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HomeMy WebLinkAboutHEWLETT-PACKARD, BUILDING FOUR - PDP - 54-88G - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR HEWLETT-PACKARD COMPANY BUILDING 4 FORT COLLINS, COLORADO January 13,1998 THE SEAR -BROWN GROUP I I Standards in Excellence I I n li THE SEAR BROWN GROUP FULL -SERVICE DESIGN PROFESSIONALS FORMERLY RBD, INC. 209 SOUTH MELDRUM FORT COLLINS, COLORADO 80521-2603 970-482-5922 FAX:970-482-6368 January 13, 1998 Mr. Basil Hamdan City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 SUBJECT: Final Drainage and Erosion Control Study Hewlett-Packard Building 4, Dear Basil: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for the Hewlett-Packard Building 4. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, The Sear -Brown Group Prepared By: NEW YORK • PENNSYLVANIA COLORADO•UTAH STANDARDS IN EXCELLENCE r` Reviewed By: Kevin Gingery, P.E. Senior Engineer HOIJAL OPPORTUNITY EMPLOYER FINAL DRAINAGE AND EROSION CONTROL STUDY FOR HEWLETT-PACKARD BUILDING 4 FORT COLLINS, COLORADO December 22, 1997 Prepared for: IDC Portland Office 2020 S.W. Fourth Avenue, 3rd Floor Portland, Oregon 97201 Prepared by: The Sear -Brown Group 209 S. Meldrum Fort Collins, Colorado 80521 (970) 482-5922 RBD Job No. 799-001 1,. TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION I A. Location I 1 B. Description of Project II. DRAINAGE BASINS A. Major Drainage Basin Description 2 B. Sub -Basin Descriptions 2 C. SWMM Model Compliance 2 III. DRAINAGE DESIGN CRITERIA A. Regulations 3 3 B. Development Criteria Reference and Constraints C. Hydrological Criteria 3 D. Hydraulic Criteria 3 E. Variances from Criteria 3 IV. DRAINAGE FACILITY DESIGN A. General Concept 4 4 B. Specific Details V. STORM WATER QUALITY A. General Concept 6 VI. EROSION CONTROL 6 A. General Concept B. Specific Details VII. CONCLUSIONS 7 A. Compliance with Standards B. Drainage Concept 8 8 C. Storm Water Quality 8 D. Erosion Control Concept REFERENCES 8 APPENDIX VICINITY MAP I HYDROLOGY 3 DESIGN OF INLETS, STORM SEWER AND RIP RAP 11 j;. RIPRAP DESIGN EROSION CONTROL CHARTS, FIGURES AND TABLES EXCERPTS FROM BUILDING 5 REPORT, Ioo YEAR SWMM MODEL 61 65 73 87 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR HEWLETT-PACKARD BUILDING 4 FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Hewlett-Packard Building 4 site is located in southeast Fort Collins (see vicinity map in the Appendix), north of Harmony Road and east of County Road 9 within the southwest 1/4 of section 33, township 7 north, range 68 west of the 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The Hewlett-Packard Building 4 site is north of the existing Fort Collins Hewlett- Packard office and industrial park. The site encompasses approximately 32 acres. The existing topography generally slopes from west to east at approximately 0.7 percent. Native grasses overlaying lean clay with sand or sandy lean clay cover the majority of the site. In the southern portion of the site there are existing parking lots with modular buildings. There are newly constructed parking areas and an office building, Building 5, are located east of the site. The existing Building 2 is southeast of the construction area. H. DRAINAGE BASINS A. MaJor Basin Drainage Description The Hewlett-Packard site lies entirely within the Fox Meadows Drainage Basin which is approximately bounded by Horsetooth Road on the north, Harmony road on the south, the Cache La Poudre River and I-25 on the east and Lemay Avenue on the west(refer to the general location Map in the Appendix). A Master Plan for the Fox Meadows Drainage Basin (Basin H) was Prepared by Resource Consultants, Inc., in 1981. This area was studied again by Nolte and Associates in 1990 when a master drainage plan was prepared for the Hewlett-Packard site. Nolte's master drainage report did not alter any of the assumption or conclusions which were made in the Fox Meadows Master Drainage Plan. The Regional Channel located along County Road 9 and the north boundary of the Hewlett-Packard property which was recommended in the Nolte report was designed and built with the Hewlett-Packard Building 5 project. The channel was designed for the 100 year storm and discharges to the north detention pond. The north detention pond discharges to a series of detention ponds to the south through an existing 30 inch diameter pipe. Nolte's report recommended that the 30 inch diameter outlet pipe of this north pond be enlarged to 48 inch diameter at the full development of the entire Hewlett Packard site. This increased diameter is required to avoid surcharging the north detention pond which would result in uncontrolled overland flow. It is not clear at which point in the development the outlet pipe would be enlarged. The upgrading of this outlet pipe is outside the scope of this project and is not being constructed at this time. B. Sub -Basin Drainage Description Historically the site receives flows from the west at two discharge points along County Road 9. Flows discharge from the Symbios site through 2-30 inch diameter concrete pipe under County road 9 at the top of the regional drainage channel. Flow from a second discharge point at the northwest corner of the Hewlett-Packard property will ultimately come from three sources (1) Symbios Logic (2) English Ranch (3) local drainage from 2 residential properties. The off -site and on -site storm runoff then flows east where it is intercepted by local roadside ditches or the ditch adjacent to the newly constructed parking lot for Building 5 which takes the runoff north to the regional drainage channel. C. SWMM Model compliance The Original Master Drainage Report for the Hewlett Packard Site, Preston Kelly Subdivision, Fort Collins, Colorado created a SWMM computer model for the site. During the development of the Packard Building 5 project the Final Drainage Study for Hewlett Packard Company Building 5 report this model was modified to reflect the new conditions as well as update the SWMM parameters to those the City of Fort Collins criteria. Please see the Appendix for a copy of the model with the revisions. The purpose of this modified SWMM model was to size the regional drainage channel which is located along the north property line of the Hewlett Packard site. The Hewlett Packard Building 4 project is located primarily in subcatchment area 32. The input file to the modified SWMM shows a catchment area to contain 31.3 acres with a percent impervious area of 60 percent. The proposed drainage catchment area has an area of 32.1 acres with a percent impervious area of 32 2 percent. Due to the nearly equivalent subcatchment area and the much smaller percent of impervious area proposed the site conditions will be well within the parameters set by the Building 5 SWMM model. