HomeMy WebLinkAboutPreliminary Soil and Slope Survey Report - PLN General - 4/18/2001 Ape- 18 01 03: 22p p. 2
I<raZOn & ASSOCIATES , INC .
GEOTECHNICAL ENGINEERING • ENVIRONMENTAL ENGINEERING
CONSTRUCTION TESTING & INSPECTION
April 18, 2001 KA#102-01039
Mr. Jerry Vermillion
10237 Kiwa Drive SE.
Olympia, Washington 98513
REPORT OF PRELIMINARY SOIL AND SLOPE SURVEY, VERMILLION
LOTS 1 THROUGH 6 LOCATED ON STATE HIGHWAY 106,MASON
COUNTY, WASHINGTON
GOVERNMENT LOT 1, SECTION 34,TOWNSHIP 22 NORTH, RANGE 3
WEST, W. M.
This report presents the results of a preliminary soil and slope survey directed at evaluating
potential erosion and landslide hazards at the referenced site in accordance with the requirements
of the Mason County Critical Areas Ordinance. The scope of the study was developed during
our site visit on April 16, 2001, and outlined in our proposal to you dated August 16, 2001. The
services performed under the referenced proposal were in general compliance with requirements
outlined in the Mason County Critical Areas Ordinance.
As shown on the attached Location map, Figure 1, the lots are located just off of State Highway
106 in Mason County, and overlook The Narrows portion of the Hood Canal to the north. At the
time of the preliminary study there were no plans for the proposed residential structures.
There was no visual evidence of previous development of the lots with the exception of a well on
Lot 1 and recently graded primitive roads,which appeared to be extensions of logging roads.
The primitive roads primarily trend in an east-west direction providing access to the proposed
building locations. It is our understanding that the property had been logged when the property
was purchased approximately 3 years ago.
Eleven Offices Serving The Western United States
20714 State Route 305 Suite 3C•Poulsbo,Washington 98370•(360)598-2126•Fax:(360)598-2127
102-01039 V-0li.A.
Rp,r 18 01 03: 22p p• 3
KA No. 102-01039
April 18,2001
Page No. 2
As previously noted, under the current development plan,minimal grading of the site, beyond
that required for construction, is anticipated. All areas of bare soil and disturbed vegetation will
be landscaped such that no erosion hazards are created or will remain following development.
With adequate care and geotechnical input construction of the proposed buildings (residence and
garage) and driveway improvements will not result in an increase of the potential landslide or
erosion hazards of the site.
Site soils were viewed in various roads cut exposures in the area. Actual subsoil conditions and
thickness may vary between the slope exposures.
GEOLOGIC SETTING
The site is located in the northwest portion of Puget lowlands, an elongate, north-south trending
structural depression and topographic trough. The Puget lowlands have been filled several times
bYglacial ice, resulting in many topographic features, which arc a result of glacial erosion and
deposition and that caused by outwash streams. The site is in an area of glaciated bedrock and
associated deposits. Site soils, topography and geology result primarily from the advance and
retreat of the Vashon Stade(most recent glacial advance)of the Frazier Continental Glaciation.
On a gross scale the typical soil sequence in the area consists of mixed sands and gravels
(Recessional Outwash) over glacial till which in turn overlies sands, gravels and silts (Advance
Outwash and pre-glacial deposits)or bedrock. In the general vicinity of the site the glacial till
caps much of the region to the south and overlies pre-glacial deposits, which arc identified on
geologic maps as Advance Outwash and older sands and gravels of the Skokomish Gravel unit.
The site proper appears to be located on edge of a rolling upland, cut along the perimeter by
drainages. In this area it appears that the till has been severely eroded and weathered exposing
the pre-glacial materials and pockets of material identified by the general term glacial drift. The
site materials were generally deposited at the base of the glacier and overridden and densified by
some 1500 or more feet of ice. Generally,the site materials are found to be dense to very dense,
however, it is not uncommon to find a layer or mantle of looser, weathered or disturbed material
over the denser soils or bedrock.
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Eleven Offices Serving The Western United States
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KA No. 102-01039
April 18,2001
Page No. 3
SURFACE CONDITIONS
As previously described, Lot 1 of the property has been previously developed to a minor extent
for a well, but it does not appear to have been significantly graded or otherwise modified. The
other lots in the plat appear in a natural condition. Topographically the potential building sites
appear as smaller areas of flatter slopes or bench bounded by moderate to steep slopes that reach
nearly to the shore of Hood Canal. The vertical height of the lower slope is on the order of
approximately 40 feet.
