V C A E N G I N E E R S, INC. C I V I L S T R U C T U R A L M B E D B E S B E

Transcription

1 V C A E N G I N E E R S, INC. C I V I L S T R U C T U R A L M B E D B E S B E LOW IMPACT DEVELOPMENT CALCULATION Washington WASHINGTON BLVD. CULVER CITY, CA March 11, 2016 PREPARED FOR: PLATFORM HAYDEN TRACT III, LLC 9900 CULVER BOULEVARD, 1A CULVER CITY, CA (310) S. Garfile d Av e., Suit e 2 10, Alh am bra, C A M ichelso n Dr. # 24 2, Irv i ne, C A

2 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 1 Table of Contents 1.0 Introduction Project Site Site Description Project Area Tributary Drainage Area Description Project Area Soil Type LID Design Criteria and Calculations LID Design Criteria Stormwater Infiltration Capture and Release Calculations Peak Mitigated Flow Rate Design Capture Volume Summary of Calculations Conclusion... 4 APPENDIX I... 5 APPENDIX II... 8 APPENDIX III... 9 APPENDIX IV APPENDIX V S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

3 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE Introduction The report demonstrates that the proposed drainage system will adequately meet the drainage needs of the project site including Low Impact Development (LID) requirements. 2.0 Project Site 2.1 Site Description Project Area The project site is located at 8888 Washington Blvd, Culver City CA, located in the jurisdiction of Culver City. The project site is comprised of 24,777.8 sf (0.57 acres) and will have 9,500 sf (0.22 acres) of green roof. The site is bounded by Landmark St to the North-East, Washington Blvd to the North-West, Higuera St to the South-West, and Lindblade St to the South-East. The pre-development imperviousness at the site is currently around 99% where most of the site s storm water is draining out to the street. The post-development imperviousness of the new project area is around 62% where storm water will be mitigated and released through a catch basin Tributary Drainage Area Description The project site is located in the Ballona Creek watershed and discharges into the Upper Franklin Canyon Reservoir, Ballona Creek, Franklin Canyon Reservoir, Hollywood Reservoir, Ivanhoe Reservoir, and Powena Reservoir as determined by the EPA Discharge Mapping Tool. The project site has two existing tributary areas while a more conservative approach was taken for the proposed site and analyzed as one tributary area as shown in the LID Calculation Plan in Appendix I Project Area Soil Type As per the Soils Report from Feffer Geological Consulting, Inc., the site is underlain by artificial fill and Quaternary alluvial deposits. Artificial fill was encountered in the field explorations to a max depth of 2 feet which generally consists of gray brown to brown silty and sandy clay. This artificial fill is characterized as medium dense to firm, moist. The alluvium soils on site consist of silty and clayey fine grained sands that are primarily medium dense to dense varying from brown to gray-green brown orangebrown and brown, moist. Groundwater was not encountered during excavations to a depth of 51.5 feet below grade. Historically the highest groundwater in this area is around 20 feet below ground surface S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

4 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE LID Design Criteria and Calculations 3.1 LID Design Criteria Design criteria and sizing calculations follow the City of Los Angeles Low Impact Development Handbook, June Calculations Stormwater Infiltration Infiltration was considered but determined to be unfeasible due to the following reasons: Per the soils report by the Feffer Geological Consulting, Inc., The high historic groundwater level is located at or slightly above the proposed base of the foundations. The foundation retaining walls below a depth of 20 feet are required to be designed to resist hydrostatic pressure. The building should be designed to resist uplift due to a potential groundwater elevation of 20 feet. Applicable pages from the 2015 Geotechnical report are included in Appendix III Capture and Release Instead, the stormwater collected from roof drains, area drains, and downspouts will be routed through a filtration system (Contech 8 x6 StormFilter) that utilizes cartridges for filtration. The stormwater will then be pumped up and released through a 10 pipe that connects to a proposed catch basin (to replace existing catch basins) located along Washington Blvd. As a result, the existing lateral will have to be upsized for the new flow being introduced to the system and extruded as the proposed catch basin will be affected by street widening. See Appendix IV for plans Peak Mitigated Flow Rate Calculation for peak mitigated flow rate (Q mitigated = 0.18 cfs) for the total drainage area was based on Tc calculator from City of Los Angeles and 85 th percentile, 24- hour rainfall data. Q peak was determined to be 1.47 cfs based on 25-year storm frequency. Calculations are included in Appendix II Design Capture Volume Required cartridges needed for the StormFilter was determined using the Cartridge treatment flow rate per Contech specs. At 0.05 cfs (22.5 gpm) per cartridge, the number required would be 4, 27 cartridges. The rainfall depth was determined from the 85 th Percentile 24-hour rainfall, rainfall data is included in Appendix II. The Design Capture Volume was sized to capture and treat 110% of the design capture volume based from post developed conditions of the site. Calculations and tables are shown in Appendix IV S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