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria and criteria as established by the Fox Meadows Basin Drainage Master Plan will be used in the preparation of this report. B. Development Criteria Reference and Constraints The Hewlett-Packard Building 4 site drainage is designed in conformance with the Fox Meadows Basin Drainage Master Plan (Basin H) and the Hewlett-Packard Master Drainage Plan by Nolte. C. Hydrological Criteria The runoff to the regional drainage channel was previously calculated for Building 5 and excerpts from that are contained in the Appendix. The most recent 100-year storm event hyetograph and infiltration parameters determined by the City of Fort Collins were used in the calculation of the runoff values. The rational method is used to determine the peak flow from the developed runoff for design of the hydraulic structures and interior roadway drainage facilities. These are designed using the 10 and 100 year rainfall criteria from the City of Fort Collins. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Drainage Criteria and are included in the appendix. E. Variances from Criteria No variances are requested for the proposed site. 3 IV. DRAINAGE FACILITY DESIGN A. General Concept The site will be designed to conform with the Master Drainage Report For Hewlett Packard, with the majority of the storm water flows being conveyed to the regional channel to the north. Offsite flows from the west and north are intercepted by the regional channel and are accounted for in the SWMM modeling. Offsite flows to the south and west are conveyed away from the site in the existing Hewlett Packard storm drainage system. West of Building 4 the storm water from all of the parking areas except for the south east section of parking flow to curb inlets and then are piped to the regional channel. The other section of parking drains to the local storm drainage system which flow south as it has historically done. The perimeter road drains to curb inlets, then to pipes and then to the regional channel. Building 4 has four main roof drain pipes which outfall to the north and east, these outfall to a collection system which empties into the regional channel. East of Building 4 is a complicated system of existing and proposed storm drains. The existing storm sewers generally take storm water to the southeast and are sized for the minor storm. The proposed system will take flows to the regional channel and be sized for the 100 year storm. B. Specific Details County Road 9, Basins OS-1, OS-2 and OS-3 lie to the west of the site and drain to the regional channel through existing inlets. The storm flows from County Road 9 are accounted for in the regional channel SWMM model as are the storm flows which enter the site from Symbios and English Ranch. The storm runoff which is generated in Basin 1 is also accounted for by the SWIvIM model. The rest of the hydrology calculations for the site are based on the rational method. Basins 21 a, 20, 19, 18, 25, 13, 17 and 14 all drain to the existing storm drain system to the south. Basins 20,19,18 and 17 will have a reduced impervious area with the removal of the existing modular buildings and associated parking. This Cl will reduce the amount of storm water which will have historically flowed through this system. Some of this extra capacity will be used by the increased hard area of Basin 25 and 13. Basin 25 and 13 have a total impervious area of 0 .83 acres. The modular buildings and the associated parking which will be removed, total 5 acres, which is a net loss of 4.2 acres of hard surface area. The rest of the storm drainage system which conveys the majority of the storm water generated by the site consists primarily of three main storm drain outfalls. Starting from the west with Basins 22 and 23. These consist primarily of parking area where each area drains to its own type `R' inlet. These Basins then drain to a pipe which flows north toward the regional channel. These storm flows are then joined by flows from the perimeter road (Basins 2,3,4 and 5). These combined flows then discharge into the regional channel. This entire length of pipe is designed for the 100 year storm. In the middle of the site Basins 24 and 26 take flows from a parking area and a landscape area west of the building north towards the regional channel, these storm.flows are joined by roof drainage from Basins 9 and 10. The storm drain pipe then connects to a type `R' inlets which receive flows from Basins 7, 8 and 34. The pipe then discharges the storm flows to the regional channel. This entire pipe system is design for the 100 year storm. The storm drainage for the eastern portion of the site is by far the most complicated. This consists of a mixture of existing and proposed storm drains. Starting from the south, Basin 14 and 16 for the most part stay in tact and discharge storm water to existing area inlets. Basin 11 and 12 generate storm water from the main roof and discharge the flows to the east, which is the top of the new proposed storm drainage system. Basins 27, 30 and 31 are small service areas to the east of the building which are served by separate