HomeMy WebLinkAboutMONTAVA - PHASE G & IRRIGATION POND - BDR210013 - SUBMITTAL DOCUMENTS - ROUND 5 - STORMWATER-RELATED DOCUMENTS (3)DRAFTSUBSURFACE EXPLORATION REPORT
MONTAVA DEVELOPMENT – TRACT E – DETENTION POND
EVALUATION OF GROUNDWATER AND SUBSURFACE CONDITIONS
FORT COLLINS, COLORADO
EEC PROJECT NO. 1172058
Prepared for:
Montava Development, LLC
430 N College Avenue, Suite 410
Fort Collins, Colorado 80524
Attn: Mr. Max Moss (Max@hf2m.com), and
Mr. Forrest Hancock (forrest@montava.com) - Development Director
Prepared by:
Earth Engineering Consultants, LLC
4396 Greenfield Drive
Windsor, Colorado 80550
DRAFT4396 GREENFIELD DRIVE
W INDSOR, COLORADO 80550
(970) 545-3908 FAX (970) 663-0282
www.earth-engineering.com
December 6, 2022
Montava Development, LLC
430 N College Avenue, Suite 410
Fort Collins, Colorado 80524
Attn: Mr. Max Moss (Max@hf2m.com), and
Mr. Forrest Hancock (forrest@montava.com) - Development Director
Re: Supplemental Subsurface Exploration and Geotechnical Engineering Services
Montava Development – Tract E – Detention/Irrigation Pond
Installation of 4 Monitoring Wells and Liner Recommendations
Fort Collins, Larimer County, Colorado
EEC Project No. 1172058
Mr. Moss and Mr. Hancock:
Enclosed, herewith, are the results of the subsurface exploration completed by Earth Engineering
Consultants, LLC (EEC) personnel for the referenced project. The results presented herein are
from the evaluation of the field observation and laboratory testing procedures obtained from four
(4) soil borings which were then converted to long-term groundwater monitoring wells (MWs)
positioned around the perimeter of the proposed detention pond currently in the design phase for
Tract E at the Montava Development project, (please refer to the site plans included herein),
which were drilled to depths of approximately 15 to 20 feet below current site grades. This study
was completed in general accordance with our proposal dated July 12, 2022.
We understand the proposed detention pond will have a top of embankment elevation of
approximately 5002 as presented on the topographic map provided to us by the project’s civil
engineering consultant, TST, Inc.- Consulting Engineers, along with a bottom or floor elevation of
approximately 4987 (normal bottom of the pond) and 4982 (bottom of the pond at the intake). The
normal high water level within the pond is planned at approximately 4998.75 and at a 100-year
elevation of 5001, which would create an approximate pond volume of 53 acre-feet (AF) or
approximately 85,506 cubic yard (CY). As presented on the enclosed site plan and TST’s civil
drawing/grading plan Sheet 6 of 10 around the perimeter of the pond will be an approximate 4.75
foot “stacked stone wall” from elevation 4999.75 to elevation 4995.0. At the base of the stone
stack wall the bottom of the pond will be sloped at a 4:1 ratio (horizontal to vertical) toward the
intake, which has an elevation of 4984 at the intake and an elevation of 4982 along the bottom of
the pond. The side walls/embankments of the pond are anticipated to be constructed with
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 2
approximate 4:1 slope (horizontal to vertical) or flatter with either an “enhanced cohesive” earthen
liner or a PVC synthetic membrane liner placed along the wetted perimeter to minimize seepage
and/or groundwater intrusion.
To evaluate and analyze the existing subsurface conditions around the outer perimeter of the
proposed pond configuration, and to assist the civil engineering consultants in the design of
either an earthen liner or synthetic liner for pond, EEC personnel were requested to perform a
subsurface exploration which consisted of drilling and sampling the subsurface conditions
around the perimeter of the proposed pond configuration, (please refer to Figure Nos. 1 and 2 in
the Appendix of this report), with a total of four (4) test borings drilled to approximate depths of
15 to 20 feet below existing site grades, and upon completion of the drilling operations, convert
the bore holes to long-term registered PVC cased piezometers/monitoring wells.
The purpose of this report is to describe the subsurface conditions encountered within the four
(4) borings/piezometers/MWs, analyze and evaluate the test data, and provide geotechnical
recommendations concerning the design and construction of the new synthetic liner for the water
storage pond.
EXPLORATION AND TESTING PROCEDURES
The four (4) boring locations were established in the field by EEC personnel using a hand-held
GPS unit referencing approximate horizontal coordinates from a “Google Earth” image of the
site, and by estimating locations from identifiable site features. The approximate locations for
the four (4) borings/piezometers/MWs, identified herein as MW-1 through MW-4, are presented
on Figure Nos. 1 and 2 in Appendix A of this report. Ground surface elevations were obtained
by using linear interpolation of contours as presented on the topographic map prepared by the
civil engineer. The topographic map was also used to create the groundwater contour map as
further discussed herein. The estimated ground surface and top of casing elevations are recorded
on each respective boring log. The locations of the test borings/piezometers and ground surface
elevations should be considered accurate only to the degree implied by the methods used to make
the field measurements.
The four (4) test borings/MWs were completed using a truck mounted, CME-75 drill rig
equipped with a hydraulic head employed in drilling and sampling operations and were advanced
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 3
using 4-1/2-inch nominal inside diameter hollow stem augers. After completing the drilling and
sampling, and prior to removal of the hollow stem augers, PVC cased piezometers were installed
in the open boreholes through the hollow stem augers. The piezometers/monitoring wells were
constructed with 2-inch nominal diameter schedule 40 manufactured well screen and riser pipe.
