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HomeMy WebLinkAboutWPO201800043 Certified Engineer's Report 2018-06-01 Geotechnical Engineering Report Liberty Hall Dam, 2798 Liberty Hall Lane Albemarle County, Virginia Underhill Project No. 18006.00 June 1, 2018 unclerhill ENGINEERING geotechnical geothermal I geoconstructic underhill ENGINEERING geotechnical I geothermal I geoconstruction June 1, 2018 Mr. Kip Mumaw Ecosystem Services 209 2nd Street SW,Suite 2A Charlottesville,VA 22903 Subject: Geotechnical Engineering Report, Liberty Hall Dam,2798 Liberty Hall Lane, Albemarle County,Virginia (Underhill Engineering Project No. 18006.00) Dear Mr. Mumaw: Underhill Engineering, LLC(Underhill) is pleased to present this Geotechnical Engineering Report for the above referenced project. Underhill provided these geotechnical engineering services in accordance with your authorization to proceed with services on January 15, 2018. Thank you for the opportunity to provide our services. If you have any questions or require additional information, please do not hesitate to contact us. Sincerely, UNDERHILL ENGINEERING,LLC Susan E. Ray, EEIT,GIT 4,44•N•46- Staff Geotechnical Engineer .'o,p,.LTH O O_ �O 'P O.Cf .S'IiOPFiER r , ' , , .,7 U W1RI RUSTPR rY O. Chris opher Webster, PE Lic.No.019910 Principal .4515 _, , T:434.531.2565 327 W.Main Street,Suite 2,Charlottesville,VA 22903 underhillengineering.com r Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia GEOTECHNICAL ENGINEERING REPORT TABLE OF CONTENTS 1.0 Executive Summary 1 2.0 Scope of Services 2 3.0 Site Information 2 3.1 Site Description 2 3.2 Proposed Construction 2 4.0 Field Services 2 4.1 Subsurface Exploration Program 2 5.0 Site Geology, Subsurface Conditions, and Soil Laboratory Testing 3 5.1 Site Geology 3 5.2 Generalized Subsurface Stratigraphy 3 5.3 Groundwater 3 5.4 Laboratory Testing 4 6.0 Geotechnical Recommendations 5 6.1 Discussion 5 6.2 Earthwork 5 6.2.1 Stripping and Preparation 5 6.2.2 Core and Cut-off Trench Fill 5 6.2.3 Shell Fill 6 6.2.4 Rock Excavation 6 7.0 Design Recommendations 7 7.1 Core and Seepage Cut-Off Trench Construction 7 7.2 Shell Construction 7 7.3 Drainage/Filter Construction 8 7.4 Spillway Design Recommendations 8 8.0 Construction Considerations 9 8.1 Site Grading and Earthwork 9 8.2 Temporary Dewatering 9 8.3 Engineering Services During Construction 9 9.0 General Specification Recommendations 10 10.0 Limitations 11 References Figures: Figure 1,Site Vicinity Map Figure 2, Location Plan Appendices: Appendix A: Subsurface Exploration Data Appendix B: Soil Laboratory Test Results Project 18006.00/June 1,2018 i Underhill Engineering,LLC Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 1.0 Executive Summary This report presents the results of the subsurface exploration,soil laboratory testing,and geotechnical engineering analysis for the project site. A summary of our recommendations follows: • The four borings drilled at the existing dam site and nine test pits excavated at the borrow site revealed a range of materials,suitable for construction of a new earthen dam. The materials were categorized into Strata A, B1, B2,and C,and were classified by their suitability for use in the construction of the dam. • Stratum A Recent Alluvium was encountered in Borings B-2, B-3,and B-4 consisting of sandy lean clay to clayey sand,clayey gravel, and silty sand to depths of 2 to 5.5 feet below the surface. Stratum A were found to be wet,very soft and loose, and contained concentrations of organic matter. Therefore,the Stratum A soils were considered unsuitable for the construction of the dam and should be undercut to expose the underlying residuum. The Stratum A soils may be used as grading fill in non-structural areas of the site. • Stratum B1 was encountered in the test pits and in the borings with the except of B-4. Stratum B1 consisted of clayey to silty sand and (low plasticity)sandy silt. This Stratum was encountered to a depth of up to 6 feet below the surface. Stratum B1 soils are of generally medium to high strength when compacted and are considered suitable for use in the construction of the shell of the dam. • Stratum B2 was encountered in the test pits to depths of 0.7 to 6 feet below the surface. Stratum B2 consisted of sandy elastic silt and sandy lean clay. These soils are of medium to high plasticity with medium strength and are considered suitable for use as cut-off trench and core fill for the dam. These soils may also be used as compacted structural fill for the shell if excess Stratum B2 soils are available. • Stratum C was classified as a disintegrated rock containing mica and was encountered in Borings B-2, B-3,and B-4 to depths of 7 to 9.7 feet below the surface. Excavated Stratum C material is considered suitable for the construction of the shell of the dam provided this material can be broken down to particle size not greater than three inches in diameter. Underhill is providing this Executive Summary solely as an overview of our findings and recommendations. Any party that relies of this report must read the full report since the Executive Summary omits several details, including those that are important to the proper interpretation and application of the report. Project 18006.00/June 1,2018 1 Underhill Engineering,LLC I t Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 2.0 Scope of Services Underhill's July 14, 2017 proposal defines the scope of services for this project. The scope is limited to the Geotechnical Engineering Services as presented therein. 3.0 Site Information 3.1 Site Description The project is located east of 2798 Liberty Hall Lane,which is located north of Garth Road/Virginia 614 in northwest of the City of Charlottesville, in Albemarle County,Virginia. A Site Vicinity Map is included as Figure 1. The site as it currently exists is situated in a forested area and accessed by a two-wheeled trodden path from 2798 Liberty Hall Lane. The site is east of the home now under construction on the property and is northwest of a large clearing. The proposed dam site is on the north side of the existing impoundment and is presently occupied by an existing a 1950's era concrete dam,which is now failing. The existing dam is approximately seven feet high and 120 feet long and includes a stream diversion wall. Ecosystem Services provided Underhill with the topographic data for the site. The topographic data indicates that the site has high relief varying from approximately 450 to 540 feet,which includes the clearing to the northwest and the clearing to the southeast. 3.2 Proposed Construction Proposed for construction is an earthen dam to replace the failing concrete dam. The proposed construction includes removal of the old dam, dredging the existing pond,and rerouting the stream, and construction of the new earthen dam and associated spillway structure. Staging areas and temporary access road are anticipated for the construction equipment mobilization. 