Correspondence MS 7-02. - COI 0
T.......12_9141 REC IVED
14845 SW 100th APR ` 202)
i Storm Drainage Report CITY OF TIGARD
/ for BUILDING DIVISION
theta- Addition to existing
NARRATIVE:
This property is a developed site with an existing house,taking access on SW 100th and sloping towards
the street at less than 20%in the front.SW 100th is paved without curbs and has an asphalt path along
the frontage.A catch basin on the southerly side of the access drive with a 12-inch concrete storm line
flowing south.The existing roof has gutters and rain drains connected to an unknown underground
system.An addition is proposed on the north and west side of the existing house with a calculated roof
area of 1272 SF. No other improvements area proposed.
Clean Water Services has provided a"Sensitive Area Pre-Screening Site Assessment" and determined
this project will not significantly impact the existing or potentially sensitive areas found near the site.
The USDA Web site finds this property to have 11C Cornelius and Kinton Silt barns.This carries a
Hydrologic group C characteristic and is known for low infiltration rates, but site specific testing can
show different results.
Residential additions having new impervious areas greater than 1000 SF are subject to the storm water
requirements of Clean Water Services to which the City of Tigard is a member.
Infiltration test:
A hand dug test pit was used to conduct an open pit infiltration test at the site.The test pit was 47"
deep with organic soils found in the top two inches followed by silt loam to the bottom.After
presoaking the rates was observed at 6 inches per hour. For design purposes a safety factor of 2 was
applied for 3 inches per hour or 20 minutes per inch.
REFERENCE:
The King County Department of Public Works, Hydrographic Program,ver 4.21B
Clean Water Services Stormwater
Keith Abel Residential Design LLC
ASSUMPTION:
Using the 25-year event storm and infiltrate the entire new impervious area into the ground
using a rain garden with 6" of free board, 6" of storage, 18" of growing medium and 3" of
"choker" and 9" of drain rock.Void space medium 0.25, rock 0.4
depth Storage area
1.0 39.2 98
1.0 75.9 98
1.5 133.3 98
STORM OPTIONS:
1—S.C.S.TYPE-1A
2-7-DAY DESIGN STORM
3—STORM DATA FILE
SPECIFY STORM OPTION:
1
S.C.S.TYPE 1-A RAINFALL DISTRIBUTION
ENTER:
FREQ(YEAR),DURATION(HOUR), PRECIP(INCHES)
25,24,3.9
Xxxxxxxxxxxxxxxxxxxxxxx S.C.S.TYPE-1A DISTRIBUTION xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
XXXXXXXXXXXX 25-YEAR 24-HOUR STORM xxxx 3.90"TOTAL PRECIP. Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
ENTER:A(PERV),CN(PERV),A(IMPERV),CN(IMPERV),TC FOR BASIN NO. 1
0.0,86,0.029,98,5
DATA PRINT OUT:
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
.0 .0 86.0 .0 98.0 5.0
PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
.03 7.67 385
ENTER(d:](path]filename[.ext]FOR STORAGE OF COMPUTED HYDROGRAPH
SPECIFY: C-CONTINUE, N-NEWSTORM, P-PRINT, S—STOP
ENTER OPTION
RESERVOIR ROUTING INFLOW/OUTFLOW ROUTINE
SPECIFY (d:][path]filename[.ext) OF ROUTINE DATA)
C:data100
DISPLAY ROUTING DATA(Y or N)
Y
ROUTING DATA:
STAGE (FT) DISCHARGE(CFS) STORAGE(CU-FT) PERN-AREA(SQ-FT)
.00 .00 .0 .0
1.00 .00 39.2 98.0
2.50 .00 75.9 98.0
3.00 .00 133.3 98.0
AVERAGE PERM-RATE: 20.0 MINUTES/INCH
SATURATED PERM-RATE: 20.0 MINUTES/INCH
GROUND STORAGE BEFORE SATURATION: .00 CU-FT/SQ-FT
ENTER [d:][path]filename[.ext] OF COMPUTED HYDROGRAPH:
C:100th
INFLOW/OUTFLOW ANALYSIS:
PEAK-INFLOW(CFS) PEAK-OUTFLOW(CFS) OUTFLOW-VOL(CU-FT)
.03 .00 0
INITIAL-STAGE(FT) TIME-OF-PEAK(HRS) PEAK-STAGE-ELEV(FT)
.00 10.67 2.90
PEAK STORAGE: 120 CU-FT
INFILTRATED VOLUME: 251 CU-FT
ENTER [d] [path] filename [.ext] FOR STORAGE OF COMPUTED HYDROGRAPH
The design was also run through the Presumptive Approach Calculator to verify both water quality and
quantity.This design for total infiltration meets the Clean Water Services requirements for Water
Quality, Hydromodification,and LID as identified in Chapter 4, Design and Construction Standards.Since
the facility is designed for the 25-year event with a safety factor applied it is not anticipated that the
facility would ever overflow. If overflow did occur it would drain directly in the right of way.
