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Report arrz0/9-ccCc) /to&v fit/ rF?��� as(1- 520 South Main Street,Suite 2531 Phone 330.572.2100 ‘, Akron, Ohio 44311 www.gpdgroup.com GPD Engineering and Architecture Professional Corporation GO February 25, 2019 V Job #2016355.42 Storm Water Quality Review and Analysis Starbucks — Tigard Towne Square 16200 SW Pacific Highway HE Tigard, OR 97224 „, eV ED Prepared For: MAR 7 Starbucks 2019 CITY OF TIGARD Civil Designer: BUILDING DIVISION Tyler Budd Project Manager: Tom Conner ��D PRopS. ♦`� NG t NEB dip Design Date: �� February 21, 2019 `r P 7! Project Number: 2016355.42 •�REGON� A. 02/28/19 EXPIRES:06/30/2020 • Tyler Budd, Civil Designer 2 February 25, 2019 Table of Contents Section 1: • Project Information • Design and Analysis Section 2: • Drainage Map • USDA Web Soil Survey Report Section 3: • Excerpt from Chapter 4 (Section 4.05), Runoff Treatment and Control of the R&D 17-05 Manual Tyler Budd, Civil Designer 3 February 25, 2019 Section 1 Project Information The project is located at 16200 SW Pacific Highway, Suite Z3, Tigard, OR 97224 as part of a larger shopping center. The proposed improvements consist of renovating an existing bank building, reconfiguring part of the parking lot and adding a dumpster enclosure and pad. Because the project consists of adding or modifying over 1,000 SF of impervious area, the City of Tigard and Clean Water Services requires water quality to be addressed with the development. It is not known whether the existing site has water quality treatment already, so it is assumed that the full amount of required treatment area, as calculated below, will need to be treated in the proposed water quality unit. Runoff is currently pitched to (2) inlets on site. The water will then be directed through a ADS Bayfilter before being released back into the existing storm water system. Design and Analysis • The water quality requirements for City of Tigard are governed by Chapter 4 of the current Clean Water Services Design and Construction Standards (see section 3). To determine the amount of impervious area needed in design, we referred to section 4.05.5, which gives the formula shown below for all developments other than single family and duplex, which result in the permanent removal of 1,000 SF or greater of impervious area. Treatment= New Imp. + 3(Modified Imp. - Permanently Removed Imp.) New Impervious 1,150 SF Removed Impervious 2,650 SF Modified Impervious 6,760 SF Using this formula and the numbers shown, we are able to determine 13,480 SF of impervious area is required to be treated for water quality. See drainage map in section 2 showing the area being treated. For the purpose of this report and following Clean Water Services guidelines, modified impervious pavement is considered to be any pavement or concrete that is removed and replaced full depth. The area being milled and overlaid is not considered full depth replacement and therefore not included in this modified impervious number. New impervious surface is any area being turned into impervious surface that was existing landscaping and removed impervious is any impervious area being replaced with landscaping. A review of section 4.05.3 c.1 of the R&O manual for water quality indicates a list of items that can be used for treatment: Tyler Budd, Civil Designer 4 February 25, 2019 A) Vegetated Swale B) Extended Dry Basin C) Constructed Water Quality Wetland D) Structural Infiltration Planter E) Non-structural Infiltration Planter(rain garden) F) Flow-through Planter G) LIDA Swale H) Street-Side Planter I) Landscape Filter Strip J) Vegetated Corridor as a Filter Strip These items all appear to not be feasible to construct in relation to the work being proposed, they would all require additional and unnecessary earthwork, construction, inspection, and maintenance. Section 4.05.8 in the R&O Manual states proprietary treatment systems shall be used in certain situations. This project falls under section 4.05.8.c.2 to make it qualified to use a proprietary treatment device: Treatment of runoff from an adjoining commercial, industrial, or multi-family, or condominium parcels which share a common parking lot. We have recommended the use of an ADS Bayfilter device. Based on the amount of area needing to be treated, we calculated the necessary water quality volume from the formula below: 0.36(in.) x Area(sq_ft.) Water Quality Volume(eu.ft_) = 12(in./ft.) The required water quality volume is 395.4 cf. From here, we calculated the water quality flow from the formula below: Water Quality Volume(cu.ft.) Water Quality Flow(cfs) = 14,400 seconds The required water quality flow for this project was determined to be 0.027 cfs. After this is determined, the ADS Bayfilter can be sized based on their flow specifications. Tyler Budd, Civil Designer 5 February 25, 2019 BayFilterT'Model csl Numbero' "raairte n Cc[it1i2 r- Treatman',Capacity- Treatment Capacity- ;.