2023-01-19__Appendix_E_Geotechnical_Engineering_and_Attachments.pdf

DESIGN DOCUMENTATION REPORT

Saint Vrain Creek

Flood Risk Reduction Project

Longmont, Colorado

Appendix E – Geotechnical Engineering

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Table Of Contents

1. GEOLOGY AND FOUNDATION CONDITIONS

1.1. General

1.2. Field Investigations

1.3. Site Geology

1.3.1. Bedrock

1.3.2. Overburden

1.4. Groundwater

1.5. Borrow Materials

2. GEOTECHNICAL ENGINEERING ANALYSIS

2.1. Settlement

2.2. Foundation Underseepage

2.3. Embankment Seepage

2.3.1. General

2.3.2. Cofferdam

2.3.3. Final Levee Section

2.3.4. Seepage at Drainage Structure

2.4. Slope Stability

2.5. Swelling Soil

2.6. Corrosion and Sulfates

2.7. Structural Loading

3. References ii

List of Figures

Figure 1: Geologic Map of Boulder and Weld Counties Figure 2: Topographic/Bathymetric Survey with Borehole Locations Figure 3: Top-of-Bedrock Elevation Extrapolated from Borehole Data Figure 4: Gradation of Tested Alluvium Samples (from sampling by CH2M in 2015-2016) Figure 5: Atterberg Limits of Proposed Clay Borrow Material Figure 6: Photo of Clay Borrow Pile at Dry Creek Community Park Figure 7: Comparison of Cofferdam With and Without Cutoff Wall (Case A) Figure 8: Pressure Drop over Sheetpile Wall (Case A) Figure 9: Swell Potential in Boulder County

List of Tables

Table 1: Soil Hydraulic Conductivity Parameters Table 2: Cofferdam Seepage Analysis Loading Scenarios and Flowrates Table 3: Final Levee Seepage Analysis Loading Scenarios and Flowrates Table 4: Soil Strength Parameters Table 5: Slope Stability Analysis Results

List of Attachments

1. St Vrain Creek Soil Borings and Test Data (CH2M, 2015-2016)

2. St Vrain Creek Soil Borings and Test Data (USACE, 2021)

3. Borrow Site Borings and Test Data (Terracon, 2022)

4. GeoStudio Seepage and Stability Models

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1. GEOLOGY AND FOUNDATION CONDITIONS

1.1. General

The project site is located in the northern part of the Colorado Piedmont, immediately east of the Southern Rocky Mountains. It is an area of low hills and plains of alluvial or eolian origin underlain by Upper Cretaceous (100-66 million years ago) sedimentary rocks. The surficial soils along Saint Vrain Creek consists mainly of alluvium of Upper Pleistocene to Upper Holocene age (deposited 13,500 years ago to modern day). The alluvium is typically described as poorly sorted (i.e. well graded) silty or clayey sand with gravel. Cobble sized gravel is also commonly encountered within the alluvium. Below the alluvium deposits lies Pierre Shale bedrock, which is approximately 4,800 feet thick in the region. The Pierre Shale is typically described as a dark gray shale or claystone with interbedded layers of siltstone or fine-grained sandstone.

Figure 1: Geologic Map of Boulder and Weld Counties Source: Madole, 2016

1.2. Field Investigations

Initial geotechnical investigations for the Resilient St Vrain Project were contracted to CH2M by the City of Longmont and were performed between 2015 and 2016. The results of the CH2M investigations and subsequent testing is included as Attachment 1. In 2021, five additional soil borings were drilled through the existing Izaak Walton Pond berm by the U.S. Army Corps of

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Engineers, Omaha District (USACE) drill crew. The results of the USACE investigations is included as Attachment 2. Finally, Terracon performed three borings at the clay material borrow site identified by the Project Sponsor (located at Dry Creek Community Park) in 2022.

The results of the Terracon investigations and testing is included as Attachment 3. The locations of all borings are shown on Sheet B-101 of the contract drawings.

1.3. Site Geology

1.3.1. Bedrock

Borings drilled through the existing Izaak Walton Pond embankment and surrounding area encountered Pierre Shale bedrock between 12 and 17 feet below ground surface. Depth to bedrock was extrapolated from the boring data and mapped across the site (see the figures below). The top of bedrock generally drops in elevation to the east, or the direction of the creek flow. The rock was described as weak, slightly weathered at the top several feet, and thinly bedded, which is consistent with the description given on the geologic map. Though Pierre Shale is a consolidated sedimentary rock, its engineering properties are often more similar to that of a hard clay soil than rock.

Soil borings performed for this project did not include rock coring. However, deep rock coring into the Pierre Shale was performed in 2019 by Shannon and Wilson for the Boston Ave Bridge Replacement Project which is located about 300 feet downstream of the proposed embankment tie-off. Unconfined compressive strength tests were performed on seven rock core samples and the strength ranged from 1640 to 2941 psi (118 to 212 tsf).

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Figure 2: Topographic/Bathymetric Survey with Borehole Locations

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Figure 3: Top-of-Bedrock Elevation Extrapolated from Borehole Data

1.3.2. Overburden

Approximately 12 to 17 feet of alluvium was encountered below the surface in borings drilled through the existing Izaak Walton Pond embankment and the surrounding area. The alluvium consists mainly of a well-graded mix of sand and gravel with less than 20% fines. The results of gradation tests on this material are shown in the figure below. The presence of cobble sized particles within the alluvium was inferred from the auger response during drilling and have usually been observed in nearby excavations. Some borings through the existing berm encountered between 1 and 3 feet of clay fill directly below the surface which was placed when the berm was rebuilt following the 2013 flood event. No clay material was encountered in the overbank areas around the pond.

The elevation difference between the surveyed pond bottom and the extrapolated top-of-bedrock indicates that there is a relatively thin (less than five feet) layer of sediment on some parts of the pond bottom. This sediment is likely a sandy or silty material and is the product of runoff or was deposited when the embankment breached during the 2013 Flood Event. There has been no testing or sampling of this material.

