Schematic Design Stormwater Site Plan University Ridge Bellingham, Washington Tax Parcel Number: 380332 172175 Prepared By: Freeland & Associates, Inc. 220 West Champion St., Suite 290 Bellingham, WA 98225 (360) 650-1408 Prepared For: Ronald T. Jepson & Associates, P.S. 222 Grand Avenue Bellingham, WA 98225 (360) 733-5760 April 2013
Table of Contents ENGINEER'S DECLARATION... 3 STORMWATER SITE PLAN... 4 Existing Conditions Summary... 4 Project Overview... 5 Onsite Soils... 5 Offsite Analysis - Downstream... 6 Offsite Analysis - Upstream... 7 DOE AND CITY OF BELLINGHAM MINIMUM REQUIREMENTS... 8 Minimum Requirement #1 - Preparation of Stormwater Site Plans ( SSP )... 9 Minimum Requirement #2 - Construction Stormwater Pollution Prevention Plan (SWPPP).. 9 Minimum Requirement #3 - Source Control of Pollution... 9 Minimum Requirement #4 - Preservation of Natural Drainage Systems and Outfalls...10 O Minimum Requirement #5 - On-site Stormwater Management...10 Minimum Requirement #6 - Runoff Treatment...10 Minimum Requirement #7 - Flow Control...11 Minimum Requirement #8 - Wetlands Protection...11 Minimum Requirement #9 - Basin/Watershed Planning...11 Minimum Requirement #10 - Operation & Maintenance...12 FIGURES... 13 Figure 1 - Vicinity Map...14 Figure 2 - NRCS Hydrologic Soils Map......15 Figure 3 - Offsite Analysis...19 Figure 4 - Offsite Upstream Basins...20 Figure 5 - Existing Conditions Basin Map...21 Figure 6 - Proposed Conditions Basin Map...22 CALCULATIONS... 23 Offsite Upstream Basin...24 Stormwater Flow Control Calculations...25 Bioretention Facility Calculations...28 APPENDICES...... 30 Source Control BMPs...31 Construction Erosion Control BMPs...32 Geotechnical Report......33 2
ENGINEER'S DECLARATION I, Jean-Paul Slagle, a Professional Engineer registered in the State of Washington as a Civil Engineer, do hereby declare that the University Ridge Schematic Stormwaterr Site Plan dated April 2013 was prepared by, or under my personal supervision, and that said Report was prepared in accordance with generally accepted engineering practices. I hereby affirm that, to the best of my knowledge, information and belief, subject Report was prepared in full compliance with the 2005 Washington State Department of Ecology Stormwater Management Manual for Western Washington (2005 DOE SWMM), City of Bellingham Municipal Code 15.42.060, and all Technical Standards adopted there under. Jean-Paul Slagle WA P.E. #43224 This report is not intended to be a final l site plan for this project or any individual proposed improvements, and is not intended for use as part of any review of critical area. Existing drainage and site conditions or improvements not mentioned are beyond the scope of this report. 3
STORMWATERR SITE PLAN The Stormwater Site Plan (SSP) is the comprehensive report containing all of the technical information and analysis necessary for regulatory agencies to evaluatee the proposed development for compliance with stormwater requirements. Existing Conditions Summary The subject property, which is currently unaddressed, occupies Tract F of Cedar Ridge Division 2. The parcel occupies 485,6944 square feet (11.15 acres) and is bound by Puget Street to the east, mostly undeveloped Consolidation Avenue right-of-way to the south, the Cedar Ridge subdivision to the west, and undeveloped property owned by the City of Bellingham to the north. The subject property is currently undeveloped and has a ground cover of mature second growth forest. Topography information, prepared by Jepson & Associates, Inc., shows that the property slopes to the west northwest at approximately 25%. Wetlands have been identified to the north of the project and are located on parcels owned by the City of Bellingham. The associated wetland buffer extends south into the site by 85-foot. It appears that any development outside of the 85-foot buffer will not impact or divert any stormwater runoff contributing to the wetlands because the contours run almost perpendicular to the wetland buffer line. Currently, the entire subject property drains overland to the adjacent portions of the Cedar Ridge Division 2 along Nevadaa Street. Stormwater runoff ultimately ends up in the Nevada Street right-of-way drainage system owned and maintained by the City of Bellingham. Downstream from the project site, stormwater is conveyed west to the Cedar Ridge subdivision drainage system and through the