HomeMy WebLinkAboutGeotech Investigationtants lncn
GsotGchnlel / Envlronmentel Engincerlng. ltlat€ridt Tcttlng
June 19,2018
Deb Fiscus
Garfield County Landfill
0075 County Road 246A
Rifle, Colorado 81650
Job Number:02-5136
Subject: Preliminary Geotechnical Investigation
and Geologi c Hazard Evaluation, West
Parcel Development, Garfield County
Landfill (GCLF), Rifle, Colorado
Dear Ms. Fiscus:
An approximate2}-acre parcel located at the west side of GCLF is owned by Garfield County
and intended for future landfill use as the facility develops. An open and vacant area at the north
side ofthe landfill access road andjust before the scale house encompasses a portion ofthe 20-
acres. For discussion purposes this will be referenced as the West Parcel Development O[PD).
The general vicinity is shown on Figwe 1 and the WPD area is shown on Figure 2.
Backsround
Based upon Garfield County's directive during approximately 2009, NWCC developed
conceptual designs to construct an engineered and robust polyethylene doublelined cell including
leak detection at the WPD in response to Energy and Production (E&P) Industry pressure to
dispose highly contaminated E&P wastes at GCLF. The intent was to respond to industry waste
disposal needs while limiting potential environmental release liabilities through consfruction of a
waste disposal cell adequately designed to contain these highly contaminated materials.
A Sfiategic Solid Waste Management Plan (SSWMP) (NWCC/AECOM, May 2014) was
developed and implemented by the Garfield Board of County Commissioners during 2014 to
systematically develop the landfill into a self-sustaining enterprise system through thoughtful and
careful planning. The E&P waste cell was recommended with the addition of a solidification
basin. However, shortly after implementation of the SSWMP, a down-turn in the E&P industry
occured, E&P waste receipts declined, and continues to date. Therefore, the county determined
to suspend discussions regarding this facility.
To help expedite landfill planning and help determine how the WPD might best be used, GCLF
requested that NWCC, Inc. (NWCC) conduct a preliminary geotechnical evaluation of the WPD.
Numerous options exist and use of the parcel should be encompassed in overall landfill
development, planning, and revision of the SSWMP. This geotechnical phase is a first step and
additional evaluation (e.g. groundwater characterization) may be required depending on what the
final intended use of the WPD will be.
NWCC conducted field activities on September 28, 20I'l that included obtaining data from
cursory observations, excavation and logging of five test pits, soil sampling, and subsequent
analysis. GCLF provided excavation services. Soil samples were fransported to the NWCC
(970) 879-7888. Fax (970) 879-7891
2580 Copper Ridge Drive . Steamboat Springs, CO 80487
Geotechnical Investigation - West Parcel Development June 19,2018
Geotechnical Laboratory located in Steamboat Springs, Colorado for soil classification and
materials properties testing. Field activities and findings are surnmarized below.
Site Conditions
The WPD was undeveloped and vacant during site activities and appears to be situated within a
previous burn area. The vegetation consists of sage brush, sparse weeds, and grasses and the
topography is variable and generally slopes moderately down to the south-southwest. West
Sherrard Creek intermittently flows along the east side of the parcel and two intermittent
drainages are located north to south, one through the approximate middle and one along the west
side of the WPD. Surface water was not observed in these intermittent drainages during site
activities. Natwal gas pipelines are located along the east and south perimeters of the WPD.
Ge olo gic H az ard C onditi ons
Landslide or signs of slope instability were not observed in the WPD and cut slopes or
excavations are anticipated to be relatively stable. NWCC concurs with the Land Transfer Audit
(Land Transfer Audit, West Garfield County Landfill, TerraMatrix, May 1995) findings that,
"Steep slopes on the north edge ofthe property pose a geologic hazard for the northern portions
of the property. Hazards include rock fall and mass movement. A majority of the site is free
from geologichazards."
Based on NWCC's site observations, terrain at the WPD is relatively flat while the overall terrain
gently slopes to the south and southwest. The immediate land surface at the north side of the
WPD is further from the cliff base and does not rise nearly as high or as steeply as along the north
and northwest sides of the main landfill areas. The slope appears stable as the topography is
relatively flat and the area appears well drained. Even though clays are present on-site, the swell
potential appears relatively low and should not have an adverse impact on proposed structures, if
properly designed and constructed. Overall, geologic hazards at the WPD appear minimal and
less likely than in the main landfill area along the cliff base.