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Figure 4: Gradation of Tested Alluvium Samples (from sampling by CH2M in 2015-2016)

1.4. Groundwater

Groundwater levels encountered during drilling generally correlated to the water surface elevation in Saint Vrain Creek and Izaak Walton Pond. Given the mostly granular pervious foundation materials, it is expected that groundwater outside of the creek channel and pond will rapidly rise and fall based on the creek and pond water elevation. Izaak Walton Pond is primarily groundwater fed, and since the St Vrain Creek flooding in 2013 and resulting levee breach and subsequent repairs, the pond water surface elevation has tended to vary to match the creek water surface. This indicates a quick hydraulic connection between the pond and creek channel through the existing sandy/gravelly berm material. It is expected that the proposed lowering of the creek channel may lower the normal groundwater elevations in the area and may affect the pond water level.

1.5. Borrow Materials

Quality lean clay fill material for use in levee/dam construction is not common in the Colorado Front Range area. The proposed clay borrow source for use in constructing the new embankment is located in Dry Creek Community Park, about 2.5 miles southwest of the project site. The borrow source is currently a stockpile of approximately 27,000 cubic yards of material that was previously excavated by the City of Longmont for the construction of a detention pond and then stockpiled in a corner of the park (see the photo below). Three borings were drilled through the mound to confirm soil type and suitability. All three borings encountered sandy lean to fat clay as shown in the figure below and Attachment 3.

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Figure 5: Atterberg Limits of Proposed Clay Borrow Material

Figure 6: Photo of Clay Borrow Pile at Dry Creek Community Park

CLAY BORROW PILE

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2. GEOTECHNICAL ENGINEERING ANALYSIS

2.1. Settlement

Because of the relatively low height and flat sideslopes of the levee, and the compressive strength of the shale bedrock that comprises the foundation, no special provisions for settlement were judged to be necessary. Sand/gravel material used to construct the cofferdam and any sediment deposits on the pond bottom are expected to experience primary consolidation and settlement during construction with little to no secondary consolidation following construction.

Clay materials used for levee construction shall be moisture conditioned and mechanically placed and compacted, and should not experience noticeable consolidation after construction.

2.2. Foundation Underseepage

Because the new levee embankment will be founded on or at a similar elevation to the shallow shale bedrock, no special provisions for foundation underseepage control are required. The design channel bottom will be below the top-of-bedrock elevation, and any seepage flow through the shale will be negligible. Furthermore, the final levee section will include a seepage cutoff wall which extends from the pond water surface to the underlying shale. These features, as they relate to embankment though-seepage, are discussed in the following section.

2.3. Embankment Seepage

2.3.1. General

As an incidental benefit to the project Sponsor, the new levee construction is sequenced so that the water surface in Izaak Walton Pond may be maintained both during and after construction in order that the existing recreational and irrigation infrastructure in and around the pond is not affected by the project. This presents an unusual condition where, due to the expected water surface elevations in the pond and the lowered creek channel, the levee will be reversely hydraulically loaded (i.e. there will be a higher water surface on the protected side of the levee than on the riverside) during non-flood loading conditions and during construction.

Seepage through the cofferdam and final levee sections was modelled in the Seep module of Geostudio 2021, a two-dimensional finite element modeling software distributed by GEO- SLOPE International, Ltd. Soil hydraulic conductivity values were determined from grain size correlations or from published typical values and are summarized below. Three loading scenarios were analyzed for each geometry, as described in the results, see Table 2 and Table 3.

These loading scenarios were chosen to represent the maximum seepage pressures that could occur. The top-of-bedrock elevation and cutoff wall were assumed to be no-flow boundaries for seepage and no material properties were entered for those materials.

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Table 1: Soil Hydraulic Conductivity Parameters

2.3.2. Cofferdam

Initially, a cofferdam will be constructed within Izaak Walton Pond to allow for the removal of the existing berm while maintaining a consistent pond water surface. The cofferdam base will be comprised of granular fill which will be derived from the excavated overburden across the project site and will be processed to remove cobbles and gravel larger than one inch in diameter.

The underwater fill crest will be at elevation 4963 feet, which is approximately one foot above the current water surface, and be 70 feet wide. Clay fill will be placed above the underwater granular fill up to the cofferdam crest at elevation 4969 feet. The cofferdam will have a 12-foot crest width and a 10-foot-wide pondside bench for recreation and maintenance access. A geotextile fabric will be placed on the horizontal plane between the two sections to prevent movement of materials due to seepage. The cofferdam will impound approximately 7 feet of water in the pond during construction.

Two geometries for the Cofferdam were modeled – one with a seepage cutoff wall, and one without a wall. Three loading cases were analyzed for each, to represent the worst-case loading scenarios.

Table 2: Cofferdam Seepage Analysis Loading Scenarios and Flowrates

Analysis Case St Vrain Creek WSE

Izaak Walton Pond WSE

Total Flow through Section (gpm/linear ft)

With Cutoff Wall Case A – Non-Flood Loading 4956 4965 -0.00029* Case B – St Vrain at Top-of-Dam 4969 4965 0.0032 Case C – St Vrain at Top-of-Dam and no water in Pond 4969 N/A 0.0060

Without Cutoff Wall Case A – Non-Flood Loading 4956 4965 -0.50* Case B – St Vrain at Top-of-Dam 4969 4965 0.47 Case C – St Vrain at Top-of-Dam and no water in Pond 4969 N/A 0.98

*Negative sign indicates flow direction is from pond into creek channel.

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Figure 7: Comparison of Cofferdam With and Without Cutoff Wall (Case A)

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Based on these results, a cutoff wall is necessary to prevent an excessive quantity of seepage from the impounded pond through the cofferdam section and to control groundwater levels within the creek channel during construction. Alternative methods for seepage cutoff were considered, and a steel sheetpile wall was selected as the most feasible option. Open trenching and backfilling were deemed unfeasible due to the expected high groundwater from the pond.

