The groundwater remediation industry continues to progress towards less expensive, more sustainable in situ remedies. However, in situ treatment requires site-specific performance data that can be difficult or impossible to obtain using conventional laboratory microcosm studies. To improve the representativeness of laboratory scale treatability studies, and aid in remedial technology implementation, we developed the In Situ Microcosm Array (ISMA). This autonomous diagnostic device enables the deployment of 10 flow-through sediment columns within a standard 10-cm groundwater-monitoring well. Suspended at the desired aquifer depth, the fully encapsulated ISMA meters groundwater directly from the aquifer to microcosms containing competing remedial technologies. Field demonstrations of the instrument were performed in two aquifers contaminated, respectively, with trichlomethylene and hexavalent chromium, and with perchlorate. A cost assessment positions ISMA deployment costs within the range of conventional laboratory testability studies. Results demonstrate the ISMA's utility to perform cost-effective, high-throughput, screenings of multiple intervention strategies in the field, without impacting the subsurface environment examined.