Report 3aTao� 3 - coo lo
RECEIVED
JUN 2 7 2013
CITY OFTIGARD
BUILD'BUILDINn nWWISION
MEMORANDUM (111 Cardno
90) PROp G/Z7/t3 Shaping the Future
To: City of Tigard c �.' NE-�S�Oy
1 3 8P 5415 SW Westgate Drive
From: Atalia Raskin, PE Suite 100
Water Resource Project OREGON Portland,Oregon 97221
Engineer Y d• = USA
"fez, °• o "
Date: June 27, 2013 ' S+gMPSCN( Phone (503)419.2500
Fax (503)419-2600
Project: Greenway Town Center EXPIRES•, /3J/2v/y ,
Cardno#: 21303210
Re: Stormwater Analysis www.cardno.com
This memorandum will summarize the stormwater management approach for the Greenway Town
Center redevelopment project. The site is located west of SW 1215 Ave on SW Scholls Ferry Rd.
The proposed design follows the City of Tigard and Clean Water Services (CWS) stormwater
standards.
Project Overview
The proposed redevelopment project will complete ADA improvements to the site in support of the
proposed grocery store. Site improvements included plaza space and walkway improvements and
regarding handicap parking stalls.
The property area is 7.64 acres of commercial buildings and parking lot. Slopes range from 1 to
4% downward to the north. Site soils are Aloha Silt Loam, hydrologic group C.
Water Quality
The City of Tigard has agreed to enforce the surface water management regulations established
by CWS. CWS requirements for stormwater treatment are found in Chapter 4 of the Design and
Construction Standards. This site falls under the redevelopment standards. Table 4-1 of the CWS
Manual provides a matrix for determining how much water quality treatment is required. The area
of impact is approximately 7.6% of the total site area. Therefore, disturbed impervious area plus
50% of undisturbed impervious area must be treated.
Total Impervious %Treatment Treatment
Area (sf) Area Area (sf)
Disturbed 25,187 _ 100% 25,187
Undisturbed 265,114 50% 132,557
Total 290,300 - 157,744
Table 1 —Treatment Area Table
Water quality treatment will be provided by a Contech StormFilter Vault. StormFilters are designed
to treat urban runoff including TSS, soluble heavy metals, oil and grease, total nutrients, by
providing a high level of water quality treatment. Each standard size cartridge filter has a treatment
capacity of 0.033 cfs (15 gpm).
Australia • Belgium • Indonesia • Kenya • New Zealand • Papua New Guinea
United Arab Emirates • United Kingdom • United States • Operations in 60 Countries
Page 2
June 27,2013
Cardno
Shaping the Future
Water Quality Volume(cu-ft) = 0.36(in)x 159,905(so-ft) =4,797 cu-ft
12 (in/ft)
Water Quality Flow=4,797(cu-ft)=0.333 cu-ft/sec
14,400
Ten StormFilter cartridges are required to treat the required site area. An internal bypass vault will
be used to ensure less than 1.80 cfs enters the cartridge chamber.
Water Quantity
Detention will not be provided. The proposed project does not increase the amount of impervious
area at the site and will therefore no increase the amount of flow downstream of the site.
Conveyance
The NRCS Curve Number unit hydrograph method was used for this analysis. The Clean Water
Services jurisdiction uses the design storm of 24-hour duration based on the standard Type 1A
rainfall distribution. The precipitation depth for the 25-year storm event is 3.90. The selected
pervious CN is 79, Open Space in Fair Condition. A time of concentration of 5 was used for this
analysis.
The replaced conveyance system is being installed to construct the proposed treatment vault, and
collect runoff from the proposed grocery store awning. A third storm line will collect runoff from the
loading dock behind the grocery store. Maximum possible flow is shown in the conveyance spread
sheet as Of. A ratio of Q/Qf equal to 1.00 is a pipe at maximum capacity. The conveyance system
will have the capacity to convey the 25-year storm event as all Q/Qf ratios are less than one. The
pipes were verified to convey and contain the peak runoff from a 25-year design storm. See
attached conveyance table.
Conclusion
The proposed redevelopment project at Greenway Town Center will install a Contech StormFilter
Vault to provide water quality treatment to 48% of the site. The site will not increase the amount of
site runoff; therefore detention and a downstream analysis are not required.