Other methods such as slurry walls or deep soil mixing are not preferred due to the risk of hydraulic fracturing and resulting internal erosion of the embankment which will be hydraulically loaded during construction.

The cutoff wall will be 15 feet tall with its top set at elevation 4965 feet, which is two feet above the top of underwater fill placement. This height and elevation were chosen to ensure that the wall will completely cut off seepage through the 10 to 12 feet of underwater granular fill material and sediment deposits on the pond bottom. Seepage through the underlying shale is expected to be negligible, but excess pile length will allow for approximately three to five feet of penetration into the top surface of the shale layer where weathered. This is to ensure adequate cutoff at the bedrock/overburden interface. Though fracturing of the shale during sheetpile driving is possible, the rock is very soft and is expected to self-heal over time. In addition, the overlying granular fill material will immediately collapse into any underlying voids or cracks and act as a flow limiter. Joint sealant will be applied to control leakage at the sheetpile section interlocks.

During construction, a test section will be installed to assess drivability of the steel sheets into the embankment and foundation. A standard PZ-35 sheetpile section was chosen to ensure adequate strength for driving sheets into shale. However, pile shoes may be utilized if necessary to protect the pile ends being driven into the shale. Once construction is complete, the cutoff wall will be left in place within the final levee section, as described in the following section.

Pulling the sheetpile sections is not preferred as this may create a weak zone within the embankment that could lead to future seepage and stability issues.

2.3.3. Final Levee Section

The final levee section will be constructed by placing additional clay fill above and along the riverside slope of the cofferdam section. By this method, the cofferdam section, including the underwater granular fill and seepage cutoff wall, will become part of the final levee embankment. The final levee section will have a 25-foot-wide crest and 1V:4H sideslopes. The same loading cases described for the cofferdam were analyzed for the final levee geometry and are described below.

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Table 3: Final Levee Seepage Analysis Loading Scenarios and Flowrates

Analysis Case St Vrain Creek

WSE

Izaak Walton Pond

WSE

Total Flow through Section (gpm/linear

ft) Case A – Non-Flood Loading 4956 4965 -0.0019* Case B – St Vrain at Top-of-Levee 4972 4965 0.0014 Case C – St Vrain at Top-of-Levee and no water in Pond 4972 N/A 0.0020

*Negative sign indicates flow direction is from pond into creek channel.

The seepage flow nets generated by Geostudio were inspected to identify concentrations of flow lines that could indicate locations of high seepage pressure gradients. An excessively high pressure gradient could lead to internal erosion of soil within the embankment. See Attachment 4 for printouts of the GeoStudio seepage analysis models. From the results, the following observations are made:

1. The native overburden and underwater fill underlying the clay fill act as drains and the pressure gradient through these materials is very low. Assuming no cutoff wall, the total horizontal gradient through base of the levee embankment is about 0.06 for Case A, 0.05 for Case B, and 0.11 for Case C. From published piping models, soil piping of this predominantly course-grained sandy material is unlikely for horizontal gradients less than about 0.20.

2. The highest pressure gradient within the section is located within the clay fill behind (in the direction of flow) and over the top of the sheetpile wall because the clay fill acts as a confining layer over the more pervious granular fill and native overburden. The clay fill is sufficiently cohesive to resist internal erosion. Furthermore, the geotextile filter fabric placed between the clay and underwater fill will prevent movement of clay into the underlying granular fill.

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Figure 8: Pressure Drop over Sheetpile Wall (Case A)

CRITICAL GRADIENT LOCATED

OVER TOP OF WALL

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2.3.4. Seepage at Drainage Structure

A drainage filter will be installed around the outfall (riverside levee slope) of the drainage structure at Station L 305+25 in order to control seepage from the impounded pond to the creek channel along the pipe/soil interface. The drainage filter is designed in accordance with Engineering Manual (EM) 1110-2-2902 and contains a 3-foot-wide sand diaphragm around the pipe and CLSM located 40 feet from the pipe outfall in order to collect seepage and relieve pore-water pressure within the embankment.

Due to the prescribed construction sequencing, a 26-foot-wide gap will be left in the cutoff wall for drainage structure installation. A temporary ring dam will be placed on the pondside of the structure location to control seepage and groundwater for construction. Backfill over the structure will consist of all impervious (clay) fill. Because the all-clay levee section will have a very narrow profile length relative to its cross-section width, the pipe drainage filter and the underwater fill sections on either side of the structure is expected to control and relieve any seepage along this portion of the embankment.

2.4. Slope Stability

A 4H:1V sideslope was selected for both the riverside and pondside slope in accordance with City of Longmont specifications for slopes adjacent to public trails. Slope stability analyses were performed for the final levee cross sections with varying loading conditions in the pond and creek channel in accordance with Engineering Manual (EM) 1110-2-1913.

The slope stability of the final levee section was modelled in the Slope module of Geostudio 2021 utilizing the Morgenstern-Price Method of Slices. The embankment geometry, phreatic surface, and the pore water distribution were obtained from the seepage analyses described in Paragraph “Embankment Seepage”. The strength parameters used in the analysis were initially conservatively estimated from published typical values (Das, 2013) and are summarized in the table below. Bedrock was omitted from the analysis; it is assumed that failure surfaces will be confined to the overburden and/or embankment material. Given the relatively flat slopes of the proposed embankment and the high factors of safety obtained from the analysis (see Table 4), no further soil strength testing was deemed necessary.

Table 4: Soil Strength Parameters

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A summary of results is included in the table below. For Case II, a simplified hydrograph was applied in which the creek channel drops at steady rate from top-of-levee to low flow conditions over 12 hours. The low-permeability material on the riverside slope is likely to experience high pore-water pressure as the water surface drops faster than the soil can drain, creating a lower Factor of Safety for slope stability. Case IV was not analyzed since there is a very low probability of an earthquake coinciding with a flood event and the project is located in a relatively low seismic hazard zone. See Attachment 4 for printouts of the GeoStudio stability analysis results.

