Mitigation for Basin D will be handled with the installation of a Contech CDS hydrodynamic separator (CDS2015-4). The WQCV has been determined to be 196 cubic feet (calculations attached). This unit is to be located to the north of the existing Inlet-1. Specifications and details for the CDS unit are attached, and meet the intents of the URMP under section 8.5.4 for sub-surface BMPs. The Inspection and Maintenance Guide for this unit has been attached to this report. 08/21/2019 Pitkin County Courthouse Plaza Building Addition Temporary Sally Port 10/14/2016 2 of 2 Please let us know if you have any questions or comments for this submission and this supplement to the drainage report letter. Sincerely, JVA, INCORPORATED By: ____________________________________ GREGORY W. SCHROEDER, P.E., CFM Project Manager 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg - Temp. Sally Port 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 10/14/16 Ph: (970) 404 3100 By: RMM Pitkin Co. Admin Bldg - Temp. Sally Port Revised Developed Storm Runoff Calculations Design Storm : 100 Year Point Hour Rainfall (P1) : 1.23 B a s i n N a m e D e s i g n P o i n t A r e a ( a c ) R u n o f f C o e f f t c ( m i n ) C * A ( a c ) I ( i n / h r ) Q ( c f s ) T o t a l t c ( m i n ) S C* A ( a c ) I ( i n / h r ) Q ( c f s ) I n l e t T y p e Q i n t e r c e p t e d Q c a r r y o v e r Q b y p a s s P i p e S i z e ( i n ) or e q u i v a l e n t P i p e M a t e r i a l S l o p e ( % ) P i p e F l o w (c f s ) M a x P i p e Ca p a c i t y ( c f s ) L e n g t h ( f t ) V e l o c i t y ( f p s ) t t ( m i n ) To t a l T i m e (m i n ) N o t e s A 1 0.31 0.81 5.00 0.25 6.32 1.60 9.90 0.32 6.32 1.99 Roof Conveyance System 1.99 - - 12 in PVC 2.0% 2.3 7.0 60 2.9 0.34 10.24 A+B B 2 0.11 0.55 9.90 0.06 4.66 0.29 9.90 0.06 4.66 0.29 12" Area Drain 0.29 - - 6 in PVC 2.0% 0.3 1.1 20 1.5 0.23 10.13 C 3 0.12 0.78 5.00 0.09 6.32 0.58 5.00 0.33 6.32 2.10 Combination Curb Inlet 0.58 - - 12 in PVC 2.0% 2.1 7.0 47 2.7 0.29 5.29 C+E D 4 0.54 0.54 11.20 0.29 4.42 1.29 11.20 0.29 4.42 1.29 Existing 2'x2' Area Inlet 1.29 - -Existing E 5 0.30 0.81 5.00 0.24 6.32 1.52 5.00 0.24 6.32 1.52 Roof Conveyance System 1.52 - - 8 in PVC 2.0% 1.5 2.4 15 4.3 0.06 5.06 F 6 0.11 0.51 11.40 0.06 4.39 0.25 11.40 0.06 4.39 0.25 Sheet Flow Discharge 0.25 - - G 7 0.10 0.54 5.00 0.05 6.32 0.34 5.00 0.05 6.32 0.34 Sheet Flow Discharge 0.34 - - Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 2402c - Rational Calculations-RevisedTSP.xlsx Q100 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg - Temp. Sally Port 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 10/14/16 Ph: (970) 404 3100 By: RMM FLOW CALCULATIONS - GRATE INLET SUMP CONDITION (Reference: Urban Drainage and Flood Control District Drainage Criteria Manual, 2001, V.1, Section 3.3.6) (Note: Spreadsheet assumes orifice condition for fully developed flow.) INLET TYPE:BASIN: Orifice Equation:Q = Cd*Ao*(2gH)^0.5 K = Clogging Coefficent value for multiple inlets Adjust Ao (open area) due to clogging as follows: N Grate 1 1 Effective Area Opening Ae = (1-C) Ao, where:2 1.5 C = K * Co / N 3 1.75 N = Number of Inlets 4 1.88 Co = Single Inlet Clogging Factor:5 1.94 Co(grate) = 0.5 (50% clogging) 6 1.97 7 1.98 8 1.99 Number of inlets:N =1 Inlet Dimensions and Effective Open Area: Grate Opening:Ao(g) =2.1 ft^2 Total Ao(g) = 2.10 ft^2 K = 1.00 C = K*Co/N = 0.50 Ae(g) = (1-C)Ao = 1.05 ft^2 Allowable depth:H =2.0 in = 0.1666667 ft Constants:g = 32.20 ft/s^2 Cd = 0.67 Flow Calculations: Grate Flow:Q = Cd * Ae(g) * (2g*H)^0.5 Qg= 2.30 CFS Total Intercepted Flow with 1 inlet(s) and an allowable depth of 2 inches is 2.3 cfs Required Flow (Q 10 ) = 0.59 cfs Bypass = 0.0 cfs Required Flow (Q 100 ) = 1.29 cfs Bypass = 0.0 cfs 2'x2' Inlet D 2402c - Rational Calculations-RevisedTSP.xlsx Basin D Exist Inlet 08/21/2019 Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Friday, Oct 14 2016 Existing 8 Inch CPP Circular Diameter (ft) = 0.67 Invert Elev (ft) = 7902.11 Slope (%) = 5.00 N-Value = 0.020 Calculations Compute by: Known Q Known Q (cfs) = 1.30 Highlighted Depth (ft) = 0.43 Q (cfs) = 1.300 Area (sqft) = 