07-0135 Stormwater Plan 031808Construction Stormwater Pollution
Prevention Plan
FOR
Today's Dental
502 E Yelm Ave
Yelm, WA 98597
March 14, 2008
Proponent: Judd and Sarah Sherman
(360)458-1976
Prepared by: Lucas Johnson, E.I.T.
Reviewed by: Justin Goroch, P.E.
BCRA
2106 Pacific Avenue, Suite 300
Tacoma, WA 98402
(253) 627-4367
[iCRA~
RECEIVED
MdR 1 8 208
I hereby state that [his report for the Today's Dental project has been prepared by
me or under my supervision and meets the standard of care and expertise which is
usual and customary in this community for professional engineers.
,y'14I08
,~:a
W
NALE
EXPIRES D6 4
Table of Contents:
1. Construction Stormwater Pollution Prevention Elements ..................... ...................... 1
Element 1: Mark Clearing Limits .......................................................... ...................... I
Element 2: Establish Construction Access .......................................... ...................... I
Element 3: Control Flow Rates .............................................................. ..................... 2
Element 4: Install Sediment Controls ................................................... .....................2
Element 5: Stabilize Soils ....................................................................... ..................... 2
Element 6: Protect Slopes ...................................................................... ..................... 3
Element 7: Protect Drain Inlets ............................................................. ..................... 3
Element 8: Stabilize Channels and Outlets ......................................... ..................... 3
Element 9: Control Pollutants ................_......-.............._....................... .....................3
Element 10: Control De-Watering ......................................................... ..................... 3
Element 11: Maintain BMPs .................................................................... .....................4
Element 12: Manage the Project ........................................................... .....................4
2. Project Description ........................................................................................ ..................... 5
3. Existing Site Conditions ................................................................................. ..................... 5
4. Adjacent Areas ............................................................................................... .....................6
5. Critical Areas .................................................................................................. .....................6
6. Soil .................................................................................................................... ..................... 6
7. Potential Erosion Problem Areas ................................................................. .....................7
8. Construction Phasing ..................................................................................... .....................7
9. Construction Schedule ................................................................................... ..................... 7
10. Financial/Ownership Responsibilities .....:................................................... ..................... 7
11. Engineering Calculations ............................................................................... ..................... 8
Attachments:
Attachment A Vicinity Map
Attachment B Site Plan
Attachment C Geotechnical Report
CONSTRUCTION STORMWATER
POLLUTION PREVENTION PLAN REPORT
Construction Stormwater Pollution Prevention Elements
The following paragraphs describe how the twelve Construction Stormwater
Pollution Prevention minimum requirements well be satisfied for the Today's
Dental project.
Element 1: Mark Clearing Limits
The clearing limits for [he Today's Dental project are the property lines.
These clearing limits, along with any trees that are to be preserved, will be
clearly marked prior to any land disturbing activities with plastic, metal, or
stake wire fence (BMP C103: High Visibility Plastic or Metal Fence or BMP 0104:
Stake and Wire Fence). Alternatively, the clearing limits may be marked by silt
fence. Items to be preserved will be clearly marked in order to prevent
damage to the site feature. There are no sensitive areas or buffers on or near
the site.
When possible, the duff layer, native topsoil, and natural vegetation will
remain undisturbed (BMP 0101: Preserving Natural Vegetation). However, if
they cannot be retained in place, they will be stockpiled on-site and covered to
prevent erosion. The site vegetation and topsoil will be replaced immediately
upon completion of the ground disturbing activities.
Element 2: Establish Construction Access
Construction vehicles will access the Today's Dental site via a single access
point in the east corner of the site (located on the southeast boundary line).
This entrance will be stabilized with a 12" thick pad of quarry spans or crushed
rock (BMP C105: Stabilized Construction Entrance). Since the construction
process will be broken into three phases, it may be necessary to relocate the
construction entrance to the middle of the southeast boundary line. If
relocation is necessary, it will take place following the completion of Phase 2
work. If the entrance becomes filled with dirt, it will be refurbished by
dislodging the riprap and reconstructing the pad. Alternatively, new material
will be added to the pad to provide storage for additional sediment.
Sediment transport is not foreseen to be a problem because the site is so small
(approximately 0.57 acres). Therefore a wheel wash or tire bath will not be
required.
Should sediment be tracked on to the street, the roads will be cleaned
thoroughly at the end of each day, or more frequently during wet weather
(BMP 0107: Construction Road/Parking Area Stabilization). This will be done to
prevent sediment from entering waters of the state. All sediment removal will
be done by means of shoveling or pickup sweeping. It will then be transported
to a controlled sediment disposal area. Only after sediment is removed in this
manner can the streets be washed. All street wash wastewater will be pumped
back onto site or discharged at an acceptable off-site location. Effort will be
taken to prevent dirty stormwater from discharging into systems tributary to
state surface waters.
Element 3: Control Flow Rates
The Today's Dental project does not require a downstream analysis,
stormwater detention/retention facility, permanent infiltration ponds, or any
other type of flow control structure. This is due to the small site size and
phasing of construction.
Element 4: Install Sediment Controls
All stormwater runoff from disturbed areas will pass through the silt fence
(BMP C233: Silt Fence) that is to be installed prior to any land disturbing
activities. It will be installed around the perimeter of each phase. The silt
fence will be inspected weekly at the end of the work week and subsequent to
each storm event. Any damage to the silt fence will be repaired immediately.
Sediment accumulation in excess of design limits will be removed from the silt
fence upon identification of the condition and prior to a forecasted storm
event. The construction superintendent responsible for these actions will be
responsible for maintenance of the erosion and sediment control facilities.
