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PZ - GEOTECH Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 1 Michael Weaver 4000 North McDermott Road Meridian, Idaho 83642 April 20, 2019 Page 1 of 20 File 19174-A Re: Geotechnical Recommendation Report 400 North McDermott Road Meridian, Idaho Michael: As per your authorization, in August 2018, SITE personnel logged and sampled eight test pits at your property located at 4000 North McDermott Road in Meridian, Idaho. It is assumed that the proposed subdivision will include ACHD right of ways and lots for single-family residences. The test pits were excavated on a property consisting of a single parcel. The property is located on the east side of North McDermott Road one half mile south on McMillan Road in Meridian, Idaho. Tax parcel number S-0433234140, 7.0 acres, and the provided address were confirmed on the Ada County Assessor's website. Based upon our research, observations, and laboratory test results, the site is acceptable for the proposed residential subdivision development. Recommendat ions for construction are included herein. We appreciate this opportunity to be of service. When appropriate, we would like to discuss continuing our role as geotechnical consultant during construction. Please contact our office if additional information o r services are required. Respectfully submitted, Bob J. Arnold, PE SITE Consulting, LLC Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 2 INVESTIGATION SITE observed the excavation of eight test pits at locations intended to provide full coverage of the subject property. Test pit logs and an aerial photo with test pit locations are included in the Appendix. Locations are based upon field observation and handheld GPS and have not been survey located. In general, surface soils consist of a lean clay or low plasticity silt with sand. In two of eight test pits silty sands were the near surface soils. No fat clay soil was observed or sampled. Gravel and sand soil was contacted at an average depth of 4 -5 feet but were as shallow as one foot in test pit #TP-8. These sand and gravel soils extend to depths greater than our test pits which were typically terminated just below the depth where groundwater was encountered. Monitoring wells were installed in all eight test pits for future groundwater monitoring. Test pit logs were generated and are included in the Appendix. Additional research was performed searching for well logs within the section where the subject property is located. Well logs for Section 33, township 4 north, range 1 west were reviewed on the IDWR website. A total of four well logs were found and have been included in the Appendix. One is for the subject property. Three shallow wells (110-120 feet deep) located south, east, and north of the subject property indicate the static groundwater elevation is 6 to 20 feet deep. The onsite well is 400 feet deep and the well log indicates artesian flow. The current property owner and client confirm the onsite well is artesian. It was also confirmed that the McFadden Drain, which flows along the north and east boundary, is sourced by two artesian wells, one in the southeast corner of the subject property and one offsite to the east. Groundwater monitoring for this irrigation season has been started and should continue monthly until October. Property owner should contact SITE and authorize continuing groundwater measurements. It is noted that this is a preliminary investigation prepared to determine if development as a residential subdivision is feasible. ACHD and Meridian City have rules concerning test pit placement in relation to proposed stormwater injection facilities. Additional test pits may be required to comply with these rules and should be anticipated. SITE should be contacted by a retained civil engineer to confirm that this report will be acceptable to all reviewing agencies. Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 3 DESIGN & CONSTRUCTION RECOMMENDATIONS General Earthwork It is anticipated that this project will be very similar to the Jump Creek Subdivision development to the south of this property on the west side of McDermott Road. ACHD right of ways, lots for single family residences and storm water disposal by shallow injection or surface detention methods. All non-organic soil encountered on the property is acceptable for filling of building o r residential lots. Therefore, materials removed from the street sections and subsurface stormwater storage areas can be utilized as structural fill. The only exception is the surface soil that contains excessive organic materials. Removal of the majority of the organic materials will require grubbing of approximately four to six inches of surface soils but deeper areas can be expected. Deeper grubbing may be required in areas along the property boundaries and surface ditches where small trees and bushes ar e present. The depth of grubbing is to be adjusted in the field to ensure that organic materials are properly removed from beneath future pavements and structural fills. If used for fill, the surface soils will require moisture contents within two percent of optimum for effective compaction. These soils will easily become