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PZ - GeoTech 208-440-6276 * bjarnoldpe@msn.com ( 1 ) Post Office Box 190537 * Boise, Idaho 83719 Mr. Dan Lardie Leavitt & Associates Engineering 1234 1st Street South Nampa, Idaho 83651 Amended October 15, 2016 September 15, 2016 File 16173BR Page 1 of 21 Re: Preliminary Geotechnical Report Proposed Bannock Ridge Subdivision Near South Mesa Way and East Victory Road Meridian, Idaho Dan: Our report has been amended to include the labwork that was not completed when our original report was published. No recommendations have changed in this amendment. As per your authorization, on September 14, 2016, SITE observed the excavation of three test pits on the subject property. These test pits were intended to generate a working knowledge of the subsurface soil conditions on the subject pro ject. The test pits were located in the pastures behind (west of) the home at 3101South Mesa Way in Meridian, Idaho. These locations are where stormwater facilities are planned. Based upon the observed conditions the site is acceptable for construction of the planned residential development. Recommend ations for constructing civil improvements and residential houses are provided herein. We appreciate this opportunity to be of service. Please call should there be any questions or the need for additional geotechnical services. Respectfully submitted Bob J. Arnold, PE SITE Consulting, LLC 208-440-6276 * bjarnoldpe@msn.com ( 2 ) Post Office Box 190537 * Boise, Idaho 83719 EXECUTIVE SUMMARY SOIL PROFILE - The soil profile on this property is very similar to soils encountered by this engineer during construction of Springhouse Subdivision directly across Victory Road from this property. The site surface is covered with 3.5 to 4.0 feet of brown, moist, silty sand or sandy silt with some clay likely present. Below this is a THIN layer of clean, clay free pitrun type sand and gravel. At approximately eight feet deep the pitrun becomes very dense and includes fine clay soils. These materials are very firm and rigid with percolation and conductivity rates approaching zero. CLEARING & GRUBBING - Grubbing depths of 4 to 6 inches can be anticipated to remove most organic materials. This is to be adjusted in the field at the time of construction. Deeper excavation can be anticipated along the fences and where larger trees and bushes are present. Large trees will have deep roots that must be removed. DEMOLITION - While some onsite buildings (homes) are to remain, others are to be demolished. All foundation concrete and slab on grade concrete is to be removed. This is to be confirmed at the time of demolition. Crawlspaces or basements beneath demolished buildings are to be backf illed with structural fill as described herein. PAVEMENT DESIGN – Based upon an R-Value of R =13 and a Traffic Index of TI = 6 a pavement section of 2.5" HMA, 4.0" ISPWC Base and 10.0" ISPWC Subbase is recommended. STORM WATER DISPOSAL - Shallow basins that drain into the top of the clean, non - clay containing pitrun layer encountered in all three test pits are recommended. A percolation rate of 4.5 in/hr was measured in these soils in Springhouse Subdivision during ACHD observed testing. It is noted that a percolation rate of P=0.25 in/hr was measured in the deeper clay containing sand and gravels. Confirmation of percolation rate at the time of construction is recommended and may be required by ACHD. It is noted that the clay containing pitrun soil extend to depths greater than our deepest onsite exploration of 17 feet below grade. These soils were present to greater than 22 feet at Springhouse Subdivision. GROUNDWATER - Groundwater was observed entering two test pits (TP1 & TP3) at 6.0-7.0 feet below grade. TP2 was excavated to 17 feet deep and was dry when the monitoring well was installed. Future groundwater re adings will be gathered and reported in later reports. It is noted that two well logs found on the IDWR website for lots within Kachina Estates Subdivision, where this property is located, indicate the static water level is greater than 20 feet deep. 208-440-6276 * bjarnoldpe@msn.com ( 3 ) Post Office Box 190537 * Boise, Idaho 83719 STRUCTURAL FILL - Since surface soils included elastic silts and lean clay, care must be taken if these materials are to be used as structural fill on building lots. Compaction of clay containing soils may seal crawlspaces and yard areas, greatly reducing percolation. Compaction of any fill placed within building pads or right of ways must exceed 95% of the maximum dry