Ex situ remediation technology has been the primary method for treating groundwater contaminated with poly- and perfluoroalkyl substances. These pump and treat systems are expensive and energy intensive. To address the need for effective in situ remediation technology, a reactor to be used within a subsurface well has been developed. The reactor allows for contaminant destruction methods such as ultrasound to be used in situ. This invention eliminates the need for pumps and aboveground treatment. In addition it produces no waste products that must be treated further.