Attenuation of contaminants of emerging concern during surface-spreading aquifer recharge

Abstract

The attenuation of a diverse suite of contaminants of emerging concern (CECs) and bulk water quality changes was evaluated at a surface-spreading aquifer recharge operation across a detailed subsurface profile (9 locations), representing both short- and long-travel times (10 h to 60 days). Seventeen CECs were detected in the recharge basin and the concentrations of all were reduced during soil aquifer treatment (SAT), with 11 of the target compounds attenuated by > 80% after 60 days of travel time. Select CECs (atenolol, gemfibrozil, N,N-diethly-3-methylbenzamide, meprobamate, tris(2-chloroethyl)phosphate, and primidone) and bulk water organic-carbon measurements (total organic carbon, biodegradable organic carbon, size-exclusion chromatography and fluorescence excitation–emission matrices) were identified as monitoring parameters that can be used to assess SAT performance at surface-spreading operations.

Introduction

The increasing scarcity of water supplies has led to the utilization of reclaimed water, i.e. treated wastewater, in a variety of reuse applications. For example, planned potable reuse, a process through which reclaimed water is eventually incorporated into drinking water supplies, is increasing as a resource for diverse water portfolios. Reclaimed water is an attractive resource because it is not subject to climatic variations and because it is produced in the growing urban areas clamoring for freshwater reserves. However, reclaimed water contains unregulated contaminants of emerging concern (CECs), which include pharmaceuticals, household chemicals, personal care products, disinfection byproducts, insecticides, and suspected endocrine disruptors. Though many of these CECs are present at very low levels (ng/L), potential health concerns have given rise to numerous scientific investigations regarding the occurrence, concentration, transport, degradation, and aquatic fate (Ternes, 1998, Kolpin et al., 2004, Focazio et al., 2008, La Farré et al., 2008, Benotti et al., 2009, Mompleat et al., 2009, Wells et al., 2009).

Managed aquifer recharge (MAR) encompasses several physical processes used to replenish and augment groundwater resources and is often an integral part of planned potable reuse (Asano et al., 2007). MAR can include direct injection in the subsurface or infiltration via surface-spreading basins. The process of surface spreading has the added benefit of additional constituent removal and transformation in the basin and during percolation (referred to as soil aquifer treatment or SAT). Treatment in the basin is provided passively by volatilization and photodecomposition and during SAT from physical filtration, adsorption to soil particles, microbial biotransformation, and dilution with native groundwater. This type of natural attenuation is an attractive option because it requires minimal energy and chemical inputs and does not create a waste stream, in contrast to processes like membrane treatment.

Surface spreading using recharge basins is one of the most common and oldest methods for groundwater recharge (Todd, 1980). However, there is still concern of fate and transport of unregulated CECs during SAT. Several earlier studies have characterized the transformation and removal of some CECs during SAT for travel times ranging from ~ 1 day to 8 years (Drewes et al., 2003a, Drewes et al., 2003b, Montgomery-Brown et al., 2003, Mansell and Drewes, 2004, Snyder et al., 2004, Grünheid et al., 2005, Amy and Drewes, 2007, Massmann et al., 2006). However, due to limited well installations, few field studies have extensively examined the subsurface profile of CECs for travel times less than 3 days.

In this study the fate and transport of a suite of 26 CECs and bulk organic matter during a surface-spreading aquifer recharge operation, located in the Montebello Forebay, Los Angeles County, California, were assessed. This systematic study was carried out at a well-equipped surface-spreading recharge basin treating reclaimed water. Synoptic sampling was performed for both short (10 h to 3 days) and longer travel times (~60 days). Individual CECs were identified along with bulk water quality parameters that could be used to indicate the performance for this particular surface-spreading aquifer recharge operation.