area inlets. All these Basins contribute to the new proposed sewer. Basin 32, which is the truck loading area is served by a strip drain which then outfalls to the new proposed sewer. The new proposed sewer then connects to an existing manhole. Continuing with the eastern portion of the site, the roof drainage from Building 1 and Basin 16 flow into the existing system which flows north. Basin 15, the roof area of a new chemical storage building joins the existing system and flows from basin 16. The roof drainage from this building flows to a storm sewer to the east of the building. Basins 29 and 28 are primarily part of a service road at the back of the chemical storage building. These are served by to area inlets located near their original locations. The flows from these basins are taken by the same proposed pipe which serves the chemical storage building. This pipe conveys storm water to the north where it connects to the same existing manhole as mentioned above in the previous paragraph. 9 At this point it is worth mentioning that the existing pipe, an 18 inch diameter storm drain at a 0.3% slope does not have enough capacity to drain the 100 year storm from the areas that are draining to it. It is our impression that the existing storm sewer system was designed for the minor storm and not the major storm. In order to relieve this capacity problem, a relief storm drain to the north is proposed. This new proposed storm drain, which outfalls to the north is approximately 5 feet higher than the other incoming and outgoing sewers. The reason for the difference in elevations is the depth of the existing storm drainage system and a conflict between the existing sanitary sewer and the new proposed relief storm sewer going to the north. The new relief sewer will work well by allowing the existing system to act as it did before and allow the new proposed flows to go to the regional channel as conceived in the master drainage plan. The design for the relief sewer is based on the conservative assumption that all of the 100 year flow will pass to the regional channel. In general the depths in the parking areas are less than 1.0 feet. Basin 33 is an existing basin which discharges to existing area inlets. Basin OS-4 is an existing basin which is the present chemical storage area which is set below the surrounding grade. It is served by it own area inlets. V. STORM WATER QUALITY A. General Concept Beginning in October of 1992, the water quality of storm water runoff was required to be addressed on all final design utility plans. Hewlett-Packard is anticipating construction beginning in the Summer of 1998. Therefore for this study, we have sought to find various Best Management Practices for the treatment of storm water quality runoff. Runoff is conveyed by a grassed lined regional channel through existing detention ponds in order to provide an opportunity for pollutants to be removed. The detention pond releases at a very slow rate therefore many of the pollutants will settle out. VI. EROSION CONTROL A. General Concept The Hewlett-Packard Building 4 site is in the moderate wind and moderate rain erodability Zones per the City of Fort Collins zone maps. The potential exists for erosion problems during construction, and after construction until the disturbed ground is again vegetated. In accordance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance 0 standard is 79.7% during construction and 93.8% after construction. The erosion control specified on the Final Drainage and Erosion Control Plan will result in a performance standard during construction of 86.6% and 99.56% after construction. B. Specific Detail Prior to overlot grading all silt fence must be in place and gravel inlet filter must be placed on all existing area inlets. Within 30 days of the start of overlot grading the contractor will need to have the finish surface in place. If not, all areas which will not be covered by a hard surface such as asphalt, walks or building will have a roughened surface. The areas covered by road and parking lot must have a 1 inch layer of gravel mulch (1/4" to 1 '/2" gravel) applied at the of at least 135 tons/acre. After installation of the concrete sidewalk, culvert and curb inlets, the inlets shall be filtered with a combination of concrete blocks, %Z" wire screen and 3/4" coarse gravel. After installation of the storm drains, riprap protection and gravel inlet filters shall be installed. If the disturbed areas will not be built within one growing season, a permanent seed shall be applied. The estimate of probable costs for erosion control is ($25,751) x (1.5) _ $38,626 for an escrow amount. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading can begin. VII. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. B. Drainage Concept The proposed drainage concepts adequately provide for the developed runoff from the site and are within the parameters set out in the Master Drainage Plan for G Hewlett Packard. C. Water Quality ontrol Because storm water quality has become a requirement, the site has addressed this storm water aspect. Swales and detention ponds have been used to improve the water quality. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the Hewlett-Packard Building 4 Expansion. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standards will be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort Collins erosion control criteria. REFERENCES 1Storm Drainage �st n Criteria and Constriction ctanards h the Ci of Fort . --g c� llin , Colorado, May 1984, Revised January 1992. 2, rrosion Control Reference Manual for Construction Sites by the City of Fort Collins. _Cg1 rad , January 1991. 3. Fox Meadows Basin(basin H) Drainage Master Plan, Fort Collins, Colorado, by Resource Consultants Inc., February 25, 1981. 4. Master Drainage Report, Hewlett Packard Site, Preston Kelly Subdivision, Fort Collins, Colorado, by Nolte and Associates, revised October 1990. A- VICINITY MAP N.T.S.