too wet or too dry for effective compaction. These soils can be expected to perform poorly if wet and subjected to rubber tired equipment. If construction is to occur during wet weather or wet surface soil conditions, low-pressure, tracked mounted construction equipment is recommended. Rutting caused by the contactor using rubber-tired equipment on a wet subgrade can be expected and should be repaired at contractor expense. This information is to be supplied to earthwork contractors prior to construction. Structural fills less than three feet deep are to be compacted to 95 % of the maximum dry density by ASTM D698, Standard Proctor. For deeper fills, and fill intended to contain re-routed ditches or canals or storm water runoff, all fill material and the subgrade surface are to be compacted to 98 % of the maximum dry density as determined by ASTM D698, Standard Proctor. Structural fill is to extend laterally outside foundations a distance equal to the depth of structural fill. Structural fill should be placed in uniform, thin horizontal lifts, moisture conditioned as necessary, and compacted to the above requirements. Compaction of fine-grained soils will greatly reduce the infiltration rate for surface water, effectively sealing the ground surface and crawlspace floors to percolation. Ripping of yard areas prior to placement of topsoil and fine grading may improve percolation in individual back yards. Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 4 Inspection & Testing A qualified engineer or his representative should monitor fill placement to ensure the work is performed in accordance with these recommendations. Testing should be performed in accordance with ASTM Test Methods D3017-88 and D2922-91 (nuclear densometer). Field nuclear moisture - density testing shall be performed on each lift of compacted fill for every 2500 square feet of surface area. It is noted that structural fill can pass compaction tests and still be unacceptable if pumping, rutting, or deflecting under vehicle or foot traffic. It should be anticipated that the Meridian City Engineering and / or Building Department will request these test results prior to or at the time of home / building construction. 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. Demolition It is assumed that the existing homes and outbuildings will be demolished. After demolition, inspection is to confirm the removal of all foundation and slab on grade concrete. Any encountered septic tanks and wells are to be abandoned as per IDWR and IDEQ requirements. Excavations caused by demolition, grubbing of ditches, or over excavation of soft or wet areas are to be backfilled with structural fill. All subgrade soils present in the test pits can be used as structural fill on building lots and within right of ways. If encountered, blending clay surface soils with onsite or imported sand and gravels will improve surface drainage. Excavations Shallow excavations and trenches that do not exceed four 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 standing open without support over any extended period of time can be expected to be quite variable. This information is provided for planning purposes. It is our opinion that maintaini ng 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, and federal requirements. Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 5 Pavement Section Given the lean clay surface soils, ACHD’s standard pavement section for residential right of ways is appropriate for this development. Material Layer Residential Street TI=6 Asphaltic Concrete 2.5” Base Coarse (¾” minus) 4.0” Subbase (Pitrun) 14.0” It is noted that it is common for the local jurisdiction to require a standard design or to match existing pavement section when working on collector or arterials. Therefore, ACHD (or ITD) should be consulted about construction within the North McDermott Road right of way. Foundation System The proposed single-family residences may be supported on conventional, continuous, and isolated pad foundations founded upon the native soils or upon structural fill extending to these native soils. Based upon proper placement and compaction of structural fill, bearing pressures of up to 1500 psf are allowed. A one -third increase in allowable bearing capacity is permitted when transient loads such as wind or seismic are included. Either crawlspaces or slab on grade floors are acceptable. Foundations outside crawlspaces or basements are to be properly waterproofed to prevent surface water from flowing between stem and basement walls and foundations. Foundations drains are encouraged on lots with structural fill placed below foundations. Roof drainage is not to flow through foundation drains. Infiltration pits for drainage are to be at least fifteen feet from and must extend to three feet below the nearest foundation. Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 6 Slab on Grade Concrete Care must be taken so that all excavations below concrete floors and slabs are properly backfilled in accordance with the structural fill recommendations outlined herein. This is very critical where a slab will extend over utility trenches or retaining wal l backfill. Trenches and wall backfill areas are to be filled in lifts and benched each lift so that fill is not placed against a vertical soil face greater than three feet tall. Testing is to confirm that compaction has been achieved. Areas of excessive yielding should be excavated and backfilled with structural fill. Slab on grade floors, sidewalks and pavements should be placed atop a minimum of 0.5 feet of granular structural fill materials. Any additional fill used to increase the elevation of slab on grade concrete should meet the requirement for structural fill. After construction of the building pad, a six-inch granular mat should be provided below the floor slabs. The mat should consist of sand or sand - gravel mixture with non-plastic fines. The material should all pass a 3/4-inch sieve and should contain less than seven percent passing the # 200 sieve. The mat shall be compacted to the requirement for structural fill. All slabs should be suitably reinforced to make them as rigid as possible. Proper joints should be provided at the junctions of the slab and foundation system so that independent movement can occur without causing damage. Storm Water It is recommended that storm runoff be directed away from all open excavations and not be allowed to puddle on subgrade soils. Due to the presence of shallow groundwater, disposal of groundwater in surface detention or retention ponds or constructed lakes or ponds is recommended. If water is to percolate through the surface soils a percolation rate of P= 1.0 inch/hour is recommended for design. If drainage facilities are extended to free draining materials (and backfilled if needed with additional free materials) a percolation rate of P = 6 inch/hour is to be used for design. Extension to free draining conditions is to be confirmed at the time of construction. Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 7 Underground Utilities Test pits revealed that deep utilities trenches may require dewatering. It is not anticipated that large excavators will experience any difficulties excavating the onsite materials. No bedrock formation was encountered on the subject property. Sloughing of trenches can be expected when working below the groundwater surface. Contractor Inspections This report has been prepared with the intent to provide specific design information to the developer and the civil engineering consultant. It is not intended to act as any contractors “Due Diligence” or subsurface inspection prior to estimating construction costs or actual construction. Contractors that estimate material quantities, material depths, or the volume and depth to groundwater based solely upon this re port do so at their own risk. It is recommended that such values be confirmed as close as possible to the time / date of construction at specific locations as detailed in design plans. Monitoring wells installed by SITE are the property of the landowner an d with their permission can be used by contactors to determine the depth to groundwater at the time of construction. Wells should not be destroyed or removed without contacting SITE and the property owner for approval. General Comments After the plans and specifications for construction are completed, it is recommended that this consultant be provided the opportunity to review the final design and specifications. This review will confirm that the earthwork recommendations have been properly interpreted and implemented. At that time, it may be necessary to submit supplementary recommendations. This review is a part of this service and will not result in additional invoicing unless additional research and recommendations are needed. Appendix Follows Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 8 APPENDIX Aerial Photo with Test Pit Location Test Pits Logs (8) Soil Log Legend / Abbreviations and Acronyms Project & Adjacent Well Logs (4) Groundwater Monitoring Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 9 Google Earth Aerial Photo Locations by handheld GPS Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 10 TEST PIT LOG Test Pit: TP-1 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: NE Corner, West Half Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Moist, Firm, Sandy, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-5.0 Brown, Moist, Firm, Sandy, Clay 5.0-8.0 Brown/Tan, Moist, Firm, Sand, Gravel, Cobble 8.0 Bottom of Excavation @ 8.0 Ground Water Encountered @ 8.0 Monitoring Well Installed TEST PIT LOG Test Pit: TP-2 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: SW corner of Property Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Dry, Firm, Sandy, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-5.0 Brown, Moist, Firm, Sticky, Sandy, Lean CLAY (CL) 3.0 100 98 97 90 79 68.5 16.5 33 15 CL 5.0-6.0 Tan, Wet, Firm, Silty/Clayey, SAND (SM-SC) 5.5 100 99 98 92 45 21 15.2 16.4 24 8 ML-CL 6.0-8.0 Brown/Tan, Wet, Firm, Sand, Gravel, Cobble 8.0 Bottom of Excavation @ 8.0 Ground Water Encountered @ 8.0 Monitoring Well Installed Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 11 TEST PIT LOG Test Pit: TP-3 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: NW Corner of Property Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Dry, Firm, Sandy Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-5.0 