In January 2021 water quality trends reports were initiated that showed the monthly evolution of 19 water chemistry parameters on Marco Island. These trends revealed that Dissolved Oxygen (DO) in the Marco waterbody has been declining for five years now and some locations on the island are becoming hypoxic. Many episodes of algal blooms have been reported. These are leading indicators of eutrophic conditions, or the beginning of the death of the waterbody.
A Hypoxia Investigation was then completed that showed that declines of the oxygen levels of the waterbody are directly related to the phosphorus in the reuse water that is processed by the Wastewater Treatment Plant (WWTP). The Marco reuse water contains five mg/L of nitrogen and four mg/L of phosphorus. Phosphorus in fertilizer is banned on Marco. Even minute amounts of phosphorus will trigger algal blooms. The state mandated limits for reuse water are nitrogen less than three mg/L and phosphorus less than one mg/L (Grizzle-Figg Statute).
Marco has been granted an agricultural reuse water permit that actually has no limits at all for these nutrients. Fertilizer on Marco contains nitrogen only (no phosphorus per ordinance) and was found to be a secondary root-cause of the polluted water on the island. The primary root-cause of declines in oxygen in the Marco waterways is phosphorus in the WWTP reuse water.
An independent consultant completed an extensive Nutrient Source Evaluation of the Marco waterbody. This project took over one year to complete and the conclusion was that Marco should " ... address reuse and fertilizer first."
A subsequent report was developed that showed that the Marco WWTP process is called a "Modified Ludzak-Ettinger (MLE)" process. EPA documents show that this process does not have the capability to remove phosphorus.
The new WWTP in Everglades City (2022) will be an Advanced Wastewater Treatment (AWT) process that will reduce the phosphorus and nitrogen in the wastewater effluent to the state mandated levels of nitrogen less than three mg/L and phosphorus less than one mg/L.
There is now an array of options being considered for responding to the decline of the Marco water quality, including the issuance of a public Request for Information (RFI) for an engineering study to evaluate the alternatives and costs for reducing or eliminating phosphorus and nitrogen from the reuse water as well as potable water on Marco Island. This RFI would generate a consolidated list of the current technology providers for the Marco City Councilors to select from to conduct an engineering study in a highly professional and competent manner to finally resolve this vexing environmental issue.
A preliminary cost estimate from the consultant (Dr. Harper) was that it might cost between $5 million and $10 million to upgrade the WWTP so that the reuse water no longer pollutes the Marco waterways. On the other hand, EPA documents estimate the cost to remove 99% of the phosphorus from the reuse water to be as low as $200,000 using chemical precipitation.
Citizen of Marco Island