In general, the piezometers consisted of an approximate 10 foot section of flush threaded slotted
well screen at the bottom of the boreholes with flush threaded solid riser pipe, as required, to
extend the piezometers above ground level. The screen portion of the piezometers were
backfilled with 10/20 silica sand, with an approximate 2-foot bentonite plug/seal placed above
the sand layer, and then backfilled with a blend of the auger cuttings generated and bentonite to
the existing ground surface elevations. A 4-inch by 4-inch by 4-foot in length steel proactive
casing encased in concrete was installed at the surface of MW. Cross-sectional schematics of the
piezometer/MW installations are indicated on the attached boring logs. Photographs taken
during our field exploration are included in the appendix of this report.
The State of Colorado Division of Water Resources was notified of intent to construct
monitoring holes prior to beginning the field exploration. Copies of those notices with
acknowledgement from the State Engineer’s Office are attached with this report. The well
construction and test reports will be provided to the Division of Water Resources including
copies of the boring logs provided with this report. If the monitoring wells will remain in place
longer than 18 months, it will be necessary to notify the Division of Water Resources and
complete registration of those wells. Piezometer installation was completed by a licensed water
well driller and was completed in accordance with the water well construction rules from the
Division of Water Resources.
Samples of the subsurface materials encountered were obtained using split barrel (Standard
Penetration Test / SPT) sampling procedures. In the split barrel/SPT sampling procedures,
standard sampling spoons are advanced into the ground by means of a 140-pound hammer falling
a distance of 30 inches. The number of blows required to advance the split barrel sampler is
recorded and is used to estimate the in-situ relative density of cohesionless soils and, to a lesser
degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. In
conjunction with the split spoon samples, two (2) composite samples of the overburden subsoil
materials were also collected from the test borings for further laboratory analyses. All samples
obtained in the field were sealed and returned to the laboratory for further examination,
classification, and testing.
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 4
Laboratory moisture content tests were completed on each of the recovered split-spoon samples.
In addition, the unconfined strength of select samples was estimated using a calibrated hand
penetrometer. Atterberg limits and washed sieve analysis tests were completed to evaluate the
quantity and plasticity of fines in selected subsurface samples. Additional laboratory testing
procedures included moisture-density relationship/standard Proctor density (ASTM Specification
D698) and falling head permeability characteristics (ASTM Specification D5856) on the
bulk/composite samples collected during the drilling operations. Results of the outlined tests are
indicated on the attached boring logs and summary sheets.
As part of the testing program, all samples were examined in the laboratory by an engineer and
classified in accordance with the attached General Notes and the Unified Soil Classification
System, based on the soil’s texture and plasticity. The estimated group symbol for the Unified
Soil Classification System is indicated on the boring logs and a brief description of that
classification system is included with this report.
SUBSURFACE CONDITIONS
An EEC field engineer was on site during the drilling operations to evaluate the subsurface
conditions encountered and direct the drilling activities. Field logs prepared by EEC site
personnel were based on visual and tactual observation of disturbed samples and auger cuttings.
The final boring logs included with this report may contain modifications to the field logs based
on the results of laboratory testing and evaluation. Based on the results of the field borings and
laboratory evaluation, subsurface conditions can be generalized as follows.
Sparse vegetation/weed growth/agricultural growth, as evident in the site photographs in the
Appendix of this report was encountered at the surface of each test boring/piezometer. The
subsurface materials encountered beneath the surficial layer generally consisted of sandy lean
clay transitioning to a poorly graded sand with gravel with depth, which extended to the depths
explored, approximately 15 to 20 feet. The overburden cohesive subsoils were generally soft to
medium stiff in-situ, and when properly moisture conditioned and compacted, appeared to
exhibit permeability characteristics conducive for earthen liner material; however, due to the
groundwater conditions and the proposed design of the pond, consideration should be given to
synthetic liner with a sufficient amount of cover to minimize the potential for groundwater
seepage/intrusion into the pond, as well as a slurry wall.
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 5
The stratification boundaries indicated on the boring logs represent the approximate locations of
changes in soil and rock types. In-situ, the transition of materials may be gradual and indistinct.
GROUNDWATER CONDITIONS
Observations were made while drilling, shortly thereafter and again on December 1, 2022, to
detect the presence and depth to hydrostatic groundwater within the completed borings. At the
time of our subsequent groundwater measurement episode on December 1, 2022 groundwater
was measured at depths ranging from approximately 8 to 12 feet below existing site grades. The
recorded measurements are listed on the upper right hand corner of each boring log/piezometer
included in the Appendix of this report.
Fluctuations in groundwater levels can occur over time depending on variations in hydrologic
conditions, fluctuations in the proposed water storage pond elevations, irrigation demands, and
other conditions not apparent at the time of this report. Monitoring in cased borings, such as
those installed for this project and protected from the infiltration of surface water, can more
accurately evaluate the depth and fluctuation in groundwater levels. EEC anticipates performing
periodic groundwater measurements over the next several months, especially after the
installation of either the earthen liner of the synthetic liner, to evaluate the groundwater
fluctuations and to evaluate the effectiveness of the liner, (i.e., an evaluation of the equilibrium
of water levels inside and outside of the pond configuration). The observations provided in this
report represent groundwater conditions at the time of the field exploration, and may not be
indicative of other times, or at other locations.
As part of our geotechnical engineering assessment we prepared a groundwater contour map,
included in the Appendix of this report, based on the approximate groundwater level reading
measurements obtained on December 1, 2022. The contour elevations were based on the
approximate ground surface elevations at each boring location, and the approximate depth at
which groundwater was encountered. As shown on the Groundwater Contour Map, the
hydrologic gradient/piezometric surface flow of the measurable amount of water is in the south
to southeast direction. The groundwater contour map presented herein on approximate 1-foot
intervals, is for illustration purposes only; variations may exist between boring locations across
the site and at different times of the year. It should be noted that the measured groundwater
contour elevation of the proposed pond configuration on December 1, 2022 was at an
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 6
approximate elevation of 4992; whereas the proposed bottom of the pond is currently designed at
elevations of 4987 and 4982, which is approximately 5 to 10 feet into the groundwater surface.