Element 5: Stabilize Soils
All soils on the Today's Dental site, whether at final grade or not, will not
remain exposed and unworked for more than 2 days during the period from
October 1 to April 30. Soils will no[ remain exposed and unworked for more
than 7 days during the period from May 1 to September 30. Furthermore, soils
will be stabilized at the end of each shift prior to all holidays or weekends if
needed. The need for stabilization will be based on the weather forecast.
Soil stabilization is not foreseen as a problem since the slopes on the site are
mild and well vegetated. However, if stabilization is required, it may be done
with one or more of the following practices: temporary and permanent
seeding, sodding, mulching, plastic covering, erosion control fabrics and
matting, soil application of polyacrylamide (PAM), the early application of
gravel base on areas to be paved, and dust control. If any stockpiles will be
located on site, they will be stabilized from erosion, protected with sediment
trapping measures, and located away from storm drain inlets, waterways, and
drainage channels.
Element 6: Protect Slopes
The slopes on the Today's Dental project are very mild and well vegetated.
They range from flat to approximately four percent. Because of these factors,
the site will not require any slope protection. Off-site stormwater (run-on) is
not an erosion concern because the soil has such a high infiltration capacity.
The proposed site grading will cause runoff to flow from north to south, as it
currently does. However, the proposed site will be divided into two separate
drainage basins. Grading changes will not significantly change the direction of
flow or the potential for slope runoff. All excavated material shall be placed
on the uphill side of trenches, consistent with safety and space considerations.
The reasoning for this is to prevent runoff from entering the open trench and
causing erosion.
Element 7: Protect Drain Inlets
As a means of preventing sediment from entering the conveyance system, all
storm drain inlets will be protected with catch basin inserts (BMP 0220: Storm
Drain Inlet Protection). Inlet protection will be installed for existing inlets that
will collect runoff from the construction site and any newly constructed inlets.
Existing inlets in Yelm Avenue, Solberg Street, and Jefferson Street that are
adjacent to the site will be protected. The inlets will be inspected weekly at a
minimum and daily during storm events. At a minimum, sediment will be
removed from the inlet protection devices once sediment has filled one-third
of the available storage. Approach roads will be kept clean in order to prevent
sediment from reaching inlets.
Element 8: Stabilize Channels and Outlets
The project site has no existing or proposed channels or outlets. Therefore no
stabilization is required.
Element 9: Control Pollutants
Pollution of stormwater is not anticipated to be a problem on the Today's
Dental project. However, since concrete will be handled on site, BMP C151:
Concrete Handling will be implemented. This includes, but is not limited to,
washing out concrete only in formed areas awaiting installation of concrete and
recycling unused concrete. In general, disposal of concrete will take place in
such a manner that it does not violate groundwater or surface water quality
standards.
Element f0: Control De-Watering
The need to de-water is not anticipated. However, if it is encountered, water
from trench de-watering shall be conveyed to a suitable infiltration location on
site or transported off-site in a vehicle. Off-site transport will take place in a
vehicle such as a vacuum flush truck, for legal disposal in a manner that does
not pollute state waters. Highly turbid or otherwise contaminated dewatering
water, such as from construction equipment operation will be handled
separately from stormwater.
Element i1: Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be
maintained and repaired as needed to assure continued performance of their
intended function. All maintenance and repair will be conducted in
accordance with standard procedures for the BMPs.
Sediment control BMPs will be inspected weekly or after arunoff-producing
storm event during the dry season, and daily during the wet season.
Within 30 days after the site has been stabilized, all temporary erosion and
sediment control BMP's shall be removed. If any BMP's are required to be in
place longer than 30 days following site stabilization, they will be removed
once they are no longer needed. All trapped sediment will be removed or
stabilized on site. Soil that has been disturbed due to the removal of BMP's or
vegetation shall be permanently stabilized.
Element 12: Manage the Project
Site clearing and grading, including the construction of the sediment trap, will
be performed only after the erosion and sediment control measures have been
constructed. To further prevent soil erosion, the project will be divided into
three phases. Phasing the project construction will limit the amount of the
project area that is exposed to construction activities for any given time.
Clearing, grading, and other soil disturbing activities will not take place from
October 1 to April 30 unless it can be shown to the satisfaction of the local
permitting authority that silt-laden runoff will be prevented from leaving the
site. The local permitting authority shall take enforcement action if sediment
leaves the site causing a violation of the surface water quality standard,
clearing and grading limits are violated, or erosion and sediment control
measures are not maintained. Activities may be exempt from seasonal
restrictions. They include routine maintenance and repair of BMP's, routine
maintenance of public facilities or existing utility structures that does not
expose soil or result in removal of vegetative cover, and activities where there
is 100% infiltration of surface water runoff within the site in approved and
installed erosion and sediment control facilities.
A Certified Professional in Erosion and Sediment Control, who can be on-site or
on-call at all times, will be identified by the contractor. All BMPs will be
inspected, maintained, and repaired as needed to assure continued
performance of their intended function.
The Construction SWPPP will be retained on-site or at a nearby location. It will
be modified whenever there is a change that has, or could have, a significant
effect on the discharge of pollutants to waters of the state.
2. Project Description
The Today's Dental project is located at the north corner of the Solberg Street
NW and Yelm Avenue W intersection. The site consists of parcels 21724142300
and 217241452200, both of which are zoned C-1 Commercial. The site lies in
Section 24, Township 17N, Range 1 E. See Appendix A for a vicinity map.
The project is comprised of a 0.57-acre site which will contain a newly
constructed dental office building and parking lot. Construction will be divided
into three phases as a means of maintaining building operations. The site will
have ingress/egress points from Solberg Street. Site improvements include a
stormwater filtration system, stormwater infiltration system, domestic water
service, fire hydrants, and STEP sewer system.
Nearly all of the 0.57 acre site will be disturbed during the construction
process. As previously mentioned, site construction will be completed in
phases, which will reduce the environmental impact of the construction
activities. See section 8. Construction Phasing for more details.
