CANOD.pdfCity of Edmonds
Critical Area Notice of Decisiol
Applicant:
'Tovyi
Property Owner:
C" 11 VI
Critical Area File
I U U 12 -
Permit Number:
Site Location:
C"') (a -7
Parcel Number:
lr';71 f)i 01 b
Project Description:
'V!
0 Conditional Waiver. No critical area report is required for the project described above.
There will be no alteration of a Critical Area or its required buffer.
The proposal is an allowed activity pursuant to ECDC 23.40.220, 23.50.220, and/or
23.80,040.
The proposal is exempt pursuant to ECDC 23,40.230.
Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and
ff sediment control plan in compliance with ECDC 18.30.
Critical Area Report Required. The proposed project is within a critical area and/or a critical area
buffer and a critical area report is required. A critical area report has been submitted and evaluated
for compliance with the following criteria pursuant to ECDC 23.40,160:
I The proposal minimizes the impact on critical areas in accordance with ECDC 23.40.120,
Mitigation sequencing;
2. The proposal does not pose an unreasonable threat to the public health, safety, or welfare
on or off the development proposal site;
I The proposal is consistent with the general purposes of this title and the public interest;
4. Any alterations permitted to the critical area are mitigated in accordance with ECDC
23.40.110, Mitigation requirements,
5, The proposal protects the critical area functions and values consistent with the best
available science and results in no net loss of critical functions and values; and
6. The proposal is consistent with other applicable regulations and standards.
F -I Unfavorable Critical Area Decision. The proposed project is not exempt or does not adequately
mitigate its impacts on critical areas and/or does not comply with the criteria in ECDC 23.40.160 and
the provisions of the City of Edmonds critical area regulations. See attached findings of
noncompliance.
Favorable Critical Area Decision. The proposed project as described above and as shown on the
attached site plan meets or is exempt from the criteria in ECDC 23.40,160, Review Criteria, and
complies with the applicable provisions of the City of Edmonds critical area regulations. Any
subsequent changes to the proposal shall void this decision pending re -review of the proposal.
E] Conditions, Critical Area specific condition(s) have been applied to the permit number referenced
above. See referenced permit number for specific condition(s).
IZV
A C ' IJI
G4 i VI A '(AZL6 -" 01,
Reviewer Signature Date
Appeals: Any decision to approve, condition, or deny a development proposal or other activity based on the
requirements of critical area regulations may be appealed according to, and as part of, the appeal procedure, if any,
for the permit or approval involved.
Revised 12/16/2010
TI,
& ASSOCIATES91NC.
Enjeed, Magi
JUN 7, 2012
11% WaHacc n ang
8328 7114 1 giolpY
Kemnore, VV'A 98028
Dc�
SUMCCI: acoteChnic'I.1 17,1-19ineering StIl(ly
Clang Reldmwe,
73x3 -- 1731--dsti,cot SW'
L& Job M,). 12-05,S
1WRODIXTION
EuNh
Ave undermand 01 the dev elopli ]ell[ of a ShIgle-ha ails' residence, replacing, We codstin,1;
rcsidence occqqjg the Site, is Planned IN the stjj,�jfct pro -1)" 10CHt0d at dic: above
address in Edmorjcjs, �Ve �Ij, Pet
k cotisaderedt-or �; 4) Undcrsland that onsite. dj.�,po&j I 01,stormivater
l Y01M MqUeSw IM INIVC COIDIACIC(I H geotechnica] 0112
de$, eloranom of, the site, ']-Ile PUrl,,, ""incerinq) SlUd� J4 -"r 1110 PDN)oscd
Of HAS MY is u) characterize die swWrIce (soil
d1u) groundixater) conditions of the S, y,,,, V
Ell ()21 itts i.t9r"rlta mid rwovide geoleclInical er dispos;-fl
stabilizatioij, NcOlDlUendations f'or onshe sun"liwater disposal. �grading, sjope
crt-)skRl luk"On- SUFMC Ond grounIvner drahnige controI, and building,
kmmdwkm support. PAACMcd in alt
Our findings of the StIrf,,
9 k,, C a r),
19213 OWN) Fujacc? tNr-,, , Konniore, Washingtoij 98028
PhOne (426) 483r,9134 - Fax (425) 486-2746
(Lily' 7, 201`?
Chang Residence
L&A Job No. 12-058
Pa e ')
subsurface conditions of the site and gcotechnical, recommendations for the proposed
development
SCOPE OF SERVICES
OUr PrUPOSed scope of SCI-OCCS f0r the geotechnical, engineering study comprises
specifically the l'ollowing:
1, Review geologic and soil conditions at and in the vicinity of the subject project site
based on a published geologic map.
2
Explore subsurface conditions of the site xvith backhoe test pit' to depths where a
firm bearing soil stratum is reached or to the maxinium depth {about I0 feet deep)
capable b,,, the backhoe used in test it excavation. whichexcr is encountered first.
I p
3. Conduct laboratory gradation te,,t,.-, in accortfiance AST,"M D422 on two soil
samples obtained from targeted soil laver's) in test pit,, the result of which will be
Used to determine whether imsite soils are suitable for storinwater disposal by
infiltration. Determine soil type of soil samples in accordance N-Ndth USDA Texture
Triangle and provide rccommendation for design infiltration rate per Washington
State Dcpartment of Ecology 2005 Stormyvater Nlanallel-lient Manual for Western
)k_a,shington for onsite infiltration facilities if sultable soil is found,
4. Perforryi mcessany geotechnical en
gineering anahsis based on soil data obtained
from the test pits.
5
�. Prepare a written report to present Mir findings, conclusions and geotechnical
reconin-lendations.
LIU & ASSOCIATES� INC.
