Return to Index

Retention/Percolation Area Invention



The Florida Department of Environmental Regulation (DER) was the agency which, from the mid-1970s to the mid-1990s, handled regulation, management, conservation, compliance and enforcement of a wide range of environmental and natural resource activities in the state of Florida, United States. It performed a regulatory role, relying on air and water quality standards and waste management regulations. It was specifically tasked with the goals of:

·        keeping Florida’s waters clean

·        keeping Florida’s air clear of pollutants

·        keeping Florida’s land free from contamination

In the 1950’s and 1960’s the water quality in the Bay area was starting to degrade. The Department of Health made up requirements for cleaning up sewage from homes, including septic systems required in lieu of direct discharge. This improved the water quality, but it still was getting bad. Scuba diving in Tampa Bay was impossible, visibility was nonexistent. I put in one time near Oldsmar. After a 15 minute swim (seeing nothing and getting stung by jellyfish) I struggled out and walked a half mile around a small bay back to where I started. I could not go back the way I came across the water, it was too nasty.

 The second source of pollution in our bays was rainwater runoff, at the time it was not restricted at all. Everything from oil being dumped into our storm sewers to fertilizer was finding its way into the bays.  In 1976 the DER came up with requirements for cleaning storm water runoff.

Stormwater entering the bay includes a huge load of material that nature tries to eliminate. As rainfall travels over roofs and the ground, it picks up various contaminants including soil particles and other sedimentheavy metalsorganic compounds, animal waste, and oil and grease. The materials require oxygen to decompose; this is called the biological oxygen demand (BOD).  Stormwater  contains high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a buildup of nutrients and eutrophication (the dying of the water body). The nutrients can in turn encourage the overgrowth of algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of the oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins.


The requirements the DER came up with for treating stormwater were extensive. I attended a public meeting in Tallahassee where their solution was presented. We sat at a table, about 30 of us, with the DER personnel at the head of the table giving a presentation using an overhead projector. The hour long presentation was amazing. The scientists working for the State had come up with an extremely complicated plan. The plan was to have every site that people wanted to develop (from a convenience store on the corner to a 1500 acre project) include a stormwater treatment plant.

The project engineer was to prepare a report to be submitted to the State. Included in the report were the following (but not limited to):

A) The amount of material coming out of the air and deposited on the roof of all proposed homes and other buildings which the rain will dislodge (dust, grit, etc.) and the resulting biological oxygen demand (BOD) load that it would produce.

B) The amount of fertilizer which the homeowners or businesses would apply to any vegetation, the amount of nitrogen and phosphorus the fertilizer would contain, how much of it would run off, and the resulting BOD load that it would produce.

C) The amount of cat, dog, wildlife, and other animal waste that would be deposited on the entire project, the amount of nitrogen and phosphorus the waste would contain and the resulting BOD load that it would produce.

D) The amount of oil and grease that would drip off of vehicles and would be deposited in their coming and goings, and the resulting BOD load that it would produce.

E) The amount of oils and material that would leach out of asphalt and the resulting BOD load that it would produce.

F) The amount of oil, food, and other materials people would dump from changing the oil in their car and in general discharge from their cars and the resulting BOD load that it would produce.

All of the above would have to be taken into account using sophisticated integrals in order to design the stormwater treatment plant. The mathematical formulas were amazingly complex.  The design of the stormwater treatment plant would most likely take weeks or months to prepare, the State would then review the design, come up with a response, the engineer would have to redo the plan and resubmit it, as many times as the State desired, a very costly and time consuming process.

The stormwater treatment plant itself would be a complex of huge containers for grit removal and treatment basins, air pumps for aerating the stormwater, stilling basins, etc., all needing electrical power to function. The State would have inspectors to insure that the treatment plants were operating properly. For a typical subdivision this would cost in the hundreds of thousands of dollars.

The audience was aghast, to put it mildly. After the presentation, the people around the table were asked for their comments. One gentleman said, “If you [the State] have a problem with water quality, YOU fix it, I am not going to.” Another said, “I am not going to build such a plant, I will sell you a piece of my property and you can build whatever you want.” Others were concerned about the feasibility of treating the immense amount of water which runs off during our intense rainstorms. In general, no one was impressed with the proposed requirements and were resistant to do anything of the sort.


When it came around to my turn to speak, I stood up and said, “I have run enough SWMM, STORM, and HEC2 computer programs to know that 94% of all the pollutants are washed off of a site during a 1” rainfall event. If, instead of a treatment plant, we collect this runoff in a retention/percolation area, the sun will disintegrate the phenols (oils) and the plants will take up the nitrogen and phosphorus, thus taking care of all the pollution.”

My solution would require the developer to give up some land to catch any debris, oils, and all of the pollutants, but it would not have to include sophisticated equipment to treat the water.

My solution was adopted. The State’s solution was scrapped, it was withdrawn. There is no way that the State’s solution would have gone as far as mine. The idea that a treatment plant would sit empty for days, weeks, or even months, and then be hit with thousands of gallons (in some cases millions of gallons) of water and be expected to treat that water is crazy. The legislation had already been drawn up and sent out, we were just supposed to say “OK” and then it would become law. I was proud to say that I had stepped in and provided a simple and effective alternative. No local official would have been able to understand the complex report, and it would have been easy to fudge the data. Not with my solution! A fifth grader could do the calculation.

My solution is a very simple calculation to solve how much volume would be needed for the retention pond, ½ inch of water over the site to be developed. No complex formulas. In fact my solution has been adopted in Georgia and other States.

Over the past 40 years, even though the DER no longer exists, the solution was adopted by all of the State of Florida. In this area SFWMD has taken it up and enforces it, trash and pollutants have been stopped at the source. Our bays and streams have immeasurably been improved. The sea grasses have returned, the fish and aquatic animals have returned as well.

There is no telling how much this simple solution has improved the environment. The developers have complied (obviously somewhat reluctantly), and the State was somewhat miffed that they were not able to create more bureaucracy, but in 40 years the only change that was made was the additional requirement that the water percolate in 72 hours so mosquitoes do not multiply. Otherwise the solution has been kept intact! All engineers and developers know the requirement; it is now in the fabric of the design process.

My friends jokingly said that I should put up a sign by retention areas around the State; the sign would say “Complements of John Herrick, your environment is safer.”