Approximately 350 yd' of material will cut from the site and less than 50 yd' of
material will be filled.
3. Existing Site Conditions
The current site has a dental office building on the southwesterly parcel (No.
21724142300) and a single family residence on the northeasterly parcel (No.
21724142200). The existing ground cover is a combination of lawn,
landscaping, and gravel with trees sparsely located around the site perimeter.
In general, the site slopes from north to south with slopes ranging from
relatively flat to 4%. In the current condition, site stormwater sheet flows
from north to south. Basedon the soils information and the shallow site
grades, it appears that the site currently infiltrates all of the onsite storm
water.
The Today's Dental site has an upper sod and topsoil layer that ranges from 6
inches to one foot in depth. This rests on top of a black ash layer with gravel
that ranges in depth from 2.5 to 3.0 feet. Underlying the ash layer is gravely
glacial outwash with cobbles and boulders. This outwash extends to the depth
explored, which was a maximum of 10 feet. No groundwater was encountered
in any of the soil explorations. The soils are capable of infiltrating runoff at a
high rate. The design infiltrate rate is suggested to be 10 inches/hour. See
Attachment C for the geotechnical report.
There have been no erosion problems associated with this site and we do not
foresee any difficult site conditions. Based on the survey, there appears to be
no fuel tanks or wells on the site.
There are currently no known critical or sensitive areas on or near the project
site. However, there is a septic tank and drain field that will require removal.
It is located near the northernmost point of the southwesterly parcel. The
septic system will be decommissioned per Department of Ecology
requirements.
4. Adjacent Areas
The site is bordered to the northwest by multi-family residences and a
commercial building. Jefferson Avenue NW borders the site to the northeast,
Yelm Avenue W (SR 510) borders the site to the southwest, and Solberg Street
NW borders the site to the southeast.
Based on soil information provided in the geo[echnical report, it appears that
the project area runoff infiltrates into the site soils. Since the site has such a
good infiltration ability, stormwater flow management will be achieved by
utilizing an underground infiltration facility. A downstream analysis is not
provided in this report since infiltration will be utilized.
It appears that the site does not accept any off-site runoff. Based on the
survey and generally mild slopes, current runoff from adjacent sites also
appears to infiltrate into the soil.
5. Critical Areas
There are no known areas on or immediately adjacent to the site that would be
classified as a critical area.
6. Soil
A geotechnical report was completed for the site by EBRA Inc. and has been
included as Attachment C. It indicates that the Today's Dental site has an
upper sod and topsoil layer that ranges from 6 inches to one foot in depth.
This rests on top of a black ash layer with gravel that ranges in depth from 2.5
to 3.0 feet. Underlying the ash layer is gravely glacial outwash with cobbles
and boulders. This outwash extends to the depth explored, which was a
maximum of 10 feet. No groundwater was encountered in any of the soil
explorations. Further information regarding the on-site soils can be found in
the geotechnical report dated January 4, 2006 (See Appendix C).
E3RA, Inc. has classified the black ash as SP-SM and the glacial outwash as SP
per the USCS Soil Classification system. The soils are capable of infiltrating
runoff at a high rate. The design infiltrate rate is suggested to be 10
inches/hour.
Potential Erosion Problem Areas
All areas of the site that will have exposed underlying soils due to grading have
the potential for erosion problems. However, the erosion and sedimentation
control measures specified on the plans, and the generally flat terrain, will
minimize any potential for erosion and sedimentation problems.
8. Construction Phasing
The construction phasing will take place in the order listed below. Each phase
will include, but may not be limited to, the indicated tasks. Some portions of
the steps may be performed out of sequence as conditions require.
Phase 1:
• Install STEP system and necessary pipe lines
• Maintain current dental building operations
Phase 2:
• Construct new dental building
• Tie all utilities into new dental building
Phase 3:
• Demolish old dental building
• Install storm drainage structures and pipe lines within phase limits
• Construct new curb and gutter, sidewalk, and parking lot
9. Construction Schedule
Construction is anticipated to begin in the spring of 2008. The civil site
development work is anticipated to be completed and stabilized during the fall
of 2008. During the time period from October 1 to April 30 (wet season) no
soils will remain exposed and unworked for more than two days. This will
prevent soils from becoming unstable and more susceptible to erosion.
10. Financial/Ownership Responsibilities
The property owner, Judd and Sarah Sherman, will be responsible for bonds
and other required securities.
11. Engineering Calculations
Due to the small size of the site and construction phasing, neither a sediment
trap nor a pond is required. Therefore engineering calculations are not
necessary.
Attachment A
Vicinity Map
J l l j~
Attachment B
Site Plan
Attachment C
Geotechnical Report
PO Box 40890
Tacoma WA 98444
253-537-9400
253-5375401 faz
E3RA
fanuary 4, 2006
T06397
Yelm Dental Center, LLC
502 Yclm Avenue West
Yelm, WA 98579
Attention: Dr. Sarah Sherman
Subject: Geotechnical Engineering Report
Planned Commercial Development
502 Ye(m Avenue West, P/N 21724142300
107 Solberg Sheet, P/N 2 1 7247 422 00
Yelm, Washington
Dear Sarah:
E3RA is pleased to submit this report describing the results of our geotechnical engineering evaluation For the
residential development planned aT 502 Yelm Ave West and 707 Solberg Street in Yebn, Washiun on.
This report has been prepared for @te exclusive use of Yelm Deutal Center, LLC and their consultants, for
specific applieafion to this project, in accordance with generally accepted geotechnical engineering practice.
1.0 SITE AND PROJECT DESCRIPTION
The planned commercial development is located on the corner of SA 510 and SW Solberg St. in Yelm,
Washington, as shown on the enclosed Location Map (Figure 1). I[ consists oftwo rectangular parcels that
measure about 80 feet fronting SR 510 and 300 feet fronting Solberg Street. The project site is currently
bordered by SR 570 to the southwest, Jefferson Ave to the northeast, and Solber St to the east. Surface
topography is relatively level.