Table 5: Slope Stability Analysis Results Analysis Case St Vrain Creek

WSE

Izaak Walton

Pond WSE Factor of

Safety Case I – End of Construction 4956 4965 3.3 (Riverside)

3.9 (Pondside) Case II – Sudden Drawdown 4972 to 4956 over 12 hours 4965 2.7 (Riverside) Case III – Steady Seepage from Full Flood Stage 4972 4965 3.9 (Pondside) Case IV - Earthquake Not analyzed

Based on these results, the expected factors of safety for slope stability exceed the minimum values required by EM 1110-2-1913 for all evaluated conditions.

2.5. Swelling Soil

Swell-susceptible soil and bedrock is common along the Front Range area of Colorado. In 2014, Shannon and Wilson performed swell testing on similar shallow shale samples for the Main Street (US Hwy 287) Bridge Replacement Project, located about one mile downstream of the levee embankment. The results for swell testing on these samples were +1.0% and +1.4% with swell pressures (the pressure required to reload the sample back to zero swell) of 900 and 1,400 psf. These values are consistent with swell tests performed on samples collected along the other RSVP reaches which report none to very little swell potential along the creek corridor. Mapping presented in the Geologic Hazard Study for Boulder County (Cesare, 2017) provides further confirmation of low swell potential along the Saint Vrain Creek corridor. Based on relatively high loading of the levee embankment on the foundation, as well as the expected elevation of the groundwater table above bedrock, no special provisions for swelling soil are necessary.

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Figure 9: Swell Potential in Boulder County Source: Cesare, 2017

2.6. Corrosion and Sulfates

The clay soil and bedrock materials in the Front Range area of Colorado can be corrosive to subsurface steel elements. In 2020, Shannon and Wilson tested one sample of alluvial soil and one sample of shale bedrock for the Boston Ave Bridge Replacement Project which is located about 300 feet downstream of the proposed embankment tie-off. The resistivity measured in the samples was 3,300 ohm-cm (moderate to severe corrosivity) for the alluvium and 940 ohm-cm (severe corrosivity) for the shale. Corrosivity of soils based on resistivity was determined from Army Technical Manual (TM) 5-811-7, Table 2-1.

The concentrations of water-soluble sulfates in the samples were 100 ppm (0.01%) for the alluvium and 400 ppm (0.04%) for the shale. Based on these results, the exposure class is “S0” (no exposure) according to ACI 201.2R, Table 6.1.4.1a. However, it is common to encounter

IZAAK WALTON POND

E-16 higher sulfate concentrations in the shale material within the Colorado Front Range area, possibly corresponding to an exposure class as high as “S2” (severe).

2.7. Structural Loading

The following soil properties are provided for determining soil pressures applied to below-grade features of the irrigation pumphouse. These values are derived from typical published values (Das, 2013) for the sandy material which is expected to be encountered at the project site.

Saturated Unit Weight: 110 pcf Internal Friction Angle: 30° Cohesion: 0 psf Allowable Excess Bearing Pressure: 2,000 psf Active Earth Pressure Coefficient: 0.3 Passive Earth Pressure Coefficient: 3.2 At-Rest Earth Pressure Coefficient: 0.5

3. REFERENCES

1. Cesare, Inc. (31 March 2017), Geologic Hazard Study, prepared for Boulder County, CO

2. Das, Braja M. (2013), Fundamentals of Geotechnical Engineering, Fourth Edition, published by Cengage Learning

3. Madole, Richard (2016), Geologic Map of the Longmont Quadrangle, published by the Colorado Geological Survey

4. Shannon & Wilson (May 2021), Geotechnical Report, Boston Avenue Bridge over St Vrain Creek, prepared for Atkins North America, Inc.

5. U.S. Army Corps of Engineers (30 October 1992), Engineering Manual (EM) 1110-2- 1905, Bearing Capacity of Soils

6. U.S. Army Corps of Engineers (30 April 2000), Engineering Manual (EM) 1110-2-1913, Design and Construction of Levees

7. U.S. Army Corps of Engineers (31 December 2020), Engineering Manual (EM) 1110-2- 2902, Conduits, Pipes, and Culverts associated with Dams and Levee Systems

Attachment 1:

St Vrain Creek Soil Borings and Test Data

(CH2M, 2015-2016)

MC = 0.1%

Gravel = 49% Sand = 44% Fines = 7% (lab test) Chattering and hard drilling, cobbles likely within soils to bedrock

SANDY SILT (ML)

dark brown, moist, fine grained sand

(TOPSOIL)

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM)

dense to medium dense, tan to brown, dry to moist, fine to coarse grained sand

(ALLUVIUM)

POORLY GRADED GRAVEL WITH SAND (GP)

loose, brown, moist to wet, fine to coarse grained sand

(ALLUVIUM)

SILTY GRAVEL WITH SAND (GM)

dense, tan to brown, moist to wet, medium to coarse grained sand, grading coarser with depth

(ALLUVIUM)

BEDROCK (CLAYSTONE), firm, blue-gray, moist, fissured

(PIERRE SHALE)

Boring terminated at 16.5 ft bgs.

6-14-22 (36)

12-14-11 (25)

4-5-5 (10)

6-16-30 (46)

11-6-15 (21)

6-14-22 (36)

12-14-11 (25)

4-5-5 (10)

6-16-30 (46)

11-6-15 (21)

12.0

2.0

11.0

13.0

18.0

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

G-07-C

LOCATION : Longmont, CO

END : 2/13/2015 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 2/13/2015

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4973.1 ft

WATER LEVEL : 10.0 ft bgs

COORDINATES : 1302341.6 N, 3106183.5 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

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H _1

2.