Brown, Moist, Firm, Sticky, Silty, SAND (SM) 3.0 100 99 95 90 82.4 20.8 31 8 ML 5.0-8.0 Brown/Tan, Moist, Firm, Sand, Gravel, Cobble 8.0 Bottom of Excavation @ 8.0 Ground Water Encountered @ 8.0 Monitoring Well Installed TEST PIT LOG Test Pit: TP-4 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: SE Corner, West Half Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Moist, Firm, Sandy, Clay With Root Zone / Organic Layer 6-8” 1.0-2.0 Brown, Moist, Firm, Sandy, Clay 2.0-5.0 Brown/Tan, Moist, Firm, Silty, SAND (SM) 3.0 100 99 72 54 39 31 25.1 21.7 NP NP ML 5.0-9.0 Tan, Moist, Firm, Sand, Gravel, Cobble 9.0 Bottom of Excavation @ 9.0 Ground Water Encountered @ 9.0 Monitoring Well Installed Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 12 TEST PIT LOG Test Pit: TP-5 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: NNE Corner of Property Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Moist, Firm, Sandy, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-4.0 Brown, Moist, Firm, Sandy, Lean, CLAY (CL) 3.0 100 98 95 76 67 62.5 10.3 28 9 CL 4.0-6.0 Brown/Tan, Wet, Firm, Sand, Gravel, Cobble 6.0 Bottom of Excavation @ 6.0 Ground Water Encountered @ 6.0 Monitoring Well Installed TEST PIT LOG Test Pit: TP-6 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: NEE Corner of Property Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Dry, Firm, Sand, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-3.0 Brown, Dry, Firm, Sandy, Clay/Silt 3.0-16.0 Brown/Tan, Moist, Firm, Sand, Gravel, Cobble 16.0 Bottom of Excavation @ 16.0 Ground Water Encountered @ 16.0 Monitoring Well Installed Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 13 TEST PIT LOG Test Pit: TP-7 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: SE Corner of Property Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Dry, Firm, Sand, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-4.0 Brown, Dry, Firm, Sand, Clay/Silt 3.0-6.0 Brown/Tan, Moist, Firm, Sand, Gravel, Cobble 6.0 Bottom of Excavation @ 6.0 Ground Water Encountered @ 6.0 Monitoring Well Installed TEST PIT LOG Test Pit: TP-8 File #: 19174-A Client: Michael Weaver Date Excavated: 8/2/18 Project: 4000 North McDermott Excavated By: Top Grade Location: Center, East Half Logged By: J. Meusch, PM - SITE DEPTH SOILS DESCRIPTION (feet) 3/4" 1/2" 3/8” # 4 # 10 # 40 # 100 #200 %M LL PI Fines 0.0-1.0 Brown, Dry, Firm, Sand, Clay/Silt With Root Zone / Organic Layer 6-8” 1.0-7.0 Brown, Moist, Firm, Sand, Clay/Silt 7.0-9.0 Brown/Tan, Wet, Firm, Sand, Gravel, Cobble 9.0 Bottom of Excavation @ 9.0 Ground Water Encountered @ 9.0 Monitoring Well Installed Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 14 SOIL LOG LEGEND UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM STANDARD TEST METHOD D 2487 FOR CLASSIFICATION OF SOIL FOR ENGINEERING PURPOSES) MAJOR DIVISIONS TYPICAL DESCRIPTIONS GRAVEL & < 5% - #200 GW Well-graded gravel, gravel-sand mixture, little or no fines. GRAVELLY GP Poorly-graded gravel, gravel sand mixture, little or no fines COARSE SOILS 5-12% -#200 GM Silty gravel, gravel-sand-silt mixtures GRAINED <50% - #4 >12% - #200 GC Clayey gravel, gravel-sand-clay mixtures SOILS SAND & < 5% - #200 SW Well-graded sand, gravelly sand, little or no fines. < 50% - #200 SANDY SP Poorly-graded sand, gravelly sand, little or no fines SOILS >12% - #200 SM Silty sand, sand-silt mixtures > 50% - # 4 SC Clayey sand, sand-clay mixtures SILTS & INORGANIC ML Inorganic silt and very fine sand, rock flour, silty or clayey fine sand or clayey silt with slight plasticity FINE CLAYS CL Lean clay-low to medium plasticity, gravelly, sandy, or silty clay GRAINED LL < 50% ORGANIC OL Organic silt and organic silty clay of low plasticity SOILS SILTS & INORGANIC MH Elastic silt, micaceous or diatomaceous fine sand or silty soil. > 50% - #200 CLAYS CH Fat clay - high plasticity LL > 50% 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 IBC International Building Code ISPWC Idaho Standard for Public Works Construction HMA Hot-Mix Asphalt NP Non-Plastic PCC Portland Cement Concrete TP Test Pit USCS Unified Soil Classification System pcf Pounds per Cubic Foot psf Pounds per Square Foot tsf Tons per Square Foot psf/f Pounds per Square Foot / Foot Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 15 ADJACENT WELL LOGS Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 16 Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 17 Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 18 Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 19 Post Office Box 190537 - Boise, Idaho 83719 site.consulting.idaho@gmail.com - 208-440-6276 Geotechnical Services / Soil Testing & Inspection Services Pa g e 20 GROUNDWATER MONITORING Nothing Follows TP #1 2 3 4 5 6 7 8 Hub Elevation Casing Height 2.58 3.00 3.67 3.08 4.00 4.58 3.67 4.83 Casing Elevation 3/13/2019 9.0 10.0 9.2 12.1 9.5 9.5 9.9 12.5 WaterDepth 6.4 7.0 5.5 9.0 5.5 4.9 6.2 7.7 4/10/2018 9.0 10.0 9.3 12.0 9.3 9.7 9.8 12.5 WaterDepth 6.4 7.0 5.6 8.9 5.3 5.1 6.1 7.7 ACHD required Groundwater reported as elevations and not depth. Therefore a surveyor must be retained to locate the the wells both horizontally and vertically.