Plans call for the removal of the existing home and dental office and construction of a new dental office,
associated parlting, and a stnrm water infiltration faciliTy. The properties will have access from Solberg St.
2.0 EXPLORATORY METHODS
We explored surface and subsurfaoe conditions at the project site on November 18, 2006. Our exploration
program comprised Ste following elements:
A surface reconnaissance of the two parcels;
Ten test pits (designated TP-1 through TP-3), advanced across the site;
One Grain Size analyses of on-site soils;
Three Infilfration Tests; and
January 5, 2007
T06397 / Yeln Dental
A review of published geologic and seismologic maps and literature.
E3RA- Inc_
'fable I summarizes the approximate functional locations and termination depths of cur subsurface
explorations, and Figure 2 depicts their approximate relative locations. The foI lowing text sections describe
the procedures used for excavation of test pits-
TABLE 1
APPROXIMATE LOCA"CLONS AND DEYTIIS OF EXPLORATIONS
Termination
Depth
Explorafion Functional Locafion (feet)
*TP-1 Southwes[site g
*TP-2 Central part east site 7 p
*TP-3 Central site 10
* Includes infiltation test
'Che specific number and locations of our explorations were selected in relation to the existing site features,
under the constraints of surface access, and underground utility conflicts.
It should be realized that the explorations performed and utilized for this evaluation reveal subsurface
conditions only at discrete locations across the project site and that actual conditions in other areas could vary.
Furthermore, the nature and extent of any such variations would not become evident until additional
exporations areperformed or until construction activities have begun. Ifsignifieant variations are observed at
that time, we may need to modify our conclusions and recommendations contained in [his report to reflect the
actual site conditions.
2.1 Test Pit Procedures
lTu exploratory test pits were excavated with asteel-hacked excavator operated by au independent firm
working under subwntraet to E3RA. An engineer from out firm continuously observed the test pit
excavations, logged the subsurface conditions, and collected samples. ARer we logged each test pit, the
excavator operator backfilled it with excavated soils and tamped the surface.
The enclosed Test Pit Loge indicate the vertical sequence of soils and materials encountered in each test pit,
based on our field classifications. Where a soil conmet was observed to be gradational or undulating our logs
indicate the average contact depth. We estimated the relative density and consistency of the io-sim soils by
means of the excavation characteristics and the stability of the test pit sidewalk. Our logs also indicate the
approximate depths of any sidewall caving or groundwater seepage observed in the test pits, as well as all
sample numbers and sampling locations.
2_2 lnfiltratiou Test Procedures
We performed falling head infiltration tesk at a depth of about? feetwithin test oits'IP-], 2, and 3. All falling
head tests were performed in general accordance with the falling head type infiltration testing procedure
described in the EPA publication On-site Wastewater Treatment and Disposal System 1980, described below,
January 5,2007 C3RA. Inc.
T06397 / Yelm Dental
A 6-inch-diameter PVC pipe was tamped 3 to 5 inches into the soil ofrhe upper parr of the infiltration layer,
then 2 inches of coarse, clean drain rock was placed at the bottom of the pipe to prevent scouring. Soil was
placed and tamped outside the pipe for stabilization and io prevent upwelling oftcstwatcr around the pipe. "fhe
pipe was then filled twice with I foot of water to pre-sahuaie the test soils-because, in all cases, 1 Foot of
water infiltrated the test soils in less than 10 minutes, further satm~ation was deemed unnecessary and the
intltration test proceeded.
"the pipe was then filled with 6 inches of water, and, because site soils were found to be rapidly permeable,
the time required for infiltration ofthe entire 6 inch column of water was recorded. We repeated this
procedure three limes at each test location and used only the slowest offhe 3 eocorded infdtration rates in
our analysis.
3.0 SITE CONDC110N5
The following sections of text present onr observations, measurements, fmdings, and interpretations regarding
surface, soil, groundwater, seismic, liquefaction, and infiltration conditions.
3.1 Surface Conditions
The project site is relatively Icvel with no noticeable change in elevation.
The502 Yelm Ave Westparcel currently has an existing Yelm Dental Office and 107 Solberg Sheet currently
has a home on the lot. The remainder of the siics are yard or parking.
Vegetation onsite consists of grass and some small yard trees.
No signs of wrfaee flow, such as stream channels or erosional scars, were noted during our reconnaissance.
No ponds are onsite. No seeps or springs were observed.
3.2 Soil Conditions
Our on-site explorations revealed fairly nearly uniform neaz-surface soil conditons. Generally, we observed
an upper sod and topsoil layerthat ranged in thickness from % to a bit less than 1 foot in thickness overlaying a
black ash layer with gravel ranging to a depth of about 2 1/2 [0 3.0 feet Onderlying the ash layer, we
observed, to the termination of our explorations, which reached a maximum of about 10 feet, gravely glacial
o¢twesh with cobbles and boulders. The soils appeared Co become somewhat sandier and slightly less to the
north and west. Caving was noted at depths of about 4 1 /2 to 5 feet m the test pits, suggesting that water will
readily infilhate at these depths due to the naNre oftlte soils and lack of silts.
The enclosed exploration logs provide a detailed description of the soil strata encountered in onr subsurface
explorations.
3.2.1 Laboratory Testine
Our Gmin Size Analyses of the sandy gravel in test pits 'IP-1, found within the zone where infiltration will
likely occur (7 feet below cuQenY grades) indicate that the silt content is m the range of 5 perce¢t.
The mois<;rre cement cfscls within the zone ofinfiltration is abvut5 percem as well. Weinterret most ofihe
upper soils as being close to optimum moisture.