The Coastal Zone Atlas of Washington, Mason County volume, identifies the site area as being
on slopes considered to be of intermediate stability. The map "Relative Slope Stability Of The
Southern Hood Canal Area,Washington" (Map I-853-F, 1977, Washington State Department of
Natural Resources, Division of Geology and Earth Resources) identifies slopes on the lots as
Class 2. Class 2 slopes are considered "normally stable areas that may become unstable if
modified by man". During our reconnaissance of the area it was observed that the only indicator
of past and ongoing soil movement, i.e.,bowed tree,bare ground, soil slumps, etc. was a surficial
slide area on lot 1.
Based on our reconnaissance observations, it is our opinion that the slopes on the lots generally
reflect and match the slope stability mapping of the area.
On the slopes the vegetative cover is comprised of an open, mixed-aged woods of deciduous and
evergreen trees over an open to dense understory of ferns, brush and shrubs. Most of the trees on
the lower slopes are older, while the upper slopes appear to be comprised of younger trees.
A general reconnaissance of the lots and adjacent areas was made to identify areas of ground
water seepage. A stream on lot I is fcd by a spring further upland on lot 1. No other obvious
springs or seeps were located on the slopes. However,moist surface soils were noted on lots 5,
6, and 7 in areas of proposed construction. The moist areas were attributed to near surface layer
of lower permeability, possibly glacial till. Based on the soils observed in cuts and on slopes
development seasonally perched water or the development of temporary zones of outwatering
should not be unexpected on slopes or in excavations.
Krazan&Associates,Inc.
Eleven Offices Serving The Westem United States
Apr 18 01 03: 23p P• 5
KA No. 102-01039
April 18,2001
Page No.4
SOIL PROFILE AND SUBSURFACE CONDITIONS
The"Geology and Related Ground Water Occurrence, Southeastern Mason County,
Washington" (Water Supply Bulletin Number 29, State of Washington, Department of Water
Resources 1970) indicates that the site and adjacent areas are underlain by Advance Outwash
�
over the Skokomish Gravels."
On maps prepared by the Soil Conservation Service (SCS) it appears that the lots lay on or very
near the contact between two soil types of the Alderwood series. Based on the SCS mapping it
appears that the northern (lower)portion of the lots are underlain by Alderwood gravelly loam,
15% to 30% slopes (soil type Ad) while the southern (upland) slopes are underlain by
Alderwood gravelly sandy loam, 5% to 15% slopes (soil type Ab). The SCS indicates that the
Alderwood-type soils are derived from a parent material of glacial till with the Ad-type soils
typically located in areas of gullies and deeply cut banks of streams while the Ab-type soils are
usually found on undulating to rolling moraines.
Based on the soils observed exposed at various locations in the area, it is our opinion that the site
soils are generally consistent with the regional maps of the area. Differences between the
mapped and observed soil conditions appear as a result of mapping scale, availability of
exposures, and intended map usage. These differences are generally minor and not unexpected.
CONCLUSIONS AND RECOMMENDATIONS
GENERAL
Based upon our site observations and review of readily available materials, it is our opinion that
the potential for ground movement in the area back of the site slopes is low. Similarly, the
potential for large-scale landsliding on the slopes on this property, in either the natural condition
or resulting from the proposed development, appears to be low. The slopes are mapped as of
intermediate stability or Class 2 stability depending on the reference and the overall slope
stability under the present conditions appears good and should remain unchanged with adequate
developmental planning and follow through.
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Eleven Offices Serving The Western United States
Rpr 18 01 03: 23p P• 6
KA No. 102-01039
April 18,2001
Page No. 5
Following our review of the Mason County critical areas ordinance, it is our opinion that Lot. I
of the subject property meets the requirements for definition as a landslide and erosion hazard
area. Although it is our opinion that the property meets the requirements of the ordinance for
definition as a critical area, it is also our opinion that the proposed building site can be safely and
satisfactorily developed through geotechnical design and sound site planning. As previously
noted, it is our preliminary opinion that overall the proposed development in and of itself will
create a minimal risk of erosion or landslide damage, no disturbance of the steeper slopes is
expected, and the development will have little if any effect on adjacent properties.
The site does not appear to meet the classification requirements to be designated as a seismic
hazard area as defined in the Mason County ordinance. However, the property is located in
seismic zone 3 as defined by the Uniform Building Code (UBC), as is much of western
Washington. In the event of an earthquake of adequate magnitude and/or duration some soil
movement on the slope is possible if other conditions are right,but the potential for soil
movement on this property is no greater than that on the adjacent developed lots or for properties
elsewhere with similar slope and soil conditions. Additionally, the slope core soils appear to be
in a dense to very dense condition. The preliminary recommendations contained in this report
were developed considering the potential for slope failure, and that future structures are expected
to be designed in accordance with current UBC seismic zone 3 requirements, or potentially more
stringent future requirements.