G

LB

; S

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A T

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COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y P

E

MC = 2.4%

Bulk Sample - 5'-7'

MC = 3.7%

Gravel = 49% Sand = 36% Fines = 16% (lab test) drill chattering, possible cobbles

MC = 7.8%

Gravel =34% Sand = 58% Fines = 8% (lab test)

MC = 18.7%

LL = 38%

PL = 21%

PI = 17%

LEAN CLAY (CL)

very stiff, dark gray-brown, moist, trace gravel and sand

(FILL)

CLAYEY GRAVEL WITH SAND (GC)

medium dense to dense, orange-brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

POORLY GRADED SAND WITH CLAY AND GRAVEL (SP-SC)

dense, brown, moist to wet, fine to coarse grained sand and gravel

(ALLUVIUM)

BEDROCK (CLAYSTONE), hard, blue-gray, moist, fissured

(PIERRE SHALE)

11-10-9 (19)

10-11-14 (25)

10-15-21 (36)

16-18-32 (50)

15-14-30 (44)

6-15-25 (40)

11-10-9 (19)

10-11-14 (25)

10-15-21 (36)

16-18-32 (50)

15-14-30 (44)

6-15-25 (40)

15.0

17.0

0.0

16.0

18.0

18.0

SS

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

L-12-C

LOCATION : Longmont, CO

END : 1/12/16 13:05 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/12/16 12:20

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4972.4 ft

WATER LEVEL : 14.0 ft bgs

COORDINATES : 1302202.5 N, 3106931.9 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

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E C

H _1

2.

G

LB

; S

T V

R A

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_2

.G P

J;

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A T

A T

E M

P

LA

T E

F

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4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Boring terminated at 20.8 ft bgs.

36-50/3" (50/3")

36-50/3" (50/3")

9.0 MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

L-12-C

LOCATION : Longmont, CO

END : 1/12/16 13:05 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/12/16 12:20

SHEET 2 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4972.4 ft

WATER LEVEL : 14.0 ft bgs

COORDINATES : 1302202.5 N, 3106931.9 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y grass and snow at surface drill chattering, possible cobbles

MC = 3.8%

Bulk Sample - 7'-9'

MC = 6.3%

Gravel = 37% Sand = 47% Fines = 16% (lab test)

MC = 17.9%

Fines = 7% (lab test)

MC = 15.8%

LEAN CLAY WITH SAND (CL)

stiff, brown, moist, fine to coarse grained sand

(FILL)

CLAYEY SAND WITH GRAVEL (SC)

very dense, moist, gray-brown, fine to coarse grained sand and gravel

(ALLUVIUM)

becomes wet

POORLY GRADED SAND WITH CLAY (SP-SC)

medium dense, brown, wet, fine to medium grained sand, some coarse grained sand

(ALLUVIUM)

BEDROCK (CLAYSTONE), very hard, blue-gray, moist, fissured

(PIERRE SHALE)

Boring terminated at 15.4 ft bgs.

3-4-5 (9)

13-15-35 (50)

25-30-36 (66)

50/5" (50/5")

10-11-12 (23)

29-50/5" (50/5")

50/5" (50/5")

3-4-5 (9)

13-15-35 (50)

25-30-36 (66)

50/5" (50/5")

10-11-12 (23)

29-50/5" (50/5")

50/5" (50/5")

18.0

14.0

17.0

0.0

18.0

11.0

5.0

SS

SS

SS

SS

SS

MOD

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-11-C

LOCATION : Longmont, CO

END : 1/15/16 12:55 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 12:10

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4966.1 ft

WATER LEVEL : 7.5 ft bgs

COORDINATES : 1302221.9 N, 3107105.7 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

MC = 9.2%

LL = 32%

PL =17%

PI = 15%

Fines = 41% (lab test)

MC = 4.6%

Gravel = 34% Sand = 53% Fines = 13% Drill chattering, possible cobbles

MC = 17.6%

Fines = 7% (lab test)

MC = 14.2%

LEAN CLAY WITH SAND (CL)

stiff, dark brown, moist, fine to coarse grained sand

(FILL)

CLAYEY SAND (SC)

loose, brown, moist, fine to coarse grained sand, trace gravel

(ALLUVIUM)

CLAYEY SAND WITH GRAVEL (SC)

medium dense, gray-brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

POORLY GRADED SAND WITH CLAY (SP-SC)

medium dense to dense, gray to dark gray, wet, fine to coarse grained sand

(ALLUVIUM)

becomes WITH GRAVEL

BEDROCK (CLAYSTONE) WITH LAYERS OF FINE SAND, very hard, brown to blue-gray, moist, fissured

(PIERRE SHALE)

3-5-6 (11)

2-3-3 (6)

7-15-9 (24)

6-7-18 (25)

10-15-18 (33)

50/6" (50/6")

3-5-6 (11)

2-3-3 (6)

7-15-9 (24)

6-7-18 (25)

10-15-18 (33)

50/6" (50/6")

18.0

11.0

14.0

15.0

10.0

6.0

SS

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-05-C

LOCATION : Longmont, CO

END : 1/15/16 14:40 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 14:10

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4967.2 ft

WATER LEVEL : 8.0 ft bgs

COORDINATES : 1302146.6 N, 3107074.1 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

ELEV

4971.7

4968.0

4964.0

4960.0

4956.0

4955.2

DEPTH

0.30

4.00

8.00

12.00

16.00

16.85

BL

O

W S/

0.

5f t

N

N60

LE

G

EN

D

FIELD CLASSIFICATION OF MATERIALS

(Description)

WELL GRADED SAND WITH

SILT (SW-SM) fine to coarse, subrounded Fill

LEAN CLAY WITH SAND (CL-

ML) subrounded; black, dry, some fine to coarse sand, trace coarse gravel, some iron staining Fill

CLAYEY GRAVEL WITH SAND

(GC) medium to coarse, angular;

subrounded; grayish brown, moist, little clay Alluvium

POORLY GRADED SAND WITH

SILT AND GRAVEL (SP-SM) fine to coarse, subrounded;

subrounded; brown to gray, moist, gravel ~1" Alluvium

SILTY SAND WITH GRAVEL

(SM) subangular; medium, subrounded; gray to black, wet, some coarse gravel, 10-15% silt, black material could be organics Alluvium

(Shale) black, very weak, sandy Pierre Shale

Borehole finished at 16.8

REC

Sa m p N o.