The enclosed laboratory testing sheets graphically present our test results, and Table 2 summaries these
results.
January 5, 2007 E3RH, Inc.
TOo397 / Yelm Dental
TARLE2
LAB012ATORY TTSST RESIJI,TS FOR NON-ORGANIC ON-SITE SOILS
Soil Sample and Moisture Gravel Content Sand Content Sil t/Clay
Depth Couteut
(percent)
~tercent) Content
(percent) ( ercent)
TP-l, S-1, 7 Ceet
5.1
70
24.8 ~
52
3.3 Groundwater Couditions
At the time of our reconnaissance (November 1$ 2006), we did not observe groundwater in any of oar
explorations, which extended to depths of up [0 10 feet No significant mottling was observed.
I[ is not anticipated that ground water will be encountered during typical onsite construction activities.
3.5 Seismic Condifio~~s
Based ottour analysis ofsubsurface exploration logs and our review ofpublished geologic maps, we interpret
soil conditions on the site to cortespond with aseism is site class Se, as defined by Table 1615.1 S ofthe 2003
International Building Cade (lBCJ. According to the IBC, the site is Seismic Region 3.
3.6 Liguefactlon Potenfial
Liquefaction is a sudden increase th pore water pressure and a sudden loss of soil shear strength caused by
shear strains, as could result from an earthquake. Research has shown [hat saturated, loose, fine to medium
sands with a fines (silt and clay) convent less than about 20 percent arc most susceptible to liquefaction. We
did not observe easily Liquefiable soils onsite.
3.7 Infltratlon Conditions
A storm water infiltration faciliTy is planned for the site. Tn our three test pits located in the vicinity of this
facility, test pits TP-1, 2, and 3, we observed loose silty sandy gravel with a fines content that averaged about 5
percent. According [o the U.S.D.A. Textural Triangle, our laboratory analyses of this soil indicate that it is a
gavel, course sand Type A with an infiltration rate of 1 minute/inch.
The results of our infiltration tests are presented in Table 3. Because ini7ltration was moderately rapid, we
recorded [he time necessary fora 6 inch high column ofwater to infiltrate completely as discussed in section
2.2 above. Based on our field testing, the Average Infiltration Rate for soils a[ a depth of7 feet is 3.0 minutes
per inch. After incorporafmg a Factor of SafeTy of 2, we recommend a Desigu Infiltration Ratc of 6 minutes per
inch QO inches perhour).
TABLE 3
FIELD INFILTATION TEST RESULTS
Test Depth below Field Iutlltrafiou Rate for 6
Number Locafion existing grades inch Column
Icet
T-I TP-I, parking azea 7 20 min/6 inches
T-2 TP-2, front yard of home 7 20 min/6 inches
T-3 TP-3, backyazd of home 7 8 mot/6 iuches
January 5, 2007
T06397 / Yelm Dental
E3 RA, Inc.
4.0 CONCLGSIONS AND RECOMMENDATIONS
Plans call for the preparation ofa new dental office, paved parking, and infiltration of storm water on site. We
o1Fer the following conclusions and recommendations:
I?easibili Rased on our field explorations, research, and analyses, the proposed
development appears feasible Crom a geotechnical standpoint, provided That the
recommendations in Section 4 and in This report afro followed.
Foundation Oofions: We recommend convemienal spread footings supported on firmly
compacted native soils. Recommendations for spread footings arc provided in Section 4_
Floor Options: We recommend either a concrete slabon-grade orjoist-supported floors for
the proposed commercia(structure. Some over-excavation will be necessary for slab-on-grade
floors. Recommendations for station-grade floors are included in Section 4.
Onsite Infiltration: Based on our onsite infiltration tests and sots analyses, we recommend at
Design Infiltration Rate of 6 minutes per inch for soils in the vicinity of the planned
infiltration facility.
Asphalt Pavement: Structural fill subbases appcar do not appear to be necessary provided ttta[
sulrgrades are compacted to 95 percent maximum dry density. A pavement section,
consisting of 2 inches of asphalt pavement over a 4 inch crushed rock base, is recommended
for the planned parking area.
The following text sections ofthis report present our specific geotechnical conclusions and recommendations
concerning site preparation, spread footings, slab-on-grade floors, drainage, subgrade walls, and structwalfill.
The WSDOT Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-1Q
Standard Specifications for Road, Bridge, and Municipal Construction, and IvI21-ol, Standard Plans for
Road, Bridge, and Municipal Construction, respectively.
4.1 Site Preparation
Preparation ofthe project site should involve erosion control, temporary drainage, clearing, stripping, cutting
filling excavations, and subgrade compaction.
Erosion ControC Before new conshuction begins, an appropriate erosion control system should be installed.
This system should collect and filter all surface m¢ off through either silt fencing or a series of properly placed
and secured straw bales. We anticipate a system ofberrns and drainage ditches around construction areas will
provide an adequate collection system. Ifsilt fencing is selected as a filter, this fencing fabric should meet the
requirements of WSDOT Standard Specification 9-33.2 Table 3. In addition, silt fencing should embed a
minimum of 6 inches below existing grade. If straw baling is used as a 51ter, bales should be secured to the
ground so that they will not shift under the weigh[ of retained water. Regardless of[he silt filter selected, an
erosion control system requires occasio¢al observation and maintenance. Specificallg holes in the filter and
areas where the fitter has shifted above ground surface should be replaced or repaired as soon as they are
identified.
Temoorarv Drainaee: We recommend intercepting and diverting any potential sources of surface or
near-surface water within the construction zones before stripping begins. Because the selection of an
appropriate drainage system will depend on the water quantity, season, weather conditions, conshuction
January 5. 2007 E3RA, Inc.