5 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE Summary of Calculations Table 1. Mitigated Run-off Discharge (Qmitigated) I.D. Area (SF) Area (acres) % Pervious % Impervious L (ft.) Slope Qmit (cfs) Vol.peak (ac-ft.) A Conclusion The municipal stormwater program requires the preparation of LID (Low Impact Development) to address runoff pollution from post-development projects. The LID should identify Best Management Practices (BMPs) that are appropriate for the watershed pollutants of concern and especially the water constituents that would be generated from the designated project. The goal for the design is to capture and mitigate the volume of runoff produced from the 85 th Percentile for 24-hr rainfall storm event. As demonstrated in this report VCA concludes and recommends that the Contech StormFilter system is more than adequate to handle the minimum design flow required for treatment of the LID peak mitigated flow rate and volume and the flow generated by a 25-year frequency storm S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

6 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 5 APPENDIX I Tributary Area (LID Calculation Plan) 1041 S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

7 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

8 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

9 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 8 APPENDIX II Tc Calculations 1041 S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

10 Peak Flow Hydrologic Analysis File location: Z:/VCA Projects 4/1365 to XXX/ Washington Blvd/Calcs/LID References/8888 Washington Blvd - Entire Site-25yr.pdf Version: HydroCalc Input Parameters Project Name 8888 Washington Blvd Subarea ID Entire Site Area (ac) 0.57 Flow Path Length (ft) Flow Path Slope (vft/hft) yr Rainfall Depth (in) 5.5 Percent Impervious 0.62 Soil Type 2 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in) Peak Intensity (in/hr) Undeveloped Runoff Coefficient (Cu) Developed Runoff Coefficient (Cd) Time of Concentration (min) 5.0 Clear Peak Flow Rate (cfs) Burned Peak Flow Rate (cfs) Hr Clear Runoff Volume (ac-ft) Hr Clear Runoff Volume (cu-ft)

11 Peak Flow Hydrologic Analysis File location: Z:/VCA Projects 4/1365 to XXX/ Washington Blvd/Calcs/LID References/8888 Washington Blvd - Entire Site-0.75 inch.pdf Version: HydroCalc Input Parameters Project Name 8888 Washington Blvd Subarea ID Entire Site Area (ac) 0.57 Flow Path Length (ft) Flow Path Slope (vft/hft) inch Rainfall Depth (in) 0.75 Percent Impervious 0.62 Soil Type 2 Design Storm Frequency 0.75 inch storm Fire Factor 0 LID True Output Results Modeled (0.75 inch storm) Rainfall Depth (in) 0.75 Peak Intensity (in/hr) Undeveloped Runoff Coefficient (Cu) Developed Runoff Coefficient (Cd) Time of Concentration (min) 21.0 Clear Peak Flow Rate (cfs) Burned Peak Flow Rate (cfs) Hr Clear Runoff Volume (ac-ft) Hr Clear Runoff Volume (cu-ft)

12 Peak Flow Hydrologic Analysis File location: Z:/VCA Projects 4/1365 to XXX/ Washington Blvd/Calcs/LID References/8888 Washington Blvd - Entire Site-85th percentile.p Version: HydroCalc Input Parameters Project Name 8888 Washington Blvd Subarea ID Entire Site Area (ac) 0.57 Flow Path Length (ft) Flow Path Slope (vft/hft) th Percentile Rainfall Depth (in) 1.15 Percent Impervious 0.62 Soil Type 2 Design Storm Frequency 85th percentile storm Fire Factor 0 LID True Output Results Modeled (85th percentile storm) Rainfall Depth (in) 1.15 Peak Intensity (in/hr) Undeveloped Runoff Coefficient (Cu) Developed Runoff Coefficient (Cd) Time of Concentration (min) 14.0 Clear Peak Flow Rate (cfs) Burned Peak Flow Rate (cfs) Hr Clear Runoff Volume (ac-ft) Hr Clear Runoff Volume (cu-ft)

