HomeMy WebLinkAboutADU Geotech Report 2P
0-0, W.77'7, GEORESOURCES
earth science & geotechnical engineering
5007 Pacific Hwy E., Suite 16 f Fife, WA 98424 E 253.896.1011 1 www.georesources.rocks
Signature Custom Homes
10407 81h Street East
Edgewood, Washington 98372
Attn: Mr. Bill Hines
(253) 606-3228
November 20, 2017
Addendum Report: Geologic Hazards
Assessment
Proposed Single -Family Residence
1715 Morris Avenue South
Renton, Washington
PN: 7222000334
Doc ID: Signature Homes. MorrlsAve.RGA(1)
INTRODUCTION
This Addendum Report summarizes the results of our geologic hazard assessment for the
single family residence to be constructed at 1715 Morris Avenue South in the Renton area of King
County, Washington. We previously prepared an Updated Geotechnical Engineering Report:
Stormwater Feasibility dated March 31, 2017. Review comments by the City of Renton Indicated that
a steep slope and/or coal mine hazard may be present on our within 50 feet of the subject parcel, and
requested a critical areas assessment of these potential hazard to satisfy the City of Renton Critical
Areas Ordinance (RMC 4-3-050). The general location of the site is shown on the attached Site Vicinity
Map, Figure 1.
Our understanding of the project is based on our discussions with you; our previous April 12-
13, 2017 site visits; our more recent November 17, 2017 site visit; our experience In the subject area;
and our understanding of the City of Renton Critical Area Ordinance and development codes. As
stated in or original report, we understand that the proposed development will include the
construction a new single family residence with an additional dwelling until.
The Purpose of our services is to evaluate the surface and subsurface conditions across the
site as a basis for assessing potential geological hazards, The City of Renton is requiring a geotechnical
assessment of this potential hazards and the scope of services for this project will Included the
following:
1. Reviewing the available geologic and geotechnical data for the site area;
2. Visiting the site and performing a site reconnaissance to confirm site features and to assess
the site's soil, groundwater, and slope conditions;
3. Preparing an addendum report per City of Renton RMC 4-3-050,
SlgnatureHomes.MorrisAve.RGA(1).docx
November 20, 2017
page 12
We were provided a verbal authorization for this scope of work by Mr. Mike Clow of Signature
Custom Homes. No subsurface explorations or laboratory testing were completed as part of the scope
for this report
SITE CONDITIONS
Surface Conditions
The site is located in an area of existing residential development in the Renton area of King
County, Washington. According to the King County Assessor website, the parcel is generally rectangular
In shape, measures about 50 feet wide (north to south) by about 160 feet deep (east to west), and
encompasses approximately 8,080 square feet, or 0.18 acres. As stated, the site is undeveloped. The
parcel is bounded by existing residential development on the west, south, and north. The parcel is also
bounded by Morris Avenue South to the east.
The site is situated on top of a localized topographic highlands. In general, the site area slopes
down to the north at about 8 to 10 percent with onsite slopes of about 4 to 5 percent. The parcel to the
northwest of the site has a cut retaining wall near the property corner that is on the order of 6 to 8 feet
exposed height. Total topographic relief on the site is on the order of 4 to 5 feet based on King County
IMap data and as observed in the field. Existing topography obtained from King County IMap and
generally confirmed in the field is shown on Figure 2.
No evidence of slope Instability or soil movement was observed on the slope below the
proposed home site at the time of our April 12-13,2017 site visits. No evidence of standing water, seeps,
or springs was observed on the site.
Site Soils
As stated in our previous report, the USDA Natural Resource Conservation Service (NRCS) Web
Soil Survey maps the site as being underlain by Beausite gravelly sandy loam (BeC) soils. The Beausite
soils are derived from till over residuum from sandstone and are Included in hydrologic soils group C/D.
These soils have a "Moderate" erosion hazard when exposed and are Included in hydrologic soils group
C.