ANALYSIS AND RECOMMENDATIONS
Moisture Density Relationship-Standard Proctor Density
EEC personnel performed standard Proctor density (ASTM Specification D698) tests on the two
(2) composite samples of overburden cohesive materials collected during our field exploration.
For each composite sample, soil classification/Atterberg limits and minus No. 200 sieve wash
gradations in conjunction with the standard Proctor density tests were performed. The results of
the soil classification and standard Proctor density testing on the two (2) composite samples
collected during our subsurface exploration are presented in the Table below with curves
provided in the Appendix of this report.
Table I – Summary of Laboratory Compaction Characteristics and Classification of Soils
Sample ID
Standard Proctor Density Soil Classification
Optimum
Moisture
Content, %
Maximum Dry
Density, PCF
Liquid
Limit
Plastic
Index
% (-) No.
200 Sieve Description
Upper 5’ – 10’ 18.5 109.0 32 18 66.8 Sandy Lean Clay (CL)
Lower 10’ – 15’ 17.0 110.0 32 18 75.4 Lean Clay with Sand (CL)
It is our understanding the pond’s embankment modifications/improvements and the earthen
liner and wetted perimeter will be constructed with the excavated on-site overburden cohesive
soils obtained during the excavation phases. As further mentioned in this report the primary
focus is to create a uniform/consistent cohesive material having falling head permeability
characteristics of 1 x 10-7 cm/sec or slower.
Laboratory Falling Head Permeability Tests
EEC conducted a falling head permeability test (ASTM Specification D5856) on a remolded
overburden sample obtained from the soil borings as described herein. The sample was remolded
to near optimum moisture content and was compacted to approximately 95% of the material’s
standard Proctor maximum dry density (ASTM Specification D698) test results. The results from
this test indicated a coefficient of permeability (k-value) of 6.6 x 10-8 cm/sec. This measured k-
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 7
value indicates the overburden cohesive soils have permeability and/or seepage characteristics
suitable for reuse in constructing the earthen liner. The laboratory test results for the falling head
permeability sample are presented in the Appendix of this report.
General Geotechnical Considerations
Field and laboratory test results indicate the cohesive soils encountered in the piezometers are soft
to medium stiff in consistency and when properly placed and compacted, would be suitable for use
as an earthen liner material. However due to the current groundwater levels above the bottom the
designed pond elevation, consideration should be given to the use of a synthetic liner with a cover
to minimize groundwater intrusion, as well as a perimeter slurry wall. The design concept for the
liner and slurry wall will be to reduce the potential for seepage and groundwater intrusion, as
well as to enhance the holding capacity of the pond.
As evident on the Log of Borings/Piezometer Logs, and the groundwater contour map, the
groundwater levels ranged from approximately 5 to 10 feet above the current pond bottom
elevations. After the installation of the liner, readings of the piezometers/monitoring wells
should be performed to verify the effectiveness of the liner, (i.e., the equilibrium of water levels
inside and outside of the pond).
With use of an earthen liner and/or a PVC membrane liner, it is typically suggested that the
bottom of any pond be at least 3-feet above maximum anticipated groundwater level, or the
construction a deepened core trench into the underlying bedrock formation be installed to
minimize groundwater intrusion. It should be noted that the monitoring wells were only
completed to depths of approximately 15 to 20 feet below existing site grades and bedrock was
not encountered. A minimum/permanent operating level of water is also necessary to minimize
the amount of groundwater intrusion by maintaining a constant head as well as to reduce the
buoyancy effects on a PVC synthetic liner if selected for use on this pond.
The pond’s embankments/wetted perimeter should consist of a homogeneous cohesive material
constructed with relatively impervious clay material having a coefficient of permeability, (k-value)
of 1x10-7 cm/sec or slower when compacted to at least 95% of standard Proctor density (ASTM
Specification D698). We suggest the improvements of the existing embankments be cut to at an
approximate 1:1 slope and the proposed/enhanced liner be constructed on a minimum 4:1
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 8
(horizontal: vertical) or flatter slopes around the perimeter. The design of wave and slope
protection for the pond is beyond the scope of this subsurface exploration study and should be
reviewed during the final design stages.
It is recommended any vegetation within the limits of the pond configuration be stripped and
removed. It is anticipated that excavation of the pond could be accomplished by conventional
type excavation equipment; however specialized or rubber tired equipment may be necessary
when approaching the bottom of the pond due to the presence of groundwater and soft
compressible subsoils. Special precautions may be required to maintain a working platform at
the bottom of pond due to the potential for soft/compressible conditions at or near the
groundwater and/or perched surface interface.
For any proposed intake and/or outlet pipes, or any other intrusions penetrating the cohesive
embankments and/or the synthetic liner, the pipes should be properly bedded and backfilled with
approved, relatively impervious cohesive soils. The intrusions/pipes should be surrounded by a
minimum of 2-feet of relatively impervious cohesive materials having a coefficient of
permeability of 1x10-7 cm/sec. or slower when properly compacted as described herein. The
backfill should be compacted to a minimum of 95% of the material’s standard Proctor density as
determined by ASTM D698. Anti-seep collars should be placed around all inlet and outlet pipes.
Earthen Liner/Wetted Perimeter Improvements
Groundwater and/or the initial presence of a water surface as previously discussed was
encountered within the piezometers/monitoring wells at approximate depths of 8 to 12 feet below
existing site grades. To minimize the potential for groundwater fluctuations to impact and/or
enter the pond, we suggest the bottom of the pond have a minimum separation of 3-feet above
the maximum anticipate rise in groundwater and/or a minimum 3-foot earthen liner layer be
placed and compacted as part of the wetted perimeter improvements along the bottom of the
reservoir. Dewatering will be required to achieve the earthen liner improvements along the
bottom portion of the pond as the current design elevations are into the groundwater table.