Typically soils similar to those found on the site are considered to be of moderate to be of severe
erosion hazard in the disturbed state. These soils are located on the site slopes, which we
understand will not be disturbed. It is our experience that the erosion hazard risk for disturbed
areas can be mitigated through normal residential landscaping and re-vegetating of the disturbed
areas. During construction and until fully landscaped the exposed site soils will be subject to
erosion. Erosion of the exposed soils will be most noticeable during periods of rainfall and may
be controlled by the use of normal erosion control measures, i.e., silt fences,hay bales, mulching,
control ditches or diversion trenching, and contour furrowing.
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KA No. 102-01039
April 18,2001
Page No.6
All runoff from roofs, driveways, patios and hard surfaced areas should be intercepted, collected
and disposed of away from structures and site slopes,and discharged where the water will not
effect down slope structures, slopes,walls or properties. Specific recommendations for and
design of a storm water disposal system are beyond the scope of our services and should be
prepared by other consultants fully familiar with county design and discharge requirements and
slope stability considerations.
As part of our preliminary study we offer the following comments regarding the lots. It should
be noted that these comments are based only on visual observations and limited map review and
may be subject to modification following additional study.
• Lot 1 It is our understanding that a portion of the slope face sloughed during last winter. No
further movement of the sloughed area was noted during the recent earthquake.
• Lot 2 The proposed building area in the current alignment of the lot would require some
additional geotechnical study prior to development. It is our understanding that the
parameters of this lot will be modified in order to provide a more desirable building
location.
• Lot 3 The proposed building area is gently sloping and appears to be suitable for
construction.
• Lot 4. The proposed building area is adjacent to Highway 106 on a level area which appears
to be suitable for construction.
• Lot 5. The proposed building area is located on a gently sloping area which appears to be
suitable for construction. The proposed building area had wet surface soils which
were attributed to near surface glacial till.
• Lot 6. The proposed building area was a relatively level plateau area which appeared to be
suitable for development. The proposed building area had wet surface soils which
were attributed to near surface glacial till.
• Lot 7. The proposed building area was a relatively level plateau area which appeared
to be suitable for development. The proposed building area had wet surface soils
which were attributed to near surface glacial till.
Krazan&Associates,Inc.
Eleven Offices Serving The Western United States
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KA No. 102-01039
April 18,2001
Page No. 7
REPORT LIMITATIONS
This preliminary report has been prepared for the exclusive use of Mr. Jerry Vermillion and his
agents for use in preliminary planning of the referenced development. The conclusions and
recommendations in this report are preliminary and based on our interpretation of site conditions
as they presently exist and anticipatcd future construction activities. No subsurface exploration
was under taken for this preliminary study. The soil conditions described in this report and the
preliminary conclusions and recommendations contained in this report are provided for this
specific site only and should not be expanded for use on adjacent properties without additional
exploration and review of those sites by our firm. This report is preliminary and based on
limited data,the report conclusions and interpretations should not be construed as a warranty of
the subsurface conditions. There are possible variations in subsurface conditions. In the event
that the scope or location of the project should change or subsurface conditions different from
those disclosed by this study be observed or suspected, we should be advised. At that time a
review of the changed conditions will be made,and alternative or remedial recommendations
given as required.
NOTE: Although we have observed subsurface conditions as part of this study, we have not
conducted analytical laboratory testing of samples obtained, nor have we evaluated the site for
the potential presencc of contaminated soil, and have not evaluated or addressed ground water
conditions or concerns except as noted in this report. The evaluation of possible environmental
or geo-environmental considerations is beyond the scope of this report.
The owner and the contractor should make themselves aware of and become familiar with
applicable local, state, and federal safety regulations, including current OSHA excavation and
trench safety standards. Construction site safety generally is the sole responsibility of the
contractor. The contractor shall also be solely responsible for the means,method, techniques,
sequences, and operations of construction operations. The firm, Krazan & Associates, Inc.,
(including consultants and subcontractors) is providing the preceding information and
recommendations solely as a service to Mr. Jerry Vermillion. Under no circumstances should
the provision of this information or recommendations be construed to mean that the firm Krazan
& Associate, Inc., (including consultants and subcontractors) is assuming responsibility for
Krazan&Associates,Inc.
Eleven Offices Serving The Western United States
Apr 18 01 03: 24p
KA No. 102-01039
April 18,2001
Page No. 8
construction site safety or the contractor's activities; such responsibility is not implied and should
not be inferred.
Within the limitations of scope, schedule, and budget for this work, it is warranted that the work
has been done in accordance with generally accepted practices followed in this area at the time
this is report was made. No other warranty, expressed or implied is made.
Should you have any questions or concerns which have not been addressed, or if we may be of
additional assistance, please call (360) 598-2126.
Sincerely,
r Shawn E. Williams,
Senior Environmental Geologist
SEW/ah
Krazan&Associates,Inc.
Eleven Offices Serving The Western United States
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