Geotechnical Engineering Report ______

REPORT COVER PAGE

Yeader Creek Stabilization Improvements Des Moines, Iowa December 12, 2018 Terracon Project No. 08175152-01

Prepared for: HR Green, Inc. Johnston, Iowa

Prepared by: Terracon Consultants, Inc. Des Moines, Iowa REPORT COVER LET TER T O SIGN December 12, 2018

HR Green, Inc. 5525 Merle Hay Road, Suite 200 Johnston, Iowa 50131

Attn: Mr. Chad Mason, P.E. P: (636) 812-4210 E: [email protected]

Re: Geotechnical Engineering Report Yeader Creek Stabilization Improvements Des Moines, Iowa Terracon Project No. 08175152-01

Dear Mr. Mason:

We have performed geotechnical engineering services for the referenced project in general accordance with the Standard Agreement for Subconsultant Services, HR Green Project No. 170850, dated September 14, 2018. After the initial field exploration was completed, the locations of proposed improvements was altered, Terracon received approval for an additional three borings via email on November 13, 2018. This report presents the findings of the subsurface exploration and provides geotechnical considerations and recommendations concerning the proposed channel improvements along the applicable portions of the Yeader Creek tributaries.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Theodore D. Bechtum, P.E. Brett E. Bradfield, P.E. Project Engineer Senior Engineering Consultant

Terracon Consultants, Inc. 600 SW 7th Street, Suite M Des Moines, Iowa 50309 P (515) 244 3184 F (515) 244 5249 terracon.com REPORT TOPICS

INTRODUCTION ...... 2 SITE CONDITIONS ...... 2 PROJECT DESCRIPTION ...... 4 GEOTECHNICAL CHARACTERIZATION ...... 5 GRAVITY RETAINING WALLS ...... 6 STABILITY ANALYSES ...... 8 EARTHWORK...... 16 ENVIRONMENTAL CONSIDERATIONS ...... 20 GENERAL COMMENTS ...... 20 SIGNATURE PAGE ...... 21 ATTACHMENTS ...... 22

Note: This report was also delivered in a web-based format. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS EXPLORATION AND TESTING PROCEDURES SITE LOCATION AND EXPLORATION PLANS EXPLORATION RESULTS SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

Responsive ■ Resourceful ■ Reliable INTRODUC TION Geotechnical Engineering Report Yeader Creek Stabilization Improvements Des Moines, Iowa Terracon Project No. 08175152-01 December 12, 2018

INTRODUCTION

Geotechnical engineering exploration and analysis has been completed for the evaluation of portions of the creek stabilization improvements proposed on the Yeader Creek tributaries in Des Moines, Iowa. The exploration consisted of 8 geotechnical borings to depths ranging from approximately 20 to 30 feet below existing ground surface (bgs) and 6 hand auger borings to depths ranging from approximately 5 to 13 feet bgs.

The purpose of these services is to provide information, professional opinions, and/or geotechnical recommendations relative to:

■ Subsurface soil and rock conditions ■ Groundwater conditions ■ Cursory slope stability evaluation of ■ Earthwork and subgrade preparation planned improvements ■ Bearing conditions for planned improvements

Maps showing the sites along the channel and boring locations are shown in the Site Location and Exploration Plan section. The results of the laboratory testing performed on soil samples obtained from the sites during the field exploration are included on the boring logs and/or as separate graphs in Exploration Results.

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description Exploration was requested by HR Green in the following areas: See Site Location and Exploration Plan ■ Area 1: North of Yeader Creek and south of 511 Titus Avenue (Vicinity of Boring 1) Location ■ Area 2 (Wall shown on Sheet V.01): East of Yeader Creek tributary and west of 5310 and 5304 SE 5th Street (Vicinity of Boring 2, 3 and 4). ■ Area 3 (Wall shown on Sheet V.02): South of Yeader Creek and west of Yeader creek tributary near 5201 South Union Street (Vicinity Boring 5, 6, and 12)

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Item Description ■ Area 4 (Wall shown on Sheet V.03): East of Yeader Creek Tributary and west of 100 East Kenyon Avenue (Vicnity of Boring 7 and 13) ■ Area 5: Yeader Creek Tributary, east of 17 East Kenyon Avenue (Vicinity of Boring 8) ■ Area 6: West of Yeader Creek Tributary and east of 5513 South Union Street (Vicinity of Boring 9 and 10). ■ Area 7 (Wall shown on Sheet V.04): East of Yeader Creek Tributary and west of 5512 Southeast 1st Court (Vicinity of Boring 11 and 14)

Existing conditions generally consist of eroded stream banks near the Current Ground existing creek. Vegetation consists of trees, shrubs, and grass, with reduced Cover vegetation in areas of recent erosion. In general, the area outside the creek banks has relatively flat or rolling topography in areas with minor erosion. Near the stream, the ground slopes relatively steeply to the existing stream, often creating a ravine, with occasional indications of prior bank failures. Elevations and apparent slopes interpreted from the information provided by Nilles and HR Green are provided below: The ground slopes vary along the waterways with areas of nearly vertical slopes, and the following descriptions are only an approximate indication of actual conditions.

■ Area 1: Creek flow line elevation of about 53 feet (City of Des Moines datum). North bank has apparent 0.5:1 (horizontal : vertical) slope with elevation of about 66 feet at top of slope. South bank has apparent 1.5:1 slope with elevation of about 60 feet at top of slope. ■ Area 2 (Wall shown on Sheet V.01): Creek flow line elevations of about 72 to 77 feet. East and west creek banks generally have a 1.5:1 slope, with areas steeper than 1:1. The elevation is about 88 to 91 feet at top Existing Topography of east slope and 83 feet at top of west slope. ■ Area 3 (Wall shown on Sheet V.02): Creek flow line elevation of about 69 to 72 feet. West creek bank generally has a slope of about 3:1, with areas steeper than 1:1 near the steam channel. The elevation is about 86 feet at the top of the west slope. ■ Area 4 (Wall shown on Sheet V.03): Creek flow line elevation of about 77 feet. East and west creek banks generally have slopes of about 1:1 or 1.5:1, with areas steeper than 1:1. The elevation is about 93 feet at the top of the east slope and about 95 feet at the top of the west slope. ■ Area 5: Creek flow line elevation of about 82 to 83 feet. West and east bank has an apparent 1:1 slope with elevation of about 100 feet at top of west bank and 92 feet at top of east bank. ■ Area 6: Creek flow line elevation of about 86 to 90 feet. West bank has apparent 1:1 slope or steeper with elevation of about 95 to 100 feet at top of slope.

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Item Description ■ Area 7 (Wall shown on Sheet V.04): Creek flow line elevation of about Existing Topography 86 to 90 feet. East bank has an apparent 1.5:1 to 1:1 slope, with areas (cont.) steeper than 1:1. The elevation is about 100 feet at top of east slope. Rip rap has been placed in occasional locations of erosion or bank collapses or sloughing, and debris and refuse was occasionally encountered at the Current streambank ground surface and/or embedded in the banks. Much of the existing stream distress bank is anticipated to be prone to potential instability with increases in pore water pressure, possibly due to rain events, and scour and erosion/removal of material at base of creek.

PROJECT DESCRIPTION

Item Description Based on meetings with HR Green, Terracon understands gravity walls will be considered at Areas 2, 3, 4, and 7. Information at each of the walls was provided on the V Sheets provided by HR Green, dated October 18, 2018.

■ Area 2 (Wall shown on Sheet V.01): Proposed gravity wall with height of about 7 feet or less and length of about 160 feet on the east side of Yeader Creek behind 5304 and 5310 SE 5th Street. ■ Area 3 (Wall shown on Sheet V.02): Proposed gravity wall with height of about 7 feet or less and length of about 59 feet on the west side of Yeader Creek behind the apartments at 5201 South Union Street. ■ Area 4 (Wall shown on Sheet V.03): Proposed gravity wall with height of about 12 feet or less and length of about 98 feet on the east side of Yeader Creek behind 100 Kenyon Avenue. ■ Area 7 (Wall shown on Sheet V.04): Proposed gravity retaining wall with height of about 8 feet or less and length of about 186 feet on the Project Description east side of Yeader Creek behind 5506, 5512, and 5518 SE 1st Court. ■ Terracon understands that current channel slopes adjacent to the planned walls at Areas 2, 3, 4, and 7 will be flattened to about 3:1 from planned top of wall elevations to near the creek channel, with slopes of about 2:1 occasionally at the creek channel (total slope height less than about 7 to 12 feet, with about 2 to 3 feet of occasionally steepened slope near the channel). These slopes are planned to be protected from toe and slope erosion. Terracon anticipates vegetation will be used to help minimize the potential for surficial sloughs. ■ Earlier versions of project plans indicated retaining walls or slope flattening at Areas 1, 5, and 6, but Terracon understands that stabilization improvements including flattening of current back slopes or erosion protection are not currently planned in Areas 1, 5 and 6. Borings were completed in these areas based on preliminary direction from HR Green, and the logs are provided in Exploration Results for reference.

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Item Description ■ Terracon understands the gravity retaining wall systems consisting of pre-cast concrete blocks are planned. Drainage will be provided Retaining Wall behind/below the retaining walls. Construction ■ Terracon understands retaining walls will be design-build by selected contractor.

GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface soil and groundwater conditions based upon our review of the data, geologic setting, and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical recommendations. Conditions encountered at each exploration point are indicated on the individual logs. The GeoModel and boring logs are provided in the Exploration Results section.

Stratification boundaries on the GeoModel and boring logs represent the approximate location of changes in soil types; in situ, the transition between materials may be gradual. As noted in General Comments, the characterizations are based on widely spaced exploration points across the site, and variations are likely.

NRCS SSURGO soils data indicates the explored areas adjacent to Yeader Creek are represented by alluvium near surface soils. Existing fill was encountered in Borings 5 and 6 (Area 3) and Boring 13 (Area 4), and were underlain by the apparent alluvial soils. Zones of refuse and rubble were encountered in the existing fill at Borings 5 and 6, and a hydro-carbon odor was observed by the drill crew at a depth of about 12 feet in Boring 6.

