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CC - Stormwater Report
CENTURION ENGINEERS. INC. Prepared By: Property Location: Matthew Reinhart, P.E. Addition Circle Centurion Engineers, Inc Boise, ID 83705 2323 S.Vista Ave Ste 206 Boise, ID 83705 www.centengr.com STORMWATER REPORT AND CALCULATIONS FOR ADDISON CIRCLE SUBDIVISION May 28, 2024 U N Prepared by: ©N5r y Matthew Reinhart CL 74 2 � o a�Q � Centurion Engineers, Inc. mareinhart@centengr.com `Tfyy RE�� 208.343.3381 Page 1 of 4 Cent ur io n Eng ineer s, Inc . Introduction: The project,Addison Circle Subdivision, is located south of W. McMillan Road,west of S. Black Cat Road, and east of School Avenue in Kuna, Idaho. The subdivision will be located east of a previous phase, Silver Trail Subdivision No 9 and north of Silver Trail Subdivision No 7. gElffifl w Mc ,- Project Site TBM TBM 1 n NIHEUILE CREEK- Y 5 NOT T SCALE Figure 7:Vicinity Map Drainage Areas The project has a total area of 0.93 acres. Drainage generated on the site will be retained on the site. The site is composed of a single tributary watershed area. Site street grading directs runoff to a catch basin at the end of the proposed cul-de-sac. Runoff volume generated on the site are calculated by means of rational method hydrology for a 60-minute duration. See Appendix I for the Watershed Map. Page 2 of 4 Centurion Engineers, Inc . Weighted "C"Values and Peak Flow Calculations: The tributary watershed is composed of a multi-family residential,paved roadway,and landscaped cover types. The weighted "C" values were developed from the AND Section 8000 — Drainage and Stormwater Management, Figure 8011.2.1 Coefficients of Runoff. From the figure,the runoff coefficients for multi-family residential is 0.60 to 0.75. The lower range C-value of 0.60 was used for this project, because the covers for the roadway was added in to result in a weighted C of 0.67. See Appendix I I for the Q,00 peak flow, seepage bed, and sand/grease trap calculations. Sand & Grease Traps and Horizontal Seepage Bed: Storm water runoff from the site surface flows to an infiltration basin located at the end of the cul-de-sac in the landscaped area. Due to a water table at approximately 7.5 feet below the ground surface, a horizontal seepage design was used. The horizontal seepage bed was designed per Eagle City standard detail SD-03. Runoff first enters a catch basin and then flows to a sand/grease trap to clean the runoff and to settle out silts. Flows continue to horizontal gravel seepage beds through an 18-inch perforated plastic pipe where it drops down through a sand bed to add to the groundwater. Once constructed, the sub-surface seepage pits will be owned and maintained by the Ada County Highway District. Geotechnical Report: The Geotechnical Engineering Investigation report was prepared by Atlas Technical Consultants, dated February 22, 2024. This report has indicated that there are a few site-specific criteria within this development for developing storm water infiltration facilities. The report has indicated that seasonal high groundwater was fairly shallow at approximately 7.5 feet below the existing ground surface in the area of the proposed seepage bed. During construction, after excavation, the contractor is required to perform a geo-technical perc test at the level of infiltration to confirm or alternatively mediate for the measured infiltration rate. Site Consulting recommends a percolation rate of 1.8 inches/hours for the site's seepage bed design. The Geotechnical Report can be found in Appendix 111. Page 3 of 4 Centurion Engineers, Inc . Appendices Page 4 of 4 Centurion Engineers, Inc . Appendix Watershed Map OAKCREEK SUBDIVISION No. 3 BLOCK 7 14 SETTLERS CANAL Block 1 0 0 Watershed Area = 0.93 acres x Ct. W_Torana Ct. x U z 0 Block 1 I I n n n I n 1I U R'�ti VICINITY M A P CENTURION ENGINEERS. INC. Consulting Engineers, Land Surveyors, Planners ADDISON CIRCLE SUBDIVISION Telephone s Vista Ave 33 206 ww.c ID 937Qn BOISE, IDAHO ' Telephone 2Q8.343.33B1 I www.cenlengr.com �Hc►Ne�¢y SCALE: 1"=40' SHEET 1 OF 1 E:\—JOBFILE\HC11\Storm Drainage\HC11 Oak Creek Sub Linework.dwg 5-24-24 04:35:56 PM mareinhart Centurion Engineers, Inc . Appendix II Weighted Runoff Coefficient, Retention Volume, Horizontal Seepage Bed Sizing, Sediment Tank Design G&-T U R/O CENTURION ENGINEERS, INC. Consuiting Engineers, Land Surveyors, Planners 2323 S. Vista Ave Ste 206 Boise, I❑ 83705 Telephone 208.343.3381 1 www.centengr.com Date: 24-May-24 Job No: HC11 Job Name: Addison Circle Subdivision Calc By: MR Project Site: Addison Circle Subdivision Area Area Runoff CxA Description Coeff., Single Family Residential 22794.62 0.52 0.60 0.31 Roadway 13767.8 0.32 0.95 0.30 Landscaped Area 4012.07 0.09 0.07 0.01 0 0.00 0.00 0.00 Totals: 40,574 0.9315 ac 0.62 ac Weighted Runoff Coefficient for Typical Lot, C = 0.6664 Cl ALL+C.,A,t.....—CHAY" - A testa: Design Storm: 100-year Rainfall Intensity,i = 0.96 In/hr sec V = CiA x 60 minx 60 min Volume to Retain,V= 2,145 c.f. Required Volume to Retain,V x 1.15= 2,467 c.f. for Long-Term Sedimentation CENTURION £NGIN£ERS, INC. Consulting Engineers, Land Surveyors, Planners 2323 S. Vista Ave Ste 206 Boise, ID 83705 Telephone 208.343.3381 1 www.centengr.com HORIZONTAL SAND FILTER DESIGN Job No: HC11 Job Name: Addison Circle Subdivision Calc By: MR Infiltration Rate= 1.80 in/hr 50%of 3.6 in/h,per Atlas Rpt,2/22/24 Horizontal Seepage Bed Equivalent Bed Width= 10.00 feet Horizontal Seepage Bed Equivalent Bed Length= 100.00 feet Total Area= 1000 s.f. Bed Depth= 6.00 feet Bed Volume= 6,000 c.f. Drain Rock Void Ratio= 0.40 Storage Capacity of Horizontal Seepage Bed= 2040 cf with 15%sedimentation 0.40 x 0.85 x L x W x D Contact Area for Horizontal Seepage Bed Window: Depth of Bed= 6.00 feet Length of Bed=1 110.00 feet Seepage Bed Contact Area= 660 s.f. One-Hour Infiltration Volume= 99 cf/hr not used when using Eagle's method. Effective Retained Volume= 2,139 c.f. 0.40 x Lx W x D x 1-hr Infiltrtation Vol Required Volume to Retain,V= 2,467 c.f. from previous sheet Adequate Seepage Bed Size? No Drain Time= 25 hours Time to infiltrate 100%volume Meets Drain Time Criteria? Yes Drains within 48 hours? Opening Width Below Baffle(Throat)= 50 in Larken 1000 Gat CB FG2027 Opening Height Below Baffle(Throat)=1 21 in Area of Throat= 7.29 s.f. Sediment Tank Throat Velocity= 0.17 fps V=Q/A Meets Max Allowable Throat Velocity Criteria? Yes Is velocity less than 0.5 fps? SAND/GREASE TRAP PER SD-01 GEOTEXTILE OBSERVATION WELL 12" DIA PERFORATED PIPE FILTER FABRIC I (DO NOT PENETRATE LINER) 1'-6" MIN -------------------- ------------V, -------------------- 0000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000 C a H %" TO 2" WASHED i� DRAIN ROCK 2" MIN v . SHGWL = L 1. ALL GEOTEXTILE SEAMS SHALL OVERLAP 1 FOOT MINIMUM. 2. IMPERVIOUS LINER SEAMS MUST BE SEALED OR OVERLAPPED MINIMUM 1'. 3. PERFORATED PIPE INVERT MUST BE BELOW PIPE INVERT INTO SAND AND GREASE TRAP PER SD-01. 4. BED WIDTH SHALL REMAIN CONSTANT. 5. A MINIMUM V--6" COVER FROM TOP OF BED TO FINISH GRADE IS REQUIRED. GEOTEXTILE FILTER FABRIC 3.00' W 6" MIN FREE W. DRAINING ASTM C-33 MATERIAL FILTER H SAND , 1Yz" TO 2" WASHED DRAIN ROCK 1% 2" MIN SHGWL — IMPERVIOUS LINER EXTEND MIN 1' INTO FREE DRAINING MATERIAL CITY OF EAGLE STANDARD DRAWING DRAINAGE DESIGN HORIZONTAL SEEPAGE BED NO- STANDARDS S D — Q 3 m\cuaT"0\1&-0W1\SUm&W D"s Centurion Engineers, Inc . Appendix III Geotechnical Report 7 L f:zIL F- i . S I r 1• i r y, J Q• a r i GEOTECHNICAL INVESTIGATION BLACK CAT RESIDENTIAL SUBDIVISION 4535 North Black Cat Road Meridian, ID PREPARED FOR: Adam Markowich Elevate Homes LLC 3327 North Eagle Road, Suite 110 Meridian, ID 83646 PREPARED BY: Atlas Technical Consultants, LLC February 22, 2024 2791 South Victory View Way B240122g Boise, ID 83709 �,r�"7'C7rT�ci� Mrs 0 2791 South Victory View Way Boise, ID 83709 (208)376-4748 1 oneatlas.com February 22, 2024 Atlas No. B240122g Adam Markowich Elevate Homes LLC 3327 North Eagle Road, Suite 110 Meridian, ID 83646 Subject: Geotechnical Investigation Black Cat Residential Subdivision 4535 North Black Cat Road Meridian, ID Dear Adam Markowich: In compliance with your instructions, Atlas has conducted a soils exploration and foundation evaluation for the above referenced development. Fieldwork for this investigation was conducted on February 5 and 6, 2024. Data have been analyzed to evaluate pertinent geotechnical conditions. Results of this investigation, together with our recommendations, are to be found in the following report. We have provided a PDF copy for your review and distribution. Often, questions arise concerning soil conditions because of design and construction details that occur on a project. Atlas would be pleased to continue our role as geotechnical engineers during project implementation. If you have any questions, please call us at (208) 376-4748. Respectfully submitted, Gavin Marron, El Ethan Salove, PE Staff Engineer Geotechnical Engineer Jacob Schlador, PE Geotechnical Practice Manager- Northwest Distribution: David Crawford, Centurion Engineers (PDF Copy) Page 1 �TrT-G7T-�. CONTENTS 1. INTRODUCTION ...................................................................................................................2 1.1 Project Description........................................................................................................2 