Deep Injection Wells Protect Surface Waters From Harmful Effects of Wastewater Discharge

Coastal waters throughout Florida, including Tampa Bay, Biscayne Bay and the Indian River Lagoon, are recovering from decades of environmental harm because utilities are phasing out surface water discharge of treated wastewater in favor of environmentally safe disposal methods.

Many utilities, especially in southern Florida, rely on deep injection wells, which discharge treated wastewater 1,000 to 3,000 feet below the land surface, to protect rivers, lakes and bays from negative impacts of effluent disposal. Modern treatment methods, stringent construction requirements, natural cleansing in the subsurface and formidable natural barriers combine to protect underground drinking water sources.

Although deep wells protect the environment, some utilities are struggling under strict enforcement of an outdated, technical rule that has no corresponding environmental benefit. Adherence to the no migration rule has raised concerns of a building moratorium in some communities, while others may be forced to revert back to surface water discharge.

The rule was intended to protect future drinking water sources in the event hazardous wastes migrated after being discharged into deep injection wells. Yet deep wells for hazardous wastes have been banned, and municipal deep wells have achieved over 20 years of safe operation. There have been no impacts on any potable water system, nor has any theoretical future source of underground drinking water been negated by deep injection and suspected migration of wastewater from receiving zones.

Treated wastewater injected into deep wells:

• Is freshwater, of higher quality than the brine that naturally exists in the receiving zone.

• Is sometimes of higher quality than freshwater withdrawn from supply wells.

• Undergoes natural treatment, including bacterial dieoff and filtering, in the subsurface.
  

• Does not exceed drinking water standards any more than the native waters in the subterranean, brackish aquifers.

• Would simplify the purification process if brackish waters from below ever were withdrawn and treated for human consumption.

In addition to deep wells, ocean outfall offers a high-volume, year-round discharge alternative. However, no new outfalls have been permitted since the 1970s, pipeline construction would be expensive and could threaten delicate reefs, and there is no consensus on environmental impacts. Reuse is not an alternative to other disposal options in wet weather; moreover, reuse is insufficient for larger communities because of its low disposal volume, and the expense is considerable (over $1 billion for Dade County, for example).

St. Petersburg's 10 deep wells are key to the operation and expansion of the city's popular residential reuse irrigation system, which accommodates an average 25 million gallons per day of treated wastewater. Because of the limited capacity, especially during rainy months, the remaining 22 million gallons per day are discharged into deep wells. Without flexibility in deep well regulations, the city would spend over $100 million to retrofit treatment plants for disposal in Tampa Bay, an expensive reversal in the public policy of surface water protection.

Reuse and other methods of wastewater reclamation are desirable methods of water conservation, yet in Florida's rainy climate, a high-volume, all-weather backup management system is required.

For many utilities, that system is deep well injection. Without deep wells, widescale surface water discharges would return, and consumers would pay billions more for less-efficient and less protective management systems.

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