Consideration could be given to installing a slurry wall around the perimeter the pond to further
reduce the potential for groundwater intrusion. A slurry wall subcontractor should review the
contents of this report and provide supplemental recommendations accordingly. A 90-day water
balance/seepage analysis may be required for the proposed Montava Tract E Pond
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 9
improvements. Included below are typical guidelines for developing a water storage pond.
The performance of the raw water storage pond may be required to conform to the “Colorado
State Engineer Guidelines for Lining Criteria for Gravel Pits” dated August 1999. The general
guidelines state the following:
“1.0 Design Standard: The intent of the reservoir lining design is to achieve
groundwater inflow (leakage rate) into the reservoir that is not greater than 0.03
ft3/day/ft2 (1x10-5 cm3/cm2/sec) multiplied by the length of the perimeter wall in feet,
multiplied by the average vertical depth of the perimeter wall as measured from the
ground surface to the pit bottom along the toe of the pit side slope, plus 0.0015
ft3/day/ft2 (5x10-7 cm3/cm2/sec) multiplied by the area of the bottom of the liner
system or natural bedrock bounded by the perimeter wall.
2.0 Construction Standards: The applicant must demonstrate the constructed liner
meets the requirements of the design by performing appropriate quality control
observations and tests. The applicant shall provide written documentation of the
work performed and results of the quality control field and laboratory tests.
3.0 Performance Standards: The Performance Standard shall be three times the
Design Standard as described above. The performance Standard shall be applied
to an initial test of competency of the liner, as well as to the on-going operation of
the reservoir.
3.1 Initial Liner Test
For Mined Pits: The unregulated groundwater inflow to the reservoir will be tested
by evacuating the contents of the reservoir and observing the inflow of water over a
period of 90 days. The start of the test will be under essentially dry conditions.
If the Montava Tract E pond is to conform, a water balance must be performed to demonstrate
the balance of the inflows (i.e. precipitation and groundwater) and outflows (i.e. evaporation)
equals the change in storage volume by a minimum of a 90-day test. Ongoing monitoring of the
water balance may also be required as determined by the Division Engineer.”
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 10
The berms/embankments surrounding the pond should be lined as part of the wetted perimeter
with an approved earthen liner material. Approved materials used in the earthen
liner/embankment should be placed in maximum 9-inch thick loose lifts, adjusted in moisture
content, and compacted to at least 95% of the materials’ maximum dry density as determined in
accordance with ASTM Specification D698. The moisture of the liner materials should be
adjusted to be within the range of ±2% of standard Proctor optimum moisture at the time of
compaction. All earthwork/compaction activities should be field verified/approved by means of
field density testing procedures and visual observations. The approved liner material, when
compacted to at least 95% of the materials’ maximum dry density should have a coefficient of
permeability of 1 x 10-7 cm/sec or slower. The liner thickness is a function of the material used
to construct the earthen embankments, the material’s in-situ permeability characteristics, as well
as the piezometric head or volume of water planned for short and/or long term purposes.
Based on our understanding of the proposed pond and our experience with materials with similar
properties, we expect the majority of on-site overburden cohesive soils, excluding the fine
granular silty sand without some sort of enhancement provided, would be suitable for use as a
low permeability earthen embankment material as intended.
Care should be taken to provide a consistent, uniform low permeability cohesive material for use
as the earthen liner. The materials’ permeability should continually be evaluated during
construction to verify acceptance, and upon completion of the pond, in-situ flex-wall
permeability tests (ASTM Specification D5084) should be performed for final compliance
purposes.
Other Considerations and Recommendations
Groundwater was observed at depths of approximately 8 to 12 feet below present site grades.
Excavations extending to the wetter soils could create difficulties for backfilling of the
utility/pipe trenches with drying of the subgrade soils required to use those materials as backfill.
In general, the subgrade soils could be used as backfill soils although care will be necessary to
maintain sufficient moisture to reduce potential for post-construction movement.
Excavations into the on-site soils will encounter a variety of conditions. Excavations into the
clays can be expected to stand on relatively steep temporary slopes during construction;
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 11
however, caving soils may also be encountered especially in close proximity to the groundwater
table. Groundwater seepage should also be anticipated for utility excavations. Pumping from
sumps may be utilized to control water within the excavations. Well points may be required for
significant groundwater flow, or where excavations penetrate groundwater to a significant depth.
The individual contractor(s) should be made responsible for designing and constructing stable,
temporary excavations as required to maintain stability of both the excavation sides and bottom.
All excavations should be sloped or shored in the interest of safety following local and federal
regulations, including current OSHA excavation and trench safety standards.
GENERAL COMMENTS
The analysis and recommendations presented in this report are based upon the data obtained
from the soil borings performed at the indicated locations and from any other information
discussed in this report. This report does not reflect any variations, which may occur between
borings or across the site. The nature and extent of such variations may not become evident until
construction. If variations appear evident, it will be necessary to re-evaluate the
recommendations of this report.
It is recommended that the geotechnical engineer be retained to review the plans and
specifications so comments can be made regarding the interpretation and implementation of our
geotechnical recommendations in the design and specifications. It is further recommended that
the geotechnical engineer be retained for testing and observations during earthwork and
foundation construction phases to help determine that the design requirements are fulfilled.
This report has been prepared for the exclusive use of Montava Development, LLC and/or
assignees for specific application to the project discussed and has been prepared in accordance
with generally accepted geotechnical engineering practices. No warranty, express or implied, is
made. In the event that any changes in the nature, design, or location of the project as outlined in
this report are planned, the conclusions and recommendations contained in this report shall not
be considered valid unless the changes are reviewed and the conclusions of this report are
modified or verified in writing by the geotechnical engineer.