Prepared By:
Bruce D.Goldson, PE
,gy Ff
Theta PRO �
April 23, 2021 ite\jt-4o ,
err_ 7120 )
il 1,
drititfP(, 4,j' 18. 9 50
C'F D GO‘-0
EXPIRES: / / /✓J/
SIGNATURE DATE:
I
1
1
1
NEW IMPERVIOUS AREA= 1,272 S.F. /
ADDITION 1
_ 1
T
1
CONNECT TO ROOF DRAW / I 1 --
1 \ / I I
EXISTING HOUSE
\ /
TO REMAIN
\\\
_ I—�
1 t— `-`" —1—12'A1"TRAPPED
— I CAT BASIN
Lj� a WITHI1B"SOW
_r--,-_
I L_I— iJ I
1
re
EXISTING 1
1 AC DRIVEWAY I
1 1
1
RAIN GARDEN T-''1----„, Gamow-
SEE SHEET 2
I 1 1
I BB' - /
1
ITEST PIT m
0 20 40 CATCH BASIN
SW 100TH AVENUE / DITCH
SCALE: 1"=20' �t_� ID < �„
12"O STORM
2021-400 STORM DRAINAGE REPORT
'Z'1--1_ t - a 1 1 G 14845 SW 100th Avenue 1
ENGINEERING - SURVEYING - PLANNING Tigard, Oregon PO Box 1345 503-481-8822 2
Lake Oswego.Oregon 97D35 email: thetaeng@corrx;astnet
/ 20'FREEBOARD /
/ 1T /
/ 14' /
ZONE B
ocko
1 B"SQUARE SPLASH
BLOCK OR 4"ROCK
o j
m
a ZONE A --- z
oN
J
\ f
ZONE B
6"FREEBOARD
3:1 / 6"STORAGE 3:1
18"OF(3-WAY MBO MEDIUM
3"OF 1/4"OPEN GRADED AGGREGATE
9"OF 1 34"-3%a"WASHED DRAIN ROCK
RAIN GARDEN
SCALE: 1 " = 5'
ZONE A PLANTING
115 PER 100 SQ.FT. = 113 @ 1"-0"0.C.
37 CAREX DEWEYANNA,DEWEY SEDGE
37 CAREX DENSA,DENSE SEDGE
39 DESCHAMPSIA CESPITOSA,TUFTED HAIR GRASS
7ONF R PLANING
26 POLYSTICHEM MUNITUM,SWORD FERN
2021-400 STORM DRAINAGE REPORT
Z 1 c 14845 SW 100th Avenue 2
ENGINEERING - SURVEYING - PLANNING Tigard, Oregon
PO Box 1345 503-481-8822 2
Lake Oswego,Oregon 97035 email: thetaeng@comcast.net
A , =p Presumptive Approach Calculator ver. 1.2 Catchment Data
4 ' ;7) Catchment ID: A
Project Name: 100th Date: 04/25/21
Project Address: 14845 SW 100th Permit Number: 0
Tigard, Oregon Run Time 4/24/2021 3:03:4D PM
Designer: Goldson
Company: theta
Drainage Catchment Information
Catchment ID IA
Catchment Area
Impervious Area 1,272 SF
Impervious Area 0.03 ac
Impervious Area Curve Number, CN;mo 98
Time of Concentration, Tc, minutes 5 min.