_IIIb 7, 0 1
Chang Residence
L&A Job -Ko, 12-058
Page I
A geotechnical staff from our office was on site to direct the subsurface cxploration
program. and examined the soil and geologic conditions encountered and tuaintaincd logs,
of tile test pits,
SITE CON I'
SURFACE CONDITIONS
The general location of the pr(�ject site is -shown on Plato I ---- Vicinity Map. It is situated
on and near the top of a nioderatel), to steep. Nvesterly declining, hillsidc. As shown oil
Plate 2 Site and Exploration Location Plan, the site is located at the end of 173' Street
SW. bounded by a Y , tial
I joint use dri-ve�vav to its noa-th, and is as b\ residen
development to the :south, east and west- Within the site. the grf)lund vencraill! slopes
down westward gently over niost of its interior (at about 8.5'% grade). ffien moderateIN
steeply down to the west along its central -,,vest boundary (at about 31% gradc), to the
nordiNvest near its northwest corner (as steep as 7-51,'o grade locally) and to the southwest
near its southwest. comer (at about 3 1 % grade).
`file C\istino house
In
on the site was
demolished and the site
cleared
dUl-illY 011f Site
exploration work,
Still standing oil
the site are very large
and taR,
evergreen and
deciduous trees dotling the south side of the site,
GEOLOGIC SETTING
The Geologic Mqg-ail -jh
-Idn-ionds East arid Part of the FArnonds West Quad_rangles.
Washington, b--,- Jarnes P-Minard, published by, t% S. Cicological Survey in 1993, was
referenced for the acoloaie and soil conditions at the rcsidcnc,,-, site. According to this
LILA & ASSOCIATES, INC.
July -1, 2012
Chang Residence
L Job No, 12-058
Page 4
publication, the surficial soils at and in the vieinity of the sujcct residClICC,54C is Mapped
as a Vashon till (Q t} Soil unit underlain by an Advance outwash (Qvwj) soil unit.
The deposits of the Vashon till soil unit were plowed directly under glacial ice during the
p .1-1
most recent -glaciation period as the glacier advanced over an eroded, irregular surface of
older fim-nations and sediments. This soil unit is composed of a inixture ol'unsorted clay,
silt, sand., gravel, and scattered cobbles and boulders. The Va-shon till soil over the top
two to three feet is nornially -weathered to a medium -dense state,, and is moderately
permeable and compressible. The underlying fi-esh till soil, conit'1101-11-Y I-eleffed to ds
"hard pan", is very- dense and weakly cemented. 'rhe fresh till soil possesses a
compressive strength comparable to that of to-w-Dgade concrete and call remain stable 01)
steep natural slopes or man -make cuts for a long period, The fresh till deposits, are
pnictically Impervious to stormwater infiltration, If remained undisturbed and well -
drained, the fresh till soil can provide excellent foundation support to structures with little
settlement expected, This Soil Unit mainly existing on the subject prqjject site and it uphill
vicinity.
11e deposits of the advance outwash soil unit are composed of stratified sand and taravel
with ven, minor arnount of silt and clay, laid down by the melt -water of advancing glacial
is of the last glacier then overriddcri by the stilt advancing glacier. Due to their
goneraliv ,ranl-dear composition, the advance outwash deposits are of moderately high
permeability and drairis fairly well. The advance ouw ash deposits are gencralty derisc to
very dense in their natural_ undisturbed state. Where exposed on slopes -with poor
sge,
vogetation cover and sul�jectecl to storm rLinoff erosion or gri-mridwater cepa the,
L11'j'& ASSOCIATES, INC,
July 7%, 2012
Chang Residence
T,&A Job No, 1 2�058
Page 5
advance outwash soils in the to 21 to 4 lett can be gradually weathered and eroded and
may slouo, i and redeposit to a flatter inclination, Natural slopes or man-madc cuts in
advanceutwash deposits in their native state can reinain stable for an extended period of
time. If remain undisturbed and property drained the underlying fresh advance outw ash
soil can provide good foundation stipport. Nvitli little settlement e,\pected for light to
nioderateiv heavy smictures. This soil unit exists riminly under the till deposits and is
likely exposed on the hillside Mom, the subject projJect site.
SOIL CONDITION
Subsurface conditions of the sulliect plat site were explored Avith four test pits. These. test
pits were excavated on June 20.4 2012, ��,ith a rubber tired backhoe, to depths from 9.0 to
11,0 feet. The approxiniate locations of the test pits are shown on Plate 2 - Site and
Exploration Location Plan. The test pits were located with cither at tape measure or by
visual reference to existing
topographic features in the field and oil, the topographic
onl
should their locatioY -ate to the measuring
survey map, and ns ould be considered % accui
method used,
A geotechnical engineer from our office was present. during subsurfticQ exploration.. who
exannined the soil and geologic conditions encountered and completed logs of test bits,
Soil sarnples obtained from tact) soil Ij1v(.-r in the test pits were visuall), classified in
goneral accordance \,�,ith United Soil Classiticatioll Systcjn, a copy of which is presented
on Plate 3. Detailed descriptions of soil layers oncountcred during site exploration are
presented in test pit logs on Plates 4 and 51
LIU & ASSOCIATE S. INC.
J u I -, � 7, 2) 0 12)
Cham, lZesides ce
L&A Job No, 12-058
Page 6
-1 fie test pits encountered a layer of loose organic topsoil, from 12 to 18 inches thick,
mantling the site. The topsoil is undcriain by a laver (if weathered soil of light -brown if.)
tan, medium-cicnse, silty fine, sand with a trace to some gravel,, from 1.6 to 4,5 feet thick,
Underlying this iveathered soil to the depth explored is a fight -grade., fresh till deposit of
very dense, vveak-ly cemented, gravelly, silty, line sand. about I. to 3.S feel thick. This
till deposit is underlain to the depths explored by a gray fi-esh advance outwash deposit of
densc, clean to slightly silty, fine to medium Sand with as trace to son-te gravel.
GROUNDWATER CONDITION
Groundwater was not encountered by any of the four test pit excavated on the su�ject
prqject site. Tlic very-derise. weakly-cernented, J`resh till deposit underlying the site at
shallow depth is ofextremel� low perjjjeabilit; and would perch stortriwatcr infiltrating,
into the mcwe permeable star ficial snails. The arnount of and the depth to this near -surface
perched ground -water may fluctuate seasonally depending oil precipitation. vegetation
cover. Site Utili7atioii,, etc. This perched ground may accul.milate and rise in thc,�",-ct
winter nionths and dry , LIP in the dry summer months.
