Water Supply Restoration Program
Filter Systems

GAC filters have been installed and maintained by the State of Florida since January 1984, and were originally only for wells contaminated with EDB. Since that time additional contaminants such as solvents, other pesticides and petroleum products have been added to the list of substances filtered by GAC. We currently maintain approximately 1,185 of these system, about 80 percent of which are operating on EDB contaminated wells. There are approximately 150 filters currently operating on wells contaminated with solvents and approximately 110 filters on wells with petroleum contaminants.

Performance data for carbon filters indicates that these filters perform extremely well for most groundwater contaminants. The configuration of each installation is determined by the removal efficiency for that particular contaminant and the expected peak demand. For designing, installing, and maintaining the system, contaminants are classified as EDB (and DBCP), other pesticides and solvents, and petroleum.

Because carbon is so effective at removing EDB, the most common filter system used for this contaminant consists of a five micron pre-filter, a flow meter, a single 54-inch tall by 10-inch diameter GAC tank, and an ultra-violet light for disinfection. This system has a capacity of 6 gallons per minute (gpm) and is sufficient for the average home. Where the demand is somewhat higher, a single 52-inch high by 12-inch diameter tank is used which has a capacity of 10 gpm. For even higher flow requirements, multiple tanks are installed in parallel to match the demand. For very high levels of EDB, a second tank, or polishing tank, is added to ensure that the EDB is effectively removed. The filter media for all systems installed for EDB is exchanged annually.

Systems installed on wells contaminated with other pesticides or solvents are similar to the EDB systems. However, because we have collected less data for these systems, they all include a polishing tank. Selected filter systems, which were installed on wells with very high concentrations of solvents or petroleum products, were sampled quarterly to obtain performance data on removal efficiency. These sampling results indicated that the GAC filters were so successful in removing the contaminants that the filters are now exchanged annually, except where the contaminant is Vinyl Chloride (VC) or Methyl-Tert-Butyl-Ether (MTBE). Filters on wells with VC are exchanged every six months and filters on wells with MTBE continue to be sampled quarterly and exchanged after a breakthrough at the mid-point. [Samples are obtained at a raw water port, a port between each lead tank and polishing tank (called the mid-port), and at the finish water port. These samples are analyzed at the DOH chemical laboratory in Jacksonville.]

Reverse Osmosis
Back to top

While testing in areas with EDB and other pesticide contamination, nitrate levels greater than the State's standard of 10 mg/L were often discovered. In 1992 the Department began to restore or replace these nitrate-contaminated wells. In cases where a connection to public water system is not cost-effective, POU reverse osmosis (RO) filters are installed, usually under the kitchen sink. These filters have a total dissolved solids (TDS) indicator light to show when the filter is no longer working properly. Over 400 of these filters have been installed to date, of which, approximately 315 are still in operation. All RO filters are exchanged annually.

Ion Exchange
Back to top

Where the MCL for nitrate is exceeded at a non-community water system as defined in Rule 62-550, Florida Administrative Code, and the WSRP's assistance is requested, a POE nitrate filter must be installed. For these systems an ion exchange filter, containing a nitrate removal resin, is installed which is similar in appearance to the carbon filters, although the process is quite different. These filters are sampled quarterly, because they need to be regenerated with a brine solution, to ensure the resin is performing satisfactorily.