City drainage systems that consist of a seriess of open ditches an enclosed pipes. Stormwater in the City's system finally drains to Lincoln Creek, approximately 0.6 miles northwest of the project site as the crow flies. Refer to the "Off Site Analysis" for further detail of downstream drainage systems. An existing stormwater pond is constructed in the Puget Street right-of-way to the southeast of the project and the outfall discharges to a ditch in the Consolidation Street right-of-way. The ditch continues down the Consolidation Street right-of-way until it reaches a City of Bellingham storm drain system which conveys the runoff directly west until it reaches Lincoln Creek. This 4
ditch system does not contribute runoff to the subject property or the downstream conveyance that receives stormwater runoff from the property. Project Overview Currently, the site is completely undeveloped. The proposed development includes four new apartment buildings, a clubhouse with amenities, right-of-way improvements in Consolidation Avenue from the current terminus to the driveway entrance, associated parking areas, and utility extensions. Section 15.42.060 of the Bellingham Municipal Code (BMC) outlines the requirements for erosion control and stormwater facilities in the City. Based upon this code, Minimum Requirements #1-10 of the "Large Development Minimum Requirements" apply since the project will create more than 5,000 square feet of impervious surface. Stormwater will be managed on site with a underground detention facility to achieve flow control and a rain garden, located downstream of detention, for treatment. Proposed flow control facility will be located on a flat bench created for the parking areas. The terracing of the site will be accomplished with retaining walls and the apartment structures. Refer to Minimum Requirement #6: Stormwater Treatment for further information regarding the rain garden. Refer to Minimum Requirements #7: Flow Control for further information regarding the proposed stormwater detention facility. Onsite Soils According to USDA's NRCS website, soils on site are identified as "Squalicum Gravelly Loam", hydrologic group 'B'. A copy of the online soil map is attached in the Figures portion of this report for reference. Conversations with staff from Jepson & Associates, Inc. regarding the construction of the Cedar Ridge subdivision downhill of the project identified groundwater near the surface and in the construction of the utilities trenches. Further conversations with staff from GeoEngineers, Inc. identified other projects in this area with a thin gravelly loam lens over impermeable or near impermeable glacial till or sandstone bedrock. According to Appendix B of Volume III of the 2005 Department of Ecology Stormwater Management Manual for Western Washington, outwash soils (hydrologic soil groups 'A' and 'B') over high groundwater or an impervious soil layer have low infiltration rates and act like till soils (hydrologic soil group 'C') Where groundwater or an impervious soil layer is within 5 feet from 5
the surface, outwash soils may be modeled as till soils in Western Washington Hydrology Model (WWHM). GeoEngineers, Inc. has performed test pits and/or borings on the subject parcel to determine soil conditions, depth to bedrock, and location of groundwater. Glacial till was found on site and GeoEngineers, Inc. has classified the soils as hydrologic group 'C' soils. Offsite Analysis - Downstream An existing catch basin, located at the northwest corner of the project site, is available to collect stormwater runoff from the project. The catch basin drains west to Nevada Street through a 18- inch plastic pipe that was installed in 2002. Stormwater in the Nevada Street drainage system flows north through a series of 18-inch pipes for approximately 800 feet before it collects in a stormwater management facility between Honeysuckle Place and Thimbleberry Place. After passing through the water quality swale and detention pond, stormwater continues to flow north through 24-inch pipes in Nevada Street right of way for approximately 530 feet. At the intersection with Edwards Street, stormwater turns west and flows through a 24-inch concrete pipe to an open ditch along the south side of Edwards Street. The open ditch continues for approximately 100 feet before stormwater is re-collected in a 24-inch PVC culvert. This culvert directs