Site Soils & Infiltration Testing Data
Infiltration Testing Procedure: Open Pit Falling Head
Native Soil Field Tested Infiltration Rate(It„,): 6 in/hr
Bottom of Facility Meets Required Separation From
High Groundwater Per BES SWMM Section 1.4: Yes
Correction Factor Component
CFtast(ranges from 1 to 3) 2
Design Infiltration Rates
Idsgn for Native (lies,/CF,eJ,): 3.00 in/hr
Idso„for Imported Growing Medium: 2.00 in/hr
Execute SBUH
SBUH Results Peak Rate Volume
(cfs) cj,fl
---PR 0.005 66
0.0350 2-yr 0.018 230
0.0300 4- n 5-yr 0.022 283
1 i
0.0250 10-yr 0.026 336
0.0200 ' ‘ 25-yr 0.03 389
,1 0.0150 •
0 0.0100
a: �..
0.0000 ++N++++-4+H4i4
0 0 0
O 0 0 O O O O0 0 O
-0.0050 N N i� v $ s (0 0) O
Time (min.)
Printed: 4/24/2021 3:06 PM
Facility Des Data
r-• Presumptive Approach Calculator ver. 1.2 Catchment ID: A
�,--� Run Time 4/24/2021 3:08.48 PM
Project Name: 100th Catchment ID: A Date: 4/28/2021
Instructions:
1.Identify which Stormwater Hierarchy Category the facility.
2.Select Facility Type.
3.Identify facility shape of surface facility to more accurately estimate surface volume,except for Swaim
and sloped planters that use the PAC Sloped Facility Wodtsheet to enter data.
4.Select type of Moiety configuration.
5.Complete data entry for all highlighted cells. }
Catchment facility will meet Hierarchy Category: 1 ^ r aw i
Goal Summary: Vv{
+Cd�
REM ILTT box below needs to display... A
Ilkrarch>n %N'hlbl Requirement v
wagn
Pnd.. 10.yr(cite disposal)m a
Reduction m
(.+.site infitmoon with a surface inatnmion fa.ii l PASS PARS
Facility Type e Basin °
Fac1IIt . h e ReetanglalSquare Facility Configuration: B p orege D •Ih I PLAN 1tR..—I—I„.eASIN/SWALE
Facility Bottom "' Storage Depth I
Area .� Focally cM D at
Bottom Area t -
;tAAi;3t Jg —__� �'�-�%JI
Side e y ``•, \ \
x •1 GROWING MEDIUM —O lIow
'."�. . dr
w^.. sd<'> .: - •. ROCK I l� Calculation Wdl �� Rock St a IIwwtfi Guide
ectton
Rock eollom Are9 on29 �r
Max.RoCk Star.
DATA FOR ABOVE GRADE STORAGE COMPONENT BELOW GRADE STORAGE BD1 Area
Facility Bottom Area• 08 sf Rock Storage Bottom Area• 268 of <Warning 1 4 SF
Bottom Width= 8.0 ft Rock Storage Depth= 12 In
Facility Side Slope• 3 to 1 Rock Void Ratio= 0.3 1
Storage Depth 1• S In '.
Growing Medium Depth= 18 In
Freeboard Depth= N/A in
Surface Capacity at Depth 1= Se cf Rock Storage Capacity= 77 cf
Infiltration Area at 7S%Depthl= 148 SF
GM Design Infiltration Rate= 2.00 In/hr Native Design Infiltration Rate• 3.00 Inthr
Infiltration Capacity= 0.007 cfs Infiltration Capacity= 0.018 cfs
Overflow
RESULTS Volume
Pollution ldrn PAC
Reduction PASS 0 CF 0% Surf.Cap.Used
0% Rock Cap.Used
10-yr PASS 0 CF 68% Surf.Cap.Used
0y. Rock Cap.Used
FACILITY FACTS
Total Facility Area Including Freeboard= *VALUE!
Sizing Ratio(Total Facility Area/Catchment Area)= ',VALUE!