In general, the borings except Borings 3 and 8 encountered cohesive overburden soils exhibiting variable plasticity (lean clays and fat clays) and variable sand contents. Sand seams and pockets were occasionally encountered in the alluvial soils. The alluvial soils generally exhibited medium stiff to stiff consistency with a zone of very soft to soft soils in Boring 1, 12, and 14. Borings 1, 5 to 7, 10, 11, and 12 terminated in the apparent alluvial clay or sand soils.

Shale and residual clay soils were encountered below the alluvial deposits in Borings 2, 4, 9, 13, and 14 and just below the ground surface in Borings 3 and 8. The shale often transitioned from residual clay to highly to moderately weathered with depth. Borings 2 to 4, 8 and 9 terminated in the residual clay and shale.

Groundwater conditions were observed while drilling and shortly after completion of drilling at the soil borings completed with a drill rig. The water levels observed in the boreholes can be found on the boring logs in Exploration Results and in the table below.

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Approximate Depth to Groundwater (feet) 1 Boring Number While Drilling After Drilling

1 16 15 2 13 14 5 13 16 6 17 16 9 12 10 12 13 15½ 13 19 19½ 14 14 12½ 1. Below ground surface

A relatively long period may be necessary for a groundwater level to develop and stabilize in a borehole. Long term observations in piezometers or observation wells sealed from the influence of surface water are often required to define groundwater levels in materials of this type.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff, level of nearby waterways, and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structures may be different than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GRAVITY RETAINING WALLS

The proper design and analysis of a gravity block retaining wall system should include consideration of external, internal, and global stability. The external stability considers the wall mass and any supplemental reinforced backfill zone as a monolithic block, and includes sliding, overturning, and bearing capacity failure of the wall. The internal stability should consider the strength and mechanical connections or interlocking of the selected wall system. Global stability considers the failure of the slope cross-section above and below the limits of the retaining wall components. The results of these analyses are dependent upon the wall configuration, wall type, slope geometry, surcharge loading, groundwater, as well as soil characteristics (texture, density, shear strength, and moisture content).

Evaluation of the internal stability and final external stability of the wall is the responsibility of the wall designer and was not part of our scope of services and not considered in our analyses. Terracon completed a general characterization of the influence of planned improvements on

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external global stability at one location at each of the four planned wall areas. The results of these analyses and associated considerations/opinions are presented in Stability Analysis.

We recommend that Terracon is retained to review grading plans and the design of the retaining wall systems by the selected design-build contractor with regard to external, internal, and global stability, if desired.

Gravity Retaining Wall Design Considerations

The walls should be designed with a leveling pad comprised of properly compacted, well-graded crushed stone or concrete mud mat. If lateral resistance is needed to be derived from passive soil pressures, in addition to protection against movements due to frost action, we suggest that the leveling pad be designed with a minimum embedment depth of at least 42 inches, as measured from the base of the foundation to the lowest adjacent grade. The base of the wall should be constructed to minimize infiltration of surface water into the leveling pad.

It should be noted that drainage of retained soil behind a retaining wall system is essential in maintaining the integrity of the proposed wall. Saturation of the retained soil can significantly reduce the material strength and jeopardize the stability of the wall structure. Thus, we recommend that a drainage system be constructed to reduce the potential for surface water infiltration or groundwater accumulation behind the retaining wall.

Terracon anticipates the walls could be designed with a maximum contact bearing pressure of up to 1,500 psf and the base of retaining walls should bear on medium stiff to stiff native clay soils, or on new fill extending to suitable native materials. The actual wall contact pressure and surcharge loadings should be considered in the final external stability analyses. The maximum contact bearing pressure will depend on the final wall configuration, and Terracon should be retained to review the bearing capacity of the soils supporting the wall during construction. Overexcavation will be required where relatively lower strength soils are encountered or contact pressures exceed the bearing capacity of the soil.

Retaining Wall Foundation Construction Considerations

Retaining wall foundation excavations should be observed by Terracon. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. Where unsuitable bearing soils are encountered at the wall base, the excavations should be extended deeper to suitable soils or as directed by the retaining wall designer and/or geotechnical engineer, and backfilled with properly compacted granular materials.

The base of the wall foundation excavation should be free of water and loose soil prior to placing the aggregate leveling pad and wall backfill. Should the soils at bearing level become excessively dry, disturbed or saturated, or frozen, the affected soil should be removed prior to wall construction

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STABILITY ANALYSES

Slope stability analyses for a general characterization of the influence of planned improvements were requested at one location at each of the four planned walls. Cursory global slope stability analyses were completed by Terracon at:

■ Gravity Wall at Area 2 (Plan Sheet V.01 – Approx. Station 0+40) ■ Gravity Wall at Area 3 (Plan Sheet V.02 – Approx. Station 0+20) ■ Gravity Wall at Area 4 (Plan Sheet V.03 – Approx. Station 0+45) ■ Gravity Wall at Area 7 (Plan Sheet V.04 – Approx. Station 1+47)

As presented in Gravity Retaining Walls, the general stability analyses do not consider internal stability or final external stability of the still to be designed retaining wall, and the final external and internal stability of the wall will need to be determined by the wall designer.

Stability Analysis Criteria

The planned configurations of the gravity walls and altered grading for the creek and tributary slopes are provided on Sheets V.01, V.02, V.03, and V.04, prepared by HR Green, dated October 18, 2018. These configurations are generally described in Project Description. The configurations developed by HR Green were used in Terracon’s analyses of stability of the completed channel. One-cross section was considered by Terracon at each wall.

Borings performed in the general areas of the analyzed cross-section locations were used to develop a generalized profile of subsurface conditions present in the areas. As presented on the boring logs and in Geotechnical Characterization, the subsurface conditions appear to generally consist of relatively low strength clay soils, possibly derived from alluvial deposits, underlain with shale bedrock. Borings completed at or near each of the 4 proposed walls were used to develop a general characterization of stratigraphy at the analyzed cross-section.

Global slope stability analyses were completed utilizing the computer software ”SLOPE/W”, using the Morgenstern-Price methodology utilizing optimized circular failure mode analysis. Extensive searches were performed that resulted in hypothetical failure surfaces with the lowest factors of safety against slope failure for the different conditions at each cross-section, i.e., relative amount of relief and existing slope.

As used in engineering, a Factor of Safety is considered to be the sum of resisting forces (those forces which resist movement or failure) divided by the sum of driving forces (those forces which promote movement or failure). As applied to soil slope stability analysis, factors that resist movement are primarily the soil shear strength (friction and cohesion), mechanical or man-made devices to reinforce the slope, and/or counterweight measures at the lower portions of the slopes.

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Factors that drive or promote slope movement are primarily upland soil mass, surcharge loads and gravity, groundwater or pore water pressure, and seepage forces, where present.

To avoid movement or failure, the resisting forces must be greater than the driving forces and their ratio, or Factor of Safety, must be greater than 1. When driving forces exceed the peak resisting forces, movement occurs. Often times, the remaining strength of the failed soil mass, or soil in the zone of shear planes (referred to as residual strength) is lower than the peak strength. Increasing or improving stability of slopes involves increasing the resisting or stabilizing forces or decreasing the driving (destabilizing) forces.

Slopes that appear stable may have a factor of safety only slightly above 1. Sometimes only minor changes to slope geometry, erosion at the toe of slopes or creek banks, surface water flow, or changes in groundwater levels can affect stability of slopes. Movements related to instability can occur rapidly or slowly.

Soil slopes that have noticeably failed provide useful information regarding the conditions of the slope and soil strength characteristics at the time of failure. The factor of safety at the distressed slopes can be considered to be 1.0 and a slope model can be developed. The slope model requires information about the slope geometry, assumed shape of failure surface, stratigraphy, shear strength and unit weight of the materials, pore water pressures, and presence of other imposed loadings. Much of this information is collected during field exploration at the site, and then is used to constitute the back-analysis model. Back-analysis is the iterative process of developing a suitable slope model from the assumed near-failure condition. This model is helpful to better understand the condition of the existing slope, and aids in the evaluation of changes in overall stability by the planned grading changes, and for the development of measures that should be considered to improve or maintain the overall factor of safety of the slope.

We used back-analysis methods to correlate shear strength parameters for the slope stability models. Current conditions of slopes were modeled to have factors of safety near 1.0 to develop these parameters; however, actual factor of safety of current slopes are likely somewhat higher since the slopes are intact. When new slope configurations are modeled with these pre- determined shear strength values, the new analysis would indicate either a relative improvement of slope stability, or a decrease which would indicate changes in design should be considered to maintain stability equal to or above current conditions.

Slope Geometry and Soil Strength Parameters

The effective stress shear strength parameters for each soil stratum were estimated from published correlations between Atterberg limits and clay content determined from tests performed on representative samples. Shale parameters were estimated from field results, laboratory testing, and publications. A back-analysis calculation was also used to adjust some of the shear strength parameters.

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When used, soil total stress shear strength parameters were generally evaluated from standard penetration test N-values and/or unconfined compressive strength tests from each soil stratum.

The estimated shear strength parameters for each stratum, as obtained from the field results, laboratory testing, and back-calculation analyses, are shown in the following table. Computer outputs showing the section, estimated subsurface profile, strength parameters, groundwater conditions and the cross section of the hypothetical failure surfaces with the computed relative lowest factor of safety on the current slope topography are provided in Supporting Information.

Subsurface Material Shear Strength Parameters

Total Stress Parameters Effective Stress Strength Parameters Material Friction Angle Cohesion (c’) Friction Angle Cohesion (c’) (Φ’) psf (Φ’) psf

Fat Clay 0 1,200 23 50

Lean Clay 1 (occasionally variable 0 300 to 800 26 to 27 0 to 50 sand content)

Residual Shale 0 600 12 100

Shale 0 2,000 15 200

Existing Fill 2 0 750 23 50

1. Some variation in parameters used depending on zone / depth in soil profile. Zone of higher strength sandy lean clay encountered at wall V.01 modeled with total stress cohesion of 1,500 psf. 2. Used to model existing fill encountered in Boring B-13 only.