stormwater to an open ditch on the north side of Edwards Street, whichh then drains to a culvert inlet at the intersection of Moore Street. A 24-inch PVC pipe conveys stormwater northwest across Moore Street t to an open drainage channel along the west side of Moore Street right of way. The drainage channel extends approximately 580 feet north through unimproved right of way and collects in a 24-inch concrete pipe. The concretee pipe drains east for 150 feet through unimproved Whatcom Street right of way until it reaches a private, 24-inch concrete pipe. This private concrete pipe flows north and west behind a commercial development (currently developed with a Cost Cutter grocery store, Little Caesar's Pizza, and several other stores) for approximately 950 feet until it reaches a catch basin in Lakeway Drive. The existing storm main in Lakeway Drive is a 36-inch concrete pipe that flows west approximately 400 feet before it connects to a culverted section of Lincoln Creek on the north side of Lakeway Drive. Shortly before connecting to the Lincoln Creek culvert, the drainage system in Lakeway Drive reduces to a 30-inch concrete pipe and then to a 24-inch 2 concrete pipe at the connection to Lincolnn Creek. Reference the Figure 3 - Offsite Analysis in the Figures section of this report for additional information. 6
Offsite Analysis - Upstream The proposed project site has two contributing offsite basins. The basin closest to the site includes the west half of the Puget Street right-of-way from the existing pond in the Consolidation right-of-way in the south to the edge of the wetland buffer adjacent to the project site in the north. The other offsite basin contributes to a culvert crossing under Puget Street and directly discharges onto the site as a point discharge. This basin includes the portions of Puget Street, Queen Street, Consolidation Avenue, and the single family residencess in between the streets. Reference the Figure 4 - Offsite Upstream Basins map in the Figures section of this report for additional information. Figure 4 has been prepared using the City of Bellingham City IQ online GIS program and confirmed with a site visit. Further analysis of the offsite basins is in the Calculations section of this report. 7
DOE AND CITY OF BELLINGHAM MINIMUM REQUIREMENTS Minimum stormwater management requirements for this project have been determined using the 2005 Department of Ecology Stormwater Management Manual for Western Washington (2005 DOE SWMM or DOE Manual) and BMC 15.42.060. With more than 5,0005 square feet new impervious surfaces, the project is subject to Minimum Requirements 1 through 10. MINIMUM REQUIREMENT SUMMARY LARGE PARCEL NEW DEVELOPMENT Minimum Requirement Not Applicable Variance Requested Standard Requirements Incorporated Comments (Report Section Reference or BMP Identifier) # Description 1 Preparation of Stormwater Site Plans 2 Construction Stormwater Pollution Prevention Plan See "Additional Comments" 3 Source Control of Pollution 4 5 Preservation of Natural Drainage Systems and Outfalls On-Site Stormwater Management 6 Runoff Treatment 7 Flow Control 8 Wetlands Protection 9 Basin/Watershed Planning 10 Operation and Maintenance # Additional Comments 2 A copy of the Construction SWPPP will be included in the civil construction drawings. 8
Minimum Requirement #1 - Preparation of Stormwater Site Plans ( SSP ) This report serves as a Stormwater Site Plan (SSP). All stormwater management systems have been designed according Department of Ecology (DOE) and City of Bellingham standards. A construction Stormwater Pollution Prevention Plan (SWPPP) will be prepared and incorporated into the construction documents.. Minimum Requirement #2 - Construction Stormwater Pollution Preventionn Plan (SWPPP) A SWPPP narrative is provided within the civil site plan drawings to ensure that the SWPPP is on site during construction. Each of the twelve elements of a SWPPP must be considered and included in a Construction SWPPP unless site conditions render the element unnecessary and the exemption from that element is clearly justified in the narrative of the SWPPP. The SWPPP shall include, at a minimum, the narrative, the Stormwater Site Plan and copies of Best Management Practice detail sheets that will be utilized as a part of the SWPPP. During construction, the contractor shall maintain a copy of the SWPPP on site and shall update or