COUTES Stormwater Report.pdf

PRELIMINARY STORMWATER

DRAINAGE REPORT

Central Oregon Unit Training Equipment Site Holistic Site Improvements

Submitted to:

Oregon Military Department

Prepared for:

Keller Associates, Inc 245 Commercial St SE, Suite 210 Salem, OR 97301

Prepared by:

Flagline Engineering, LLC 1011 SW Emkay Dr

STE 207

Bend, OR 97702

January, 9 2022 kyleb Image kyleb Text Box

PAGE INTENTIONALLY LEFT BLANK

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TABLE OF CONTENTS

I. Project Description

II. Background

A. Existing Conditions

B. Proposed Conditions

III. Storm Drainage Calculations

A. Flow Calculations and Sizing Methodology

B. Inlets, Catch Basins and Stormwater Pre-treatment

C. Storm Drain Pipes

D. Retention Facilities

E. Retention Sizing Summary

APPENDICES:

Appendix A Geotechnical Report

Appendix B Stormwater Site Plan

Appendix C Drainage Maps kyleb

I. Project Description

The Central Oregon Unit Training Equipment Site (COUTES) is in the City of Redmond, Oregon just east of the Redmond Municipal Airport (RDM). The site is approximately 18 acres of developed area currently in use by the Oregon Military Department.

Figure 1-COUTES Vicinity Map

The Proposed improvements at the site include:

New domestic water well o Utilize existing well building o Drill and install new well head

Military vehicle hot wash facilities o Enclosed building o Washing equipment o Wastewater treatment/disposal

Military vehicle cold wash facilities o Covered area o New graveled access o Washing equipment o Wastewater treatment/disposal

General stormwater upgrades o Construct new stormwater ponds o Install inlets and pipe where necessary to improve drainage function and prevent issues with ponding throughout site.

o Pick up building downspout lines where possible and route to stormwater pond

II. Background

The proposed improvements will be constructed at the existing COUTES site and will serve new programming requirements identified for the facility. This report focuses on the stormwater improvements proposed for the site and outline the assumptions and design for the proposed system.

A. Existing Conditions

The project site is the existing COUTES facility, located east of the 23 end of runway 5-23 at the RDM airport. Adjacent properties consist of undeveloped property to the south, north, and east. The project site is currently developed with buildings and gravel surfacing for travel ways.

A geotechnical report, Geotechnical Exploration Report COUTES OMD dated October 12, 2021, has been completed for the site by the Wallace Group. A copy of the geotechnical report has been included as Appendix A. The geotechnical report indicates that explorations at the site uncovered undocumented existing fill materials that are underlain by native silty-sand, calcite-cemented ‘hardpan’, and basalt bedrock. The undocumented fill materials were measured at depths ranging from 1 to 2 feet below ground surface and consisted of crushed gravel. The NRCS soil survey classifies these soils as Hydrologic Group B.

Existing site runoff flows generally to the west through primarily surface flow. The existing runoff appears to discharge off-site at the western boundary in a wide flow path without many obvious single discharge points.

B. Proposed Conditions

A site plan showing the proposed stormwater improvements is shown below in Figure 2 and included in Appendix B. The proposed stormwater improvements include a series of inlets, and pipes to convey stormwater from the surface to new retention ponds located in the undeveloped land to the north and west of the site.

The proposed improvements were located based on Owner feedback regarding problem areas around the site as well as investigation of the existing site surface to determine low points that may cause ponding during storm events. In addition to surface collection, the improvements also include connecting the existing and proposed building downspouts to the new storm system to convey this water away from building areas. The existing downspouts currently outfall onto the site surface resulting in collection of stormwater near buildings.

The proposed ponds are designed to retain up to the 100-yr storm event. Both ponds are also equipped with emergency outfalls for unforeseen storm events or frequency that may cause the ponds to overflow. These emergency outfalls will route this excess stormwater to locations away from buildings and the site. Retention ponds were chosen for the site due to the relatively flat nature of the existing terrain. This flat terrain makes it difficult to locate outfall facilities that would allow for stormwater to be discharged away from the site lower than upstream structures in order to prevent surcharging and flooding at the site.

The site is bisected by an existing gravel road and two separate stormwater systems are shown for each side of the site. To the west of the existing road, the proposed stormwater system is considered the primary installation. To the east of the gravel road, an optional storm system, referred to as the additive bid, is shown to upgrade the drainage and routing near the shooting range and proposed cold wash rack building.

Figure 2-Proposed Stormwater Site Plan

III. Storm Drainage Calculations

The proposed storm system was designed following standard design and sizing practices as outlined in the Central Oregon Stormwater Manual (COSM).

A. Flow Calculations and Sizing Methodology

Calculations for runoff were performed via the COSM standards. The SCS TR-55 hydrologic method was selected and used to perform hydraulic calculations for this proposed site. Chapter 5 of the COSM references this method as an acceptable methodology for performing hydraulic calculations, especially for small urban and rural watersheds (25 square miles are less). The COUTES site meets all the criteria for this hydrologic methodology.

TR-55 methodology parameters are given below.

Design Storm Event – 25-year (Per COSM). Both 25-year and 100-year were evaluated.

