Regulatory Compliance of H Retention Basin Using Rhombo Balls - 16151

Elevated pH conditions in the Savannah River Site 281-8H Retention Basin will have to be resolved prior to the issuance of a new National Pollutant Discharge Elimination System permit. The 281-8H retention basin collects rain water runoff, cooling tower blow downs and steam condensate from H Area Tank Farm operation processes. The basin discharges to a South Carolina Department of Health and Environmental Control National Pollutant Discharge Elimination System permitted out-fall, H-12. The permit requires the out-fall to meet certain discharge requirements. The National Pollutant Discharge Elimination System permit requires the pH to be within the range 4.8 to 8.5. The 281-8H Retention Basin has a steady history of elevated pH levels, above 8.5, especially during the warmer months of the year, normally March through October. The rise in pH has been attributed to the exponential growth of algae which occurs during the warm months of the year. The increased algae colonies undergo photosynthesis which depletes the CO₂ in the basin water and subsequently raises the pH level. The current permit allows simultaneous discharge of low pH well water, pH between 4.6 and 5.0, and the 281-8H Retention Basin water which provides blending to achieve regulatory compliance. The regulatory agency indicated in 2010 that adding well water to achieve compliance of pH limits will not be allowed when the new permit is issued in the future. Therefore, a solution to the high pH had to be identified and implemented in order to ensure regulatory compliance. A system engineering evaluation was conducted to determine the best solution to the large algae colonies and high pH levels. The evaluation identified options in four primary categories as well as some combination of those categories to control algae growth and to ultimately increase the amount of CO₂ in the basin. Eleven evaluation criteria were developed for the various options, and a percentage (out of 100%) was assigned to related groups of criteria. Twenty-six options were evaluated during this process. The highest ranking options determined from the evaluation were the 12-sided Rhombo ball floating cover, biological digester and a combination of the digester and the floating cover. Option 3, a combination of the top two choices, was chosen as the best approach. The Rhombo cover along with the initial shock application of a biological digester has worked to eliminate algae growth and lower the pH level. The Rhombos have significantly lowered the basin pH level from greater than 9 to less than 7, which is within the regulatory compliance pH requirements of 4.8 to 8.5. The system engineering evaluation and subsequent solution chosen are useful in many venues. The application of the 12 sided Rhombo ball's unique ability to nestle together no matter which way they turn is advantageous to applications/problems that need to block 99.99% sunlight from a body of water. The 281-8H Retention Basin required nine 18 wheeler truckloads with trailers that were 16.2 m (53 Ft) long and filled with Rhombo balls. The basin required a total of approximately 700,000 Rhombo balls to be fully covered. They are easy to install and handle. The Rhombo balls have wind resistance up to 120 Km/hr (75 MPH) and have a life expectancy of 25 years. This application can be used to control plant and algae growth and is effective in evaporation reduction at 99%. (authors)