1.2 Scope of Investigation...................................................................................................2 2. SITE DESCRIPTION .............................................................................................................3 2.1 Regional Geology .........................................................................................................3 2.2 General Site Characteristics .........................................................................................3 3. SEISMIC SITE EVALUATION...............................................................................................3 3.1 Geoseismic Setting.......................................................................................................3 3.2 Seismic Design Parameter Values ...............................................................................4 4. SOILS EXPLORATION .........................................................................................................4 4.1 Exploration and Sampling Procedures..........................................................................4 4.2 Laboratory Testing Program .........................................................................................4 4.3 Soil and Sediment Profile..............................................................................................5 4.4 Volatile Organic Scan ...................................................................................................5 5. SITE HYDROLOGY................... _.................................................................................5 5.1 Groundwater.................................................................................................................5 5.2 Soil Infiltration Rates.....................................................................................................6 5.3 Infiltration Testing..........................................................................................................6 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS.............................7 6.1 Foundation Loading Information ...................................................................................7 6.2 Foundation Design Recommendations.........................................................................7 6.3 Crawl Space Recommendations...................................................................................8 6.4 Floor, Patio, and Garage Slab-on-Grade......................................................................9 7. CONSTRUCTION CONSIDERATIONS ................................................................................9 7.1 Earthwork......................................................................................................................9 7.2 Grading .......................................................................................................................10 7.3 Dry Weather................................................................................................................10 7.4 Wet Weather...............................................................................................................10 7.5 Soft Subgrade Soils ....................................................................................................10 7.6 Frozen Subgrade Soils ...............................................................................................11 7.7 Structural Fill...............................................................................................................11 7.8 Fill Placement and Compaction ..................................................................................12 7.9 Backfill of Walls...........................................................................................................13 7.10 Excavations...............................................................................................................14 7.11 Groundwater Control.................................................................................................14 8. GENERAL COMMENTS .....................................................................................................15 9. REFERENCES ....................................................................................................................16 Atlas No. B240122g Page I i Copyright©2024 Atlas Technical Consultants �TrTG7T�� TABLES Table 1 — Seismic Design Values .................................................................................................4 Table 2 —Typical Soil Profiles.......................................................................................................5 Table 3 — Groundwater Data.........................................................................................................6 Table 4 — Generalized Soil Infiltration Rates.................................................................................6 Table5 — Soil Bearing Capacity....................................................................................................8 Table 6 — Fill Material Criteria..................................................................................................... 12 Table 7 — Fill Placement and Compaction Requirements........................................................... 12 APPENDICES Appendix I Warranty and Limiting Conditions Appendix II Vicinity Map Appendix III Site Map Appendix IV Geotechnical Investigation Test Pit Log Appendix V Geotechnical General Notes Appendix VI Important Information About This Geotechnical Engineering Report Atlas No. B240122g Page I ii Copyright©2024 Atlas Technical Consultants 1. INTRODUCTION This report presents results of a geotechnical investigation and analysis in support of data utilized in design of structures as defined in the 2018 International Building Code (IBC). Information in support of groundwater and stormwater issues pertinent to the practice of Civil Engineering is included. Observations and recommendations relevant to the earthwork phase of the project are also presented. Revisions in plans or drawings for the proposed development from those enumerated in this report should be brought to the attention of the soils engineer to determine whether changes in the provided recommendations are required. Deviations from noted subsurface conditions, if encountered during construction, should also be brought to the attention of the soils engineer. 1.1 Project Description The proposed development is in the City of Meridian, Ada County, ID, and occupies a portion of the NE'/4NE'/4 of Section 33, Township 4 North, Range 1 West, Boise Meridian. The site to be developed is approximately 1.89 acres. Site maps included in the Appendix show the project location. This project will consist of a 9-lot residential subdivision with 8 buildable lots. Tortana Street will be extended and terminate in a cul-de-sac. It is anticipated that the existing structures onsite will be demolished. Retaining walls are not anticipated as part of the project. Drainage is expected to be directed to onsite infiltration facilities. Location of the infiltration facilities are unknown at this time. Atlas has not been informed of the proposed grading plan. 1.2 Scope of Investigation Our scope of work was completed in general accordance with our proposal dated January 19, 2024 and authorized on January 23, 2024. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between Elevate Homes LLC and Atlas. Atlas' scope of services included the following: • Subsurface exploration via test pits. • Infiltration testing for stormwater management planning. • Field and laboratory testing of materials encountered and collected. • Preparation of this report, which includes project description, site conditions, and our engineering analysis and evaluation for the project. • The scope of work did not include design recommendations specific to individual residences. Atlas No. B240122g Page12 Copyright©2024 Atlas Technical Consultants 2. SITE DESCRIPTION 2.1 Regional Geology The project site is located within the western Snake River Plain of southwestern Idaho and eastern Oregon. The plain is a northwest trending rift basin, about 45 miles wide and 200 miles long, that developed about 14 million years ago (Ma) and has since been occupied sporadically by large inland lakes. Geologic materials found within and along the plain's margins reflect volcanic and fluvial/lacustrine sedimentary processes that have led to an accumulation of approximately 1 to 2 km of interbedded volcanic and sedimentary deposits within the plain. Along the margins of the plain, streams that drained the highlands to the north and south provided coarse to fine-grained sediments eroded from granitic and volcanic rocks, respectively. About 2 million years ago the last of the lakes was drained and since that time fluvial erosion and deposition has dominated the evolution of the landscape. The project site is underlain by the "Gravel of Whitney Terrace" as mapped by Othberg and Stanford (1993). Sediments of the Whitney terrace consist of sandy pebble and cobble gravel. The Whitney terrace is the second terrace above modern Boise River floodplain, is thickest toward its eastern extent, and is mantled with 2-6 feet of loess. 