Curve Number (CN) – Weighted curve numbers were utilized for all drainage basins, based on hydrologic soil group B and selected from the appropriate category of the NRCS runoff curve numbers chart data.

Rainfall Specifications – The SCS Type I, 24 hour storm event was utilized for all calculations per the COSM.

Time of Concentration (TC)– The SCS TR-55 TOC methodology was used to calculate the time of concentration for each drainage basin.

Area – Basin areas in acres. Map of contributing basins included in Appendix C.

B. Inlets, Catch Basins and Stormwater Pre-treatment

A Standard ODOT Inlet, Type CG-2 (DWG RD366) is proposed for collection of stormwater. The inlet includes a sump to allow for density separation of pollutants.

Old Castle Precast oil water separators are proposed just before each pond to provide pre-treatment of stormwater before entering the retention facilities.

C. Storm Drain Pipes

ASTM D3034 PVC pipe is proposed for the system piping.

D. Retention Facilities

Retention ponds are proposed for the site in order to collect and contain stormwater and mitigate excess build up around the site. These facilities are anticipated to experience infiltration based on the soil hydraulic group. Due to the proximity to the airport, the ponds are proposed to be filled with riprap for a depth of 3’ to mitigate free water surfaces, which can be a wildlife attractant. Based on soil conditions found during the geotechnical site investigation, both ponds are anticipated to fully drain through soil infiltration within 48 hours of a 100-year storm event. This is based on a low-end infiltration rate of 2.5in/hr reported in the Geotechnical Report, which listed rates of 2.5in/hr up to 5in/hr for the site. This assumption does not consider evaporation rates, which will further help in emptying the pond after a storm event.

Both the primary and additive bid areas were evaluated using the methodologies outlined previously in this section. Both areas were evaluated using a CN of 85, which represents gravel roads for a soils group B. While there are roof and some concrete areas contributing to the flows, the worst-case TC based on the hydraulically most distant point.

The ponds were designed to contain the full 100-year storm event for each subbasin area. A summary of the 25-year and 100-year events has been provided in the tables below. Existing survey data in the vicinity of the ponds did not fully encompass the pond design envelopes and outfall locations, so some assumptions were made regarding the existing terrain in order to complete this stage of the design. In the next phases of design, these areas will be picked up by the surveyor to confirm the pond designs shown for this submittal.

Contributing Basin Data Basin Area (AC) CN TC (min) Q25 (CFS) Q100 (CFS)

Primary 9.93 85 7.3 8.27 11.47 Additive Bid 5.60 85 10.4 4.36 6.01

Table 1: Basin Data

Pond Data

Pond Total Volume (cf)

Pond Depth (ft)

25-year Storm Depth (ft)

100-year Storm Depth (ft)

Primary 66,211 9 3.74 5.21 Additive Bid 21,800 7 4.48 5.7

Table 2: Pond Data

IV. Final Design Requirements

For the final design of the stormwater improvements, the following items will be completed by the design team:

1. Additional survey to pick up topography data west of the ponds

2. Survey of the existing building downspout locations to tie into the proposed stormwater system

3. Infiltration tests performed in the locations of the proposed retention ponds to establish localized infiltration values for the soil kyleb

Appendix A

Geotechnical Report kyleb

GEOTECHNICAL EXPLORATION REPORT

COUTES OMD

2899 EAST HIGHWAY 126

REDMOND, OREGON

October 12, 2021

Wallace Group Project No. 21183 (1)

Copyright 2021 Wallace Group, Inc.

ONLY KELLER ASSOCIATES AND ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC PROJECT FOR

WHICH THIS REPORT WAS PREPARED.

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A Report Prepared For:

Keller Associates c/o Mr. Peter Olsen, P.E.

131 SW 5th Avenue, Suite A Meridian, ID 83642

GEOTECHNICAL EXPLORATION REPORT

COUTES OMD

2899 EAST HIGHWAY 126

REDMOND, OREGON

Wallace Group Project Number 21183 (1)

Prepared By:

Adam Larson, P.E.

Project Geotechnical Engineer

Lisa M. Splitter, P.E., G.E.

Senior Geotechnical Engineer

The Wallace Group, Inc.

62915 NE 18th Street, Suite 1 Bend, OR 97701

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EXECUTIVE SUMMARY

The Wallace Group, Inc., (Wallace Group) completed a geotechnical engineering exploration for the proposed Central Oregon Unit Training Equipment Site – Oregon Military Department (COUTES OMD) improvements project, located at 2899 East Highway 126 in Redmond, Oregon (Figure 1, Vicinity Map). A figure with exploration locations is shown on Figure 2, Exploration Location Map.

At the time this report was written, preliminary plans or schematics were not yet available;

however, based on discussions with the Client, we understand that proposed improvements will include a new well building and two new ‘wash racks’. We understand that the well building will be single-story and be constructed using Concrete Masonry Unit (CMU) blocks. Additionally, the wash racks will single-story structures designed to accommodate vehicles and equipment for cleaning. There will one wash rack that is enclosed within a pre-engineered metal building, while the other wash rack will be open-sided. At this time, detailed architectural and structural plans were not available; however, we anticipate the improvements have shallow cast-in-place concrete foundations and have concrete slab-on-grade flooring. Additional improvements will include underground utility infrastructure installation, and stormwater collection and disposal systems.

