Loading...
HomeMy WebLinkAbout20-22 Geotechnical Report ECS MID-ATLANTIC, LLC Geotechnical Engineering Report Snowden Bridge Regional Pond Ezra Lane Winchester, Frederick County, Virginia ECS Project Number 01:31598 April 26, 2022 Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page i TABLE OF CONTENTS EXECUTIVE SUMMARY ......................................................................................................................... 1 1.0 INTRODUCTION .............................................................................................................................. 2 2.0 PROJECT INFORMATION ................................................................................................................. 3 2.1 Project Location/Current Site Use/Past Site Use ................................................................................ 3 2.2 Proposed Construction ........................................................................................................................ 4 2.3 Regional/Site Geology ......................................................................................................................... 4 2.3 Karst Terrane Considerations .............................................................................................................. 5 3.0 FIELD EXPLORATION AND LABORATORY TESTING ........................................................................... 8 3.1 Subsurface Characterization ............................................................................................................... 8 3.2 Groundwater Observations ................................................................................................................. 9 3.3 Laboratory Testing ............................................................................................................................... 9 4.0 DESIGN RECOMMENDATIONS ...................................................................................................... 10 4.1 Stormwater Management Structures ............................................................................................... 10 4.2 Corrosion Potential ............................................................................................................................ 12 5.0 SITE CONSTRUCTION RECOMMENDATIONS .................................................................................. 13 5.1 Subgrade Preparation........................................................................................................................ 13 5.1.1 Stripping and Grubbing ............................................................................................................... 13 5.1.2 Proofrolling ................................................................................................................................. 13 5.1.3 Site Temporary Dewatering ........................................................................................................ 13 5.2 Earthwork Operations ....................................................................................................................... 14 5.2.1 Existing Undocumented Fill ........................................................................................................ 14 5.2.2 Engineered Fill ............................................................................................................................ 14 5.2.3 High Plasticity Soils ..................................................................................................................... 16 5.2.4 Rock Excavation .......................................................................................................................... 16 5.3 Karst Related Recommnedations ...................................................................................................... 17 5.3.1 Karst Risk and Construction Issues ............................................................................................. 17 5.3.2 Karst Earthwork Recommendations ........................................................................................... 18 5.4 Utility Installations ............................................................................................................................. 18 6.0 CLOSING ....................................................................................................................................... 20 Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page ii APPENDICIES Appendix A – Drawings & Reports • Site Vicinity Map • Boring Location Diagram Appendix B – Field Operations • Subsurface Exploration Procedure: Standard Penetration Testing (SPT) • Reference Notes for Boring Logs • Boring Logs (SWM-01 through SWM-05) Appendix C – Laboratory Testing • Laboratory Test Results Summary • Liquid and Plastic Limits Test Report • Grain Size Analyses Appendix D – Additional Figures • French Drain Installation Procedure • Typical Dam Cross Section and Drainage Detail • Benching Detail • Karst Auger Refusal Scenario Diagram Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 1 EXECUTIVE SUMMARY The following summarizes the main findings of the exploration, particularly those that may have a cost impact on the planned development. Further, our principal foundation recommendations are summarized. Information gleaned from the Executive Summary should not be utilized in lieu of reading the entire geotechnical report. • Based on the borings performed, undocumented fill was observed in borings SWM-02, SWM-03, and SWM-05. These fill soils are associated with the former farm pond that occupied the area, stockpiled soils, and construction of the adjacent CSX railroad. Undocumented fill soils should be removed and replaced with structural fill. • Groundwater was not encountered within any of the borings performed; however, perched groundwater may be encountered during earthwork operations specifically at the interface between the fill and natural soils, and at the transition from natural soils to bedrock. • The area is conducive to the development of karst terrane (i.e. sinkholes, caverns, voids, etc.). These may impact development and may adversely affect the overall performance of the stormwater management pond. A pond liner should be constructed as part of the overall development of the pond. • High-plasticity CLAY (CH) was observed within several of the borings conducted up to approximately 10.5± feet below the ground surface. The CH material can be utilized as a pond liner for the proposed stormwater management facility. • Auger refusal, which is indicative of depth to bedrock, was encountered at depths ranging from 9.2± feet to 17.0± feet below the ground surface. The rock is suitable for reuse as fill; however, size and gradation restrictions for rock used as fill may require further mechanical degradation in the form of rock crushing and blending with site clay soils prior to use. In general, the site appears suitable for construction, the primary factors that could affect the proposed development are karst terrane, shallow rock, and the presence of highly plastic clays. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 2 1.0 INTRODUCTION The purpose of this study was to provide geotechnical information for the design of a stormwater management pond as well as to provide general recommendations for mass grading of the overall site. Our understanding of the proposed development is based on the Snowden Bridge Station Regional Pond plans prepared by GreyWolfe, Inc. dated February 18, 2022, and provided by you on March 17, 2022. Our services were provided in accordance with our Proposal No. 65540-GP, dated March 22, 2022, as authorized by you on March 24, 2022, which includes Terms and Conditions of Services. This report contains the procedures and results of our subsurface exploration and laboratory testing programs, review of existing site conditions, engineering analyses, and recommendations for the design and construction of the project. The report includes the following items. • A brief review and description of our field and laboratory test procedures and the results of testing conducted. • A review of surface topographical features and site conditions. • A review of area and site geologic conditions. • A review of subsurface soil with pertinent physical properties. • Final soil exploration boring logs • Recommendations for site preparation and construction of compacted fills, including an evaluation of on-site soils for use as compacted fills and identification of potentially unsuitable soils and/or soils exhibiting excessive moisture at the time of sampling. • Recommendations for the stormwater management pond. • Evaluation and recommendations related to groundwater control. • An evaluation of soil and rock excavation issues. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 3 2.0 PROJECT INFORMATION 2.1 PROJECT LOCATION/CURRENT SITE USE/PAST SITE USE The project site is located in Winchester, Frederick County, Virginia. The overall project site is located at the southeast quadrant of the intersection of Red Bud Road and CSX railroad track. Existing site grades range from EL. 689± feet to EL. 665± feet, dropping downward from west to east. The stormwater management pond will be bound by the existing CSX rail yard and train tracks to the north and the east, Red Bud Road to the south, and open vacant parcels with numerous soil stockpiles to the west. Based on historical aerial images of the area, the southern area of the pond appears to have once been a farm pond. This appears to be the case until 2002 at which point it appears that soil and boulder stockpiles were placed within the farm pond area. During our exploration, a site walk was performed to explore this area and confirmed the presence of numerous boulder piles which at this point have mature trees in and around them. Additional stockpiles appear to have been recently placed in this area as well, as evidenced by their lack of vegetation growth. The approximate location of the project site with respect to surrounding streets is depicted below and on the Site Vicinity Map in Appendix A. Site Location NOT TO SCALE SITE NORTH Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 4 2.2 PROPOSED CONSTRUCTION The proposed development includes the installation of a stormwater management pond. The pond will have a proposed bottom of pond elevation of EL. 661± feet, and a top of embankment elevation of EL. 677± feet. Stormwater is planned to be conveyed through the embankment via a 48-inch diameter concrete riser structure, fitted with a trash rack, having an invert elevation of EL. 661.0 feet, and top of riser elevation of EL. 671.0 feet. The riser structure will be fitted with a 6-inch gate valve, as well as at 15- inch inlet pipe with an invert elevation at EL. 668.2 feet, and a 24-inch inlet pipe with an invert elevation at EL. 666.3 feet. Based on the proposed grading plan, the mass grading will include cuts on the order of 9± feet to 12± feet to reach the bottom of pond elevation and fills on the order of 12± feet to create the south portion of the embankment where the riser structure will convey water through the embankment. 2.3 REGIONAL/SITE GEOLOGY The site is located within the Valley and Ridge Physiographic Province of the Appalachian Highlands. According to the Geologic Map of the Winchester Quadrangle (Orndorff, et. al. USGS OFR-03- 461, 2003) the project site is underlain by the Ordovician Age Pinesburg Station Dolomite and Rockdale Run Formation. A portion of the referenced geologic map is presented below. Geologic Map (Winchester Quadrangle, Orndorff, et. al., 2003) Opr – Pinesburg Station Dolomite (Middle Ordovician) – Dolostone with minor chert nodules. Thickness ranges from 650 to 875 feet. Rockdale Run Formation (Middle and SITE NOT TO SCALE NORTH Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 5 Lower Ordovician) – Interbedded limestone and dolostone. Thickness is approximately 1,500 feet. The Pinesburg Station Dolomite is generally described as a predominately light gray, fine grained dolostone which weathers to a yellowish to drab-gray color. The Rockdale Run Formation is generally described as an interbedded bluish-gray limestone and gray dolostone with several distinctive chert zones and algal structures associated with clastic limestone. These units are stratigraphically bounded by the underlying Stonehenge Formation, and the overlying Lincolnshire Limestone, both primarily consisting of a lithological package of carbonate units generally described as a dark to light gray, fine to medium grained limestones with minor chert lenses. Structurally, the area is characterized by moderately to high angle bedding with varying dip directions. Reported bedding dips in the vicinity of the site are approximately 45± degrees to the southeast with a northeast strike. Several anticlinal-synclinal fold pairs area mapped in the general vicinity of the project area. The site is situated along the eastern limb of a southwest plunging anticline. A small left lateral strike- slip fault is mapped within a few hundred feet to the south of the project site. Numerous faults have created repeated lithologies and disrupted stratigraphic columns across the geographic area. 2.3 KARST TERRANE CONSIDERATIONS Karst terrane is characterized by caves, caverns, voids, soil domes, internal drainages, losing streams, and topographical features such as sinkholes and closed depressions. A highly variable top of rock profile is commonly encountered. These features are the result of the dissolution of soluble bedrock such as limestone, dolostone and evaporites by groundwater and/or the infiltration of surface water. As water enters fractures, bedding planes and other bedrock discontinuities within soluble bedrock, it slowly dissolves the rock and enlarges the discontinuities. Over geologic time, this results in the formation of solution channels or underground passages and ravines which may develop into surficial manifestations such as sinkholes and closed depressions. The dissolution of bedrock is generally a very slow process. However, soil may be eroded, or raveled, into the enlarged bedrock fractures creating soil domes and eventually surface depressions and potential sudden ground subsidence. Grading and excavations often hastens the formation of karst manifestations as new surface and subsurface drainage pathways are formed where water is allowed to flow and/or pond. Based on Virginia Energy online mapping resources, the site and surrounding area is impacted by karst development, with sinkholes identified in the geographic area. The nearest sinkhole identified on Virginia Energy Karst Maps is located approximately 400 feet west of the proposed pond location. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 6 Two additional sinkholes are also mapped in the immediate area of the proposed pond. The yellow circles in the figure below depict the mapped sinkholes located near the project. Karst Feature Map (Virginia Energy) The bedrock within the general geographic region is characterized by folded and faulted soluble carbonate lithologies interbedded with non-carbonate lithologies. These carbonate formations are generally highly calcareous, moderately to highly solution prone, and typically weather differentially to produce a pinnacled top of rock profile. A pinnacled top of rock is characterized by areas of shallow bedrock, termed pinnacles, with intervening areas of deeper soils, termed cutters. The degree of weathering or solutioning is often controlled by lithological variations and structural orientations. Where structural discontinuities, such as thrust faults, intersect or in areas which are highly fractured, such as related to folding, solutioning is intensified creating low areas and seams that are typically filled with residual clay soils. Conversely, more competent, high areas represent slightly too non-fractured lithologies that are often coarser grained and only slightly solution prone. The underlying carbonate formations of the geographic area are highly susceptible to karst development. Contributing characteristics and factors controlling the karst development includes the synclinal/anticlinal fold pairs, joint sets and high angle bedding within the area. Based on the structural orientations and the prevailing anticlinal/synclinal fold pair structural style in the project area, the underlying bedrock is likely highly fractured. Fracture sets typically develop in association with folding and faulting due to the regional stresses induced in the rock during the tectonic events. Three fracture sets typically develop in folded rocks. The fracture sets developed are generally parallel to the fold axis, or axial planar fractures, perpendicular to the fold axis and perpendicular to the bedding plane. Karst development is enhanced along these fracture sets due to the increased permeability and surface water infiltration. Within areas of intersecting fractures and other bedrock discontinuities, an increased risk for karst development is expected. Residual soils derived from the chemical weathering of the underlying carbonate bedrock are typically Lean to Fat CLAY (CL,CH) soils with varying amounts of limestone fragments, cobbles and boulders. It should be noted that large, detached boulders and cobbles may be present as “float” blocks within the SITE NOT TO SCALE NORTH Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 7 soil mantle overlying the carbonate bedrock. These “float” blocks are potentially large, commonly exceeding three (3) feet in one dimension and will induce auger refusal with standard geotechnical rotary auger drill rigs. The limestone “float” blocks are soil supported and do not represent the actual bedrock surface when encountered within a boring. The zone, or area, where most active dissolution and ground water fluctuations occur is generally referred to as the “epikarst” zone in karst literature. Epikarst is defined as the interface zone between soil and rock in karst landscapes and is characterized by small fractures and solution pockets that may or may not be filled with water and/or soil. Epikarst is the uppermost weathered zone of carbonate rocks with substantially enhanced and more homogeneously distributed porosity and permeability, as compared to the bulk rock mass below. This zone typically has fractured bedrock with soil infilling, numerous “float” blocks and “detached” pinnacles of limestone and generally overlies competent, less fractured bedrock at depth. The epikarst zone is usually the area of most active solutioning, soil raveling and sinkhole development, if present. In areas with well-developed epikarst conditions, surface drainage channels are often sparse due to the homogenous infiltration due to the larger aerial extents with consistent subsurface conditions which inhibit development of preferential drainage pathways. Diffuse infiltration in these areas result in few surface drainage features. Mature epikarst conditions are often geomorphologically expressed as rolling terrains with broad swales and ridges. Observations of the project site are consistent with these conditions, indicating a well-developed epikarst system. Due to the natural weathering and residual soil development processes in karst terrane, the surficial soils occasionally exhibit higher densities/consistencies than the underlying soils closer to the bedrock interface. Deeper soils tend to exhibit lower in-situ density and strength and generally have higher silt content with corresponding lower clay content. Therefore, the residual soils encountered near the soil/bedrock interface tend to be of lower bearing capacity. In addition, the soils near this interface may be in a saturated condition due to the development of perched groundwater on top of the bedrock. Risks associated with developing in Karst can include the formation of sinkholes that may form beneath buildings, roadways, utility lines, stormwater management ponds, dams, and other manmade structures. These features can occur as a gradual erosion of soils into the subsurface causing settlement damage to structures over a long period of time, or rapidly in the case of a sudden cover collapse sinkhole as has been witnessed in the recent past in other areas of the country. In addition to sinkhole hazards, the sudden collapse of cave roofs due to overloading by structures can also occur. Karst hazards may sometimes lead to personal injury but rarely do they result in loss of life. Property damage due to Karst hazards can range from simple inconvenience to catastrophic property loss. Considering the mapped presence sinkholes at the project site, there is an inherent risk of karst development that could impact the proposed pond. It should be noted that sinkhole development is generally unpredictable and subsurface explorations cannot completely eliminate the possibility of sinkhole development at a project site. Therefore, some risk of additional sinkhole development does exist for the site given this geologic setting. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 8 3.0 FIELD EXPLORATION AND LABORATORY TESTING Our exploration procedures are explained in greater detail in Appendix B including the insert titled Subsurface Exploration Procedures. Our scope of work including drilling five (5) soil borings to a depth of 20± feet or prior auger refusal in the embankment and stormwater management facility. Our borings were located with a handheld GPS unit and their approximate locations are shown on the Boring Location Diagram in Appendix A. 3.1 SUBSURFACE CHARACTERIZATION The soils identified in the attached boring logs are generally consistent with the regional geology. The soil profile appears to have been derived from the in-place physical and chemical weathering of underlying limestone and dolostone bedrock. Our field exploration indicated surface materials consisting of up to 8± inches of topsoil at the boring locations. The subsurface conditions encountered were generally consistent with published geological and soils mapping. The following sections provide generalized characterizations of the soil and rock strata encountered during our subsurface exploration. For subsurface information at a specific location, refer to the Boring Logs in Appendix B. Approximate Depth Range Stratum Description Ranges of SPT(1) N-values (bpf) 3-8 inches (Surface cover) n/a Topsoil N/A 0.4-5.5 feet I Clayey GRAVEL (GC FILL), FAT CLAY with Gravel (CH FILL) 3-9 0.3-20 feet II Fat CLAY (CH), Silty GRAVEL with Sand (GM), Sandy SILT with Gravel (ML), Clayey GRAVEL with Sand (GC) 5-50/4” Notes: (1) Standard Penetration Test Auger refusal was encountered within all of our borings between the depths of 9.2± feet and 17.0± feet except for boring SWM-04 which extended to the boring termination depth of 20± feet. Auger refusal is generally abrupt in limestone and dolostone geology. A Karst Auger Refusal Scenario Diagram has been included in the appendix of this report to illustrate this condition. High plasticity Fat CLAY (CH) was encountered in all of the borings performed to depths ranging from 7.5± feet to 10.5± feet below the existing ground surface. Highly plastic soils are typically encountered in areas underlain by limestone and dolostone bedrock. Highly plastic soils are prevalent onsite and are expected to be encountered in unexplored areas or between boring locations. Existing undocumented fill was encountered in Borings SWM-02, SWM-03, and SWM-05. The areas where existing undocumented fill was encountered is within the areas of the farm pond and stockpiles, as well as the north portion of the site where the CSX railroad has been constructed. Boring SWM-01 was offset from it originally intended location in order to avoid drilling in recently placed stockpiled soils. Existing undocumented fill should be expected within this area and should be further explored with test pits at the time of construction to determine the extent of existing fill during earthwork operations. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 9 3.2 GROUNDWATER OBSERVATIONS Groundwater seepage was not observed during our exploration in any of the soil borings performed to the depths explored; however, perched water conditions may occur at the site during extended wet weather conditions. Perched groundwater conditions can develop in areas with shallow rock or where low permeability materials underlie higher permeability materials. Specifically, precipitation that enters the site, either directly or from overland flow, begins to percolate through the low to moderately permeable surficial soils. Once the water percolation reaches the bedrock or low permeable strata, it perches and begins to flow at the interface of the rock and the soil and within the fractured surface of the bedrock. The groundwater flow continues down gradient, with the perched water table occasionally surfacing to form springs and intermittent streams. The groundwater is related to precipitation, although springs may exist in the lower lying areas for extended periods of time without recharge. The groundwater conditions at this site are expected to be significantly influenced by surface water runoff and rainfall. The highest groundwater observations are normally encountered in the late winter and early spring. Variations in the location of the long-term water table may occur as a result of changes in precipitation, evaporation, surface water runoff, and other factors not immediately apparent at the time of this exploration. The site may also be subject to severe desiccation during extended dry periods. Therefore, earthwork operations in the winter and spring are more likely to encounter difficulties with perched conditions than those operations undertaken in the summer or fall. For long-term planning purposes, we strongly urge that mass grading operations be undertaken to coincide with favorable weather periods. 3.3 LABORATORY TESTING The laboratory testing consisted of selected tests performed on samples obtained during our field exploration operations. Classification and index property tests were performed on representative soil samples. We performed natural moisture tests, Atterberg Limit tests, and gradation analysis tests on selected samples. Each sample was visually classified on the basis of texture and plasticity in accordance with ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) and including USCS classification symbols, and ASTM D2487 Standard Practice for Classification for Engineering Purposes (Unified Soil Classification System (USCS)). After classification, the samples were grouped in the major zones noted on the boring logs in Appendix B. The group symbols for each soil type are indicated in parentheses along with the soil descriptions. The stratification lines between strata on the logs are approximate; in situ, the transitions may be gradual. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 10 4.0 DESIGN RECOMMENDATIONS 4.1 STORMWATER MANAGEMENT STRUCTURES General: The proposed SWM pond is planned as a wet pond with a proposed bottom elevation at EL. 661.0 feet and a normal pool level at EL. 668.2 ft. The required cuts from the existing surface elevation are on the order of approximately 9± feet to 12± feet. A 60 feet long and 72 feet long gabion wall will be constructed along the northern and western area of the proposed pond, respectively. The proposed top of embankment is planned at EL. 677.5 feet. Stormwater conveyance will be handle by a 48-inch diameter concrete riser structure with a 24-inch diameter reinforced concrete outlet pipe that will be constructed to flow through the proposed earthen embankment. Embankment Foundations: The soils encountered within the various borings conducted within the proposed SWM pond facility generally consisted of undocumented fill consisting of Clayey GRAVEL (GC FILL), and Fat CLAY with Gravel (CH FILL). The natural soils encountered at the site generally consisted of Fat CLAY (CH), Silty or Clayey GRAVEL with Sand (GM), and Sandy SILT with Gravel (ML) underlain by limestone and dolostone bedrock. Groundwater was not encountered within the recently performed borings in the area of the planned SWM pond; however, we do anticipate perched groundwater to be encountered in localized areas at the interface between both the undocumented fill and natural soils, as well as between the natural soils and bedrock. However, significant groundwater-related construction problems are not anticipated. Additionally, the onsite soil materials are highly disturbance and moisture sensitive. Steps should be taken to document that site drainage is directed away from the facility during construction operations. It should be noted that all groundwater and any precipitation or surface runoff should be handled with conventional trenching and pumping operations or diversion berms, and steps should be taken so that site drainage is directed away from the facilities during construction. Embankment Fill Placement: Generally, the materials found within the project site have sufficiently low permeability such that excessive seepage through these materials is not expected to be a problem. Acceptable soil types for construction of the embankments include soils having a USCS designation of ML, CL, CH and SM or SC having a minimum of 25% passing No. 200 sieve. Considering the relatively low permeability soils encountered on site and our recommendation to line the pond, a cut-off trench for the facility is not considered necessary. Any fill material placed below storm water structures or pipes in the embankment area should consist of the same material described above for the embankment. Fill materials are to be placed in lifts not exceeding 8-inches in loose thickness, moisture-conditioned to within 2 percentage points on the wet side of the optimum moisture content, and compacted with a sheepsfoot or tamperfoot roller to a minimum of 95% of the maximum dry density determined in accordance with ASTM D 698 or VTM-1. Free draining materials should not be utilized in the construction of the embankment. Prior to the placement of each lift of new fill, the soil subgrade should be scarified to facilitate the amalgamation of adjacent layers. It is recommended that new fill soils be benched into the existing soils to provide adequate soil interaction of these materials. If the top of an exposed layer is smooth, it should be rerolled with a sheepsfoot roller, or scarified prior to the placement of the next lift of fill. Although it is desirable to seal off fill surfaces on a daily basis using a steel drum or rubber tired roller, these surfaces should be scarified the following day prior to fill activities to reduce the creation of planes of seepage or slippage within the embankment structure. The preparation of fill subgrades and the operations of fill placement should be observed on a full-time basis by an authorized representative of the GER to document that unsuitable materials are removed and fill is constructed in compliance with the recommendations contained within this report. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 11 In order to facilitate the establishment of grass on the embankment slopes, it is considered acceptable to place a 6-inch-thick topsoil layer on the face of the embankment slopes. The topsoil should be placed in 6-inch lifts and compacted with at least four passes of a track dozer. Embankment Cross Section: Design of the stormwater management ponds should be in accordance with current Commonwealth of Virginia and Frederick County requirements. We recommend that the side slopes of the pond and embankments be no steeper than 3H:1V and that the top of the embankment section be constructed in accordance with Virginia DEQ requirements. The embankment should be prepared in accordance with the recommendations in the sections entitled Subgrade Preparation, Earthwork Operations, Fill Placement, and Embankment Fill Placement. We recommend that the embankment of the pond be constructed as homogeneous section, utilizing suitable soils as described in the Embankment Fill Placement section above, and be compacted with a sheepsfoot roller. Since the design drawings show that the principal outlet for the pond is designed to be a conventional riser and outlet pipe, we recommend placing a concrete cradle beneath the upstream two-thirds (⅔) outlet of the pipe measured from the riser or inlet structure. The downstream one-third (⅓) of the pipe should be surrounded by 12-inch thick layer of open graded coarse aggregate (VDOT No. 78 stone) wrapped with a suitable non-woven geo-textile having an apparent opening size (AOS) of 70. Fine aggregate may be used in lieu of the geotextile. A drainage blanket at the downstream end of the pipe will serve to collect any seepage along the conduit which could result in a soil piping failure. The drainage pipe should be day-lighted through the end walls into slotted piping. Details regarding the concrete cradle and drainage system are shown on the Typical Dam Cross Section and Drainage Detail included in the Appendix of this report. The principal spillway should be installed as the embankment is being constructed. Excavating through the completed embankment to install the principal spillway is not recommended. Pond Liner: The project drawings indicate a clay liner as part of the overall design of the pond. Due to the karst nature and potential for shallow bedrock conditions within the area of the proposed wet pond, we agree that a pond liner should be provided. The pond liner may consist of natural on-site clay soils that meet the requirements for pond liner specified by the Virginia Department of Environmental Quality (VADEQ). These requirements are presented below. The pond liner should have a minimum thickness of 2 feet. Additionally, it should be noted that the pond liner will have to be compacted to a minimum of 95% of the Standard Proctor maximum dry density. The contractor should plan and budget for this effort along with potential moisture conditioning of the clay. The pond liner should extend across the full basin width and to the expected high-water level. For permanent ponds, all clay liner specifications as required by VADEQ should be met. For the proposed pond, the liner material should meet the permeability and compaction requirements presented in the following table. The onsite soils may be suitable to meet the requirements for the pond condition, but additional laboratory testing should be performed prior to construction. Property Test Method (or equal) Unit Specification Permeability* ASTM D-2434 cm/sec Less than 1 x 10-6 Plasticity Index ASTM D-423 and D-424 % Not less than 15 Liquid Limit ASTM D-2216 % Not less than 30 Clay Particles Passing ASTM D-422 % Not less than 30 Clay Compaction* ASTM D-698 % 95% of Standard Proctor Density *min requirements for temporary pond liners. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 12 Based on the results of the subsurface exploration, soils meeting the above requirements are expected to be available on-site. Foundation for Outlet Works: The outlet works for the proposed pond will consist of a 48-inch diameter concrete riser structure equipped with a trash rack that discharges to a 24-inch reinforced concrete pipe through the earthen embankment to an existing drainage swale. The design drawings indicate the construction of an 8-inch thick concrete pad beneath the 48-inch riser structure. We recommend that the proposed riser structure and concrete pad be supported on suitable firm residual soils, bedrock or engineered fill constructed over suitable natural soils. Based on the soils encountered at boring SWM-03, the concrete pad will be founded at EL. 659.0 feet in medium dense to dense natural residual Silty GRAVEL with Sand (GM) material. Therefore, anticipate these soils to have an allowable soil bearing capacity of 2,500 psf. Most of the soils at the foundation bearing elevation are anticipated to be suitable for support of the proposed structure. If soft or unsuitable soils are observed at the bearing elevation, the unsuitable soils should be undercut and removed. Any undercut should be backfilled with lean concrete (f’c ≥ 1,000 psi at 28 days) up to the original design bottom of footing elevation; the original footing shall be constructed on top of the hardened lean concrete. Although not anticipated, additional undercutting of foundations may be required if highly plastic soils are present below the foundation. Please see the section titled High Plasticity Soils detailed in this report. It should be recognized that the soil will probably be moisture and disturbance sensitive. Therefore, excavation for the outlet structure should proceed in an expeditious manner in order to reduce exposure of the bedding soils. The foundation excavation should be observed, and the bearing pressure of the footing subgrade tested by an authorized representative of the GER. 4.2 CORROSION POTENTIAL Soil corrosion potential was evaluated based on the NRCS mapping database for corrosion potential of both concrete and steel. These risk potentials are summarized in the Table below. Based on the mapped results, the soils encountered on site are considered to exhibit a low to moderate concrete corrosion potential, and high steel corrosion potential. Soil Corrosion Potential by Soil Type (per NRCS) Mapping Unit Map Unit Name Corrosion of Concrete Potential Corrosion of Steel Potential 5B Carbo Silt Loam, 2 to 7 percent slopes Low High 5C Carbo Silt Loam, 7 to 15 percent slopes Low High 32B Oaklet Silt Loam, 2 to 7 percent slopes Moderate High Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 13 5.0 SITE CONSTRUCTION RECOMMENDATIONS 5.1 SUBGRADE PREPARATION 5.1.1 Stripping and Grubbing The subgrade preparation should consist of stripping all vegetation, rootmat, topsoil, existing fill, and any soft or unsuitable materials from 5 feet beyond the toe of Structural Fills. Boring logs performed in “undisturbed” areas of the site contained an observed 3 to 8 inches of topsoil. Deeper topsoil or organic laden soils may be present in wet, low-lying, and poorly drained areas. In the wooded areas of the site, particularly around the former farm pond, the root balls may extend as deep as about 2 feet and will require additional localized stripping depth to completely remove the organics. ECS should be retained to verify that topsoil and unsuitable surficial materials have been removed prior to the placement of structural fill or construction of structures. 5.1.2 Proofrolling Prior to fill placement or other construction on subgrades, the subgrades should be evaluated by an ECS field technician. The exposed subgrade should be thoroughly proofrolled with construction equipment having a minimum axle load of 10 tons [e.g. fully loaded tandem-axle dump truck]. Proofrolling should be traversed in two perpendicular directions with overlapping passes of the vehicle under the observation of an ECS technician. This procedure is intended to assist in identifying any localized yielding materials. Where proofrolling identifies areas that are unstable or “pumping” subgrade those areas should be repaired prior to the placement of any subsequent Structural Fill or other construction materials. Methods of stabilization include undercutting, moisture conditioning, or chemical stabilization. The situation should be discussed with ECS to determine the appropriate procedure. Test pits may be excavated to explore the shallow subsurface materials to help in determining the cause of the observed unstable materials, and to assist in the evaluation of appropriate remedial actions to stabilize the subgrade. 