2.1.1 The Melbourne RO plant

 2.1.2 Operating the plant

2.1.3 Concentrate Disposal

     The concentrate is discharged into the Eau Gallie River under NPDES permit (FL0043443), which allows 1.25 MGD [4,750 m3/d] of concentrate to be discharged. Appendix A presents the results of the monitoring program (1995-1998) required by the permit.  Flow, water quality factors (turbidity, temperature, conductance, pH), major ions (chloride, sodium, sulfate, magnesium, calcium, fluoride), metals (aluminum, iron, copper, chromium, silver, zinc, strontium), dissolved gases (oxygen and hydrogen sulfide), nutrients (phosphorus, nitrogen), and radionuclides (radium 226 and 228, gross alpha) are monitored regularly (Table 2-1). The permit also requires semi-annual chronic and annual acute toxicity tests.
    While most of these parameters meet state standards, difficulties arise in meeting the permit limitations for radioactivity and the toxicity of the concentrate.  As a matter of fact, in 1997, the NPDES permit for the Melbourne ROWTP has not been renewed for September 1998 due to failure to meet various effluent limits set forth in the permit.  The limits set by the NPDES permit for silver (an average of 0.5 mg/l instead of 0.05mg/l), chloride (an average of 2,500 mg/l instead of 1,370 mg/l), total nitrogen (an average of 2.0 mg/l instead of 1.7 mg/l) and combined radium (226+228) (an average of 50 pCi/l instead of 19 pCi/l) concentrations were exceeded and the minimum dissolved oxygen concentration was not met in 1995 and 1996.  The copper level exceeded the surface water quality criteria for Class III, Marine Waters (62-302.400 FAC) from May 1995 to March 1996 but those abnormal level have been recognized to have been caused by laboratory error.  Moreover, the concentrate failed all toxicity tests with the mysid shrimp during the same period (Ferraro, 1996 and 1997).  The results for the years 1997 and 1998 were of better quality but were not taken into account in the renewal of the permit.
    An agreement between FDEP and the city of Melbourne has been reached and a consent order delivered by FDEP has been issued until September 1999.  The consent order allows surface discharge in the Eau Gallie River for a limited time with careful monitoring and requires that the city of Melbourne finds a more suitable discharge location.  After careful considerations of other alternatives, deep well injection and ocean discharge, a permit of surface discharge to the Indian River Lagoon (IRL) near the Eau Gallie Causeway has been requested by the City of Melbourne.  The plan was to discharge the concentrate to the IRL via a multiport discharge pipe located 2,000 feet from the shoreline equipped with a 100 feet diffuser (Ferraro, 1998).  Numerous public concerns have been raised about this project.  The public fears fresh water input, toxicity of the concentrate and the impact it may have on the lagoon. Nevertheless, any toxicity problem should be handled by an appropriate dilution within the allowed mixing zone, 5 feet around the diffuser.  Moreover, the concentrate from the MROWTP is similar to "Predominantly Marine Waters" according to rule 62-302.200 (21) (FAC) with a chloride content greater than 1,500 mg/l and fresh water input impact on the estuarine waters of the lagoon should be mitigated.  In any case, the mere 1.25MGD (or even the proposed 3.3 MGD) only represent a negligible fraction of the freshwater input from groundwater seepage and rainfall.  As of today, the SJWMD has pressured the city of Melbourne into abandoning this option and investigating farther the deep well alternative by renewing the city permit to pump surface water from Lake Washington for the South WTP to the express condition that the concentrate would not be discharged in the lagoon.
 

2.2 The Indian River Lagoon Area.

    Most of the RO facilities found in the Indian River Lagoon area are small units with capacity of less than 0.1 MGD [380 m3/d].  Only seven plants (including Melbourne ROWTP) have a capacity greater than 1 MGD [3,800 m3/d] and use various methods for concentrate disposal (see Table 2-1).  The smaller capacity plants employ land application methods to a greater degree (irrigation in Martin County, percolation pond for the Harbor Branch facility in St. Lucie) (Mickley et al, 1993) which limit or eliminate their surface discharges to canals and ditches.
 

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