Project synopsis:  Ground water at the landfill of a military base was contaminated with Arsenic (As) at a very low level of 22 ppb, Manganese (Mn) at 1.7 ppm and Iron (Fe) at 47 ppm. These metal levels were higher than the discharge limits required by the county water board. The base was looking for the best available process treatment system to meet metals discharge requirements.

Phase 1:  The base, through a prime contractor, conducted primary feasibility studies for the best treatment chemistry. The concern was that the metal contents were already very low, especially arsenic, and needed to be reduced further to meet discharge requirements. Based on independent analytical laboratory results, the MetFloc™ process was shown to provide superior results, and hence was chosen as the method of remediation of the landfill groundwater. In partnership with a subcontractor, a treatment system was designed, built and installed at the landfill.

Unit description:  The treatment system consists of an equalization tank, a primary holding tank, and four treated clean water holding tanks (one 700, one 30,000, and two 20,000 gallon tanks). All tanks are equipped with low, medium and high-level float switches that are monitored. The MetFloc™ chemical holding tanks are equipped with low-level alarm float switches. The system is fully automated with an Allen Bradley PLC and a SCADA system running on a Wonderware software system. Two carbon bed filters are used for secondary treatment and for removal of anticipated low levels of organics. Three LMI metering pumps are used for the dosing of MetFloc™ chemicals. These are injected in-line through static mixers. Because of the very low amount of sludge produced, an automated gravity bed filter with a 25-micron filter paper is used for filtration of solids. The piping for the unit is PVC schedule 80.

Process Run:  Groundwater is pumped from a groundwater well equipped with three level float switches and a sump pump. The treatment process is initiated when the water level in the well is at the high-level float switch position. Well water is then pumped to an equalization tank and through the treatment system. The MetFloc™ chemicals are proportionally injected in-line based on pre-determined dosage rates. The reaction is very fast. The treated water is then pumped through the gravity bed filter to remove the solids and then to an intermediate holding tank. The water is then pumped through two carbon bed filters and then to a clean water holding tank. From here the water is pumped to a 30,000-gallon storage tank. Based on the level float switches, the clean water is pumped to two 20,000-gallon storage tanks up at landfill. The tanks are equipped with a sprinkler, and the water is used for dust suppression and irrigation at the landfill.

The system automatically goes into recirculation mode when all clean water holding tanks are full. The unit shuts down when the low-level float switch is activated and the well is dry.

Project Results:  Over a six-year project period, quarterly samples were sent to an independent US EPA certified lab for analysis before and after treatment. The results were always below regulatory agency discharge limits