5.1.3 Site Temporary Dewatering The contractor shall make their own assessment of temporary dewatering needs based upon the limited subsurface groundwater information presented in this report. Soil sampling is not continuous, and thus soil and groundwater conditions may vary between sampling intervals (typically 5 feet). If the contractor believes additional subsurface information is needed to assess dewatering needs, they should obtain such information at their own expense. ECS makes no warranties or guarantees regarding the adequacy of the provided information to determine dewatering requirements; such recommendations are beyond our scope of services. Dewatering systems are a critical component of many construction projects. Dewatering systems must be selected, designed, and maintained by a qualified and experienced (specialty or other) contractor familiar with the geotechnical and other aspects of the project. The failure to properly design and maintain a dewatering system for a given project can result in delayed construction, unnecessary foundation subgrade undercuts, detrimental phenomena such as ‘running sand’ conditions, internal erosion (i.e., ‘piping’), the migration of ‘fines’ down-gradient towards the dewatering system, localized settlement of nearby infrastructure, foundations, slabs-on-grade and pavements, etc. Water discharged from any site dewatering system shall be discharged in accordance with all local, state and federal requirements. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 14 Limited Excavation Dewatering: Based upon our subsurface exploration at this site, as well as significant experience on sites in nearby areas of similar geologic setting, we believe construction dewatering at this site will be mainly limited to removing accumulated precipitation, seepage from excavations, and localized seepage from perched water or springs. Strategies for Addressing Perched Groundwater: The typical primary strategy for addressing perched groundwater seeping into excavations is pumping from trench (or French) and sump pits with sump pumps. A typical sump pump drain (found in a sump pit or along a French drain) is depicted below. The inlet of the sump pump is placed at the bottom of the corrugated pipe and the discharge end of the sump is directed to an appropriate stormwater drain. Sump Pit/Pump Diagram Details of a typical French drainage installation are included in Appendix D. A typical French drain consists of an 18 to 24-inch wide by 18- to 24-inch-deep bed of AASHTO #57 (or similar open graded aggregate) aggregate wrapped in a medium duty, non-woven geotextile and (sometimes) containing a 6-inch diameter, Schedule 40 PVC perforated or slotted pipe. Actual dimensions should be as determined necessary by ECS during construction. After the installation has been completed, the geotextile should be wrapped over the top of the aggregate and pipe followed by placement of backfill. The top of the drain should be positioned at least 18 inches below the design subgrade elevations. Drains should not be routed within the proposed embankment limits. Pumping wells or a vacuum system could also be used to address groundwater. These techniques often are only effective during the initial depletion of the perched water quantity and may quickly be ineffective at addressing accumulation of water from rain, snow, etc. 5.2 EARTHWORK OPERATIONS 5.2.1 Existing Undocumented Fill Existing Undocumented Fill was encountered in borings SWM-02, SWM-03, and SWM-05 and are generally associated with the former farm pond, soil stockpiles, and adjacent CSX railroad construction. Existing undocumented fill is not acceptable for foundation support and should be removed and replaced with acceptable compacted materials or lean concrete. The aerial extent of this fill should be assessed prior to mass grading so that a plan for it’s removal and replacement can be devised. 5.2.2 Engineered Fill Prior to placement of Engineered Fill, representative bulk samples (about 50 pounds) of on-site and/or off-site borrow should be submitted to ECS for laboratory testing, which will typically include Atterberg limits, natural moisture content, grain-size distribution, and moisture-density relationships (i.e., Proctors) Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 15 for compaction. Import materials should be tested prior to being hauled to the site to determine if they meet project specifications. Alternatively, Proctor data from other accredited laboratories can be submitted if the test results are within the last 90 days. Satisfactory Engineered Fill Materials: Materials satisfactory for use as Engineered Fill should consist of inorganic soils with the following engineering properties and compaction requirements. ENGINEERED FILL INDEX PROPERTIES Subject Property Building and Pavement Areas LL < 45, PI<20 Max. Particle Size 6 inches Fines Content Min 25 % passing #200 sieve Max. organic content 5% by dry weight ENGINEERED FILL COMPACTION REQUIREMENTS Subject Requirement Compaction Standard Standard Proctor, ASTM D698 Required Compaction* 95% of Max. Dry Density Moisture Content -3 to +3 % points of the soil’s optimum value Loose Thickness 8 inches prior to compaction * Where the fill depth will be 8 feet or more, we recommend that the fill soils be compacted to a minimum of 98% of Max Dry Density On-Site Borrow Suitability: The onsite materials are generally expected to be suitable for reuse as embankment and grading fill. During the cooler and wetter periods of the year, delays and additional costs should be anticipated. At these times, reduction of soil moisture may need to be accomplished by a combination of mechanical manipulation and the use of chemical additives, such as lime or cement, in order to lower moisture contents to levels appropriate for compaction. Alternatively, during the drier times of the year, such as the summer months, moisture may need to be added to the soil to provided adequate moisture for successful compaction according to the project requirements. Fill Placement: Fill materials should not be placed on frozen soils, on frost-heaved soils, and/or on excessively wet soils. Borrow fill materials should not contain frozen materials at the time of placement, and all frozen or frost-heaved soils should be removed prior to placement of Structural Fill or other fill soils and aggregates. Excessively wet soils or aggregates should be scarified, aerated, and moisture conditioned. Embankment Fill Placement: The timing for placement of backfill for diversion conduit through/beneath the pond embankment should be planned to reduce the risk of piping of soil materials, based on the recommendation included herein. Generally, the materials found within the project site have sufficiently low permeability such that excessive seepage through these materials should not be a problem. For temporary stormwater management structures, the project owner should anticipate that maintenance and repairs will be required during the service life of the pond. For permanent ponds, the portion of the diversion pipe that passes beneath the embankment structure should receive a concrete cradle that extends up to the springline of the pipe prior to backfilling. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 16 Fill materials are to be placed in lifts not exceeding 8 inches in loose thickness, moisture-conditioned to within 2 percentage points on the wet side of the optimum moisture content and compacted with a sheepsfoot or tamperfoot roller to a minimum of 95% of the maximum dry density determined in accordance with ASTM D 698, Standard Proctor Method. Free draining materials should not be utilized in the construction of the embankment. It is recommended that new fill soils be benched into the existing soils to provide adequate soil bonding of these materials. If the top of an exposed layer is too smooth, it should be rerolled with a sheepsfoot roller, or scarified prior to the placement of the next lift of fill. Although it is desirable to seal off fill surfaces on a daily basis using a steel drum or rubber-tired roller, these surfaces should be scarified the following day prior to fill activities to reduce the creation of planes of seepage within the embankment structure. The preparation of fill subgrades and the operations of fill placement should be observed on a full-time basis by an authorized representative of the Geotechnical Engineer of Record (GER) to check that unsuitable materials are removed, and fill is constructed in compliance with the recommendations contained within this addendum letter. 5.2.3 High Plasticity Soils High plasticity Fat CLAY (CH) was encountered in all of the borings performed for this project. Highly plastic soils are generally encountered in areas underlain by limestone and dolostone bedrock. These soils can develop significant shrink/swell problems with variations in moisture content. As earthwork operations proceed, additional Atterberg Limits and Expansion Index tests are recommended in order to evaluate suitability of questionable on-site soils. High plasticity soils that cannot be shown to have “very low” expansion potential should be dealt with in accordance with the recommendations presented below. Where expansive soils are encountered at foundation bearing level, the foundations may either step down to bear at a depth of 4 feet below finished exterior grade, or the area may be undercut and backfilled to the original bearing elevation. Undercutting of the storm structure foundations and backfilling with granular backfill or gravel is not recommended, as this would create a reservoir condition that could saturate the plastic soils. Undercut foundations shall be backfilled with properly compacted, suitable fine- grained soil or preferably, lean concrete to the original bearing elevation. Foundations undercut in plastic soils should be excavated using a neat excavation and backfilled entirely with lean concrete. If the footings are stepped down to bear at a minimum depth of 5 feet below the finished exterior grades, the foundations may bear on either high or low plasticity soils. At this depth, the foundations are considered to be below the depth of typical seasonal moisture change. 