GEOLOGIC HAZARDS AND MITIGATION
Erosion Hazard
The surficial topsoil and ��,cathered soilare of low res stance against erosion, while the
underlying very -dense fresh till and dense advance oumash deposits are cif ri-toderately-
I
high to higli resistance against a
inst crosion. There is a re -tote cliance that erosion maN, occur
in the weaker surficial soils over the steeper ,jrezjs of the site if it, is devoid of vegetation
cover and overly saturatedProgressive erosion can lead to shallow. shirt- ?lie as udflows
JLIU & ASSOCIATES, INC.
July 7. 2012
Chang Residence
T,&A Job No. 12-059
Page 7
in the steeper at -ca. To mitigate .such erosion hazard, vegetation outside of construction
limits should be preserved and maintained. Unpaved exposed finished ground within the
site, resulted from construction activities Should be re -seeded and re -vegetated as soon a',s
possible, Concentrated storniNvater should not be discharged uncontrolled onto the
ground Nvithin the site or the adlacent slopes, Stormwater over iniperViOUS SllrfilceS, SUCK
as roofs, and paved drive\�,ay. should be captured by an underground drain line system
connected to roof downspouts or by catch basins installed in paved drive-�-vay, Water
collected by these drain line systems shauld be tightlined to discharge into a storm sewer
or suitable stott-n-water disposal facilities, such as infiltration. trenches,
Land -slide Hazard
The site is generall\, underlain at shailow depth by very -dense till and dense advance
outwash deposits, These soils are ot- high to very -high shear Strengt7th and have high
resistance against slope failure. Therefore., as lcyng as the site is pr perk drained, the
potential for deep-seatcd slides to ocCUY on the site should be minimal.
Seismic Hazard
The Puget Sound region is in an active scisinic zone. 'rhe site is underlain at
depth by very-ki-ise till and dense a& -at ce outwash deposits of high to very -high shear
stretiq -id.slides, it r:
,th, Therefore, the potential for seisinic hazards, such. as ]at - , liquef ctio 1,
lateral soil spreading, to occur oil the Site ShOUld be minimal if the erosion mitigation,
drainage control, site stabilization measures recommended in this report are fully
implemented, The proposed residences- hoNvever. should be designed fo ismic f
_r sel orces
induced by stroma earthquakes, Based on the sol conditions encountered by the test pits.
LIU & ASSOCIATES, INC.
Jttiv 71. 2012
Chang Residence
UA Job No. 12-059
Pape 9
it is our opinion dint Scist-sic U'se Caroup I and Site Class D ShOUld be used in the scisnijc
design of the proposed residences in accordance xvith the 2009 lritt=ttional Building
C
Code (113C).
CONCLUSION AND RECOINNEANENDATIONS
GENERAL
The site is underlain at shaflo�v depth by very -dense till anti dense advance oumvash
deposits. The proposed ne-Nv residence ma�l be supported on footing JOUndations poured
on or into these cotripetent soils, Biiscd on the soil data obtained from the test pits
excavated on the site, infiltration trenches inay be constructed near the southwest corner
ot'the site to dispose storinwater onsite,
TEMPORARY DRAINAGE AND EROSION CONTROL
Ilre onsite surficial topsoil and weathered soil contain a higji percentage of fines which
are sensitive to moisture and cart be easily disturbed by construction trafflic, A layer of
clean, 2 -to -4 -inch quarti, spalls should be placed over areas of frequent traffic, such as the
entrance to the site, as required, to protect the siubgrade soils from disturbance by
construction iralfic.
A silt fence should be installed along the doviil-iill side of construction area: to i-ninimize
transport ol'sedinietit onto neighboring properties or the streets, The bottom of the filter
t"
cloth. of the silt fences sliould be anchored in a trench filled with onsite soil,
LIU & ASSOCIATES, INC.
July 7, 2012
Chang Residence
L&AJob No12-059
J�Iaue 9
t--
Ditches or interceptor trench drains should be installed around the construction areas, as
reClUired, to intercept and drain away stort-ja ninoff and near -surface grountiNvater seepage.
Water captured by such ditches or interceptor trench drains should be discharged into a
nearby storn-i inlet or dispersed through perforated PVC dispersion pipes onto well -
vegetated areas '��--Ithin the site. The dispersion pipes should sufficiently long and set
h0ri7ontal such that water flowing out ol'the pipes would be at -a 1mv veJocily and spread
over a large area tis fret cause erosion pr(�bleyjj. 'j'he storm inlet, ifinto %,vhicl) stomiNvater
is to be discharged., should be covered with a non-wo-ven filter I-abric sock to prevent
sediment from entering the sterni sewer system. The filter sock should be clealled
frequently
equently during construction to prevent cloggingand should be removed after
Z71'
corripletion of construction,
Spoil soils shoold be hauled offol'the site as soon as possible, Spoil soils and imported
structural f g und
ill material to be stored on site should be located in arras where the ro
SUrfiICC is no steeper than 15% gradc. and should be covered with plastic tarps; securely
Nvei-, C7 -is
1_p11ted down with sandbags, as required. for protection agaii st erosion.
SITE PREPARATION AND GENERAL GRADING
Vegetation within construction limits should be cleared and grubbed, Topsoil, unsuitable
Z'
soil in the root zone and loose w-eathered soils should be cornpletelY stripped within
buildins.o pad of the residences and in areas subject to traffic and stnictural load. The
exposed soils should be compacted to a non-y'ItIding state. as required, with a vibraton7
cortipactor and proor-rolled xvith a piece ol'heavy earthwork equipment where possible.
LIQ: & ASSOCIATES, INC.
July 7, 2012
Chang Residence
L&A Job No, 12-0 8
Page 10
EXCAVATION AND FILL SLOPES
Under no circumstance should excavation slopes be steeper than the limits specified by
local, state and federal safety rcgggulatlons if -workers have to perform construction work in
excavated areas. Unsupported temporary cuts greater than 4 feet in height Should be no
steeper than 1H:lV in surficial topsoil and -,keathercd Soil,,, of Sillyline sand and no
steeper than I/M: IV in undcrk inn vera -dense till and dense advance outwash soils with
an overall depth of crit no more than 15 feet. Perinanem, cut banks should be no
than 2-1/414:1V in topsoil and weathered soil, and no steeper than 1-11211:1V in
underlying till and advance outwash deposits \vith an overall depth of cut no more than 15
feet, The soil units and the stabilitAr of cut slopes should be observed and verified by a
,geotechnical engineer during, excavation.