Stability Analysis Results

As previously mentioned, global slope stability analyses were completed utilizing the computer software ”SLOPE/W”, using the Morgenstern-Price methodology utilizing optimized circular failure mode analysis. For the sections analyzed, extensive searches were performed that resulted in hypothetical failure surfaces representing the lowest relative factors of safety with respect to slope failure for the waterway slopes and adjusted channel geometry.

The profiles of the natural ground surfaces and alternations at the analyzed cross sections were estimated from the project E and V Sheets provided to Terracon. The soil layer profiles for our analysis sections were interpolated or estimated from borings performed in the vicinity of the analyzed cross sections.

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The following locations were evaluated:

n Gravity Wall at Area 2 – (Plan Sheet V.01 Approx. Station 0+40 +/-) n Gravity Wall at Area 3 – (Plan Sheet V.02 Approx. Station 0+20 +/-) n Gravity Wall at Area 4 – (Plan Sheet V.03 Approx. Station 0+45 +/-) n Gravity Wall at Area 7 – (Plan Sheet V.04 Approx. Station 1+47 +/-)

The results of the analyses for these cross-section conditions are presented in the following table. Computer outputs showing the stability section, strength parameters, groundwater conditions and the cross section of the hypothetical failure surface with the computed relative lowest factor of safety are provided on in Supporting Information. The factors of safety listed for each existing and altered channel cross-section are relative to one another, and it would be preferred to express the results as “new channel modification results in a relative change in stability at this location”.

Sheet B.03, dated October 16, 2018 provided by HR Green indicates the gravity wall blocks will have a width of about 4 feet. The V and E sheets provided by HR Green show a wall width of about 1 foot. In the slope stability analyses, as summarized below, the wall was modeled with a gravity block width of about 4 feet and unit weight of 140 pcf. The downslope location of the wall shown on the V and E sheets was approximately maintained, with the wall widths extended upslope beyond the limits shown on the V and E sheets.

Summary of Slope Stability Analyses Results

Computed Supporting Minimum Analysis Location 1 and Condition Information Comments Factor of Page # Safety Hypothetical failure Area 2 Gravity Existing Slope 1 1.07 surface extends into Wall shale bedrock Sheet V.01 Hypothetical failure Station 0+40 +/- Proposed Wall 2 2 1.09 surface extends into shale bedrock ■ New wall of planned height and grading maintains similar global stability factor Summary: of safety as current condition.

Existing Slope 3 0.99 -- Area 4 Gravity Reduction from current Wall Proposed Wall 2 4 0.74 condition Sheet V.03 Conceptual remediation Station 0+45 +/- Proposed Wall 5 1.06 for shear key with Remediation constructed under wall

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Summary of Slope Stability Analyses Results

Computed Supporting Minimum Analysis Location 1 and Condition Information Comments Factor of Page # Safety ■ New wall of planned height and grading reduces factor of safety by about 25% ■ Slope stability remediation (such as shear key) needed to maintain similar Summary: global stability factor as current condition. See Remedial Stability Measures. Shear key remediation was considered and depicted in global stability analysis provided on Supporting Information Page #5. Area 3 Gravity Existing Slope 6 1.05 -- Wall Sheet V.02 Reduction from current Proposed Wall 2 7 0.98 Station 0+20 +/- condition ■ New wall of planned height and grading reduces factor of safety by about 7%. ■ Slope stability remediation is needed to maintain or increase the global stability factor of safety relative to current condition. See Remedial Stability Summary: Measures. A shear key constructed under the wall (as conceptually considered for the wall shown on Sheet V.03 at Area 4) could be considered as a potential remediation option. Area 7 Gravity Existing Slope 8 1.05 -- Wall Sheet V.04 Reduction from current Proposed Wall 2 Station 1+47 +/- 9 0.81 condition ■ New wall of planned height and grading reduces factor of safety by about 23% ■ Slope stability remediation is needed to maintain or increase the global stability factor of safety relative to current condition. See Remedial Stability Summary: Measures. A shear key constructed under the wall (as conceptually considered for the wall shown on Sheet V.03 at Area 4) could be considered as a potential remediation option. Notes Applicable to Each Table 1. Refers to section location and station. 2. Factor of safety provided is for long term soil shear strength condition.

As indicated in the above table, the planned channel grading improvements with the gravity wall system show reductions in overall computed degree of safety of the slopes for walls shown on sheets V.02, V.03 and V.04. Conceptual improvements were considered for the wall system planned at Area 4 and shown on Sheet V.03 (most significant reduction in relative stability factor of safety), and similar improvements would likely be applicable for the other locations in conjunction with the planned gravity walls.

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Conditions associated with rises in groundwater levels (e.g. rainfall and/or flooding), rapid drawdown conditions after channel flooding, and erosion of toe material will all increase the risk of slope instability. These mechanisms are anticipated to be responsible for previous slope instabilities. Based on the analyses completed by Terracon, all proposed creek channel improvements would be subject to similar or greater risk of instability due to these factors. Furthermore, many of the creek channel improvements indicate a reduction in relative factor of safety as compared to current conditions, which indicates potential slope instability after equalization of normal pore water pressure conditions.

The proposed creek channel improvements appear to move the hypothetical slope failure surface upslope and engage more material mass. As a result, the consequences of slope failure after channel improvements could be more significant.

Structures are currently located near the top of the creek channel slopes in some areas. Surcharge loadings were not considered in our analyses, and it should be understood that existing structures located in vicinity of the channel and wall improvements could result in surcharge loads and effect overall stability of slopes. Consideration should be given to underpinning vital structures to help reduce the risk of future movement.

It is important to understand that the analyses completed by Terracon were at locations where slope failures were not readily apparent. Previous areas of slope instability appear to have occurred at locations in the areas of the proposed walls shown on Sheet V.01 (Area 2) and Sheet V.04 (Area 7), and appear to be characterized by a scarp and reduced or distorted elevation relative to nearby locations. The factor of safety for slopes associated with previous failure surfaces will be approximately 1.0. As such, any increase in driving forces without a corresponding increase in resisting forces will lead to further slope movement. It is anticipated that fill placement (such as at the “backfill to match grade” locations shown on the V sheets) in areas of previous slope instability will lead to further movement along the existing failure surfaces. Remediation or placement of material at the toe of the slope will be needed to reduce the potential for future movement.

The proposed retaining wall shown on Sheet V.03 (Area 4) appears to tie into an existing retaining wall at station 0+98. The existing wall appears to show signs of distress and movement. If the existing wall is not stabilized, the proposed wall design must consider the potential for further movement and possible failure of the existing wall.

Remedial Stability Measures

Every slope will have a finite failure probability associated with its particular geometry. The appropriate factor of safety for a slope should reflect the degree of confidence the engineer has in the selection of soil and groundwater conditions, as well as consequence of failure. For slope conditions that are in stages of noticeable failure, it is customary in geotechnical engineering to

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Based on observations during our site visits, it appears that slope failures had occurred in relatively isolated locations, with shallow, surficial failures near the stream along much of the corridor. In our opinion, as the waterway erodes these materials, the overall stability of the current slopes will reach a critical state, resulting in additional slope instability. Additional slope failures further encroach on or extend into private property beyond the waterway easement. Improvements for lining the channel to reduce erosion will reduce the likelihood of these progressive movements

Subsurface drainage measures could be considered in upslope locations to control the level of groundwater and improve stability. Subsurface drainage improvements are often effective in improving stability of slopes; however, limitations would include the depths and elevations that drains can be installed while maintaining positive gravity flow discharge to the creek level. Trench drains with a suitable drain pipe and granular backfill would likely be needed in a series of skewed orientations to the creek channel rather than parallel orientations. Terracon can assist in selecting locations, spacing and depths for trench drains.

As discussed in Stability Analysis Results, the proposed changes in channel slopes and additions of retaining walls in the evaluated areas are anticipated to develop a reduced factor of safety or negligible changes to the factor of safety of the channel slope. Remedial improvement measures could be considered, such as:

■ development of reinforced backfill zones further laterally behind the back of gravity block walls, ■ key trenches backfilled with high shear strength materials below the wall, or ■ soil nailing.

Geotechnical reinforcement could be placed in backfill zones behind the retaining walls to improve the stability of the completed wall system. Select granular materials are used for the reinforced fill, and this would involve exporting and importing materials. The reinforced backfill zones might need to extend more than conventionally used lengths of about 70% of the wall height to create a stability improvement relative to existing conditions. Relatively broader cuts to construct additional length of reinforcement, or reinforcement in conjunction with an additional remediation method is anticipated to gain an appreciable effect on existing slope stability. Trees, vegetation, and possibly nearby structures would also be lost during excavations for the reinforced soil areas.

A key trench at the base of the proposed walls or near base of channel could be reviewed as a possible remedial slope stability improvement measure. Proper depth of embedment of the key trench will need to be considered in the design and construction in order to extend adequate depth

Responsive ■ Resourceful ■ Reliable 14 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01 below historic or hypothetic failure surfaces. A key trench was conceptually reviewed at the wall shown on Sheet V.03 for Area 4. The conceptual review included a key trench depth of about 10 feet below the base of the wall and bottom width of about 5 feet. Low strength cohesive soils are anticipated to extend more than 10 feet below the base of the wall based on borings performed in this area, and shale bedrock with relatively low shear strength was encountered, which limits the increase in factor of safety associated with a key trench in this location. The applicability of the key trenches will depend on the desired factor of safety increase relative to existing conditions and constructability of the system. Given the anticipated depth of excavations for the key trench required to increase the factor of safety for the wall and slope configuration shown on Sheet V.03, it will be important to implement construction measures to prevent slope movements during construction, and to control groundwater. Excavation and construction of the key trenches in successive relatively short segments should be considered. The key trenches would be backfilled with high shear strength materials such as interlocking coarse grained granular materials or lean concrete. Protection against scour extending into these materials would be required at the toe of the slope. Similar construction, dewatering, and protection considerations would be applicable to other walls where key trenches are used as remediation. Terracon can complete additional review and analysis of these slope improvement measures on request.

