Deep Injection Wells Injection Capacity Evaluation for Disposal of RO Concentrate and Facility Process Wastewater

Two deep injection wells have been constructed and tested in Polk County, Florida to dispose of reverse osmosis concentrate from the treatment of regional reclaimed water and process wastewater flows. The injection wells are completed in Cretaceous aged formations to a total depth of 8000 feet below land surface and are the deepest injection wells in the state of Florida. Based on injection capacity evaluations, each injection well will have an anticipated maximum operational injection rate of approximately 1.3 million gallons per day (900 gallons per minute).

The injection zone is composed of moderately permeable limestone along with sequences of low permeability limestone and dolostone beneath a 1100-foot-thick anhydrite sequence. The injection zone has extremely high salinity, with total dissolved solids concentrations greater than 200,000 mg/L. The high salinity of the injection zone significantly increases the density of the formation fluids and presented unique challenges to performing pump tests, analyzing formation pressures resulting from injection testing, and assessing the portion of the open borehole available for injection.

A significant amount of data has been collected and analyzed within the injection zone from packer tests, coring, geophysics, and short-term step injection tests to acquire a better understanding of how the well and formations will respond to operational use. The short-term testing data indicates that the injectate is primarily utilizing the formation above 5000 feet below land surface; however, long-term operation will likely utilize all permeability in the borehole. Since this well will be receiving a combined waste stream, a plugging and precipitation study is being conducted to evaluate the risks and potential pretreatment to minimize geochemical issues.