Subsurface explorations generally encountered undocumented existing fill materials that were underlain by native silty-sand, calcite-cemented ‘hardpan’ and basalt bedrock. The fill materials generally extended from the surface to depths ranging between 1- to 2-feet below ground surface (bgs) and consisted of crushed gravel. Below the fill materials, the silty-sand extended to depths ranging between 1- to 5-feet bgs. Refusal to excavation was encountered in all exploration locations on cemented ‘hardpan’ soil and basalt bedrock.

Based on this exploration, the sites appear suitable for the expected development from a geotechnical perspective, provided the recommendations contained in this report are incorporated into design and construction.

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TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 GENERAL

1.2 PROJECT DESCRIPTION

1.3 PURPOSE AND SCOPE OF SERVICES

2.0 FIELD EXPLORATION

2.1 SUBSURFACE EXPLORATION

3.0 LABORATORY TESTING

4.0 EXISTING SITE CONDITIONS

4.1 SURFACE

4.2 SUBSURFACE CONDITIONS

4.2.1 Undocumented Fill Materials………………………………………………………………………………….. 4

4.2.2 Silty-Sand…………………………………………………………………………………………………………………4

4.2.2 Calcite-Cemented Hardpan………………………………………………………………………………………5

4.2.4 Basalt Bedrock………………………………………………………………………………………………………… 5

4.3 GROUNDWATER

5.0 SEISMIC CONSIDERATIONS

5.1 REGIONAL AND SITE GEOLOGY

5.2 SEISMIC DESIGN CRITERIA

6.0 CONCLUSIONS AND PRELIMINARY RECOMMENDATIONS

6.1 EXCAVATIONS AND GRADING

6.1.1 Site Preparation……………………………………………………………………………………………………….8

6.1.2 Structural Fill Materials and Placement………………………………………………………………….. 9

6.2 FOUNDATIONS

6.3 FLOOR SYSTEMS AND EXTERIOR FLATWORK

6.4 DRAINAGE CONSIDERATIONS

6.4.1 Infiltration Testing…………………………………………………………………………………………………. 13

6.5 PAVEMENT RECOMMENDATIONS

6.5.1 Parking Areas and Access Drives…………………………………………………………………………….14

6.5.2 Pavement Material Specifications…………………………………………………………………………. 15

7.0 ADDITIONAL SERVICES

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7.1 DESIGN AND CONSTRUCTION PERIOD ENGINEERING SERVICES

7.2 CONSTRUCTION INSPECTION AND TESTING

8.0 LIMITATIONS

9.0 REFERENCES

10.0 PROFESSIONAL AUTHENTICITY

TABLES

Table 6.1.2, Engineered Fill Specifications Table 6.4.1, Test Pit Infiltration Test Summary

FIGURES

1. Vicinity Map

2. Exploration Location Map

APPENDICES

A. Field Exploration Summary B. Laboratory Test Results C. Seismic Design Criteria D. Exploration Photos

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1.0 INTRODUCTION

1.1 GENERAL

The Wallace Group, Inc., (Wallace Group) completed a geotechnical engineering exploration for the proposed Central Oregon Unit Training Equipment Site – Oregon Military Department (COUTES OMD) improvements project, located at 2899 East Highway 126 in Redmond, Oregon (Figure 1, Vicinity Map). A figure with exploration locations is shown on Figure 2, Exploration Location Map.

1.2 PROJECT DESCRIPTION

At the time this report was written, preliminary plans or schematics were not yet available;

however, based on discussions with the Client, we understand that proposed improvements will include a new well building and two new ‘wash racks’. We understand that the well building will be single-story and be constructed using Concrete Masonry Unit (CMU) blocks. Additionally, the wash racks will single-story structures designed to accommodate vehicles and equipment for cleaning. There will one wash rack that is enclosed within a pre-engineered metal building, while the other wash rack will be open-sided. At this time, detailed architectural and structural plans were not available; however, we anticipate the improvements have shallow cast-in-place concrete foundations and have concrete slab-on-grade flooring. Additional improvements will include underground utility infrastructure installation, and stormwater collection and disposal systems.

1.3 PURPOSE AND SCOPE OF SERVICES

The purpose of this exploration was to evaluate general subsurface conditions within the potential development areas to provide recommendations for foundations, earthwork considerations, site preparation, and other geotechnical aspects related to site development.

Our scope of services included the following tasks:

Review regional and project area geology;

Explore subsurface conditions with test pits and perform density testing on shallow soil using a dynamic cone penetrometer (DCP);

Perform infiltration testing in two locations of anticipated drainage swales;

Perform engineering evaluations for the feasibility of geotechnical-related aspects of development; and Prepare this design-level geotechnical report summarizing our findings, conclusions, and recommendations.

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2.0 FIELD EXPLORATION

2.1 SUBSURFACE EXPLORATION

Subsurface conditions were explored on September 27, 2021. Three (3) test pits, designated TP- 01 through TP-03, were excavated to depths ranging from approximately 1- to 5-feet below ground surface (bgs). Test pits were excavated with a Takeuchi mini excavator operated by Terry Shine Excavating of Bend, Oregon. A Wallace Group geotechnical professional logged the test pits, performed dynamic-cone penetrometer (DCP) testing, and visually classified the materials encountered. The test pit logs, located in Appendix A, describe the materials encountered at each location explored. The soil and bedrock types between explorations are anticipated to be similar; however, variation should be expected. The stratigraphic contacts indicated at each point of exploration represent the approximate boundaries between soil and bedrock types. The approximate locations of the test pits are shown on Figure 2.

