STRP Conversion Has Benefited Marco Island

Attachments

Guest Commentary Graph #1.pdf

The Septic Tank Replacement Program (STRP) on Marco Island was controversial when it was originally proposed. STRP was implemented in phases beginning in 2006 with final completion in 2014. What was the impact? Some residents contend that the STRP made the water quality on Marco worse, not better. Could this be true?

A 20-year database was constructed to explore the relationship between the implementation of the STRP and the level of Total Nitrogen (TN) in the Marco waterways. We found that as the STRP project was implemented, the TN in the waterbody regularly dropped. The STRP was beneficial!

The explanation is that when a home utilizes a septic system, solids are collected in the septic tank and periodically pumped out. The nutrients, nitrogen and phosphorus, flow into the septic drain-field and then into the water table. With the STRP, the sewage is collected and treated at the Wastewater Treatment Plant (WWTP). In this process, 80% of the nitrogen in the sewage is “nitrified” and sent as a gas into the atmosphere. Not a problem since the air is mostly nitrogen gas. So instead of the nitrogen going into the water table, it is sent to the atmosphere. The STRP reduced the nitrogen load going into the waterbody significantly.

The suggestion that water quality has dropped since the STRP was implemented is accurate. Marco seems to have solved one problem (nitrogen impairment) and then created another problem (algal blooms). A classic case of unintended consequences. 

Phosphorus in the reuse water (purple pipes) is not removed with the Marco WWTP process and has been directly linked to algal blooms in the waterbody. The waterbody oxygen has been dropping for five years now, coincident with the completion of the STRP.

Step by step, the City of Marco Island has been reducing the size of its nutrient “footprint”: the STRP conversion knocked out 80% of the nitrogen from the sewage collected; completely banning phosphorus from fertilizer dropped 100% of this source to zero; a ban on all fertilizer in the summer months eliminated 25% of this source of nitrogen; the WWTP reduced the nitrogen in the reuse water by 50% in 2019. All good steps.

The next step is to upgrade the WWTP to eliminate the reuse water phosphorus that is polluting the waterways and causing the algal blooms. The water clarity on Marco is very poor year-round as the waterways are full of microscopic algae. Seagrass has died off in the bays. Let’s take the next step!

Eugene Wordehoff

Marco Island, Florida