2.2 General Site Characteristics The following details regarding site conditions are based on visual observations and review of available geologic and topographic maps and imagery: • Current Site Conditions: The site is approximately 1.89 acres. A single-story residential structure is present in the northern portion of the site with a barn structure present in the central portion of the site. The remainder of the site consists of agricultural fields. An unnamed irrigation canal runs east to west along the northern property boundary. A drainage swale borders the southern edge of the site and Black Cat Road is present to the east of the project site. • Vegetation: Vegetation on the site consists primarily of landscape trees and grasses adjacent to the structure. The remainder of the site consists of native weeds and grasses. • Topography: The site is relatively flat and level. • Drainage: Stormwater drainage for the site is achieved by percolation through surficial soils. The site is situated so that it is unlikely that it will receive any drainage from off-site sources. 3. SEISMIC SITE EVALUATION 3.1 Geoseismic Setting Soils on site are classed as Site Class D in accordance with Chapter 20 of the American Society of Civil Engineers (ASCE) publication ASCE/SEI 7-16. Structures constructed on this site should be designed per IBC requirements for such a seismic classification. Our investigation revealed low hazard potential resulting from potential earthquake motions including: slope instability, liquefaction, and surface rupture caused by faulting or lateral spreading. Atlas No. B240122g Page13 Copyright©2024 Atlas Technical Consultants 3.2 Seismic Design Parameter Values The ASCE 7-16 seismic design parameter values have been provided below. Table 1 —Seismic Design Values Seismic Design Parameter Design Value Site Class D "Default' Site Modified Peak Ground 0.198 Acceleration, PGAM Ss 0.290 (g) S1 0.106 (g) Fa 1.568 Fv 2.388 SMs 0.455 SM1 0.253 Sos 0.303 Sol 0.169 4. SOILS EXPLORATION 4.1 Exploration and Sampling Procedures Field exploration conducted to determine engineering characteristics of subsurface materials included a reconnaissance of the project site and investigation by test pit. Test pit sites were located in the field by means of a Global Positioning System (GPS) device and are reportedly accurate to within fifteen feet. Upon completion of investigation, each test pit was backfilled with loose excavated materials. Re-excavation and compaction of these test pit areas are required prior to construction. Samples obtained have been visually classified in the field, identified according to test pit number and depth, placed in sealed containers, and transported to our laboratory for additional testing. Subsurface materials have been described in detail on logs provided in the Appendix. Results of field and laboratory tests are also presented in the Appendix. Atlas recommends that these logs not be used to estimate fill material quantities. 4.2 Laboratory Testing Program Along with our field investigation, a supplemental laboratory testing program was conducted to determine additional pertinent engineering characteristics of subsurface materials. Laboratory tests were conducted in accordance with current specifications. The laboratory testing program for this report included: Atlas No. B240122g Page14 Copyright©2024 Atlas Technical Consultants �TrT-G7T_�. • Atterberg Limits Testing —ASTM D4318 • Grain Size Analysis —ASTM C117/C136 • Resistance Value (R-value) and Expansion Pressure of Compacted Soils — Idaho T-8 As to date, the R-value test results have not been received and, therefore, have not been included within this report. Atlas will forward the results in the form of an addendum once the R-value test results have been received. 4.3 Soil and Sediment Profile The profile below represents a generalized interpretation for the project site. Note that on site soils strata, encountered between test pit locations, may vary from the individual soil profiles presented in the logs. Table 2 —Typical Soil Profiles Soil Horizons • . . Consistency/Relative Depthsil Density Soils 0 to 2 feet Lean Clay with Sand Medium Stiff to Stiff Intermediate 2 to 7.5 feet Sandy Silt/Silty Sand Stiff to Hard/Medium Soils Dense Deeper Soils 7.5 to 9.5 feet Poorly Graded Sand with Gravel Medium Dense 'Calcium carbonate cementation was noted within portions of this horizon. During excavation, test pit sidewalls were generally stable. However, moisture contents will affect wall competency with saturated soils having a tendency to readily slough when under load and unsupported. 4.4 Volatile Organic Scan Soils obtained during on-site activities were not assessed for volatile organic compounds by portable photoionization detector. Samples obtained during our exploration activities exhibited no apparent odors or discoloration typically associated with this type of contamination. Groundwater encountered did not exhibit obvious signs of contamination. 5. SITE HYDROLOGY Existing surface drainage conditions are defined in the General Site Characteristics section. Information provided in this section is limited to observations made at the time of the investigation. Either regional or local ordinances may require information beyond the scope of this report. 5.1 Groundwater During this field investigation, groundwater was encountered in test pit 1 at a depth of approximately 7.5 feet bgs. Atlas has previously performed 5 geotechnical investigations within 0.50 mile of the project site. Information from these investigations has been provided in the table below. Atlas No. B240122g Page15 Copyright©2024 Atlas Technical Consultants �TrT-G7Tdr-W� Table 3— Groundwater Data Approximate Distance Direction from Site GroundwaterDepth from Site (mile) (feet . . ML January 2021 0.15 North 12.3 August 2020 0.22 Northeast 7.3 to 8.9 September 2021 0.38 Southeast 5.3 to 7.8 November 2011 0.40 West 5.0 to 11.2 April 2021 0.50 Northeast 7.8 to 8.2 Furthermore, according to groundwater monitoring data collected by Atlas approximately 0.22 mile to the northeast of the project site from August 2020 to May 2021, groundwater was measured at depths ranging between 4.99 to 8.9 feet bgs. Based on historical data of similarilly developed areas, Atlas believes that groundwater depths have been heavily influenced by the flood irrigation activities have taken place on surrounding agricultural properties. However, the amount of influence the irrigation had on the high groundwater level is unknown. As the area becomes more developed and floor irrigation activities cease, groundwater depths should get deeper with time. Therefore, Atlas recommends that groundwater monitoring be conducted to determine a seasonal groundwater high. ;.2 Soil Infiltration Rates Soil permeability, which is a measure of the ability of a soil to transmit a fluid, was tested in the field. For this report, an estimation of infiltration is also presented using generally recognized values. Typical infiltration rates comprising the generalized soil profile for this study have been provided in the table below. Table 4 — Generalized Soil Infiltration Rates it. FV11(inches per hour) Lean Clay with Sand <2 Sandy Silt 2 to 4* Silty Sand** 4 to 8 Poorly Graded Sand with Gravel** >12 *The presence of cementation/induration may reduce infiltration rates to near zero. **Infiltration into and/or within close proximity to groundwater may reduce infiltration rates to near zero. 5.3 Infiltration Testing Infiltration testing was conducted in general accordance with the Ada County Highway District (ACHD) Policy Manual. The test location was presoaked prior to testing. Pre-soaking increases soil moistures, which allows the tested soils to reach a saturated condition more readily during testing. Saturation of the tested soils is desirable in order to isolate the vertical component of infiltration by inhibiting horizontal seepage during testing. Atlas No. 13240122g Page16 Copyright©2024 Atlas Technical Consultants �lrl—G7T�11 On February 6, 2024, testing was conducted within silty sand sediments at a depth of 5.7 feet bgs in test pit 2. A stabilized infiltration rate of 3.6 inches per hour was achieved during testing. This rate must be reduced as outlined in the Ada County Highway District (ACHD) Policy Manual. Atlas recommends a design infiltration rate of 1.8 inches per hour. The reason for the decreased infiltration rate is to account for long term saturation of the soils and the potential for less permeable soils to settle into the bottom of the infiltration facilities. Atlas recommends that all infiltration facilities be constructed in accordance with the local municipality requirements. 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS Various foundation types have been considered for support of the proposed structures. Two requirements must be met in the design of foundations. First, the applied bearing stress must be less than the ultimate bearing capacity of foundation soils to maintain stability. Second, total and differential settlement must not exceed an amount that will produce an adverse behavior of the superstructure. Allowable settlement is usually exceeded before bearing capacity considerations become important; thus, allowable bearing pressure is normally controlled by settlement considerations. 