Site Geology
As stated in our previous report, according to the Geologic Map of the Renton Quadrangle, King
County, Washington, by D.R. Mullineaux (1965), the site is in an area underlain by Renton formation jr).
No areas of landslides or landslide debris are mapped on or within the vicinity of the site.
No evidence of deep seated erosion or other active landslide activity was observed at the time
of our site visit. No areas of landslide deposits or mass wasting are noted on the referenced map
within the immediate vicinity of the site.
CRITICAL AREAS RECOMMENDATIONS
Based on the results of our data review, site reconnaissance, and our experience in the area,
It is our opinion that neither a landslide hazard, nor coal mine area exists on or within the vicinity of
the site.
SignatureHomes.MorrisAve.RGA(1).docx
November 20, 2017
page 13
Geologically Hazardous Areas per City of Renton Municipal Code (RMC 4-3.050)
Lands to Which These Regulations Apply and Non-regulated Lands: The following critical
areas are regulated by this Section. Multiple development standards may applyto a site feature based
upon overlapping critical area(s) and/or critical area classifications:
a. Flood hazard areas.
b. Steep slopes (must have a minimum vertical rise of fifteen feet (15)), landslide hazards,
erosion hazards, seismic hazards, and/or coal mine hazards or on sites within fifty feet (50') of steep
slopes, landslide hazards, erosion hazards, seismic hazards, and/or coal mine hazards classified under
RMC 4-3-050G5a which are located on abutting or adjacent sites.
The review comments by the City of Renton on our previous Stormwater Feasibility Letter
dated January 15, 2016 and revised on March 31, 2017, indicate that the site is mapped to be within
50 feet of a steep slope and coal mine hazard areas. Based on our previous April 12 and 13 site visits,
and our more recent November 17, 2017 site visit, and review of published geological literature, we
offer the following comments relating to steep slopes and coal mine hazards.
The City classifies steep slopes per RMC 4.3.050.G,5.a as either a sensitive slope or a protected
slope per the following definitions:
Sensitive Slopes: A hillside, or portion thereof, characterized by; (a) an average slope of
twenty five percent (25%) to less than forty percent (40%) as Identified in the City of
Renton Steep Slope Atlas or in a method approved by the City; or (b) an average slope of
forty percent (40%) or greater with a vertical rise of less than fifteen feet (15') as identified
In the City of Renton Steep Slope Atlas or in a method approved by the City; (c) abutting
an average slope of twenty five percent (25%) to forty percent (40%) as identified in the
City of Renton Steep Slope Atlas or In a method approved by the City. This definition
excludes engineered retaining walls.
Protected Slopes: A hillside, or portion thereof, characterized by an average slope of
forty percent (40%) or greater grade and having a minimum vertical rise of fifteen feet
(151) as Identified In the City of Renton Steep Slope Atlas or in a method approved by the
City.
The subject site is located on top of the south Renton glacial upland area, with the regional
topography generally sloping down to the north, west, and south. Slopes around the subject site
generally range from about 4 to 5 percent. According to King County IMap, there is a slope of about
30 to 33 percent that is to the northwest of the site, but this slope is actually a retaining wall on the
adjacent parcel that has an exposed height of about 6 to 8 feet. We have assumed this wall was
permitted and properly engineered and Is therefore stable. Slopes between 25 to 30 percent with
about 10 feet of relief occur along Davies Avenue South, more than 250 feet west of the subject site.
The steep slope down to the Green River valley is more than 500 feet from the site. In our opinion,
there are some Isolated sensitive slopes west of the subject property, but these slopes have
apparently been stabilized by retaining walls. Given the mapped soil types and developed nature of
the area, the impacts to and from these slopes will be minimal.
GEORESOURCES
SlgnatureHomes.MorrisAve.RGA(1).docx
November 20, 2017
page 14
The City classifies coal mine hazard areas per RMC 4-3.050.G,5.e as either a low, medium, or
high hazard per the following definitions:
• Low Coal Mine Hazards (CL): Areas with no known mine workings and no predicted
subsidence. While no mines are known in these areas, undocumented mining is known to
have occurred.