0.24 Velocity (ft/s) = 5.43 Wetted Perim (ft) = 1.25 Crit Depth, Yc (ft) = 0.54 Top Width (ft) = 0.64 EGL (ft) = 0.89 0 1 Elev (ft)Section 7901.75 7902.00 7902.25 7902.50 7902.75 7903.00 Reach (ft) 08/21/2019 JVA Incorporated Job Name: Pitkin Co. Admin Bldg - Temp. Sally Port 214 8th Street, S 210 Job Number: 2402c Glenwood Springs, CO 81601 Date: 10/14/16 Ph: (970) 404 3100 By: RMM WATER QUALITY CAPTURE VOLUME Water Quality Enhancement Provided For Basins A, B, C, & E Basin Name Area (ac.)Imperviousness I*A Basin D 0.54 0.53 0.29 *Basin D includes a tree reduction to impervious area per Section 8.4.1, URMP as outlined below Impervious area: 14,016.0 Tree Canopy Area: 5,943.0 Decid. Reduction (.15): 891.5 Effect. Imp. Area: 13,124.6 Eff. Imperviousness 0.50 WQCV (watershed-inches) = 0.10 Total WQ Area (sf) = 23,522 WQCV (cu. Ft.)=196.0 (Reference: "Urban Runoff Management Plan – A Guide to Stormwater Management in the City of Aspen”, City of Aspen, Revised December 2014 Edition) 2402c - Rational Calculations-RevisedTSP.xlsx WQCV Basin D 08/21/2019 CDS® Inspection and Maintenance Guide ENGINEERED SOLUTIONS 08/21/2019 Maintenance The CDS system should be inspected at regular intervals and maintained when necessary to ensure optimum performance. The rate at which the system collects pollutants will depend more heavily on site activities than the size of the unit. For example, unstable soils or heavy winter sanding will cause the grit chamber to fill more quickly but regular sweeping of paved surfaces will slow accumulation. Inspection Inspection is the key to effective maintenance and is easily performed. Pollutant transport and deposition may vary from year to year and regular inspections will help ensure that the system is cleaned out at the appropriate time. At a minimum, inspections should be performed twice per year (e.g. spring and fall) however more frequent inspections may be necessary in climates where winter sanding operations may lead to rapid accumulations, or in equipment washdown areas. Installations should also be inspected more frequently where excessive amounts of trash are expected. The visual inspection should ascertain that the system components are in working order and that there are no blockages or obstructions in the inlet and separation screen. The inspection should also quantify the accumulation of hydrocarbons, trash, and sediment in the system. Measuring pollutant accumulation can be done with a calibrated dipstick, tape measure or other measuring instrument. If absorbent material is used for enhanced removal of hydrocarbons, the level of discoloration of the sorbent material should also be identified during inspection. It is useful and often required as part of an operating permit to keep a record of each inspection. A simple form for doing so is provided. Access to the CDS unit is typically achieved through two manhole access covers. One opening allows for inspection and cleanout of the separation chamber (cylinder and screen) and isolated sump. The other allows for inspection and cleanout of sediment captured and retained outside the screen. For deep units, a single manhole access point would allows both sump cleanout and access outside the screen. The CDS system should be cleaned when the level of sediment has reached 75% of capacity in the isolated sump or when an appreciable level of hydrocarbons and trash has accumulated. If absorbent material is used, it should be replaced when significant discoloration has occurred. Performance will not be impacted until 100% of the sump capacity is exceeded however it is recommended that the system be cleaned prior to that for easier removal of sediment. The level of sediment is easily determined by measuring from finished grade down to the top of the sediment pile. To avoid underestimating the level of sediment in the chamber, the measuring device must be lowered to the top of the sediment pile carefully. Particles at the top of the pile typically offer less resistance to the end of the rod than consolidated particles toward the bottom of the pile. Once this measurement is recorded, it should be compared to the as-built