Additional remedial measures to improve slope stability could be considered, but were not conceptually reviewed as part of this report, and potential limitations and complexities for the design and construction of these improvements are presented below. These measures are not presented in any particular order of ease or cost of construction, and the suitability or effectiveness would likely be dependent on the overall extent of the instability or improvement needed. n Soil nail slope reinforcement o Soil nail systems are installed by either drilling and grouting methods, or air cannon methods. o Nails would need to extend significant lateral distances to extend beyond hypothetical failure surfaces. n Installation of “stub” concrete drilled shafts or aggregate piers at locations at the base of the wall o Drilled elements that are backfilled with select granular material or concrete could be used to develop increased shear resistance. o Proper depth of embedment and spacing of the drilled elements will need to be considered in the design and construction in order to extend adequate depth below historic or hypothetical failure surface zones.

Additional analysis of any of these methods, along with additional subsurface exploration would be needed. Formal recommendations for these methods can be developed upon request

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Slope Instrumentation

Instrumentation, such as survey monuments that would not be disturbed by the earthwork construction, should be established at the toe of slopes, top of slopes, and on wall facing in regularly spaced intervals and situations specific to critical structures or greater heights to evaluate if lateral/vertical movement of the improvements are occurring.

The monuments could be surveyed on a regular basis and the surveying of lateral/vertical positions should be accurate to at least ¼ inch. Inclinometers could also be installed to serve this purpose, but would be better suited for walls and slopes of significant height. Instrumentation best suited for the project and locations can be provided when the project plans for the improvements are finalized, contractors selected, and methods are discussed. We recommend that the geotechnical instrumentation be installed and monitored right after the construction phase, with some limited instrumentation possibly being installed near the toe of the slope prior to construction.

EARTHWORK

Site Preparation

Site preparation for the construction of the new walls should commence with stripping of vegetation, organic soils, and any soft, frozen or otherwise unsuitable materials from the site surface. Root systems of trees and brush should be grubbed. Re-use of stripped soil materials containing organic matter should be limited to landscaped areas or areas not requiring structural fill.

During the site preparation for areas where new fills are placed on existing slopes, care should be taken to ensure good bond between the new fill and existing soils. Existing slopes should be benched to provide horizontal surfaces for placement and compaction of new structural fill. The benching and removal of weak near surface soils, where encountered, would help to reduce the potential for creating a plane of weakness at the interface of the existing slope and new fill. The widths of cut to establish benches should be limited to less than 5 feet in consideration of reducing removal of material at the toes of slopes which could affect the global stability during construction.

Prior to placement of fill, the exposed subgrades should be scarified to a depth of 9 inches, moisture conditioned, and recompacted to the density and moisture content ranges recommended in section Compaction Requirements. The surficial compaction should aid in providing a firm base for compaction of new fill and help delineate soft or disturbed areas that may exist at or near the exposed subgrade level. Unstable areas should be undercut to stable materials and the zone replaced with new structural fill.

Responsive ■ Resourceful ■ Reliable 16 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01

The initially prepared subgrades and subgrade stability in structural fill areas should be observed and tested by Terracon. Terracon personnel should also observe and test fill placement and compaction.

Site Preparation Drainage and Dewatering

Groundwater is anticipated to be encountered in cut and excavations areas along the slopes. We recommend that the contractor verify the groundwater conditions/depth immediately prior to construction. If signs of groundwater within cut or excavation depths are encountered, any dewatering and diverting of collected seepage necessary should commence prior to or during early phases of earthwork. Water and any softened soils should be removed from all fill placement and compaction surfaces. Diversion ditches and trench drains should be considered along the perimeter of cut areas.

Existing drain tiles should be located, mapped and removed or rerouted/restored to a suitable outlet. The potential impact on adjacent properties drained by these tiles should be evaluated, and rerouting to a suitable outlet could be necessary in order to maintain drainage, and potentially to maintain stability of the slopes.

Some of the temporary construction drainage facilities might eventually be removed, filled or graded during latter phases of the project; however, some construction drainage measures could assist in permanent drainage aspects of the project and should be reviewed during construction.

Site grades should be maintained so surface water will flow away from construction areas. Low elevation areas that collect surface water should be improved during early phases of the grading so that water does not continue to accumulate in these areas. During earthwork operations, all exposed subgrades should be properly sloped to provide rapid drainage so that water does not accumulate on surfaces and soften the subgrades. Standing water should be removed as soon as possible to reduce wetting or disturbance of the subgrade soils).

Excavation Considerations

Temporary excavations will be required during grading operations, and construction of new structures. The stability of these excavations are critical to the integrity of the existing facilities. As a minimum, all temporary excavations should be sloped or braced as required by Occupational Safety and Health Administration (OSHA) regulations to provide stability and safe working conditions. Contractors, by their contract, are usually responsible for designing and constructing stable, temporary excavations and should shore, slope or bench the sides of the excavations as required, to maintain stability of both the excavation sides and bottom. All excavations should comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards.

Responsive ■ Resourceful ■ Reliable 17 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01

Planned excavations or cuts could impact the stability of the slopes. Excavations may need to be performed in short segments and the segments completed prior to progressing to the next segment.

Operation of heavy construction equipment on the top or on the slopes of the waterway valley should be avoided. Routes for construction equipment traffic should be planned in non-sensitive relatively flat areas to reduce any potential impact on the stability.

Structural Fill Material Types

Other than aggregate for reinforced backfill, drainage purposes, pipe bedding, or specified granular backfill, we anticipate that a mix of on-site soils removed from excavations and grading could be used as fill for shaping of new grades. Structural fill should meet the following material property requirements:

Soil Type Fill Source 1 Acceptable Location for Placement (USCS Classification) n Shaping and grading of slopes On-Site Soils Lean clay and sandy lean clay (CL) n Unreinforced wall backfill zone n Air drying should be anticipated n Backfill below wall system overexcavations Imported Granular Granular n Reinforced backfill zone 2 Soils (GW, GP, GM, GC, SW, SP) n Specific gradations required for drainage course materials n Not recommended in structural fill Unsuitable Materials Organic clays (OL, OH) areas 1. Controlled, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the geotechnical engineer for evaluation. 2. Wall designer must specify gradation requirements for soils to be placed in reinforced soil zone.

Compaction Requirements

Item 1 Description n 9 inches or less in loose thickness when heavy, self-propelled compaction equipment is used. Fill lift thickness n 4 inches in loose thickness when hand equipment (e.g., jumping jack, vibratory plate compactor, etc.) is used. 2 Compaction of cohesive soil n At least 95%

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Item 1 Description n Below structures: at least 98% Compaction of granular material 2, 3 n Adjacent to structures: at least 95% or as determined by the wall designer n Within the range of 0% to +4% of optimum moisture Moisture content of cohesive soil 4 content

Moisture content of granular material 4, 5 n Workable moisture levels.

1. Compaction and moisture content levels referenced to ASTM D698 standard Proctor maximum dry density and optimum moisture content, respectively. 2. We recommend structural fill be tested for moisture content and compaction during placement. Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved. 3. If the granular material is a coarse sand or gravel, is of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254). 4. Moisture content values as determined at the time of placement and compaction. 5. Specifically, moisture levels should be maintained at levels satisfactory for compaction to be achieved without the granular fill material bulking during placement or pumping when proofrolled.

Grading and Drainage and Landscaping

The site soils and new subgrades prepared with them are considered susceptible to erosion. Exposed slopes should be protected from erosion. Erosion protection, such as vegetation or rip- rap materials, of sloped and grade surfaces should be established as soon as possible.

Sloped areas that are distressed from erosion and development of rills or scour should be promptly repaired. Repairs may require removal of soils in a relatively wide and benched configuration to allow for proper bonding of new fill.

Grades during and following construction should slope to prevent ponding of water.

Earthwork Construction Considerations

Unstable subgrade conditions could develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. The use of light construction equipment would aid in reducing disturbance. The use of remotely operated equipment, such as a backhoe, and other light track-mounted equipment would be beneficial to perform cuts and reduce subgrade disturbance. Should unstable subgrade conditions develop, stabilization measures involving excavation and replacement with new structural fill will need to be employed.

Responsive ■ Resourceful ■ Reliable 19 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01

The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation; placement and compaction of structural fill; and backfilling of excavations.

ENVIRONMENTAL CONSIDERATIONS

An apparent hydrocarbon odor was noted by the driller in the soils encountered at a depth of about 12 feet bgs in Boring 6. The source of the odor is not known. Geotechnical design and construction recommendations included in this report do not address the potential effects of contamination on the proposed project. If the detection of an unidentified odor is a concern, additional studies should be conducted to identify the odor, its source and its concentration and determine its impact on the project.

GENERAL COMMENTS

Our analysis and opinions are based on our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon should be retained to provide observation and testing services during grading, excavation, foundation construction, and other earth-related construction phases of the project. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third party beneficiaries intended. Any third party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance on the services and any work product is limited to our client, and is not intended for third

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parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety, and cost estimating including, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

SIGNATURE PAGE

I hereby certify that this engineering document was prepared by me or under my direct personal supervision and that I am a duly licensed Professional Engineer under the laws of the State of Iowa.

______December 12, 2018__ Theodore D. Bechtum, P.E. Date

My license renewal date is December 31, 2020.

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22 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01

EXPLORATION AND TESTING PROCEDURES

Boring Layout and Elevations: The field exploration consisted of eight geotechnical borings to depths ranging from approximately 20 to 30 feet below existing ground surface (bgs) and six hand auger borings to depths ranging from approximately 5 to 13 feet bgs designated. Terracon personnel provided the boring layout based on direction from HR Green and the Yeader Creek Steam Stabilization – Phase 2 Preliminary Drawings, dated July 27, 2018. Supplemental boring layout (borings designated 12 to 14) was based on V sheets dated October 18, 2018 provided by HR Green. Coordinates at the borings locations were generally obtained with a handheld GPS unit (estimated horizontal accuracy of about ±10 feet) and approximate elevations were generally obtained by interpolation from the survey information provided by Nilles, dated September 13, 2018, or from the V sheets prepared by HR Green. The survey data appeared incomplete in the vicinity of Borings 5 and 6, and Terracon personnel approximated the elevations at Borings 5 and 6 using a surveyor’s level and rod referencing the manhole rim (elevation 79.81 feet) northeast of the intersection of Yeader Creek and South Union Street. The relative elevations of Borings 2, 3, and 4 were approximated by using a survey level and rod. Elevations provided on the logs are rounded to the nearest foot. The locations and elevations of the borings are considered accurate only to the degree implied by the means and methods used to define them. If more precise locations and elevations are desired, we recommend the borings be surveyed.