D-1

D-2

LABORATORY

G ra ve l

Sa nd

Fi ne s

LL PI M

C

AS

TM

C la ss REMARKS

Boring Designation L21-BH01

DRILLING LOG DIVISION

Northwestern INSTALLATION Sheet 1 of 1

1. PROJECT 10. COORDINATE SYSTEM VERTICAL

Walton Pond - St Vrain levee Longmont, CO

NAD 1983 StatePlane Colorado North FIPS 0501 Feet NAVD88

LOCATION COORDINATES LOCATION METHOD:

N: 1301725.94 E: 3106291.94

2. HOLE NUMBER

L21-BH01

3. DRILLING AGENCY

Omaha Drill Crew 11. DATE BORING

STARTED

Nov 19 2021

COMPLETED

Nov 19 2021

4. NAME OF DRILLER 12. HAMMER TYPE EFFICIENCY (%)

Chris Miner

5. EQUIPMENT 13. SIZE AND TYPE OF BIT

Geoprobe 4.25" HSA'

6. DIRECTION OF BORING

Vertical

DEG FROM VERTICAL BEARING

14. ELEVATION SURFACE

15. ELEVATION GROUND WATER

4972.0' 4965.5'

7. THICKNESS OF OVERBURDEN 16.9' 16. TOTAL NUMBER CORE BOXES

8. DEPTH DRILLED INTO ROCK

9. TOTAL DEPTH OF BORING 16.9'

17. SIGNATURE AND TITLE OF INSPECTOR

Tyler Anderson, Geologist

USACE FORM 1836 Boring Designation L21-BH01 Sheet 1 of 1

MC = 0.3%

Bulk Sample - 5'-7':

MC = 3.4%

Gravel = 74% Sand = 20% Fines = 7% (lab test)

MC = 8.0%

MC = 11.7%

Weathered the first 4"

MC = 9.1%

Dry Unit Weight = 110.8 pcf

LEAN CLAY WITH SAND (CL)

AND GRAVEL, dark brown, moist, trace cobbles

(FILL)

CLAYEY GRAVEL WITH SAND (GC)

with cobbles, brown, moist

(FILL)

POORLY GRADED GRAVEL WITH CLAY AND SAND (GP-GC)

medium dense, reddish brown to orange brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

becomes gray, very dense

BEDROCK (CLAYSTONE), very hard, brown to blue-gray, moist, fissured

(PIERRE SHALE)

Boring terminated at 15.3 ft bgs.

9-10-10 (20)

7-9-8 (17)

50/6" (50/6")

20-29-50/6" (79/12")

50/4" (50/4")

9-10-10 (20)

7-9-8 (17)

50/6" (50/6")

20-29-50/6" (79/12")

50/4" (50/4")

8.0

10.0

6.0

18.0

4.0

SS

SS

SS

SS

MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

L-04-C

LOCATION : Longmont, CO

END : 12/9/15 16:45 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 12/9/15 16:15

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 4" SS

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4965.1 ft

WATER LEVEL : 7.0 ft bgs

COORDINATES : 1302032.5 N, 3107220.5 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Cobbles observed at surfacePOORLY GRADED SAND WITH SILT AND GRAVEL (SP-SM) medium dense, tan to brown, dry to moist, fine to coarse grained sand

(ALLUVIUM)

becomes very dense to dense, gray, and wet

BEDROCK (CLAYSTONE), hard, blue-gray, moist, fissured

(PIERRE SHALE)

Boring terminated at 15.8 ft bgs.

13-15-15 (30)

5-8-20 (28)

9-26-50/8" (76/14")

11-17-16 (33)

50/9" (50/9")

13-15-15 (30)

5-8-20 (28)

9-26-50/8" (76/14")

11-17-16 (33)

50/9" (50/9")

18.0

10.0

10.0

18.0

9.0

SS

SS

SS

SS

MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

G-06-C

LOCATION : Longmont, CO

END : 2/12/2015 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 2/12/2015

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4966.6 ft

WATER LEVEL : 7.5 ft bgs

COORDINATES : 1301903.2 N, 3107336.0 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y snow at surface

MC = 23.6%

LL = 27%

PL = 18%

PI = 9%

Fines = 41% (lab test)

MC = 20.0%

Fines = 22% organic odor

MC =10.1%

LEAN CLAY WITH SAND (CL)

very stiff, dark brown, moist, fine to coarse grained sand

(FILL)

CLAYEY SAND WITH GRAVEL (SC)

loose, brown, moist, fine to coarse grained sand and gravel

(FILL)

CLAYEY SAND (SC)

very loose, dark brown, moist to wet

(ALLUVIUM)

SILTY SAND WITH GRAVEL (SM)

very loose, dark gray, wet, fine to coarse grained sand and gravel

(ALLUVIUM)

BEDROCK (CLAYSTONE), very hard, blue-gray, moist, fissured

(PIERRE SHALE)

3-8-12 (20)

6-4-2 (6)

2-2-2 (4)

2-2-1 (3)

2-1-2 (3)

26-50/6" (50/6")

3-8-12 (20)

6-4-2 (6)

2-2-2 (4)

2-2-1 (3)

2-1-2 (3)

26-50/6" (50/6")

18.0

0.0

18.0

5.0

0.0

12.0

SS

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-08-C

LOCATION : Longmont, CO

END : 1/15/16 15:55 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 15:30

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4965.4 ft

WATER LEVEL : 7.0 ft bgs

COORDINATES : 1301438.0 N, 3107887.4 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Boring terminated at 20.4 ft bgs.

