norkrigeo.pdf01119/2006 17:31 4258275424 EDM 06-41 .
Associated Earth Sciences, Inc.
11 -® N a
Ldp /
PAGE 02/06
January 19, 2006
Project No. KE05914A crpry
op
Norkri Corporation�-
711.4 212" Street 5E.
Woodinville, Washington 98072
Attention: Mr. Vince Norberg
Subject: Soil Infiltration Ratc and
Infiltration Testing Results
239XX 104'h Avenue West
Edmonds, Washington
JUL Z b 2006
EECE
Reference: Infiltration Testing Results
239XX 104' -Avon e West
Edmonds, WashingtonDecember 29, 29, 2005 v L 2096
��VFLC�P�g�1�1' �
CITY Q5F EDAQ 'OTR.
Dear Mr. Norberg:
This letter presents the results of the subsurface exploration and infiltration testing recently
completed at the above -referenced site and supersedes and replaces our referenced letter. As
requested, ase recommended infiltration rate presented herein is in conformance with the 2005
King ' County Surface Winer Resign .iMfanw.r ung County ' Manual). 'Our -work has been
completed in general accordance with our scope of work letter dated December :12, 2005, nd
in accordance ' with generally accepted geotechnical enginee3rit g practices in effect at the time
of this study.
SITE AND PROJECT CONDITIONS
The subject property consists of a vacant single lot and a 4 -lot short plat located on the =t
side of the street within the 23900 block of 10,e Avenue West in l d.monds, Washington
(Figure 1). - Two homes currently exist on the short plat parcel; an older, single -story home
within the northwest pbftion of the short plat, which is to be demolished, and a two-story
residence, which is to remain within the southeast portion of the short plat, The single lot has
approximately 173 feet of £tentage along 104`h Avenue 'Vilest and occupies appro�ately 0.27
acres. The rectangular -shaped. short plat parcel is situated to the eafst of the single lot and
occupies ars area of appToxi.mAtely 0.85 acres'. Both parcels are relatively flat -lying and at
qn WGISs•,r nra ivI e... 444 e-tr cwze'.
nlfiSfuna 7! f r1Tii11 l4H�SUC. SLf;ig 1Vt! • nRlaarly rapt 7a41�s • rilC�rle 42 o<�"�v1 •rax Y[a
Event 2911111 H" A,;ez Sidle 2. EverOMWA 98201 • Phone 425 7.89.03 7 * h* 425 252-3408
01/19/2006 17.31
4256275424
AES1
PAGE 03/@6
approximately the same elevation as westerly adjacent 104`x' Avenue Nest. It is our
understanding that current playas call for construction of a single-family, wood -frame residence
on die single lot and on each of the three undeveloped lots within the short plat. The purpose
of this sturdy is to evaluate infiltration rates for on-site infiltration of storm water runoff from
the lets to be developed.
SUBSURFACE CONDITION$
In order to evaluate infiltration gates, infiltration testing was conducted within exploration pits
on the single lot and on each of the three lots within the short plat to be developed.. The
locations of the exploration pits are, depict on the Site and Exploration Plan, Figure 2.
Exploration pits El' -1 through EF -4 were initially excavated to a depth of approximately 2 .feet
at which depth infiltration testing was performed.. Immediately after completion of infiltration
testing, the cxplo3ratiou pits were excavated to a depth of approximately 10 feet. Conditions
encountered in the exploration pits were observed and logged by a geombnical engineer from
our firm.
As shown on the attached field logs, approximately 6. to S inches of organic topsoil was
encountered in our explorations. The upper 1 inch of the topsoil encountered within
exploration pit EP -3 included %-inch crushed rock presumably placed to improve the surface
of the driveway.
Native sediments encountered blow the topsoil layer generally consisted of loose (upper, I
foot) to medium dense, moist to very moist, light reddish brown (upper 2 feet) to gray, fine to
coarse sand with gravel and few cobble. We interpret these native sediments to be
representative of Vashon recessional outwash. The Vasbotz recessional outwash consists of
sediments that were deposited by ztteltwater streams that manated from the reteatiwg glacial
ice during the latter portion of the Vashon Stade of the Fraser Glaciation ending approximately
12,500 years ago. The lower density and light reddish brown color observed in the upper
portion of the native stratum is interpreted to be the result of weatheriAg. The Vashon
recessional outwash sediments extended beyond the maximum depth of our site exploration.
Reference is made to the D.B. Booth, B.F. Cox, K.G. Troost, and S.A. Shimel 2004
composite geologic map of the Sno-King Area, University of Washftton, Seattle -Area
Geologic Mapping Project, scale 1:24,000, Our tterpretatlon of the sedbrients awuntered in
our explorations is in general agreement with the regional geologic map.
Hydrology
No ground water seepage was encountered during our exploration. It should. be ;noted that the
depth and/or occurrence of ground water seepage may vary due to such factors as changes in
season„ precipitation, and site use.
2
0111912005 17:31 4258275424 AESI PAGE 04105
INFILTRATION TESTING
It is our undmtanding that current plans call for infiltration of stem water runoff on each of
the four lots to be, developed. Field infiltration testing was conducted in accordance with the
Environmental Protection Agency (EPA) Falling Head Fest procedure. Four infiltration tests
were conducted, cue in etch of the (bur exploration pits excavated as a part of or,#.ir study. The
locations of the exploration pits in which the infiltration tests were conducted are depicted on
Figure 2.