Permanent fill embankments required to support Structural load should be constructed
Nvith compacted stnictural till placed over proof -rolled, undisturbed. vcii.-dense till and
dense advance outwash deposits after the unsuitable surficial soils are stripped. Fill
embankments placed over areas steeper than 15% grade should be Structurally supported,
Sloping ground steeper than 15��' grade should be benched with vertical steps not
e -recoding 4 fleet tall after stripping of the surticial unsuitable soils and prior to
constructing permanent fill embankment. The siope of permanent fill embanlancrits
should be no steeper than 2414HAV. Upon completion. the sloping face of penilancrit
fill embankments should be thoroughly compacted to a non-vielding state with a hoe -
pack,
LR1 & ASSOCIATES, INC.
Jtilv 7, 2012
'hang 'Residence
L&A Job o.12-058
Page II
The above recornmended cut and fill slopes are under the assumption that groundwater
seepage would not be encountered during construction. If ground -water is encOUTItered,
Z:7 t7
the construction work should be ininiediatelv halted and the slope stabilltv, re-evaluated,
The slopes may have to be flattened and other ii-wasures taken to stabilize the slope.,,,.
Stormwater should not be allowed to flow uncontrolled over cut and fill slopcs
Pernianent cut slopes or fill ciribankments should be seeded and vegetated as soon as
possible for erosion protection and long-tcri-n stabiliq', and should be covered Nvith clear
plastic, sheets., as required. to protect them fi-om erosion until the vegetation is fully
established,
STRUCTURAL FILL
Structural fill is the, fill thilt SPP arts structural or traffic load. Structural fill should
consist of clean granular soils free of organic and other deleterious substances and with
particles not larger than three inches. Structural fill should have as moisture content
Nvithin one percent of its optimum moisture content at the time of placerrient. The
optimurn moisture content is the water content in the soils that enable the soils tci be
compacted to the highest dry density for a given compaction eff'ort.
Onsite soils meeting the above requireirients mai, , be used as structural fill. Imported
material tai be used as sti-LiCtUral fill should be cleati, free -draining,, granular soils
containitig iso more than 5 percent by weight finer than the No. 200 sieve based 011, the
fraction of the material passing No, 4 sieve,, and should have individual particles not
laraer than four inches,
LIU & ASSOCIATES, INC.
J,ulv 7- 20121
Chang Residence
L&A Job No, 12-058
Page I ?
The ground over which structural fill is to be placed should be prepared in accordance
With recommendations in the `J 1'E PRETAR-ATION AND GENERA -L GRA -DING and
EXCAVATICYNT ANT) M.T., SLOPES sections of this report. Structural fill should be
constructed in lifts no more than 10 inches thick in its loose state. with each lift
compacted toy a minimum percentage of the MUXin-Wrn dry density determined by AST -N!
D 15 157 (Modified Proctor Method) as follows;
Applicalion 11/16 of Maxin-airn DrN, Density_
Within b-uildingpads and under foundations 95"'
or top 3 fm and 90% below
Roadw,ay/drivs
eway ubgrade 95% R
Retaining wall backfill 92(Mo
titilitv trench backfill 95% for top 4 fett and 90,,, below
BL4LDING FOUNDATIONS
Conventional footing foundationsinay he used to suppoi-t the proposed residence, The
footing foundations should be coristructcd on or into the underlying very -dense till and/or
dense advance outwash deposit, Water should not be allowed Lo accumulate in excavated
rbotin!-rl, trenches. Disturbed soils in footing trenches should be completely rernoved doNvn
to UndiStLffbled. native, fresh till soils prior to pouring concrete for the footings.
If the above reconmictidations are implemented and obsen cd, our rcconijaiended dcsign
criteria for footing foundations are as folloxvs
LIU & ASSOCIATES, INC.
July 7- 2012
Chang Residence
L&A Job No. 12-058
Page
-�p
The allovvablc . soil bearing pressure for design of footing foundations,, including
dead and live loads, shoutd be no t1reater than 3.000 fist if constructed on or into
[Ile underlying veiA-dense till and/or dense advance otitwash soil.. and should not
exceed 2,500 psf Id constructed on structural Fill built on the -,e competent basal
soil, The footing bearing soil should be verified onsite by a geoteelinical ellginocr
after the looting trenche4 are excavated and before the footings poured.
e, The n-iininrurn depth to bottom of perimeter footings beloNv actiacent final exterior
grade should be tic., less than 19 inches. 'llie minirnurn depth to bottom of the
interior footings beloxv top of floor slab should be no less than 12 inches,
The rnininium Nvidth should be no less than 16 inches for continuous footings, and
no less than 1-4 inches for individual footings, except those fo()tin"-s SUPPOrtinE:'�
jight-�veigtht decks or porches.
A one-third increase in the above recommended allowable soil bearingpressure nia-y' be
Z7 1
kised when considerina short-terml. tran itory, -wind or seismic loads. For looting
foinidations designed and constructed per reconimendations above, we estimate that the
nia-.\irnurn total post -construction settlement of the building should be 3/4 inch or legs; and
the differential settlement across building width should be 1/2 inch or less.
Lateral loads on the proposed residence ma�r be resisted by the friction force between the
foundations and the subgrade soils or the passive earth pressure acting on the below -grade
portion of the foundations, For the latter, the foundations must be poured "neat" against
undisturbed soils or backfilled �vith a clean, free - draining, compacted structural fill. We
recommend that an equivalent fluid density (EFF) of 300 pef (pounds per cubic foot) for
theThe above passive pressure
. passive earth pressure be used for lateral resistance.
LIQ? & ASSOCIATES, INC.
Jath,- '7,2012
Charge Residency
i.