A more complete description of the sampling techniques and soil-classification terminology is presented in Appendix A.

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3.0 LABORATORY TESTING

Soil samples were transported to our Bend geotechnical laboratory where they were visually classified and prepared for laboratory analyses. Laboratory tests were conducted in general accordance with standard procedures and included the following:

Moisture Content, ASTM D2216;

Gradation Analyses, ASTM C117 / C136; and Classification of Soil for Engineering Purposes, ASTM D2487.

Laboratory test results are included in Appendix B.

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4.0 EXISTING SITE CONDITIONS

4.1 SURFACE

The subject site has been substantially developed. Large portions of the property are developed with structures, gravel-surfaced, and asphalt access drives and equipment parking areas. Other portions of the exploration area are undeveloped and support native vegetation consisting of mature western junipers, sagebrush, and rabbitbrush. At the time this report was written, topographic survey was not yet completed; however, based on our site reconnaissance, the terrain is relatively level.

4.2 SUBSURFACE CONDITIONS

Subsurface explorations generally encountered undocumented existing fill materials that were underlain by native silty-sand, calcite-cemented ‘hardpan’, and basalt bedrock. The fill materials generally extended from the surface to depths ranging between 1- to 2-feet below ground surface (bgs) and consisted of crushed gravel. Below the fill materials, the silty-sand extended to depths ranging between 1- to 5-feet bgs. Refusal to excavation was encountered in all exploration locations on cemented ‘hardpan’ soil or basalt bedrock.

4.2.1 Undocumented Fill Materials

Undocumented fill was encountered in several locations extending from the surface to depths ranging from approximately 1- to 2-feet bgs. This material is associated with the existing developments consisting of access drives and parking areas. The fill material generally consisted of crushed basalt aggregate base course (ABC). This material is suitable for re-use as structural fill, if necessary.

4.2.2 Silty-Sand

Native, silty, sandy soil was encountered in all exploration locations extending from the surface or below the fill materials. The silty-sand soil extended to depths ranging from approximately 1-to 5-feet bgs in the areas explored and was underlain by cemented soil or basalt bedrock.

Gradation tests indicate the native soil generally classifies as silty-sand (SM), according to the Unified Soil Classification System (USCS). Where tested, the native silty-sand soil samples contained 26.8 to 33.6 percent clay- and silt-sized particles, had a moisture content ranging between 5.7 to 15.4 percent, and contained trace gravel-sized particles. The silty-sand was slightly moist, tan to brown, and fine- to coarse-grained. Based on relative density recordings using a dynamic cone penetrometer (DCP), the native silty-sand was generally medium dense to dense. With increasing depth, the soil contained more gravel and cobble-sized particles.

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4.2.3 Calcite-Cemented Hardpan

Below the silty, sandy soil, a layer of calcite-cemented soil was encountered in TP-03 that caused refusal with the excavation equipment. Refusal to excavation was encountered at approximately 4-feet bgs. The cemented soil classifies geologically as caliche but is locally referred to as ‘hardpan’. The hardpan was slightly moist, light brown to white, angular, fine- to coarse-grained, and moderately cemented.

4.2.4 Basalt Bedrock

Basalt bedrock was encountered beneath the native soil in locations where refusal was not encountered in the cemented hardpan soil. Where encountered, the depth to basalt bedrock ranged from 1- to 5- feet bgs. The basalt bedrock caused refusal to excavation with the mini excavator and mass excavations will require drilling and blasting, or hydraulic hammers to remove. Based on previous experience on nearby projects we anticipate the basalt bedrock has moderately high strength (R3-R4), and compressive strength will likely be in the range of 3,000 to 12,000 pounds per square inch (psi).

4.3 GROUNDWATER

Groundwater was not encountered in the explorations and should not influence site development. Localized perched water may occur at the soil and/or cemented soil interface during wet periods. A review of well logs obtained from the Oregon Water Resource Department indicates groundwater is at least 350 feet bgs in the project area.

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5.0 SEISMIC CONSIDERATIONS

5.1 REGIONAL AND SITE GEOLOGY

The site is located within the High Lava Plains Physiographic Province of central Oregon, near the adjacent Cascade Range foothills to the west. This relatively young volcanic region is characterized by a multitude of volcanic cones and buttes, lava flows, and lava tubes. The region exhibits moderate topographic relief and is relatively smooth in nature. The region exhibits a poorly developed drainage network with few canyons and gullies because of central Oregon’s location in the rain shadow formed by the Western and High Cascade Mountains.

Yearly precipitation averages between 8 and 15 inches. Except for isolated lake (lacustrine) sediments and fluvial deposits, most of the rocks in the province are volcanic, and thick accumulations of basaltic lava and welded tuff are common. The underlying rock formation mapped at the project site is the Pleistocene era Basalt of Newberry.