6.1 Foundation Loading Information Loads of up to 4,000 pounds per lineal foot for wall footings, and column loads of up to 50,000 pounds were assumed for settlement calculations. Total settlement should be limited to approximately 1 inch and differential settlement should be limited to approximately '/2 inch, provided the following design and construction recommendations are observed. 6.2 Foundation Design Recommendations Considering subsurface conditions and the proposed construction, it is recommended that the structure be founded upon conventional spread footings and continuous wall footings. The following recommendations are not specific to the individual structures, but rather should be viewed as guidelines for the subdivision-wide development. Based on data obtained from the site and test results from various laboratory tests performed, Atlas recommends the following guidelines for the net allowable soil bearing capacity: Atlas No. B240122g Page17 Copyright©2024 Atlas Technical Consultants �TrT-G7Tdr-W� Table 5 — Soil Bearing Capacity MW Footings must bear on competent, undisturbed, 1,500lbs/ft2 native lean clay with sand soils, sandy silt soils, or Not Required for Native q , compacted granular structural fill. Existing organics Soil A /3 increase is allowable and fill materials(if encountered)must be completely if the alternative basic removed from below foundation elements.' An load combinations of excavation depth of approximately 0.5 foot bgs 95% for Granular Section 1605.3.2 of the should be anticipated to expose proper bearing Structural Fill 2018 IBC are used in soils.2 design. 'It will be required for Atlas personnel to verify the bearing soil suitability for each structure at the time of construction. 'Depending on the time of year construction takes place,the subgrade soils may be unstable because of high moisture contents. If unstable conditions are encountered,over-excavation and replacement with granular structural fill and/or use of geotextiles may be required. The following sliding frictional coefficient values should be used: 1) 0.35 for footings bearing on native lean clay with sand soils and sandy silt soils and 2) 0.45 for footings bearing on granular structural fill. A passive lateral earth pressure of 300 pounds per square foot per foot (psf/ft) should be used for lean clay with sand soils and a passive pressure of 350 psf/ft should be used for sandy silt soils. For granular structural fill, a passive lateral earth pressure of 496 psf/ft should be used. Footings should be proportioned to meet either the stated soil bearing capacity or the 2018 IBC minimum requirements. Unsuitable soil types encountered at the bottom of footing excavations should be removed and replaced with granular structural fill. Excessively loose or soft areas that are encountered in the footings subgrade will require over-excavation and backfilling with granular structural fill. To minimize the effects of slight differential movement that may occur because of variations in the character of supporting soils and seasonal moisture content, Atlas recommends continuous footings be suitably reinforced to make them as rigid as possible. For frost protection, the bottom of external footings should be 24 inches below finished grade. Foundations must be backfilled in accordance with the Backfill of Walls section. 6.3 Crawl Space Recommendations All residences constructed with crawl spaces should be designed in a manner that will inhibit water in the crawl spaces. Bottom of crawl spaces must be elevated at least 2 feet above seasonal high groundwater elevation. Atlas recommends that roof drains carry stormwater at least 10 feet away from each residence. Grades should be at least 5 percent for a distance of 10 feet away from all residences. In addition, rain gutters should be placed around all sides of residences, and backfill around stem walls should be placed and compacted in a controlled manner. Atlas No. 13240122g Page18 Copyright©2024 Atlas Technical Consultants 6.4 Floor, Patio, and Garage Slab-on-Grade Organic, loose, or obviously compressive materials must be removed prior to placement of concrete floors or floor-supporting fill. In addition, the remaining subgrade should be treated in accordance with guidelines presented in the Earthwork section. Areas of excessive yielding should be excavated and backfilled with granular structural fill or suitable structural fill. Fill used to increase the elevation of the floor slab should consist of granular structural fill and suitable structural fill meeting the requirements detailed in the Structural Fill section. Fill materials must be compacted to a minimum 95 percent of the maximum dry density as determined by ASTM D 1557. A free-draining granular mat should be provided below slabs-on-grade to provide drainage and a uniform and stable bearing surface. This should be a minimum of 4 inches in thickness and compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557. The mat must consist of aggregate base material as specified in the Structural Fill section. A moisture-retarder should be placed beneath floor slabs to minimize potential ground moisture effects on moisture-sensitive floor coverings. The moisture-retarder should be at least 15-mil in thickness and have a permeance of less than 0.01 US perms as determined by ASTM E96. Placement of the moisture-retarder will require special consideration with regard to effects on the slab-on-grade and should adhere to recommendations outlined in the ACI 302.1 R and ASTM E1745 publications. Upon request, Atlas can provide further consultation regarding installation. 7. CONSTRUCTION CONSIDERATIONS 7.1 Earthwork Excessively organic soils, deleterious materials, or disturbed soils generally undergo high volume changes when subjected to loads, which is detrimental to subgrade behavior in the area of pavements, floor slabs, structural fills, and foundations. Mature trees, brush, and thick grasses with associated root systems were noted at the time of our investigation. It is recommended that organic or disturbed soils, if encountered, be removed to depths of 1 foot (minimum), and wasted or stockpiled for later use. However, in areas where trees are/were present, deeper excavation depths should be anticipated. Stripping depths should be adjusted in the field to assure that the entire root zone or disturbed zone or topsoil are removed prior to placement and compaction of fill materials. Exact removal depths should be determined during grading operations by Atlas personnel, and should be based upon subgrade soil type, composition, and firmness or soil stability. If underground storage tanks, underground utilities, wells, or septic systems are discovered during construction activities, they must be decommissioned then removed or abandoned in accordance with governing Federal, State, and local agencies. Excavations developed as the result of such removal must be backfilled with fill materials as defined in the Structural Fill section. Atlas No. B240122g Page19 Copyright©2024 Atlas Technical Consultants Atlas should oversee subgrade conditions (i.e., moisture content) as well as placement and compaction of new fill (if required) after native soils are excavated to design grade. Recommendations for structural fill presented in this report can be used to minimize volume changes and differential settlements that are detrimental to the behavior of footings, pavements, and floor slabs. Sufficient density tests should be performed to properly monitor compaction. 7.2 Grading Positive grades must be maintained surrounding structures and pavements, including exterior slabs. The interface of plant bedding materials and underlying soils should be graded to provide drainage away from site elements. Otherwise, bedding materials may direct water to underlying fine-grained soils, which increases the potential for localized heave. Excessive watering of landscaping should be avoided. If structures are to be tightly clustered, limiting space between two adjacent foundation systems, subsurface drains may be required to alleviate water ponding during short, intense storm events. 7.3 Dry Weather If construction is to be conducted during dry seasonal conditions, many problems associated with soft soils may be avoided. However, some rutting of subgrade soils may be induced by shallow groundwater conditions related to springtime runoff or irrigation activities during late summer through early fall. Solutions to problems associated with soft subgrade soils are outlined in the Soft Subgrade Soils section. Problems may also arise because of lack of moisture in native soils and fill materials at time of placement. This will require the addition of water to achieve near- optimum moisture levels. Low-cohesion soils exposed in excavations may become friable, increasing chances of sloughing or caving. Measures to control excessive dust should be considered as part of the overall health and safety management plan. 7.4 Wet Weather If construction is to be conducted during wet seasonal conditions (commonly from mid-November through May), problems associated with soft soils must be considered as part of the construction plan. During this time of year, fine-grained soils such as silts and clays will become unstable with increased moisture content, and eventually deform or rut. Additionally, constant low temperatures reduce the possibility of drying soils to near optimum conditions. 