4.0 Field Services 4.1 Subsurface Exploration Program Underhill's geotechnical engineering study included a subsurface exploration program consisting of four mechanically-advanced test borings drilled along the proposed earthen dam alignment. The subsurface exploration program was performed to evaluate the subsurface conditions and develop generalized stratigraphy at the test locations. The evaluation of the soils'characteristics included visual and limited laboratory classification and evaluation of density or stiffness based on the results of the Standard Penetration Test(SPT)obtained (with Corrected N (N60)values where appropriate). Underhill's drilling subcontractor,Ayers and Ayers, Inc., drilled the test borings on March 7, 2018, under the observation of Underhill's Engineer. The approximate locations of the test boring are presented in Figure 2,following the text of this report. Test boring logs are included in Appendix A. Soil samples retrieved from the subsurface exploration program will be held for 45 days unless the Client requests other disposition. Project 18006.00/June 1,2018 2 Underhill Engineering,LLC Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 5.0 Site Geology,Subsurface Conditions,and Soil Laboratory Testing 5.1 Site Geology Underhill's review of the available geologic data, including the state geologic map of Virginia, indicates the site geology consists of Proterozoic porphyoblastic biotite-plagioclase augen gneiss. The site's overburden consists of residuum (commonly clays and low plasticity silts) overlying the parent material. Recent Alluvium is present above the residuum along the existing stream channels as indicated by the subsurface exploration. 5.2 Generalized Subsurface Stratigraphy Underhill developed the following generalized subsurface stratigraphy based on the results of the subsurface exploration program,the soil laboratory test results, and review of the local geology: Topsoil: • Topsoil was not present in Boring B-1 but was up to 0.5 feet thick in the other boring locations. Root mat was also encountered within the topsoil layer. Stratum Al (Recent Alluvium): • Stratum A consists of moist to wet clayey gravel (GC)to sandy lean clay (CL). • These soils contain varying concentrations of root fragments and other organic matter. • Borings B-2 to B-4 revealed Stratum A from 2 to 6 feet below the ground surface. • Standard Penetration Test(SPT) Corrected N (N60)values= zero (Weight of Hammer, WHO)to 18. • Natural Water Content(W)value=26.5%(for the selected sample tested). Stratum B1 (Silty Sand and Low-Plasticity Silt Residuum): • Stratum B consists of medium dense silty sand (SM)to sandy silt(ML). • These soils contain varying amounts of mica. • Boring B-4 did not reveal Stratum B1. Boring B-1 revealed Stratum B1 until termination at 25.5 feet below the ground surface. • SPT(N60) =7 to 75. • Natural Water Content Average (Wavg) =21.4% (from seven samples tested). Stratum C(Disintegrated Rock Residuum): • Stratum C consists of disintegrated rock residuum. • These soils contain varying amounts of mica. • SPT(N60) =0 to 75. 5.3 Groundwater Groundwater was not encountered during drilling of the four boreholes. Groundwater was measured at about EL 442 and 451 (feet) at drilling completion before the augers were removed in Borings B-1 and B- 2, respectively. Groundwater was measured at about EL 446 and 456 after the augers were removed in B-1 and B-3, respectively. Fluctuations in the hydrostatic water table should be expected to occur over time, depending on variations in precipitation, surface runoff, pumping, flooding, evaporation, stream levels, and similar factors. Project 18006.00/June 1,2018 3 Underhill Engineering,LLC Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 5.4 Laboratory Testing Selected specimens were retrieved from the subsurface exploration program for soil laboratory testing. Soil laboratory testing assigned by Underhill consisted of the following: • Twelve natural water contents(ASTM D2216), • Two Atterberg Limits tests(ASTM D4318), • Two gradation tests(after ASTM D422/D1140), • One standard proctor(ASTM D698), and • One hydraulic conductivity test(ASTM D5084). The soil laboratory testing was performed to aid in the classification of the soils encountered in the subsurface exploration program,and to provide index test values for use in the development of design recommendations. Laboratory testing was performed by Underhill's subconsultant laboratory, GeoTesting Express, and reviewed and interpreted by Underhill. Natural water content values of specimens tested are presented in the respective logs and summarized above in Section 5.2. A summary of the soil laboratory test results is included in Appendix B. Soil laboratory index testing indicated the following for the combined sample retrieved from Test Pits TP-1 and TP-3: • ASTM Classification: ELASTIC SILT with sand (MH) • AASHTO Classification: A-7-5 (clayey soils) • Liquid Limit value: 55 • Plasticity Index(PI)values: 21 • The natural water content values of these specimens were near to 1 percent wet of their Plastic Limit value. • Permeability at 5 psi effective stress calculated by Hydraulic Conductivity: 3.1 x 10-6 centimeters/second Soil laboratory index testing indicated the following for specimens retrieved from Test Pit TP-9: • ASTM Classification: Lean CLAY with sand (CL) • AASHTO Classification:A-7-6(clayey soils) • Liquid Limit value: 47 • Plasticity Index(PI)values: 22 • The natural water content values of these specimens were near to 3 percent wet of their Plastic Limit value. Project 18006.00/June 1,2018 4 Underhill Engineering,LLC 1 Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 6.0 Geotechnical Recommendations 6.1 Discussion Underhill evaluated a solid core earthen dam for the project site and considered the non-organic on-site residual soil generally suited for use in the construction of the core and cut off trench (Stratum B2)and the shell (Strata B1, B2,and C). The embankment should have upstream and downstream slopes of 3H:1V for stability considerations. Underhill also recommends a cut-off trench constructed of low permeability clay material (Stratum B2)above rock grades to reduce the potential for seepage and piping through the foundation soils. Four borings were drilled along the proposed dam alignment and revealed Stratum A Recent Alluvium, Strata B1 and B2 soil Residuum,and Stratum C Disintegrated Rock. The Recent Alluvium,designated as Stratum A and occurring to a depth of 2 to 5.5 feet below the surface, is considered unsuitable for the construction of the dam. Stratum B1, consisting of silty to clayey sand and sandy silt, is suitable for use in the shell of the dam. Stratum C Disintegrated Rock may also be used as shell material provided it can be broken down to a maximum particle size not greater than three inches in diameter. Stratum B2, which consists of the higher plasticity sandy elastic silt,should be reserved for use in the core and cut off trench. The nine test pits excavated at the borrow site generally consisted of residuum categorized as Stratum B1 or B2. The borrow area soils were observed to have in situ moisture contents typically 10 percent wet of the anticipated optimum moisture content(OMC). The ideal moisture for dam construction is 2% wet of optimum. Therefore, spreading, aerating, and possibly disking may be needed to achieve the moisture content suitable for compaction depending upon the time of year of earthwork construction. Note also that drying may not be possible during wetter times of the year(e.g. late Fall,Winter,early Spring). 6.2 Earthwork 6.2.1 Stripping and Preparation The contractor should remove the existing dam in its entirety, but may remove it in phases if that is advantageous to assist in sequencing of the construction of the new dam. Before any fill placement or undercutting below design subgrade level,the Geotechnical Engineer should evaluate the soils for suitability. Evaluation techniques may include probing with a penetrometer,observing proofrolling by a loaded dump truck or other loaded, rubber tire wheeled equipment, drilling hand augers,observing test pits, or a combination of these methods. The contractor should excavate areas deemed unsuitable by the Geotechnical Engineer and replace these areas with suitable fill. In preparation for stockpiling material for use on the new dam construction,the borrow area should be stripped of vegetation and topsoil. Based on the measurements of existing topsoil, a stripping depth of at least 6 inches is recommended for preliminary planning purposes. The material from the borrow area should be stockpiled on site and protected with plastic sheeting to reduce infiltration from precipitation. 