Subsurface Conditions
To investigate subsurface conditions, five test pit locations were proposed. Prior to test pit
excavation, a surveyor under confract with GCLF located the proposed test pits. GCLF excavated
the five test pits using a Volvo EC300 EL trackhoe. Excavations continued unfil the limits of the
trackhoe were reached or refusal. The approximate test pit locations are shown in Figure 2. Test
pit locations were not surveyed.
The subsurface conditions encountered were variable and generally consisted of a relatively thin
layer ofnatural topsoil and organic materials overlying interbedded clays, gravels and sands to
the maximum depth investigated. Test Pits 1 through 3 were excavated to 21 feet below the
existing ground surface (bgs), which was the maximum reach for the trackhoe. Practical rig
refusal with the tackhoe on boulders was encountered in Test Pits 4 and 5 at depths of 16 and 17
feet bgs, respectively. Graphic logs of the exploratory test pits, including the associated legend
andnotes, are provided in Figures 3 and4.
A layer of natural topsoil and organic material was encountered at ground surface in all the test
pits and ranged from 2 to 10 inches in thickness. Interbedded clays, gravels and sands with
numerous cobbles and boulders were encountered beneath the topsoil and organic materials in all
of the test pits and extended to the maximum depth excavated in each test pit. The interbedded
clays, gravels and sands were fine to coarse grained with numerous cobbles and boulders, low
plastic, medium dense to stiff, dry to slightly moist, and brown in color. Samples of the soils
ITWCC,Inc.
Geotechnical Investigation - West Parcel Development
Garfield County Landfill, Garfield County, Colorado
May29,2018
obtained from the test pits at various depths classified as CL to CL-GC to GC to CL-SC soils
in accordance with the Unified Soil Classification System.
Groundwater was not encountered in the test pits during the field investigation; however,
groundwater levels in monitoring wells at the adjacent landfill increase and decrease
with seasonal changes. Shallow groundwater is typically perched atop impervious
bedrock and believed to be recharged through precipitation and seasonal runoff. Bedrock was
not encountered in any ofthe test pits.
Soil Sample Collection
A total of 10 soil samples were collected including, one sample at Test Pit 1 from 20 to 2I
feet bgs, three at Test Pit 2 from 5 to 6, Il to 12, and 19 to 20 feet bgs, three at Test Pit 3 from 2
to 3, 10 to 11, and 17 to 18 feet bgs, one at Test Pit 4 from 7 to 8 feet bgs, and two at Test Pit 5
from 1 to 2 and 9 to 10 feet bgs. For testing puq)oses, portions of each sample were
composited at the laboratory into sample 1P*.
Laboratorv Results
Samples obtained from the test pits were examined and classified in the laboratory by the
project engineer and principal engineer, prior to conducting the testing. Laboratory testing
included natural moisture content, grain size analysis, liquid and plasfic limits,
standard Proctor, unconfined compressive strength and falling head permeability testing.
Laboratory testing was conducted in general accordance with applicable ASTM/AASHTO
specifications. Results of the labomtory tests are summarizedin Table 1.
Based upon testing of the 10 collected samples, in-situ moisture contents ranged from 5.2
to 8.0%; liquid limits ranged from 23 to 29o/o and plasticity indices from 9 to l4%.
Composite sample lP was screened on the /+-inch sieve and a standard Proctor test was
conducted on the materials passing the 314 -inch sieve in accordance with ASTM D 698. The
standard Proctor Test provides maximum remolded dry density and optimum moisture content
data to assess material conditions for compaction and construction pwposes. Sample lP
classified as a CL-SC soil (gravelly sand and clay), the optimum moisture content is I3.5%
and the maximum remolded dry density was 117.8%. The Proctor test results are shown on
Figure 5 and summuizedin Table 1.
Relatively undisturbed, hand drive samples were taken as the Proctor Test was completed.