Attachments:
Basin Delineation Map
Hydrologic Soil Group
Table 2-2a
Table 4-1
Conveyance Table
Hydrologic Soil Group—Washington County,Oregon
t
N N
N
515370 515400 515430 515460 515490 515520 -'
45°25 39" iz _ 45°26'39'
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51 - I S 45.26 30"
515370 515400 515430 515460 515490 51 20 51'.50
Map Scale.1'.1,350 if printed on A size(8.5"x 11")sheet.
°
rj IMeters
10 20 40 60
A
0 50 100 200 300
USDA Natural Resources Web Soil Survey 6/14/2013
Conservation Service National Cooperative Soil Survey Page 1 of 4
Hydrologic Soil Group—Washington County,Oregon
MAP LEGEND MAP INFORMATION
Area of Interest(AOI) Map Scale:1:1,340 if printed on A size(8.5"x 11")sheet.
Area of Interest(AOI) The soil surveys that comprise your AOI were mapped at 1:20,000.
Soils
Soil Map Units Warning:Soil Map may not be valid at this scale.
Soil Ratings Enlargement of maps beyond the scale of mapping can cause
n A misunderstanding of the detail of mapping and accuracy of soil line
placement.The maps do not show the small areas of contrasting
0 AID soils that could have been shown at a more detailed scale.
B Please rely on the bar scale on each map sheet for accurate map
0 B/D measurements.
C Source of Map: Natural Resources Conservation Service
(] CAD Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
Coordinate System: UTM Zone 10N NAD83
El D This product is generated from the USDA-NRCS certified data as of
Not rated or not available the version date(s)listed below.
Political Features Soil Survey Area: Washington County,Oregon
Cities Survey Area Data: Version 10,Aug 20,2012
Water Features Date(s)aerial images were photographed: 8/4/2005
Streams and Canals The orthophoto or other base map on which the soil lines were
Transportation compiled and digitized probably differs from the background
Rails imagery displayed on these maps.As a result,some minor shifting
of map unit boundaries may be evident.
Interstate Highways
US Routes
Major Roads
Local Roads
USDA Natural Resources Web Soil Survey 6/14/2013
i Conservation Service National Cooperative Soil Survey Page 2 of 4
Hydrologic Soil Group—Washington County,Oregon
Hydrologic Soil Group
Hydrologic Soil Group—Summary by Map Unit—Washington County,Oregon(OR067)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
1 Aloha silt loam C/D 6.5 83.1%
45A Woodbum silt loam.0 to 3 C 1.3 16.9%
percent slopes
Totals for Area of Interest 7.8 100.0%
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.These 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 (A/D, BID, 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 in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
St),‘ Natural Resources Web Soil Survey 6/14/2013
mein Conservation Service National Cooperative Soil Survey Page 3 of 4
Hydrologic Soil Group—Washington County,Oregon
Tie-break Rule: Higher
',DA Natural Resources Web Soil Survey 6/14/2013
Conservation Service National Cooperative Soil Survey Page 4 of 4
Chapter 2 Estimating Runoff Technical Release 55
Urban Hydrology for Small Watersheds
Table 2-2a Runoff curve numbers for urban areas if
misommum
Curve numbers for
Cover description hydrologic soil group
Average percent
Cover type and hydrologic condition impervious area V A B C D
Fully developed urban areas (vegetation established)
Open space(lawns,parks,golf courses,cemeteries,etc.)a':
Poor condition(grass cover<50%) 68 79 86 89
Fair condition(grass cover 50%to 75%) 49 69 79 84
Good condition(grass cover>75%) 39 61 74 80
Impervious areas:
Paved parking lots,roofs,driveways,etc.
(excluding right-of-way) 98 98 98 98
Streets and roads:
Paved;curbs and storm sewers(excluding
right-of-way) 98 98 98 98
Paved;open ditches(including right-of-way) 83 89 92 93
Gravel(including right-of-way) 76 85 89 91
Dirt(including right-of-way) 72 82 87 89
Western desert urban areas:
Natural desert landscaping(pervious areas only)4' 63 77 85 88
Artificial desert landscaping(impervious weed barrier,
desert shrub with 1-to 2-inch sand or gravel mulch
and basin borders) 96 96 96 96
• Urban districts:
Commercial and business 85 89 92 94 95
Industrial 72 81 88 91 93
Residential districts by average lot size:
1/8 acre or less(town houses) 65 77 85 90 92
1/4 acre 38 61 75 83 87
1/3 acre 30 57 72 81 86
1/2 acre 25 54 70 80 85
1 acre 20 51 68 79 84
2 acres 12 46 65 77 82
Developing urban areas
Newly graded areas
(pervious areas only,no vegetation)5/ 77 86 91 94
Idle lands(CN's are determined using cover types
similar to those in table 2-2c).