Subsurface Exploration Procedures: The soil borings were advanced with an ATV-mounted drill rig and GeoProbe using continuous flight solid stem augers, and soil sampling was performed using thin-wall tube and split-barrel sampling procedures. In the thin-walled tube sampling procedure, a thin-walled, seamless steel tube with a sharp cutting edge is pushed hydraulically into the soil to obtain a relatively undisturbed sample. In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon is driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths. We observed and recorded groundwater levels during and after drilling and sampling. The other borings were advanced with a hand auger and samples from auger cuttings were obtained for each soil/rock layer interpreted by the drill crew and occasional thin-wall tube samples were obtained. Borings were backfilled with auger cuttings and bentonite chips after completion.

Our exploration team prepared field boring logs as part of the drilling operations, which include sampling depths, penetration distances, and other sampling information. These field logs include visual classifications of the materials encountered during drilling and our interpretation of the subsurface conditions between samples. Final boring logs, prepared from the field logs, represent

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 1 of 2 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152-01

the geotechnical engineer's interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

In the laboratory, water content tests were performed on portions of the recovered samples. The dry unit weight of intact, thin-walled tube samples was determined. Unconfined compressive strength and hand penetrometer tests were performed to estimate the consistency of select samples of fine-grained soils. Atterberg limits tests and grain size distribution testing were performed on select soil samples. The results of the laboratory tests are shown on the boring logs in Exploration Results at their corresponding sample depths.

The samples were described in the laboratory based on visual observation, texture and plasticity, and the laboratory testing described above. The descriptions of the soils indicated on the boring logs are in general accordance with the General Notes and the Unified Soil Classification System (USCS), both summarized and included in Supporting Information

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 2 of 2 SITE LOCATION AND EXPLORATION PLANS

Contents: Site Location Plan Exploration Plan (6 pages)

Note: All attachments are one page unless noted above. SITE LOCATION Yeader Creek Stabilization Improvements ■ Des Moines, Iowa December 12, 2018 ■ Terracon Project No. 08175152

GENERAL SITE VICINITY

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY NOT INTENDED FOR CONSTRUCTION PURPOSES QUADRANGLES INCLUDE: DES MOINES SW, IA (1/1/1976) and DES MOINES SE, IA (1/1/1976). EXPLORATION PLAN – AREA 1 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION PLAN – AREA 2 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION PLAN – AREA 3 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION PLAN – AREA 4 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION PLAN – AREA 5 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION PLAN – AREA 6 and 7 Yeader Creek Stabilization Improvements ■ Des Moines, IA December 12, 2018 ■ Terracon Project No. 08175152

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS AERIAL PHOTOGRAPHY PROVIDED NOT INTENDED FOR CONSTRUCTION PURPOSES BY MICROSOFT BING MAPS EXPLORATION RESULTS

Contents: GeoModels (Areas 1 to 7) Boring Logs (B-1 through B-14) Grain Size Distribution (2 pages)

Note: All attachments are one page unless noted above. GEOMODEL - AREA 1 Yeader Creek Stabilization Improvements Des Moines, Iowa 10/11/2018 Terracon Project No. 08175152

66 1

52 2

50 15 16 48 ELEVATION (MSL) (feet) ELEVATION 46

40 25.5

38 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration 4 and bedding structure.

LEGEND

Lean Clay/Fat Clay Sandy Lean Clay

Lean Clay

Silty Sand

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. GEOMODEL - AREA 2 Yeader Creek Stabilization Improvements Des Moines, Iowa 10/11/2018 Terracon Project No. 08175152

92 2

86 2

9 82 4

80 3 3

78 13 13 2 14 3 76 4 6 4 5 74 3 7.5 ELEVATION (MSL) (feet) ELEVATION 72 4 70

66 25.5

64 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration 4 and bedding structure.

LEGEND

Sandy Lean Clay Shale

Fat Clay Lean Clay

Highly Weathered Shale Fat Clay with Sand

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. GEOMODEL - AREA 3 Yeader Creek Stabilization Improvements Des Moines, Iowa 12/4/2018 Terracon Project No. 08175152

6 85 5

12 80 1 1

75 12 12 13

70 16 2 16 17 13

65 15.5

ELEVATION (MSL) (feet) ELEVATION 2 2

60 20.5

55 30.5 30.5

50 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration and 4 bedding structure.

LEGEND

Fill Silty Sand Lean Clay with Sand

Lean Clay Clayey Gravel

Sandy Lean Clay Fat Clay

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. GEOMODEL - AREA 4 Yeader Creek Stabilization Improvements Des Moines, Iowa 12/4/2018 Terracon Project No. 08175152

92 13

88 1

86 6 84

80 7 78

76 2 2 74

ELEVATION (MSL) (feet) ELEVATION 5 19 72 19.5

68 24

66 3 25.5

64 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration and 4 bedding structure.

LEGEND

Poorly-graded Sand Lean Clay Highly Weathered Shale

Fat Clay Fat Clay with Sand

Fill Lean Clay with Sand

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. GEOMODEL - AREA 5 Yeader Creek Stabilization Improvements Des Moines, Iowa 10/11/2018 Terracon Project No. 08175152

84 8

82 3 80 4.5 78

68 ELEVATION (MSL) (feet) ELEVATION 66

58 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration 4 and bedding structure.

LEGEND

Poorly-graded Sand

Highly Weathered Shale

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. GEOMODEL - AREAS 6 and 7 Yeader Creek Stabilization Improvements Des Moines, Iowa 12/4/2018 Terracon Project No. 08175152

102 9 10 11 14 100

96 2 94 2 92 2 9.5 90 10 2

12 88 12.5 13 86 14

84 ELEVATION (MSL) (feet) ELEVATION 82 18 19.5 80 4 78 4 76 24.8 25.4 74 This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Model Layer Layer Name General Description

Existing Fill Sandy lean clay with occasional sand seams, refuse, and 1 rubble.

Alluvium Variable plasticity cohesive soils. Medium stiff to stiff with 2 zones of very soft to soft. Occasoinal sand layers 3 Fat clay Possible residual shale

Shale Highly to moderately weathered. Variable coloration and 4 bedding structure.

LEGEND

Fat Clay Lean Clay/Fat Clay

Shale Fat Clay with Sand

Lean Clay with Sand Lean Clay

NOTES: First Water Observation Layering shown on this figure has been developed by the geotechnical Second Water Observation engineer for purposes of modeling the subsurface conditions as Final Water Observation required for the subsequent geotechnical engineering for this project. Numbers adjacent to soil column indicate depth below ground surface. Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time. Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details. BORING LOG NO. 1 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5392° Longitude: -93.6057° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 65 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone LEAN TO FAT CLAY (CL/CH), trace sand, dark gray brown, medium stiff to stiff 11 1 3540 27 96

1-2-2 5 13 2 27 48-21-27 92 N=4 1500 (HP) 13 2000 (HP) 3 2750 29 92

2-2-2 18 4 33 10 N=4 1000 (HP)

2 13.0 52+/- LEAN CLAY (CL), trace sand, brown with gray, medium stiff 15 17 5 1500 27 95 36-19-17 93

17.0 48+/- SILTY SAND (SM), fine to medium grained, brown, very loose

19.5 45.5+/- 0-0-0 25 SANDY LEAN CLAY (SC), dark gray 16 6 20 N=0 27 brown, very soft to soft 500 (HP)

0-0-2 15 7 38 33-20-13 66 N=2 25.5 wood fragments (possible tree root) 39.5+/- 25 500 (HP) observed in Sample 7 Boring Terminated at 25.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

Advancement Method: See Exploration and Testing Procedures for a Notes: Power Auger description of field and laboratory procedures used and additional data (If any). See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Auger Cuttings and Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-17-2018 Boring Completed: 09-17-2018 16' While Sampling 15' After Boring Drill Rig: 844 Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 18' After Boring BORING LOG NO. 2 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5361° Longitude: -93.6069° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

2 5.0 86+/- 2-3-4 5 16 2 30 63-25-38 94 FAT CLAY (CH), trace sand, dark gray N=7 brown, stiff 3500 (HP) 10 3000 (HP) 3 2830 27 93

9.0 82+/- FAT CLAY (CH), trace sand, gray and 2-3-5 18 4 24 56-23-33 93 brown with maroon, stiff, possible residual 10 N=8 clay 3500 (HP) 3

13.0 78+/- SHALE*, brown with gray, highly weathered 15 15 5 1430 26 96 42-23-19 91

17.0 74+/- SHALE*, olive gray with brown, highly weathered, laminated

4 10-22-17 17 6 18 20 N=39

22.0 69+/- SHALE*, olive gray with maroon, highly to moderately weathered, laminated

18-23-40 16 7 16 25.5 65.5+/- 25 N=63 Boring Terminated at 25.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic *Classification of rock materials has been estimated based on observation of disturbed samples. Core samples and/or petrographic analysis may reveal other rock types. Advancement Method: See Exploration and Testing Procedures for a Notes: Power Auger description of field and laboratory procedures used and additional data (If any). See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-17-2018 Boring Completed: 09-17-2018 13' While Drilling 14' After Boring Drill Rig: 844 Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 20' After Boring BORING LOG NO. 3 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5362° Longitude: -93.607° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 79 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone SHALE*, brown, residual clay to highly 1 29 weathered shale 3

2120 34 90 4.0 75+/- 10 2 SHALE*, olive gray, highly weahtered 4 5.0 74+/- 29 Boring Terminated at 5 Feet 5