6.2.2 Core and Cut-off Trench Fill Material used as compacted structural fill for the construction of the core and cut-off trench should classify as ML, MH,or CL according to ASTM D-2487. Based on the subsurface exploration and soil Project 18006.00/June 1,2018 5 Underhill Engineering,LLC i' Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia laboratory testing,Stratum B2 meets the criteria for the core and cut-off trench fill. Stratum B2 was encountered in each of the nine test pits excavated in the borrow area. Underhill recommends placing compacted structural fill in maximum 8-inch thick horizontal, loose lifts and compacting each lift to at least 95 percent of maximum dry density in accordance with ASTM D-698, Standard Proctor. Water content of fill for the core and cut-off trench construction at the time of compaction should be in the range between the Optimum Moisture Cotent(OMC)and 4 percent wet of the OMC. A sheepsfoot roller should be used to compact both the cut-off trench and the core to limit horizontal seepage paths between lifts. Alternatively,the surface of each lift should be scarified prior to additional lift placements. Gradation Tests (ASTM D-422),Atterberg Limits(ASTM D-4318), and a Standard Proctor Test(ASTM D- 698)were performed on bulk samples from the proposed borrow area (TP1/TP3, and TP9). Appendix B presents the results of the laboratory tests. The gradation test indicated that the samples TP1/TP3 and TP9 contained 71 and 78 percent fines, respectively. The fines from each sample were tested to obtain their Atterberg Limits,which indicated generally low plasticity with Liquid Limit values ranging from 47 to 55,and Plasticity Index values of between 21 and 22. The soils meet the requirements of for core and cut-off trench fill as indicated above. The contractor may use the non-organic portions of material excavated in the borrow areas. The use of the material in the borrow area as compacted core and cut-of trench fill will depend on the moisture content and the ability of the contractor to prevent contamination of the material with organic matter during the stripping and stockpiling operations. Stratum B2 samples had moisture content values in the range from 28.2 to 35.8 percent. The Standard Proctor test conducted on sample TP1/TP3 indicated an optimum moisture of 25.4 percent. Therefore, Underhill anticipates that the borrow area soils will require some moisture conditioning to achieve recommended compaction. 6.2.3 Shell Fill Material used as compacted structural fill for the construction of the core and cut-off trench should classify as ML,CL, SC, or SM according to ASTM D-2487. Based on the subsurface exploration and soil laboratory testing,Strata B1 and B2 meet the criteria for the shell fill. Stratum C also meets the criteria for use as shell fill, but should be broken down to a particle size not greater than three inches in diameter before placement. Stratums B1 and B2 were encountered in the nine test pits,while Stratum C was encountered in Borings B-2, B-3, and B-4. The Contractor should place compacted structural fill in maximum 8-inch thick horizontal, loose lifts and compact each lift to at least 95 percent of maximum dry density in accordance with ASTM D-698, Standard Proctor. Water content of fill for the shell construction at the time of compaction should be not more than 2 percent dry of optimum or 2 percent wet of optimum. As is recommended for the core fill, a sheepsfoot roller should be used for compaction to limit horizontal seepage paths between lifts. Alternatively,the surface of each lift should be scarified prior to additional lift placement. 6.2.4 Rock Excavation The subsurface exploration indicated disintegrated rock on the project site. Rock outcrops were also observed in the area of the project during site visits. Based on the observations and the proposed Project 18006.00/June 1,2018 6 Underhill Engineering,LLC r Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia grades, Underhill anticipates that the contractor may need to employ rock excavation techniques to remove these materials. The subsurface exploration indicated hard disintegrated rock in the areas of B-2, B-3, and B-4. Disintegrated rock is defined as residual material with Standard Penetration Tests Corrected N Values (N60) between 60 blows per foot and refusal. Refusal is a penetration resistance of 100 blows per two inches or less. Table 1 indicates the estimated elevations of the disintegrated rock at the boring locations for the project. Table 1—Anticipated Disintegrated Rock Grades Test Boring Estimated Elevation of Disintegrated Rock(feet) B-2 451 B-3 446 B-4 454 7.0 Design Recommendations 7.1 Core and Seepage Cut-Off Trench Construction As indicated in Section 7.1, Underhill recommends the use of a core within the dam and a cut-off trench to limit seepage by providing a discontinuous seepage plane between the fill and the foundation. The core and seepage cut-off trench should be located beneath the centerline of the dam. The cut-off trench should be excavated to rock. Underhill anticipates that the cut-off trench will extend to approximately 10 feet at its deepest point. Note that a cut-off trench is not required where competent rock is exposed at foundation grade. The seepage cut-off trench should extend upward into the embankment,sloping as required for stability, but no steeper than 1H:1V maximum,forming the core of the dam. The trench invert should slope at 1H:1V to alleviate friction build up along the contact with the embankment fill material. 7.2 Shell Construction The embankment geometry considered for the analysis was provided by Ecosystems Services. Upstream and downstream embankment slopes of 3H:1V with a foundation of residual soils over hard disintegrated rock were adopted. Strength parameters for the embankment fill were based on correlations with soil classifications. Based on the parameters,the proposed 3H:1V slope angles should provide a suitable factor of safety against slope failure. The embankment fill will rest on natural residual soils in most areas. Where the embankment fill rests on an exposed rock surface,the Geotechnical Engineer should evaluate the surface prior to placement of fill. Project 18006.00/June 1,2018 7 Underhill Engineering,LLC r , Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 7.3 Drainage/Filter Construction To reduce the potential for the development of uplift pressure beneath the downstream slope,the construction of a filter blanket beneath the downstream slope is recommended. The drain should extend laterally along the toe for the entire width of the floodplain. The Geotechnical Engineer should evaluate the extent of the drain in the field. The drain should be constructed with clean sand conforming to ASTM C-33 standards. The sand drain should be constructed to envelop a stone collector zone, 12 to 18 inches in thickness, using VDOT No.89 stone. The design should include a rigid perforated pipe bedded in the stone collector zone about one-third to one-fourth of the distance from the downstream toe to the crest. At least 6 inches of stone should surround the collector pipe. The pipe should be perforated so that the stone cannot enter the pipe. At least two lateral outlet pipes should be installed for the drain system within the floodplain. Collector and outlet