drawing for the unit to determine weather the height of the sediment pile off the bottom of the sump floor exceeds 75% of the total height of isolated sump. Cleaning Cleaning of a CDS systems should be done during dry weather conditions when no flow is entering the system. The use of a vacuum truck is generally the most effective and convenient method of removing pollutants from the system. Simply remove the manhole covers and insert the vacuum hose into the sump. The system should be completely drained down and the sump fully evacuated of sediment. The area outside the screen should also be cleaned out if pollutant build-up exists in this area. In installations where the risk of petroleum spills is small, liquid contaminants may not accumulate as quickly as sediment. However, the system should be cleaned out immediately in the event of an oil or gasoline spill should be cleaned out immediately. Motor oil and other hydrocarbons that accumulate on a more routine basis should be removed when an appreciable layer has been captured. To remove these pollutants, it may be preferable to use absorbent pads since they are usually less expensive to dispose than the oil/water emulsion that may be created by vacuuming the oily layer. Trash and debris can be netted out to separate it from the other pollutants. The screen should be power washed to ensure it is free of trash and debris. Manhole covers should be securely seated following cleaning activities to prevent leakage of runoff into the system from above and also to ensure that proper safety precautions have been followed. Confined space entry procedures need to be followed if physical access is required. Disposal of all material removed from the CDS system should be done in accordance with local regulations. In many jurisdictions, disposal of the sediments may be handled in the same manner as the disposal of sediments removed from catch basins or deep sump manholes. 08/21/2019 CDS Diameter Distance from Water Surface Sediment Model to Top of Sediment Pile Storage Capacity ft m ft m yd3 m3 CDS2015-4 4 1.2 3.0 0.9 0.9 0.7 CDS2015 5 1.5 3.0 0.9 1.3 1.0 CDS2020 5 1.5 3.5 1.1 1.3 1.0 CDS2025 5 1.5 4.0 1.2 1.3 1.0 CDS3020 6 1.8 4.0 1.2 2.1 1.6 CDS3030 6 1.8 4.6 1.4 2.1 1.6 CDS3035 6 1.8 5.0 1.5 2.1 1.6 CDS4030 8 2.4 4.6 1.4 5.6 4.3 CDS4040 8 2.4 5.7 1.7 5.6 4.3 CDS4045 8 2.4 6.2 1.9 5.6 4.3 CDS5640 10 3.0 6.3 1.9 8.7 6.7 CDS5653 10 3.0 7.7 2.3 8.7 6.7 CDS5668 10 3.0 9.3 2.8 8.7 6.7 CDS5678 10 3.0 10.3 3.1 8.7 6.7 Table 1: CDS Maintenance Indicators and Sediment Storage Capacities 800.925.5240 www.ContechES.com Support • Drawings and specifications are available at www.contechstormwater.com. • Site-specific design support is available from our engineers. ©2014 Contech Engineered Solutions LLC Contech Engineered Solutions LLC provides site solutions for the civil engineering industry. Contech’s portfolio includes bridges, drainage, sanitary sewer, stormwater, earth stabilization and wastewater treament products. For information, visit www.ContechES.com or call 800.338.1122 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS AN EXPRESSED WARRANTY OR AN IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. SEE THE CONTECH STANDARD CONDITION OF SALES (VIEWABLE AT WWW.CONTECHES.COM/ COS) FOR MORE INFORMATION. The product(s) described may be protected by one or more of the following US patents: 5,322,629; 5,624,576; 5,707,527; 5,759,415; 5,788,848; 5,985,157; 6,027,639; 6,350,374; 6,406,218; 6,641,720; 6,511,595; 6,649,048; 6,991,114; 6,998,038; 7,186,058; 7,296,692; 7,297,266; 7,517,450 related foreign patents or other patents pending. cdsMaintenance 11/14 ENGINEERED SOLUTIONS 08/21/2019 CDS Inspection & Maintenance Log CDS Model: Location: Water Floatable Describe Maintenance Date depth to Layer Maintenance Personnel Comments sediment 1 Thickness 2 Performed —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— 1. The water depth to sediment is determined by taking two measurements with a stadia rod: one measurement from the manhole opening to the top of the sediment pile and the other from the manhole opening to the water surface. If the difference between these measurements is less than the values listed in table 1 the system should be cleaned out. Note: to avoid underestimating the volume of sediment in the chamber, the measuring device must be carefully lowered to the top of the sediment pile. 2. For optimum performance, the system should be cleaned out when the floating hydrocarbon layer accumulates to an appreciable thickness. In the event of an oil spill, the system should be cleaned immediately. 