Seismically, the project site is in a northwest-trending zone of en echelon faults that parallel the High Cascade Mountain Range. These structural features extend northward from a convergence zone at Newberry Volcano and are generally referred to as the Sisters Fault Zone. This zone includes the Tumalo, Rimrock, Black Butte, and Green Ridge Faults and may represent a structural transition between the Brothers and Metolius Fault zones (Geomatrix, 1995), or mark the eastern boundary of the High Cascades Graben (Taylor, 1981). The nearest faults from the Sisters Fault Zone are roughly traced approximately 7 miles southwest of the project. Generally, this portion of the Sisters Fault Zone is thought to be last active during the Late Quaternary, and less than 130,000 years old (USGS, 2021).

5.2 SEISMIC DESIGN CRITERIA

Central Oregon lies in an area of low to moderate seismic risk. The 2019 Oregon Structural Specialty Code (OSSC), based on the 2018 International Building Code (IBC), requires that structures be designed to sustain the maximum considered earthquake.

Finished floor elevations (FFE) and the grading plan were not available at the time this report was written; however, the site is relatively level, and we anticipate the finished subgrade for the development will be underlain by less than 5 feet of native silty-sand or structural fill. Hard basalt bedrock will typically be located at a depth less than 5 feet bgs within the building footprints. The overburden soil and bedrock will not be liquefiable during earthquakes. Other seismically related hazards, including lateral spreading and landslides are not applicable for this project. Based on our evaluation of the soil and rock encountered in the explorations and other

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Related seismic design criteria are presented in Appendix C.

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6.0 CONCLUSIONS AND PRELIMINARY RECOMMENDATIONS

Based on the results of field exploration, laboratory testing, engineering analyses, and our local experience, it is our opinion that the site is suitable for the anticipated development from a geotechnical perspective provided the recommendations provided in this report are included into design. The primary geotechnical concern is the presence of undocumented fill materials within the development area. The fill materials were up to 2-feet thick in the areas explored and should be removed within the proposed development area of the proposed structures.

6.1 EXCAVATIONS AND GRADING

Preliminary grading design plans were not available at the time this report was prepared;

however, based on current site grades, we anticipate cuts and fills will generally be less than approximately 3-feet to remove organic soil, undocumented fill materials, and to achieve design subgrade elevation for the foundations. Cuts to remove the undocumented fill materials, native silty-sand soil, and cemented soil materials can generally be excavated with conventional earth-moving equipment such as excavators and small dozers. Large excavators equipped with rock teeth on the bucket will be required to remove heavily cemented material, especially for deep utility installations and drywell construction. Basalt bedrock will likely be encountered where footings, deep utilities, or drywells are constructed. Typically, basalt bedrock will require hydraulic hammering or drilling and blasting to efficiently be removed. We do not anticipate groundwater will be encountered during the expected earthwork operations.

6.1.1 Site Preparation

We recommend that all development areas are stripped of organic soil and undocumented fill materials to expose native silty-sand soil. The development area should be considered to extend five feet beyond the perimeter of the building pads, access drives, and parking areas. All roots larger than 0.5-inch diameter should be removed within development areas. Once the organic soil, roots, and undocumented fill materials are removed, the subgrade should be moisture-conditioned and compacted with suitable compaction equipment.

After removal of unsuitable materials as noted above, the subgrade in building pads should be proof-rolled with a loaded 10-cubic-yard-dump truck, or full 4,000-gallon water truck, to confirm subgrade stability prior to placing new fill. Any deflection observed during proof-rolls should be addressed. If unstable (“pumping”) soil is observed in isolated areas, remedial measures may consist of further compaction, including moisture-conditioning (aeration), or over-excavation and replacement with granular, structural fill. Pumping-soil conditions are

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6.1.2 Structural Fill Materials and Placement

Where structural fill is needed to raise grades beneath load-bearing elements, such as floor slabs, footings, and paving areas, we recommend it consist of appropriately graded sand and gravel having 100 percent passing a two-inch sieve, less than 30 percent retained on the ¾-inch sieve, and less than 20 percent passing a No. 200 sieve. On-site, existing fill materials should be suitable for reuse as structural fill provided the material is processed and meets the specifications provided in Table 6.1.2. On site, native soil would not be suitable for re-use as structural fill due to the high content of silt particles. We recommend structural fill have a maximum dry density (ASTM D1557) of at least 90 pounds per cubic foot (pcf).

In addition, we recommend:

Structural fill be moisture-conditioned to within a range of +/- 2 percent of optimum moisture content, placed in 8-inch loose, level lifts, and compacted as recommended in Table 6.1.2, Engineered Fill Specifications Summary.

Structural fill should not be placed during freezing weather or on frozen subgrade to avoid potential thaw settlement.

Wallace Group periodically observe the fill placement and test the fill for grain-size and compaction.

Foundation backfill material should consist of screened, on-site native soil; approved, processed existing fill; or imported 2-inch minus sand and gravel, having less than 20 percent passing the No. 200 sieve. Foundation backfill should also be compacted to reduce moisture infiltration below proposed developments.

Table 6.1.2, below, summarizes the placement and compaction specifications for anticipated uses of structural fill for this project.

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Table 6.1.2 Engineered Fill Specifications Summary

COUTES OMD

2899 East Highway 126

Redmond, Oregon

Material Type & Specifications

Placement Location Placement Specifications

Base Course – Crushed Aggregate, ¾-inch minus, <8% passing #200 sieve.

