How To Actually Remove Pollutants From The IRL
– Dr. Tom Waite, Founder, Ferrate Solutions® Inc
There was a recent Op Ed published in Florida Today, “Help Reduce Pollution in Lagoon” by Drs. Gilmore and Loftus that caught my attention. The column discussed our interactions with the IRL, and how our lifestyle is contaminating it. They rightfully pointed out how our love of neat landscaping is partly responsible for excessive nutrient loading to the IRL. In addition, they highlight the fact that contaminants common to stormwater runoff, including pesticides and other toxic materials, are also harming the lagoon. All these contaminants are now showing up in the different ecosystems collectively known as the IRL. These observations are important reminders to all of us about how we need to modify our lifestyles to become more in tune with the health of our lagoon.
What caught my eye about this article was the observation they made that all the contaminants described were transported to the lagoon through streams or canals. They noted that even in rural areas of the county, canals can transport nutrient contaminants to the lagoon within four or five hours of their introduction. They also noted the county has so many canals feeding into the lagoon that contaminants from most properties remote from the lagoon are all contributing to the pollution. They also noted that septic tanks are contributing large amounts of nutrients directly into the lagoon, an observation that has been made many times in the recent past.
Understanding the mechanisms of input of nutrients and other contaminants to the IRL is critical to finding cost-effective solutions for preventing the degradation of our natural resource. While lifestyle changes are important, and will help to limit inputs of unwanted pesticides, herbicides, and nutrients, there needs to be large-scale, positive infrastructure modifications to remove existing nutrient sources, and prevent the addition of more contaminants. There is a continual debate in Brevard County about what these large-scale actions should be. The decisions for prioritizing efforts to remove or limit the input of nutrients and contaminants have been made with input from many stakeholders, and their decisions have been reflected in the amount of resources dedicated to different remedial approaches. For example, an evaluation performed by an engineering firm a few years ago compared various methods for removing nutrients in the lagoon and the cost for doing so. Also taken into account in this evaluation was the amount of nutrients that could be removed by the different approaches. Their findings showed that muck removal would remove the largest amount of nutrients from the ecosystem, at the cheapest cost. Therefore, Brevard County has moved forward with that recommendation over the past few years, and hundreds of tons of nutrients have been removed over that period – much of it due to the use of Ferrate. Interestingly, septic tank removals were also shown to remove a significant amount of nutrients but that the conversion to sewers is extremely expensive. Additionally, their findings showed that modifications to existing septic tanks would be very expensive and the amount of nutrients that would be removed was much less.
It now appears that there will be funding reallocations away from dredging with an increase in septic tank removal. When you also take into account the large-scale sewer installation plus additions to waste treatment plants receiving this waste you realize that this will be an exorbitantly high cost, and this is what has precluded any previous action on these options.
So, how do we move forward? We know we have to significantly reduce the input of nutrients and toxic compounds entering our lagoon. We also must work within the limits of our means, which requires that well thought-out decisions must be made describing the path forward. Clearly, septic tanks located right along the shores of the IRL need to be removed and replaced with sewers and this should be a priority.
But dredging must also continue, and as recent analyses from the dredging efforts have shown that water in the coastal canals are already, and have been for decades, heavily impacted by effluents from septic tanks. This has resulted in thick layers of toxic muck that has been dubbed as “black mayonnaise”. Nutrients in the muck do not remain in the muck but dissolve up into the water column, continually adding to an already excessively-high nutrient content level, causing harmful algal blooms that ultimately removes oxygen from the ecosystem. This continual cycle of uncontrolled algal growth robs sea grasses of the ability to grow and manatees the ability to feed.
However, as noted in passing by Drs. Gilmore and Loftus, canals that originate inland are the bigger culprits in transporting nutrients and toxic materials into the IRL.
Data from studies performed by the Florida Institute of Technology over the past five years have quantified the amount of nutrients entering the IRL. According to their data, the annual inputs of both nitrogen and phosphorus from the four major tributaries to the IRL were similar to the amount of the benthic flux of nitrogen and phosphorus in the north IRL. In addition, they determined that greater than 70% of the total nitrogen and phosphorus delivered to the IRL via the major tributaries occurred during storm events in the rainy season of the year. Their studies focused on the Eau Gallie River, Crane Creek, Turkey Creek, and the Saint Sebastian River. These data demonstrate that nutrient inputs to the IRL are primarily via the main canals and creeks noted above. If dredging is going to be reduced, than it becomes even more important to prevent the input of nutrients and contaminants from nearby septic tanks, but also, stormwater runoff into the lagoon that enters via canals.
Because of the projected exorbitant cost of sewering large areas in Brevard County, this option has been put off and instead, small-scale, piecemeal remediation efforts have become the common approach. Small plots of wetlands, and retention ponds coupled with simple concrete water collection devices are being installed throughout the county in an attempt to stop the input of tons of contaminants. The effectiveness of these small-scale systems cannot be reliably measured, therefore they continue to be installed with the hopes that some nutrient removal is achieved. It is time now to move forward by building components of an effective, overall master plan to keep nutrients and contaminants out of the lagoon.
Managing the quality of water transported to the IRL via the main tributaries is critical. Historically, Florida has evolved by draining water from the swamps, so that there would be dry land for farming and development. Canals drain water from the land. All ground water and its contaminants and nutrients move towards the nearest canal, therefore septic tank effluent moves from the leaching field to the nearest canal. Stormwater runoff from highways and agricultural lands also moves towards the nearest canal. Therefore, as quantified in the FIT study, the canals will contain most of the nutrients and contaminants that are being transported to the IRL. This transport is also condensed to the rainy season (four months), and other studies have shown that most of the contaminants in the canal water are present only during the first few hours of a rain event. During normal low flow periods, the nutrient and toxin content is low (1/10 of that measured at high flow). This means that any treatment of these flows to remove contaminants does not have to occur on a continuous basis.
Managing water quality in the IRL by controlling input from canals, creeks and rivers is the most cost-effective approach available. As noted earlier, removing septic tanks and substituting sewers with waste treatment plant upgrades is cost prohibitive, at least in the near future. Because of this enormous cost however, all efforts at truly solving the water quality issues in the IRL are essentially on hold. The costs associated with replacing septic tanks with sewer lines are totally driven by the construction costs associated with just putting pipes in the ground. Over 85% of total costs of building a complete sewerage system are associated with digging ditches and disrupting communities for the installation of sewer pipes. The costs associated with waste treatment component of a sewerage system are minimal in the overall scheme. The fact that stormwater runoff and septic tank leachate is already being collected and transported into point sources (canals, rivers or creeks) needs to be realized. Therefore, the largest cost component in solving this issue is already in place in Brevard County. Focused treatment systems placed at strategic points on the canals can treat to remove nutrients and other toxins without impacting existing waste treatment facilities. These can be easily located at any point on a canal before it discharges into the IRL. In fact, two existing waste treatment plants are already located on or near canals (Crane Creek and Eau Gallie River). These facilities could be easily expanded to treat the Canal water flowing past. These relatively inexpensive systems would eliminate the need to replace septic tanks in the respective drainage areas (approx.150 mi2)