I Average runoff condition,and la=0.2S.
2 The average percent impervious area shown was used to develop the composite CN's.Other assumptions are as follows:impervious areas are
directly connected to the drainage system,impervious areas have a CN of 98,and pervious areas are considered equivalent to open space in
good hydrologic condition.CN's for other combinations of conditions may be computed using figure 2-3 or 2-4.
s CN's shown are equivalent to those of pasture.Composite CN's may be computed for other combinations of open space
cover type.
4 Composite CN's for natural desert landscaping should be computed using figures 2-3 or 2-4 based on the impervious area percentage
(CN=98)and the pervious area CN.The pervious area CN's are assumed equivalent to desert shrub in poor hydrologic condition.
5 Composite CN's to use for the design of temporary measures during grading and construction should be computed using figure 2-3 or 2-4
based on the degree of development(impervious area percentage)and the CN's for the newly graded pervious areas.
(210-VI-TR55,Second Ed.,June 1986) 2-5
TABLE 4-1
IMPERVIOUS AREA REQUIRING TREATMENT
ON REDEVELOPMENT SITES
Existing Existing Impervious Impervious Area Required
Impervious Area on Area Disturbed by to Treat
Site Redevelopment
<5,280 sq.ft. < 100% No new treatment required
> 5,280 sq.ft. and < 1,000 sq.ft. No new treatment required
<0.5 acres > 1,000 sq.ft. 100%of impervious area
< 1,000 sq.ft. No new treatment required
Disturbed impervious area
>1000 sq.ft. and<25% +25%of undisturbed
>0.5 acres and impervious area
< 5 acres Disturbed impervious area
>25%and < 50% + 50%of undisturbed
impervious area
> 50% 100%of impervious area
< 1,000 sq.ft. No new treatment required
Disturbed impervious area
> 5 acres >1000 sq.ft. and<50%' + 50%of undisturbed
impervious area
> 50% 100%of impervious area
4.05.6 Water Quality Volumes and Flows
a. 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).
b. 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.)
c. 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
R&O 07-20 9BRUNOFF TREATMENT AND CONTROL
June 2007 8BChapter 4 - Page 11
STORMWATER CONVEYANCE CALCULATIONS
JOB: Greenway Town C
PROJECT: 21303210
FILE: 3210-CD-SBUH-Conveyance.xls
Design Storm: 25 YR
Storm Duration: 24 HRS
Precipitation: 3.9 IN
Manning's"n" 0.013
AREA AREA CN AREA CN TIME Q PIPE SLOPE Qf Q/Qf Vf VNf ACTUAL LENGTH INC.
TOTAL PERV. PER. IMP. IMP. (MIN) (CFS) SIZE V TIME
LINE (AC) (AC) (AC) (IN) (FT/FT) (CFS) (%) (FPS) (%) (FPS) (FT) (MIN)
Roof Lateral 0.11 0.00 79 0.11 98 5.00 0.11 6 0.0493 1.25 0.09 6.36 0.29 1.84 253.00 2.29
Loading Dock 0.11 0.00 79 0.11 98 5.00 0.12 6 0.0296 0.97 0.12 4.93 0.32 1.57 123.83 1.31
To Vault 4.01 0.34 79 3.67 98 5.00 3.91 15 0.0063 5.14 0.76 4.19 0.96 4.02 84.01 0.35
3210-CD-SBUH-Conveyance.xls\ONSITE CONVEYANCE25YR
6/14/2013 4:52 PM
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I V , ; - Replaced Impervious Area = 25,187 sq-ft
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�� Area Draining to Treatment Vault
Q r \ Total = 174,860 sq-ft
epp- .� Impervious Area = 159,905 sq-ft
1� Pervious Area = 14,955 sq-ft
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