Falling head permeability and unconfined compressive sfrength tests were conducted on the
remolded samples. Based upon laboratory results, the remolded permeability of the sample
compacted to 98.7 percent of the maximum Proctor denstty and 1.3 % below the optimum
moistwe content was 6.82 x l0-7 centimeters per second (cm/sec) and a sample compacted to
95.5% of the maximum Proctor density and 3.1 %o above the optimum moisture content was
2,400 pounds per square foot (psf). Results of the falling head permeability tests are shown in
Table2.
Preliminarv Geotechnical Recommendations
The intent of conducting the limited geotechnical evaluation was to provide cursory information
for planning purposes. Since the fuhre use of the WPD is unknown, this investigation
is considered a first step to help evaluate what other investigations, if any, may
be required depending on proposed uses of the parcel. NWCC understands that a scale
house move to the landfill access road in this area is planned. This report, augmented by
geotechnical engineer field observations, may be used to design improvements associated
with the planned scale house move (e.g. scale house foundation, road base, and parking area
base).
NWCC, Inc.
Geotechnical Investigation - West Parcel Development Iune 19,2018
The parcel may be considered adequate for numerous uses (e.9. septage treatment facility and/
or impoundments, recycle area, borrow source, solar panel farm). However, to achieve optimal
use of the parcel, carefrrl and thoughtful planning is required.
Preliminary Foundation Recommendations
NWCC believes a feasible foundation system for the proposed buildings and./or stuctures
at the site will consist of spread footings or reinforced mats placed on the natwal clays,
gravels and sands or on properly compacted structural backfill materials. NWCC
suggests that the recommendations outlined below be followed in the preliminary
design of the buildings and sfructure foundations.
1) NWCC recommends the footings and./or mats be placed on the clays, sands and gravels
or properly compacted structural backfill materials be designed using an allowable soil
bearing pressure of 3,000 psf. Based on the assumed swell potential of the on-site clays,
NWCC recommends the footings and/or mats also be designed using a minimum
deadload pressure of 500 psf.
2) NWCC recommends a Site Class C designation be used in structural design calculations
in accordance with Table 20.3-1 in Chapter 20 of ASCE 7-10.
3) Lateral resistance of foundations placed on the natural soils or properly compacted fill
materials will be developed as sliding resistance of the footing on the foundation
materials. Sliding friction at the bottom of the footings or mats can be taken as 0.40
times the vertical dead load. Passive pressure against the sides of the footings or mats
can be calculated using an equivalent fluid unit weight of 250 pcf. Compacted fill placed
against the sides of the footings or mats to resist lateral loads should be compacted to at
least 100% of the maximum standard Proctor density determined in accordance with
ASTM D698.
4) Footings and mats should be placed well enough below final backfill grades to protect
them from frost heave. Thirty-six (36) inches is recognized by the local building
authority.
5) Based on experience, NWCC estimates total settlement for footings and mats designed
and consfiucted as discussed in this section will be approximately I inch. Care should be
taken when excavating the foundations to avoid disturbing the supporting materials.
Disturbing the bearing materials may increase settlements.
Preliminary Site Grading Recornmendations
NWCC assumes site grading at the site could include cut and fills, ranging from 5 to 30 feet in
depth, depending on the proposed development plan. The following recommendations should be
observed for preliminary site grading design and construction.
l) Temporary cuts for foundation construction should meet OSHA safety standards for
trenching and temporary excavations. Permanent, unretained cuts should not exceed a
2(H):1(V) configuration. Permanent cut slopes should be limited to 30 feet in height or
less unless stable bedrock is encountered. The risk of slope instability will be
significantly increased if groundwater seepage is encountered in the cuts. NWCC should
be notified immediately to evaluate the site if seepage is encountered or deeper cuts are
planned. Additional investigations and/or stabilization measures may be wa:ranted at
that time.
2) Contractor must provide a consffuction sequencing plan for excavation, wall construction
and bracing and backfilling for the steeper and more sensitive portions of the site prior to
starting the excavations or construction.
IYWCC,Inc.
Geotechnical Investigation - West Parcel Development
Garfield County Landfill, Garfield County, Colorado
May29,2018
3) Fills up to 30 feet in height can be constructed to a 2(H):1(V) or flatter configuration.