5.2.4 Rock Excavation Based upon the auger refusal depths encountered in four out of the five soil borings performed at the site we anticipate blasting or hoe-ramming may be necessary. The soil borings encountered auger refusal at elevations ranging between EL. 653± feet to feet to EL. 669± feet (or between 9.2± and 17.0± feet below the ground surface). Depending on the final cut elevations, utility line invert elevations, and the variability of the underlying rock surface, rock excavation or blasting may be necessary. Excavations beyond the soil boring termination depths in the limestone/dolostone bedrock may require controlled blasting operations. Within local excavations for utility lines, we anticipate that hoe-ramming will be feasible if excavation is to extend below these levels. For the construction planning and final pay quantities, we recommend that the following definition be used to define hard rock excavation material for the project specification: Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 17 “Rock shall be defined as those natural materials which cannot be excavated in an open excavation with a Caterpillar Model D-8, heavy duty track-type tractor, weighted at not less than 285 hp flywheel power and equipped with a single-shank hydraulic ripper, capable of exerting not less than 45,000 lbs. breakout force, or equivalent machinery. For trenches and pits, rock shall be defined as those materials that cannot be excavated with a Caterpillar Model No. 345 L track-type hydraulic excavator, weighing not less than 99,000 lbs., equipped with a 30-inch wide short-tip radius rock bucket, rated at not less than 345 hp flywheel power with bucket-digging force of not less than 39,000 lbs, or equivalent machinery. Boulders or masses of rock exceeding one cubic yard in volume shall also be considered rock excavation. This classification does not include materials such as loose rock, concrete, or other materials that can be removed by means other than drilling and blasting, rock trenching, or hoe-ramming, but which for reasons of economy in excavating, the contractor chooses to remove by drilling and blasting, rock trenching, or hoe-ramming techniques.” When reviewing these data for planning purposes, consideration of the excavation capabilities of different equipment will be necessary. For example, a backhoe will likely not be able to excavate weathered rock materials as easily as a trackhoe or ripper. At the same time, ripping may not be an appropriate excavation method for the desired activities. The values derived herein have been provided for informational purposes and are not intended to suggest or recommend excavation methods for utility infrastructure. Irregularities as described below in the base of the excavation are acceptable, if rock materials are encountered. For the purposes of bid documentation, any irregularity of up to 1 foot vertically for 10 feet of horizontal distance is acceptable. Proper control of blasting operations is critical at the site, along with timing of blasting operations. Care should be exercised when blasting in close proximity to existing utility lines. The potential for overblasting should be recognized during both the design and construction phases. We strongly recommend the GER meet with the grading contractor and any blasting specialists to review shot patterns and blasting procedures at the time of construction to reduce difficulties associated with overblasting. If overshooting occurs, the loose or disturbed materials should be removed and replaced with controlled, compacted fill placed in accordance with the recommendations included in this report. 5.3 KARST RELATED RECOMMNEDATIONS 5.3.1 Karst Risk and Construction Issues Karst geology presents the developer with unique hazards and these hazards significantly increase the risk associated with developing a site. Risks associated with developing in Karst are related to the infiltration of surface waters and solutioning by groundwater over extended geologic time frames. Site development activity inherently changes the surface and groundwater flow patterns. Although sinkholes stem from geologic conditions within the underlying rock that have developed over significant time periods, they are often triggered by present day changes in the surface and subsurface drainage patterns. Creating new drainage channels and impoundments for stormwater management activities during land development, collection of groundwater in utility pipelines, leaking utilities, and pumping of groundwater for mining or water supply purposes are some anthropogenic influences that have led to the development of unsuspected karst problems. When developing in karst prone geology, there is always a risk that karst hazards may impact the project, either during construction, or years and decades after the completion of construction. Sinkholes can occur as a gradual erosion of soils into the subsurface causing settlement damage to surface features and development over a long period of time, or rapidly in the case of a sudden cover collapse sinkhole as has Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 18 been witnessed in the recent past in other areas of the country. In addition to sinkhole hazards, the sudden collapse of cave roofs due to overloading by structures can also occur. Karst hazards may sometimes lead to personal injury but rarely do they result in loss of life. Property damage due to Karst hazards can range from simple inconvenience to catastrophic property loss. 5.3.2 Karst Earthwork Recommendations In order to reduce the potential for future sinkhole development which could impact foundation performance, positive surface drainage should be maintained both during and after construction. We recommend that the following preventative measures be followed (where practical) to reduce the potential inducement of sinkhole formation in proposed development areas. 1. All earthwork operations should be graded to drain away from the buildings and structural areas at all times.  Upon completion of daily earthwork operations, the ground surface should be sealed by thorough rolling to reduce infiltration of precipitation and facilitate runoff. 2. All sediment control management facilities should be located outside of planned construction areas.  Inlets associated with storm drain systems should not be utilized as temporary sediment control devices during construction. 3. During construction, care should be taken to reduce the ponding of surface water.  Excavations should be excavated and backfilled the same day, if possible, or the founding soils must be provided with a mud mat to protect from water infiltration. 4. Excavations should be protected from surface water by diversion dikes or other means to direct surface water around the excavation. 5. Visual observations during all earthwork operations should be carried out in order to detect any previous unexposed or recently created collapse features.  Any such feature should be called to the GER’s attention for remedial improvement. 6. Final site grading should include sloping grades and piping of downspouts away from the limits of the excavation (building envelope) made for building construction to prevent introducing unwanted water to building foundation areas. Irrigation within the building envelope should be avoided. The piping of downspouts should be anticipated. If irrigation is to be used or piping of downspouts is undesirable, we recommend that the uppermost 2 feet of building backfill consist of low permeability engineered fill that can be demonstrated to provide a remolded permeability of 1x10-6 centimeters per second or less. On-site clayey soils are expected to be suitable for this purpose, however soils proposed for this use should be tested in the laboratory or in the field after placement to confirm their permeability. 7. All storm piping should be designed such that joints and structure tie-ins remain watertight with allowance for some settlement. Leaking storm pipes promote subsurface seepage and can instigate sinkhole development in the form of surficial dropouts with little or no warning. We recommend that all available geotechnical data be made available to the GER and/or their onsite representative during earthwork operations. It should be clearly understood that the total elimination of hazards associated with Karst is not practical. Even after implementing the recommendations contained within this report, Karst hazards are still possible. 