13 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 9 APPENDIX III Excerpts from Feffer Geological Consulting Inc. Proposed Four-Story Mixed Use Building Over One Subterranean Level Soils Report 1041 S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

14 November 11, 2015 File No Platform Hayden Tract III, LLC 9900 Culver Boulevard, 1A Culver City, California Subject: GEOTECHNICAL INVESTIGATION Proposed Four-Story Mixed Use Building Over One Subterranean Level 8888 W Washington Boulevard, Culver City, CA Dear Joseph Miller: As requested, Feffer Geological Consultants performed a geotechnical investigation at the subject site. The purpose of this investigation was to evaluate the geotechnical conditions at the site in the areas of the proposed construction and to provide geotechnical parameters for design and construction. Based on our investigation, it is our opinion that the proposed construction is feasible from a geotechnical standpoint provided the recommendations contained herein are incorporated into the project plans and specifications. This report should be reviewed in detail prior to proceeding further with the planned development. When final plans for the proposed construction become available, they should be forwarded to this office for review and comment. We appreciate the opportunity to be of service. Should you have any questions regarding the information contained in this report, please do not hesitate to contact us. Sincerely, FEFFER GEOLOGICAL CONSULTING, INC. Joshua R. Feffer Dan Daneshfar Principal Engineering Geologist Principal Engineer C.E.G P.E Distribution: Addressee (1)

15 November 11, 2015 File No: Page W Washington Boulevard 1.0 INTRODUCTION 1.1 PURPOSE The purpose of this investigation was to evaluate the existing geotechnical conditions at the subject site and to provide design and construction criteria for the proposed mixed use development. 1.2 SCOPE OF S The scope of work performed during this investigation involved the following; Research and review of available pertinent geotechnical literature; Subsurface exploration consisting of the drilling of two borings (B1, B2); Sampling and logging of the subsurface soils; Laboratory testing of selected soil samples collected from the subsurface exploration to determine the engineering properties of the underlying earth materials; Engineering and geologic analysis of the field and laboratory data; and Preparation of this report presenting our findings, conclusions, and recommendations for the proposed construction. 1.3 SITE DESCRIPTION The project site is located between on the south side of Washington Boulevard on a relatively flat pad in Culver City, CA (Figure 1). The site is currently occupied by one-story commercial building and associated parking lot (Figure 2). The subject site is surrounded by small businesses and commercial/retail properties. A recent aerial photograph of the site is shown as Figure 3. Surface drainage is by sheet flow to the north or front of the property. 1.4 PROPOSED CONSTRUCTION Based on the information provided to us, the project will consist of construction a new four-story mixed use building over one subterranean parking level. The existing one story commercial building will be removed from the site. A Site Plan and Cross Sections showing the proposed development are included in Appendix C.

16 November 11, 2015 File No: Page W Washington Boulevard 3.0 SITE GEOLOGY, SEISMICITY, POTENTIAL HAZARDS 3.1 SITE GEOLOGY Regional Geologic Maps 1 and the subsurface exploration indicated that the property is underlain by Quaternary Age Alluvium (Qa) (Figure 4) overlain by fill. Descriptions of the materials encountered in our exploratory borings are described below Fill-Af The fill consists of fine grained silty and sandy clay. The color varies from gray-brown, to brown. The fill is moist medium dense to firm. Fill was found in all borings down to a depth of approximately two feet Alluvium-Qa The alluvium consists of silty and clayey fine grained sands which vary from brown to graygreen brown orange-brown and brown. The alluvium was moist, medium dense to dense, containing occasional shells. The alluvium is generally weakly horizontally layered with no significant structural planes. Generally, the alluvium becomes more granular with depth Lakewood Formation At a depth of 25 to 27.5 feet below the ground surface, shells were encountered in the borings that are indicative of a marine environment. The material at and below these depths is part of the Pleistocene age Lakewood Formation which is Pleistocene in age and over-consolidated Groundwater Groundwater was not encountered during the recent excavations to a depth of 51.5 feet. Historically highest groundwater in this area of Culver City is estimated to be 20 feet below the ground surface (Plate 1.2, Historically Highest Groundwater Contours and Borehole Log Data Locations, Beverly Hills 7½ Minute Quadrangle in Seismic Hazard Zone Report, SHZR-023). 1 Yerkes, T.W., 1991 Geologic Map of the Beverly Hills and Van Nuys (south ½) Quadrangles, Los Angeles County, Dibblee Geological Foundation Map DF-31