... A .Job No. 112,05
Page 1
assumes that the backfill is level. or inclines upward aAvay from the foundations for as
horizontal distance at least 1.5 times the depth of the foundations below the final raadc.
A coefficient of friction of 0.55 beorN een the foundations and the strbgrade soils may be
used. The above recommended sail parameters are unfactored values, and to proper factor
of safety should he used in calculating the resisting lorces against lateral loads on the
proposed residence.
SLAB -ON -GRADE FLOORS
Slab-on—rade floors, if used for the residence. should be placed cin firin subgrarde sails
frrQ. ared as outlined in the STTE PREPARATION AND tai':
Ally 7,2012
Chang Residence
L&A Job No. 12-058
'acne Is
with excessive flexing or pumping should be over-excavaied and re-conipacted or
replaced Nv,'ith a structural fill or crushed rock, placed and compacted in accordance with
the recommendations provided in the STRUCTURAL FTI T, section ail` this report.
We recommend that to layer of compacted.. 7/8 -inch crushed rock base (CRB)E be placed
for the driveway. This crushed rock base should be at least 4 inches thick. This crushed
rocL base should be overlain witli a 2-incli a
splialt treated base (ATB) topped by a 2-inch-
th,ick, Class B asphalt concrete (AG) surflicial c)ur-.-,O-
INFILTRATION TRENCHES
General
A clean. fine to rnediurn scand deposit was encountered at 5,0 feet deep in Test Pit 2,
located near the SOLIthvest corner of the site, which will be capable of supportin-al,
infiltration trenches to dispose stormwater onsjte. Our recoi-nmendations 1'()r the
construction of infiltration trenches is shown Plate 6. Construction of infiltration trenches
should be nionitored by as geoteelinical engincei%
The above-relerenced geologic map shows that lie steep slope west of the sues jest pr(ject
site is composed of dense advance out�vasb sod, This advance outwash soil 'unit is
stand niched by and underlying two Vasbon, till soil units lying uphill and downhill ofthe
steep slope. Therefore, despite arca:3 of locally steep slope hillside below the Subject
pro�ject site should be quite stable and the construction of infiltration trenches in the near
ofthe southwest corner ol'the pri1ject site should have minimal impact on ffie stability of
the hillside below.
LIU & ASSOCIATES, INC.
July 7. 2012)
"hang Residence
I �&A Job Noy 12-058
Page 16
P.-irticle Size Distribution Tests
Two soil saniples: Sample No, I from lest Pit 2 at 6.0 feet deep and Sample No. 2 from
Test Pit 4 at &0 feet deep. were taken to HW A laboratory for Particle Size Distribution
tests to deten-nine the infiltration rates of' the target advance outwash deposit. Soil
Sample I was classified as "poorly graded sand" ivhile Soil Sample 2 was classified as
-silty sand". The report of these tests is presented on Plates A-1 and A-2 in the attached
APPENDIX,
As summarized on Plate A-21, Soil Sample 1 had as clay content of 0,9%, silt content of'
6A% and gra-vel/sand content of 917% and Soil Sample 2 had as clay content of 2.4%7 silt
content of and gravel/sand content. of 718.1`4), According to the UISDA (U.S.
Department of Agricuittire) Texture Triangle chan, shown on Plate A-3 in the attached
Appendix, Suit Sample I can be classified as "sand" v,-hfle Soil Sample 2 as "loarny
sand!"
Design Infiltration Rate for Infiltration Trenches
The StorniNvater INJ mtgeqj�.qt Martual for Western Washington, 2005 Edition. published
by Washhing
gton State Departt-Tient of F_,,cologj,, is used to determine the design infiltration
rate of the tarLyel advance out -wash soil stramm for infiltration trenches to be constructed
for dispose stoirnwater onsite. According to the table of Rccommended Infiltration Rales
Based on USDA Soil Textural Classificafion shmvn on Plate A-4, the estimated short-
tensa infiltration rate Nvould be 8 iph (inches per hour) and the estimated long-ran-rin
infiltration rate with a Correction Factor of 2 v,,ould be 2 iph for Soil Sample 1. and
would be 2 iph and 6.5 iph., respectively, for Soil Sample 2,
LRJ & ASSOCIATES, INC.
Julv 7. 20112
Chang Residence
L&A Job No. 12'-058
Page 17
As shmIn on. Plate A-2, the Dj() size ("the size of 10% passing) is 0,093 inch for Soil
Sample I and 0.016 inch for Soil Sample 21 it) accordance with the -soil particle si7c
distribution test results. According to the table of Alternative Reconlinendcd Infiltration
Rates Based On ASTM Gradation Testing presented on Plate A-5,1 lb'v, interpolation. the
estimated long-term infiltrf.A1011 rate is 1.91 1ph fbr Soil Sainp! I e No, I and 0,85 iph for
Soil Sample 2.
Basod on the test results above, we reconuriend the infiltration trenches be installed in the
vicinity of Test Pit 2, We recommend a design infiltration rate of 1.90 iph be used for the
design of infiltration trenches to be consmicted in the vicinity offest Pit 2)
Infiltration Trench Construction
The trenches should be cut at least 6 inches into the, advance outwash deposits ofclean.
gray. fine to medium sand deposit, To reach this target soil stratum the infiltration
trenches should be excavated at least 5.5 feet deep or more, 'I -he soil unit at bottom of'
infiltration trenches should be verified by as geotechnical engineer.
The infiltration trenches should be set back, at least 5 feet from property lines and 10 feet
frorn nearb-v bifflding foundations, Tho soil unit and trench cut bank stability should be
verified by at gleotechnical engincer during excavation, The trenches .should be cut Nvith
slopes recommended in the hXCAVA:I'ION AND FILL SLOPES section in, this report,
Otherwise, a trench block shOUld be used to prolect workers in the trenches.
The infiltration trenches ShOUld be at least 4 leet. wide. Aie side �%.alls of the trenches
should be lined with a layer of non -woven filter fabric, such as MIRAT1 140NS. The
LIST & ASSOCIATES, INC.