pipes should be HDPE or PVC(SDR-35 or similar). The downstream end of the drain system should terminate into a toe drain as described below. A toe drain should be provided beneath the downstream toe of the embankment to control the outlet of seepage through the embankment and maintain adequate downstream slope integrity and stability. The toe drain should extend laterally along the toe for the entire width of the floodplain and up each abutment to an elevation of 5 feet below permanent pool level. The toe drain should consist of a trench parallel to the toe of the slope,approximately 4 feet deep or a minimum of three feet into dense residual soils. In areas where alluvial soils are removed, exposing the rock surface,the toe drain should extend to rock. The trench should be a minimum of 4 feet wide at the bottom with sides sloped at 1H:1V. The drain should consist of VDOT No. 78 aggregate surrounded by drainage geotextile(Mirafi 140 N or equivalent). A 4-inch I.D. slotted,corrugated HDPE pipe should be placed in the aggregate backfill, on a bedding of 6 inches of stone above the bottom of the trench. The drain should be constructed parallel to and 5 feet upstream from the downstream toe. The contractor should be prepared to provide dewatering during installation of the toe drain and ensure stability of trench slopes in accordance with Virginia VOSH regulations.The sand/stone drains should be located a minimum depth of two feet from the ground surface to promote grass growth. 7.4 Spillway Design Recommendations To accommodate the design storm flows, an open channel principal spillway is proposed to replace the existing channel on the east side of the proposed dam structure. The boring logs indicate that the spillway excavation will be founded in residual soils and partially weathered (disintegrated) rock. Based on Underhill's experience with earth cut spillways in similar conditions, surface erosion over time should be anticipated to influence the cut slope stability. Subsequently, protective erosion control measures should be included (e.g. a cast-in-place concrete wall/chute) separating the open channel spillway from the earthen embankment fill to reduce the erosion potential. A small diameter ductile iron conduit is anticipated to be constructed to lower the water level when needed. This conduit should be constructed with gasketed, mechanical joints and supported on a concrete cradle (or backfilled with flowable fill if the conduit is less than 8 inches in diameter). The conduit should be cambered to account for settlement of the embankment materials. To further reduce Project 18006.00/June 1,2018 8 Underhill Engineering,LLC 1 Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia piping erosion potential along the conduit,the conduit should be connected to the drainage system (i.e. filter blanket) described in Section 7.3. 8.0 Construction Considerations 8.1 Site Grading and Earthwork The on-site soils are susceptible to moisture changes,will be easily disturbed, and difficult to compact under wet weather conditions. Drying and reworking of the soils are likely to be difficult and may not be possible during wet winter months. During periods of extended wet weather, project planning should consider that these soils cannot be effectively dried and should consider the need for importing select fill materials. Therefore, it will be important that the earthwork phases of this project be performed during the warmer,drier times of the year to limit the potential for disturbance of on-site soils and reduce the amount of fill imported to the site. Traffic on stripped or undercut subgrades should be limited to reduce disturbance of underlying soils. The Contractor should provide site drainage to maintain subgrades free of water and to avoid saturation and disturbance of the subgrade soils before placing compacted structural fill or moisture barrier material.This will be important during all phases of the construction work.The Contractor should be responsible for reworking of subgrades and compacted structural fill that were initially considered suitable but were later disturbed by equipment and/or weather. Although not revealed by our subsurface exploration,earthwork activities may encounter groundwater during excavation to grade, especially during times of heavy precipitation.Therefore,the Contractor may need to provide temporary dewatering such as trenching and/or pumping from sumps to control the surface and/or groundwater. 8.2 Temporary Dewatering During the demolition of the existing dam as well as the construction of the new dam,the contractor will likely encounter water seepage. Local trenching and sump pumping will likely be adequate for localized dewatering. Sumps should extend at least 5 feet below the base of the excavation or to rock. The contractor may need to use larger pumps to dewater the excavation for larger water volumes. The contractor should be made responsible for dewatering methods. 8.3 Engineering Services During Construction The engineering recommendations provided in this report are based on the information obtained from the subsurface exploration and laboratory testing. However,conditions on the site may vary between the discrete locations observed at the time of the subsurface exploration. The nature and extent of variations between borings and between test pits may not become evident until during construction. To account for this variability, Underhill should provide professional observation and testing of subsurface conditions revealed during construction as an extension of our design phase engineering services.These services will also help in evaluating the Contractor's conformance with the plans and specifications. Project 18006.00/June 1,2018 9 Underhill Engineering,LLC , Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia The Geotechnical Engineer should observe the installation of the embankment,spillway structures, conduit and bedding,and filter drains to evaluate whether the construction is carried out in accordance with the intent of the recommendations. Proper construction of the concrete cradle, backfilling of the diversion conduit, and construction of the downstream filter are especially critical as the zone along the conduit is the most likely place for the development of seepage through the embankment. Improper construction of the diversion conduit could possibly result in excessive leakage and/or failure of the embankment. 9.0 General Specification Recommendations The Project Construction Documents should include an allowance to account for possible additional costs that may be required to construct the dam,as recommended in this report. Costs may be incurred for a variety of reasons including variation of soil between borings,greater than anticipated unsuitable soils, need for borrow fill material,wet on-site soils,obstructions, rock excavation,temporary dewatering,etc. Add/deduct unit prices in the construction contract are recommended so adjustments can be made for the actual work performed for the following: • Scarifying and drying wet and/or loose subgrade soils. • Undercutting unsuitable soils and replacement with compacted structural fill. The project documents should indicate the Contractor's responsibility for providing adequate site drainage during construction. Inadequate drainage can lead to disturbance of soils by construction traffic and increased volume of undercut. The project documents should also delegate the Contractor responsible for reworking of subgrades and compacted fill initially considered suitable, but later disturbed by equipment and/or weather. This report may be made available to prospective bidders for informational purposes.The project specifications are recommended contain the following statement: Underhill Engineering, LLC has prepared this geotechnical engineering report for this project. This report is for informational purposes only and is not part of the contract documents. The opinions expressed represent the Geotechnical Engineer's interpretation of the subsurface conditions, tests, and the results of analyses conducted.Should the data contained in this report not be adequate for the Contractor's purposes, the Contractor may make, before bidding, independent exploration, tests and analyses. This report may be examined by bidders at the office of the Owner, or copies may be obtained from the Owner at nominal charge. Additional data and reports prepared by others that could have an impact upon the Contractor's bid should also be made available to prospective bidders for informational purposes. Project 18006.00/June 1,2018 10 Underhill Engineering,LLC f . Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia 10.0 Limitations The analyses and recommendations submitted in this report study are based on the information revealed by the subsurface exploration.This report attempts to provide for normal contingencies, but the possibility remains that unexpected conditions may be encountered during construction. Underhill has prepared this study to aid in the evaluation of the site. It is intended for use concerning this specific project and should not be used for other purposes. The recommendations provided within are based on information on the site and proposed construction as described in this report. Changes regarding existing conditions or changes in locations or grades should be brought to Underhill's attention so that recommendations can be modified as needed. Underhill has endeavored to complete the services identified herein in a manner consistent with that level of care and skill ordinarily exercised by members of the profession currently practicing in the same locality and under similar conditions as this project. No other representation, express or implied, is included or intended, and no warranty or guarantee is included or intended in this report,or other instrument of service. Project 18006.00/June 1,2018 11 Underhill Engineering,LLC 1 • Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia References Evans, Nick H. and Rader, E.K. (1993) Geologic Map of Virginia,Virginia Division of Mineral Resources, Charlottesville, Virginia. Project 18006.00/June 1,2018 i Underhill Engineering,LLC i Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia Figures Figure 1, Site Vicinity Map Figure 2, Location Plan Project 18006.00/June 1,2018 ii Underhill Engineering,LLC FIGURE 1 .. SITE 2798 Liberty Hall Ln aid 1 • V ' N..4 °Wingate Farm k• f r Y a O m �q '4 ! Y Z ..i. .0' R- o 614 r. m Garth-Rd to r 2018 Google •, 17 �rilia Image from Google Earth No Scale Liberty Hall Dam Site Vicinity Map underhill ENGINtLFONG 2798 Liberty Hall Lane geotechnical geothermal geoconstruction Project 18006 Albemarle County,Virginia 6 a FIGURE 2:LOCATION PLAN Project 18006 Liberty Hall Dam,2798 Liberty Hall Lane Albemarle County,Virginia ----- -------:"';77-71 i ,_„--.•::::-_-__;,"' -,N,",'..---:::::----'„-'•••-' - , .. )S:::"',',: : ''‘.7-: ::.,,,ii"-::-Zi:--;:::...:::-:'-f---.'"-:;%'//%0----'' '''•'''' -''''' % ''/" - i ' A s ''• N\\;\\ --"---'‘'''*--'\:',\:-.:717":-.. .:S,Z-_-.-!----.:--.:-.:-=-7.--_-:_:_'-'2"..7 -1-4,..-:':::::.?/'i--'''r.' ' "--1.. -/-. ;2/ t (,,, ..., uq,..,i \ . .. '--..._..__-----, \ '•-..„:"---......::-----:.:-.=:-....":-;-_-:Z,..7:7:.-_--::::-._-:._.-.--7-:.,_.-'‹,..,,..-... ,,,SOIL BORING (--,,...„ , -L., --„_ --- , 0. •-,,,,,- , •ELEV=480.71'„ -.,sc.-; 1„ 4., ...f" r--t '‘, t„, 1 '.\-;.•":.,N „ „.....,,,.\\,,,,, •:":*,,. , ',„ 4-4 „........---- ----------:::" --' - „ , „— `,.. ''‘,'‘. t „1"? ' \--'? \ ',.. •.--.• •- - • --" T.- -- - -.., ,,,--. , -,k • -:‘,--'‘. \ \\,,s,:•••,'.• -, 1 , , „--- -"I — LOCATION 0.F DAM,FAILURE j,.. ,..,)_ ‘,s'-- .-,''\:-.--„,, •.,._ , , -,„ , / EXISTING EARTHEN DAM ...... CONCRETE WALL„ '‘ ,;: \ ' ' .' s.. '.- -.-,.,..._, -- ----/.-------.....-;,--, t."----x--;-_-",;,,- , .,-,..\-:,...,:•-•,\--‘,:s„:-,,,'-\\.`k.,;,,,,;',,.:,,,, N.„, . . , , \:\ , )4..„._ k•-.../ , / \,..,- p.-- _:,-" '-,,..x.''',.C3,_, 11:-......?„7.SOIL BORING ----,-;.,. .,,`:S°V-r"*5-'i-f,-.7%''''''''' *V, '-•-•-",' \ ....s*, \ \\ \ ,NN. `.. ', 1 .' .., , t N '''\\ , ' . 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'" .... , .----....„ ',„ N„ N., // ''4„.2, ''‘....\-2.."`*."•-•,'"---..„"Q."--'.",'Sc-,-"--::::::;:-..---.'4."-t:',„\.•NiNk.„,,I.::::--„,,,--_, '''.'''-. "-.., ---.... -,,, -/,,, ;I II I'-,,'1,' ....---;-:ELEV=457.84' /1- \2''''',\--",...--''''',"*--\- *\‘*",\•."-------•**,,\\..\%"--\%„:',-",‘,-:‘,;:,:':::-.''', -'---. 'I'---_---..'---....',/4' ,/'. ;f 1 it.% '' -....::::-=''---------- ..,--3 .... , , , 1 TT, ..k ;,, ''... --_-.....-----__,...... -„,..,..--..,„, I„, •:"' '' ..*-, •• .. - -.. ‘ t ( (! 0\ \-. -•-•,--::-., -•-..• --''',,c -2:-----/ ,',1• ,%'(''`'.i7,r'--.'''. s' ' '--. --- "*".--', -- .1.,\,2\ ‘ '1 \ •\'''s,',END OF EXISTING CONCRETE WALL--------_-_---.:.-:_,,,/:_--->t- , ,......,. .., , „..,..., --, , , , ,_, .... ,.._4..,,_ STREAM **---- ---.- *". ' s2*----N.,,‘s'- ',, \-- •1 %` \til., \' I I ll!''''''I. '-------,"---izz-z---2----'" -----, • 4,:.* -I.", I.-' \ \ \ SOIL BORING ti"--zzi'---:-;.;:".---------------------------------------- '-, -----,-'•„:"2-,`"4,\ 1 ,\ ' '.-,V.‘ )\TA t\%\ • ,' , "-- Ev=480.78' '(1 1 1'i/i)\1111A 1"--^-- '''...-.--------'- '' '' C... Ns.- '' %• "--,, :- --ii,------------------------------------------------ ,, \s..,•,\\ -1 i li i'r,'•f , , 1 ) ,L. _ ,- ‘..sr.,--,„-...:: „::-.... ,-z---:,.:..,---;:_-,-,:!.......-------- -::::----II::::-------_. .,N.:-',„'",'------,\\‘• 1 ',I‘\-- 1.1 I li 1 i I/ ,,./ t ( .... .: '---.7::-------" -- ,---..... ::::-:- L.'-....,, , 4--:;:::-,-;;;;.z.F.:: :::::.-.:;'---:,--","-:::---,-=-'7_.... \,•,....:-......:-._ i:, ; / I ' •- -:::,----1.4c,--„J-,'----, \N ''-:,-:::-.---=::.--'•,'70-....:%::-.1:"./;--z;-;--::-..::-.-.>"'",-----:::.--`....-.---,---7.--,----:-- - i1 7 I i 1--..--------•...1 -__ 1/1, III,) 3 —,.......ir,... 1 ,...'. -„,:‘ '., \‘1\ i)1Y111 -4-4.1.-.1. ''',".------:;:- -, s-‘si- I I/ \ .1:1tpihr, , l',61%."17%\-,\,\si.w 11 il , •-.-..<::\ ‘ \\ ., (k 1 I (Vigil Oty''., I , ( .'‘...,-"‘t--,-,`,/,)--',.-,"---,,'\ \ "?, '',t) 1 \..\ ) ' I, ,,,"--,----.."!:-.•;.,.-././7-/-----':,../-",-'7,--------":,_,----.".:_:11:-.-----,_:::---:: I‘1 )211ill/111)t } '' \ ...,..-----)//,:';;•:,;--%'t-, „1\\\•-\ ) c( fv , ,, /7-- ,:-'-:,::"";::::::::;:----::1'2-2-:::::::::.,::_:,::::. ) I 0 j :,,I I, //Alb;I I I 1 't, i' ' 1,1,;/ , •., s,*,-\\ \1 1 I , / 1„1,/ ,.•....-":„..--' --_,y-r-_,_-:_:;_______...--:_::::::::-: ; I i 1,:' !//j! 11/3 1 Miff/f I) I, :is_ 1,../..„,..,-' ___PA-'i "\--..., 'N, ‘‘,, '1, '1 I I I\ 1J ,,_ LEGEND . '-' •---"\- _,-'i/ ,: \I i; , ', • ....----- ..'„,./. // -.• E --- •.) (10 APPROXIMATE TEST BORING LOCATION „--.._,1i,,• ilv•-• ..,,'...../1 1-7.?" 1)\ I, -\. . •-/'-''''''',/-,iill\-.... 1‘ I. 1, \ .1 1 I 1/t:'/,'‘,..' ,.,..-'-'i „,"--,/. .,,,....":,/.-',-,,, „,,„,...............„,,_ Scale:No scale Note:Base drawing provided by Ecosystem Services underhill ENGINEERING gava 1 gm.