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H2A Engineers Evaluate Feasibility of Converting an Existing DPE System to TPE

written by Shannon

TPE Schematic

H2A’s Shannon Walker, PE, and Si Xu, EIT, recently completed an engineering evaluation of the feasibility of converting an existing dual-phase extraction (DPE) system to two-phase extraction (TPE). The conversion would increase groundwater drawdown and applied vacuum, thereby improving groundwater capture. The evaluation involved determining necessary well flows and associated friction losses based on the existing pipe network. The blower types and sizes required to achieve the desired well flow and design vacuum were specified based on known system losses, losses to the formation, and vacuum versus flow relationships.

Prior to completing the engineering evaluation, H2A personnel led field survey efforts to collect information about the existing pipe network including diameters, distances, fittings, and vertical elevation changes. This data, in conjunction with extensive site-specific DPE pilot test data previously developed by H2A, formed the basis for the design calculations. System friction losses were estimated using the Darcy-Weisback equation. The equivalent length method was used to estimate the losses associated with various fittings (i.e., bends, reducers/enlargers, and valves) located throughout the system. Because fully turbulent flow was assumed, the Sacham equation was used to approximate a fully numerical solution for friction factor.

Note: Figure obtained from the U.S. Environmental Protection Agency’s Design Guidelines for Conventional Pump-and-Treat Systems published in 1997 (EPA/540/S-97/504).

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