Environment 21, LLC

Are we still protecting the environment?

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Courtesy of Courtesy of Environment 21, LLC

Growing public awareness and concern for controlling water pollution led to enactment of the Federal Water Pollution Control Act Amendments of 1972. As amended in 1977, this law became commonly known as the Clean Water Act. Since its inception we have seen the evolution of Stormwater Best Management Practices to meet the demands of treatment and pretreatment of stormwater runoff from the roof drains of our houses to the industrial businesses. From Detention ponds and hydrodynamic Separators to filter cartridge systems there are a variety of products and solutions available. Now 31 years later Stormwater Best Management Practices are being installed on sites across the world. Studies are showing that more and more municipalities are committing more of their yearly budget to Stormwater Management.

But are we really making a difference? Just like automobiles, all equipment and systems require maintenance and service. The average hydrodynamic separator requires quarterly to semi-annual inspection, with cleaning required at least once a year. So what happens when these systems are not inspected or cleaned on a regular basis? Detention ponds are designed to specific excavation depths in order to provide for collection of stormwater runoff from sites and allow for collection of sediment scoured off the pavement. A commonly used number is approximately 500 pounds/acre/ year of sediment is washed off the pavement, in addition to floatable oils, phosphorus, heavy metals and other pollutants. Depending on the size of the site thousands of pounds of sediment is collected in detention pond on an annual basis. Are these ponds able to still perform to their original design requirements or store there design volumes. When is the last time you saw your detention pond cleaned out to its original design? Utilizing the previous number of approximately 500 pounds/acre/year now applied to a five foot diameter hydrodynamic separator, assuming you capture the estimated 80% (400 pounds) per year as required by many regulatory agencies you will utilize 0.25 feet of depth per year. Majority of the hydrodynamic separator manufacturers recommend cleaning of their products at 15-25% of the depth below the invert of the outlet pipe because once the maximum storage depth is exceeded the system will begin to re-suspend the collected sediment. So if you have a 4.0 foot sump in 4 years you should be cleaning the system or everything collected is starting to be washed out of the system.

According to many permit requirements throughout the country at the completion of a project the owner is required to have a maintenance program in place for the permanent stormwater management practices. How many times have you driven by a subdivision pond and seen cattails growing or cups floating in the ponds? In my travels I have visited many of different hydrodynamic separators and have found many of these systems to have been forgotten about. It is great that we are enforcing the use of best management practices and require verification that they meet the specific performance standards, but when do we start enforcing the up keep of these systems? After all you paid all that money for performance wouldn’t you still like it to perform.

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