J u I v 7, 210 121
Chang Residence
L&A Job o.12-058
page 18
trenches are then filled with clean washed 3,E`4 to inch gravel or crushed rock to
��,ithin about 10 inches of the finish �,rade. 'llie dispersion pipes should be constructed of
4 -inch rigid PVC pipes and laid level in the bra el or crushed rock filled trenches at about
16 inches below the top of trenches. 'The top of the gravel or crusbcd rock fill should also
be covered with the filter 111 brie liner. -1-he remaining, trenches should then be backfilled
with compacted onsite clean soils. Ilic bra el or crushed rock fill should be placed in
lifts no more than 1.0 inclies thick in loose state, .Kith each lift compacted to a non -
yielding state Nvith a vibrator , mechanical compactor. Stormwater captured over pa-ved.
driveway should be routed into a catch basin equipped with an oil -water separator before
being released into the infiltration trenchels.
ED W-MUMMEAMMIUM
Building Footrint Excavation
T I
Building footprint excavation for the proposed residence. if encountering groundwater
seepage., should have the bottom of excavation sloped and ditches excavated along the
bases cit` grit banks to direct collected groundwater into sump pits frorn which water can
be pumped out. A layer of 2 -inch crushed rock should be placed over footing bearing
subg,rade soils,, as required, to protect the sails from diStUrbance by construction traffic.
This crushed rock base should be built to a few inches above groundwater level. but not
Icss th�an 6 inches thick. The crush rock base should be compacted in 12 -inch lifts to a
tion -yielding state Nvith a vibratory mechanical compactor.
LIU & ASSOCIATES, INC.
July 7. 01
ChMij Ikesiderice
t7
L&A Job No, 12-058
Page 19
Runoff Over Impervious Surfaces
Storm runoff over irriperViOUS -Surfaces, such as roof and paved driveway. should be
collected by underground drain line sv'stenis connected to downspouts and by catcl) basins
installed in paved drive-,xay. Stonnwater thus collected should be tightlined to discharge
into a nearby storm sewer or a suitablc storniiatter disposal facility sys-tern, such as
infiltration trenches.
I
Building Footing Drain
A subdrain system should be installed, around the, perimeter footings of the new
residence. 'I'li -ated. rigid..
,e subdrain should consist of a 4 -int perlbi
drain pipes, laid a few inches below bottom of the perimeter footings of the building, 'The
trench Lind the drain line should have a. sufficient gradient (10,5" ji) ininjinum) to generate
floN,v by gravit.y. The drain fine should be wrapped in a non-N�,�oven filter fabric sock and
conipletely enclosed in clean Nvashed gravel. The remaining trench may be back-filled
with clean onsite soil, Water collected by the perimeter looting subdrain system should
be tightlined. scparately From the roof anti surface stormwater drain lines. to discharge
into a stor'ni sewer or a suitable stormwater disposal facilit-y, such as infiltration trenches.
Surface Drainage
Water should not be allowed to stand in atly -1,rcas where toutings., on -grade -slabs, or
pavement is to be constructed. Finish ground surfaces should be graded to direct surf' ace
rUnuff away from the proposed residence, We recommend the finished ground be sloped
at as gradient of 3 percent inininiurn for as distance of at least TO feet away from the
buildings, except in the areas to be paved.
L & ASSOCIATES., INC,
July 7. 201')
Chang Residence
L&A Job No. 1 2-05cg
Page 20
Sufficient number of'cleanOUts at strategic locations should be provided for underground
drain lines. The underground drain lines should be cleaned and maintained periodically=
to preient :loggii
n&
RISK EVALUATION STATEMENT
The sut�jcct site is underlain at shalloNv depth by very -dense till and dense advance
outwash deposits, These basal soils are of high. shear strength and the Site ShOUld be quite
st.-able. Proper and adequate erosion mitieation and surtace and groundwater drainagQ
control are k-ev to maintain site stabihiv during and after completion of construction, It is
our opinion that if the reconmiendations in, this report are fully implenicrited and observed
during construction and following the completion of eoflStt-Wion, the areas disturbed will
be able to remain stable® and will not increase the potential for soil movement. In our
opinion, the risk for darnages to the proposed development and from the development to
ad acent properties from soil, instability should be minimal.
LIMITATIONS
This report lias been prepared for the specific application to this pr(ject for the exclusive
use by Dr. Wallace Chang and his associates, representatives.. con5ultants and contractors.
We reconunend that this rQpc)rt,. in its entirety, be included in the prt1ject contract
documents for the inforniation of the prospective contractors for their estimating and
1�
bidding purposes and for compliance with the recommendations in this report during
construction. The conclusions and interpretations inthis report however. should not be
LIU & ASSOCIATES, IN -C.
July 7.201`1
Chang Residence
C�
1,&,A Job No, 11-058
Page 21
construed as at \varranty of the subsurfiace conditions. The scope of this study dots not
include services related to construction safety precautions and our recommendations are
not intended to direct the contractor's n)c-thods. techniques, sequences or procedures-,
except as specifically described in this repoil for design considerations. flie
construction of the subject prqjeci shoUld be monitored and inspected by a geotechnical
engineer.
Our reconu-nendations and conclusions are based on the geologic and soil conditions
encountered in the test pigs. and our c,periencc and engineering udanent. The
cone] u1sions and rccomniendations are professional opinions derived in a mariner
consistent with the level of care and skill ordinarily exercised by other member's of the
profession currently practicino, under shnilar conditions in this area. No warrant-%,,.
expressed or implicd. is made.
The actual subsurface conditions of the site may vary from those encountered by the test
p i The nature and extent of such variations inay not becorne evident until construction
starts. Tf variations appear then,, -wc should be retained to re-evaluate the
reconurrendations of this report. and to verify or niodit"y then) in writing prior to
proceeding further with the construction of the proposed devc1opritent,
RIBMUM
We are pleased to be of service to you on this projtct, Please feel 1'iee to contact US if'VOU
have any questions reg-arding this report or need furtber consultation.
- t: P
L I U & ASSOCIATES, INC.
July 7. 201?
Chang Residence
Paae 22
Six plates and Appendix attached
Yours wry truty.
LIU (R, ASSOCIATES. INC.
JS. (Julian) Liu, Ph.D., PE.