density as determined by Standard Proctor (ASTM D- 698). Structural fill must pass compaction testing and visual inspection for stability. Fill that passes compaction but is observed to rut or deflect under construction traffic is to be rejected. FOUNDATION DESIGN - Bearing pressures of up to 1500 psf are available on the native soils and tested and approved structural fills consisting of native soils. Foundations are to be sealed with mopped, sprayed, or rolled on sealer and embedded at least 24 inches below adjacent grade for frost protection. Foundation sealer can be deleted if slab on grade floors are constructed. Construction of slab on grade floors must included a code complying vapor barrier (retarder). Basements are not recommended without first conducting a long term groundwater study or installation of a engineered dewatering system. FOUNDATION BACKFILL - Building Code requires that soils used to back fill foundations meet the compaction requirements stated above. Low-density foundation backfill has been shown to be a major contributing factor to water accumulating in crawlspaces throughout the Treasure Valley. Homebuilders are encouraged to properly backfill all foundations. This is especially critical on lots where structural fills have been placed below the foundation. FOUNDATION ELEVATION - Foundation elevation and site grading must conform to the requirements of the Building Code. Elevation and grading must promote drainage away from the foundation. Landscaping should be designed to promote drainage away from foundations. Flowerbeds and landscaped areas must be designed such that irrigation water and roof runoff is not retained against foundations. STORMWATER & DRAINAGE - Roof gutters are recommended with down spouts directed away from foundations and not on to foundation backfill soils. Proper design and maintenance of sprinkler systems is required. Excessive watering may lead to water entering the crawl spaces. Drip type sprinkler heads should be used in flowerbeds near foundations. Lawn area sprinklers should not spray toward foundations or cause water to accumulate near foundations. 208-440-6276 * bjarnoldpe@msn.com ( 4 ) Post Office Box 190537 * Boise, Idaho 83719 TABLE OF CONTENTS EXECUTIVE SUMMARY ............................................................................................. 2 TABLE OF CONTENTS .............................................................................................. 4 INTRODUCTION ......................................................................................................... 5 General ............................................................................................................. 5 Purpose and Scope .......................................................................................... 5 Authorization..................................................................................................... 5 Warranty and Limitations .................................................................................. 5 RESEARCH & DOCUMENTATION ............................................................................ 6 Field Exploration ............................................................................................... 6 Laboratory Testing ............................................................................................ 6 SITE DESCRIPTION / INFORMATION ....................................................................... 7 General ............................................................................................................. 7 Subsurface Conditions ..................................................................................... 7 CONSTRUCTION RECOMMENDATIONS ................................................................. 8 Residential Foundation Systems ...................................................................... 8 Structural Fill ..................................................................................................... 8 Stormwater Control ........................................................................................... 8 Excavations ...................................................................................................... 9 Slab on Grade Concrete ................................................................................... 9 Flexible Pavement Sections ............................................................................. 9 General Comments .......................................................................................... 