17 November 11, 2015 File No: Page W Washington Boulevard 5.4 EARTHWORK General If the proposed construction will require grading of the site; it should be done in accordance with good construction practice, minimum code requirements and recommendations to follow. Grading criteria are included within Appendix D Site Preparation and Grading Based on our understanding of the proposed development, we recommend that footings be founded in alluvium below a depth of five feet. Prior to the start of grading operations, utility lines within the project area, if any, should be located and marked in the field so they can be rerouted or protected during site development. All debris and perishable material should be removed from the site. Although currently not anticipated, all permanent cut and fill slopes should not be constructed steeper than 2:1. If fill is to be placed the upper six to eight inches of surface exposed by the excavation should be scarified; moisture conditioned to two to four percent over optimum moisture content, and compacted to 90 percent relative compaction 2. If localized areas of relatively loose soils prevent proper compaction, over-excavation and re-compaction will be necessary Excavation Characteristics The borings did not encounter hard earth materials. Difficult excavation conditions are not anticipated. However, the soil at the site has considerable amounts of sand and gravel and caving may occur in some excavations Groundwater and Associated Design Groundwater was not encountered during the recent excavations at a depth of 51.5 feet. Wet conditions and actual groundwater may be encountered due to seasonal fluctuations. If groundwater is encountered, dewatering may be required and should be designed by a dewatering contractor and engineer. The high historic groundwater level is located at or slightly above the proposed base of the foundations. The foundation retaining walls below a depth of 20 feet are required to be designed to resist hydrostatic pressure. The building should be designed to resist uplift due to a potential groundwater elevation of 20 feet. Slab subdrainage and associated pumps are not required for this project. A mat foundation may be required to provide appropriate waterproofing and resistance to uplift. Recommendations for a mat foundation are provided below. 2 Relative compaction refers to the ratio of the in-place dry density of soil to the maximum dry density of the same material as obtained by the "modified proctor" (ASTM D ) test procedure.

18 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 10 APPENDIX IV Utility and Storm Filter Plans 1041 S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

19 D WASHINGTON BOULEVARD C L N 54 19'00" E F 1 PL FUTURE DEVELOPMENT PL 9 LANDMARK STREET C L N 35 43'28" W A B C A WASHINGTON BLVD SHEET NOTE: POST DEVELOPMENT IMPERVIOUS AREA PERVIOUS AREA PRE DEVELOPMENT 0.35 ACRES 0.22 ACRES IMPERVIOUS AREA 0.57 ACRES PERVIOUS AREA 0 ACRES 8888 WASHINGTON BLVD LID UTILITY PLAN PROJECT NO: REVISIONS VERTIGO OFFICE BUILDING 8888 WASHINGTON BOULEVARD CULVER CITY, CA ARCHITECTS

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21 V C A ENGINEER S, INC. CIVIL STRUCTURAL MBE DBE SBE 11 APPENDIX V Pipe Sizing Calculations 1041 S Garf i el d Av e #21 0, Al ha mbra CA M ichelso n Dr. # 24 2, Irv i ne, C A

22 VCA Engineers, Inc. Storm Drain Pipe Sizing Client: PLATFORM HAYDEN TRACT III, LLC Job No Project: 8888 Washington Blvd Date: 3/16/ Washington Blvd Culver City CA, Engineer: VCA Pipe Sizing Calculations Pipe Capacity (d/d) is 75-85% to be conservative Pipe ID: P cfs Calculations for Velocity and Discharge D = ft Diameter of Pipe n = Manning's Roughness Coefficient S = ft/ft 0.50 % Slope of Pipe d = 7.5 inches 0.63 ft Flow Depth d/d = 0.75 Proportional Depth of Flow theta = radians Angle of Flow a = 0.44 sq.ft Area of Flow p = 1.75 ft Wetted Perimeter r = 0.25 ft Hydraulic Radius Using Manning's Equation, for pipe at flow depth 'd' v = 3.81 fps Flow Velocity Q = cfs Flow Rate