T06397/Yelm Dental
sequcnco, and contractor's methods, final decisions regard ing drainage systems aze beshnnde in the field at the
time of conslructioa Rased on our current understanding of the construction plans, surface and subsurface
conditions, we anticipate that curbs, berms, or ditches placed around the work areas will adequately intercept
surtace wafer runoff.
Clearing and Stripoine: After surface and near-surface water sources have been connolled, the constmetion
areas should be cleared and stripped ofall duff, and topsod. Our explorations indicate That a thickness of % io
i foot of topsoil will be encountered across the site. Alsq it should be realized that iCthe stripping operation
proceeds duriug wet weather, a generally greater snipping depth might be necessary to remove disturbed
moislum-sensitive soils; therefore, snipping is best perFonned during a period of dry weather.
Site Excavations: Based on our explorations, we cspect that site excavations will encounter loose soils that
can be easily excavated by conventional earth working equipment.
Dewaterine: We do not anticipate dewatering to be necessary on This project.
Tentporarv Cut Slopes: AIL temporary soil slopes associated with site coning or excavations should be
adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper
than 1'/ H:1 V, and should conform to WISHA, regulations.
Suberade Compaction: Exposed subgrades for footings and floors should be compacted to a firm, unyielding
state before new concrete or fillsoils are placed. Any localized zones of looser granular soils observed within
a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any
organic, soft, or pumping soils observed within a subgrade should be overexeavated and replaced wittr a
suitable strucNral fill material.
Site Eilline: Our conclusions regard'utg the reuse of on-site soils and our comments regarding wet-weather
fitting are presented subsequenfly. Regardless ofsoil type, all fill should be placed and compacted according
to our recommendations presented in the Strucrural Fifl section of this report. Specifically, building pad fill
soil should be compacted to a uniform densiTy of at least 95 percent (based on ASTM:D-1557).
Oo-Site Soils: We offer the following evaluation oFthese on-site soils in relation to potential use as structural
fill:
Surficial Sod and Tonsoif: The sod and topsoil mantling the site is not suitable for use as
structural 511 under any crremnstawes, due to high organic content. Consequently, these
materials can be used only for non-structural purposes, such as in landscaping areas.
Black Ash: The black silty sandy gravel that underlies the site is curtently near optimum
moisture content and might possibly be reused as stmctural 511, depending on conditions at
Yime of construction. 5 is more moisture sensitive [hen the outwash below and will be difficult
to reuse during we[ weather conditions.
Glacial Outwash: The sandy gravel with cobbles and boulders that underlies the site is
currently near optimum moisture content and can be reused as stmctural fill. This soil is less
moisrre sensitive and can likely be reused in wet weather conditions.
4.2 Spread Footines
1n our opinion, conventional spread footings will provide adequate support for the proposed structure if the
subgrades are properly prepared. We offer the following comments and recorttmendafions for purposes of
January 5, 20C7
1063571 Yelm Dental
footing design and eonstmetioa
E3RA. Inc.
Footine Denths and Widths: Far Frost and erosion prolec[ioq the base of all exterior footings should bear at
least 24 inches below adjacent outside grades. To limi[Post-construction settlements, continuous (wall) and
isolated (column) footings should beat Icasl ] 8 and 24 inches wide, respectively.
Bearin¢ Suberadcs and Beari^ e Pressuros: 'the native ashy layer and glacial outwash underlying the proposed
building footprint at subgrade elevations will adequately support spread footings. [n general, before fooling
concrete is placed, any localized ::ones of loose soils exposed across the footing subgrades should be
compacted m a firm, unyielding condition, and any localized zones of soft, organic, or debris-laden soils should
beover-excavated and replaced with suitable snuctural fill.
Suberade Observation: All footing subgrades should amsistofeitherfinn,unyielding, native soils or suitable
strucNral fill materials. Footings should never be cast atop loose, soft, or frozen soil, slough, debris, existing
unconnolled ftll,ors'urfaces wvered by standing water Wereeommend tha[the condition ofall subgrades be
observed by an E3RA representative before any concrete is placed.
Bearine Pressures: [n our opinion, Cor static loading footings that bear on properly prepared subgrades can be
designed forthe maximum allowable soil bearingpressures of2500 psf. A one-third increase in allowable soil
bearing capacity may be used for short-term loads created by seismic or wind related activities.
Footine Settlemems: We es[hnate that total post-construction settlements of properly designed Footings
bearing on properly prepared subgrades will not exceed I inch. Differential settlements for comparably loaded
elements may approach one-half of this value over horizontal distances of approximately 50 feet.
Foofine and StemwaRBaekfilC To provide erosionprotection and lateral Load rasistance, we reconunend that
all footing excavations be back{dled on both sides of the footings, retaining walls, and stemwalls after the
concrete has cured. Either imported stmc[urat fill ornon-organic on-site soils can be used for this purpose,
wntingent on suitable moisture content at the time ofplacement. Regardless ofsoil type, all footing backfill
soil should be compacted to a density of at least 90 percent (based on ASTM:D-1557).
Lateral Resistance: Footings that have been properly baekfilled as recommended above will resist lateral
movements by means ofpassive earth pressure and base friction. We recommend using an allowable passive
earth pressure of 300 psf for the granular backfill. We recommend an allowable base friction coefficient of
0.35 for granular soils.
4.3 Slab-On-Grade Floors
In our opinion, soil-supported slab-on-grade floors can be used in [he proposed structure if the subgrades are
properly prepared. Weofferthe following comments and recommendations concemmgslab-on-gradefloors.
Floor Subbase: Strucmralfill subbases do not appear to be needed undersoil-supported slab-on-grade floors, if
the existing native subgrade can be thoroughly compacted. If subgrade compaction is no[ feasible, we
recouunend that granulaz fill be placed to a depth of 12 inches below finish subgrade.