Base Course Beneath Slabs on

Grade, Pavement, and Footings

Maximum 6” lifts; compacted to minimum 95% of modified Proctor density (ASTM D1557) for floor slabs, footings, 92% for pavement, exterior slabs and sidewalks.

Structural Fill - Granular, Inorganic soil, 2-inch minus, <30% retained on ¾-inch sieve, <20% passing #200 sieve. Non-plastic.

Maximum dry density of at least

90 pcf.

Beneath Slabs on Grade, Exterior

Slabs, Pavement, Sidewalks, and

Footings

Maximum 8” lifts; compacted to minimum 95% of modified Proctor density (ASTM D1557) for floor slabs, footings, all fill exceeding 5 feet vertical, 92% for pavement, exterior slabs and sidewalks.

Utility Trench and General Backfill

– 2-inch minus sand & gravel, <20% passing the No. 200 sieve, or on-site soil materials.

Utility Trench Backfill, Foundation

Wall Backfill

Maximum 8” lifts; compacted to minimum 95% of modified Proctor density (ASTM D1557) beneath footings, floor slabs, 92% for exterior pavement and sidewalks, 90% in non-structural areas.

Granular Landscape Fill –

Inorganic soil, 3-inch minus.

Landscaped Areas Fill depth less than 4 feet, compaction not required. Fill depths greater than 4 feet, compact to a minimum of 85% of modified Proctor (ASTM D1557).

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6.2 FOUNDATIONS

We recommend the proposed structures are supported on conventional shallow spread and continuous footings, bearing on compacted native soil and structural fill. We recommend footings bearing on properly compacted native soil and structural fill should be designed for a maximum allowable bearing pressure of 2,500 pounds per square foot (psf). Where basalt bedrock is exposed at the bottom of footing elevations, we recommend over-excavation of 6-inches and replacement with compacted aggregate base course (ABC). Where native soil is exposed at the bottom of footing excavations, we recommend the soil is compacted with suitable equipment.

The following criteria should also be incorporated into project plans and specifications:

Exterior footings should bear below frost depth. A minimum foundation burial depth of

18 inches is required by Deschutes County for frost protection.

Continuous strip footings should be at least 12 inches wide. Isolated pad footings should be at least 18 inches square.

Structural fill placed beneath footings should be compacted to at least 95 percent of modified Proctor maximum density, ASTM D1557. Building pad fill should extend at least five feet laterally beyond the outside edge of footings.

Structural fill should be placed in level lifts and be benched if placed on slopes.

Placement and compaction of structural fill should be observed and/or tested by a

Wallace Group technician working under the direction of a professional engineer.

6.3 FLOOR SYSTEMS AND EXTERIOR FLATWORK

Native soil and new structural fill will likely be exposed at slab subgrade level for the structures.

The proof-rolled and compacted native soil and new structural fill will provide adequate support for the floor slabs, provided the subgrade is prepared in accordance with Section 6.1.1

– Site Preparation. New structural fill below interior slab on grade should be compacted to at least 95 percent of ASTM D1557 as indicated in Table 6.1.2, Engineered Fill Specifications Summary.

We recommend a minimum of 6 inches of crushed aggregate base course (ABC) be placed beneath the interior slab-on-grade. The base course should comply with the specifications shown in Table 6.1.2, Engineered Fill Specifications Summary, and be compacted to at least 95 percent of ASTM D1557. If more than six inches of material is needed to establish bottom-of-slab level, either additional base course or structural fill, compacted to a minimum of 95

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62915 NE 18th St, Ste 1, Bend, OR 97701 p | 541.382.4707 f | 541.383.8118 wallacegroup-inc.com percent of ASTM D1557, can be used to raise the subgrade level. For interior slab design we recommend a modulus of subgrade reaction (k) of 150 pounds per cubic inch (pci).

Light-duty concrete flatwork, such as sidewalks, should be underlain by a minimum of 4 inches of crushed aggregate leveling course compacted to at least 92 percent of ASTM D1557.

Structural fill beneath light duty exterior slabs and sidewalks should be placed in lifts not exceeding eight-inches thick. All organic material, including roots larger than 0.5-inch in diameter, and other deleterious material exposed at slab or sidewalk subgrade elevations should be removed to firm, unyielding native soil and replaced with structural fill.

The regional groundwater table in the project area is at least 350 feet bgs, so placement of a vapor retarder beneath slab-on-grade floors does not appear warranted for this site. In addition, an increasing body of evidence suggests vapor retarders trap moisture between the slab and membrane, aggravating or promoting slab curling and other problems (i.e., loosened floor coverings and mold). Current industry standard; however, is to place a vapor retarder on top of the crushed rock layer. Vapor barriers may be warranted if moisture sensitive flooring or equipment is anticipated.

Even with a capillary break or vapor barrier, there is the possibility some floor moisture or dampness may occur because of inadequate perimeter drainage or other unforeseen conditions (i.e., plumbing leaks and broken waterlines). These post-construction conditions should be addressed separately by qualified specialists with local knowledge of slab moisture protection systems, flooring design, and other components that may be influenced by moisture intrusion. Our report addresses present subgrade conditions for slab support only and does not evaluate future, potential moisture conditions.