Fill areas should be prepared by stripping topsoil and organics, scarification and
compaction of exposed subgrade to at least 95%o of the maximum standard Proctor
density and within 2% of optimum moisture content as determined by ASTM D698. Fills
should be benched/keyed into natural hillsides after the topsoil and organic materials
have been stipped using minimum 6-foot wide benches. Fill materials may consist of
the on-site soils (exclusive of topsoil, organics or silts) and should be uniformly placed
and compacted in 6 to 8 inch loose lifts to the minimum density value and moisture
content range indicated above.
4) Where unstable fill surfaces cannot be stabilized by scarification and recompaction,
additional stabilization measures will likely be required. These measures may include
additional subexcavation and bacldrll with imported granular materials and/or placement
of stabilization fabric (Mirafi 500X or equivalent) or geogrid products. Stabilization
requirements are likely to be variable based on subsoils, groundwater levels and surface
runoff conditions at the time of construction, and should be evaluated by NWCC at the
time of construction.
5) Surface drainage features should be provided around all permanent cuts and fills and
steep natural slopes to direct surface runoff away from these areas. Cuts, fills and other
stripped areas should be protected against erosion by revegetation or other methods.
Areas of concentrated drainage should be avoided and may require the use of riprap for
erosion contol.
6) A registered professional engineer experienced in site plan preparation in this arid to
semi-arid geographic area is recommended for site grading and drainage plan preparation.
7) Subgrade preparation and placement of materials should be observed and tested by
NWCC in the field and laboratory for compliance with the contract documents.
Conclusions
Based on NWCC's site observations, the results of the field and laboratory investigations, and
experience with other projects at the GCLF, NWCC believes that the soil properties are
acceptable for various construction purposes provided the structures are properly designed and
constructed. Hazardous geologic conditions at the site that would render the proposed WPD
unfeasible were not observed.
Limitations
This report has been prepared in accordance with generally accepted geotechnical engineering
practices in this area. The conclusions and preliminary recommendations submitted in this report
are based upon the data obtained from the exploratory test pits advanced at the approximate
locations shown on the site plan, the results of the laboratory investigation and NWCC's
experience with similar projects in this area. The test pits were widely spaced to evaluate the
subsurface conditions in the vicinity of the WPD. We believe that this information gives a high
degree of reliability for anticipating the conditions across the site. However, the
recommendations contained in this report are professional opinions and cannot control nature, nor
can they assure the subsoil and groundwater conditions beneath or adjacent to those observed.
Professional judgments based on the subsurface conditions encountered are presented in this
report. They are based partly on evaluation of technical information gathered, partly on our
observations made during the field investigation, partly on our assumptions regarding the
proposed construction, and partly on our experience with other projects having similar subsurface
conditions. NWCC does not warranty or guarantee the performance of the project in any respect;
NWCC, Inc.
Geotechnical Investigation - West Parcel Development June 19,2018
only that our engineering work and judgrnent rendered meet the standard of care in our profession
at the time it was rendered.
This report is based on the investigation at the described site and on the assumed construction as
stated herein. If either of these conditions is changed, the results would also most likely ohange.
Therefore, NWCC strongly recommends that our firm be contacted prior to finalizing the
construction plans so that we can verify that our recommendations are being properly
incorporated into the construction plans. Man-made or nafural changes in the conditions of a
property can also occur over a period of time. In addition, changes in requirements due to state of
the art knowledge andlor legislation do from time to time occur. As a result, the findings of this
report may become invalid due to these changes. Therefore, this report is subject to review and
not considered valid after aperiod of 3 years or if conditions as stated above are altered,
If you have any questions regarding this report or if we may be of further service, please do not
hesitate to contact us.
Sincerely,
NWCC,Inc.
Erika K, Hill, E,I.T.
Project Engineer ,.
Reviewed by Brian
Principal Engineer
Z:Uobs\02"5136 Gorffold County Landfill\Engineering\
West Parcel Dovolopmeht\GcLF WpG Preliminary Geo Inv snd Oeohlzsrd Evnluation
NWCC, Inc.