10 APPENDIX .................................................................................................................. 11 208-440-6276 * bjarnoldpe@msn.com ( 5 ) Post Office Box 190537 * Boise, Idaho 83719 NTRODUCTION GENERAL This report presents the results of a Geotechnical Investigation performed for a proposed residential development to be called Bannock Ridge Subdivision. The property is located on west side of South Mesa Way and north of East Victory Road. The proposed subdivision includes lots 1,2, & 3 - Block 2 of Kachina Estates Subdivision. Addresses of 2940, 3101 and 3155 South Mesa Way are assigned to the three homes on the properties. Each of these properties include approximately 4-4.5 acres with large single family residences, barns, shed, pastures and corrals common. It is understood that the homes are to remain but most outbuildings, included barns and sheds, will be demolished. The proposed subdivision will include an internal, ACHD, right of way with approximately 32 new lots for single family residences. See the provided plans in the Appendix for additional details. PURPOSE & SCOPE The purpose of this investigation was to determine the subsurface soil conditions at the subject site and provide recommendations for civil and residential construction. The field investigation included a subsurface exploration by means of three excavated test pits, the collection of soil samples, and the laboratory testing of sampled soil materials. All available data was reviewed along with the design information provided or assumed. Next an engineering analysis of the obtained data and the provided design information was performed and this report was prepared. This report summarizes our findings, conclusions and recommendations. AUTHORIZATION SITE Consulting, LLC received e-mailed authorization to proceed with this geotechnical investigation from the client August 4, 2016. Authorization to proceed and the use of the recommendations provided by SITE indicate the client’s acceptance of the scope of work and the warranty and limitations provided herein. WARRANTY AND LIMITATIONS Exploration and evaluation of subsurface conditions documented herein is considered sufficient to form a basis for the recommended foundation design. The provided recommendations are based on the available soil information and preliminary design details either assumed or furnished by the client. SITE warrants that these recommendations have been promulgated after being prepared in accordance with locally accepted professional engineering and geotechnical engineering practice. No other warranties are implied or expressed. 208-440-6276 * bjarnoldpe@msn.com ( 6 ) Post Office Box 190537 * Boise, Idaho 83719 RESEARCH & DOCUMENTATION FIELD EXPLORATION On September 14, 2016 SITE supervised the excavation of three test pits by Culver Excavation of Boise, Idaho. A large, rubber tire, backhoe was used to perform this investigation. Our staff logged the test pits in the field and gathered representative samples from the test pits. The samples were field classified, labeled according to test pit number and depth, sealed in plastic storage bags and transported to the laboratory for further testing. Test pits were advanced at or near locations discussed with the client, and were intended to be at or near stormwater facilities. Each test pit was advanced to a depth where deeper excavation was not possible due to sloughing soils or limitation of the backhoe. Groundwater was encountered in two of three test pits at 6-7 feet deep. A hand held GPS unit was used to determined test pit locations. These locations were then plotted on an aerial photo obtained from Google Earth. The Aerial Photo is included in the Appendix. The test pit locations shown are believed to be accurate to within several feet of the actual test locations. LABORATORY TESTING In addition to the field investigation, a supplemental laboratory-testing program was conducted to determine additional pertinent engineering characteristics of the foundation soils. The laboratory-testing program included supplementary visual classification and moisture content determinations on selected samples. Selected samples were subjected to Grain Size Analysis, Moisture Content Determination and Atterberg Limits. An R-Value sample was sent to a specialty soil lab for testing. All phases of the laboratory testing program were conducted in general accordance with applicable ASTM Standards. 