The native soil has low frost heave potential in the present moisture condition. However, if a source of moisture becomes present, the soil will exhibit some frost heave. Exterior slabs could heave on the order of ¾-inch if the silty-sand subgrade soil is saturated and sub-freezing temperatures occur. Exterior slabs should be depressed from doorway thresholds ¾-inch to accommodate frost heave. The most effective and economical method to control frost heave is provision for adequate drainage of surface runoff away from slabs and other foundation elements.

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6.4 DRAINAGE CONSIDERATIONS

Foundation and slab performance are influenced by drainage conditions around the perimeter of the proposed structures. Adequate drainage should be provided and maintained throughout the life of structures and water must not be allowed to infiltrate below the foundation. We recommend the ground surface is sloped to drain surface water away from the buildings without ponding. We recommend gutters and downspouts be installed to collect and discharge roof drainage away from the foundation. The ground surface adjacent to foundations should be sloped away from foundations at least 5 percent in landscaped areas and 2 percent in hard-surfaced areas.

6.4.1 Infiltration Testing

Infiltration testing was performed at two locations (IT-01 and IT-02), (see Figure 2, Exploration Location Map). The testing location was selected by the project civil engineer in an area of potential stormwater disposal. The infiltration testing was performed at depths of approximately 2-feet bgs. The infiltration testing was conducted in general accordance with Method 4C-Test Pit Method of the Central Oregon Stormwater Manual (COSM). The test pit was excavated with relatively vertical sides and level bottom to facilitate measuring the wetted surface area.

Field-measured infiltration rates in inches per hour and calculated, factored infiltration rates in gallons per minute per square foot of wetted area (per COSM) are shown in Table 6.4.1.

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Table 6.4.1 Test Pit Infiltration Test Summary

Infiltration Test

Depth

(feet)

Infiltration Rate

(inches per hour)

Factored Infiltration Rate per COSM

(cfs/square foot/foot of head)

IT-01 2.5 5 1.29 x 10-4

IT-02 2 1.5 1.58 x 10-5

The infiltration rate in inches per hour is based on a 30-minute “falling head” test, as prescribed in COSM and does not include a factor of safety. The COSM rate shown for factored infiltration rate are based on 2.5-hour tests. The factored rate listed above includes a safety factor of 1.7 for fine sand.

6.5 PAVEMENT RECOMMENDATIONS

6.5.1 Parking Areas and Access Drives

We anticipate that traffic will likely consist of light automotive and occasional service vehicles.

Traffic during construction will consist of heavier vehicles with higher wheel loads and precautions should be taken to prevent damage to any newly constructed pavement.

The proof-rolled, inorganic-native-granular soil, and properly compacted new structural fill will provide, in our opinion, adequate subgrade support for asphalt-paved-parking areas associated with the development. Proper roadway section drainage, including site drainage to avoid ponding of water adjacent to roadway areas, will aid in reducing the potential for pavement distress. Structural fill in paved areas should consist of processed on-site native soil or imported sand and gravel meeting the requirements of Table 6.1.2, Engineered Fill Specifications Summary. Roadway subgrade fill should be placed in maximum 8-inch lifts, loose thickness, moisture-conditioned, and compacted to at least 92 percent of ASTM D1557.

Based on the project soil conditions and assumed traffic loads for asphalt-paved parking and access drives, we recommend a pavement section of 3-inches of Asphaltic Concrete (AC) underlain by 6-inches of crushed ABC. Concrete pavement, if constructed, should consist of a

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62915 NE 18th St, Ste 1, Bend, OR 97701 p | 541.382.4707 f | 541.383.8118 wallacegroup-inc.com minimum of 6-inches of concrete underlain by 8-inches of ABC. Concrete pavement is recommended for areas with heavy anticipated wheel loads.

A minimum of 6-inches of properly compacted ABC is recommended for unpaved paths.

Support for unpaved gravel paths will be provided by properly prepared subgrade. Prior to placing and compacting ABC, the subgrade and/or structural fill should be prepared as recommended in Section 6.1.1 of this report.

6.5.2 Pavement Material Specifications

The AC should be dense-graded, hot mix asphalt concrete (HMAC) as specified in ODOT Section 00745 plus the following supplemental specifications for density testing:

The HMAC mix design for the roadways should be Level 2.

The asphalt binder should be PG 64-28, or as specified by the Civil Engineer.

The ABC should be ¾-inch minus, dense graded aggregate as specified in ODOT Sections

00641 and 02630.10.

Road-mixed ABC is permitted per Section 00641. Road-mixed ABC allows water to be added on-site for compaction vs. pug-milled materials processing.

The HMAC should be compacted to a minimum of 92 percent of the Rice theoretical maximum density. The ABC should be compacted to a minimum of 92 percent of ASTM D1557.

Supplemental Specifications for Density Testing: The roadway AC and ABC should be field tested for in-place density. Density test frequency should be based on a “roll-pattern” or standard City of Redmond procedures.