*i twwiwamatw• i Liberty Hall Dam,2798 Liberty Hall Lane Appendix A Albemarle County,Virginia Subsurface Exploration Data Test Boring Logs, B-1 through B-4 Test Pit Logs,TP-1 through TP-9 Note: Elevations at the test boring locations were provided by Ecosystem Services. Elevations at the test pit locations are based on information from Google Earth. The elevations and locations should be considered no more accurate than the means and methods used to obtain them. Project 18006.00/June 1,2018 iii Underhill Engineering,LLC Project: 2798 Liberty Hall Lane Boring No. B-1 underhill ENGINEERING Charlottesville,Albemarle County,Virginia Project No. 18006 geotechnical j geothermal geoconstruction Drilling Contractor: Ayers and Ayers, Inc. Drill Rig Type:CME-45 Foreman: M. White Method: 2-1/4"HSA Logged By: C.Webster Groundwater Observations Started: 3/7/18 Date Time Depth Casing Caved(feet) Finished: 3/7/18 Encountered 03/07/18 --- Location: See Location Plan Completion 03/07/18 10:48 AM 19.0 --- --- GS ELEV:460.8' Casing Pulled 03/07/18 11:00 AM 14.5 --- 0 ca > E o Soil Group Name: modifier,color,moisture, 7 p density/consistency,grain size,other descriptors N a L tD t) 3 v Remarks y co E N O Rock Description:modifier,color,hardness/degree of 0 cocutt. concentration,bedding and joint characteristics,solutions,void conditions 0-1.5 n 4+4+9 Fine to medium sandy SILT, contains mica, ML drilled on Jeep moist- red, brown, and tan trail,W=20.9% 2.0-3.5 r 6+18+16 2.5 Fine to coarse SILTY SAND, contains mica, SM RESIDUUM moist-white and tan W=31.1% 4.0-5.5 n 5+3+6 do, red-brown, white, and tan 7.0-8.5 n 14+14+14 7.0 Fine sandy SILT, contains mica, ML High moist-tan concentration of mica, W=27.4% 9.0-10.5 n B1 6+7+10 12.0 Fine to medium SILTY SAND, contains mica, SM moist-tan, white, and red brown 13.5-15.0 r 17+25+24 77 19.0-20.5 n 14+14+10 17.0 Fine to coarse SANDY SILT, contains mica, ML w= 18.6% moist-tan, white, and red-brown 24.0-25.5 n 23+21+19 22.0 Fine to medium SILTY SAND, contains mica, SM moist-white and tan Test Boring Terminated @ 25.5' Key: Boring Log: Sheet 1 of 1 n Standard Penetration Split Spoon Sampler(SPT) Bulk/Bag Sample 1 Stabilized Groundwater Mil Shelby Tube Groundwater at time of drilling NOTES: 1. Boring elevations obtained from Ecosystem Services 2. Boring backfilled upon completion Project: Proposed Dam, 2798 Liberty Hall Ln Boring No. B-2 Underhill ENGINEERING Albemarle County,Virginia Project No. 18006 E��F,e�,��,i y�o���,st��a���� Drilling Contractor: Ayers and Ayers, Inc. Drill Rig Type:CME-45 Foreman: M. White Method: 2-1/4" HSA Logged By: C.Webster Groundwater Observations Started: 3/7/18 Date Time Depth (ft) Casing Caved (feet) Finished: 3/7/18 Encountered 03/07/18 --- Dry Location: See Location Plan Completion 03/07/18 11:55 AM 7.0 GS ELEV: 457.6' Casing Pulled 03/07/18 12:22 PM --- o. E G Soil Group Name: modifier,color,moisture, 3 O density/consistency,grain size,other descriptors U n U Remarks - a 3 N E N o 0 Rock Description: modifier,color, hardness/degree of ja- 0 fn m concentration, bedding and joint characteristics,solutions,void conditions Forest material, root mat, and topsoil 0-1.5 r A 1 - 1/12" 0.5 Fine to coarse SILTY SAND, SM RECENT wet-dark-gray and dark-brown ALLUVIUM 2.0-3.5 n 11+12+17 2.0 Fine to medium SILTY SAND, contains mica, SM moist-white and tan RESIDUUM 4.0-5.5 r B1 5+16+12 do white, tan, and brown W = 17.3% 7.0-8.0 n 32+68 7.0 DISINTEGRATED ROCK, contains mica, moist- brown and gray 9.0-10.5 n 22+43+57/4.5" C 13.5-15.0 n 25+25+48 Test Boring Terminated @ 15.0' Key: Boring Log: Sheet 1 of 1 n Standard Penetration Split Spoon Sampler(SPT) Xi Bulk/ Bag Sample 1 Stabilized Groundwater IIIII Shelby Tube V Groundwater at time of drilling NOTES: 1. Boring elevations obtained from Ecosystem Services 2. Boring backfilled upon completion Project: Proposed Dam,2798 Liberty Hall Ln Boring No. B-3 Underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical geothermal geoconstruction Drilling Contractor: Ayers and Ayers, Inc. Drill Rig Type:CME-45 Foreman: M. White Method: 2-1/4"HSA Logged By: C.Webster Groundwater Observations Started: 3/7/18 Date Time Depth(ft) Casing Caved(feet) Finished: 3/7/18 Encountered 03/07/18 Location: See Location Plan Completion 03/07/18 12:35 PM Dry GS ELEV:455.6' Casing Pulled 03/07/18 12:38 PM 9.7 d O —. £ 0c Oa 0 Soil Group Name:modifier,color,moisture, 3 O density/consistency,grain size,other descriptors cn s m co u v Remarks Z. a 3 U) O E N O O Rock Description:modifier,color,hardness/degree of 0 CO coconcentration,bedding and joint characteristics,solutions,void conditions Root mat and topsoil 0-1.5 V 3+3+2 0.3 Fine to coarse sandy LEAN CLAY, trace gravel, CL RECENT A cont. root frag, moist-red-brown &dark gray ALLUVIUM 2.0-3.5 Q 4+7+6 2.5 Fine to coarse CLAYEY GRAVEL with sand, GC W=26.4% wet- red and white 4.0-5.5 r 4+4+5 4.0 Fine to medium SILTY SAND, contains mica, SM W= 13.4% moist-red and gray B1 7.0-8.5 or 13+16+12 7.0 Fine to medium sandy SILT, contains mica, ML RESIDUUM _ V moist-tan, red-brown, and white 9.0-10.5 Q 4+23+77 - 9.7 DISINTEGRATED ROCK, contains mica, moist-tan, red-brown, and white C 13.5-13.9 r 100/4.5" do, brown Test Boring Terminated @ 13.9' Key: Boring Log: Sheet 1 of 1 n Standard Penetration Split Spoon Sampler(SPT) Bulk/Bag Sample 1 Stabilized Groundwater IIIII Shelby Tube Groundwater at time of drilling NOTES: 1. Boring elevations obtained from Ecosystem Services 2. Boring backfilled upon completion r c Project: Proposed Dam, 2798 Liberty Hall Ln Boring No. B-4 Underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical',geothermal geoconstruction Drilling Contractor: Ayers and Ayers, Inc. Drill Rig Type:CME-45 Foreman: M. White Method: 2-1/4" HSA Logged By: C.Webster Groundwater Observations Started: 3/7/18 Date Time Depth(ft) Casing Caved(feet) Finished: 3/7/18 Encountered 03/07/18 -- Location: See Location Plan Completion 03/07/18 1:41 PM Dry GS ELEV:460.7' Casing Pulled 03/07/18 1:47 PM Dry m rn .—. 15 EL E C C Soil Group Name: modifier,color,moisture, density/consistency,grain size,other descriptors to r -• Qwcoi v Remarks ' I- 3 N E o 0 Rock Description_modifier,color,hardness/degree of G m concentration,bedding and joint characteristics,solutions,void conditions Root mat and topsoil 0-1.5 n 4+4+7 0.5 Fine to coarse sandy LEAN CLAY, trace gravel, CL cont. root frag, moist-red-brown &dark-gray RECENT 2.0-3.5 n A 11+10+14 2.0 Fine to coarse CLAYEY GRAVEL with sand, GC ALLUVIUM moist-brown and white 4.0-5.5 n 5+6+12 4.0 Fine to coarse CLAYEY SAND with gravel, SC w=21.2% moist-mottled brown and gray relict structure 7.0-8.5 n 35+49+16/2" 7.0 DISINTEGRATED ROCK, contains mica RESIDUUM moist- red brown, tan, and gray 9.0-10.5 Q 45+45+10/0.5"do, brown, gray, and tan C Augers grinding below 11.5' 13.5-13.8 0 100/3.5" do, brown Test Boring Terminated @ 13.8' Key: Boring Log: Sheet 1 of 1 n Standard Penetration Split Spoon Sampler(SPT) NI Bulk/Bag Sample 1 Stabilized Groundwater IIIII Shelby Tube V Groundwater at time of drilling NOTES: 1. Boring elevations obtained from Ecosystem Services 2. Boring backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. 