DRAFTEarth Engineering Consultants, LLC
EEC Project No. 1172058
Montava Development – Tract E – Detention Pond
Fort Collins, Colorado
December 6, 2022
Page 12
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report, or if we can be of further service to you in any other way, please do not
hesitate to contact us.
Very truly yours,
Earth Engineering Consultants, LLC
David A. Richer, P.E.
Senior Geotechnical Engineer
cc: TST, Inc. – Consulting Engineers - Jonathan Sweet (jsweet@tstinc.com)
DRAFTEarth Engineering Consultants, LLC
DRILLING AND EXPLORATION
DRILLING & SAMPLING SYMBOLS:
SS:Split SpoonͲ13/8" I.D., 2" O.D., unless otherwise notedPS:Piston Sample
ST:ThinͲWalled TubeͲ2" O.D., unless otherwise notedWS:Wash Sample
R:Ring Barrel SamplerͲ2.42" I.D., 3" O.D. unless otherwise noted
PA:Power AugerFT:Fish Tail Bit
HA:Hand AugerRB:Rock Bit
DB:DiamondBit=4",N,B BS:Bulk Sample
AS:Auger SamplePM:Pressure Meter
HS:Hollow Stem AugerWB:Wash Bore
Standard"N"Penetration:Blowsperfootofa140poundhammerfalling30inchesona2ͲinchO.D.splitspoon,exceptwherenoted.
WATER LEVEL MEASUREMENT SYMBOLS:
WL:Water LevelWS:While Sampling
WCI:Wet Cave inWD :While Drilling
DCI:Dry Cave inBCR:Before Casing Removal
AB:After BoringACR:After Casting Removal
Waterlevelsindicatedontheboringlogsarethelevelsmeasuredintheboringsatthetimeindicated.Inpervioussoils,theindicated
levelsmayreflectthelocationofgroundwater.Inlowpermeabilitysoils,theaccuratedeterminationofgroundwaterlevelsisnot
possible with only short term observations.
DESCRIPTIVE SOIL CLASSIFICATION
Soil Classification is based on the Unified Soil Classification
system and the ASTM Designations DͲ2488.Coarse Grained
Soils have move than 50% of their dry weight retained on a
#200sieve;theyaredescribedas:boulders,cobbles,gravelor
sand.FineGrainedSoilshavelessthan50%oftheirdryweight
retained on a #200 sieve; they are described as :clays, if they
are plastic, and silts if they are slightly plastic or nonͲplastic.
Major constituents may be added as modifiers and minor
constituents may be added according to the relative
proportions based on grain size.In addition to gradation,
coarsegrainedsoilsaredefinedonthebasisoftheirrelativeinͲ
place density and fine grained soils on the basis of their
consistency.Example:Lean clay with sand, trace gravel, stiff
(CL); silty sand, trace gravel, medium dense (SM).
CONSISTENCY OF FINEͲGRAINED SOILS
Unconfined Compressive
Strength, Qu, psf Consistency
<500 Very Soft
500Ͳ1,000 Soft
1,001Ͳ2,000 Medium
2,001Ͳ4,000 Stiff
4,001Ͳ8,000 Very Stiff
8,001Ͳ16,000 Very Hard
RELATIVE DENSITY OF COARSEͲGRAINED SOILS:
NͲBlows/ft Relative Density
0Ͳ3Very Loose
4Ͳ9Loose
10Ͳ29Medium Dense
30Ͳ49Dense
50Ͳ80Very Dense
80 +Extremely Dense
PHYSICAL PROPERTIES OF BEDROCK
DEGREE OF WEATHERING:
Slight Slight decomposition of parent material on
joints.May be color change.
Moderate Some decomposition and color change
throughout.
High Rock highly decomposed, may be extremely
broken.
HARDNESS AND DEGREE OF CEMENTATION:
Limestone and Dolomite:
Hard Difficult to scratch with knife.
Moderately Can be scratched easily with knife.
Hard Cannot be scratched with fingernail.
Soft Can be scratched with fingernail.
Shale, Siltstone and Claystone:
Hard Canbescratchedeasilywithknife,cannotbe
scratched with fingernail.
Moderately Can be scratched with fingernail.
Hard
Soft Can be easily dented but not molded with
fingers.
Sandstone and Conglomerate:
Well Capable of scratching a knife blade.
Cemented
Cemented Can be scratched with knife.
Poorly Can be broken apart easily with fingers.
Cemented
DRAFTGroup
Symbol
Group Name
Cu≥4 and 1<Cc≤3E GW Well-graded gravel F
Cu<4 and/or 1>Cc>3E GP Poorly-graded gravel F
Fines classify as ML or MH GM Silty gravel G,H
Fines Classify as CL or CH GC Clayey Gravel F,G,H
Cu≥6 and 1<Cc≤3E SW Well-graded sand I
Cu<6 and/or 1>Cc>3E SP Poorly-graded sand I
Fines classify as ML or MH SM Silty sand G,H,I
Fines classify as CL or CH SC Clayey sand G,H,I
inorganic PI>7 and plots on or above "A" Line CL Lean clay K,L,M
PI<4 or plots below "A" Line ML Silt K,L,M
organic Liquid Limit - oven dried Organic clay K,L,M,N
Liquid Limit - not dried Organic silt K,L,M,O
inorganic PI plots on or above "A" Line CH Fat clay K,L,M
PI plots below "A" Line MH Elastic Silt K,L,M
organic Liquid Limit - oven dried Organic clay K,L,M,P
Liquid Limit - not dried Organic silt K,L,M,O
Highly organic soils PT Peat
(D30)2
D10 x D60
GW-GM well graded gravel with silt NPI≥4 and plots on or above "A" line.