Figures
1 ioii CO-OIADOito a.i J:ritlei.
rcsco5.000 w t GSS: rn7:ii.ooar !r
10sr8!.00Q'f/rntrsl oco rli N/G5S.::.00( rr
l-
I :f;.:.::. _o?t t.:. :.r-i C.i-:r.,. r-........_+r. 1. _
GARFIELD COUNTY LANDFILL
1
.O
FI
frLAAZ
H<6
oa.aao
AAp=
(Jf
q
i>Hrzl
tz7 ZvuF
ffi
$,
m o r o=oo o o c=oo z > Idcm o tr Irze E = fi=l
d F ! rda9 r i dlri
= q > r*t
E E fi EE'
- ol's =F
o-iFz=ga
I
oo c oo
=tsH49>0a-f,d662@
oF69PTH;toogn trg
6z
6I
czo
u
iEgFet=c*FcHE
E I I Es65 *sfigH
R d E F E3 ESEEx 5 d e t= Fii
'Hf; * 5 z
MFH
ilt-r: g
1l
IFIH
H
c
ou
ofi
5
mz
I
ozIo
-
-5
a
q(
s(/
.3
(
"3
a
fc -)$;ET E $
o
f s++- "J"e"'q dI
s
T
.\$
t ltt ?t.i ''Ll r H
e
1
,6
t i*
)
/'t
E
a
I
E
%l
,t
I
I\
)
q-g
/
c
/
tsd
ss
T
!
!e
r
t
T
I
Tt
tI
g
I
/
I
3o
(
f;-2--F
t
N
o
Es*
FE6E385*
ErEhFYT'OHZItJ4>1 ?H
Fo
C) 'l>ld
4a5'lz,r
<FltrFd
Hffi
)
&i
i
!
d
3
\
I
s
R
d
e
i
i
i
.ri
!
I
+
R
Teet Pif. I Test Pit 2 Test Pit 3
Depth (ft)
0 0
5 5
10 10
15 15
20 20
25 25
T,EGEND:NOTES:
1) Test pits vere excavated on September 28,' 2OL7 rith a Volvo EC300 EL trackhoe
provided by client.a TOPSOI AND ORGANICS
w
CIAYS, GRAVELS AND SANDS - Interbedded,
fine to coarse grained with numerous
cobbles and boulderg, lor plastic, medium
dense to stiff, dry to slightly moist and
brorn.
2l Test pit locations rere determined by' instrument survey provided by client.
3)
4)
The elevations of the test pits were
not measured and the logs are drawnto t,he depths investigated.
I Large Disturbed Bag Sample.The lines betveen materials shorn on the
test pit logs represent the approximate
boundaries betveen material types and
transitions may be gradual.
Title:LOG, LEGEND AND NOTES
Dete:
5/3o/2018
1970)87sm. Fs (070)EB7&1
2S &ptd RBF Dil.
Sbmhd Stlns, trd &87
Job Name: 'ITest Parcel Development Job No.
02-5136
Ioca$oa:Garfield County, Colorado It8ure B
Test Pit 4 Test Pit 5
Depth (ft)
0 0
5 5
10 10
15 15
20 20
25 25
I,EGEND:NOTES:
a TOPSOI AND ORGANICS.1)Test pits lrere excavated on September 28,
2017 rith a Volvo EC300 EL trackhoe
provided by client.
CLAYS, GRAVELS AND SANDS - Interbedded,
fine to coarse-grained, ritb numeroua
cobbles and boulders, low plastic, medium
dense to stiff, dry to slightly moist and
brown.
2)Teet pit locations were determined by
instrument survey provided by client.
3)The elevations of the test pits vere
not meaeured and the logs are drarnto the depths investigated.
I
I
Large Disturbed Bag Sample.
4)The lines betreen materials shorn on the
test pit logs represent the approrimate
boundarieg betreen naterial tyles and
transitions may be gradual.Indicates depth of practical rig refusal on
boulder.
Tltle:LOG, LEGEND AND NOTES
Dete:
5/3O/2Ot8
(970)87$7E&. Fd(070)87e7&1
2S OpF Rtsgs 0to3
sbnbd sginF, mEdo u87
Job Nane: 'IYest Parcel Development Job No.