• Medium Coal Mine Hazards (CM): Areas where mine workings are deeper than two
hundred feet (200') for steeply dipping seams, or deeper than fifteen (15) times the
thickness of the seam or workings for gently dipping seams. These areas may be affected
by subsidence.
• High Coal Mine Hazard (CH): Areas with abandoned and improperly sealed mine
openings and areas underlain by mine workings shallower than two hundred feet (200') in
depth for steeply dipping seams, or shallower than fifteen (15) times the thickness of the
seam or workings for gently dipping seams. These areas may be affected by collapse or
other subsidence.
According to the Washington State DNR OFR 94-7, the site Is located north of the Sunbeam
and Patton coal mines as shown on Plate K-33. The site is also located west of the Renton coal mine
as shown on Plate K-32. A map showing the location and approximate lateral extent of the mines
created from the Washington State Department of Natural Resources Geological information Portal
is attached as Figure 3. Copies of the K-32 and K33 coal mine maps are attached as Figures 4 and 5.
It appears that the Patton coal mine workings are located within the NE quarter of the SE quarter of
Section 19, and the Sunbeam Mine is located within the SW quarter of the SE quarter of Section 19.
Based on the DNR GIS maps, it appears that the actual project Is more than 200 feet north of mine
area. Furthermore, based on the coal mine maps, it appears that workings were likely more than 200
feet below grades. It is our opinion that the risk from coal mine related subsidence is minimal, and
the site should be classified as CL. The risk for subsidence at the subject site is no greater than the
adjacent properties, which are currently developed.
LIMITATIONS
We have prepared this report for use by Signature Custom Homes and other members of the
design team, for use in the design of a portion of this project. The data used in preparing this report
and this report should be provided to prospective contractors for their bidding or estimating purposes
only. Our report, conclusions and interpretations are based on our observations of subsurface
conditions, data from others and limited site reconnaissance, and should not be construed as a warranty
of the subsurface conditions.
GEORESOURCES
SlgnatureHomes.MorrisAVe.RGA(1).docx
November 20, 2017
page 15
We have appreciated the opportunity to be of service to you on this project. If you have any
questions or comments, please do not hesitate to call at your earliest convenience.
Respectfully submitted,
GeoResources, LLC
Kyle E. Billingsley, EIT
Engineering Staff
/I
I KEITH SCOTT SCHEMB91
Keith S. Schembs, LEG
Principal
KEB:KSS:DCB/kss/
Doc to: SlgnatureHomes.MorrisAve.RGA(1)
Attachments: Figure 1: Site Location Map
Figure 2: Site Vicinity Map
Figure 3: USGS Geologic Map
Figure 4: K-32 Coal Mine Map
Figure 5: K-33 Coal Mine Map
Dana C. Biggerstaff, PE
Senior Engineer
GEORESOURCES
.3.
[1
0
�1•gL�
w
1r.T
w
r-
_ rY
� c
�a
0.
S 17th It a "�
9
4
v.
it
II V.
rc ��
ti.