GW-GC well-graded gravel with clay OPI≤4 or plots below "A" line.
GP-GM poorly-graded gravel with silt PPI plots on or above "A" line.
GP-GC poorly-graded gravel with clay QPI plots below "A" line.
SW-SM well-graded sand with silt
SW-SC well-graded sand with clay
SP-SM poorly graded sand with silt
SP-SC poorly graded sand with clay
Earth Engineering Consultants, LLC
IIf soil contains >15% gravel, add "with gravel" to
group name
JIf Atterberg limits plots shaded area, soil is a CL-
ML, Silty clay
UNIFIED SOIL CLASSIFICATION SYSTEM
Soil Classification
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests
Sands 50% or more
coarse fraction
passes No. 4 sieve
Fine-Grained Soils
50% or more passes
the No. 200 sieve
<0.75 OL
Gravels with Fines
more than 12%
fines
Clean Sands Less
than 5% fines
Sands with Fines
more than 12%
fines
Clean Gravels Less
than 5% fines
Gravels more than
50% of coarse
fraction retained on
No. 4 sieve
Coarse - Grained Soils
more than 50%
retained on No. 200
sieve
CGravels with 5 to 12% fines required dual symbols:
Kif soil contains 15 to 29% plus No. 200, add "with sand"
or "with gravel", whichever is predominant.
<0.75 OH
Primarily organic matter, dark in color, and organic odor
ABased on the material passing the 3-in. (75-mm)
sieve
ECu=D60/D10 Cc=
HIf fines are organic, add "with organic fines" to
group name
LIf soil contains ≥ 30% plus No. 200 predominantly sand,
add "sandy" to group name.
MIf soil contains ≥30% plus No. 200 predominantly gravel,
add "gravelly" to group name.
DSands with 5 to 12% fines require dual symbols:
BIf field sample contained cobbles or boulders, or
both, add "with cobbles or boulders, or both" to
group name.FIf soil contains ≥15% sand, add "with sand" to
GIf fines classify as CL-ML, use dual symbol GC-
CM, or SC-SM.
Silts and Clays
Liquid Limit less
than 50
Silts and Clays
Liquid Limit 50 or
more
0
10
20
30
40
50
60
0 102030405060708090100110PLASTICITY INDEX (PI)LIQUID LIMIT (LL)
ML OR OL
MH OR OH
For Classification of fine-grained soils and
fine-grained fraction of coarse-grained
soils.
Equation of "A"-line
Horizontal at PI=4 to LL=25.5
then PI-0.73 (LL-20)
Equation of "U"-line
Vertical at LL=16 to PI-7,
then PI=0.9 (LL-8)
CL-ML
DRAFTMW-1MW-3MW-2MW-4Figure 1: Monitoring Well Location DiagramMontava Irrigation Storm Water PondFort Collins, ColoradoEEC Project #: 1172058 Date: December 2022EARTH ENGINEERING CONSULTANTS, LLCApproximateLocations for 4GroundwaterMonitoring Wells,20' - 25'Legend
DRAFTMW-1MW-3MW-249934992MW-44991(5005)(5001.5)(5003)(5002.5)[4993.5][4993][4992][4991]Figure 2: Groundwater Contour DiagramMontava Irrigation Storm Water PondFort Collins, ColoradoEEC Project #: 1172058 Date: December 2022EARTH ENGINEERING CONSULTANTS, LLCApprox. Locations for4 GroundwaterMonitoring Wells,20' - 25'LegendApproximate GroundSurface ElevationsApproximateGroundwaterElevationsApproximateGroundwater ContoursEstimated DirectionalFlow(5005)[4992]
DRAFT
DRAFTDATE:
RIG TYPE: CME55
FOREMAN: AK
AUGER TYPE: 4 1/4" HSA
SPT HAMMER: AUTOMATIC
SOIL DESCRIPTION D N QU MC DD -200
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL
AGRICULTURAL / CORN STUBBLE FIELD _ _
1
_ _
2
_ _
3
SANDY LEAN CLAY (CL) _ _
brown 4
moist, stiff to medium stiff _ _
SS 5 13 18.2
_ _
6
_ _
7
_ _
8
_ _32 18 66.8 18.5 109.0
9
_ _
SS 10 9 20.0 36 23 62.2
_ _
*transitioning to LEAN CLAY with SAND (CL) 11
_ _
12
_ _
13
_ _32 18 75.4 17.0 110.0
14
_ _
SS 15 9 18.9
_ _
16
_ _
17
_ _
18
SAND & GRAVEL _ _
brown / red 19
mist to wet, medium dense _ _
SS 20 9 13.6
_ _
21
_ _
22
BOTTOM OF BORING DEPTH 22' _ _
23
_ _
24
_ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe
25 Silica Sand
_ _
Earth Engineering Consultants, LLC
Note: a 4-inch by 4-inch - 4-foot in length
steel protective cover encased in concrete
was positioned at the surface
FINISH DATE
APPROX. SURFACE ELEV
WATER DEPTH
PIEZOMETER / MONITORING WELL LEGEND
Flush Threaded Riser Pipe
Grout
Bentonite Seal
10/28/2022 Checked 12-1-22 11' 5"
Composite Sample MW-1 thru
MW-4 - Upper 5 to 10 Feet:
SANDY LEAN CLAY (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Composite Sample MW-1 thru
MW-4 - Upper 10 to 15-Feet:
LEAN CLAY with SAND (CL)