1 P-1 underhill ENGINEERING Albemarle County, Virginia Project No. 18006 geotechnical,geothermal geoconstruction Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713574 Date Time Depth UTM (17S) Northing: 4221114 Encountered 03/06/18 Dry GS ELEV: 525 Completion 03/06/18 9:30 AM Dry aa) E N Soil Group Name: modifier, color, moisture, c.) Remarks cn density/consistency, grain size, other descriptors Topsoil 1.0 1.0 Medium stiff, fine to coarse sandy ELASTIC MH SILT, moist- red RESIDUUM 2.0 B2 w = 34.5% 3.0 4.0 4.0 Medium dense, fine to coarse CLAYEY SAND, SC moist- red-brown Difficult 5.0 B1 excavation 5.5 Dense, fine to coarse SILTY SAND, SM Saprolite 6.0 moist- yellow-brown and dark-brown 7.0 Test Pit Terminated at 6.0 FT 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-2 underhill ENGINEERING Albemarle County, Virginia Project No. 18006 geotechnical geothermal geoconstruction Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713597 Date Time Depth UTM (17S) Northing: 4221090 Encountered 03/06/18 --- Dry GS ELEV: 533 Completion 03/06/18 9:50 AM Dry a� E Y ,^ cn o Soil Group_Name: modifier, color, moisture, Remarks c. density/consistency, grain size, other descriptors Topsoil 1.0 1.0 Medium stiff, fine to medium sandy ELASTIC MH B2 SILT, moist- red RESIDUUM 2.0 2.0 Dense, fine to coarse SILTY SAND, SM Difficult B1 moist-dark-brown and tan excavation 3.0 4.0 Test Pit Terminated at 3.7 FT 5.0 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-3 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical geothermal geoconstruction Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713598_ Date Time Depth UTM (17S) Northing: 4221095 Encountered 03/06/18 --- Dry GS ELEV: 530 Completion 03/06/18 10:20 AM Dry aa) r oc soil Group Name: modifier, color, moisture, U Remarks density/consistency, grain size, other descriptors Topsoil 1.0 0.9 Medium stiff, fine to medium sandy ELASTIC MH SILT, moist- red 2.0 B2 RESIDUUM 3.0 W = 35.8% 4.0 5.0 6.0 B1 6.0 Dense, fine SILTY SAND, SM moist-yellow-brown 7.0 Test Pit Terminated at 6.5 FT 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-4 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnicalI geothermal geoconstruction Contractor: Montebello Logged By: C.Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713584 Date Time Depth UTM (17S) Northing: 4221085 Encountered 03/06/18 Dry GS ELEV: 527 Completion 03/06/18 11:00 AM Dry aa, E a Soil Group Name: modifier, color, moisture, U Remarks density/consistency, grain size, other descriptors Topsoil 1.0 1.0 Medium stiff, fine to medium sandy LEAN CLAY CL RESIDUUM B2 moist- red-brown 2.0 3.0 B1 3.0 Dense, fine to coarse SILTY SAND, SM Saprolite moist-yellow-brown 4.0 Test Pit Terminated at 4.0 FT 5.0 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-5 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical geothermal geoconstruction Contractor: Montebello Logged By: C.Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713574 Date Time Depth UTM (17S) Northing: 4221098 Encountered 03/06/18 Dry GS ELEV: 525 Completion 03/06/18 11:20 AM Dry 4- ai N Soil Group Name: modifier, color, moisture, Remarks density/consistency, grain size, other descriptors Topsoil 1.0 1.0 Medium stiff, fine to medium sandy ELASTIC MH B2 SILT, moist- red RESIDUUM 2.0 3.0 3.0 Stiff, fine to medium SANDY SILT, ML B1 moist-tan and dark-brown 4.0 5.0 Test Pit Terminated at 4.5 FT 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-6 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical geothermal geoconstruction Contractor: Montebello Logged By: C.Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713562 Date Time Depth UTM (17S) Northing: 4221107 Encountered 03/06/18 Dry GS ELEV: 521 Completion 03/06/18 11:45 AM Dry r aa) oSoil Group Name: modifier, color, moisture, v Remarks density/consistency, grain size, other descriptors Topsoil 1.0 0.9 Medium stiff, fine to medium sandy ELASTIC MH B2 SILT, moist- red RESIDUUM 2.0 2.5 Stiff, fine to medium SANDY SILT, cont. rock ML 3.0 B1 frag, moist- yellow-brown and dark-brown 4.0 Test Pit Terminated at 4.0 FT 5.0 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-7 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical geothermal geoconstruction Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713550 Date Time Depth UTM (17S) Northing: 4221101 Encountered 03/06/18 Dry GS ELEV: 516 Completion 03/06/18 11:55 AM Dry r o E r oSoil Group Name: modifier, color, moisture, U Remarks density/consistency, grain size, other descriptors Topsoil 1.0 1.0 Medium stiff, fine to medium sandy ELASTIC MH B2 SILT, moist- red RESIDUUM 2.0 W = 33.1% 3.0 3.0 Dense, fine to coarse SILTY SAND, SM Saprolite B1 moist-tan, brown, and dark-brown 4.0 5.0 Test Pit Terminated at 6.0 FT 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-8 underhill ENGINEERING Albemarle County, Virginia Project No. 18006 eotechnlcal geothermal geoconstruction Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 _ Groundwater Observations UTM (17S) Easting: 0713560 Date Time Depth UTM (17S) Northing: 4221084 Encountered 03/06/18 Dry GS ELEV: 517 Completion 03/06/18 12:05 PM Dry a • i co oSoil Group Name: modifier, color, moisture, coRemarks density/consistency, grain size, other descriptors Topsoil 1.0 0.7 Medium stiff, fine to medium sandy ELASTIC MH B2 SILT, rock fragments, moist- red RESIDUUM 2.0 3.0 B1 3.0 Very stiff, fine to medium SANDY SILT, SM Saprolite moist-tan and dark-brown 4.0 Test Pit Terminated at 3.8 FT 5.0 6.0 7.0 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion Liberty Hall Dam,2798 Liberty Hall Lane Appendix B Albemarle County,Virginia Soil Laboratory Test Results Moisture Content of Soil and Rock—ASTM D2216 (2 Sheets) Particle Size Analysis—ASTM D422 (2 Sheets) Atterberg Limits—ASTM D4318 (2 Sheets) Compaction Report—ASTM D698 Hydraulic Conductivity—ASTM D5084 Project 18006.00/June 1,2018 iV Underhill Engineering,LLC Liberty Hall Dam,2798 Liberty Hall Lane Appendix B Albemarle County,Virginia Summary of Soil Laboratory Tests Sample Location TP1/TP3 TP-9 Sample Type Combined Bulk Combined Bulk Sample Depth (ft) 1.0-6.0 1.5-2.5 Stratum B1 and B2 B1 and B2 Description, Symbol ELASTIC SILT with sand, Lean CLAY with sand, USCS(AASHTO) MH (A-7-5) CL(A-7-6) Natural Water Content (%) 35.2 28.2 Passing No.4 Sieve 99 100 Passing No.40 Sieve 88 95 Passing No.200 Sieve 71 78 Liquid Limit 55 47 Plastic Limit 34 25 Plasticity Index 21 22 Project 18006.00/June 1,2018 V Underhill Engineering, LLC Project: Liberty Hall Dam (Borrow Area) Test Pit No. TP-1 underhill ENGINEERING Albemarle County,Virginia Project No. 18006 geotechnical'igeothermal geoconstrucuon Contractor: Montebello Logged By: C. Webster Equipment Type: CAT 304E CR Mini-Ex Date: 3/06/18 Groundwater Observations UTM (17S) Easting: 0713568 Date Time Depth UTM (17S) Northing: 4221057 Encountered 03/06/18 Dry GS ELEV: 520 Completion 03/06/18 12:20 PM Dry ai E .0 CtS o soil Group Name: modifier, color, moisture, Cl) Remarks cn density/consistency, grain size, other descriptors Topsoil 1.0 0.9 Medium stiff, fine to coarse sandy ELASTIC MH W = 28.2% SILT, moist- red 2.0 RESIDUUM 3.0 B2 4.0 4.0 Medium dense, fine to coarse CLAYEY SAND, SC moist- red-brown 5.0 B1 5.5 Hard, fine to coarse SILTY SAND, SM Saprolite 6.0 moist-yellow-brown and dark-brown 7.0 Test Pit Terminated at 6.3 FT 8.0 9.0 10.0 Key: Test Pit Log: Sheet 1 of 1 NOTES: 1. Test pit elevation obtained from Google Earth 2. Test pit backfilled upon completion . Boston GeoTesting Atlanta Chicago EXPRESS Los Angeles New York Technologies to manage risk for infrastructure www.geotesting.com Geotechnical Test Report 4/26/2018 GTX-307945 Liberty Hall Dam Albemarle County, VA Client Project No.: 18006.00 Prepared for: Underhill Engineering, LLC Client: Underhill Engineering, LLC ,,.0'1.111111111111111""\„. Project: Liberty Hall Dam GeoTesting Location: Albemarle County, VA Project No: GTX 307945 Boring ID: Sample Type: - Tested By: jbr EXPRESS Sample ID: --- Test Date: 04/16/18 Checked By: emm Depth : --- Test Id: 450045 Moisture Content of Soil and Rock - ASTM D2216 Boring ID Sample ID Depth Description Moisture Content,% B-1 - -- 0-1.5 ft Moist, dark reddish brown sandy silt 20.9 B-1 - -- 4-5.5 ft Moist, dark gray silt 31.1 B-1 - -- 9-10.5 ft Moist, dark olive gray silt 27.4 B-1 - -- 19-20.5 ft Moist, dark grayish brown silty sand 18.6 B-2 - -- 4-5.5 ft Moist, dark brownish gray silty sand 17.3 B-3 - -- 0-1.5 ft Moist, dark grayish brown clay 26.4 B-3 - -- 4-5.5 ft Moist, dark grayish brown silt 13.4 B-4 - -- 4-5.5 ft Moist, grayish brown clay 21.2 Notes: Temperature of Drying : 110°Celsius printed 4/26/2018 11:02:56 AM • Client: Underhill Engineering, LLC Project: Liberty Hall Dam 6ieoTesting Location: or ng ID: Albemarle County, VAB Sample Type: Project Tested By:: jbrGTX-307945 EXPRESS Sample ID: --- Test Date: 04/16/18 Checked By: emm Depth : --- Test Id: 450019 Moisture Content of Soil and Rock - ASTM D2216 Boring ID Sample ID Depth Description Moisture Content,% TP-1 - -- 1-4 ft Moist, red clay 34.5 TP-3 - -- 1-4 ft Moist, red clay 35.8 TP-7 - -- 2.5-3 ft Moist, red clay 33.1 TP-9 - -- 1.5-2.5 ft Moist, red clay with sand 28.2 Notes: Temperature of Drying : 110°Celsius printed 4/26/2018 11:03;41 AM Client: Underhill Engineering, LLC Project: Liberty Hall Dam GeoTesting Location: Albemarle County, VA Project No: GTX 307945 Boring ID: TP1/TP3 Sample Type: bag Tested By: jbr EXPRESS Sample ID: Combined bulk Test Date: 04/16/18 Checked By: bfs Depth : 1-6 ft Test Id: 450031 Test Comment: --- Visual Description: Moist, yellowish red silt with sand Sample Comment: --- Particle Size Analysis - ASTM D422 c - .