5:@( 191.; ti: .`• 19ni 91
0
26th °t
Cs:r
+ 2CAI
Approximate Site Locations
(Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/)
i
s
Not to Scale
GeoResources, LLC Site Location Map
5007 Pacific Highway East, Suite 16 Proposed Single Family Residence
Fife, Washington 98424 1715 Morris Ave S
Phone: 253.896-1011 Renton, Washington
Fax: 253-896-2633
Doc ID: SignalureCustomHomes.MOniSAVe.F November 2017 Figure 1
6 —T—
N
JJJ i
a,
r � 61419 61621 � b �
T C
6
1418 �•1 61615 61614, 61615 61416 41625 61624 b
61425 I b i '
bI41
i i 611011 , 1421 Q)
61)03 4 N Z 1)05
l
i i S k�( 6 ]04 1 VOS 6506
1x1111 v 6170Y� , 6 06 }
n1e
-n
6 6712 b17ll 1 i 1714 yi
33 Y WSl) 0/ yv66071 661i� 6619 -
1 —02 0� 61715 �� — ?23
P
171i� ) '17221�7t0 61)16 '� {
d1719I
1 �iF 111 6Ins
61 , [
\ t l.'S I v 6gssi iii d2 1726
,( 716' bvz7 �1= 6sxo
1
ll
t
b61 i [_ i 2fIna! ITJS i
i t'_4iea ` i paot, '\1nii i 'i 6isosi �� 6rs`47 a Sismi
,
805
1808. �4 4
�so3 ,� • X
1Ri, , �l OS 603
0Si) 5'--
6 0 60
1 1�
i%1 4 1 61811 f i
6160 �61E12 1�i 61413
isle I lan� _
819 �
1
11 v'„ 1-- V-� e b
l)} {'�
t,�f', r ��6ie24 eisni �en� ( t 652
19 61
�i '�I1Cn St I
t-
i[
001�f 013 .3� 6325 ( 901 61?04 1 6419 ,i 6425 65°I1 1 soJ b 1. �u
—i
Approximate Site Locations
(Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/)
ncl�v:
Not to Scale
GeoResources, LLC Site Vicinity Map
5007 Pacific Highway East, Suite 16 Proposed Single Family Residence
Fife, Washington 98424 1715 Morris Ave S
Phone: 253-896-1011 Renton, Washington
Fax: 253.896-2633
Doc ID:SignalureCustomHomes.MorrisAVe.F November 2017 Figure 2
I�
■
c
Q
Jtk LI
TMPo
+� SI
i - J
Approximate Site Location
Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965)
K33
Sunbeam Mine
Patton Mine
Renton Coal Co.
577tl,St
S
Sah t
Renton Coal Co.
K31
Renton Mine
Seattle Elec. Co.
all,st
1
(1
t
rp\45'
4v��
r
9t i`t
5VI
iC 1I
!.\iAPi
-
pritllb5\
_.
st!»vi�sv A
r.
syst sti
151h I
L
vii
t.
ii
t �S
7811 ft, C
Sf t�
5W 19N
t
t
� 1
±E 21 ISt
SL :)n:f PI
I�
■
c
Q
Jtk LI
TMPo
+� SI
i - J
Approximate Site Location
Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965)
GeoResources, LLC
5007 Pacific Highway East, Suite 16
Fife, Washington 98424
Phone: 253.896-1011
Fax: 253-896-2633
to
USGS Geologic Map
Proposed Single Family Residence
1715 Morris Ave S
Renton, Washington
Doc ID: SignatureCuslomHomes.MorrisAVe.F November 2017 Figure 3
1
K33
Sunbeam Mine
Patton Mine
Renton Coal Co.
Renton Mine
K32
Renton Coal Co.
K31
Renton Mine
Seattle Elec. Co.
GeoResources, LLC
5007 Pacific Highway East, Suite 16
Fife, Washington 98424
Phone: 253.896-1011
Fax: 253-896-2633
to
USGS Geologic Map
Proposed Single Family Residence
1715 Morris Ave S
Renton, Washington
Doc ID: SignatureCuslomHomes.MorrisAVe.F November 2017 Figure 3
1
is
Approximate Site Location
(Map From Washington state department of natural resources geologic Information portal -coal mine hazard maps
https://geologyportal.dnr.wa.gov/#coag
GeoResources, LLC
5007 Pacific Highway East, Suite 16
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
K-32 Coal Mine Map
Proposed Residential Development
1715 Morris Ave S
Renton, WA
i
Approximate Site Location
(Map From Washington state department of natural resources geologic information portal -coal mine hazard maps
https://geologyportal.dnr.wa.gov/#coag
GeoResources, LLC
5007 Pacific Highway East, Suite 16
.Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
K-33 Coal Mine Map
Proposed Residential Development
1715 Morris Ave S
Renton, WA