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic *Classification of rock materials has been estimated based on observation of disturbed samples. Core samples and/or petrographic analysis may reveal other rock types. Advancement Method: See Exploration and Testing Procedures for a Notes: Hand Auger description of field and laboratory procedures used and additional data (If any). See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Auger Cuttings and Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-17-2018 Boring Completed: 09-17-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 4 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5363° Longitude: -93.607° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 81 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES LEAN CLAY (CL), trace sand, dark brown 1 23

2 25 2 3.5 77.5+/- FAT CLAY (CH), with sand, trace gravel, dark gray brown 3 18 5 6.0 75+/- FAT CLAY (CH), brown with olive gray, 3 4 16 7.5 possible residual clay 73.5+/- Boring Terminated at 7.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

Advancement Method: See Exploration and Testing Procedures for a Notes: Hand Auger description of field and laboratory procedures used and additional data (If any). See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Auger Cuttings and Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-17-2018 Boring Completed: 09-17-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 5 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5371° Longitude: -93.6159° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Surface Elev.: 84 (Ft.) FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone FILL - SANDY LEAN CLAY , brown

1 20 104

4.0 80 FILL - LEAN CLAY , with refuse, with sand, trace gravel, dark brown and brown 5 2 17 102 48-22-26 83 1 3 16 110 8.0 76 FILL - SANDY LEAN CLAY , brown and gray 5-7-8 12 4 17 10 N=15

12.0 72 LEAN CLAY (CL), trace sand, dark brown, medium stiff

2-3-3 10 5 25 15 N=6 3000 (HP)

1-2-3 18 6 32 20 N=5 1000 (HP) 2

24.0 60 SANDY LEAN CLAY (CL), brown and gray, 1-2-3 12 7 27 medium stiff 25 N=5 1000 (HP)

28.0 56 SILTY SAND (SM), trace gravel, brown, medium dense 5-6-8 8 16 30.5 53.5 30 N=14 Boring Terminated at 30.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 09-19-2018 Boring Completed: 09-19-2018 13' While Drilling 16' After Boring Drill Rig: 897 Driller: JG 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 20' on 09/20/2019 BORING LOG NO. 6 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5371° Longitude: -93.6154° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Surface Elev.: 85 (Ft.) FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone FILL - LEAN CLAY , with sand, trace rubble, brown and dark brown 1 24 98

4.0 81 SANDY LEAN CLAY, trace rubble, brown and dark brown 5 2 17 109 56 1 3 16 101

9.0 76 FILL - SANDY LEAN CLAY , with sand 2-2-3 8 4 21 seams, brown and dark brown 10 N=5

12.0 Driller's Note: Hydro-carbon odor 73 observed at about 12 feet LEAN CLAY (CL), trace sand, dark brown, medium stiff 2-3-4 12 5 29 15 N=7 2000 (HP)

2-3-3 12 6 37 20 N=6 500 (HP) 2

24.0 61 SANDY LEAN CLAY (CL), brown and gray, 1-2-3 12 7 27 medium stiff 25 N=5

27.0 58 SILTY SAND (SM), trace gravel, brown, medium dense

29.5 55.5 10-6-4 12 8 19 CLAYEY GRAVEL (GC), with sand, brown, 30 N=10 30.5 medium dense 54.5 14 Boring Terminated at 30.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

Advancement Method: See Exploration and Testing Procedures for a Notes: Power Auger description of field and laboratory procedures AS1 = 0 - 12' used and additional data (If any). AS2 = 12-27' See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Auger Cuttings and Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-19-2018 Boring Completed: 09-19-2018 17' While Drilling 16' After Boring Drill Rig: 897 Driller: JG 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 20' on 09/20/2019 BORING LOG NO. 7 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5357° Longitude: -93.6149° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 78 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES 0.5 SAND (SP), trace gravel, medium to 77.5+/- coarse grained, brown 1 27 FAT CLAY (CH), with sand seams, dark 2 1390 26 96 2 gray brown, medium stiff

5.0 73+/- 3 32 Boring Terminated at 5 Feet 5

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 09-20-2018 Boring Completed: 09-20-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 8 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5351° Longitude: -93.615° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 83 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES 0.3 SAND (SP), with gravel, fine to medium 82.5+/- grained, brown 1 22 FAT CLAY (CH), gray, very stiff, possible 3 residual clay

12 2 4130 19 107 4.5 78.5+/- Boring Terminated at 4.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic *Classification of rock materials has been estimated based on observation of disturbed samples. Core samples and/or petrographic analysis may reveal other rock types. Advancement Method: See Exploration and Testing Procedures for a Notes: Hand Auger description of field and laboratory procedures used and additional data (If any). See Supporting Information for explanation of Abandonment Method: symbols and abbreviations. Boring backfilled with Auger Cuttings and Bentonite Chips

WATER LEVEL OBSERVATIONS Boring Started: 09-20-2018 Boring Completed: 09-20-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 9 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5341° Longitude: -93.615° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 100 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone FAT CLAY (CH), trace sand, dark gray brown, stiff to medium stiff 8 1 4400 32 88

2-2-3 5 17 2 26 N=5

10 3 2980 25 98 50-19-31 96

9.0 91+/- 2 FAT CLAY (CH), trace sand, gray with 2-2-3 18 4 26 brown, medium stiff to stiff 10 N=5

becoming gray 15 23 5 2180 24 98

18.0 82+/- SANDY SHALE*, olive gray with brown, highly weathered 16 20 19-47-50/4" 6 18

4 22.0 78+/- SHALE*, gray, highly weathered, laminated

24.8 75+/- 8 35-50/4" 7 16 Boring Terminated at 24.8 Feet

WATER LEVEL OBSERVATIONS Boring Started: 09-17-2018 Boring Completed: 09-17-2018 12' While Drilling Drill Rig: 844 Driller: MD 10' After Boring 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 10 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5343° Longitude: -93.6149° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

10 2 4310 18 89 2 5.0 95+/- LEAN CLAY (CL), with sand, gray 5 3 16 7.0 93+/- LEAN TO FAT CLAY (CL/CH), trace sand, gray

9.5 90.5+/- 4 8 Boring Terminated at 9.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 09-18-2018 Boring Completed: 09-18-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 11 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5342° Longitude: -93.6148° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 100 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES FAT CLAY (CH), with sand, trace gravel, dark brown 1 27 2.0 98+/- LEAN CLAY (CL), trace sand, dark brown 2 27

5.0 95+/- FAT CLAY (CH), trace sand, dark gray 5 brown, stiff 24 3 2280 25 92 2

4 24

10.0 90+/- FAT CLAY (CH), trace sand, gray with 10 brown 5 32

13.0 87+/- 6 29 Boring Terminated at 13 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 09-18-2018 Boring Completed: 09-18-2018

Drill Rig: Hand Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 12 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5369° Longitude: -93.615° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 80 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone 1.5 LEAN CLAY (CL), trace sand and gravel, 78.5+/- brown FAT CLAY (CH), trace sand, dark gray, 9 4000 (HP) 1 4660 27 91 stiff to very stiff 4.0 76+/- LEAN CLAY (CL), trace sand, gray, stiff to 2-3-3 medium stiff 5 14 2 25 N=6 2500 (HP) 9 2000 (HP) 3 2990 26 95

0-2-2 9 4 29 2 10 N=4 1000 (HP)

13.0 67+/- LEAN CLAY (CL), trace sand, gray, soft

15 17 500 (HP) 5 760 36 83

17.0 63+/- LEAN CLAY (CL), with sand seams, gray, soft

0-0-2 16 6 28 20.5 59.5+/- 20 N=2 Boring Terminated at 20.5 Feet 500 (HP)

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 11-16-2018 Boring Completed: 11-16-2018 13' While Drilling 15.5' After Boring Drill Rig: Power Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 18.5' After Boring BORING LOG NO. 13 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5359° Longitude: -93.6147° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

Approximate Surface Elev: 91 (Ft.) +/- FIELD TEST WEIGHT (pcf) GRAPHIC LOG MODEL MODEL LAYER UNCONFINED CONTENT (%) WATER LEVEL COMPRESSIVE SAMPLE TYPE RECOVERY (In.) STRENGTH (psf) OBSERVATIONS DEPTH ELEVATION (Ft.) PERCENT FINES Approx. 2 inch root zone FILL - LEAN CLAY , trace sand, dark 2.0 brown 89+/- FILL - SANDY LEAN CLAY , trace gravel, 9 3000 (HP) 1 2310 26 100 1 brown with dark brown 4.0 87+/- FILL - SANDY FAT CLAY , trace gravel, 3-4-6 brown 5 18 2 20 6.0 85+/- N=10 FAT CLAY (CH), trace sand, dark brown, 6000 (HP) very stiff 8 4500 (HP) 3 4580 28 91

9.0 82+/- LEAN CLAY (CL), trace sand, dark gray, 2-3-4 18 4 27 medium stiff to stiff 10 N=7 3000 (HP)

14.0 77+/- FAT CLAY (CH), with sand, trace gravel, 2 gray, stiff 15 12 2000 (HP) 5 3590 24 100

19.0 72+/- LEAN CLAY (CL), with sand, trace gravel, 0-2-3 18 6 27 gray, medium stiff 20 N=5 1000 (HP)

24.0 67+/- FAT CLAY (CH), with sand, gray brown, 6-10-12 3 18 7 26 25.5 very stiff, possible residual clay 65.5+/- 25 N=22 Boring Terminated at 25.5 Feet

Stratification lines are approximate. In-situ, the transition may be gradual. Hammer Type: Automatic

WATER LEVEL OBSERVATIONS Boring Started: 11-26-2018 Boring Completed: 11-26-2018 19' While Sampling Drill Rig: Power Auger Driller: MD 19.5' After Boring 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152 THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 BORING LOG NO. 14 Page 1 of 1 PROJECT: Yeader Creek Stabilization Improvements CLIENT: HR Green, Inc.

SITE: Des Moines, Iowa ATTERBERG LOCATION See Exploration Plan LIMITS

Latitude: 41.5343° Longitude: -93.6148° LL-PL-PI WATER RESULTS Sample ID DRY UNIT DEPTH (Ft.)