7.5 Soft Subgrade Soils Shallow fine-grained subgrade soils that are high in moisture content should be expected to pump and rut under construction traffic. During periods of wet weather, construction may become very difficult if not impossible. The following recommendations and options have been included for dealing with soft subgrade conditions: • Track-mounted vehicles should be used to strip the subgrade of root matter and other deleterious debris. Heavy rubber-tired equipment should be prohibited from operating directly on the native subgrade and areas in which fill materials have been placed. Atlas No. B240122g Page110 Copyright©2024 Atlas Technical Consultants Construction traffic should be restricted to designated roadways that do not cross, or cross on a limited basis, proposed roadway or parking areas. • Soft areas can be over-excavated and replaced with granular structural fill. • Construction roadways on soft subgrade soils should consist of a minimum 2-foot thickness of large cobbles of 4 to 6 inches in diameter with sufficient sand and fines to fill voids. Construction entrances should consist of a 6-inch thickness of clean, 2-inch minimum, angular drain-rock and must be a minimum of 10 feet wide and 30 to 50 feet long. During the construction process, top dressing of the entrance may be required for maintenance. • Scarification and aeration of subgrade soils can be employed to reduce the moisture content of wet subgrade soils. After stripping is complete, the exposed subgrade should be ripped or disked to a depth of 1'/2 feet and allowed to air dry for 2 to 4 weeks. Further disking should be performed on a weekly basis to aid the aeration process. • Alternative soil stabilization methods include use of geotextiles, lime, and cement stabilization. Atlas is available to provide recommendations and guidelines at your request. 7.6 Frozen Subgrade Soils Prior to placement of fill materials or foundation elements, frozen subgrade soils must either be allowed to thaw or be stripped to depths that expose non-frozen soils and wasted or stockpiled for later use. Stockpiled materials must be allowed to thaw and return to near-optimal conditions prior to use as fill. The onsite, shallow clayey and silty soils are susceptible to frost heave during freezing temperatures. For exterior flatwork and other structural elements, adequate drainage away from subgrades is critical. Compaction and use of granular structural fill will also help to mitigate the potential for frost heave. Complete removal of frost susceptible soils for the full frost depth, followed by replacement with a non-frost susceptible granular structural fill, can also be used to mitigate the potential for frost heave. Atlas is available to provide further guidance/assistance upon request. 7.7 Structural Fill The following table defines the types of fill material that is suitable for use on the project. Refer to the Fill Placement and Compaction section for recommended placement locations for each fill type listed below. Atlas No. B240122g Page 111 Copyright©2024 Atlas Technical Consultants �TrT-G7T_�. Table 6— Fill Material Criteria Fill Type 0' ISPWC Section 801 for 1-inch, 3-inch, or 6- Granular Structural Fill inch Uncrushed Aggregate and 12 inches ISPWC Section 802 Aggregate Base Aggregate Base ISPWC Section 802 for Type 1 Crushed 12 inches Aggregate Base Structural Subbase ISPWC Section 801 for 3-inch or 6-inch 12 inches Uncrushed Aggregate Suitable Structural Fill Onsite/imported CL, ML, SM, and GM soils 6 inches that are free of organics and debris *Initial loose thickness,prior to compaction. 7.8 Fill Placement and Compaction Requirements for fill material type and compaction effort are dependent on the planned use of the material. The following table specifies material type and compaction requirements based on the placement location of the fill material. Table 7 — Fill Placement and Compaction Requirements Fill Location I . . Foundations Granular Structural Fill 95% of ASTM D1557 Interior Slab-on-Grade Granular Structural Fill or 95% of ASTM D1557 Suitable Structural Fill Top 4 Inches of Interior and Exterior Aggregate Base Material 95% of ASTM D1557 Slab-on-Grade Below Flexible Pavement Subgrade Granular Structural Fill or 95% of ASTM D698 or and Exterior Flatwork Areas Suitable Structural Fill 92% of ASTM D1557 Foundation Wall Backfill* Granular Structural Fill or 95% of ASTM D1557 Suitable Structural Fill Utility Trench Backfill Granular Structural Fill or Per ISPWC Section 306 Suitable Structural Fill *Retaining wall backfill material cannot exceed a maximum particle size of 4-inches. Prior to placement of fill materials, surfaces must be prepared as outlined in the Earthwork section. Fill material must be placed in horizontal lifts not exceeding 6-inches in thickness for fine-grained soils and 12-inches in thickness for granular structural fill, aggregate base material, and subbase material. All fill material must be moisture-conditioned to achieve optimum moisture content prior to compaction. During placement all fill materials must be monitored and tested to confirm compaction requirements have been achieved, as specified above, prior to placement of subsequent lifts. In addition, compacted surfaces must be in a firm and unyielding condition. Atlas personnel should be onsite to verify suitability of subgrade soil conditions, identify whether further work is necessary, and perform in-place moisture density testing. Atlas No. 13240122g Pagel12 Copyright©2024 Atlas Technical Consultants Sufficient density tests should be performed to properly monitor compaction. At a minimum, Atlas recommends one test per lift as follows: • Structures— 1 test every 5,000 square feet • Pavement and Exterior Flatwork Areas — 1 test every 10,000 square feet • Foundation and Retaining Wall Backfill — 1 test every 500 square feet • Utility Trench Backfill — 1 test every 100 linear feet Silty soils require very high moisture contents for compaction, require a long time to dry out if natural moisture contents are too high, and may also be susceptible to frost heave under certain conditions. Therefore, these materials can be quite difficult to work with as moisture content, lift thickness, and compactive effort becomes difficult to control. If silty soil is used for fill, lift thicknesses should not exceed 6 inches (loose), and fill material moisture must be closely monitored at both the working elevation and the elevations of materials already placed. Following placement, the exposed surface must be protected from degradation resulting from construction traffic or subsequent construction. It is anticipated that fine-grained soils will not be suitable for reuse during the wet season. Use of silty soils (GM, SM, and ML) as structural fill below footings is prohibited. For structural fill below footings, areas of compacted backfill must extend outside the perimeter of the footings for a distance equal to the thickness of fill between the bottom of foundation and underlying soils, or 5 feet, whichever is less. If material contains more than 40 percent but less than 50 percent oversize (greater than 3/4-inch) particles, compaction of fill must be confirmed per ISPWC Section 202.3.8.C.3. Material should contain sufficient fines to fill void spaces and must not contain more than 50 percent oversize particles. 7.9 Backfill of Walls Backfill materials must conform to the requirements of structural fill, as defined in this report. For wall heights greater than 2.5 feet, the maximum material size should not exceed 4 inches in diameter. Placing oversized material against rigid surfaces interferes with proper compaction and can induce excessive point loads on walls. Backfill shall not commence until the wall has gained sufficient strength to resist placement and compaction forces. Further, retaining walls above 2.5 feet in height shall be backfilled in a manner that will limit the potential for damage from compaction methods and/or equipment. It is recommended that only small hand-operated compaction equipment be used for compaction of backfill within a horizontal distance equal to the height of the wall, measured from the back face of the wall. Backfill should be compacted in accordance with the specifications in the Fill Placement and Compaction section, except in those areas where it is determined that future settlement is not a concern, such as planter areas. In nonstructural areas, backfill must be compacted to a firm and unyielding condition. Atlas recommends in these areas that the top 12 inches must consist of a low permeability (clay or silt) soil to limit surface water infiltration. Atlas No. B240122g Page113 Copyright©2024 Atlas Technical Consultants Proper grading away from structures is critical. The surface must be graded away from the structure. In addition, Atlas recommends that roof drains carry stormwater at least 10 feet away from the structure. 