General

A BOULDER PROPOSAL: Filtration for Deep Well Injection

As the earth’s climate continues to heat up and weather around the globe becomes increasingly extreme, debates on how to protect the environment grow similarly heated. Heavy rainwater discharges like the one from polluted Lake Okeechobee in Florida’s Kissimmee River Valley is one example that requires quick action in order to protect the ecology of its surrounding estuaries. While many technological options are being considered, one option dating back several decades may be the answer to this new problem: deep well injection.

Deep well injection – a method of disposing of liquid waste into the geologic "boulder zone" – is cost-effective and can be used quickly when needed. A typical injection well extends several thousand feet down from the surface into highly saline, permeable injection zones such as deep sandstone or limestone, remaining below an impermeable layer.

Widespread use of injection wells began in the 1930s to dispose of brine generated during oil production. In the 1950s, as chemical manufacturing increased, chemical companies began injecting industrial wastes into deep wells as an inexpensive option for the disposal of unwanted and often hazardous industrial byproducts. These wells are permitted and regulated by the U.S. Environmental Protection Agency (EPA), who currently regulates around 850,000 underground injection wells under the Safe Drinking Water Act.

The EPA defines six classes of wells based on their use:

Class I industrial and municipal waste disposal wells (approximately 800 exist in the U.S.)
Class II oil and gas related injection wells (180,000)
Class III solution mining wells (18,500)
Class IV shallow hazardous and radioactive waste injection wells (banned in 1984).
Class V wells for non-hazardous fluids (650,000)
Class VI geologic sequestration wells for CO2 (no data)

Particularly interesting from a filtration perspective are Class I and II wells. Preservation of these wells is essential to maintaining a low operational cost while the well is mandated for use. Since wells are generally thousands of feet deep, it’s critical to protect the porosity of the injection formation zone. High concentrations of suspended solids (typically >2 ppm) can lead to plugging, which can significantly shorten the life of the well and in turn may cost many millions of dollars to treat or replace.

There is no single filtration recommendation, possibly due to the wide variation of strata in the injection zone. Depending on the site, low-end technology such as bags or melt blown filters may suffice, and in some instances sub-micron filtration may apply, which then requires a suitable prefiltration scheme. Wells typically have high flow rates which makes large diameter filters such as the High Flow or High Flow RF an ideal choice as both the prefilter and final filter. Where sub-micron filtration is required, membrane filters such as the WaterTEC provide an economical approach while meeting critical retention requirements.

Want to see inside a deep injection well? Get ready to go 3,000 feet into the “boulder zone”...