08/21/2019 10" 3"3" 34" 42" 5" 10" 10" 8" 10" 4" 8" 8" 10" 15" 12"15" 6" 6" 4" 6" 2"2" 6" 5" 2" 2"2" 5" 3" 3" 6" 3" 4" 3" 3"3" 3" 4"8" 8"8" 3" 4" 3" 36" 36" 36" 18" 12" 12"10" 12" 36" 12" 12" BE N C H BE N C H BE N C H 10"9"11"13"10"12"8"12"6"8" 37" 24" 29" 17" 19" 9" 14" 14" 14" 10" 15"5"15" 8" 2-5" 3-4" 3" 2-4" 2-3" 6"16" 6" 6" 6" 8"8" 12" 8" 6" 2-10" 7911.67TRD 10 9 7912.00TRD 9 10 7912.04TRD 11 11 7912.22TRD 13 17 7911.74TRD 10 18 7912.29TRD 12 15 7912.81TRD 8 6 7912.58TRD 12 15 7912.89TRD 6 6 7913.00TRD 8 13 7913.72TRD 37 25 7913.50TRD 36 19 7913.40TRE 27 15 7911.44TRE 24 12 7912.27TRE 29 15 7911.80TRD 17 18 7911.33TRD 19 15 7910.16TRE 9 6 7910.18TRE 14 10 7907.83TRD 14 10 7905.87TRD 14 20 7910.34TRD 18 20 7914.42TRE 10 8 0.00TRD 15 12 0.00TRD 5 8 0.00TRD 15 12 0.00TRE 8 10 0.00TRD 2-5 6 0.00TRD 3-4 5 0.00TRD 3 4 0.00TRD 2-4 5 0.00TRD 2-3 4 0.00TRE 6 6 0.00TRE 16 13 0.00TRD 6 8 0.00TRD 6 6 0.00TRD 6 6 0.00TRD 8 7 0.00TRD 8 7 0.00TRD 12 10 0.00TRD 8 9 0.00TRD 6 6 0.00TRD 2-10 10 7914.39TRD 10 5 7914.10TRD 3 3 7914.11TRD 3 3 7914.45TRD 34 18 7914.09TRD 42 24 7912.56TRD 5 5" 7912.86TRD 10 3.5 7910.91TRD 10 10 7910.70TRD 8 8 7908.54TRD 10 10 7908.77TRD 4 5 TB 7885.99TRD 6 5 7886.66TRD 4 5 7887.30TRD 6 5 7888.62TRD 2 3 7888.80TRD 2 3 7887.50TRD 6 8 7890.54TRD 5 7 7893.34TRD 2 37893.36TRD 2 3 7893.28TRD 2 3 7888.19TRD 5 8 7899.06TRD 8 10 7897.37TRD 8 10 7905.94TRD 10 15 7906.67TRD 15 20 7908.24TRD 12 157908.54TRD 15 18 7906.75TRD 6 15 7913.46TRD 36 18 7912.72TRD 36 20 7912.11TRD 36 20 7912.97TRE 18 15 7912.55TRE 12 10 TB1 7913.33TRE 12 10 TB2 B 7912.45TRE 10 8 7912.95TRE 12 10 7911.64TRD 36 20 7910.91TRP 12 8 7910.39TRP 12 12 7888.13trd 3 15 7887.48trd 3 15 7898.87trd 6 18 7897.84trd 3 12 7897.04trd 4 15 7894.39trd 3 12 7890.43trd 3 12 7891.50trd 3 15 7890.95trd 3 15 7891.96trd 4 12 7885.70trd 8 12 7885.86trd 8 12 7886.27trd 8 12 7887.03trd 3 10 7887.17trd 4 10 7887.49trd 3 12 SHEET NO. DRAWN BY: DATE: JOB #: DESIGNED BY: C JVA INC CHECKED BY: NO . DA T E DE S ' D RE V I S I O N D E S C R I P T I O N D' W N 2402c JVA, Incorporated 214 8th St., Suite 210 Glenwood Springs, CO 81601 Phone: 970.404.3100 www.jvajva.com E-mail: info@jvajva.com CONSULTING ENGINEERS PI T K I N C O U N T Y S H E R I F F & A D M I N . F A C I L I T Y AS P E N , C O L O R A D O 06/30/2016 NOT FOR CONSTRUCTION - ISSUED FOR: 06.30.2016 PERMIT SETFIG 1 HI S T O R I C D R A I N A G E B A S I N S GWS RMM RMM N KE V I N A . T O N E P R O F E SSIONA L E N G I NEER COL O R A D O REGIS T E R E D 28699 08/21/2019 10" 3"3" 34" 42" 5" 10" 10" 8" 8" 8" 10" 15" 12"15" 6" 6" 4" 6" 2"2" 6" 5" 2" 2"2" 5" 3" 3" 6" 3" 4" 3" 3"3" 3" 4"8" 8"8" 3" 4" 3" 18" 12" 12"10" 12" BE N C H BE N C H 10"9"11"13"10"12"8"12"6"8" 37" 24" 29" 17" 19" 14" 15"5"15" 8" 2-5" 3-4" 3" 2-4" 2-3" 6"16" 6" 6" 6" 8"8" 12" 8" 6" 2-10" 7911.67TRD 10 9 7912.00TRD 9 10 7912.04TRD 11 11 7912.22TRD 13 17 7911.74TRD 10 18 7912.29TRD 12 15 7912.81TRD 8 6 7912.58TRD 12 15 7912.89TRD 6 6 7913.00TRD 8 13 7913.72TRD 37 25 7913.40TRE 27 15 7911.44TRE 24 12 7912.27TRE 29 15 7911.80TRD 17 18 7911.33TRD 19 15 7910.18TRE 14 10 7910.34TRD 18 20 0.00TRD 15 12 0.00TRD 5 8 0.00TRD 15 12 0.00TRE 8 10 0.00TRD 2-5 6 0.00TRD 3-4 5 0.00TRD 3 4 0.00TRD 2-4 5 0.00TRD 2-3 4 0.00TRE 6 6 0.00TRE 16 13 0.00TRD 6 8 0.00TRD 6 6 0.00TRD 6 6 0.00TRD 8 7 0.00TRD 8 7 0.00TRD 12 10 0.00TRD 8 9 0.00TRD 6 6 0.00TRD 2-10 10 7914.39TRD 10 5 7914.10TRD 3 3 7914.11TRD 3 3 7914.45TRD 34 18 7914.09TRD 42 24 7912.56TRD 5 5" 7912.86TRD 10 3.5 7910.91TRD 10 10 7910.70TRD 8 8 7885.99TRD 6 5 7886.66TRD 4 5 7887.30TRD 6 5 7888.62TRD 2 3 7888.80TRD 2 3 7887.50TRD 6 8 7890.54TRD 5 7 7893.34TRD 2 37893.36TRD 2 3 7893.28TRD 2 3 7888.19TRD 5 8 7899.06TRD 8 10 