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Job #2016355.42
Storm Water Quality Review and Analysis
Starbucks — Tigard Towne Square RECEIVED
16200 SW Pacific Highway
Tigard, OR 97224 MAR 2 6 2019
For: CITY OF TIGARD
Prepared
BUILDING DIVISION
Starbucks
Civil Designer:
Tyler Budd
Project Manager:
Tom Conner 4�0,0 PROFS
1,1G1144. 6>0
Design Date: t• R
February 21, 2019 92464P •
" - <l *MA*
Project Number: /
2016355.42 OREGON�
'fir 11.pi
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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&O 17-05 Manual
Tyler Budd, Civil Designer 3 February 25, 2019
Section 1
Proiect 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
3) 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:
Water Quality Volume(cu.ft.) = 0.36(in.) x Area(sq.ft.)
1? (inft.)
The required water quality volume is 395.4 cf. From here, we calculated the water
quality flow from the formula below:
Water Quality Flow(cfs) = Water Quality Volume Icu.ft.)
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
BayFiltero"Model 'recall Number c 0 atr an'Cr-t &eatment Caper-t,r Treat nenl C.:racity
Carttriuk , /. f. 232 r'h:;t 545 iefsl
BF-8-1 - 1 o a5 C
BF-60-2 G:( _ 01(
BF-72-3 .. 0 1:; 0?0 0 30
BF-84-4 .1 0 20 ti 27 0 6C
BF-96-5 `at' 5 0 25 T.5n
BF-96-6 0f 0 0 3,- tf>rl G.FC
BF-96-7 (4'0 G 47 1 d7
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
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Conservation Service National Cooperative Soil Survey Page 1 of 3
• Soil Map—Washington County,Oregon
MAP LEGEND MAP INFORMATION
•
Area of Interest(AOl) Spoil Area The soil surveys that comprise your AOI were mapped at
Area of Interest(AOI) Q Stony Spot 1:20,000.
Soils 05 Very Stony Spot Warning:Soil Map may not be valid at this scale.
Li Soil Map Unit Polygons
Wet Spot Enlargement of maps beyond the scale of mapping can cause
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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 Line Features
Special Point Features scale.
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 r Rails Source of Map: Natural Resources Conservation Service
(; Closed Depression Web Soil Survey URL:
olio Interstate Highways Coordinate System: Web Mercator(EPSG:3857)
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A. Lava Flow Back round accurate calculations of distance or area are required.
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of the version date(s)listed below.
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Soil Survey Area: Washington County,Oregon
® Miscellaneous Water Survey Area Data: Version 16,Sep 18,2018
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Rock Outcrop 1:50,000 or larger.
+ Saline Spot Date(s)aerial images were photographed: Aug 3,2014—Aug
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Natural Resources Web Soil Survey 2/11/2019
doom 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%
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378 Quatama loam,3 to 7 percent 1.3 40.8%
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Totals for Area of Interest 3.1 , 100.0%
USDA Natural Resources Web Soil Survey 2/11/2019
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
April2017 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
April2017 Chapter 4—Page 12
b. Water Quality Surface Area(applies to facilities in Section 4.05.3.c.1(D)-
(I))
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
April2017 Chapter 4—Page 14
Agnes Lindor
From: Agnes Lindor
Sent: Thursday, April 11, 2019 10:44 AM
To: gripley@gpdgroup.com
Cc: Kenny Fisher;Albert Shields
Subject: SIT2019-00009 Starbucks
Good morning Guy-
Upon review of your site work permit for Starbucks located at 16200 SW Pacific Highway. Engineering has requested
that a storm drainage report be submitted for review. Please contact Kenny Fisher for more information, copied on this
email. Your permit is on hold under we receive the additional information.Thanks,
Agnes Lindor I Associate Planner
City of Tigard I Community Development
13125 SW Hall Boulevard
Tigard, Oregon 97223
Phone: 503.718.2429
Email:AgnesL@tigard-or.gov
1