�c Camemges _" ,efd 53Cids) 5451cfsl BF-48-1 48' 1 05 3 907 0.10 BF-60-2 BY 2 010 520 BF-72-3 72 3 015 ^) (13:) BF-84-4 84' .. 0 20 Li%T. 1;) BF-96-5 95. _ 0 25Ci 33 0 52 BF-96-6 0;: 5 0 3C L.-J n F; BF-96-7 it 47 0 7J Based on this table, the required Bayfilter to accommodate the necessary water quality flow is the BF-48-1 model with (1) 522 cartridge. This requires a 48" manhole, as detailed by ADS, to be installed on site with the cartridge inside. See utility plan for placement and invert information. The ADS Installation Manual shall be referenced for additional information. Conclusion After reviewing the City of Tigard water quality requirements and LIDA approaches, it was determined the most practical approach is to install the ADS Bayfilter as described above. The Bayfilter design will require some storm sewer to be replaced, but we believe it is more practical than the regrading and maintenance that would be needed for installing a surface water quality approach. The Bayfilter will provide a less impactful approach and will provide the required treatment underground. Tyler Budd, Civil Designer 6 February 25, 2019 Section 2 N 2 - _ _ _ _ --(1-.1-lil'i'l-. fl ® STARBUCKS COFFEE 1+,a ° COMPANY_ f -.-T �>rt��Pa ximnl�InfW SEATTLE,WASHINGTON 98134 POO)318-1575 - • - : -- Yd 1 Vd - 00 -FF. yd r _ "E9EpLLWNA9RM9VE4FG1M901E _ - ve _ �� 70���,yd CON IRnofapit, 0u01S 0y IHEBJIF • �. -Ug�� va P9WiRn Uf sI WR RTTECggaIIUX. 1 - - ` NHI TSIM MNTHEE iIECp40150 IM T< • E I txkNIXKWL01EOR�NIPAR115WRE0 LEPImPPOP YNINIx R 100 E Qi V501xaXVwM1ER :M10NER RVIT IlPE.P1000NGIOMG RoEa N111KK1 IIEPRW NPonEN COMFY 65.PRBIKMS CGRNMttA1. — 'csE uuwxcsarosPEaRaroxsalk N2NfE010 cYF1E5S0E61fi EMfOR1 I PSOi] IV15iMBVSSE OIIE MX CN IS B GW 1 IEIttER PR ISNYLIMVEMIr�VfiAIIW k 6(o S` XCA'.AB AIEF.,EPI6I AIEV • �_ - ---__ 41 GEd11FD BiBAfiREFLFM B9 �- J .A N- I ' I f xPOPI Es J� r �. SLMPWIsiEWU1EVE0.9iw130,fp1Se ❑ o I I Ill D (-........1 /pII, I _ A gRNYY XRaG 9N6lliWL01 1I f 1 I /+ 1) P i J 1 q II rill LC NJ a ` ` . No Q L1V/ LEGEND ,SE II IVA% —,q 4 <20 / I r WAIEROLWPT'SUMS VS s { U, / N l litV Ns I ks O »VO %N w~ C Cla O 90 I uQ .O� w Oa CC Fn— ff I— r STORE 418 1!Y \ I PROJECTS. 08T53029 ISAkmre. Save Sea, - ¢ wwGEP STYx lmxx F PR06l:INM OEBK#kR 50000G.P V o adoar - \ ! B..m.mnwW w. BM N onml.. 6IM nne DRANAGE MAP WALE ASWWWAN SFIEEINABER P1 a Soil Map—Washington County,Oregon 3 o 4 C H 515790 515910 515930 515897 515970 5158D 515910 45°24'9'N 1 45°249 N 1" 414, jr' i X Z Y /j/ rt ! I x�x j+C'eb... ` , ifr . i Ia 'f ..: 1 ` v. . 1 . 1.n11 e '1 � A r 3 l ' 1 , 'r '37AN* > .1X :.i 016-4- • emu; mET "g a n r �„ . lit ''C ri [=r._ Lic S,riceLx�- wr �8('19 elf,mk©c6{I�o t �, 45.24'3"N 45.24'3'N 515790 515810 515820 515550 5153713 515990 515910 eMap Scale:1:837 if printed on A portrait(8.5"x 11")sheet. N Meters 0 10 20 40 60 Feet /V l, a o so 1Eo 240 Map projection:4 Web Mercator Comer coordinates:WGS84 Edge tics:UTM Zane 1ON WGS84 USDA Natural Resources Web Soil Survey 2/11/2019 Conservation Service National Cooperative Soil Survey Page 1 of 3 • Soil Map—Washington County,Oregon • MAP LEGEND MAP INFORMATION Area of Interest(AOl) g Spoil Area The soil surveys that comprise your AOI were mapped at Area of Interest(AOI) 1:20,000. 0 Stony Spot Soilsett Very Stony Spot Warning:Soil Map may not be valid at this scale. Soil Map Unit Polygons 7 Wet Spot Enlargement of maps beyond the scale of mapping can cause ry Soil Map Unit Lines misunderstanding of the detail of mapping and accuracy of soil A,, Other line placement.The maps do not show the small areas of • Soil Map Unit Points contrasting soils that could have been shown at a more detailed Special Point Features •' Special Line Features scale. V Blowout Water Features Streams and Canals Please rely on the bar scale on each map sheet for map ® Borrow Pit measurements. Transportation X Clay Spot 4-1-4 Rails Source of Map: Natural Resources Conservation Service 0Closed Depression Web Soil Survey URL: ~0 Interstate Highways Coordinate System: Web Mercator(EPSG:3857) • Gravel Pit oho US Routes Maps from the Web Soil Survey are based on the Web Mercator Gravelly Spot Major Roads projection,which preserves direction and shape but distorts Landfill distance and area.A projection that preserves area,such as the Local Roads Albers equal-area conic projection,should be used if more ¢ Lava Flow accurate calculations of distance or area are required. 