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1 <br /> 43 ENGINEERING DESCRIPTION <br /> r <br /> Implementation of DPE involves construction of extraction wells(or modification of existing monitoring <br /> wells) and installation of extraction and treatment equipment Figure 4-1 presents a schematic of a typical <br /> DPE system Generally,the technology required for design and construction of a DPE system is well <br />' established and is largely based on experience gamed from implementation of separate SVE and <br /> groundwater extraction systems Specific design factors related to the method of DPE employed ultimately <br /> determine the physical as well as operating characteristics of the system and influence its ability to achieve <br /> site-specific remediation goals The following subsections discuss general DPE system design and describe <br /> ' characteristics of the three types of DPE systems <br /> 4.3.1 Dual-Phase Extraction System Design <br /> DPE system design considerations include extraction well construction, anticipated vapor and water flow <br /> rates,vapor/liquid separation requirements, and vapor and liquid treatment requirements Site <br /> characteristics,including soil pneumatic and hydraulic conductivities,contaminant vertical and horizontal <br /> distributions,potential groundwater treatment and discharge requirements,and the presence of existing <br /> monitoring or extraction facilities,largely determine which type of DPE will meet remedial design <br /> objectives most effectively <br /> 4.311 Pilot Testing <br /> ' Well placement and extraction system capacity and design are usually based on the results of pilot testing <br /> Pilot test activities focus on both water and vapor extraction characteristics Frequently, aquifer hydraulic <br /> ' properties are determined by aquifer step testing followed by pump testing A conventional vapor <br /> extraction test may also be conducted to determine soil vapor flow characteristics and vadose zone of <br /> influence DPE pilot testing is then conducted to determine both step and steady-state characteristics of the <br /> rextraction system Parameters that may be monitored during testing include the following <br /> ' Induced vacuum versus distance <br /> ' Water drawdown versus distance <br /> 4-5 <br />