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EM 1110-1-4001 3 Jun 02 . Valley and both were contaminated with TCE and PCE The first example is a relatively simple site where two extraction wells were operated simultaneously for nearly two years at a steady flow rate with a number of shutdown periods Vapor sampling was performed only with the combined flow Individual wells were not sampled The second example is from a more complicated site where from one to four wells were operated simultaneously in various configurations with varying extraction rates and two rebound tests over a five year period Modeling of this more complicated site required a detailed review Of extraction rates,durations, and measured concentrations from both individual wells and the combined flow in the manifold a Case Study Site I Historical operation of SVE at Site 1 was simultaneous extraction from two wells without any flow balancing(i c ,the same vacuum was applied to both wells) In addition,only total flow was measured and all extracted concentrations were collected from the combined vapor stream Therefore,historical data do not exist for the concentrations and masses removed from individual wells The historical TCE concentrations measured in the combined stream during the first year and half of SVE at Site 1 are illustrated in Figure F-3 Startup of the system involved a couple of brief shutdowns and a long shutdown occurred after the first month The system was re-started during the ninth month The extraction history used to model the process consisted of 69 constant flow segments but these were generally either 400 cubic feet per minute or zero The extraction rates, start times and stop times were estimated from monthly status reports The assumed soil properties for the modeling are listed in Table F-1 Kd was set equal to one because organic carbon was not detected in any soil samples from the site F-15