50/5"

(50/5") 50/5"

(50/5")

5.0 MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-08-C

LOCATION : Longmont, CO

END : 1/15/16 15:55 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 15:30

SHEET 2 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4965.4 ft

WATER LEVEL : 7.0 ft bgs

COORDINATES : 1301438.0 N, 3107887.4 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

MC = 11.1%

LL = NV

PL = NP

PI = NP

Fines = 13% (lab test) organic odor

MC = 12.1%

MC = 9.0%

LL = NV

PL = NP

PI = NP

Fines = 11% (lab test)

FAT CLAY (CH)

MOTTLED WITH ORANGE-BROWN SILT, very stiff, dark gray-brown, moist

(ALLUVIUM)

becomes sandy, with gravel, fine to coarse grained sand and gravel

SILTY SAND WITH GRAVEL (SM)

very dense, brown to gray, wet, fine to coarse grained sand and gravel

(ALLUVIUM)

POORLY GRADED SAND WITH SILT AND GRAVEL (SP-SM)

loose, dark gray, wet, fine to coarse grained sand and gravel

(ALLUVIUM)

becomes medium dense becomes very loose

BEDROCK (CLAYSTONE), very hard, blue-gray, moist, fissured

(PIERRE SHALE)

3-6-10 (16)

6-8-48 (56)

2-2-3 (5)

2-14-8 (22)

2-2-2 (4)

26-50/6" (50/6")

3-6-10 (16)

6-8-48 (56)

2-2-3 (5)

2-14-8 (22)

2-2-2 (4)

26-50/6" (50/6")

10.0

18.0

5.0

12.0

10.0

12.0

SS

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-09-C

LOCATION : Longmont, CO

END : 1/15/16 16:50 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 16:05

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4964.0 ft

WATER LEVEL : 2.0 ft bgs

COORDINATES : 1301671.1 N, 3107624.2 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Boring terminated at 20.4 ft bgs.

50/5"

(50/5") 50/5"

(50/5")

5.0 MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-09-C

LOCATION : Longmont, CO

END : 1/15/16 16:50 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/15/16 16:05

SHEET 2 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4964.0 ft

WATER LEVEL : 2.0 ft bgs

COORDINATES : 1301671.1 N, 3107624.2 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y large cobbles and boulders at surface imbedded in SC 30% fines (visual observation) Drill chattering to 7.5'

MC = 7.2%

gravel in tip of sampler

Bulk Sample - 5'-7':

MC = 2.2%

Gravel = 37% Sand = 49% Fines = 13% (lab test) Cobble piece in tip of sampler

MC = 2.3%

Fines = 10% (lab test)

MC = 3.8%

Fines = 8% (lab test) sampler bouncing off of cobbles/boulders upon hammer impact

MC = 8.1%

CLAYEY SAND WITH GRAVEL (SC)

medium dense, brown, wet to moist, fine to coarse grained sand and gravel

(FILL)

CLAYEY SAND WITH GRAVEL (SC)

medium dense to dense, gray to brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

POORLY GRADED SAND WITH CLAY AND GRAVEL (SP-SC)

TO POORLY GRADED GRAVEL WITH CLAY AND SAND (GP-GC), very dense, gray-brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

POORLY GRADED GRAVEL WITH CLAY AND SAND (GP-GC)

dense to very dense, gray-brown, moist to wet, fine to coarse grained sand and gravel

(ALLUVIUM)

BEDROCK (CLAYSTONE), very hard, blue-gray, moist, fissured

(PIERRE SHALE)

8-6-8 (14)

11-10-7 (17)

18-17-18 (35)

18-23-34 (57)

18-24-26 (50)

50/3" (50/3")

45-50/3" (50/3")

35-50/3" (50/3")

8-6-8 (14)

11-10-7 (17)

18-17-18 (35)

18-23-34 (57)

18-24-26 (50)

50/3" (50/3")

45-50/3" (50/3")

35-50/3" (50/3")

1.0

3.0

0.0

12.0

16.0

1.0

0.0

9.0

SS

SS

SS

SS

SS

SS

MOD

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-07-C

LOCATION : Longmont, CO

END : 1/25/16 13:25 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/25/16 12:15

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4967.9 ft

WATER LEVEL : 15.0 ft bgs

COORDINATES : 1301613.4 N, 3107769.8 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Boring terminated at 23.3 ft bgs.

50/4"

(50/4") 50/4"

(50/4")

4.0 MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

L-07-C

LOCATION : Longmont, CO

END : 1/25/16 13:25 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 1/25/16 12:15

SHEET 2 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4967.9 ft

WATER LEVEL : 15.0 ft bgs

COORDINATES : 1301613.4 N, 3107769.8 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Fe+ deposits

MC = 0.8%

Gravel = 43% Sand = 52% Fines = 5% (lab test)

Drill chattering, hard drilling - cobbles likely till bedrock

MC = 7.5%

SANDY SILT (ML)

brown, moist, fine grained sand

(TOPSOIL)

SANDY LEAN CLAY (CL)

reddish brown, moist, trace organics

(FILL)

POORLY GRADED SAND WITH SILT AND GRAVEL (SP-SM)

medium dense to loose, orange-brown, moist, fine grained sand

(ALLUVIUM)

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM)

very dense, brown to tan, moist to wet, fine to coarse grained sand

(ALLUVIUM)

BEDROCK (CLAYSTONE), weathered, blue-gray, moist, fissured

(PIERRE SHALE)

becomes very hard

Boring terminated at 18 ft bgs.