modify the SWPPP as necessary for the current conditions on site. The contractor's schedule and available crew, equipment, and materials will be determined after this project goes to bid. Accordingly, some BMPs that have been specified may not be necessary, while other additional BMPs may be required. This project will disturb more than one acre of soil and will require an NPDES permit from Washington State Department of Ecology. As such, the project shall retain a Certified Erosion and Sediment Control Lead (CESCL) to determine which BMPs are necessary as site conditions change during construction. The contractor or CESCL shall add any BMP specifications that have not already been included in the SWPPP. Minimum Requirement #3 - Source Control of Pollution Pollution will be controlled at the source to the maximum extent possible. Concerns for multifamily residential building activities are vehicle parking, vehicle washing and oil changing, minor repairs, and temporary storage of garbage. Potential pollutant generating sources can occur at vehicle parking lots and from washing of vehicles. Runoff from parking lots may contain undesirable concentrations of oil and grease, suspended particulates, and metals such as lead, cadmium, and zinc. All known, available and reasonable source control BMPs have 9
been applied to the design and layout of the site and stormwater plans. Source control BMPs for multifamily developments have been reproduced from the DOE Manual and will be provided in the Appendix of this report. Minimum Requirement #4 - Preservation of Natural Drainage Systems and Outfalls No significant stormwater diversions are proposed as a part of this project. The natural drainage pattern for the project is sheet flow to the west northwest with the drainage system in Nevada Street being the ultimate destination. An 18" stormwater conveyance pipe was stubbed into the property during the construction of the Cedar Ridge Division 2 development which will bring the developed stormwater runoff to the Nevada Street stormwater system. The upstream basin will continue to flow through the property. The flow will be collected in a pipe and conveyed to the base of the site. Minimum Requirement #5 - On-site Stormwater Management Stormwater will be managed on site using a single detention facility and a centralized rain garden. Further discussion of these systems are available in Minimum Requirements #6 and #7. Per the NRCS Online Soil Service, soils on site are classified as hydrologic group 'B', which can be suitable for infiltration. Test pits by GeoEngineers have found that the soils onsite are actually composed of glacial till and they function as a type 'C' hydrologic soil. Near surface hardpan, steeps slopes, and existing single family residences located immediately down gradient of the project restricts the use of infiltration on the site. Further information is located in the geotechnical report attached in the Appendix. Dispersion has also been investigated for the site. At this time, it is determined not to be feasible due to limited dispersion areas, steep slopes, and single family residences located immediately down gradient of the area. Minimum Requirement #6 - Runoff Treatment Enhanced treatment is required for multifamily developments discharging to fish bearing streams. The project is proposing a centralized bioretention facility (also known as a rain 10
garden) located near the existing 18" outlet for the project. The bioretention facility has been sized, using WWHM3 continuous runoff model, to filter a minimum of 91% of the influent runoff file. Stormwater that filters through the imported soil mix is considered to have received the equivalent of enhanced treatment. Bioretention facility calculations are available in the Calculations section of this report. Oil control is not provided for the project. In general, all-day parking areas, such as multifamily apartment complexes, are not intended to be defined as high-use sites and should not require oil control options listed in the Department of Ecology Stormwater Manual. Minimum Requirement #7 - Flow Control Proposed impervious surfaces and converted pervious surfaces are subject to flow control requirements. Flow control willl be provided by a single underground detention facility with a control structure that will be installed beneath the proposed parking areas. Discharges from the