7l Background 416, Marsh or swamp . Aerial Photography This product is generated from the USDA-NRCS certified data as of the version date(s)listed below. ATtr Mine or Quarry Soil Survey Area: Washington County,Oregon Cir Miscellaneous Water Survey Area Data: Version 16,Sep 18,2018 O Perennial Water Soil map units are labeled(as space allows)for map scales Roc Outcrop 1:50,000 or larger. } Saline Spot Date(s)aerial images were photographed: Aug 3,2014—Aug 23,2014 Sandy Spot The orthophoto or other base map on which the soil lines were . . Severely Eroded Spot compiled and digitized probably differs from the background • Sinkhole imagery displayed on these maps.As a result,some minor shifting of map unit boundaries may be evident. Slide or Slip • Sodic Spot • moorsi>> Natural Resources Web Soil Survey 2/11/2019 Conservation Service National Cooperative Soil Survey Page 2 of 3 • Soil Map—Washington County,Oregon Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 37A Quatama loam,0 to 3 percent 1.8 59.2% slopes 376 Quatama loam,3 to 7 percent 1.3 40.8% slopes Totals for Area of Interest 3.1 100.0% • ',irk Natural Resources Web Soil Survey 2/11/2019 i Conservation Service National Cooperative Soil Survey Page 3-of 3 Tyler Budd, Civil Designer 7 February 25, 2019 Section 3 b. Approaches shall be designed so that flow from the development is treated off-line from the storm conveyance system and reconnected to upstream flows following treatment. If an off-line approach is not feasible, additional capacity in the approach may be required for upstream flow. c. Discharges to sensitive areas shall maintain the hydro period and flows of pre-development site conditions to the extent necessary to protect the characteristic functions of the sensitive area. Conversely, discharge of flows that may be critical to downstream water quality sensitive areas into other catchments will not be permitted unless addressed in the applicant's Service Provider Letter. d. The stormwater quality approaches shall be designed for a dry weather storm event totaling 0.36 inches of precipitation falling in 4 hours with an average storm return period of 96 hours. e. All water quality approaches shall be designed in accordance with this Chapter. 4.05.5 Impervious Area Used In Design The following apply for development which creates or modifies 1,000 square feet or greater of impervious surface. Development which results in both new and modified impervious surface will result in a combined treatment requirement, as described below: a. For new home construction on a single family or duplex lot of record the water quality approach shall be sized based on 2,640 square feet of impervious surface per dwelling unit. The actual impervious surface may be utilized when the lot size is less than 2,000 square feet, or the development creates or modifies impervious surface not associated with new home construction, up to a maximum of 2,640 square feet. b. For single family and duplex residential partitions and subdivisions, stormwater quality approaches shall be sized for all impervious area created by the development and for all existing impervious area proposed to remain on site. All existing and proposed residences on individual lots shall be sized at the rate of 2,640 square feet of impervious surface area per dwelling unit. For the purpose of design calculations, the actual impervious surface can be utilized as an alternative to 2,640 square feet per dwelling unit when the average lot size on a single-family residential project is less than 2,000 square feet. c. For all developments other than single family and duplex, including row houses and condominiums, the stormwater quality approaches shall be sized to treat all new impervious surfaces and three times the modified R&O 17-5 RUNOFF TREATMENT AND CONTROL April 2017 Chapter 4—Page 11 impervious surface, up to the total existing impervious surface on the site. The area requiring treatment is shown in the formula below: Treatment=New Impervious+3(Modified Impervious) When modification results in the permanent removal of 1,000 square feet or greater of impervious surface, the treatment approach shall be sized for three times the replaced impervious surface, in addition to the new impervious surface. In this case, the area requiring treatment is shown in the formula below: Treatment=New Imp. + 3(Modified Imp. -Permanently Removed Imp.) Impervious areas shall be determined based upon building permits, construction plans, or other appropriate methods of measurement deemed reliable by District and/or City. 4.05.6 Water Quality Approach Sizing Methods a. Water Quality Volumes and Flows (applies to approaches in Section 4.05.3.c.1 (A)-(C)) 1. Water Quality Storm The water quality storm is the storm required by regulations to be treated. The storm defines both the volume and rate of runoff. The water quality storm is defined in Subsection 4.05.4 (d). 