Caoillarv Break and Vapor Barrier To retard the upward wicking of groundwater beneath the floor slab in
areas where moisture sensitive floor coverings will be used, such as offices, we recommend that a capillary
break be placed over [he subgrade. Ideally, this capillary break would consist of a 4-inch-thick layer ofpea
Pavel or other clean, uniform, well-rounded gravel, but clean angular gravel can be used if it adequately
prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crossmff, V isqueen, or Moistop)
should be placed over [he capillary break to serve as a vapor barrier. During subsequent casting ofthe concrete
slab, the wnfrac[or should exercise eaze to avoid puncturing this vapor barrier.
January 5:2007
T06397 i Yelm Dental
E3RA. Ina
4.4 Drainage Systems
We offer the following recommendations and comments for drainage design for construction purposes.
Perimeter Drains: We recommend Chat the buildings be encircled with a perimeter drain system io collect
seepage wafer. This drain should consist of a 4tinch-diameter perforated pipe widrin an envelope of pea gravel
or washed rock, extending at leas[ 6 inches on all sides of the pipe_ The gravel envelope should he wrapped
with filter fabricto reduce the migration of Gnes from the surrounding soils. Ideally, the drain invert would be
installed no more than 8 inches above the base of the perimeter footings.
Subfloor Drains: 1?eeause Floor subgrades will on a granular material, we do not recommend the use of
Subfloor drains.
Dsschage Considerations: Lfpossible, all perimeter drains should discharge to asuitable dishcarge location.
Runoff Water: Roof-mnoff and surface-runoff water should not discharge iuto the perimeter dain system.
Instead, these sources should discharge into separate tightline pipes and be routed away from the building to a
storm drain or other appropriate location.
Grading and Capping: Final site grades should slope downward away from the building so that runoff water
will flow by gravity to suimble collection points, rather than ponding near the building. Ideally, the area
surrounding the building would be capped with concrete, asphalt, orlow-permeability (silty) sails to minimize
or preclude surface-water infiltration.
4.5 Asphalt Pavement
Since asphaltic pavements will be used for fhe parking area and, possibly, driveways, we offer the following
comments and recommendations for pavement design and construction.
Suberade Preparation: All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded
dump tmekor heavy wmpac[or. Any localized zones ofyielding subgrade disclosed during this proof-rolling
operation should be over excavated to a maximum depth of 12 inches and replaced with a suitable structural
fill material.
Yavemen[ Materials: For the base worse, we recommend using imported crushed rock. Native materials shall
be adequate as a subbase.
Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt concrete
pavement over a crushed rock base worse. Using the estimated design values stated above, we recommend
using [he following conventional pavement sections:
Minimum Thickness
Pavement Course Parking Areas High Traf£c and Driveway
Areas
Asphalt Concrete Pavement 2 inches 3 inches
Crpshed Rnrk Rye d •^.Ches 5 inrhec
Gtanular Fill Subbase (if needed) l2 inches l2
Comuaction and Observation: Alt subbase and base course material should be compacted to at least 95 percent
January 5, 2007 E3RA, Inc
T06397 / Yelm Dental
ofthe Modifed Proctor maximum dry density (ASTM D-I SS7), and all asphalt concrete should becompacted
to at least 92 perwnt of the Kice value (ASTM I}204]). We recommend that an E3RA representative be
retained [o observe the compaction of each course before any overlying layer is placed. For the subbase and
pavememt course, compaction is best observed by means of fi'equent density testing. For the base course,
mefhodology observations and hand-probing are more appropriate Phan density testing.
PavemenE Life and Maintenance: No asphaltic pavement ismaintenance-tree- The above descrihed pavement
sections present our minimum recommendations for an average level of performance during a 20-year design
life;therefore, an average level of maintenance will likely be required Furtherznore, a20-year pavement life
Typically assumes That an overlay will be placed after about 10 years. 'fhieker asphaltond/orthicker base and
subbase courses would o0cr better long-term performance, but would cost more initially; thimrer courses
would be more susceptible to"alligatot'cracking and other failure modes. Assuch, pavement design can be
wmsidered a compromise between a high initial cost and law maintenance costs versus a Low initial cost and
higher maintenance costs.
4.6 Structural Fill
The term "structural fill" refers to any placed under foundations, retaining walls, slab-on-grade floors,
sidewalks, pavemenh, and other structures. Our comments, conclusions, and recommendations concerning
structural fill aze presented in the following paragraphs.
Materials: Typical stmclural fill materials include clean sand, gravel, pea gravel, washed rock, crashed rock,
well-graded mixtures of sand and gravel (commonly called "gravel bortow" or "pit-run"), and miscellaneous
mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived from pulverizing
the parent materials, are also potentially useful as structural fill in certain applications. Soils used fur structural
fi(I should not contain any organic mafter or debris, nor any individual particles greater than about b inches m
diameter.
Fill Placement: Clean sand, granuli[hie gravel, crushed rock, soil mixtures, and recycled materials should be
placed m horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly
compacted with a mechanical compactor.
Compaction Criteria: Using the Modified Proctor test (ASTM:1}1557) as a stamdard, we recommend that
structural 511 used for various on-site applications be compacted to the following minimum densities:
Fill Application Minimum
Compacfiou
Footing subgrade and bearing pad 95 percent
Foundation backfill 90 percent
Slabon-grade floor subgrade and subbase 95 percent
Pavement subgrade (upper 2 feet) 95 percent
Pavement subgrade (below 2 feet) 90 peroent
Suberade Observation and Compaction Tes[i re: Regardless of material or location, all structural fill should be
placed over firm, unyielding subgades prepared in accordance with the Site Preparation section ofthis report.
The condition of all subgrades should be observed by geotechnical personnel before Crlling or construction
begins. Also, fill soil compaction should be verified by means of in-place densiTy tests performed dining fill
placement so than ~eyuac-y of so. w ~pacucr~ e;.orts may be evaluated as earthwc;k progresses.