7.10 Excavations Shallow excavations that do not exceed 4 feet in depth may be constructed with side slopes approaching vertical. Below this depth, it is recommended that slopes be constructed in accordance with Occupational Safety and Health Administration (OSHA) regulations, Section 1926, Subpart P. Based on these regulations, on-site soils are classified as type "C" soil, and as such, excavations within these soils should be constructed at a maximum slope of 1'/2 feet horizontal to 1 foot vertical (11/2:1) for excavations up to 20 feet in height. Excavations in excess of 20 feet will require additional analysis. Note that these slope angles are considered stable for short-term conditions only, and will not be stable for long-term conditions. During the subsurface exploration, test pit sidewalls generally exhibited little indication of collapse. For deep excavations, native granular sediments cannot be expected to remain in position. These materials are prone to failure and may collapse, thereby undermining upper soil layers. This is especially true when excavations approach depths near the water table. Care must be taken to ensure that excavations are properly backfilled in accordance with procedures outlined in this report. 7.11 Groundwater Control Groundwater was encountered during the investigation but is anticipated to be below the depth of most construction. Excavations below the water table will require a dewatering program. Dewatering will be required prior to placement of fill materials. Placement of concrete can be accomplished through water using a tremie. It may be possible to discharge dewatering effluent to remote portions of the site, to a sump, or to a pit. This will essentially recycle effluent, thus eliminating the need to enter into agreements with local drainage authorities. Should the scope of the proposed project change, Atlas should be contacted to provide more detailed groundwater control measures. Special precautions may be required for control of surface runoff and subsurface seepage. It is recommended that runoff be directed away from open excavations. Silty and clayey soils may become soft and pump if subjected to excessive traffic during time of surface runoff. Ponded water in construction areas should be drained through methods such as trenching, sloping, crowning grades, nightly smooth drum rolling, or installing a French drain system. Additionally, temporary or permanent driveway sections should be constructed if extended wet weather is forecasted. Atlas No. B240122g Page 114 Copyright©2024 Atlas Technical Consultants 8. GENERAL COMMENTS Based on the subsurface conditions encountered during this investigation and available information regarding the proposed development, the site is adequate for the planned construction. When plans and specifications are complete, and if significant changes are made in the character or location of the proposed development, consultation with Atlas must be arranged as supplementary recommendations may be required. Suitability of subgrade soils and compaction of fill materials must be verified by Atlas personnel prior to placement of structural elements. Additionally, monitoring and testing should be performed to verify that suitable materials are used for fill and that proper placement and compaction techniques are utilized. Atlas No. B240122g Page115 Copyright©2024 Atlas Technical Consultants � N M"=0 A 9. REFERENCES Ada County Highway District(ACHD) (2017). Ada County Highway District Policy Manual. Garden City, ID: Author. American Association of State Highway and Transportation Officials (AASHTO)(1993).AASHTO Guide for Design of Pavement Structures 1993. Washington D.C.: AASHTO. American Concrete Institute (ACI) (2015). Guide for Concrete Floor and Slab Construction: ACI 302.1 R. Farmington Hills, MI: ACI. American Society of Civil Engineers (2021). ASCE 7 Hazards Tool: Web Interface. [Online] Available: <https://asce7hazardtool.online/> (2023). American Society of Civil Engineers (ASCE) (2017). Minimum Design Loads for Buildings and Other Structures: ASCE/SEI 7-16. Reston, VA: ASCE. American Society for Testing and Materials (ASTM) (2017). Standard Test Method for Materials Finer than 75-um (No. 200) Sieve in Mineral Aggregates by Washing: ASTM C117. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2019). Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates: ASTM C136. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2021). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort: ASTM D698. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2021). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort: ASTM D1557. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2018). Standard Test Methods for Resistance Value (R-Value)and Expansion Pressure of Compacted Soils: ASTM D2844. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM)(2017). Standard Practice for Classification of Soils for Engineering Purposes(Unified Soil Classification System):ASTM D2487.West Conshohocken, PA:ASTM. American Society for Testing and Materials (ASTM)(2017). Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils: ASTM D4318. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2017). Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill Under Concrete Slabs: ASTM E1745. West Conshohocken, PA: ASTM. International Building Code Council (2018). International Building Code. Country Club Hills, IL: Author. Local Highway Technical Assistance Council (LHTAC) (2020). Idaho Standards for Public Works Construction. Boise, ID: Author. Othberg, K. L. and Stanford, L. A., Idaho Geologic Society (1993). Geologic Map of the Boise Valley and Adioining Area, Western Snake River Plain, Idaho. (scale 1:100,000). Boise, ID: Joslyn and Morris. U.S. Department of Labor, Occupational Safety and Health Administration 2( 020). CFR 29, Part 1926, Subpart P Appendix A: Safety and Health Regulations for Construction, Excavations. Washington D.C.: OSHA. Atlas No. B240122g Page116 Copyright©2024 Atlas Technical Consultants APPENDIX I WARRANTY AND LIMITING CONDITIONS Atlas warrants that findings and conclusions contained herein have been formulated in accordance with generally accepted professional engineering practice in the fields of foundation engineering, soil mechanics, and engineering geology only for the site and project described in this report. These engineering methods have been developed to provide the client with information regarding apparent or potential engineering conditions relating to the site within the scope cited above and are necessarily limited to conditions observed at the time of the site visit and research. Field observations and research reported herein are considered sufficient in detail and scope to form a reasonable basis for the purposes cited above. Limitations Due to access constraints, test pits were only advanced in the northern portion of the site. Exclusive Use This report was prepared for exclusive use of the property owner(s), at the time of the report, and their retained design consultants ("Client"). Conclusions and recommendations presented in this report are based on the agreed-upon scope of work outlined in this report together with the Contract for Professional Services between the Client and Atlas Technical Consultants ("Consultant"). Use or misuse of this report, or reliance upon findings hereof, by parties other than the Client is at their own risk. Neither Client nor Consultant make representation of warranty to such other parties as to accuracy or completeness of this report or suitability of its use by such other parties for purposes whatsoever, known or unknown, to Client nor Consultant. Neither Client nor Consultant shall have liability to indemnify or hold harmless third parties for losses incurred by actual or purported use or misuse of this report. No other warranties are implied or expressed. Report Recommendations are Limited and Subject to Misinterpretation There is a distinct possibility that conditions may exist that could not be identified within the scope of the investigation or that were not apparent during our site investigation. Findings of this report are limited to data collected from noted explorations advanced and do not account for unidentified fill zones, unsuitable soil types or conditions, and variability in soil moisture and groundwater conditions. To avoid possible misinterpretations of findings, conclusions, and implications of this report, Atlas should be retained to explain the report contents to other design professionals as well as construction professionals. Atlas No. B240122g Page117 Copyright©2024 Atlas Technical Consultants �lrl—G7T�11 Since actual subsurface conditions on the site can only be verified by earthwork, note that construction recommendations are based on general assumptions from selective observations and selective field exploratory sampling. Upon commencement of construction, such conditions may be identified that require corrective actions, and these required corrective actions may impact the project budget. Therefore, construction recommendations in this report should be considered preliminary, and Atlas should be retained to observe actual subsurface conditions during earthwork construction activities to provide additional construction recommendations as needed. Since geotechnical reports are subject to misinterpretation, do not separate the soil logs from the report. Rather, provide a copy of, or authorize for their use, the complete report to other design professionals or contractors. Locations of exploratory sites referenced within this report should be considered approximate locations only. For more accurate locations, services of a professional land surveyor are recommended. This report is also limited to information available at the time it was prepared. In the event additional information is provided to Atlas following publication of our report, it will be forwarded to the client for evaluation in the form received. Environmental Concerns Comments in this report concerning either onsite conditions or observations, including soil appearances and odors, are provided as general information. These comments are not intended to describe, quantify, or evaluate environmental concerns or situations. Since personnel, skills, procedures, standards, and equipment differ, a geotechnical investigation report is not intended to substitute for a geoenvironmental investigation or a Phase II/III Environmental Site Assessment. If environmental services are needed, Atlas can provide, via a separate contract, those personnel who are trained to investigate and delineate soil and water contamination. Atlas No. B240122g Page118 Copyright©2024 Atlas Technical Consultants Vicinity Map Figure 1 MAP NOTES: N •Delorme Street Atlas m Not to Scale 55 Site Location LEGEND Approximate Site • Location x 3i W USIICK RD E USTIC RDE USTICK RD a rn_a 3 i= rn LU: 1 WGHERRY LH, E FAIRVIEW A SR 55 H WY 5R .5 HWY ��� M�eidian ...