2. Water Quality Volume (WQV) The WQV is the volume of water that is produced by the water quality storm. The WQV equals 0.36 inches over the impervious area that is required to be treated as shown in the formula below: Water Quality Volume(cu.ft.) = 0.36 (in.) x Area(sq.ft.) 12 (in./ft.) 3. Water Quality Flow (WQF) The WQF is the average design flow anticipated from the water quality storm as shown in the formulas below: Water Quality Flow (cfs) = -Water Quality Volume(cu.ft.) 14,400 seconds or Water Quality Flow (cfs) = 0.36 (in.) x Area(sq.ft.) 12(in/ft)(4 hr)( 60 min/hr)(60 sec/min) R&O 17-5 RUNOFF TREATMENT AND CONTROL April 2017 Chapter 4—Page 12 b. Water Quality Surface Area(applies to facilities in Section 4.05.3.c.1(D)- (0) A 6% sizing factor shall be used to calculate the required water quality surface area of the selected treatment facility. A sizing factor of 6% assumes the site infiltration rate is less than 2 inches/hour. A site specific design for the site shall be required for any of the following situations: 1. An alternate sizing factor is used; 2. The impervious area contributing to an individual water quality approach is greater than 15,000 square feet; or 3. The treatment facility is used for quantity control. c. Water Quality for Vegetated Corridor as a Filter Strip (applies to Section 4.05.3.c.1(J)). The sizing of a Vegetated Corridor as a Filter Strip must meet all of the following criteria: 1. The maximum contributing impervious surface is 2,640 square feet per 50 feet of Vegetated Corridor width. 2. The contributing impervious surface must be adjacent to the Vegetated Corridor, or within the outer 40% and approved as an allowed use consistent with the Service Provider Letter. 3. The minimum depth is three times the depth of the contributing impervious surface, or one single family residence. The depth of the Vegetated Corridor treatment area shall be measured from the edge of the Sensitive Area and in the direction of stormwater flow. 4.05.7 Pretreatment a. Pretreatment Required Unless approved by the District, flow from impervious surfaces to water quality approaches shall not be allowed without pretreatment or as specified in the design criteria for specific approaches in Section 4.06. Incoming flows to the water quality approach shall be pretreated using a water quality manhole in accordance with Subsection 4.06.1 or as specified within the design criteria for specific approaches. Other pre-treatment methods such as proprietary devices, filter strip, or trapped catch basin may be approved by the District or City. R&O 17-5 RUNOFF TREATMENT AND CONTROL • April 2017 Chapter 4—Page 13 b. Proprietary Pre-Treatment Devices 1. The use of proprietary pre-treatment devices shall be permitted on a case by case basis with approval by the District or City. 2. The devices will be sized in accordance with the manufacturer's recommendations; however, the minimum treatment flow must be the water quality flow. 3. Technical submittals from the manufacturer are required, including hydraulic design criteria, particulate removal efficiency, and maintenance requirements and schedule. 4.05.8 Proprietary Treatment Systems a. Proprietary treatment systems shall meet the removal efficiency requirement defined in Section 4.05.3(a) and be approved by the District for use in the situations identified in Subsection(c)below. b. Maintenance 1. Proprietary treatment systems shall be maintained by the District or Cities except those systems used in the situations specified in Section 4.05.8(c)(1) and(2)below. 2. Proprietary systems require a long-term maintenance plan identifying maintenance techniques, schedule, and responsible parties. This maintenance plan shall be submitted and approved with the drainage report for a project. c. Proprietary treatment systems shall be allowed in situations meeting one of the following criteria: 1. Treatment of runoff from a single parcel. 2. Treatment of runoff from an adjoining commercial, industrial, or multi-family, or condominium parcels which share a common parking lot. 3. Treatment of runoff from new and expanded collector and arterial roadways where no other opportunities exist for treatment without necessitating the removal of homes or businesses. 4. Treatment of runoff from new developments in transit-oriented or similar high-density zoning classifications where the development is primarily single-family residential and the average lot size is less than 2,500 square feet. 5. Treatment of runoff as part of a master planned regional facility approved by the District. R&O 17-5 RUNOFF TREATMENT AND CONTROL April 2017 Chapter 4—Page 14