ConSUIting (Ijeotechnical EnLdneer
LRT & ASSOCIATES, INC.
RD,
16 T
Ql- I S
-D
�N
pl-.
ii 17 CITH
su 72 L
ND ST n7l-
•
171 t4i j i
V ST
$'gaW
MNI
FifJ-,--
41 U)
ST U
1 STH ST
Lsw
3745ch
CQ
T I hn,
1sw
PROJECT
r� v6p�l 76Tfl
SITE
Ta
1AIL, LST
4 kl� 178
PLL�
�-T sw - MTI
-F —
15,F FL
I pi ST
— — -- ! 1$%-lT I L W
r
, pi.
R I
lei 11 r gi
f ice_ 18 0 ST —2
r
V ZT
L I a:tu J- SW : WLSr l
18 1;31
bl�--Pll
ZiMl Who
n
-,t &Tq
PL
t,7
XIN ;31
W
t
N w
vl FL
0', g
-a
lo If - ,
X'il- °l / I , -, L I i c
188TH
FS
LN
fl 185TH PL
PL SH'is
, &
T `4, 18 qj� fl ST, sq
Jjg I ji
v!Sf PL SST
lqls-, I W' - L
ph --1 62
N Sq,
1ST STrd az,
T
1, T4 FL a, 192NED PL
vy
'TUB L 'q
< i5l-r'
as
-'o3 0 PL Fd
---930 ST IL
C>
a,
I q4Tq I -T SW
714
V
Hr.c GIr
9
196TH
�d COMO
�W, PL W
NJ_ SW --"(FILPERT RD),
ISS-TH ST SVsu�
Sr I. bg fan aT W
WO),
$TO ,
T—T
—sw
Ty
SaRf I D
202ND -ST
An AKK
'20LO , —
,5 2Qtt 201ST
-----FL —SIW
-20
nam 'T sw
M.
ST, S�i
04-fH
iT
I'ST Sw.
LITJ & ASSOCIATES. INC.
-- ---------- ----
Gotechnical �Agin e-armg Engmemering Geology , Earm Science
VICINITY MAP
CHANG RESIDENCE
73XX - 173RD STREET SW
EDMONDS, WASHINGTON
12-058 1 DATE 6/2012012
RNER)
Ld
L— — — — — — — — — — — —
73rd AvENUE W.
N C0-20'45:* W
150.32'
V.
— — — — — — — — — —
Ull" & ASSOCIATES. INC.
Geote(;hn�-W Engir,�vinq - Engineering Earth Sffi,;eflc
AND EXPLORATION LOCATION PLAN
CHANG RESIDENCE
73XX - 173RD STREET SW
EDMONDS, WASHINGTON
u
. 4,1,6
Ld
L— — — — — — — — — — — —
73rd AvENUE W.
N C0-20'45:* W
150.32'
V.
— — — — — — — — — —
Ull" & ASSOCIATES. INC.
Geote(;hn�-W Engir,�vinq - Engineering Earth Sffi,;eflc
AND EXPLORATION LOCATION PLAN
CHANG RESIDENCE
73XX - 173RD STREET SW
EDMONDS, WASHINGTON
u
MINIFIED OIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GRAVEL ;LEA's
Ofw°ik(��, ;i1#EL
OF
GRAINED„Ft RAVEL
kRETNEE O"
FINES
GROUP GROUP NAME
E
M
w I '0NELI _'RADED GRAVEL, *,`_ TO COARSE GRAVEL
I
te" ;lRLY PA'DED RAJE'�
`MLY`5AVEL
, Lz{
GC CLAYEYGPSAND
CLEAN
S � %'i,' Os'ELL GRAEEC SAND, s -,r;_ TO CCARSE SAND
AN
P rJOR.L'Y G=EU 'A ID
PACIRE THAN t.- ,i yt,_IRr THAN 50% OF
i`.AIN ? ON THE GO,ARSI: } Ri .1IONANI 'Alla HSM
SILTY S N'D
MCI 200 SIEVE ,o
FINESb
L, .r E'' ;AND
INE- SILT AND LAY � INORGANICfVlL
s
IL
SILT
_ -
N
L 'C LAY
SOILS LENS THAN 50%, G
�'N
C ,< -
} `7 f'. _, .Ed . '���L?. ftiSR�,.N f'�4w EYt,
f THAN; C;' ' AND J L
mH SILT OF HIGH ELA� Ty ELASTIC SILT
?A,SGJNG , =N THEt _
A' HIGH PLASTICITY, FAT CLAY
CH J
}
,'.
W,
r t
§
SILT,
HIGHLY ORGANIC SOILS
HI r
PT € EAT AND OT HES H,i: RG _ 30i'_S
NOTES:
SOIL N401
# 1EL_ ",ASSFICAT (:tJ IS B.A9-- D • , Vi: U ,'-r�xt:�d�dr, t; t•!
CRY ABSENCE OF MO`STURE. DLJ 70
.5OII, IIl 37.NFRAL >ACCOROID ANCE a�P 7"YtI-A024K,,
THE TOIJIC
_S?, - . €,Y M,01ST _ TRACE M _ , _ , N07 DUSTY
SOIL R O . ESTS IS Eye,5ED
._
N AST I✓215f'` a
t,rc3}� , DAPA , BUT H 'Iv W __',PYATr R
EE Y 'v�0i5T ER` !DAMP, ,1 =T IHc FELT Tri T 1-iE TijUCH
3. EtC,�.i.., .`+. `� I Es.ii,u `J,; S1.'il_ L'ENv! -T `t� �.. >.r.E I`8 ..,:'., T E.r'-�c t' �`.'�;.
EASED CIN INTEPPR EITPTION OF BLON-COUNT CzATAVIS€
;� 'v%'ET VISIBLE FREE NATES OR SATURATE i.
APEA:SANCEOF rte:"mS,,-.NtiOR TEST DATA,
SGIL c .,ix,�
uSL�vLe 'i �_:1!- I� i�rlT�31'�EQ FROM ESL= ��
t'"JATE� Ti%L E
ASSOCIATES, INC.]1L
(L I a ATI �°STEIM
-.._._E1 ulWerl ,� Ge'j i _ I vte3uf=Et;.__
_..