detention facility will be restricted by a control structure. The control structure will be fitted with several orifices that limit flows according to requirements in BMC 15.42.060. In case of rainfall events that exceed the design event, plugged orifices, or emergencies, stormwater will overtop the control structure and continue downstream contained within the proposed stormwater system. Refer to the civil plans for detailed drawings of the storage facility and control structure. Flow control calculations are further explained and provided in the Calculations section of this report. Minimum Requirement #8 - Wetlands Protection No wetlands have been identified on site, however, a wetland system is located to the north of the project. The wetland buffer line runs perpendicular to the project site contours and stormwater runoff from the project site does not appear hydrate the existing wetlands. The property is not subject to additional wetland protection requirements. Minimum Requirement #9 - Basin/Watershed Planning The entire project site is contained within the Lincoln Creek watershed. No additional flow control or treatment requirements for this watershed are identified in the City of Bellingham Comprehensive Stormwater Plan. 11
Minimum Requirement #10 - Operation & Maintenance A separate operations and maintenance manual will be prepared for the new stormwater management facilities. The manual will contain a description of the facilities, what they do, and how they work. The manual also identifies and describes maintenance tasks for each component in the facilities and the required frequency of each task. 12
FIGURES 13
Figure 1 - Vicinity Map PROJECT SITE 14
Figure 2 - NRCS Hydrologic Soils Map 15
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Hydrologic Soil Group-Whatcom County Area. Washington Hydrologic Soil Group Hydrologic Soil Group- Summary by Map Unit - Whatcom County Area, Washington (WA673) Map unit symbol Map unit name Rati ng Acres lnaoi Percent of AOI 156 Squalicum gravelly loam, 5 to 15 B 2.9 percent slopes 157 Squalicum gravelly loam, 15 to 30 B 14.5 percent slopes 159 Squalicum-Urban land complex, 5 2.4 to 20 percent slopes Totals for Area of Interest 19.S 14.7% 73.2% 12.1% 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 (AID, B/D, and CID). 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. T hese 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 (AID, B/D, or CID), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are irn group D are assigned to dual classes. Natural Resources Conservat.lon Service Web Soil Survey National Cooperative Soil Survey 1112012012 Page 3 of 4 17
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Figure 3 - Offsite Analysis LINCOLN CREEK CULVERT EXISTING STORMWATER MANAGEMENT FACILITY PROJECT SITE 19
Figure 4 - Offsite Upstream Basins CRIMSON BASIN SHEET FLOWS ONTO THE PROJECT SITE PURPLE BASIN DRAINS TO CROSS CULVERT UNDER PUGET STREET 20
Figure 5 - Existing Conditions Basin Map An on-site existing conditions basin map will be included in the final design report. 21
Figure 6 - Proposed Conditions Basin Map An on-site proposed conditions basin map will be included in the final design report. 22
CALCULATIONS 23
Offsite Upstream Basin Table C1 below is a tabulation of all of the land uses for the basin upstream of the University Ridge project. These land use delineations have been determined utilizing City of Bellingham GIS data and visually verified by a site visit. Table C1 - Offsite Upstream Basin # Address Street 1 800 Puget 2 804 Puget 3 808 Puget 4 810 Puget 5 816 Puget 6 820 Puget 7 801 Queen 8 805 Queen 9 809 Queen 10 813 Queen 11 817 Queen 12 821 Queen 13 800 Queen 14 804 Queen 15 808 Queen 16 812 Queen 17 816 Queen 18 801 Racine 19 805 Racine 20 809 Racine 21 813 Racine 22 817 Racine Parcel Totals (square feet) Parcel Totals (acres) 1 ROW ROW Totals (square feet) ROW Totals (acres) Basin Totals (square feet) Basin Totals (acres) Parcel Area Roof Area Driveway Area 10,955 2,964 1,350 11,460 2,567 3,119 11,114 1,845 1,252 11,879 1,874 590 11,630 1,978 619 10,897 1,824 420 10,929 2192 984 11,460 3045 278 11,130 2543 328 11,884 2878 678 11,691 2940 227 10,896 3246 296 7,879 2105 170 7,958 1524 609 7,965 1560 620 8,985 1728 358 8,989 1124 963 7,933 2429 196 8,027 2500 229 8,023 2594 643 9,021 1653 210 9,016 2711 239 219,721 49,824 14,378 5.044 1.144 0.330 76,428 0 4,7191 76,428 0.0 4,7191 1.755 0.0 1.083 296,149 49,824 61,569 6.799 1.144 1.413 Landscape Area 6,641 5,774 8,017 9,415 9,033 8,653 7,753 8,137 8,259 8,328 8,524 7,354 5,604 5,825 5,785 6,899 6,902 5,308 5,298 4,786 7,158 6,066 155,519 3.570 29,237 29,237 0.671 184,756 4.241 24
