There are many areas in Florida where sinkholes, karst geology, and other features can create conduits for the infiltration of surface water into groundwater aquifers. groundwater may be classified as being “under the direct influence of surface water” (UDI) if it exhibits either:

(a) a significant occurrence of vegetation parts, insects or insect parts, microorganisms, algae, or large diameter protozoa pathogens such as Giardia lamblia or Cryptosporidium that are normally found only in surface waters, or

(b) significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity or pH that closely correlate to climatological or surface water conditions.

The Department of Environmental Protection (DEP) is responsible for assessing public water wells for UDI conditions based on US Environmental Protection Agency (USEPA) procedures. The USEPA procedure determines if groundwater is under the direct influence of surface water using microscopic particulate analysis (MPA). MPA identifies organisms that occur in surface water whose presence in groundwater would clearly indicate mixing of the two. If the results show that there could be a significant risk, then the DEP will notify the system in writing.

If DEP determines that public water system is UDI, there is serious potential for contamination with Giardia or Cryptosporidium and other microorganisms that could present a serious health risk. Giardia and Cryptosporidium are extremely difficult to kill with conventional amounts of chlorine, therefore water that is classed as UDI must be treated more thoroughly than other groundwater. The system must then provide additional treatment for the well, or find a new source of water that is not UDI, or identify the source of contamination and eliminate it.

Poor well design and construction can increase the risk that a system is UDI and many times have a much greater contribution to a UDI designation than vulnerable geology. The Florida Rural Water Association recommends these actions to reduce the possibility of UDI determinations:

• Check the condition of well seals
• Assure that well and pump have a properly sized vent
• Make sure that the vent is protected and in the correct location
• Keep the well head free of algae and other organisms
• Assure that foundations and coverings are properly grouted
• Assure that the pipe packing gland and water drain from water-lubed vertical turbine pumps are drained away from the wellhead
• Make sure that aerators are clean and that check valves are in good condition
• Consider the installation of air and vacuum relief valves to reduce the chances of water being pulled back or pushed down the well