208-440-6276 * bjarnoldpe@msn.com ( 7 ) Post Office Box 190537 * Boise, Idaho 83719 SITE DESCRIPTION / INFORMATION GENERAL As indicated, the proposed subdivision includes three existing rural properties each with a single family residence, out buildings, and fenced areas for pastureland and animal holding areas. The planned location of storm water facilities allow test pits to be excavated only on the center parcel at 3101 South Mesa Way. The current property owner/tenant provided access through existing gates and driveways. SUBSURFACE CONDITIONS At the time of our exploration, the surface was firm and stable allowing complete access with the selected excavation equipment. The site surface is covered with 3.5 to 4.0 feet of brown, moist, silty sand or sandy silt with some lean clay present. Below this is a THIN layer of clean, clay free, pitrun type sand and gravel. At approximately eight feet deep the pitrun becomes very dense and include s fine clay soils. These materials are very firm and rigid with percolation and conductivity rate approaching zero. Groundwater was observed entering two test pits (TP1 & TP3) at 6.0 -7.0 feet below grade. TP2 was excavated to 17 feet deep and was dry when the mo nitoring well was installed. Future groundwater readings will be gathered and reported in later reports. IDWR records for the area around this site were searched and two well logs were copied and are included in the Appendix. One is for the south parcel of this project and the second is for a property just north of the site. The two wells indicate the static water level is greater than 20 feet deep. Well logs are included in the Appendix. 208-440-6276 * bjarnoldpe@msn.com ( 8 ) Post Office Box 190537 * Boise, Idaho 83719 CONSTRUCTION RECOMMENDATIONS RESIDENTIAL FOUNDATION SYSTEMS For conventional, shallow, residential foundations, bearing pressures of up to 1500 psf are allowed. Such foundations are to be founded a top stable native soils or tested and approved structural fill. If clay soils are present after crawlspace excavation, it is recommended that this or another engineer be contracted to evaluate the clay soil. Foundations are not to be constructed atop fat, expansive clay soil unless approved by a professional engineer. Removal and replacement of unacceptable soils may be required. Specific recommendations are to be provided for each lot where clay soils are present at the foundation support elevation. STRUCTURAL FILL Structural fill to be placed within ACHD right of ways or on building lots shall be free from organic matter or other deleterious substances and shall be non -expansive. Structural fill should be placed in uniform, thin h orizontal lifts not to exceed twelve inches in compacted thickness; moisture conditioned as necessary and compacted to a minimum relative compaction of 95% based on the ASTM Test Method D698, Standard Proctor. Compaction of structural fills should be verified by inplace density testing and construction observations. Field nuclear moisture - density testing shall be performed on at least every lift of compacted fill with one test per lot or one every 300 feet of roadway. A qualified engineer or his representative should monitor fill placement to ensure the work is performed in accordance with these recommendations. Subgrade surface and structural fill must be stable. Rutting or deflecting materials are to be rejected and repaired as needed regardless of passing compaction test results. STORM WATER CONTROL Onsite soils will become very soft and difficult to traverse if wet at the time of construction. It is therefore recommended that construction occur during dry weather. All storm runoff is to be directed away from open excavations and not be allowed to puddle on subgrade soils. If construction is to occur during wet season conditions then soft soils must be considered. If the subgrade is wet, traffic with rubber tired equipment is to be avoided since rubber tired equipment will increase rutting and deflections of wet or saturated surface soils. If construction must occur when subgrade soils are wet; geotextiles, geogrids, and lime and/or cement stabilization methods can be considered and designed as needed. 