Formatted Title
Application of Electrokinetic Remediation Combined with Pumping for Metal Remediation in a Low Hydraulic Conductivity Area
Background/Objectives
The study area is an industry that manufactures granulated and powdered micronutrients, located in São Paulo, Brazil. Groundwater in the area is contaminated with zinc, molybdenum, arsenic, barium, boron, cadmium, lead, cobalt, copper, chromium, nickel, selenium, aluminum, iron, and manganese. The lithology of the area comprises silty clay to clayey soils, related to the alteration of basaltic rocks, and the aquifer’s hydraulic conductivity ranges from 10-5 cm/s to 10-7 cm/s. Some metals plumes have already exceeded the limits of the area, reaching neighboring areas and a Permanent Preservation Area. Currently there is a hydraulic barrier in operation in the main currencies of the area but aiming to remove the mass centers of the plumes, a pilot test was conducted to evaluate the application of combined electrokinetic remediation and pumping techniques for the area's remediation. In 2014, a pilot pumping test had already been carried out, which did not reach satisfactory levels of contaminant removal.
Approach/Activities
The pilot test involved installing two pumping wells, in which electrodes were inserted, spaced 5.0 meters apart, along with the installation of observation wells at different distances from the pumping wells (2.5 m, 5.0 m, 7.0 m and 10.0 m). The test lasted 36 days. Samples were collected from the observation wells for metals analysis at the beginning and end of the test, and pumped effluent was collected during the operation at days 0, 2, 6, 13, 19, 27. In these days were also monitored the following parameters in the pumping/ electrokinesis and observation wells: groundwater level, temperature, pH, electric current, Eh, electrical conductivity, in addition to the following data at the pumping/ electrokinesis wells: voltage, current, resistance, flow, volume pumped in the period and pumping hours. Initially, graphite electrodes were installed in each pumping well, applying 30V of electrical potential (first stage). However, due to the low response obtained in terms of electrical current, after 15 days, 220V was applied (second stage). Pumping was done using electric pumps with a flow rate of 67 L/h per well.
Results/Lessons Learned
The area's low electrical conductivity, ranging between 500 and 1500 µS/cm, resulted in low electrical current, with an average value of 6.8 mA in the first stage of the test and 37.4 mA in the second stage when the voltage was increased. It was observed that increasing the voltage did not bring advantages in terms of mass removal. Approximately 94 g of metals per day were removed in both stages for the electrode/pumping pair. However, increasing the voltage might have caused the mobilization of naturally occurring iron in the geological matrix composing the aquifer, making it disadvantageous to apply high potential. Comparing the results of the test conducted in this study with the previous test in the area performed in 2014, where only the pumping technique was evaluated, a 30-fold increase in the calculated mass removal rate was observed, demonstrating the viability of applying both associated techniques to optimize the remediation of plume mass centers. A pumping radius of influence of 7.5 m and influence of the electrokinesis technique up to the distance of 12.50 m were obtained.