- Son _................................w Black Cat Residential Subdivision T—� 4535 North Black Cat Road W FRANK Rl? W F HKtIN RD W FRaNKLIN RQ E FRANKLIN RD F FR.ANKLIN R Meridian,ID N 55 Modified from DeLorme by:GJM LU February 19,2024 aq Drawing:B240122g j{ a 44 3C 46 55 C) 'R E;DUERLAND RD � 2791 S.Victory View Way Phone: (208)376-4748 Boise,ID 83709 Fax: (208)322-6515 Web: oneatlas.com Site Map Figure 2 ® NOTES: N •Not to Scale . . . CANAL a3..`.5 a3.39 s3.39 43.39 25.01 46 1 LEGEND Q Approximate Site Boundary z Q Approximate Atlas Test � Pit Location 8 Q 0' L J LJ 6,396 SF 5,335 SF 4,399 SF 4,996 SF Approximate Atlas Test Pit Location with Piezometer 0 Q TP-2 0 8 � Q U TORANA DRIVE TP 1 U Y ——— ————————— ® n $ m Open Space M 7,794 SF Black Cat Residential Subdivision 4535 North Black Cat Road �} 6 Meridian,ID 7,151 SF 6,175 SF 5.0"9 SF 5,463 Sr Modified by:GJM February 19,2024 Drawing:B240122g 2791 S.Victory View Way Phone: (208)376-4748 Boise,ID 83709 Fax: (208)322-6515 Web: oneatlas.com �TrT-G7T_� APPENDIX IV GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log#: TP-1 Latitude: 43.645909 Date Advanced: February 5, 2024 Longitude: -116.453948 Excavated by: Turn of the Century Homes Depth to Water Table: 7.5 feet bgs Logged by: Gavin Marron, El Total Depth: 9.4 feet bgs Depth Field Description and USCS Soil anad Sample Sample ep r ll • Lab • •s) Sediment Classification • bgs) Test ID ..A1111116 Lean Clay with Sand (CL): Dark brown,slightly moist to moist, medium stiff to very stiff, with 0.0-2.0 fine-grained sand. 1.0-2.0 --Organics encountered to a depth of 0.5 foot bgs. Sandy Silt (ML): Brown, dry to saturated, stiff 2.0-7.5 to hard, with fine to coarse-grained sand. GS 2.0-2.5 2.0-4.5+ A --Weak calcium carbonate cementation encountered from 3.0 to 4.5 feet bgs. Poorly Graded Sand with Gravel (SP): Light 7.5-9.4 brown, saturated, medium dense, with fine to coarse-grained sand, fine to coarse gravel, and 4-inch minus cobbles. Notes:See Site Map for test pit location. Piezometer installed to a depth of 9.4 feet bgs. • M r@MV=VA77--` L 1 I To A 28.0 NP NP 99 98 81 68 58.9 Atlas No. 13240122g Page 121 Copyright©2024 Atlas Technical Consultants �TrT-G7T_�. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log#: TP-2 Latitude: 43.646044 Date Advanced: February 5, 2024 Longitude: -116.454457 Excavated by: Turn of the Century Homes Depth to Water Table: Not Encountered Logged by: Gavin Marron, El Total Depth: 5.7 feet bgs Depth ield Description and USCS Soil and Sample Sample Dept QP Lab bgA e —k s Sediment • • bgs) Test ID Lean Clay with Sand (CL): Dark brown,slightly 0.0-2.2 moist to moist, medium stiff to stiff, with fine- GS 1.5-2.0 1.0-1.5 B grained sand. Sandy Silt (ML): Brown, dry to slightly moist, very stiff to hard, with fine to coarse-grained 2.2-4.0 sand. 3.0-4.5+ --Weak to moderate calcium carbonate cementation encountered from 2.2 to 3.8 feet bgs. Silty Sand (SM): Brown to light brown, slightly 4.0-5.7 moist to moist, medium dense, with fine to coarse-grained sand. Notes:See Site Map for test pit location. Infiltration testing conducted at a depth of 5.7 feet bgs. Lab Test ID oisture LL Sieve Analysis (% Passing) 1 #40 #100 #2001 B 1 24.0 1 35 12 99 97 89 83 77.5 Atlas No. 13240122g Page 122 Copyright©2024 Atlas Technical Consultants �TrT-G7Tdr-W� APPENDIX V GEOTECHNICAL GENERAL NOTES Unified Soil Classification System Major Divisions Symbol Soil Descriptions Gravel & GW Well-graded ravels; ravel/sand mixtures with little or no fines Coarse- Gravelly Soils GP Poorly-graded ravels; ravel/sand mixtures with little or no fines Grained < 50% GM Silty gravels; poorly-graded ravel/sand/silt mixtures Soils < coarse GC Clayey ravels; poorly-graded raded gravel/sand/clay mixtures 50% Y Y 9 p Y-9 9 Y passes Sand & Sandy SW Well-graded sands; ravel) sands with little or no fines No.200 Soils > 50% SP Poorl - raded sands; ravel) sands with little or no fines sieve coarse SM Silt sands; poorly-graded sand/gravel/silt mixtures fraction SC Clayey sands; poorly-graded sand/gravel/clay mixtures Fine- ML Inorganic silts; sandy, gravellyor clayey silts Grained Silts & Clays CL Lean clays; inorganic, gravelly, sandy, or silty, low to medium- Soils > LL < 50 plasticity clays 50% OL Organic, low-plasticity clays and silts passes MH Inorganic, elastic silts; sand ravel) or clayey elastic silts No.200 Silts & Clays CH Fat clays high-plasticity, inorganic clays sieve LL > 50 OH Organic, medium to high-plasticity clays and silts Highly Organic Soils PT Peat, humus, hydric soils with high organic content Coarse-Grained Soils SPT Blow Counts N Description Field Test VeryLoose: <4 D Absence of moisture, d to touch Loose: 4-10 Slightly Moist Damp, but no visible moisture Medium Dense: 10-30 Moist Visible moisture Dense: 30-50 Wet Visible free water Very Dense: > 50 Saturated Soil is usually below water table Fine-Grained Soils SPT Blow Counts N Description Field Test Very Soft: <2 Weak Crumbles or breaks with handling or Soft: 2-4 slight finger pressure Medium Stiff: 4-8 Moderate Crumbles or breaks with Stiff: 8-15 considerable finger pressure Very Stiff: 15-30 Strong Will not crumble or break with finger Hard: > 30 pressure Boulders: > 12 in. GS grab sample Cobbles: 12 to 3 in. LL Liquid Limit Gravel: 3 in. to 5 mm M moisture content Coarse-Grained Sand: 5 to 0.6 mm NP non-plastic Medium-Grained Sand: 0.6 to 0.2 mm PI Plasticity Index Fine-Grained Sand: 0.2 to 0.075 mm Qp penetrometer value, unconfined compressive Silts: 0.075 to 0.005 mm strength, tsf Clays: < 0.005 mm V vane value, ultimate shearing strength, tsf Atlas No. B240122g Page 123 Copyright©2024 Atlas Technical Consultants IMPOPIOnt InfOPM81100 Rhout M 0 Geolechnical-Engineeping SubWhile . . . . . . . . . . . . . .cost overruns, claims, and help. The Geoprofessional Business Association (GBA) will not likely meet the needs of a civil-works constructor or even a has prepared this advisory to help you—assumedly different civil engineer.Because each geotechnical-engineering study a client representative—interpret and apply this is unique,each geotechnical-engineering report is unique,prepared geotechnical-engineering report as effectively as solely for the client. possible. In that way, you can benefit from a lowered Likewise,geotechnical-engineering services are performed for a specific exposure to problems associated with subsurface project and purpose.For example,it is unlikely that a geotechnical- conditions at project sites and development of engineering study for a refrigerated warehouse will be the same as them that,for decades, have been a principal cause one prepared for a parking garage;and a few borings drilled during of construction delays, cost overruns, claims, a preliminary study to evaluate site feasibility will not be adequate to and disputes. If you have questions or want more develop geotechnical design recommendations for the project. information about any of the issues discussed herein, contact your GBA-member geotechnical engineer. Do not rely on this report if your geotechnical engineer prepared it: Active engagement in GBA exposes geotechnical • for a different client; engineers to a wide array of risk-confrontation • for a different project or purpose; techniques that can be of genuine benefit for • for a different site(that may or may not include all or a portion of everyone involved with a construction project. the original site);or before important events occurred at the site or adjacent to it; e.g.,man-made events like construction or environmental Understand the Geotechnical-Engineering Services remediation,or natural events like floods,droughts,earthquakes, Provided for this Report or groundwater fluctuations. Geotechnical-engineering services typically include the planning, collection,interpretation,and analysis of exploratory data from Note,too,the reliability of a geotechnical-engineering report can widely spaced borings and/or test pits.Field data are combined be affected by the passage of time,because of factors like changed with results from laboratory tests of soil and rock samples obtained subsurface conditions;new or modified codes,standards,or from field exploration(if