208-440-6276 * bjarnoldpe@msn.com ( 9 ) Post Office Box 190537 * Boise, Idaho 83719 EXCAVATIONS Dewatering of utility trenches greater than seven feet deep should be anticipated. Shallow excavations that do not exceed three feet in depth may be constructed with side slopes approaching vertical. Below this depth, it is recommended that slopes not exceed a vertical to horizontal ratio of one to one. The ability of the materials on site to maintain a vertical or near vertical excavation when stand ing open without support over any extended period can be expected to be quite variable. For deep excavations, saturated soils below the groundwater level cannot be expected to remain in position and the potential for sudden trench wall collapse exists. Proper care must be taken to protect personnel and equipment. Foundation & trench excavation shoring may be necessary. This information is provided for planning purposes. It is our opinion that maintaining safe working conditions is the responsibility of the contractor. Jobsite conditions such as soil moisture content, weather condition, earth movements and equipment type and operation can all affect slope stability. All excavations should be sloped or braced as required by applicable local, state, an d federal requirements. SLAB ON GRADE CONCRETE Concrete slab on grade floors, sidewalks and pavements should be placed atop a minimum of four inches of imported structural fill. The structural fill should consist of sand or sand - gravel mixture with non-plastic fines. The material should all pass a one inch sieve and should contain less than twelve percent passing the # 200 sieve. The granular mat shall be compacted to the requirement for structural fill. Prior to the placement of base gravel, inspection must confirm that all fat clay has been removed from beneath slab on grade concrete. If removal is impractical, then the granular structural fill should be increased to eight inches. FLEXIBLE PAVEMENT SECTION A pavement section of 2.5” / 4.0” /10.0” is recommended for subdivision right of ways within this development. This is based on an ACHD assigned Traffic Index of TI=6 and an R-Value of R=13. The R-Value sample was sent to soils specialty lab for analysis. Their completed report is included in the Appendix. All materials and methods used to construct pavements, sidewalks and other civil improvements are to comply with ACHD and / or ISPWC requirements. 208-440-6276 * bjarnoldpe@msn.com ( 10 ) Post Office Box 190537 * Boise, Idaho 83719 GENERAL COMMENTS After the plans and specifications for each subdivision phase are completed, it is recommended that this consultant be provided the opportunity to revi ew the final design and specifications. This review will confirm that the earthwork and foundation recommendations have been properly interpreted and implemented. At that time, it may be necessary to submit supplementary recommendations. Engineering inspection, construction monitoring, and materials testing have been recommended and must be performed to verify conditions and suitability of materials used for structural fills and to confirm subgrade stability and proper placement and compaction of structural fills. Any deviations from the noted subsurface conditions should be brought to the attention of this consultant. This report has been prepared for the exclusive use of the identified client and their retained design consultants and contractors. Findings and recommendations within this report are for specific application to the proposed residential subdivision as described here and apply only to the property identified. Appendix follows 208-440-6276 * bjarnoldpe@msn.com ( 11 ) Post Office Box 190537 * Boise, Idaho 83719 APPENDIX Proposed Plat Aerial Photo Test Pit Logs (3) Well Logs (2) Soil Log Legend Abbreviations and Acronyms R-Value Report Pavement Section Calcs 208-440-6276 * bjarnoldpe@msn.com ( 12 ) Post Office Box 190537 * Boise, Idaho 83719 PROVIDED PLAT (From Leavitt & Associates) Proposed Drainage Facilities in black 208-440-6276 * bjarnoldpe@msn.com ( 13 ) Post Office Box 190537 * Boise, Idaho 83719 AERIAL PHOTO with approximate Test Pit Locations NE Boring 208-440-6276 * bjarnoldpe@msn.com ( 14 ) Post Office Box 190537 * Boise, Idaho 83719 Test Pit Log Test Pit #: TP1 File: 16173B Client: Leavitt Date Excavated: 09/14/16 Project: Bannock Ridge Excavator: Culver Excavation Location: N43 34 38.73, W 116 22 53.07 Logged By: B. Arnold DEPTH SOILS DESCRIPTION 1.0" 3/4" 1/2" 3/8" #4 #10 #40 #100 #200 %M LL PI 0.0-3.5 Brown, Moist, Sandy Lean Clay (CL) with organics / Rootzone to 4-6" Bag 2.0 100 98 78 73 68.9 19.3 40 22 3.5 Gravel Contact 3.5-8.0 Tan, White & Brown, Moist to Saturated, PITRUN - Sand and Gravel Free Draining at 4.5', Clay present at 8.0' (Sample scalped on 3/4") Bag 5.0 100 85 70 55 45 14 8 6.9 3.4 NP NP 8.0 Bottom of Hole - Well Installed Excavation Halted by Sloughing Soil Groundwater at 7.0' and rising 208-440-6276 * bjarnoldpe@msn.com ( 15 ) Post Office Box 190537 * Boise, Idaho 83719 