1_
i" LJi"t i L.. -
INFILTRATION TRENCH TYPICAL SECTION
LK & ASSOCIATES—INC. CHANG RESIDENCE
73XX - 173RD STREET SW
G.aotochri'Mi Engin eenn-0 Engineering Gedrigy - E2rth .8der-ca- EDMONDS, WASHINGTON
—JOB tN40, 12-058 1 UATE 71212012 PLATE,
APPENDIX
Grain Size Distribution Test Report
Chang Residertee
7 3 xx — 173)"d Street SW
Edmonds, Washington
LIU & ASSOCIATES. INC.
0
M.
rp
Zl
-4-
0
LO
LL
00
LIJ
Lii
0
M.
rp
i
co�,ice
i
i
R
Textural Triangle U.S.D.A.
P*rcofo %SPA
Shaded area is, appj'Ecahk. Ror dc-siun of infilt'ratic,,m BINAPs,
Figure 3.27 USDA Textural Triangle
SOUrce: to Department of Agricultig,c
3-74 V`WuRl�' III — Hydrologic Analyqjs and Flow Control BAfps� Fobnjary 2005
Ica
hol'11090neOLIS SORS. These rates not consider the efforts of site
variability anal long-term clogginvi title. to F,11tation and bioniass buildup iii
the infiltration facility.
Table 17 — Recommended Infiltration Rates
based on USDA Soil Textural Classification.
Fstininted Long-
`Short-Tcrm Term (Design)
infiltratioll Correction Infiltration R2tc
Rate (in_fhr'jl Factor, CF (in A 0
Cleo l sa;idy uavels and 20 2 !0"
g"- Vel ly sand � , (hc�, Vi[)% of
thc� total _Oil sam, plv is
rf,�tah;d in thr #10 sieve)
4 2.
Lowey Smd 2 4
Sandy Loaln 0%, 2 5
Lcem 0_5 4 0
'I'roin
31 Not rec4mimendeki 16F
4-4 Rdcr to SSC -4 and SW -6 lbr Ireatinewacciciptability (;Titc.fla
kaset,l on experience with long-term full-scale infiltration pond
performance, Ec�olog`s Technical Advisor), Committee (TAC')
recommends that the sh ort -term infiltration rates be reduced as; shown in
Table, 3.7, dividing by a correction factor of 2 to 4, depending on tile Soil
textural classificatlon, 'niecorrection factors provided in Table 17
represent an average degree of lotig-term facility maintenance, TSS
reduction through pretreatment, and site variability in the subsurface
conditions, These oonditions might include deposits of ancient landslide
debris, buried stream channels, lateral grain -size variability, and other
factors that affect homogeneiq).
These correction factors could be reduced, subjeet to the approval of thl�
local jurisdiction, under the. followingy conditions:
FQtr sites %itfl little soil variability,
Where there will bei
.i high degr:ee of long -ter in facility rnaintenani;o,
I C-1
Where specific, reliable pretreatment' is employed to reduce TSS
entering the infiltration facility
........ ....
3-76 Volunif,, 1/1 Hydrologic Analysis ar)(f Flow C-OnItz)l Bjvp� Fobruary 2006
LIP"
Correction factors hil,her than thti-se provided in Table 3,7 should b�
considered for SiM960ns wherc long-term maintenance will be difficult to
imPlenlent, where little or no pretreatment is antieipated-, or where, site
COnditions are higghly vari -able or uncertain. These situations require, the
use of best professional judgment by the site engineer and the approval of
the local jurisdiction. An Operation and Maintenance plan arfd a financial
bonding plan may be required by the local jurisdiction-
ities
As an alternative to Table 3.7, recent studies by IAassmann and Butchart
(2000) were used to develop the correlation provided inTable -!,,8, These
studies compare infiltration measurements trtmi 15WI-scale infiltration
facilities to soil gradation data developed using the ASTM proeedure
(ASTIM D422). The primary source of the data used by Massmann and
Butchart ivas froln Wiltsie (1.998), who included limited infiltration
studies only carr `f County sites, However, Massmarfri and BUtchart
also included limited data front King and Clark County sites in flicir
analysis, This table proviks recommended long-term infiltration rates
that have been correlated to soil gradation parameters using the MTM
soil gradation procedure,
Tabic 3can be Used to estimate long-terin design infiltration rates
directly rrOrn Soil gradatiO111 (713W, SUbjJect to flie approval of thc local
jurisdiction. As is true ol"fable 3.7, the long-term rates provided in Table
3.8 represent average conditions regarding site variability, the degree of
long-term maintenance and pretreatment for TSS control. The long-term
infiltration rates in Table 3.9 may need to be decreased if the site is higfjl;v
variable, or if maintenance and influent characteristics are not well
controlled, The data that forms the basis for Table 3.8 was from soils that
would be classified as sands or sandy -gravek No data Nvas available for
finer soils at the tinie the table was developed. Therefore, Table 3.8 should
'lot be used for soils with a djo size (10% passing the size listed) less than
0.05 film (U.S. Standard Sieve),
* Rcfcf W 5 fLrA SSC_x, far critaL
Febmary 2m
Volar"a fil — 14YdfOlO_qk, Analysis and Flow Cor?trol 13MP,- 3-77
■ NO OWHS`*M '),IN -P33, HSIVIOHCNS cV
SCINOAOl NO
_NW, "N/Z'I '9 NOUOA-�/!,,,AS 't,/WN NJ
;M JA V G&fZ 9OfZ I —30N.3GIS3�V
S 2� -'i C]NV
NVId ONIGW89
T -
z
0
� Z
z
Az
E
Q
L MR
g
P. All, >
ti o
K
K�
A
z
nM
gag
<
M 3hNiAv Okt
-7
V. 1
z IT
A
\5E
T
A�
2e
7
4
10
tiT
R
-�7
A
-2�
M,
R,
zz
0
RE
&
M-1
H�pk
H
N
Egn
pq
H�-
-I.US-
,S5
sa
7
Nb
8,0 gE
ol
E- M
'R i, - H - a H P? 9 g. 10
Al