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61 <br /> Envirotactics <br /> An Earth Systems Company <br /> 4.0 CONCEPTUAL MODEL OF GROUNDWATER FLOW <br /> Prior to the development of a mathematical groundwater flow model, it is necessary to develop a conceptual <br /> model of subsurface conditions that summarizes important geologic, hydrologic, and hydraulic features of <br /> the groundwater system. This conceptual model will provide the framework that describes essential input <br /> parameters required by a mathematical model. Thus, the understanding of the groundwater system <br /> developed in a conceptual model is the foundation for a mathematical model. <br /> A conceptual groundwater flow model succinctly describes the principal components of a groundwater flow <br /> system and is developed from regional, local, and site-specific information. Therefore, a Hydrogeologic <br /> Desktop Study, included here in Attachment 2, was conducted for the Site that provides more regional and <br /> local detail. However, it is important to understand that only limited site-specific information was available <br /> for our consideration, consisting only of basic well permitting and construction information that were absent <br /> of borehole logging. <br /> The primary components of a conceptual model for the groundwater flow systems include: (1) areal extent, <br /> configuration, and type of aquifers and aquitards; (2) hydraulic properties of aquifers and aquitards; (3) <br /> natural groundwater recharge and discharge zones; (4) anthropogenic groundwater sources and sinks; and <br /> (5) areal and vertical distribution of groundwater hydraulic head potential. <br /> 4.1 Physiography <br /> The Site lies within the Piedmont Plateau Physiographic Province. The Piedmont Plateau is an ancient <br /> erosional surface characterized by gently rolling well-rounded hills and long low ridges. The Piedmont <br /> Plateau is 60 to 75 miles wide and ranges in altitude from 500 to 1,500 feet. The topography is consistent <br /> with this characterization in the vicinity of the Site,with rolling hills incised by many streams. Drainage in the <br /> Piedmont Plateau is generally toward the southeast because of the general northwest-southeast <br /> orientation to the stream valleys. The stream valleys are generally aligned with structural features in the <br /> underlying bedrock. <br /> 4.2 Geology <br /> Generally, in the vicinity of the Site, there are two (2) discrete lithologic units: <br /> • a surficial regolith and <br /> • a bedrock complex. <br /> The surficial regolith unit consists of unconsolidated soil and saprolite material. The saprolite is primarily <br /> residual soil derived from in-situ weathering ofthe underlying rock.The regolith is typically dominated by silty <br /> clay with varying amounts of organic matter and detritus and occasional localized deposits of quartz sand. <br /> The surficial regolith is underlain by granite and diorite bedrock at depths generally ranging from zero to 25 <br /> feet. This contact is gradational, since it was formed by the downward advancement of a weathering front <br /> into the bedrock.The bedrock is generally massive, with abundant high-angle fractures.The graphic below, <br /> which was sourced from the USGA Water-Resources Investigation Report 96-4200 titled, "Ground-water <br /> Envirotactics, LLC Page 11 of 20 Groundwater Modeling Report <br /> (732) 449-0077 Project No.6704 <br />