Printed:4/24/2021 3:10 PM
C1eanWater``Services
SENSITIVE AREA PRE-SCREENING SITE ASSESSMENT
Clean Water Services File Number 21-000795
1. Jurisdiction: Tigard
2. Property Information(example: 1S234A801400) 3. Owner Information
Tax lot ID(s): 2S111 CB02200 Name: Brad and Cassandra Barton
Company:
Address: 14845 SW 100th Ave
OR Site Address: 14845 SW 100th Avenue City,State,Zip: Tigard, OR,97224
City,State,Zip: Tigard,OR,97224 Phone/fax: 503-577-9358
Nearest cross street: Email: cassandra.neumann@gmail.com
4. Applicant Information
4. Development Activity(check all that apply)
IgI Addition to single family residence(rooms,deck,garage) Name: Marianne Wilson Stein
❑ Lot line adjustment 0 Minor land partition Company: LS Panes and Associates
❑ Residential condominium ❑ Commercial condominium Address: 16722 Boones Ferry Road
❑ Residential subdivision 0 Commercial subdivision City,State,Zip: Lake Oswego,OR, 97035
❑ Single lot commercial 0 Multi lot commercial Phone/fax: 360-521-5455
Other Email: marianne@Ispanas.com
6. Will the project involve any off-site work? ❑Yes 0 No 0 Unknown
Location and description of off-site work:
7. Additional comments or information that may be needed to understand your project
This project is an addition to an existing home.
This application does NOT replace Grading and Erosion Control Permits, Connection Permits,Building Permits,Site
Development Permits,DEQ 1200-C Permit or other permits as issued by the Department of Environmental Quality,
Department of State Lands and/or Department of the Army COE. AB required permits and approvals must be obtairt*d and
completed under applicable local,state,and federal law.
By signing this form, the Owner or Owner's authorized agent or representative, acknowledges and agrees that employees of Clean Water
Services have authority to enter the project site at all reasonable times for the purpose of inspecting project site conditions and gathering
information related to the project site. I certify that I am familiar with the information contained in this document,and to the best of my
knowledge and belief,this information is true,complete,and accurate.
Print/type name Marianne Wilson Stein Print/type title Design Manager
Signature ONLINE SUBMITTAL Date 3/11/2021
FOR DISTRICT USE ONLY
O Sensitive areas potentially exist on site or within 200'of the site.THE APPLICANT MUST PERFORM A SITE ASSESSMENT PRIOR TO
ISSUANCE OF A SERVICE PROVIDER LETTER. If Sensitive Areas exist on the site or within 200 feet on adjacent properties,aNatural
Resources Assessment Report may also be required.
❑ Based on review of the submitted materials and best available information sensitive areas do not appear to exist on site or within 2 0'of the
site.This Sensitive Area Pre-Screening Site Assessment does NOT eliminate the need to evaluate and protect water quality sensitive reas if
they are subsequently discovered.This document will serve as your Service Provider Letter as required by Resolution and Order 19- ,Section
3.02.1,as amended by Resolution and Order 19-22.All required permits and approvals must be obtained and completed under a licable
local,State and federal law.
X[ Based on review of the submitted materials and best available information the above referenced project will not significantly impa the
existing or potentially sensitive area(s)found near the site. this Sensitive Area r're-screening site Assessment does NOT eliminate th- need to
evaluate and protect additional water quality sensitive areas if they are subsequently discovered.This document will serve as your S•rvice
Provider Letter as required by Resolution and Order 19-5,Section 3.02.1,as amended by Resolution and Order 19-22.All required ••rmits and
approvals must be obtained and completed under applicable local,state and federal law.
❑ THIS SERVICE PROVIDER LETTER IS NOT VALID UNLESS CWS APPROVED SITE PLAN(S)ARE ATTACHED.
❑ The proposed activity does not meet the definition of development or the lot was platted after 9/9/95 ORS 92.040(2). NO SITE , SESSMENT
OR SERVICE PROVI ER LETTER IS REQUIRED./
�
Reviewed by i� � 4^- Date 3/26/21
Once complete,email to:SPLReview5lcleanwaterservices.org • Fax: (503)681.4439
OR mail to: SPL Review, Clean Water Services,2550 SW Hillsboro Highway,Hillsboro,Oregon 97123
Main Office • 2550 SW Hillsboro Highway • Hillsboro. Oregon 97123 • p: 503.681.3600 f: 503.681,3603 • cleanwaterservices.org
Washington County, Oregon (OR067)
Washington County, Oregon (OR067)
Map Unit Acres Percent of
Symbol Map Unit Name in AOI AOI Pa•
11C Cornelius and 0.4 100.0%
Kinton silt
loams, 7 to 12
percent slopes
Totals for Area of 0.4 100.0%
Interest