2-3-4 5 14 2 26 N=7 2500 (HP) 10 3000 (HP) 3 3480 25 97

9.0 91+/- FAT CLAY (CH), trace sand, gray, medium 2-2-3 2 15 4 24 stiff 10 N=5 2000 (HP)

13.0 87+/- LEAN CLAY (CL), with sand, brown, medium stiff to soft 15 17 1000 (HP) 5 880 32 86

19.5 80.5+/- 10-22-32 14 6 20 SILTY SHALE*, brown, highly weathered 20 N=54

22.0 78+/- 4 SHALE*, gray, highly weathered

13 24-40-50/5" 7 16 25.4 74.5+/- 25 Boring Terminated at 25.4 Feet

WATER LEVEL OBSERVATIONS Boring Started: 11-16-2018 Boring Completed: 11-16-2018 14' While Sampling 12.5' After Boring Drill Rig: Power Auger Driller: MD 600 SW 7th St, Ste M Des Moines, IA Project No.: 08175152

THIS BORING LOG IS NOT VALID SEPARATED IF FROM ORIGINAL REPORT.GEO SMART YEADER LOG-NO WELL 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 12/4/18 18' After Boring GRAIN SIZE DISTRIBUTION ASTM D422 / ASTM C136 U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS HYDROMETER 4 2 1 1/2 3 6 10 16 30 50 100 200 6 3 1.5 3/4 3/8 4 8 14 20 40 60 140 100

PERCENT FINER BY WEIGHT BY FINER PERCENT 35

0 100 10 1 0.1 0.01 0.001 GRAIN SIZE IN MILLIMETERS GRAVEL SAND COBBLES SILT OR CLAY coarse fine coarse medium fine

Boring ID Depth USCS Classification WC (%) LL PL PI Cc Cu 1 4.5 - 6 LEAN CLAY (CL) 27 48 21 27 1 14 - 16 LEAN CLAY (CL) 36 19 17 1 24 - 25.5 SANDY LEAN CLAY (CL) 38 33 20 13 2 4 - 6 LEAN CLAY with SAND (CL) 17 3 4 - 6 SANDY LEAN CLAY (CL) 17

Boring ID DepthD100 D60 D30 D10 %Gravel %Sand %Silt %Fines %Clay 1 4.5 - 6 4.75 0.013 0.001 0.0 8.0 92.0 1 14 - 16 2 0.024 0.006 0.0 6.9 93.1 1 24 - 25.5 9.5 0.056 0.014 0.2 33.8 66.0 2 4 - 6 12.5 0.022 0.002 1.9 14.8 83.3 3 4 - 6 12.5 0.177 0.012 4.5 39.6 55.9

PROJECT: Yeader Creek Stabilization PROJECT NUMBER: 08175152 Improvements

600 SW 7th St, Ste M SITE: Des Moines, Iowa Des Moines, IA CLIENT: HR Green, Inc. LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GRAIN SIZE:YEADER USCS-2 08175152 CREEK STAB.GPJ TERRACON_DATATEMPLATE.GDT 10/10/18 GRAIN SIZE DISTRIBUTION ASTM D422 / ASTM C136 U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS HYDROMETER 4 2 1 1/2 3 6 10 16 30 50 100 200 6 3 1.5 3/4 3/8 4 8 14 20 40 60 140 100

PERCENT FINER BY WEIGHT BY FINER PERCENT 35

0 100 10 1 0.1 0.01 0.001 GRAIN SIZE IN MILLIMETERS GRAVEL SAND COBBLES SILT OR CLAY coarse fine coarse medium fine

Boring ID Depth USCS Classification WC (%) LL PL PI Cc Cu 4 4.5 - 6 FAT CLAY (CH) 30 63 25 38 4 9 - 10.5 FAT CLAY (CH) 24 56 23 33 4 14 - 16 SHALE (see log) 42 23 19 5 6 - 8 FAT CLAY (CH) 50 19 31

Boring ID DepthD100 D60 D30 D10 %Gravel %Sand %Silt %Fines %Clay 4 4.5 - 6 9.5 0.005 0.2 5.7 94.1 4 9 - 10.5 2 0.003 0.0 7.1 92.8 4 14 - 16 4.75 0.013 0.003 0.0 9.4 90.6 5 6 - 8 4.75 0.014 0.0 3.8 96.1

PROJECT: Yeader Creek Stabilization PROJECT NUMBER: 08175152 Improvements

Contents: Slope Stability Analysis Cross Sections (Pages 1 to 9) General Notes Unified Soil Classification System Description of Rock Properties

Note: All attachments are one page unless noted above. Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 120 120

Color Name Model Unit Cohesion' Phi' YC 11B Gravity Wall - Sheet V.01 Weight (psf) (°) (pcf) Approx. Station 0+40 Fat Clay Mohr-Coulomb 120 50 23 Existing Conditions 110 Residual Mohr-Coulomb 120 100 12 110 Terracon Project No. 08175152 Shale

Sandy Lean Mohr-Coulomb 125 50 27 Clay Shale Mohr-Coulomb 130 200 15

100 1.07 100 ) t f (

n B-2 o i 90 90 t a v e l

E B-4

80 B-3 80

70 70

60 60 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Distance (ft)

Page 1 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 120 120 Color Name Model Unit Cohesion' Phi' Weight (psf) (°) (pcf)

YC 11B Gravity Wall - Sheet V.01 Fat Clay Mohr-Coulomb 120 50 23 Approx. Station 0+40 Residual Mohr-Coulomb 120 100 12 Gravity Wall - Long Term Conditions Shale 110 110 Terracon Project No. 08175152 Sandy Mohr-Coulomb 125 50 27 Lean Clay

Shale Mohr-Coulomb 130 200 15

Wall High Strength 140

100 1.09 100 ) t f (

n B-2 o i

t 90 90 a v e l

E B-4

80 B-3 80

70 70

60 60 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Distance (ft)

Page 2 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 110 110 Color Name Model Unit Cohesion' Phi' Weight (psf) (°) (pcf)

Existing Fill Mohr-Coulomb 120 50 23 YC 12 Gravity Wall - Sheet V.03 Approx. Station 0+45 Fat Clay Mohr-Coulomb 115 50 23 Existing Conditions Lean Clay Mohr-Coulomb 115 50 27 Terracon Project No. 08175152 Residual Shale Mohr-Coulomb 120 100 12 100 100 0.99

B-13 )

t 90 90 f ( n o i t a v e l 80 80 E

70 70

60 60 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 Distance (ft)

Page 3 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45

110 Color Name Model Unit Cohesion' Phi' 110 Weight (psf) (°) (pcf)

Existing Mohr-Coulomb 120 50 23 Fill YC 12 Gravity Wall - Sheet V.03 Approx. Station 0+45 Fat Clay Mohr-Coulomb 115 50 23 Long Term Conditions Lean Clay Mohr-Coulomb 115 50 27 Terracon Project No. 08175152 Residual Mohr-Coulomb 120 100 12 100 Shale 100 0.74 Wall High Strength 140

B-13 )

t 90 90 f ( n o i t a v e l 80 80 E

70 70

60 60 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 Distance (ft)

Page 4 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 110 110

YC 12 Gravity Wall - Sheet V.03 Approx. Station 0+45 Long Term Conditions Terracon Project No. 08175152 100 100 1.06

Color Name Model Unit Cohesion' Phi' Weight (psf) (°) (pcf) B-13 Existing Mohr-Coulomb 120 50 23 Fill

) Fat Clay Mohr-Coulomb 115 50 23 t

f 90 90

( Key High Strength 140

Lean Clay Mohr-Coulomb 115 50 27 n

o Residual Mohr-Coulomb 120 100 12 i Shale t

a Wall High Strength 140 v e l 80 80 E

70 70

60 60 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 Distance (ft)

Page 5 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 10 20 30 40 50 60 100 100 Color Name Model Unit Cohesion' Phi' Weight (psf) (°) YC 12 Gravity Wall - Sheet V.02 (pcf) Approx. Station 0+20 Fat Clay Mohr-Coulomb 115 50 23 Existing Conditions Lower Lean Clay Mohr-Coulomb 105 0 26 Terracon Project No. 08175152 Upper Lean Clay Mohr-Coulomb 120 50 27 1.05 90 90 ) t f (

n B-12 o i

t 80 80 a v e l E

70 70

60 60 0 10 20 30 40 50 60 Distance (ft)

Page 6 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 10 20 30 40 50 60 100 100

Color Name Model Unit Cohesion' Phi' Weight (psf) (°) YC 12 Gravity Wall - Sheet V.02 (pcf) Approx. Station 0+20 Fat Clay Mohr-Coulomb 115 50 23 Low er Lean Mohr-Coulomb 105 0 26 Long Term Conditions Clay Upper Lean Mohr-Coulomb 120 50 27 Terracon Project No. 08175152 Clay Wall High Strength 140 0.98 90 90 ) t f (

n B-12 o i 80 80 t a v e l E

70 70

60 60 0 10 20 30 40 50 60 Distance (ft)

Page 7 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 5 10 15 20 25 30 35 40 45 50 55 110 110

Section A Gravity Wall - Sheet V.04 Color Name Model Unit Cohesion' Phi' Weight (psf) (°) Approx. Station 1+47 1.05 (pcf) Fat Clay Mohr-Coulomb 120 50 23

105 Existing Conditions Lean Clay Mohr-Coulomb 110 0 26 105

Terracon Project No. 08175152 Shale Mohr-Coulomb 130 200 15

B-14 100 100 ) t f ( 95 95 n o i t a

v 90 90 e l E 85 85

80 80

75 75 0 5 10 15 20 25 30 35 40 45 50 55 Distance (ft)

Page 8 of 9 Yeader Creek Stabilization Improvements December 12, 2018 - Terracon Project No. 08175152 Supporting Information

0 5 10 15 20 25 30 35 40 45 50 55 110 110

Color Name Model Unit Cohesion' Phi' Weight (psf) (°) Section A Gravity Wall - Sheet V.04 (pcf) 0.81 Approx. Station 1+47 Fat Clay Mohr-Coulomb 120 50 23 Lean Clay Mohr-Coulomb 110 0 26

105 Long Term Shale Mohr-Coulomb 130 200 15 105

Terracon Project No. 08175152 Wa ll High Strength 140

B-14 100 100 ) t f ( 95 95 n o i t a

v 90 90 e l E 85 85

80 80

75 75 0 5 10 15 20 25 30 35 40 45 50 55 Distance (ft)

Page 9 of 9 GENERAL NOTES DESCRIPTION OF SYMBOLS AND ABBREVIATIONS Yeader Creek Stabilization Improvements Des Moines, Iowa October 10, 2018 Terracon Project No. 08175152

SAMPLING WATER LEVEL FIELD TESTS N Standard Penetration Test Water Initially Resistance (Blows/Ft.) Encountered Water Level After a (HP) Hand Penetrometer Auger Shelby Specified Period of Time Cuttings Tube Water Level After (T) Torvane a Specified Period of Time Standard (DCP) Dynamic Cone Penetrometer Penetration Water levels indicated on the soil boring logs are Test the levels measured in the borehole at the times indicated. Groundwater level variations will occur UC Unconfined Compressive over time. In low permeability soils, accurate Strength determination of groundwater levels is not possible with short term water level (PID) Photo-Ionization Detector observations.

