Demonstration of Managed Aquifer Recharge in a Coastal Plain Aquifer: Lessons Learned.

The sustainable water initiative for tomorrow (SWIFT) is a 378,000 m3 /day (100 MGD) managed aquifer recharge (MAR) program designed by the Hampton Roads Sanitation District (HRSD) to rehabilitate the Potomac Aquifer System (PAS) in the Coastal Plain of Eastern Virginia. Groundwater is a primary water source in Eastern Virginia with over 93% of reported use derived from the PAS. Starting in May 2018, HRSD has operated a 3780 m3 /day (1.0 MGD) MAR demonstration facility at the SWIFT Research Center (SWIFT-RC) in Suffolk, Virginia. The primary aim of the SWIFT-RC is to demonstrate, at a meaningful scale, the feasibility of MAR using deep well recharge into confined PAS hydrostratigraphic unit. The SWIFT-RC employs advanced water treatment technology to bring secondary effluent from an HRSD wastewater treatment plant to drinking water standards. Lessons learned include the evaluation and selection of a multiple barrier carbon-based treatment system to ensure water quality and maintain geochemical compatibility between MAR water and native groundwater, and the evaluation and selection of aluminum chlorohydrate for stabilizing aquifer clays immediately around the well to accept the fresher recharge water. The distribution of flow in the SWIFT-RC multiscreen recharge well and associated well injectivity were variable with time resulting from changing conditions in the well. Dynamic recharge well performance was quantified through the combined analysis of intrinsic and artificial tracer transport, in situ flowmeter testing, and water level analysis. Monitoring well nests and a depth-discrete sampling system supported a robust sampling plan to analyze chemical transport and attenuation in SWIFT-RC groundwater.

Demonstration-scale evaluation of ozone-biofiltration-granular activated carbon advanced water treatment for managed aquifer recharge.

The Sustainable Water Initiative for Tomorrow (SWIFT) program is the effort of the Hampton Roads Sanitation District to implement indirect potable reuse to recharge the depleted Potomac Aquifer. This initiative is being demonstrated at the 1-MGD SWIFT Research Center with a treatment train including coagulation/flocculation/sedimentation (floc/sed), ozonation, biofiltration (BAF), granular activated carbon (GAC) adsorption, and UV disinfection, followed by managed aquifer recharge. Bulk total organic carbon (TOC) removal occurred via multiple treatment barriers including, floc/sed (26% removal), ozone/BAF (30% removal), and adsorption by GAC. BAF acclimation was observed during the first months of plant operation which coincided with the establishment of biological nitrification and dissolved metal removal. Bromate formation during ozonation was efficiently controlled below 10 µg/L using preformed monochloramine and preoxidation with free chlorine. N-nitrosodimethylamine (NDMA) was formed at an average concentration of 53 ng/L post-ozonation and was removed >70% by the BAFs after several months of operation. Contaminants of emerging concern were removed by multiple treatment barriers including oxidation, biological degradation, and adsorption. The breakthrough of these contaminants and bulk TOC will likely determine the replacement interval of GAC. The ozone/BAC/GAC treatment process was shown to meet all defined treatment goals for managed aquifer recharge. PRACTITIONER POINTS: Floc/sed, biofiltration, and GAC adsorption provide important barriers in carbon-based treatment trains for bulk TOC and trace organic contaminant removal. Biofilter acclimation was observed during the first three months of operation in each operating period as evidenced by the establishment of nitrification. Bromate was effectively controlled during ozonation of a high bromide water with monochloramine doses of 3-5 mg/L. NDMA was formed at an average concentration of 53 ng/L by ozonation and complete removal was achieved by BAFs after several months of biological acclimation. An average 25% removal of 1,4-dioxane was achieved via oxidation by hydroxyl radicals during ozonation.