3-3-8 (11)

3-3-4 (7)

32-50/6" (50/6")

5-20-50/6" (70/12")

31-29-27 (56)

20-18 (18)

50/6" (50/6")

3-3-8 (11)

3-3-4 (7)

32-50/6" (50/6")

5-20-50/6" (70/12")

31-29-27 (56)

20-18 (18)

50/6" (50/6")

10.0

15.0

12.0

14.0

15.0

16.0

6.0

SS

SS

SS

SS

SS

MOD

MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

U-01-C

LOCATION : Longmont, CO

END : 2/13/2015 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 2/13/2015

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4967.8 ft

WATER LEVEL : 9.0 ft bgs

COORDINATES : 1301568.7 N, 3107725.7 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Drill chattering, possible cobbles to bedrock

MC = 4.8%

Fines = 24% (lab test)

Gravel in tip of sampler

MC = 8.7%

SILTY SAND (SM)

dark brown, moist

(TOPSOIL)

POORLY GRADED SAND WITH SILT AND GRAVEL (SP-SM)

medium dense, tan, moist, fine to coarse grained sand

(ALLUVIUM)

SILTY GRAVEL WITH SAND (GM)

dense to very dense, brown, moist, fine to coarse grained sand

(ALLUVIUM)

becomes wet

BEDROCK (CLAYSTONE), hard, blue-gray, moist, fissured

(PIERRE SHALE)

Boring terminated at 15.8 ft bgs.

9-9-21 (30)

18-43-43 (86)

21-50/6" (50/6")

30-32-49 (81)

50/9" (50/9")

9-9-21 (30)

18-43-43 (86)

21-50/6" (50/6")

30-32-49 (81)

50/9" (50/9")

11.0

13.0

12.0

12.0

9.0

SS

SS

SS

SS

MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

RW-24-C

LOCATION : Longmont, CO

END : 2/13/2015 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 2/13/2015

SHEET 1 OF 1

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4964.2 ft

WATER LEVEL : 10.0 ft bgs

COORDINATES : 1301436.4 N, 3107835.5 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

MC = 0.1%

Fines = 14%

LL = NV

PL = NP

PI = NP

MC = 0.7%

Gravel = 47% Sand = 47% Fines = 6% loud chattering, possible cobbles

MC = 0.3%

broken cobbles and large gravel in sampler

MC = 5.1%

SILTY SAND (SM)

medium dense, brown, moist, fine to coarse grained sand, trace gravel

(ALLUVIUM)

becomes loose, reddish brown

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM)

dense to very dense, dark brown to orange brown, moist, fine to coarse grained sand and gravel

(ALLUVIUM)

BEDROCK (CLAYSTONE), very hard, blue-gray, moist, fissured

(PIERRE SHALE)

4-6-7 (13)

5-4-5 (9)

11-17-20 (37)

50/6" (50/6")

50/6" (50/6")

50/4" (50/4")

4-6-7 (13)

5-4-5 (9)

11-17-20 (37)

50/6" (50/6")

50/6" (50/6")

50/4" (50/4")

3.0

9.0

17.0

6.0

6.0

4.0

SS

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

L-06-C

LOCATION : Longmont, CO

END : 12/9/15 15:55 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 12/9/15 15:15

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 4" SS

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4968.0 ft

WATER LEVEL : 15.0 ft bgs

COORDINATES : 1301438.0 N, 3107887.4 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Boring terminated at 22.3 ft bgs.

50/4"

(50/4") 50/4"

(50/4")

4.0 MOD

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 55

BORING NUMBER:

L-06-C

LOCATION : Longmont, CO

END : 12/9/15 15:55 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 12/9/15 15:15

SHEET 2 OF 2

DRILLING METHOD AND EQUIPMENT : 4" SS

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4968.0 ft

WATER LEVEL : 15.0 ft bgs

COORDINATES : 1301438.0 N, 3107887.4 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G E

O T

E C

H _1

2.

G

LB

; S

T V

R A

IN

_2

.G P

J;

D

A T

A T

E M

P

LA

T E

F

IL

E

.G

D T

4/

7/

COMMENTS

DRILLING DETAILS

LAB TESTS

SOIL DESCRIPTION

SOIL NAME, USCS GROUP SYMBOL,

COLOR, MOISTURE CONTENT, RELATIVE

DENSITY OR CONSISTENCY, SOIL

STRUCTURE, MINERALOGYG

R A

P H

IC

L

O

GSTANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

STANDARD

PENETRATION

TEST RESULTS

6"-6"-6" (N)

R E

C O

V E

R Y in

S A

M P

LE

T

Y

Fe+ deposits

20%-30% fines (field observation)

15% fines (field observation)

SANDY SILT (ML)

brown, moist, fine grained sand

(TOPSOIL)

SANDY LEAN CLAY (CL)

firm to stiff, reddish brown, moist

(FILL)

SILTY GRAVEL WITH SAND (GM)

dense to very dense, brown to gray, moist, fine to coarse grained sand

(ALLUVIUM)

becomes wet

BEDROCK (CLAYSTONE), very hard, blue gray, moist, fissured

(PIERRE SHALE)

2-3-4 (7)

7-6-10 (16)

19-17-20 (37)

17-25-40 (65)

20-50/4" (50/4")

2-3-4 (7)

7-6-10 (16)

19-17-20 (37)

17-25-40 (65)

20-50/4" (50/4")

SS

SS

SS

SS

SS

D E

P T

H B

E

LO

W G

R O

U N

D S

U R

F A

C E

(f t)

DRILLING CONTRACTOR AND DRILL RIG : Vine, CME 45

BORING NUMBER:

B-01-C

LOCATION : Longmont, CO

END : 6/4/2015 LOGGER : ERS

PROJECT NUMBER:

Soil Boring Log

START : 6/4/2015

SHEET 1 OF 2

DRILLING METHOD AND EQUIPMENT : 8" HSA

653819

PROJECT : Resilient St. Vrain Project, Longmont, CO

ELEVATION : 4968.2 ft

WATER LEVEL : 11.0 ft bgs

COORDINATES : 1301324.7 N, 3107974.1 E

N E

W S

O

IL

B O

R

IN

G L

O G

; D R

A F

T C

H 2M

G…