7897.37TRD 8 10 7905.94TRD 10 15 7906.67TRD 15 20 7908.24TRD 12 157908.54TRD 15 18 7906.75TRD 6 15 7912.97TRE 18 15 7912.55TRE 12 10 TB1 7913.33TRE 12 10 TB2 B 7912.45TRE 10 8 7912.95TRE 12 10 7888.13trd 3 15 7887.48trd 3 15 7898.87trd 6 18 7897.84trd 3 12 7897.04trd 4 15 7894.39trd 3 12 7890.43trd 3 12 7891.50trd 3 15 7890.95trd 3 15 7891.96trd 4 12 7885.70trd 8 12 7885.86trd 8 12 7886.27trd 8 12 7887.03trd 3 10 7887.17trd 4 10 7887.49trd 3 12 SHEET NO. DRAWN BY: DATE: JOB #: DESIGNED BY: C JVA INC CHECKED BY: NO . DA T E DE S ' D RE V I S I O N D E S C R I P T I O N D' W N 2402c JVA, Incorporated 214 8th St., Suite 210 Glenwood Springs, CO 81601 Phone: 970.404.3100 www.jvajva.com E-mail: info@jvajva.com CONSULTING ENGINEERS PI T K I N C O U N T Y S H E R I F F & A D M I N . F A C I L I T Y AS P E N , C O L O R A D O 07/29/2016 ISSUED FOR : 11.21.2016 CONSTRUCTION DOCUMENTS 1 09 / 1 6 / 2 0 1 6 RM M 09 / 1 6 / 2 0 1 6 - A D D E N D U M 0 0 3 RM M 2 10 / 1 9 / 2 0 1 6 RM M 10 / 1 9 / 2 0 1 6 - P E R M I T R E V I E W C O M M E N T S RM M 5 11 / 2 1 / 2 0 1 6 RM M 11 / 2 1 / 2 0 1 6 - C O N S T R U C T I O N D O C U M E N T S RM M 6 12 / 1 9 / 2 0 1 6 RM M 12 / 1 9 / 2 0 1 6 - C O A P E R M I T R E V I E W C O M M E N T S RM M FIG 2 PR O P O S E D D R A I N A G E B A S I N S GWS RMM RMM 06/05/1412/19/16 08/21/2019 Appendix B & Water Quality Appendix B Hydrologic Calculations 08/21/2019 PROJECT INFORMATION PROJECT NAME: PROJECT NO: DESIGN BY: REVIEWED BY: JURISDICTION: REPORT TYPE: DATE: C2 C5 C10 C100 % IMPERV 0.03 0.09 0.17 0.36 2% 0.71 0.73 0.75 0.81 90% 0.89 0.90 0.92 0.96 100% 0.71 0.73 0.75 0.81 90% 0.54 0.36 0.40 0.45 0.58 42.9% AREA (ACRES) C2 C5 C10 C100 0.18 0.03 0.09 0.17 0.36 2% 0.001 0.71 0.73 0.75 0.81 90% 0.04 0.89 0.90 0.92 0.96 100% 0.22 0.21 0.25 0.32 0.48 22.0% AREA (ACRES) C2 C5 C10 C100 0.16 0.71 0.73 0.75 0.81 90% 0.16 0.71 0.73 0.75 0.81 90.0% AREA (ACRES) C2 C5 C10 C100 0.06 0.03 0.09 0.17 0.36 2% 0.000 0.71 0.73 0.75 0.81 90% 0.01 0.89 0.90 0.92 0.96 100% 0.06 0.14 0.19 0.26 0.44 14.3% AREA (ACRES) C2 C5 C10 C100 0.063 0.03 0.09 0.17 0.36 2% 0.005 0.71 0.73 0.75 0.81 90% 0.03 0.89 0.90 0.92 0.96 100% 0.09 0.30 0.34 0.40 0.54 32.9% 0.54 0.36 0.40 0.45 0.58 42.9% D.4 LANDSCAPE ROOF ASPHALT/CONCRETE SUB-BASIN COMPOSITE TOTAL SITE COMPOSITE PERCENT IMPERVIOUSNESS D.3 LANDSCAPE ROOF ASPHALT/CONCRETE SUB-BASIN COMPOSITE SUB-BASIN SURFACE CHARACTERISTICS COMPOSITE RUNOFF COEFFICIENTS PERCENT IMPERVIOUSNESS SUB-BASIN COMPOSITE SUB-BASIN SURFACE CHARACTERISTICS COMPOSITE RUNOFF COEFFICIENTS SUB-BASIN COMPOSITE D.1 SUB-BASIN SURFACE CHARACTERISTICS COMPOSITE RUNOFF COEFFICIENTS PERCENT IMPERVIOUSNESS D.2 ROOF ROOF ASPHALT/CONCRETE COMPOSITE RUNOFF COEFFICIENTS PERCENT IMPERVIOUSNESS LANDSCAPE LANDSCAPE DRIVES AND WALKS TOTAL SITE COMPOSITE SUB-BASIN SURFACE CHARACTERISTICS City of Aspen Final 2019.06.11 JURISDICTIONAL STANDARD Pitkin County Courthouse MC17.1435 MAT LML ASPHALT/CONCRETE ROOF 6/11/2019 4:21 PM COMPOSITE_C-VALUES H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 CALCULATED BY:JOB NO: CHECKED BY:PROJECT: DATE: Is Project Urban? Yes AREA LENGTH SLOPE ti LENGTH SLOPE VEL. tt COMP.TOT. LENGTH SLOPE IMP tc tc ac ft ft/ft min ft ft/ft fps min tc ft ft/ft % First DP min (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)(16) (17) D.1 4 0.3 0.2 125 0.0200 13.6 0.00 0.0 13.6 125.0 0.02 22.0% 23.5 13.6 D.2 4 0.7 0.2 100 0.0200 5.3 0.00 0.0 5.3 100.0 0.02 90.0% 11.2 5.3 D.3 4.1 0.2 0.1 25 0.0500 4.8 0 0.00 0.0 4.8 25.5 0.05 14.3% 23.7 5.0 D.4 4.2 0.3 0.1 25 0.0900 3.3 0.00 0.0 3.3 25.0 0.09 32.9% 20.5 5.0 *Velocity (V) = CvSw0.5 TABLE 6-2 *Table 6-2, UDFCD (V.1), Chapter 6, Page 6-5 in which: Cv = Conveyance Coefficient (See Table Above) Sw = Watercourse Slope (ft/ft) BASIN DESIGN POINT C5 Cv DATA SUB-BASIN TIME (ti)(tt) Paved Areas and Shallow Paved Swales 20 Heavy Meadow 2.5 Tillage / Field Nearly Bare Ground 10 Grassed Waterway 15 5 Short Pasture and Lawns 7 Type of Land Surface Conveyance Coefficient, Cv MC17.1435 Pitkin County Courthouse STANDARD FORM SF-2 (RATIONAL METHOD PROCEDURE) REMARKS tc CHECK (URBANIZED BASINS) MAT LML 2019.06.11 INITIAL/OVERLAND TIME OF