02-5136
Iocatlon: Garfield County Landfill, Garfield County, Colorado Fkure A.}
(Jlo
otN"rr l9lo lo
"H l:illo
HIF"r l?Nlo
\lo
5oooo
Dry Density - PCF
N)oOoo(oo@O
o
(Jl
o
3
9.o
octlo(Jt
o
Ts
N)o
N)(Jr
(r)o
LI
,nLN
1,il
t{
lrn
il
W
I,rt
IA
n
(
ITI,t
1
W
tl
Yt
h
il
N
t
l1l
ffi
t
1)AI
Il
I
]l.Ll
T\I
!
n
A
v{
t
4
n
I
x
't$l.t
fiT
NV
IlYt
WI
t{
v
I
I
o
Ezo
I
€oo
ll
0)a()
q_
clo
9.oE
3oa
Ioq)
=s9_o-
oocf
t-!)
=o-
=
!noo-{on{ma,{-m
U,c
o
I
I
@D
g
o
ooql
3io
oo
3!o
c2.
o
CN
0)
3E
6-
oI
oooo:.It
=to3
oa
o)
!P-
@q))o-
olo-
a
0)
I
a)o
6oloo-
o
CD
5
=
@
o
o
o!l
3oozo
1'
=o
x.
3tr
3
oeoo
=o
{
bo
ro
C)
oItF
=9.o
c
o
oo
o:!?
9^'(,l
s
!
ooo
CLtr
o
@+
g
o)(O
@
trltc
CL
tr
i,l
N)(Jl
s
!
ooEi
c.
3
CLox
os
E,
AI
o
N)(o
No
o
o
o,
g
\t
s
an
AI
J*
5o
s
9,
Fo
ot
ING'o
5o)
s
oC'z
9
oNt(,l
(r)
o)
'nq
tr
d
gr
Tables
NWCC, Inc.
TABTE 1
SUMMARY OF LABORATORY TEST RESULTS
UNIFIED
soIL
CI,ASS.
1 zo-21 6.0 25 t2 39 26 35 Sandy Clay and
Gravel GC-CL
z 5-6 8.0 24 11 30 30 40 Sandy Gravelly CL
z II-L2 7.6 24 11 28 27 45 Sandy Gravelly
Clay
CL
2 19-20 7.1 26 13 28 30 42 Gravelly Sandy
Clay CL
3 2-3 7.O 25 I 39 29 32 Sandy Clayey
Gravel GC-GM
3 10-11 7.2 z5 11 40 27 33 Sandy Clayey
Gravel GC
3 t7-18 7.1 2?L4 36 26 38 Sandy Clay and
Gravel CL-GC
4 7-8 5.2 25 13 42 23 35 Sandy Clay and
Gravel GC-CL
5 1-2 5.7 29 T4 36 22 42 Sandy Gravel CL-GCand.
b 9-10 5.4 23 10 44 30 z6 Clayey Sandy
Gravel GC
1P 13.5r 117.8*25 10 l?".40 43 3400**Gravelly Sand
aud Clay CL-SC
SOIL or BEDROCK
DESCRIPTION
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
PERCENT
PASSING
No. 200
SIEVE
GRADATION
SAND
(%)
GRAVEL
(%)
ATTERBERG UMITS
PI,ASTICIfl
INDE(
(%\
IJQUID
IIMIT
(%)
DRY
DENSITY
(pcr)
NATURAL
MOISTURE
CONTENT
(%)
SAMPI,E LOCATION
DEPTII(feet)
TEST
PIT
roptimum moisture content and marimum dry density determined per ASTM D698.
*t Unconfined compression test performed. on remold.ed. sample with moisture content = 16.6% and dry density = 112.5 fbs/ft3
+** Proctor Sample screened off 3/4" sieve. JOB NUMBER: 0Z-b136
TabIe 2. FALLING HEAD PERMEABILITY CALCULATION
PROJEGT: West Parcel Development - Garfield County Landfill
JOB NUMBER: 02-5136
DATE: 211312018
PERM NO.1
MATERIAL: Gravelly Sand and ClaY
I SAMpLE: 1P Remolded Sample @ 98.7o/o of Maximum Std. Proctor Density & 1 .3o/o Below Optimum Moisture Content
k = 2.303 * a*UA*t (log h1/h2)
Start Time 113112018 (:A4
End Time 21121201815:25
Value Units H1=lnitial readino 102 cm
a= afea 0.635 cm2 H2=final readino 92 cm
A = Area of sample (brass liner)19.17 cm2 lloo h1/h2 0.04481
3.45 inches t = elapsed time 43852.50 seconds
8.7503 cm k = oermeabilitv 6.E2E-07 cm/sec