5.4 UTILITY INSTALLATIONS Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 19 Utility Subgrades: The soils encountered in our exploration are expected to be generally suitable for support of utility pipes should they be utilized. Undercutting and replacement of soft and wet soils may be required. It may be necessary to utilize geotextile reinforcement in conjunction with select fill or lean concrete backfill to create a suitable bearing surface for the utility line. Where rock is encountered at the utility elevation it should be removed at least 6 inches below and 8 inches outside of the edge of the utility. Utility Backfilling: The granular bedding material should be at least 4 inches thick, but not less than that specified by the civil engineer’s project drawings and specifications. We recommend that the bedding materials be placed up to the springline of the pipe. Fill placed for support of the utilities, as well as backfill over the utilities, should satisfy the requirements for Structural Fill and Fill Placement. Excavation Safety: All excavations and slopes should be constructed and maintained in accordance with OSHA excavation safety standards. The contractor is solely responsible for designing, constructing, and maintaining stable temporary excavations and slopes. The contractor’s responsible person, as defined in 29 CFR Part 1926, should evaluate the soil exposed in the excavations as part of the contractor’s safety procedures. In no case should slope height, slope inclination, or excavation depth, including utility trench excavation depth, exceed those specified in local, state, and federal safety regulations. ECS is providing this information solely as a service to our client. ECS is not assuming responsibility for construction site safety or the contractor’s activities; such responsibility is not being implied and should not be inferred. Snowden Bridge Regional Pond April 26, 2022 ECS Project No. 01:31598 Page 20 6.0 CLOSING ECS has prepared this report to guide the geotechnical-related design and construction aspects of the project. We performed these services in accordance with the standard of care expected of professionals in the industry performing similar services on projects of like size and complexity at this time in the region. No other representation, expressed or implied, and no warranty or guarantee is included or intended in this report. The description of the proposed project is based on information provided to ECS by GreyWolfe, Inc.. If any of this information is inaccurate or changes, either because of our interpretation of the documents provided or site or design changes that may occur later, ECS should be contacted so we can review our recommendations and provide additional or alternate recommendations that reflect the proposed construction. We recommend that ECS review the project plans and specifications so we can confirm that those plans/specifications are in accordance with the recommendations of this geotechnical report. Field observations, and quality assurance testing during earthwork and foundation installation are an extension of, and integral to, the geotechnical design. We recommend that ECS be retained to apply our expertise throughout the geotechnical phases of construction, and to provide consultation and recommendation should issues arise. ECS is not responsible for the conclusions, opinions, or recommendations of others based on the data in this report. APPENDIX A – Drawings & Reports Site Vicinity Map Boring Location Diagram SITE VICINITY MAP SNOWDEN BRIDGE STATION REGIONAL POND ECS PROJECT NO.31598 SHEET 1 N S EW SCALE: 1"=2000' NOTE: BASE MAP TAKEN FROM USGS TOPO, WINCHESTER & STEPHENSON, VA-WV QUADRANGLE (2016) SITE DI-1 - TOP=671.0'(15") INV IN=668.2'(6") INV IN = 661.0'(24") INV OUT=666.3'BOTTOM=659.0'24" ES-1INV=665.0'INV=673.8'2 4 "X 38 " ERC PINV=670.4'INV=670.75'INV=670.85'60' @ 0.14%30" HDPE661665670675677677670666671677677675670665661661665684680675670665664664665672 67560' GABION WALL 72' GABION WALLSWM-01SWM-02SWM-03SWM-04SWM-05SCALEPROJECT NO.SHEETDATEENGINEERDRAFTINGECS REVISIONSBORING LOCATION DIAGRAM GREYWOLFE, INC SNOWDEN BRIDGE STATION REGIONAL POND STEPHENSON, VA31598NCBRAC1'=80'104/25/2022LEGEND APPROX. BORING LOCATION0SCALE (IN FEET)408080TOPOGRAPHIC REFERENCE:DIAGRAMS WERE DEVELOPED FROM THE SITE PLAN PROVIDEDBY GREYWOLFE, INC., THE PROJECT CIVIL ENGINEER.THESE ELEVATIONS ARE REPORTED BY GREYWOLFE, INC. ATA CONTOUR INTERVAL OF 1FT.*FOR INFORMATIONAL PURPOSES ONLY*SEE APPROVED SITE PLAN FOR SPECIFIC GRADING INFORMATIONC:\Users\rcowart\OneDrive - ECS Corporate Services\Geo eProj 31500-31599\31598 Snowden Regional Pond\b-Drafting\31598_BLD.dwg, bld_11x17_landscape_clr, 4/25/2022 2:14:12 PM APPENDIX B – Field Operations Subsurface Exploration Procedure: Standard Penetration Testing (SPT) Reference Notes for Boring Logs Boring Logs (SWM-01 through SWM-05) - -- • - - - • - - • • • - — - REFERENCE NOTES FOR BORING LOGS MATERIAL1,2 1Classifications and symbols per ASTM D 2488-17 (Visual-Manual Procedure) unless noted otherwise. 2To be consistent with general practice, “POORLY GRADED” has been removed from GP, GP-GM, GP-GC, SP, SP-SM, SP-SC soil types on the boring logs. 3Non-ASTM designations are included in soil descriptions and symbols along with ASTM symbol [Ex: (SM-FILL)]. 4Typically estimated via pocket penetrometer or Torvane shear test and expressed in tons per square foot (tsf). 5Standard Penetration Test (SPT) refers to the number of hammer blows (blow count) of a 140 lb. hammer falling 30 inches on a 2 inch OD split spoon sampler required to drive the sampler 12 inches (ASTM D 1586). “N-value” is another term for “blow count” and is expressed in blows per foot (bpf). SPT correlations per 7.4.2 Method B and need to be corrected if using an auto hammer. 6The water levels are those levels actually measured in the borehole at the times indicated by the symbol. The measurements are relatively reliable when augering, without adding fluids, in granular soils. In clay and cohesive silts, the determination of water levels may require several days for the water level to stabilize.In such cases, additional methods of measurement are generally employed. 7Minor deviation from ASTM D 2488-17 Note 14. 8Percentages are estimated to the nearest 5% per ASTM D 2488-17. Reference Notes for Boring Logs (09-02-2021).doc © 2021 ECS Corporate Services, LLC. All Rights Reserved COHESIVE SILTS & CLAYS UNCONFINED COMPRESSIVE STRENGTH, QP4 <0.25 0.25 - <0.50 0.50 - <1.00 1.00 - <2.00 2.00 - <4.00 4.00 - 8.00 >8.00 SPT5 (BPF) CONSISTENCY7 (COHESIVE) GRAVELS, SANDS & NON-COHESIVE SILTS SPT5 DENSITY <5 5 - 10 11 - 30 31 - 50 >50 Very Loose Loose Medium Dense Dense Very Dense WATER LEVELS6 RELATIVE AMOUNT7 Trace With Adjective (ex: “Silty”) COARSE GRAINED (%)8 <5 FINE GRAINED (%)8 <5 DRILLING SAMPLING SYMBOLS & ABBREVIATIONS PARTICLE SIZE IDENTIFICATION DESIGNATION PARTICLE SIZES Hollow Stem Auger Power Auger (no sample) Bulk Sample of Cuttings Wash Sample Shelby Tube Sampler Split Spoon Sampler Rock Quality Designation % Rock Sample Recovery % Rock Core, NX, BX, AX Rock Bit Drilling Pressuremeter TestSS ST WS BS PA HSA RQD PM RD RC REC Boulders Cobbles Gravel: Sand: Silt & Clay (“Fines”) Fine Medium Coarse Fine Coarse 0.074 mm to 0.425 mm (No. 200 to No. 40 sieve) <0.074 mm (smaller than a No. 200 sieve) 0.425 mm to 2.00 mm (No. 40 to No. 10 sieve) 2.00 mm to 4.75 mm (No. 10 to No. 4 sieve) 4.75 mm to 19 mm (No. 4 sieve to ¾ inch) ¾ inch to 3 inches (19 mm to 75 mm) 3 inches to 12 inches (75 mm to 300 mm) 12 inches (300 mm) or larger >50 31 - 50 16 - 30 9 - 15 5 - 8 2 - 4 <2 Very Hard Hard Very Stiff Stiff Firm Soft Very Soft ASPHALT CONCRETE GRAVEL TOPSOIL VOID BRICK AGGREGATE BASE COURSE GW GP GM GC SW SP SM SC ML MH CL CH OL OH PT WELL-GRADED GRAVEL gravel-sand mixtures, little or no fines POORLY-GRADED GRAVEL gravel-sand mixtures, little or no fines SILTY GRAVEL gravel-sand-silt mixtures CLAYEY GRAVEL gravel-sand-clay mixtures WELL-GRADED SAND gravelly sand, little or no fines POORLY-GRADED SAND gravelly sand, little or no fines SILTY SAND sand-silt mixtures CLAYEY SAND sand-clay mixtures SILT non-plastic to medium plasticity ELASTIC SILT high plasticity LEAN CLAY low to medium plasticity FAT CLAY high plasticity ORGANIC SILT or CLAY non-plastic to low plasticity ORGANIC SILT or CLAY high plasticity PEAT highly organic soils WL (First Encountered) WL (Completion) WL (Seasonal High Water) WL (Stabilized) FILL POSSIBLE FILL PROBABLE FILL ROCK FILL AND ROCK 25 - 45 10 - 20 30 - 45 10 - 25 DEPTH (FT)5 10 15 20 25 30 SAMPLE NUMBERS-1 S-2 S-3 S-4 S-5 SAMPLE TYPESS SS SS SS SS SAMPLE DIST. (IN)18 18 18 18 4 RECOVERY (IN)12 18 18 8 4 DESCRIPTION OF MATERIAL Topsoil Thickness[3"] (CH) FAT CLAY, yellowish brown, moist, Įrm to sƟī (GC) CLAYEY GRAVEL WITH SAND, brown and gray, moist, dense AUGER REFUSAL AT 11.4 FT WATER LEVELSELEVATION (FT)675 670 665 660 655 650 BLOWS/6"2-3-3 (6) 4-7-6 (13) 2-3-5 (8) 17-20-30 (50) 50/4" (50/4") PlasƟc Limit Water Content Liquid Limit X─────────⚫─────────△ 6 13 8 50 50/4" CLIENT: Greywolfe, Inc PROJECT NAME: Snowden Bridge StaƟon Regional Pond PROJECT NO.:BORING NO.: 01:31598 SWM-01 DRILLER/CONTRACTOR: ECS SHEET: 1 of 1 SITE LOCATION: Redbud Road, Stephenson, Virginia 22603 LOSS OF CIRCULATION NORTHING:EASTING:STATION:SURFACE ELEVATION: 680 BOTTOM OF CASING THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN -SITU THE TRANSITION MAY BE GRADUAL WL (First Encountered) WL (CompleƟon) WL (Seasonal High Water) WL (Stabilized) DRY DRY DRY BORING STARTED: BORING COMPLETED: EQUIPMENT: Geoprobe 7822 Mar 31 2022 Mar 31 2022 LOGGED BY: NCB CAVE IN DEPTH: HAMMER TYPE: DRILLING METHOD: 9.00 Auto 3.25 HSA GEOTECHNICAL BOREHOLE LOG STANDARD PENETRATION BLOWS/FT ROCK QUALITY DESIGNATION & RECOVERY RQD REC CALIBRATED PENETROMETER TON/SF [FINES CONTENT] % DEPTH (FT)5 10 15 20 25 30 SAMPLE NUMBERS-1 S-2 S-3 S-4 SAMPLE TYPESS SS SS SS SAMPLE DIST. (IN)18 18 18 8 RECOVERY (IN)12 12 18 8 DESCRIPTION OF MATERIAL Topsoil Thickness[8"] (GC FILL) FILL, CLAYEY GRAVEL, dark brown and gray, moist, loose (CH) FAT CLAY WITH GRAVEL, brown, moist, Įrm AUGER REFUSAL AT 9.2 FT WATER LEVELSELEVATION (FT)661 656 651 646 641 636 BLOWS/6"2-4-5 (9) 3-5-5 (10) 3-5-7 (12) 10-50/2" (50/2") PlasƟc Limit Water Content Liquid Limit X─────────⚫─────────△ 9 10 12 50/2" CLIENT: Greywolfe, Inc PROJECT NAME: Snowden Bridge StaƟon Regional Pond PROJECT NO.:BORING NO.: 01:31598 SWM-02 DRILLER/CONTRACTOR: ECS SHEET: 1 of 1 SITE LOCATION: Redbud Road, Stephenson, Virginia 22603 LOSS OF CIRCULATION NORTHING:EASTING:STATION:SURFACE ELEVATION: 666 BOTTOM OF CASING THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN -SITU THE TRANSITION MAY BE GRADUAL WL (First Encountered) WL (CompleƟon) WL (Seasonal High Water) WL (Stabilized) DRY DRY DRY BORING STARTED: BORING COMPLETED: EQUIPMENT: Geoprobe 7822 Mar 31 2022 Mar 31 2022 LOGGED BY: NCB CAVE IN DEPTH: HAMMER TYPE: DRILLING METHOD: 8.00 Auto 3.25 HSA GEOTECHNICAL BOREHOLE LOG STANDARD PENETRATION BLOWS/FT ROCK QUALITY DESIGNATION & RECOVERY RQD REC CALIBRATED PENETROMETER TON/SF [FINES CONTENT] % DEPTH (FT)5 10 15 20 25 30 SAMPLE NUMBERS-1 S-2 S-3 S-4 S-5 S-6 SAMPLE TYPESS SS SS SS SS SS SAMPLE DIST. (IN)18 18 18 18 18 6 RECOVERY (IN)18 18 18 18 18 6 DESCRIPTION OF MATERIAL Topsoil Thickness[8"] (CH FILL) FILL, FAT CLAY WITH GRAVEL, dark brown and gray, moist, soŌ (CH) FAT CLAY, yellowish brown, moist, Įrm to sƟī (GM) SILTY GRAVEL WITH SAND, yellowish brown and gray, moist, medium dense to dense AUGER REFUSAL AT 17.0 FT WATER LEVELSELEVATION (FT)665 660 655 650 645 640 BLOWS/6"1-1-2 (3) 2-3-4 (7) 2-4-5 (9) 10-14-16 (30) 6-5-8 (13) 50 PlasƟc Limit Water Content Liquid Limit X─────────⚫─────────△ 3 7 9 30 13 6722 18.8 36.7 30.8 35.5 [92.5%] CLIENT: Greywolfe, Inc PROJECT NAME: Snowden Bridge StaƟon Regional Pond PROJECT NO.:BORING NO.: 01:31598 SWM-03 DRILLER/CONTRACTOR: ECS SHEET: 1 of 1 SITE LOCATION: Redbud Road, Stephenson, Virginia 22603 LOSS OF CIRCULATION NORTHING:EASTING:STATION:SURFACE ELEVATION: 670 BOTTOM OF CASING THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN -SITU THE TRANSITION MAY BE GRADUAL WL (First Encountered) WL (CompleƟon) WL (Seasonal High Water) WL (Stabilized) DRY DRY DRY BORING STARTED: BORING COMPLETED: EQUIPMENT: Geoprobe 7822 Mar 31 2022 Mar 31 2022 LOGGED BY: NCB CAVE IN DEPTH: HAMMER TYPE: DRILLING METHOD: 17.00 Auto 3.25 HSA GEOTECHNICAL BOREHOLE LOG STANDARD PENETRATION BLOWS/FT ROCK QUALITY DESIGNATION & RECOVERY RQD REC CALIBRATED PENETROMETER TON/SF [FINES CONTENT] % DEPTH (FT)5 10 15 20 25 30 SAMPLE NUMBERS-1 S-2 S-3 S-4 S-5 S-6 S-7 SAMPLE TYPESS SS SS SS SS SS SS SAMPLE DIST. (IN)18 18 18 18 18 18 18 RECOVERY (IN)18 18 12 12 18 18 12 DESCRIPTION OF MATERIAL Topsoil Thickness[8"] (CH) FAT CLAY WITH SAND, dark brown, moist, Įrm (CH) FAT CLAY, yellowish brown, moist, Įrm to sƟī (GM) SILTY GRAVEL WITH SAND, yellowish brown and gray, moist, dense (ML) SANDY SILT WITH GRAVEL, yellowish brown and gray, moist, medium dense to dense END OF BORING AT 20.0 FT WATER LEVELSELEVATION (FT)672 667 662 657 652 647 BLOWS/6"2-2-3 (5) 2-3-3 (6) 2-3-4 (7) 4-5-7 (12) 30-29-10 (39) 3-10-12 (22) 3-20-20 (40) PlasƟc Limit Water Content Liquid Limit X─────────⚫─────────△ 5 6 7 12 39 22 40 6523 23.7 31.0 28.3 31.4 [99.0 %] CLIENT: Greywolfe, Inc PROJECT NAME: Snowden Bridge StaƟon Regional Pond PROJECT NO.:BORING NO.: 01:31598 SWM-04 DRILLER/CONTRACTOR: ECS SHEET: 1 of 1 SITE LOCATION: Redbud Road, Stephenson, Virginia 22603 LOSS OF CIRCULATION NORTHING:EASTING:STATION:SURFACE ELEVATION: 676.5 BOTTOM OF CASING THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN -SITU THE TRANSITION MAY BE GRADUAL WL (First Encountered) WL (CompleƟon) WL (Seasonal High Water) WL (Stabilized) DRY DRY DRY BORING STARTED: BORING COMPLETED: EQUIPMENT: Geoprobe 7822 Mar 31 2022 Mar 31 2022 LOGGED BY: NCB CAVE IN DEPTH: HAMMER TYPE: DRILLING METHOD: 15.70 Auto 3.25 HSA GEOTECHNICAL BOREHOLE LOG STANDARD PENETRATION BLOWS/FT ROCK QUALITY DESIGNATION & RECOVERY RQD REC CALIBRATED PENETROMETER TON/SF [FINES CONTENT] % DEPTH (FT)5 10 15 20 25 30 SAMPLE NUMBERS-1 S-2 S-3 S-4 SAMPLE TYPESS SS SS SS SAMPLE DIST. (IN)18 18 18 10 RECOVERY (IN)12 18 18 6 DESCRIPTION OF MATERIAL Topsoil Thickness[6"] (GC FILL) FILL, CLAYEY GRAVEL, dark brown and gray, moist, loose (CH) FAT CLAY, yellowish brown, moist, sƟī (GC) CLAYEY GRAVEL WITH SAND, tannish brown and gray, moist, very dense AUGER REFUSAL AT 9.4 FT WATER LEVELSELEVATION (FT)667 662 657 652 647 642 BLOWS/6"3-4-5 (9) 3-4-5 (9) WOH-6-6 (12) 10-50/4" (50/4") PlasƟc Limit Water Content Liquid Limit X─────────⚫─────────△ 9 9 12 50/4" CLIENT: Greywolfe, Inc PROJECT NAME: Snowden Bridge StaƟon Regional Pond PROJECT NO.:BORING NO.: 01:31598 SWM-05 DRILLER/CONTRACTOR: ECS SHEET: 1 of 1 SITE LOCATION: Redbud Road, Stephenson, Virginia 22603 LOSS OF CIRCULATION NORTHING:EASTING:STATION:SURFACE ELEVATION: 671.5 BOTTOM OF CASING THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN -SITU THE TRANSITION MAY BE GRADUAL WL (First Encountered) WL (CompleƟon) WL (Seasonal High Water) WL (Stabilized) DRY DRY DRY BORING STARTED: BORING COMPLETED: EQUIPMENT: Geoprobe 7822 Mar 31 2022 Mar 31 2022 LOGGED BY: NCB CAVE IN DEPTH: HAMMER TYPE: DRILLING METHOD: 9.00 Auto 3.25 HSA GEOTECHNICAL BOREHOLE LOG STANDARD PENETRATION BLOWS/FT ROCK QUALITY DESIGNATION & RECOVERY RQD REC CALIBRATED PENETROMETER TON/SF [FINES CONTENT] % APPENDIX C – Laboratory Testing Laboratory Test Results Summary Grain Size Analyses Liquid and Plastic Limits Test Report S-1 18.8 S-2 36.7 S-3 30.8 CH 67 22 45 92.5 S-4 35.5 S-1 23.7 S-2 31.0 CH 65 23 42 99.0 S-3 28.3 S-4 31.4 Project: Client: Laboratory Testing Summary Sample Location Sample Number Depth (feet) ^MC (%) Soil Type Atterberg Limits **Percent Passing No. 200 Sieve Moisture - Density CBR (%) #Organic Content (%)LL PL PI <Maximum Density (pcf) <Optimum Moisture (%)0.1 in.0.2 in. SWM-03 0-1.5 SWM-03 2.5-4 SWM-03 5-6.5 SWM-03 8.5-10 SWM-04 0-1.5 SWM-04 2.5-4 SWM-04 5-6.5 SWM-04 8.5-10 Notes:See test reports for test method, ^ASTM D2216-19, *ASTM D2488, **ASTM D1140-17, #ASTM D2974-20e1 < See test report for D4718 corrected values Definitions:MC: Moisture Content, Soil Type: USCS (Unified Soil Classification System), LL: Liquid Limit, PL: Plastic Limit, PI: Plasticity Index, CBR: California Bearing Ratio, OC: Organic Content Snowden Bridge Station Regional Pond Project No.:01:31598 Greywolfe, Inc Date Reported:4/18/2022 Office / Lab Address Office Number / Fax ECS Mid-Atlantic LLC - Chantilly 14026 Thunderbolt Place Suite 100 Chantilly, VA 20151-3232 (703)471-8400 (703)834-5527 Tested by Checked by Approved by Date Received jvong Htran Dtran 4/13/2022 LL PL PI %<#40 AASHTO 67 22 45 96.2 A-7-6 65 23 42 99.4 A-7-6 LIQUID AND PLASTIC LIMITS TEST REPORT TEST RESULTS (ASTM D4318-10 (MULTIPOINT TEST)) Sample Location Sample Number Sample Depth (ft)%<#200 USCS Material Description SWM-03 S-3 5-6.5 92.5 CH Fat Clay Yellowish Brown SWM-04 S-2 2.5-4 99.0 CH Fat Clay Yellowish Brown Project:Snowden Bridge Station Regional Pond Project No.:01:31598 Client:Greywolfe, Inc Date Reported:4/18/2022 Office / Lab Address Office Number / Fax ECS Mid-Atlantic LLC - Chantilly 14026 Thunderbolt Place Suite 100 Chantilly, VA 20151-3232 (703)471-8400 (703)834-5527 Tested by Checked by Approved by Date Received jvong Htran Dtran 4/13/2022 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 110 LIQUID LIMIT ML or OLCL-ML MH or OH P L A S T I C I T Y I N D E X Dashed line indicates the approximate upper limit boundary for natural soils D90 D50 D10 D85 D30 Cu D60 D15 Cc PARTICLE SIZE DISTRIBUTION TEST RESULTS (ASTM D422-63(2007)) Sieving Hydrometer Sedimentation Dry Mass of sample, g 46.8 Particle Size % Passing Particle Size mm % Passing Very coarse, >3" sieve 0.0 3"100.0 Sample Proportions % dry mass #10 98.8 #4 100.0 #20 97.4 Gravel, 3" to # 4 sieve 0.0#40 96.2 #60 95.1 Coarse Sand, #4 to #10 sieve 1.2#100 93.9 #200 92.5 Medium Sand, #10 to #40 2.6 Fine Sand, #40 to #200 3.7 Fines <#200 92.5 USCS CH Liquid Limit 67 AASHTO A-7-6 Plastic Limit 22 USCS Group Name Fat clay Plasticity Index 45 Project:Snowden Bridge Station Regional Pond Project No.:01:31598 Client:Greywolfe, Inc Depth (ft):5 - 6.5 Sample Description:Fat Clay Yellowish Brown Sample No.:S-3 Sample Source:SWM-03 Date Reported:4/18/2022 Office / Lab Address Office Number / Fax ECS Mid-Atlantic LLC - Chantilly 14026 Thunderbolt Place Suite 100 Chantilly, VA 20151-3232 (703)471-8400 (703)834-5527 Tested by Checked by Approved by Date Received Remarks jvong Htran Dtran 4/13/2022 ÷÷ ø ö çç è æ 1m m SILTSAND FineMediumCoarseGRAVEL CLAYVery Coarse 3"2"1.5"1"3/4"1/2"3/8"#4 #10 #20 #40 #60 #100 #140 #200 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000Percentage Passing %Particle Size mm D90 D50 D10 D85 D30 Cu D60 D15 Cc PARTICLE SIZE DISTRIBUTION TEST RESULTS (ASTM D422-63(2007)) Sieving Hydrometer Sedimentation Dry Mass of sample, g 43.4 Particle Size % Passing Particle Size mm % Passing Very coarse, >3" sieve 0.0 3"100.0 Sample Proportions % dry mass #10 99.9 #4 100.0 #20 99.5 Gravel, 3" to # 4 sieve 0.0#40 99.4 #60 99.3 Coarse Sand, #4 to #10 sieve 0.1#100 97.8 #200 99.0 Medium Sand, #10 to #40 0.5 Fine Sand, #40 to #200 0.4 Fines <#200 99.0 USCS CH Liquid Limit 65 AASHTO A-7-6 Plastic Limit 23 USCS Group Name Fat clay Plasticity Index 42 Project:Snowden Bridge Station Regional Pond Project No.:01:31598 Client:Greywolfe, Inc Depth (ft):2.5 - 4 Sample Description:Fat Clay Yellowish Brown Sample No.:S-2 Sample Source:SWM-04 Date Reported:4/18/2022 Office / Lab Address Office Number / Fax ECS Mid-Atlantic LLC - Chantilly 14026 Thunderbolt Place Suite 100 Chantilly, VA 20151-3232 (703)471-8400 (703)834-5527 Tested by Checked by Approved by Date Received Remarks jvong Htran Dtran 4/13/2022 ÷÷ ø ö çç è æ 1m m SILTSAND FineMediumCoarseGRAVEL CLAYVery Coarse 3"2"1.5"1"3/4"1/2"3/8"#4 #10 #20 #40 #60 #100 #140 #200 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000Percentage Passing %Particle Size mm APPENDIX D – Additional Figures French Drain Installation Procedure Typical Dam Cross Section and Drainage Detail Benching Detail Karst Auger Refusal Scenario Diagram SUBSOILFINAL CONFIGURATIONSTEP 1STEP 2STEP 3VDOT #57AGGREGATEGEOTEXTILEFILTER FABRICSUBDRAIN USING FILTER FABRICFABRIC IS UNROLLED DIRECTLY OVER TRENCHTHE TRENCH IS FILLED WITH AGGREGATETHE FABRIC IS LAPPED CLOSED ANDCOVERED WITH BASE STONEFRENCH DRAINNOT TO SCALEINSTALLATION PROCEDURE AUGER REFUSAL AT RELATIVELY SHALLOW DEPTH ON A BEDROCK PINNACLE AUGER REFUSAL IN A DEEP SOIL CUTTER AUGER REFUSAL ON A FLOAT BOULDER GIVING A FALSE INDICATION OF SHALLOW BEDROCK AUGER REFUSAL DUE TO DEFLECTING AUGERS - CONTINUED DOWNWARD FORCE CAN CAUSE THE FAILURE OF AUGER CONNECTIONS AND LOSS OF DRILL STRING IN THE BOREHOLE KARST AUGER REFUSAL SCENARIO DIAGRAM NOT TO SCALE NOTE: AUGER REFUSAL IN ALL SCENARIO'S MAY MASK THE PRESENCE OF KARST VOIDS 1 2 3 4 1 2 3 4 GROUND SURFACE CARBONATE BEDROCK