Test Pit Log Test Pit #: TP2 File: 16173B Client: Leavitt Date Excavated: 09/14/16 Project: Bannock Ridge Excavator: Culver Excavation Location: N43 34 32.55, W 116 22 56.5 Logged By: B. Arnold DEPTH SOILS DESCRIPTION 1.0" 3/4" 1/2" 3/8" #4 #10 #40 #100 #200 %M LL PI 0.0-4.0 Brown, Moist, Silt / Sand with organics / Rootzone to 4-6" (R-Value Sample Taken) Bag 1.0 Bkt 2.5 100 97 100 91 95 82 88 75 78 65.5 60.5 18.5 16.6 39 42 19 19 4.0 Gravel Contact 4.0-8.0 Tan, White & Brown, Moist, PITRUN - Sand and Gravel Free Draining at 4.5', Clay present at 8.0' 8.0-17.0 Red, Tan, Brown, Moist, PITRUN - Sand and Gravel with Clay Very Dense, little to no percolation or conductivity 17.0 Bottom of Hole - Well installed in Dry Hole Excavation halted at limit of Backhoe NO GROUNDWATER ENCOUNTERED 208-440-6276 * bjarnoldpe@msn.com ( 16 ) Post Office Box 190537 * Boise, Idaho 83719 Test Pit Log Test Pit #: TP3 File: 16173B Client: Leavitt Date Excavated: 09/14/16 Project: Bannock Ridge Excavator: Culver Excavation Location: N43 34 40.22, W 116 22 56.55 Logged By: B. Arnold DEPTH SOILS DESCRIPTION 1.0" 3/4" 1/2" 3/8" #4 #10 #40 #100 #200 %M LL PI 0.0-3.5 Brown, Moist, Silt / Sand with organics / Rootzone to 4-6" Bag 1.5 100 93 75 63.6 14.4 NP NP 3.5 Gravel Contact 4.0-8.0 Tan, White & Brown, Moist, PITRUN - Sand and Gravel Free Draining at 4.5' Water Entering Test Pit at 6.0' Clay present at 8.0' 8.0-12.0 Red, Tan, Brown, Moist, PITRUN - Sand and Gravel with Clay Very soft and saturated due to water from above 12.0 Bottom of Hole - Well installed Excavation halted by sloughing soils Water in bottom of hole from above and rising 208-440-6276 * bjarnoldpe@msn.com ( 17 ) Post Office Box 190537 * Boise, Idaho 83719 WELL LOGS 208-440-6276 * bjarnoldpe@msn.com ( 18 ) Post Office Box 190537 * Boise, Idaho 83719 208-440-6276 * bjarnoldpe@msn.com ( 19 ) Post Office Box 190537 * Boise, Idaho 83719 SOIL LOG LEGEND UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM STANDARD TEST METHOD D 2487 FOR CLASSIFICATION OF SOIL FOR ENGINEERING PURPOSES) MAJOR DIVISIONS TYPICAL DESCRIPTIONS COARSE GRAINED SOILS < 50% - #200 GRAVEL & GRAVELLY SOILS <50% - #4 < 5% - #200 GW Well-graded gravel, gravel-sand mixture, little or no fines. GP Poorly-graded gravel, gravel sand mixture, little or no fines 5-12% -#200 GM Silty gravel, gravel-sand-silt mixtures > 12% - #200 GC Clayey gravel, gravel-sand-clay mixtures SAND & SANDY SOILS > 50% - # 4 < 5% - #200 SW Well-graded sand, gravelly sand, little or no fines. SP Poorly-graded sand, gravelly sand, little or no fines >12% - #200 SM Silty sand, sand-silt mixtures SC Clayey sand, sand-clay mixtures FINE GRAINED SOILS > 50% - #200 SILTS AND CLAYS LL < 50% INORGANIC ML Inorganic silt and very fine sand, rock flour, silty or clayey fine sand or clayey silt with slight plasticity CL Lean clay-low to medium plasticity, gravelly clay, sandy clay, silty clay ORGANIC OL Organic silt and organic silty clay of low plasticity SILTS AND CLAYS LL > 50% INORGANIC MH Elastic silt, micaceous or diatomaceous fine sand or silty soil. CH Fat clay - high plasticity ORGANIC OH Organic clay-med. or high plasticity: organic silt HIGHLY ORGANIC SOILS PT Peat, humus, swamp soil with high organic content ABBREVIATIONS AND ACRONYMS ASTM American Society for Testing and Materials ACP Asphaltic Concrete Pavement ISPWC Idaho Standard for Public Works Construction ITD Idaho Transportation Department NP Non Plastic TP Test Pit USCS Unified Soil Classification System 208-440-6276 * bjarnoldpe@msn.com ( 20 ) Post Office Box 190537 * Boise, Idaho 83719 208-440-6276 * bjarnoldpe@msn.com ( 21 ) Post Office Box 190537 * Boise, Idaho 83719 DESIGN SECTION CALCULATIONS (ACHD R-Value Method) Project:Bannock Ridge Subdivision File No.:16173B Meridian, Idaho Calc By:B. Arnold Client:Leavitt Engineering Date:09/15/16 Design Thickness Equation: T = 0.0032 (TI) (100-R)(12) = GE (inches) T=Design Thickness TI =Traffic Index =6 By Agency GE =Gravel Equivalent R =R-Value =13 By Soils Test GE=20.5 Inches ACHD ACP, 3/4" Road Base and Aggregate Subbase Actual Thickness Equivalent Thickness ACHD Asphalt Concrete Thickness =2.5 Inches ACE=5.5 Inches 3/4" Road Base Thickness Desired =4.0 Inches RBE=5.1 Inches Calculated Aggregate Subbase Thickness Equation: Subbase Thickness=SB=GE-ACE-RBE SB=9.9 Inches CALCULATED DESIGN SECTION ACHD Asphaltic Concrete=2.5 inches 3/4" Road Base =4.0 inches Aggregate Subbase =10.0 inches RECOMMENDED DESIGN SECTION Asphaltic Concrete =2.5 inches 3/4" Road Base =4.0 inches Aggregate Subbase =10.0 inches NOTHING FOLLOWS