The Future of Key West Wastewater         

In recent years, the vitality of the reef has been threatened. Recognizing the importance of the reef to the community, Key West along with federal. state, and local government agencies have joined forces with concerned environmental groups to protect and restore this natural beauty.

The City of Key West has taken aggressive steps to reduce nutrients flowing to the ocean, as evidenced by the construction of a deep injection well and the upgrade of their wastewater treatment facility to advanced wastewater treatment capability. 

The Southernmost Plant Reduces Nutrients in its Effluent

A little history….

Prior to the opening of the Key West Southernmost Wastewater Treatment Plant, raw wastewater, laden with nutrients, was discharged directly to the ocean via an ocean outfall. When OMI brought the plant on line in 1989, one of the last raw wastewater discharges to the ocean in the continental United States was terminated. Since the plant became operational, wastewater from the City of Key West flows to the plant through a 30-inch pipeline, where it is treated, disinfected, and was originally pumped through a second 30-inch pipeline to the ocean outfall.  The effluent now discharges to the new deep injection well.

Designed and built as a secondary treatment plant, it was expected to remove pollutants from wastewater and reduce nutrient levels to 20 milligrams per liter of total nitrogen and 6 milligrams per liter of total phosphorus. The Southernmost Plant frequently achieved levels of less than 4 milligrams per liter of total nitrogen biologically and with the addition of alum, <1.0 milligrams per liter of total phosphorus. These levels are just shy of the standards set by the Florida Department of Environmental Protection (FDEP) for advanced wastewater treatment (AWT) plants (which are 3 milligrams per liter of total nitrogen and 1 milligram per liter of total phosphorus). Consequently, through innovative operational technique in manipulating the plant process equipment the City's plant was achieving results normally obtained from costly advanced treatment processes.  OMI was able to frequently achieve AWT standards, but we could not guarantee them.  The people of Key West wanted guaranteed results. 

 Deep Injection Wells Mandated By FDEP

The deep injection well was the first step in providing assurance to the public that the Southernmost Plant was not contributing to nearshore water quality problems. 

The injection well being drilled at the WWTP on Fleming Key.  (Shown Above)

The completed injection well.

Deep injection wells are not new to Florida, with more than 70 systems operating successfully throughout the state since the late '70s. Indeed, the City's Comprehensive Master Plan, adopted in 1989, embraced deep injection wells as a solution to reducing nutrient discharges.

The concept of deep injection is simple. The highly polished effluent is pumped from the treatment plant directly to a steel and concrete encased well that is drilled to a depth of some 3,000 feet below ground. Once the effluent reaches the open hole at the bottom of the well, it flows into the Boulder Zone, a cavernous, limestone rock formation that contains salinity equal to that of the surrounding surface waters .

Click on image to see a bigger view of it.

Shallow Injection Wells--The Difference Runs Deep

There are approximately 350 small wastewater treatment plants scattered throughout the Keys which discharge effluent to SHALLOW injection wells. Although similar in their function of discharging treated effluent underground, shallow injection wells are vastly different from deep injection wells in design and construction. A shallow injection well extends a mere 90 feet below ground, and discharges effluent into a portion of the earth called Miami Oolite, a porous, limestone formation that is likened to a "petrified sponge", allowing water to flow freely within this zone. Since lime is widely used to treat water and wastewater, scientists theorize that perhaps any effluent discharged into the confines of the Miami Oolite formation is treated naturally over time for nutrient removal.

In contrast, a deep injection well extends more than 1/2 mile to the Boulder Zone, which lies beneath non-porous, geologically confined areas. These confining areas prevent effluent from migrating upward out of the Boulder Zone.

Comprehensive analyses conducted by nationally recognized scientists and engineers have compared alternatives with respect to feasibility, environmental soundness, and costs. Deep injection wells have continually been found to be an environmentally safe and effective means of discharging effluent, and would virtually eliminate the discharge of nutrients from the WWTP into the near shore and Outstanding Florida Waters of the Keys. Geological formations through which the well traverses serve as natural safeguards that will prevent leakage of treated effluent upward out of the Boulder Zone, through the confining layers, and into the reef.

Click on image to see a bigger view of it.

The second deep well (pictured below) was completed in July 2006.  The second well allowed us to abandon the original ocean outfall which was still in place as an emergency alternative discharge point in the event of well failure.  We removed a section of the outfall pipe, creating an air gap that makes the line unusable.

               The #2 Injection Well Being Drilled                                                                                                                 #2 Injection Well Completed. (looks just like #1)