January 5, 2007 E3RA, Inc.
T063W / Yelm Dental
Soil Nloismre Considerations: The suitability of soils ^sed for snucmral fill depends primarily on their
gr'aitt-size distribution and moisture contenC when they are placed. As the "tines" con[enT (that soil fracdon
passing the LLS. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content
Soils containing more Than about 5 percent f nes (by weight) cannot be consistently compacted to a firm,
unyielding condifion when the moisture contenC is more than 2 percentage points above or below optimum.
For fill placement during wet-weather site work, we recommend usutg "clean" fill, which refers to soils that
have a fines content of 5 percent or Less (by weight) based oo the soil fiacrion passing the U.S. No. 4 Sieve.
5.0 RECOMMENDED ADDITIONAL SERVICES
Because the future performance and integrity of the structural elements will depend largely on proper site
preparation, drainage, fill placement, and construction procedures, monitoring and testing by experienced
geotechnical persotmel should be considered an integral parr ofthe consruction process. Consequently, we
recommend that E3RA be retained io provide the following post report services:
Review all consvuction plans and specifications to verify that our design oriteriap2sented in
this report have been properly integrated into the design;
Prepare a letter addressing relevant mview comments (if required by the CiTy of Yehn);
Check all wmpleted subgrades for footings and slab-omgrade floors before concrete is
poured, in order to verify their bearing capacity; and
Prepare apost-construction letter summarizing all field observations, inspections, and test
results (if required by the City of Sumner).
6.0 CLOSURE
The conclusions and recommendations presented in th is report are based, m part, on the explorations that we
observed for this study; therefore, if variations in [he subgrade conditions are observed at a later time, we may
need to modify this report to reflect those changes. Also, because the future performance and integrity ofthe
project elements depend largely on proper initial site preparation, drainage, and construction procedures,
monitoring and testing by experienced geotechnical personnel should be considered au integral part of the
construction process. E3RA is available to provide geotechnieal monitoring of soils [Ivoughout construction.
January 5, 2007
T06397 / Yelm Dental
E3RA_ Ina
Weappreciatethe opportunity [o be ofservice on this project Lfyou have any questions regarding this report
or any aspects of the project, please feel flee to contact our off~ce_
Sincerely,
E3RA, Inc.
~~ ,,~i
4_~-
Casey R. Lowe, E.L'f.
Staff Engineer
James E Brigham, P.E.
Principal Engineer
CRL/JEB
Enclosures: Figure 1 Location Map
Figure 2 - Site & Exploration Plan
Attachment: Test Pit Logs TP-l through TP-3, Sleve Analysis
Januap~5, 2007
T06397 /Yelm Dental
E3RA. Inc.
TEST PIT LOGS -Yelm Dental Office
Death (feed Material Descriptien Samole No.
Tesf Pif TP-1
Locaton: Parking at existing dental office
Approximate ground surface elevation Unknown
0.0 - Q7 Crushed rock
0] 2.0 Medium dense, moist, black ash slty sandy gravel with boulders and cobbles (SP-SM) S-I
2.0-R5 Medium Dense, moist, tan sandy gravel w/silt; cobbles, and boulders (SP). 5-2
Test pit tennina[ed at approximately 95 Cect
Moderate caving observed at 45 fee[
No ipoundwater or mottling noted
Depth (feet) Material Description Samnle No.
Test Pit TP-2
Location: Existing home front yard
Approximate ground surface elevation: Unknown
0.0 - 0.5 Top Soil
07-2.5 Medium dense, moist, black ash silty sandy gravel with boulders and cobbles (SP-SM)
25- 10.0 Medium Dense, moist, Ian sandy gravel w/silt, cobbles, and boulders (SP). S-1
Test pit terminated a[ approximately l0 feet
Moderate caving observed at 5 feet
Na groundwater or mottling noted
Depth (feet) Material Descrintion Samole No.
Test Pit TP-3
Location: Ezis[ing home backyard
Approximate ground surface elevation: Unknown
0.0 - 0.6 Crushed rock
Ob-2.0 Medium dense, moist, black esh silty sandy gavel w/boulders and cobbles (SPSM)
2.0 - 5.5 Medium Dense, moist, tan sandy gravel with silt, cobbles, and boulders (SP).
5.5 - 10.0 Medium Dense, [an sandy graveVgravelly sand (SP). S-1
Test pit terminated at approximately 10 feet
Slight caving observed at 5.5 feet
No groundwater of mottling noted
Date Excavated: IUIS/O6 Eogged'oy: C"ni,
Particle Size Analysis Summary Data
Jab Name_ Yelm Dental Office
Job Number: T06397
Tested By: ALH
Date: 11/20/05
Boring#'. Perc#2
Sample #'. S-1
Depth: 5'
Moisture Content (%) 51
Sieve Slze Percent
Passing (%)
3.0 in. (75.0 100.0
1.5 in. (37.5 78.5
3/4 in. 19.0) 56.0
3/8 in- 9.5-mm) 36.6
No. 4 (4.75-mm) 30.1
No. 10 (2.00-mm) 10.5
No. 20 .850-mm 9.4
No. 40 (.425-mm) 7.7
No. 60 .250-mm) 6.2
No. 100 .150-mm) 5.5
No. 200 (.075-mm) 5.2
Size Fraction Percent By
Weight
Coarse Gravel 44.0
Fine Gravel 26.0
Coarse Sand 19.5
Medium Santl 2.9
Fine Sand 25
Fines 5.2
Tolal 100.0
LL
PI
D70 1.35
030 4.74
D60 27 42
Cc 0.78
Gu 1592
lSTM Classification
Group Name Brown poorly graded gravel with silt and sand
Symbol (GP-GM)
Figure
_ _~ I Soil Classification uata Sheet
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