applicable),observations made during site regulations;or new techniques or tools.If you are the least bit uncertain reconnaissance,and historical information to form one or more models about the continued reliability of this report,contact your geotechnical of the expected subsurface conditions beneath the site.Local geology engineer before applying the recommendations in it.A minor amount and alterations of the site surface and subsurface by previous and of additional testing or analysis after the passage of time-if any is proposed construction are also important considerations.Geotechnical required at all-could prevent major problems. engineers apply their engineering training,experience,and judgment to adapt the requirements of the prospective project to the subsurface Read this Report in Full model(s). Estimates are made of the subsurface conditions that Costly problems have occurred because those relying on a geotechnical- will likely be exposed during construction as well as the expected engineering report did not read the report in its entirety.Do not rely on performance of foundations and other structures being planned and/or an executive summary.Do not read selective elements only.Read and affected by construction activities. refer to the report in full. The culmination of these geotechnical-engineering services is typically a You Need to Inform Your Geotechnical Engineer geotechnical-engineering report providing the data obtained,a discussion About Change of the subsurface model(s),the engineering and geologic engineering Your geotechnical engineer considered unique,project-specific factors assessments and analyses made,and the recommendations developed when developing the scope of study behind this report and developing to satisfy the given requirements of the project.These reports may be the confirmation-dependent recommendations the report conveys. titled investigations,explorations,studies,assessments,or evaluations. Typical changes that could erode the reliability of this report include Regardless of the title used,the geotechnical-engineering report is an those that affect: engineering interpretation of the subsurface conditions within the context - the site's size or shape; of the project and does not represent a close examination,systematic inquiry,or thorough investigation of all site and subsurface conditions. the elevation,configuration,location,orientation, function or weight of the proposed structure and Geotechnical-Engineering Services are Performed the desired performance criteria; the composition of the design team;or for Specific Purposes, Persons, and Projects, . project ownership. and At Specific Times Geotechnical engineers structure their services to meet the specific As a general rule,always inform your geotechnical engineer of project needs,goals,and risk management preferences of their clients.A or site changes-even minor ones-and request an assessment of their geotechnical-engineering study conducted for a given civil engineer impact.The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical conspicuously that you've included the material for information purposes engineer was not informed about developments the engineer otherwise only.To avoid misunderstanding,you may also want to note that would have considered. "informational purposes"means constructors have no right to rely on the interpretations,opinions,conclusions,or recommendations in the Most Of the "Findings" Related in This Report report.Be certain that constructors know they may learn about specific Are Professional Opinions project requirements,including options selected from the report,only Before construction begins,geotechnical engineers explore a site's from the design drawings and specifications.Remind constructors subsurface using various sampling and testing procedures.Geotechnical that they may perform their own studies if they want to,and be sure to engineers can observe actual subsurface conditions only at those specific allow enough time to permit them to do so.Only then might you be in locations where sampling and testing is performed.The data derived from a position to give constructors the information available to you,while that sampling and testing were reviewed by your geotechnical engineer, requiring them to at least share some of the financial responsibilities who then applied professional judgement to form opinions about stemming from unanticipated conditions.Conducting prebid and subsurface conditions throughout the site.Actual sitewide-subsurface preconstruction conferences can also be valuable in this respect. conditions may differ-maybe significantly-from those indicated in this report.Confront that risk by retaining your geotechnical engineer Read Responsibility Provisions Closely to serve on the design team through project completion to obtain Some client representatives,design professionals,and constructors do informed guidance quickly,whenever needed. not realize that geotechnical engineering is far less exact than other engineering disciplines.This happens in part because soil and rock on This Report's Recommendations Are project sites are typically heterogeneous and not manufactured materials Confirmation-Dependent with well-defined engineering properties like steel and concrete.That The recommendations included in this report-including any options or lack of understanding has nurtured unrealistic expectations that have alternatives-are confirmation-dependent.In other words,they are not resulted in disappointments,delays,cost overruns,claims,and disputes. final,because the geotechnical engineer who developed them relied heavily To confront that risk,geotechnical engineers commonly include on judgement and opinion to do so.Your geotechnical engineer can finalize explanatory provisions in their reports.Sometimes labeled"limitations,' the recommendations only after observing actual subsurface conditions many of these provisions indicate where geotechnical engineers' exposed during construction.If through observation your geotechnical responsibilities begin and end,to help others recognize their own engineer confirms that the conditions assumed to exist actually do exist, responsibilities and risks.Read these provisions closely.Ask questions. the recommendations can be relied upon,assuming no other changes have Your geotechnical engineer should respond fully and frankly. occurred.The geotechnical engineer who prepared this report cannot assume responsibility or liabilityfor confirmation-dependent recommendations fyou Geoenvironmental Concerns Are Not Covered fail to retain that engineer to perform construction observation. The personnel,equipment,and techniques used to perform an environmental study-e.g.,a"phase-one"or"phase-two"environmental This Report Could Be Misinterpreted site assessment-differ significantly from those used to perform a Other design professionals'misinterpretation of geotechnical- geotechnical-engineering study.For that reason,a geotechnical-engineering engineering reports has resulted in costly problems.Confront that risk report does not usually provide environmental findings,conclusions,or by having your geotechnical engineer serve as a continuing member of recommendations;e.g.,about the likelihood of encountering underground the design team,to: storage tanks or regulated contaminants.Unanticipated subsurface • confer with other design-team members; environmental problems have led to project failures.If you have not • help develop specifications; obtained your own environmental information about the project site, review pertinent elements of other design professionals'plans and ask your geotechnical consultant for a recommendation on how to find specifications;and environmental risk-management guidance. • be available whenever geotechnical-engineering guidance is needed. Obtain Professional Assistance to Deal with You should also confront the risk of constructors misinterpreting this Moisture Infiltration and Mold report.Do so by retaining your geotechnical engineer to participate in While your geotechnical engineer may have addressed groundwater, prebid and preconstruction conferences and to perform construction- water infiltration,or similar issues in this report,the engineer's phase observations. services were not designed,conducted,or intended to prevent migration of moisture-including water vapor-from the soil Give Constructors a Complete Report and Guidance through building slabs and walls and into the building interior,where Some owners and design professionals mistakenly believe they can shift it can cause mold growth and material-performance deficiencies. unanticipated-subsurface-conditions liability to constructors by limiting Accordingly,proper implementation of the geotechnical engineer's the information they provide for bid preparation.To help prevent recommendations will not of itself be sufficient to prevent the costly,contentious problems this practice has caused,include the moisture infiltration.Confront the risk of moisture infiltration by complete geotechnical-engineering report,along with any attachments including building-envelope or mold specialists on the design team. or appendices,with your contract documents,but be certain to note Geotechnical engineers are not building-envelope or mold specialists. 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