Stormwater Flow Control Calculations Stormwater runoff from the project will receive flow control an undergroundd detention vault located under the lowest parking area. The detention vault will be composed of poured-in-place concrete walls and base with precast concrete lids. The impervious surfaces in the basin will be mix of roof area and flat, moderate, and steep parking area. For modeling purposes, all driveway, sidewalk, and landscape areas have been modeled as steep. Table C2 - Detention Facility Basin Land Use Area (square-feet) Area (acres) "Apartment" Buildings Clubhouse Parking Sidewalk Landscaping Total 49,032 1.126 4,500 0.103 140,200 3.219 13,780 0.316 172,688 3.964 380,200 8.729 Existing conditions for the Puget Basin consists of forested ground cover. The size of the existing basin is created to match the area of the proposed basin. The ground is modeled as steep due to slopes that are in excess of 25% over the majority of the basin. Onsite soils have been modeled as hydrologic soil group 'C' per the discussion in the Onsite Soils section of this report. Table C3 - Existing Facility Basin Land Use Area (square-feet) Area (acres) Forested - Hydrologic 'C' Soil Total 380,200 8.729 380,200 8.729 25
Figure C1 - Pre-development Basin Figure C2 - Post-development Basin 26
Figure C3 - Vault 27
Bioretention Facility Calculations The Department of Ecology Storm Water Manual identifies bioretention facilities as providing enhanced treatment for stormwater runoff. Enhanced treatment facilities are intended to provide a higher rate of removal of dissolved metals than basic treatment facilities. The project will utilize a single rain garden to achieve stormwater treatment for the site's stormwater runoff. Bioretention facilities, also known as rain gardens, are designed to mimic the pollutant removal mechanisms that are found in forest ecosystems. These adaptive landscape features utilize chemical, biological, and physical properties of plants, microbes, and soilss for removal of pollutants from stormwater runoff. The site s pollution generating surfaces are limited to the parking areas and the extension of Consolidation Street at 3/4 standards. These surfaces will be conveyed to a single rain garden located in the northwest corner of the site, near the 18" outlet pipe. The bioretention facility, composed of a minimum of 24" of amended sandy soils, is placed downstream of detention and has been sized to filter a minimum of 91% of the stormwater runoff and is designed using WWHM3 continuous flow hydrologic software model. This design standard satisfies enhanced treatment requirements, as identified in Volume V, Section 3.4 in the 2005 DOE Manual. Groundwater is a concern with this project due to the severity of the project slope, a shallow impermeable layer of glacial till or sandstone, and the close proximity of existing single family residences adjacent to the bioretention facility site. This bioretention facility is proposed to be completely contained within a concrete lined basin to protect the adjacent properties from additional groundwater loading. A rain garden with greater than 5,000 square feet of contributing pollution generating impervious area shall have a minimum infiltration reduction factor of 4 applied to the infiltration rate per the 2005 Low Impact Development Technical Guidance Manual for Puget Sound. A maximum long-term design infiltration rate of 2 inches per hour can be utilized in the rain garden model to provide a factor of safety in the design of greater than 4. Native herbaceous plants, that can withstand both wet and dry conditions, are recommended for installation within the rain garden. Plants shall be obtained, when possible, from nurseries with growing stock local to this region. The plant list will be specified in the final civil plans. 28
Figure C4 - Rain Garden Model 29
APPENDICES 30
Source Control BMPs Applicable source control BMPs will be included in the final draft of this report. 31
Construction Erosion Control BMPs Applicable construction erosion control BMPs will be included in the final draft of this report. 32
Geotechnical Report 33