WELL
DETAIL
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
MONTAVA DEVELOPMENT - TRACT E - DETENTION POND
NOVEMBER 2022PROJECT NO: 1172058 LOG OF BORING MW-1
FORT COLLINS, COLORADO
10/28/2022 WHILE DRILLING 16'
SHEET 1 OF 1
START DATE
5005
A-LIMITS SWELL
DRAFTDATE:
RIG TYPE: CME55
FOREMAN: AK
AUGER TYPE: 4 1/4" HSA
SPT HAMMER: AUTOMATIC
SOIL DESCRIPTION D N QU MC DD -200
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL
AGRICULTURAL / CORN STUBBLE FIELD _ _
1
_ _
2
_ _
3
LEAN CLAY with SAND (CL) _ _
brown, moist 4
soft to medium stiff _ _
SS 5 4 27.5 36 21 84.2
_ _
6
_ _
7
_ _
8
_ _32 18 66.8 18.5 109.0
9
_ _
SS 10 5 20.1
_ _
*transitioning to LEAN CLAY with SAND (CL) 11
_ _
12
_ _
SAND & GRAVEL 13
brown / red _ _32 18 75.4 17.0 110.0
moist to wet, loose to medium dense 14
_ _
SS 15 9
_ _
16
_ _
17
_ _
18
_ _
19
*with interbedded clay seams _ _
SS 20 22 9.3
_ _
21
_ _
22
BOTTOM OF BORING DEPTH 22' _ _
23
_ _
24
_ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe
25 Silica Sand
_ _
Earth Engineering Consultants, LLC
Composite Sample MW-1 thru
MW-4 - Upper 5 to 10 Feet:
SANDY LEAN CLAY (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Composite Sample MW-1 thru
MW-4 - Upper 10 to 15-Feet:
LEAN CLAY with SAND (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Note: a 4-inch by 4-inch - 4-foot in length
steel protective cover encased in concrete
was positioned at the surface
MONTAVA DEVELOPMENT - TRACT E - DETENTION POND
FORT COLLINS, COLORADO
PROJECT NO: 1172058 LOG OF BORING MW-2 NOVEMBER 2022
APPROX. SURFACE ELEV 5001.5
SHEET 1 OF 1 WATER DEPTH
FINISH DATE 10/28/2022 Checked 12-1-22 8' 5"
START DATE 10/28/2022 WHILE DRILLING 14'
WELL A-LIMITS SWELL
PIEZOMETER / MONITORING WELL LEGEND
Flush Threaded Riser Pipe
Grout
Bentonite Seal
DETAIL
DRAFTDATE:
RIG TYPE: CME55
FOREMAN: AK
AUGER TYPE: 4 1/4" HSA
SPT HAMMER: AUTOMATIC
SOIL DESCRIPTION D N QU MC DD -200
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL
AGRICULTURAL / CORN STUBBLE FIELD _ _
1
_ _
2
_ _
3
SANDY LEAN CLAY (CL) _ _
brown, rust 4
soft to medium stiff to stiff _ _
SS 53 31.6
_ _
6
_ _
7
_ _
8
_ _32 18 66.8 18.5 109.0
9
_ _
SS 10 4 31.5
_ _
*transitioning to LEAN CLAY with SAND (CL) 11
_ _
12
_ _
13
_ _32 18 75.4 17.0 110.0
14
_ _
*classified as LEAN CLAY (CL) SS 15 12 26.1 36 17 94.7
_ _
16
_ _
17
_ _
18
_ _
19
_ _
SS 20 20
_ _
21
_ _
22
BOTTOM OF BORING DEPTH 22' _ _
23
_ _
24
_ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe
25 Silica Sand
_ _
Earth Engineering Consultants, LLC
Composite Sample MW-1 thru
MW-4 - Upper 5 to 10 Feet:
SANDY LEAN CLAY (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Composite Sample MW-1 thru
MW-4 - Upper 10 to 15-Feet:
LEAN CLAY with SAND (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Note: a 4-inch by 4-inch - 4-foot in length
steel protective cover encased in concrete
was positioned at the surface
MONTAVA DEVELOPMENT - TRACT E - DETENTION POND
FORT COLLINS, COLORADO
PROJECT NO: 1172058 LOG OF BORING MW-3 NOVEMBER 2022
APPROX. SURFACE ELEV 5000
SHEET 1 OF 1 WATER DEPTH
FINISH DATE 10/28/2022 Checked 12-1-22 7' 10"
START DATE 10/28/2022 WHILE DRILLING 16'
WELL A-LIMITS SWELL
PIEZOMETER / MONITORING WELL LEGEND
Flush Threaded Riser Pipe
Grout
Bentonite Seal
DETAIL
DRAFTDATE:
RIG TYPE: CME55
FOREMAN: AK
AUGER TYPE: 4 1/4" HSA
SPT HAMMER: AUTOMATIC
SOIL DESCRIPTION D N QU MC DD -200
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL
AGRICULTURAL / CORN STUBBLE FIELD _ _
1
_ _
SANDY LEAN CLAY (CL) 2
brown _ _
moist, stiff to medium stiff 3
_ _
4
_ _
SS 56 17.6
_ _
6
_ _
7
_ _
8
_ _32 18 66.8 18.5 109.0
9
_ _
SS 10 7 20.7
_ _
*transitioning to LEAN CLAY with SAND (CL) 11
_ _
12
_ _
13
_ _32 18 75.4 17.0 110.0
14
_ _
SS 15 9 21.7
_ _
16
_ _
17
_ _
SILTY SAND with trace GRAVEL 18
tan, gray, moist to wet _ _
medium dense 19
_ _
SS 20 18 22.3
_ _
21
_ _
22
BOTTOM OF BORING DEPTH 22' _ _
23
_ _
24
_ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe
25 Silica Sand
_ _
Earth Engineering Consultants, LLC
Composite Sample MW-1 thru
MW-4 - Upper 5 to 10 Feet:
SANDY LEAN CLAY (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Composite Sample MW-1 thru