- CIn 0 0 In —N 0 0 0 0 0 0 N. If,m - .-i N l0 .i N 100 04 # # # # # * 1 I 1 1 .1 i 1 1 1 1 1 1 1 90- 1 1 4 I i .I _ 1 1 :I r 80- :1 I .1 1 _ :11 a 1 -I 1 70-. 1 i .1 - •1 .1 a, 60— :I i ,. . . . . . . C i I I il.. - , 1 .1 1 I C 50— i 4 J. . . . . . . .1 1 _ .1 1 ai I 1 40- '1 ' ' 1 — 1 4 30- .1 •1 - 1 20- I , 1 .1 I I - -I I I •1 1 1 10 I. . . . , 4. . . . . . . . .. . . .. 4 i I I I - , 1 1 I .1 I I I 1000 100 10 1 0.1 0.01 0.001 Grain Size(mm) %Cobble %Gravel %Sand %Silt&Clay Size — 1.1 27.4 71.5 Sieve Name Sieve Size,mm Percent Finer Spec.Percent Complies Coefficients D85=0.2734 mm D3o=N/A 0.75 In 19.00 100 D60=N/A D15=N/A 0.5 In 12.50 100 0.375 In 9.50 100 Dso=N/A Dio=N/A s4 4.75 99 Cu =N/A Cc =N/A *10 2.00 95 s20 0.85 92 Classification s40 0.42 88 ASTM Elastic SILT with Sand (MH) s60 0.25 84 sloo 0.15 78 AASHTO Clayey Soils (A-7-5 (16)) *200 0.075 71 Sample/Test Description Sand/Gravel Particle Shape : --- Sand/Gravel Hardness : --- printed 4/17/2018 9,01:54 AM ► • Client: Underhill Engineering, LLC /"'.11.111111111.111 Project: Liberty Hall Dam GeoTesting Location: Albemarle County, VA Project No: GTX-307945 Boring ID: TP-9 Sample Type: bag Tested By: jbr EXPRESS Sample ID: --- Test Date: 04/16/18 Checked By: bfs Depth : 1.5-2.5 ft Test Id: 450032 Test Comment: Visual Description: Moist, red clay with sand Sample Comment: --- Particle Size Analysis - ASTM D422 0 0 O 0 0 0 0 0 .-i N 1/40 .-1 N 100 # # # # # #1 I 1 1 90- . . . . . . . . . . I. I I I 80- _ 1 t 70= C 1 1 1 1 m 50_- . . . . . . . 2 I i a • 40- 30- 20- - 1 1 10_ I. . . . . . . . . . . . . .• 1 1 1 1 1 I 1000 100 10 1 0.1 0.01 0.001 Grain Size(mm) %Cobble %Gravel %Sand %Silt&Clay Size 0.0 21.5 78.5 Sieve Name Sieve Size,mm Percent Finer Spec.Percent Complies Coefficients D85=0.1539 mm D30=N/A #4 4.75 100 D60=N/A D1s=N/A #10 2.00 99 #20 0.85 97 D50=N/A Dio=N/A #40 0.42 95 Cu =N/A Cc =N/A #60 0.25 91 #100 0.15 85 Classification #200 0.075 78 ASTM Lean CLAY with Sand (CL) AASHTO Clayey Soils (A-7-6 (18)) Sample/Test Description Sand/Gravel Particle Shape : --- Sand/Gravel Hardness : --- printed 4/17/2018 9:01:54 AM s Client: Underhill Engineering, LLC Project: Liberty Hall Dam GeoTesting Location: Albemarle County,VA Project No: GTX-307945 Boring ID: TP1/TP3 Sample Type: bag Tested By: cam EXPRESS Sample ID: Combined bulk Test Date: 04/13/18 Checked By: bfs Depth : 1-6 ft Test Id: 450029 Test Comment: Visual Description: Moist, yellowish red silt with sand Sample Comment: --- Atterberg Limits - ASTM D4318 Plasticity Chart 60 - • • • 50- "UI':tine • ine 40- CH or OH .g 30_ N • 20- ♦ ,CL or OL 10* jam' MH or•OH CL-ML ML or.OL 0 1 1 --1_1 t 1 -1 I 1 1 1 0 10 20 30 40 50 60 70 80 90 100 Liquid Lin-it Symbol Sample ID Boring Depth Natural Liquid Plastic Plasticity Liquidity Soil Classification Moisture Limit Limit Index Index Content,% ♦ Combined bulk TP1/TP3 1-6 ft 21 55 34 21 -0.6 Elastic SILT with Sand (MH) Sample Prepared using the WET method 12% Retained on #40 Sieve Dry Strength: HIGH Dilatancy: SLOW Toughness: LOW printed 4/17/2018 8:58.06 AM 4 Client: Underhill Engineering, LLC �.0/��► Project: Liberty Hall Dam GeoTesting Location: Albemarle County, VA Project No: GTX 307945 Boring ID: TP-9 Sample Type: bag Tested By: cam EXPRESS Sample ID: --- Test Date: 04/16/18 Checked By: bfs Depth : 1.5-2.5 ft Test Id: 450030 Test Comment: Visual Description: Moist, red clay with sand Sample Comment: --- Atterberg Limits - ASTM D4318 Plasticity Chart 60 - : . 50- - - "U':tine • • ine 40- CH or OH C • 30- • 20- ,CL or OL 10- 1' MH•or•OH CL-ML ML otOL 0 --- +- I i 1 1 1 0 10 20 30 40 50 60 70 80 90 100 Liquid Limit Symbol Sample ID Boring Depth Natural Liquid Plastic Plasticity Liquidity Soil Classification Moisture Limit Limit Index Index Content,% ♦ TP-9 1.5-2.5 28 47 25 22 0.1 Lean CLAY with Sand (CL) ft Sample Prepared using the WET method 5% Retained on #40 Sieve Dry Strength: VERY HIGH Dilatancy: SLOW Toughness: LOW printed 4/17/2018 8:58:06 AM V Client: Underhill Engineering, LLC Project: Liberty Hall Dam GeoTesting Location: Albemarle County, VA Project No: GTX-307945 Boring ID: TP1/TP3 Sample Type: bag Tested By: cwd EXPRESS Sample ID: Combined bulk Test Date: 04/18/18 Checked By: emm Depth : 1-6 ft Test Id: 450037 Test Comment: Visual Description: Moist, yellowish red silt with sand Sample Comment: --- Compaction Report - ASTM D698 105 100 w u a 95- • zero air voids line • • • • 0 90 71\ ,‘, o 85 • 80 I - i t i -+-- - 15 20 25 30 35 Water Content, 13/0 Data Points Point 1 Point 2 Point 3 Point 4 Dry density, pcf 88.3 91.6 92.8 90.6 Moisture Content, % 21.4 23.6 26.0 27.7 Method : A Preparation : DRY As received Moisture :21 0/0 Rammer : Manual Zero voids line based on assumed specific gravity of 2.65 Maximum Dry Density= 92.9 pcf Optimum Moisture= 25.4 % printed 4/25/2018 9:32:24 PM Client: Underhill Engineering, LLC //..r......r,.a„_. Project Name: Liberty Hall Dam GeoTest.n Project Location: Albemarle County, VA EXPRESS GTX #: 307945 Start Date: 4/18/2018 Tested By: jck/trm End Date: 4/23/2018 Checked By: emm Boring #: Combined bulk Sample #: TP1/TP3 Depth: 1-6 ft Visual Description: Moist, yellowish red silt with sand Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter by ASTM D5084 Constant Volume Sample Type: Remolded Permeant Fluid: De-aired Distilled water Orientation: Vertical Cell #: --- Sample Preparation: Target Compaction: 95% of the maximum dry density (92.9 pcf) at the optimum moisture content (25.4%). Values specified by client. Assumed Specific Gravity: 2.65 Parameter Initial Final Height, in 2.63 2.50 Diameter, in 2.86 3.00 Area, in2 6.42 7.07 Volume, in3 16.9 17.7 Mass, g 494.0 528.0 Bulk Density, pcf 111.2 113.6 Moisture Content, % 25.6 34.2 Dry Density, pcf 88.5 84.6 Degree of Saturation, % 78 95 B COEFFICIENT DETERMINATION Cell Pressure, psi: 84.94 Increased Cell Pressure, psi: 90.03 Cell Pressure Increment, psi: 5.09 Sample Pressure, psi: 80.05 Corresponding Sample Pressure, psi: 84.62 Sample Pressure Increment, psi: 4.57 B Coefficient: 0.90 *B value did not increase with increase in pressure. FLOW DATA Final degree of saturation >95%. Elapsed Permeability Permeability Trial Pressure, psi Manometer Readings Time, K, Temp, K @ 20 °C, Date # Cell Sample Z1 Z2 Zi-Z2 sec Gradient cm/sec °C Rl cm/sec 4/19 1 84.9 80.1 12.5 9.5 3.0 30 24.8 3.2E-06 19.7 1.008 3.2E-06 4/19 2 84.9 80.1 12.5 9.5 3.0 31 24.8 3.1E-06 19.7 1.008 3.1E-06 4/19 3 84.9 80.1 12.5 9.5 3.0 32 24.8 3.0E-06 19.7 1.008 3.0E-06 4/19 4 84.9 80.1 12.5 9.5 3.0 34 24.8 2.8E-06 19.7 1.008 2.8E-06 PERMEABILITY AT 20° C: 3.1 x 10-6 cm/sec (@ 5 psi effective stress)