CONCENTRATION SUMMARY TRAVEL TIME TOC 6/11/2019 4:21 PM H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 CALCULATED BY:MAT JOB NO:MC17.1435 CHECKED BY:LML PROJECT:Pitkin County Courthouse DATE:2019.06.11 DESIGN STORM:2-YEAR ONE-HR PRECIP:0.47 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) D.1 4 0.22 0.21 13.6 0.05 1.50 0.07 D.2 4 0.16 0.71 5.3 0.11 2.36 0.26 D.3 4.1 0.06 0.14 5.0 0.01 2.42 0.02 D.4 4.2 0.09 0.30 5.0 0.03 2.42 0.07 I.One-Hr Precipitation Values from NOAA Atlas 14 PFDS Return Period: 2-YEAR 5-YEAR 10-YEAR 100-YEAR Depth In Inches: 0.47 0.64 0.77 1.23 *Equation 5-1, UDFCD (V.1), Chapter 5, Page 5-9 *Rainfall Intensity:In Which: I = Rainfall Intensity (Inches Per Hour) P1 = 1-Hour Point Rainfall Depth (Inches) tc = Time Of Concentration (Minutes) REMARKSAREA (AC) RUNOFF COEFF tc (MIN) BASIN DESIGN POINT DIRECT RUNOFF TOTAL RUNOFF tc (MIN) S(CxA) (AC) I (IN/HR) Q (CFS) STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) CxA (AC) I (IN/HR) Q (CFS) 88.8 1 10 . 2-YEAR 6/11/2019 4:21 PM H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 CALCULATED BY:MAT JOB NO:MC17.1435 CHECKED BY:LML PROJECT:Pitkin County Courthouse DATE:2019.06.11 DESIGN STORM:5-YEAR ONE-HR PRECIP:0.64 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) D.1 4 0.22 0.25 13.6 0.06 2.04 0.11 D.2 4 0.16 0.73 5.3 0.11 3.22 0.37 D.3 4.1 0.06 0.19 5.0 0.01 3.29 0.04 D.4 4.2 0.09 0.34 5.0 0.03 3.29 0.10 I. One-Hr Precipitation Values from NOAA Atlas 14 PFDS Return Period: 2-YEAR 5-YEAR 10-YEAR 100-YEAR Depth In Inches: 0.47 0.64 0.77 1.23 *Equation 5-1, UDFCD (V.1), Chapter 5, Page 5-9 *Rainfall Intensity:In Which: I = Rainfall Intensity (Inches Per Hour) P1 = 1-Hour Point Rainfall Depth (Inches) tc = Time Of Concentration (Minutes) REMARKSAREA (AC) RUNOFF COEFF tc (MIN) STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) CxA (AC) I (IN/HR) Q (CFS) BASIN DESIGN POINT DIRECT RUNOFF TOTAL RUNOFF tc (MIN) S(CxA) (AC) I (IN/HR) Q (CFS) 88.8 1 10 . 5-YEAR 6/11/2019 4:21 PM H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 CALCULATED BY:MAT JOB NO:MC17.1435 CHECKED BY:LML PROJECT:Pitkin County Courthouse DATE:2019.06.11 DESIGN STORM:10-YEAR ONE-HR PRECIP:0.77 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) D.1 4 0.22 0.32 13.6 0.07 2.45 0.17 D.2 4 0.16 0.75 5.3 0.12 3.87 0.46 D.3 4.1 0.06 0.26 5.0 0.02 3.96 0.07 D.4 4.2 0.09 0.40 5.0 0.04 3.96 0.15 I. One-Hr Precipitation Values from NOAA Atlas 14 PFDS Return Period: 2-YEAR 5-YEAR 10-YEAR 100-YEAR Depth In Inches: 0.47 0.64 0.77 1.23 *Equation 5-1, UDFCD (V.1), Chapter 5, Page 5-9 *Rainfall Intensity:In Which: I = Rainfall Intensity (Inches Per Hour) P1 = 1-Hour Point Rainfall Depth (Inches) tc = Time Of Concentration (Minutes) REMARKSAREA (AC) RUNOFF COEFF tc (MIN) BASIN DESIGN POINT DIRECT RUNOFF TOTAL RUNOFF tc (MIN) S(CxA) (AC) I (IN/HR) Q (CFS) STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) CxA (AC) I (IN/HR) Q (CFS) 88.8 1 10 . 10-YEAR 6/11/2019 4:21 PM H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 CALCULATED BY:MAT JOB NO:MC17.1435 CHECKED BY:LML PROJECT:Pitkin County Courthouse DATE:2019.06.11 DESIGN STORM:100-YEAR ONE-HR PRECIP:1.23 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) D.1 4 0.22 0.48 13.6 0.11 3.92 0.42 D.2 4 0.16 0.81 5.3 0.13 6.19 0.79 D.3 4.1 0.06 0.44 5.0 0.03 6.33 0.18 D.4 4.2 0.09 0.54 5.0 0.05 6.33 0.31 I. One-Hr Precipitation Values from NOAA Atlas 14 PFDS Return Period: 2-YEAR 5-YEAR 10-YEAR 100-YEAR Depth In Inches: 0.47 0.64 0.77 1.23 *Equation 5-1, UDFCD (V.1), Chapter 5, Page 5-9 *Rainfall Intensity:In Which: I = Rainfall Intensity (Inches Per Hour) P1 = 1-Hour Point Rainfall Depth (Inches) tc = Time Of Concentration (Minutes) REMARKSAREA (AC) RUNOFF COEFF tc (MIN) STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) CxA (AC) I (IN/HR) Q (CFS) BASIN DESIGN POINT DIRECT RUNOFF TOTAL RUNOFF tc (MIN) S(CxA) (AC) I (IN/HR) Q (CFS) 88.8 1 10 . 100-YEAR 6/11/2019 4:21 PM H:\MC17.1435-Pitkin County Courthouse\ENG\DRAINAGE\EXCEL\Rational (ASPEN).xlsm08/21/2019 City of Aspen Urban Runoff Management Plan Chapter 8 – Water Quality 8-30 Rev 11/2014 Figure 8.13 Aspen Water Quality Capture Volume 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 WQ C V ( w a t e r s h e d -in c h e s ) Effective Imperviousness of Tributary Area to BMP (percent) BASIN D.1 & D.2. IMP.