DEEP WELL DISPOSAL OF SECONDARY EFFLUENT IN DADE COUNTY, FLORIDA1

Abstract

ABSTRACT: Data were obtained from drilling and testing of a test injection well for deep underground injection of waste water effluent from the proposed 50‐million‐gallon‐per‐day (mgd) South District Regional Wastewater Treatment Plant of the Miami‐Dade Water and Sewer Authority, Dade County, Florida. The drilling operation progressed in stages, each stage coverting the strata to be sealed off by the 48‐inch, 40‐inch, 30‐inch, and 20‐inch casings, respectively. Total depth of the well is 3,200 feet. The top of the saline, cavernous, dolomitic Boulder Zone was found at 2,790 feet below the surface and is separated from the Floridan aquifer above by approximately 1,100 feet of confining limestone layers. These confining layers were determined, by packer testing, to be very effective. The transmissivity of the Boulder Zone was estimated to be 14 × 106 gallons per day per foot (gpd/ft) from the data obtained from pump out tests. An 8,000‐gallon‐per‐minute (gpm) injection test was conducted to confirm well performance under operating conditions. Based on all of the data obtained, it was concluded that underground injection into the Boulder Zone of secondary waste water effluent from the proposed treatment plant is feasible, both hydraulically and environmentally. A monitoring system was proposed to provide a record of the effects of injection on the subsurface environment.