(OVA) Organic Vapor Analyzer

DESCRIPTIVE SOIL CLASSIFICATION Soil classification is based on the Unified Soil Classification System. Coarse Grained Soils have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they are plastic, and silts if they are slightly plastic or non-plastic. 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, coarse-grained soils are defined on the basis of their in-place relative density and fine-grained soils on the basis of their consistency.

LOCATION AND ELEVATION NOTES Unless otherwise noted, Latitude and Longitude are approximately determined using a hand-held GPS device. The accuracy of such devices is variable. Surface elevation data annotated with +/- indicates that no actual topographical survey was conducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from topographic maps of the area.

STRENGTH TERMS RELATIVE DENSITY OF COARSE-GRAINED SOILS CONSISTENCY OF FINE-GRAINED SOILS (More than 50% retained on No. 200 sieve.) (50% or more passing the No. 200 sieve.) Density determined by Standard Penetration Resistance Consistency determined by laboratory shear strength testing, field visual-manual procedures or standard penetration resistance Descriptive Term Standard Penetration or Descriptive Term Unconfined Compressive Strength Standard Penetration or (Density) N-Value (Consistency) Qu, (psf) N-Value Blows/Ft. Blows/Ft.

Very Loose 0 - 3 Very Soft less than 500 0 - 1 Loose 4 - 9 Soft 500 to 1,000 2 - 4 Medium Dense 10 - 29 Medium Stiff 1,000 to 2,000 4 - 8 Dense 30 - 50 Stiff 2,000 to 4,000 8 - 15 Very Dense > 50 Very Stiff 4,000 to 8,000 15 - 30 Hard > 8,000 > 30

RELATIVE PROPORTIONS OF SAND AND GRAVEL RELATIVE PROPORTIONS OF FINES Descriptive Term(s) of Percent of Descriptive Term(s) of Percent of other constituents Dry Weight other constituents Dry Weight Trace <15 Trace <5 With 15-29 With 5-12 Modifier >30 Modifier >12 GRAIN SIZE TERMINOLOGY PLASTICITY DESCRIPTION Major Component of Sample Particle Size Term Plasticity Index Boulders Over 12 in. (300 mm) Non-plastic 0 Cobbles 12 in. to 3 in. (300mm to 75mm) Low 1 - 10 Gravel 3 in. to #4 sieve (75mm to 4.75 mm) Medium 11 - 30 Sand #4 to #200 sieve (4.75mm to 0.075mm High > 30 Silt or Clay Passing #200 sieve (0.075mm) Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa October 10, 2018 ■ Terracon Project No. 08175152-01

UNIFIED SOIL C L ASSIFIC ATION SYST EM Soil Classification Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A Group Group Name B Symbol Gravels: Clean Gravels: Cu  4 and 1  Cc  3 E GW Well-graded gravel F Cu  4 and/or [Cc<1 or Cc>3.0] E GP Poorly graded gravel F Coarse-Grained Soils: More than 50% of C GravelsLess than with 5% Fines:fines Fines classify as ML or MH GM Silty gravel F, G, H coarse fraction Fines classify as CL or CH GC F, G, H retained on No. 4 sieve Clayey gravel More than 50% retained C Sands: CleanMore than Sands: 12% fines E SW I on No. 200 sieve Cu  6 and 1  Cc  3 Well-graded sand Cu  6 and/or [Cc<1 or Cc>3.0] E SP Poorly graded sand I 50% or more of coarse D SandsLess than with 5% Fines: fines Fines classify as ML or MH SM Silty sand G, H, I fraction passes No. 4 Fines classify as CL or CH SC G, H, I sieve Clayey sand More than 12% fines D Silts and Clays: Inorganic: PI  7 and plots on or above “A” CL Lean clay K, L, M J PIline  4 or plots below “A” line J ML Silt K, L, M Fine-Grained Soils: Liquid limit less than 50 Organic: Liquid limit - oven dried  0.75 OL Organic clay K, L, M, N Liquid limit - not dried Organic silt K, L, M, O 50% or more passes the PI plots on or above “A” line CH K, L, M No. 200 sieve Silts and Clays: Inorganic: Fat clay PI plots below “A” line MH Elastic Silt K, L, M Liquid limit 50 or more Organic: Liquid limit - oven dried  0.75 OH Organic clay K, L, M, P Liquid limit - not dried Organic silt K, L, M, Q Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-inch (75-mm) sieve H If fines are organic, add “with organic fines” to group name. B If field sample contained cobbles or boulders, or both, add “with cobbles I If soil contains  15% gravel, add “with gravel” to group name. or boulders, or both” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly gravel,” whichever is predominant. graded gravel with silt, GP-GC poorly graded gravel with clay. L If soil contains  30% plus No. 200 predominantly sand, add D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded “sandy” to group name. sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded M sand with silt, SP-SC poorly graded sand with clay If soil contains  30% plus No. 200, predominantly gravel, add “gravelly” to group name. 2 N (D30 ) PI  4 and plots on or above “A” line. E Cu = D60/D10 Cc = O PI  4 or plots below “A” line. D x D 10 60 P PI plots on or above “A” line. F If soil contains  15% sand, add “with sand” to group name. Q PI plots below “A” line. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

Responsive ■ Resourceful ■ Reliable UNIFIED SOIL CLASSIFICATION SYSTEM 1 of 1 Geotechnical Engineering Report Yeader Creek Stabilization Improvements ■ Des Moines, Iowa October 10, 2018 ■ Terracon Project No. 08175152-01

ROCK VER SION 1 WEATHERING Term Description Unweathered No visible sign of rock material weathering, perhaps slight discoloration on major discontinuity surfaces. Slightly Discoloration indicates weathering of rock material and discontinuity surfaces. All the rock material may be weathered discolored by weathering and may be somewhat weaker externally than in its fresh condition. Moderately Less than half of the rock material is decomposed and/or disintegrated to a soil. Fresh or discolored rock is weathered present either as a continuous framework or as corestones. Highly More than half of the rock material is decomposed and/or disintegrated to a soil. Fresh or discolored rock is weathered present either as a discontinuous framework or as corestones. Completely All rock material is decomposed and/or disintegrated to soil. The original mass structure is still largely intact. weathered All rock material is converted to soil. The mass structure and material fabric are destroyed. There is a large Residual soil change in volume, but the soil has not been significantly transported. STRENGTH OR HARDNESS Uniaxial Compressive Description Field Identification Strength, psi (MPa) Extremely weak Indented by thumbnail 40-150 (0.3-1) Crumbles under firm blows with point of geological hammer, can be Very weak 150-700 (1-5) peeled by a pocket knife Can be peeled by a pocket knife with difficulty, shallow indentations Weak rock 700-4,000 (5-30) made by firm blow with point of geological hammer Cannot be scraped or peeled with a pocket knife, specimen can be Medium strong 4,000-7,000 (30-50) fractured with single firm blow of geological hammer Specimen requires more than one blow of geological hammer to Strong rock 7,000-15,000 (50-100) fracture it Very strong Specimen requires many blows of geological hammer to fracture it 15,000-36,000 (100-250) Extremely strong Specimen can only be chipped with geological hammer >36,000 (>250) DISCONTINUITY DESCRIPTION Fracture Spacing (Joints, Faults, Other Fractures) Bedding Spacing (May Include Foliation or Banding) Description Spacing Description Spacing Extremely close < ¾ in (<19 mm) Laminated < ½ in (<12 mm) Very close ¾ in – 2-1/2 in (19 - 60 mm) Very thin ½ in – 2 in (12 – 50 mm) Close 2-1/2 in – 8 in (60 – 200 mm) Thin 2 in – 1 ft. (50 – 300 mm) Moderate 8 in – 2 ft. (200 – 600 mm) Medium 1 ft. – 3 ft. (300 – 900 mm) Wide 2 ft. – 6 ft. (600 mm – 2.0 m) Thick 3 ft. – 10 ft. (900 mm – 3 m) Very Wide 6 ft. – 20 ft. (2.0 – 6 m) Massive > 10 ft. (3 m) Discontinuity Orientation (Angle): Measure the angle of discontinuity relative to a plane perpendicular to the longitudinal axis of the core. (For most cases, the core axis is vertical; therefore, the plane perpendicular to the core axis is horizontal.) For example, a horizontal bedding plane would have a 0-degree angle. ROCK QUALITY DESIGNATION (RQD) 1 Description RQD Value (%) Very Poor 0 - 25 Poor 25 – 50 Fair 50 – 75 Good 75 – 90 Excellent 90 - 100 1. The combined length of all sound and intact core segments equal to or greater than 4 inches in length, expressed as a percentage of the total core run length.

Reference: U.S. Department of Transportation, Federal Highway Administration, Publication No FHWA-NHI-10-034, December 2009 Technical Manual for Design and Construction of Road Tunnels – Civil Elements

Responsive ■ Resourceful ■ Reliable ROCK VERSION 1 1 of 2