MW-4 - Upper 10 to 15-Feet:
LEAN CLAY with SAND (CL)
Standard Proctor
ASTM D698 Results
Optimum
Moisture
Content, %
Maximum
Dry
Density,
PCF
Note: a 4-inch by 4-inch - 4-foot in length
steel protective cover encased in concrete
was positioned at the surface
MONTAVA DEVELOPMENT - TRACT E - DETENTION POND
FORT COLLINS, COLORADO
PROJECT NO: 1172058 LOG OF BORING MW-4 NOVEMBER 2022
APPROX. SURFACE ELEV 5002.5
SHEET 1 OF 1 WATER DEPTH
FINISH DATE 10/28/2022 Checked 12-1-22 11.5'
START DATE 10/28/2022 WHILE DRILLING 16'
WELL A-LIMITS SWELL
PIEZOMETER / MONITORING WELL LEGEND
Flush Threaded Riser Pipe
Grout
Bentonite Seal
DETAIL
DRAFT0%
10%
20%
30%
Project: Montava Subdivision - Tract E Detention Pond
Fort Collins, Colorado
Project No: 1172058
Date November
O-20 128.8 6.4
O-30
Proctor Designation
Rock Correction (AASHTO T 224)
Maximum Dry Density (pcf)Optimum Moisture Content
(%)
Retained
3/4"
7.2
O 125.0
O-10 126.9
8.0
130.9 5.6
90
95
100
105
110
115
120
125
130
135
140
145
0 5 10 15 20 25 30 35Dry Density (Pounds per Cubic Foot)Percent Moisture
Curves for 100% Saturation
For Specific Gravity Equal to:
2.80
2.70
2.60
Material Designation:
Sample Location:
Description:
Lower 10 to 15 feet of Overburden
Comp. Sample - MW-1 thru MW-4
Lean Clay with Sand (CL)
Atterberg Limits (ASTM D-4318)
Liquid Limit:
Plastic Limit:
Plasticity Index:
32
18
14
Passing No. 200 Sieve (AASHTO T 11/ASTM C 117): 75.4%
Standard Proctor (ASTM D-698)
Maximum Dry Density:
Optimum Moisture Content:
110.0 pcf
17.0%
EARTH ENGINEERING CONSULTANTS, LLC
SUMMARY OF LABORATORY CLASSIFICATION/MOISTURE-DENSITY
RELATIONSHIP
DRAFTMaterial Designation: Lower 10 to 15 feet of Overburden
Sample Location: Comp. Sample - MW-1 thru MW-4
Material Description: Lean Clay with Sand (CL)
Project No:
Date
EARTH ENGINEERING CONSULTANTS, LLC
SUMMARY OF LABORATORY CLASSIFICATION / MOISTURE-DENSITY RELATIONSHIP
Sieve Size Percent Passing
No. 4 100%
75.4%
99%
98%No. 40
No. 10
No. 200
Montava Subdivision - Tract E Detention Pond
Fort Collins, Colorado
1172058
November
Project:
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.0010.010.1110100Percent Finer by WeightGrain Size in Millimeters
DRAFT2 1/2" (63 mm)
2" (50 mm)
1 1/2" (37.5 mm)
1" (25 mm)
3/4" (19 mm)
1/2" (12.5 mm)
3/8" (9.5 mm)
No. 4 (4.75 mm)
No. 8 (2.36 mm)
No. 10 (2 mm)
No. 16 (1.18 mm)
No. 30 (0.6 mm)
No. 40 (0.425 mm)
No. 50 (0.3 mm)
No. 100 (0.15 mm)
No. 200 (0.075 mm)
Project: Montova - Detention Pond Monitoring Wells
Location: Broomfield, Colorado
Project No: 1172058B
Sample ID: MW1 S4 19
Sample Desc.: Well Graded Sand with Gravel (SW)
Date: December 2022
EARTH ENGINEERING CONSULTANTS, LLC
SUMMARY OF LABORATORY TEST RESULTS
Sieve Analysis (AASHTO T 11 & T 27 / ASTM C 117 & C 136)
100
Sieve Size Percent Passing
100
100
100
100
100
98
79
51
8
4.8
45
30
19
14
11
DRAFT1.18 0.26Fine12.28 1.72D30D10CuCCDecember 202212.50 3.15 2.32Montova - Detention Pond Monitoring WellsBroomfield, Colorado1172058BMW1 S4 19Well Graded Sand with Gravel (SW)D100D60D50EARTH ENGINEERING CONSULTANTS, LLCSummary of Washed Sieve Analysis Tests (ASTM C117 & C136)Date:Project:Location:Project No:Sample ID:Sample Desc.:CobbleSilt or ClayGravelCoarse FineSandCoarse Medium6"5"4"3"2.5"2"1.5"1"3/4"1/2"3/8"No. 4No. 8No. 10No. 16No. 30No. 40No. 50No. 100No. 20001020304050607080901000.010.11101001000Finer by Weight (%)Grain Size (mm)Standard Sieve Size
DRAFTLiquid Limit: 32 Plasticity Index: 18 % Passing #200: 66.8%
Initial Moisture: 18.5% Dry Density: 104.0 pcf 95.4%
Project Name: Montava Development - Tract E - Detention Pond
Location: Fort Collins, Colorado
Project Number:
Date:
Percent Compaction:
November 2022
1172058
EARTH ENGINEERING CONSULTANTS, LLC
Material Description:
Permeability Test Results (ASTM D5856)
Montava Development - Tract E - Detention Pond - Fort Collins, Colorado
brown Sandy Lean Clay (CL)
Coefficient of Permeability, k = 6.6 x 10 -8 cm/s
Sample: Composite Sample - Upper 5-Feet of Cohesive Soils MW-1 thru MW-4
0.0E+00
1.0E-08
2.0E-08
3.0E-08
4.0E-08
5.0E-08
6.0E-08
7.0E-08
8.0E-08
9.0E-08
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000Coefficientt off Permeability,, kk (cm/sec)Elapsedd Timee (min)