=50.6%.: WQCV=0.097*(1/12)*(0.38AC)*(43560SF/AC)= 133 CF 𝑉𝑉𝑉𝑉𝑉𝑉 (𝑓𝑓3 )= 𝑊𝑊𝑊𝑉 𝑖𝑖 𝑊𝑊𝑓𝑉𝑊𝑊ℎ𝑉𝑒 𝑖𝑖𝑖ℎ𝑉𝑊 𝑥 1𝑓𝑓12 𝑖𝑖𝑥 𝐴𝑊𝑉𝑊 (𝑊𝑓) 08/21/2019 08/21/2019 Area 0.38 acres 30 Weighted C 0.42 (select from Rainfall Data column D) Tc 6 minutes Particle size 50 microns CDS Model 2015-4 (select from pulldown)0.7 cfs Diameter CDS Hydraulic Capacity 10.0 cfs Rainfall Intensity1 (in/hr) Percent Rainfall Volume1 Cumulative Rainfall Volume Total Flowrate (cfs) Treated Flowrate (cfs) Operating Rate (%) Removal Efficiency (%) Incremental Removal (%) 0.02 19.8%19.8%0.00 0.00 0.46 97.1 19.3 0.04 14.1%33.9%0.01 0.01 0.91 96.9 13.7 0.06 9.4%43.4%0.01 0.01 1.37 96.8 9.1 0.08 8.8%52.2%0.01 0.01 1.82 96.6 8.5 0.10 6.4%58.5%0.02 0.02 2.28 96.4 6.1 0.12 5.7%64.2%0.02 0.02 2.74 96.3 5.5 0.14 4.8%69.0%0.02 0.02 3.19 96.1 4.6 0.16 2.9%71.8%0.03 0.03 3.65 96.0 2.8 0.18 2.5%74.4%0.03 0.03 4.10 95.8 2.4 0.20 2.7%77.0%0.03 0.03 4.56 95.7 2.6 0.25 3.1%80.1%0.04 0.04 5.70 95.3 2.9 0.30 2.9%83.1%0.05 0.05 6.84 94.9 2.8 0.35 1.4%84.5%0.06 0.06 7.98 94.5 1.3 0.40 2.8%87.3%0.06 0.06 9.12 94.1 2.7 0.45 2.4%89.8%0.07 0.07 10.26 93.7 2.3 0.50 1.2%91.0%0.08 0.08 11.40 93.3 1.1 0.75 3.3%94.3%0.12 0.12 17.10 91.4 3.0 1.00 2.5%96.8%0.16 0.16 22.80 89.5 2.2 1.50 2.2%99.0%0.24 0.24 34.20 85.6 1.9 2.00 1.0%100.0%0.32 0.32 45.60 81.7 0.8 95.6 6.5% 93.5% 89.1% 1 - Based on 10 years of hourly precipitation data from NCDC station 2220, Denver WSFO AP, Denver, CO 2 - Reduction due to use of 60-minute data for a site that has a time of concentration less than 30-minutes. Predicted Net Annual Load Removal Efficiency = BASED ON AN AVERAGE PARTICLE SIZE OF 50 MICRONS CDS ESTIMATED NET ANNUAL SOLIDS LOAD REDUCTION Pitkin County Courthouse Aspen, CO Rainfall Station # CDS Treatment Capacity Removal Efficiency Adjustment2 = Predicted % Annual Rainfall Treated = BASED ON THE RATIONAL RAINFALL METHOD 08/21/2019 Area 0.38 acres 30 Weighted C 0.42 (select from Rainfall Data column D) Tc 6 minutes Particle size 75 microns CDS Model 2015-4 (select from pulldown)0.7 cfs Diameter CDS Hydraulic Capacity 10.0 cfs Rainfall Intensity1 (in/hr) Percent Rainfall Volume1 Cumulative Rainfall Volume Total Flowrate (cfs) Treated Flowrate (cfs) Operating Rate (%) Removal Efficiency (%) Incremental Removal (%) 0.02 19.8%19.8%0.00 0.00 0.46 100.0 19.8 0.04 14.1%33.9%0.01 0.01 0.91 100.0 14.1 0.06 9.4%43.4%0.01 0.01 1.37 100.0 9.4 0.08 8.8%52.2%0.01 0.01 1.82 100.0 8.8 0.10 6.4%58.5%0.02 0.02 2.28 99.8 6.3 0.12 5.7%64.2%0.02 0.02 2.74 99.7 5.7 0.14 4.8%69.0%0.02 0.02 3.19 99.5 4.7 0.16 2.9%71.8%0.03 0.03 3.65 99.4 2.9 0.18 2.5%74.4%0.03 0.03 4.10 99.2 2.5 0.20 2.7%77.0%0.03 0.03 4.56 99.1 2.7 0.25 3.1%80.1%0.04 0.04 5.70 98.7 3.0 0.30 2.9%83.1%0.05 0.05 6.84 98.3 2.9 0.35 1.4%84.5%0.06 0.06 7.98 97.9 1.4 0.40 2.8%87.3%0.06 0.06 9.12 97.5 2.8 0.45 2.4%89.8%0.07 0.07 10.26 97.2 2.4 0.50 1.2%91.0%0.08 0.08 11.40 96.8 1.2 0.75 3.3%94.3%0.12 0.12 17.10 94.9 3.1 1.00 2.5%96.8%0.16 0.16 22.80 92.9 2.3 1.50 2.2%99.0%0.24 0.24 34.20 89.1 2.0 2.00 1.0%100.0%0.32 0.32 45.60 85.3 0.9 98.9 6.5% 93.5% 92.4% 1 - Based on 10 years of hourly precipitation data from NCDC station 2220, Denver WSFO AP, Denver, CO 2 - Reduction due to use of 60-minute data for a site that has a time of concentration less than 30-minutes. Predicted Net Annual Load Removal Efficiency = BASED ON AN AVERAGE PARTICLE SIZE OF 75 MICRONS CDS ESTIMATED NET ANNUAL SOLIDS LOAD REDUCTION Pitkin County Courthouse Aspen, CO Rainfall Station # CDS Treatment Capacity Removal Efficiency Adjustment2 = Predicted % Annual Rainfall Treated = BASED ON THE RATIONAL RAINFALL METHOD 08/21/2019 Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Type of Permeable Pavement Section A) What type of section of permeable pavement is used? (Based on the land use and activities, proximity to adjacent structures and soil characteristics.) B) What type of wearing course?1 2. Required Storage Volume A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia Ia =14.3 % B) Tributary Area's Imperviousness Ratio (I = Ia / 100)i = 0.143 C) Tributary Watershed Area ATotal = 2,613 sq ft (including area of permeable pavement system) D) Area of Permeable Pavement System APPS =236 sq ft (Minimum recommended permeable pavement area = 174 sq ft) E) Impervious Tributary Ratio RT =1.4 (Contributing Imperviuos Area / Permeable Pavement Ratio) F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 16 cu ft (WQCV = (0.8 * (0.91 * i3 - 1.19 * i2 + 0.78 * i) / 12) * Area) G) Is flood control volume being added? H) Total Volume Needed VTotal =16 cu ft 3. Depth of Reservoir A) Minimum Depth of Reservoir Dmin =6.0 inches (Minimum recommended depth is 6 inches) B) Is the slope of the reservoir/subgrade interface equal to 0%? 1 C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40)P = 0.30 D) Slope of the Base Course/Subgrade Interface S = ft / ft E) Length Between Lateral Flow Barriers L = ft F) Volume Provided Based on Depth of Base Course V = 30 cu ft Flat or Stepped: V = P * ((Dmin - 1) / 12) * Area Sloped: V = P * ((Dmin - 6*S*L - 1) / 12) * Area 4. Lateral Flow Barriers A) Type of Lateral Flow Barriers B) Number of Permeable Pavement Cells Cells = 5. Perimeter Barrier A) Is a perimeter barrier provided on all sides of the pavement system? (Recommeded for PICP, concrete grid pavement, or for any no-infiltration section.) Pitkin County Courthouse Aspen, CO Design Procedure Form: Permeable Pavement Systems (PPS) Mason Talkington Martin/Martin August 13, 2019 UD-BMP (Version 3.07, March 2018) Choose One No Infiltration Partial Infiltration Section Full Infiltration Section Choose One YES NO Choose One YES- Flat or Stepped Installation NO- Sloped Installation Choose One Concrete Walls PVC geomembrane installed normal to flow N/A- Flat installation Other (Describe): Choose One YES NO Choose One PICP Concrete Grid Pavement Pervious Concrete Porous Gravel UD-BMP_v3.07 - PPS.xlsm, PPS 8/13/2019, 3:35 PM 08/21/2019 Appendix C Hydraulic Calculations 08/21/2019 Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.010 Channel Slope 0.02500 ft/ft Normal Depth 0.33 ft Diameter 0.33 ft Discharge 0.39 ft³/s Results Discharge 0.39 ft³/s Normal Depth 0.33 ft Flow Area 0.09 ft² Wetted Perimeter 1.05 ft Hydraulic Radius 0.08 ft Top Width 0.00 ft Critical Depth 0.32 ft Percent Full 100.0 % Critical Slope 0.02175 ft/ft Velocity 4.48 ft/s Velocity Head 0.31 ft Specific Energy 0.64 ft Froude Number 0.00 Maximum Discharge 0.42 ft³/s Discharge Full 0.39 ft³/s Slope Full 0.02500 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Worksheet for 4" @ 2.5% 6/11/2019 3:53:11 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page 08/21/2019 Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.010 Channel Slope 0.01000 ft/ft Normal Depth 0.67 ft Diameter 0.67 ft Discharge 1.57 ft³/s Results Discharge 1.57 ft³/s Normal Depth 0.67 ft Flow Area 0.35 ft² Wetted Perimeter 2.10 ft Hydraulic Radius 0.17 ft Top Width 0.00 ft Critical Depth 0.58 ft Percent Full 100.0 % Critical Slope 0.00907 ft/ft Velocity 4.50 ft/s Velocity Head 0.31 ft Specific Energy 0.98 ft Froude Number 0.00 Maximum Discharge 1.69 ft³/s Discharge Full 1.57 ft³/s Slope Full 0.01000 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Worksheet for 8" @ 1.0% 11/19/2018 3:31:52 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page 08/21/2019 Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Roughness Coefficient 0.020 Channel Slope 0.05000 ft/ft Diameter 0.67 ft Discharge 1.21 ft³/s Results Normal Depth 0.41 ft Flow Area 0.22 ft² Wetted Perimeter 1.19 ft Hydraulic Radius 0.19 ft Top Width 0.66 ft Critical Depth 0.52 ft Percent Full 60.5 % Critical Slope 0.02568 ft/ft Velocity 5.43 ft/s Velocity Head 0.46 ft Specific Energy 0.86 ft Froude Number 1.64 Maximum Discharge 1.91 ft³/s Discharge Full 1.78 ft³/s Slope Full 0.02311 ft/ft Flow Type SuperCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Normal Depth Over Rise 60.47 % Downstream Velocity Infinity ft/s Worksheet for Ex. 8-Inch Pipe north from Inlet 2/26/2019 1:21:36 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page 08/21/2019 Appendix D Drainage Maps 08/21/2019