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7.0 ADDITIONAL SERVICES

7.1 DESIGN AND CONSTRUCTION PERIOD ENGINEERING SERVICES

Wallace Group will review the geotechnical and civil aspects of the project design plans and specifications, when completed, to confirm that our recommendations are incorporated into the project documents, and to make appropriate modifications, if necessary. We currently anticipate performing design review of foundation, grading, and drainage plans to document that our recommendations are incorporated into design. This review will reduce misinterpretation of our recommendations and reduce the potential for costly design changes and construction delays.

7.2 CONSTRUCTION INSPECTION AND TESTING

To maintain our role as the geotechnical engineer of record, Wallace Group will also observe and monitor earthwork construction including site preparation, placement, and compaction of engineered fill in building pad areas, utility trench backfill, foundation, and slab preparation.

The purpose of these services will be to help document that site grading and development-area-subgrade preparation complies with the recommendations of this geotechnical report and the approved project plans and specifications. If subsurface conditions are encountered during construction that differ from the conditions described herein, we will review our recommendations considering these different conditions and recommend changes in design or construction procedures.

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8.0 LIMITATIONS

Exploratory test pits performed for this study were placed to obtain an understanding of underground conditions for evaluation and design purposes. The exploration was performed using a mutually-agreed-upon scope of services. Variations from these conditions, not indicated by the test pits, are possible. These variations are sometimes enough to necessitate design modifications. Keller Associates (Client) must recognize that it is impossible to predict every physical condition that will be encountered. If unexpected conditions are observed during construction, or if the size, type, elevation, or location of the proposed structures should differ significantly from the preliminary plans, we should be notified to review the recommendations contained in this report. The professional judgments expressed in this report meet the standard of care of our profession; however, no warranty is expressed or implied.

This report may be used only by the Client and only for the intended site and for the purposes stated within a reasonable time from its issuance, but in no event, later than three (3) years from the date of the report. Land or facility use, on- and off-site conditions, regulations, or other factors may change over time, and additional work may be required with the passage of time. Any party other than the Client or their design team who wishes to use this report shall notify the Wallace Group of such intended use. Based on the intended use of the report, the Wallace Group may require that additional work be performed and that an updated report be issued. Non-compliance with any of these requirements by the Client or anyone else will release Wallace Group from any liability resulting from the use of this report by any unauthorized party.

The contractor selected for this project is responsible for supervision and direction of the actual work performed by his employees, subcontractors, and agents. Wallace Group will use accepted geotechnical engineering and testing procedures; however, our testing and observations will not relieve the contractor of his primary responsibility to produce a completed project conforming to the project plans and specifications.

This firm does not practice or consult in the field of safety engineering. We do not direct the contractor’s operations, and we cannot be responsible for the safety of personnel other than our own on the site. The safety of others is the responsibility of the contractor. The contractor should notify the owner if he considers any of the recommended actions presented herein unsafe.

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9.0 REFERENCES

American Society of Civil Engineers, 2021, ASCE 7 Hazard Tool Website Data Base.

Geomatrix Consultants, 1995, Seismic Design Mapping State of Oregon: Final Report, prepared for Oregon Department of Transportation under personal services contract 11688.

Oregon Department of Transportation, Standard Specifications for Construction, 2018.

Oregon Structural Specialty Code, 2019, based on the 2018 International Building Code.

Peterson, N.V., Groh, E.A., Taylor, E.M., and Stensland, D.E., 1976, Geology and mineral resources of Deschutes County, plate 1, Geologic map of the Redmond Area: Oregon Department of Geology and Mineral Industries, Bulletin 89-1, scale 1:24,000

Taylor, E.M., 1981, Central High Cascade roadside geology, in Johnston, D.A., and Donnelly- Nolan, J.M., eds., Guides to some volcanic terranes in Washington, Idaho, Oregon, and northern California: U.S. Geological Survey Circular 838, p. 55-83.

https://ngmdb.usgs.gov/Prodesc/proddesc_33002.htm https://ngmdb.usgs.gov/Prodesc/proddesc_33002.htm

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10.0 PROFESSIONAL AUTHENTICITY

This report has been authored and reviewed by the undersigned, respectively. This report is void if the original seal(s) and signature(s) are not included.

Adam Larson, P.E.

Project Geotechnical Engineer

Lisa M. Splitter, P.E., G.E.

Senior Geotechnical Engineer

FIGURES

APPENDIX A

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APPENDIX A

FIELD EXPLORATION SUMMARY

GENERAL

Subsurface conditions for the COUTES OMD project, located in Redmond, Oregon, were explored by excavating three (3) test pits, at the approximate locations shown on Figure 2, Exploration Location Map. Test pit logs are included in this appendix. The test pit explorations were performed on September 27, 2021. The procedures used to observe the test pits, and collect soil samples, and other field techniques are described in detail in this appendix. Unless otherwise noted, all soil sampling and classification procedures followed local engineering practices which are in general conformance with relevant ASTM procedures and the Unified Soil

Classification System (USCS). “General conformance” means that certain local and common excavation and descriptive practices and methodologies have been followed.

TEST PITS

Three (3) test pits were excavated by Terry Shine Excavating of Bend, Oregon. The test pits were observed by a Wallace Group geotechnical professional who maintained a detailed log of subsurface conditions and materials encountered and collected soil samples at appropriate depth intervals. The test pits were excavated to depths ranging between approximately 1- to 5-feet below ground surface (bgs). Bulk samples were retrieved for laboratory testing.