The EPS. Falling Head Test procedure utilizes a 5 -tach -diameter pipe driven into the soil to a.
depth of approximately b inches_ Two inches of gravel was placed across the surface of the
soil exposed within the bottom of the pipe to prevent soil disturbance. The pipe was them filled
with approximately 12 to 24 inches of water, measured above the ;gavel surface using water
from a hose bib adjacent to 1.00 Avenue West, or an alternate hose bib adjacent to the existing
house in the southeastern portion of the site. The water level was maintained within the pipe
for at least I hour at each of the test locations. According to the EPA Falling Head Test
procedure: In sandy soils mala liule or no clay, soaking is not necessary. ff cater,falung the
lode twice with 12 inches of water, the water seeps completely amV in less than 10 minutes,
the fulling head percolation test can proceed immediately. " In order to determine the need for
further soaking of on-site soils, the pipe was filled with at least 12 inches of clear water and
the time for the water to seep completely away was recorded. This was repeated at least 2
times at each infiltration test location. Time recorded for water to seep completely away
ranged from approximately 2.9 to 3,0 minutes. Eased oh this and on the sandy nature of the
soil encountered on the site, infiltration testing commenced nced immed €any without further
soaking. In preparation for each infiltration test, the pipe is filled with water to a depth of
6 inches above gravel in the bottom of the pipe, and the time required for the water in the pipe
to fall each, inch for Trach of the b inches is recorded. The infiltration rate for each, of the six
I -inch intervals is then averaged. The test is then repeated two additional times. The results
of the tests are s=m. arized below in Table I -
Table 1
Summary of Innffitraflon'Testing Results
InOltration Test No.
1 (EP -1)
Depth of Test
feet b *
2.0
Iultltratlon )date
limn No. gLches per hour
1 241
2 239
237
2 (EP -2)
2.0
1 246
2 242
3 239
3 (EP -3)
2.0
1 244
2 243
3 241
10
1 241
2 240
3 7.38
* fttt bgs - feet below gmund swface
3
0111612006 17.31 4258275424 AESI PAGE 05106
Following completion of infxltTation testing, the infiitration test locatious were excavated down
to a depth of approximately 10 feet below the existing ground surface to evaluate subsurface
conditions below the depth at which the tem were performed. Sediments eacourltered below
the testins depth consisted of recessional vutwash sand and gravel to the maximum depth
explored. No impervious strata, ground grater seepage, or mottling suggestive of seasonal
saturation was eucoun Wed.
CONCLUSIONS
Due to scale factors and effects of soil saturation during intense or prolonged storm evenu,
infiltration rates achievable on full-scale infiltration facilities typically are less flm those
measured during short-term infiltration testing, such as the EPA Falling Head Test. This is
dire to such factors as ground water mounding, the effect of lateral infiltration during srrWl-
scale testing, and the accumulation of fine -graced sediments. The 2005 King County Manual
recommends Haat correction factors be applied to in-situ infiltrations measurements to account
for uncertainties in testing, depth to the water table or impervious strata, infiltration receptor
geometry, and the potential for long-term clogging due to siltation and bio -buildup. This
method estimates the maximmn design infiltration rate, which must not exceed 20 inches per
hour. Table 2 provides the recommended range of correction factors, as taken from the Ting
County Manual.
Table 2
Correction Factors
Uncertainty in testing method
Partial Correcttism
p,ann8 - 0.5
Facility gemnetry and depth to F en = 015 to 1.0;
aqELb3=i0U5 surface 4°1w + 0.05
Potential for long-term clogging due to 0.7 to 1.0
siltation and bio -build de din on soil texttue
A = Depth from facility bottom to scasOttaf Ngh water tablclimpervkm surface.
W - width of facility.
The total ccmection factor applied is the multiple of the partial cozzecdon factors in Table 2.
The maximum correction factor possible using this mxthcd is 0.0875 (0.5 x 0.25 x 0.7). If the
maximum correcdon factor is applied to the field infiltration rates, the resultant recommended
design infiltlraWn rates range from 20.5 to 21,3 inches per hour. Therefore, we recommend a
design i0iltration rage of 20 inches per hour for the facility.
The reco=ended design, infiltration rage is based on the sail characteristics at the ixffltration
test location and depth. .Although soil conditions ;may vary outside this area, tbcy appeared to
be fairly consistent at the four explorations pit locations evaluated for this study. If stc+rm water
infiltration is to be conducted outside the areas evaluated for this study, we recomu=d that
.19
01/13/2306 17:31 4258275424 AEST PAGE 06/06
Associated Emla Scicnces, JAc. verify that subsurface condition$ at the proPosed infiltration
locations are suitable for the r=omwended infiltration rate.
We appreciate this opportunity to have been of service to you with this project. If you should
have any questions or require additional geoterhniW eUglneeria[g consultation during desiP or
development of this short plat, please do not besitatc to call.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
4;� c WA,�,,
PIRFA 1 pK.
Maire Thornton, PE Jamey S. Battermaan, U, PG, CPESG
Senior Project Engineer Senior Associate
,Anchments. Figure I. Vicinity MAP
Figure 2. Site and Exploration Plan
Exploration Logs
MTnO
KE0 91aA3
PrDJwsslM mD9t4\KMwP
5