Riverbank Filtration: Induced Infiltration and Groundwater Quality

Abstract

Riverbank filtration relies on the streambed and aquifer matrixes to reduce pathogens under varying conditions of induced infiltration resulting from changes in river stage and flow velocity. The Greater Cincinnati (Ohio) Water Works monitored hydrologic parameters and water quality at its Charles M. Bolton well field during a comprehensive flowpath study. The study determined the frequency of occurrence of high river-stage events from historical data and monitored hydrologic parameters to estimate the potential unit infiltration rate. Giardia, Cryptosporidium, algae, spores, particle counts, and turbidity were also monitored. The project investigated potential pathogen/surrogate breakthrough during several high river-stage and infiltration events. High-stage events occurred less than 4% of the time. Giardia and Cryptosporidium were not detected in any groundwater samples. Increases in surrogate concentrations were minimal and maintained >3.5-log reduction. The streambed and aquifer have the ability to buffer water quality effects from major increases in the infiltration rate.

The impact of storm events on a riverbed system and its hydraulic conductivity at a site of induced infiltration

“…There was no direct evidence that increased infiltration rates had any adverse effects on water quality. Gollnitz et al (2004) asserted that there was a need for further investigation into riverbed characteristics, particularly the impact of high-stage events on riverbed hydraulic conductivity.…”

“…The bulk of this groundwater is procured from the Great Miami Buried Valley Aquifer, an alluvial-outwash, mostly unconfined aquifer ranging from 3.2-to 4-km wide and 24-to 61-m deep. Hydraulic conductivities generally range from 60 to 120 m/d (Gollnitz et al, 2003). The nearest US Geological Survey gaging station is in Hamilton, OH, 9.5 km northeast of the Bolton well field.…”

“…This variability was based on the variability of river stage, area of pumping influence, water viscosity and riverbed permeability. The impact of infiltration rate variability on natural filtration and water quality was investigated at the Bolton well field (Gollnitz et al, 2004). Two production wells with relatively long and short associated flowpaths from the river were monitored for surface water indicators such as Giardia, Cryptosporidium, turbidity, and aerobic spores.…”

“…The USEPA has been generally reluctant to grant more than a 1.0-log credit despite studies indicating that a 3.0-or 4.0-log credit is warranted (Gollnitz et al, 2004). Hesitance toward greater acceptance of riverbank filtration as an alternative treatment option has stemmed at least in part from concern over the stability of the infiltration rate and attenuation capacity of the system during high-stage events.…”

“…Because it is composed of suspended solids deposited in the upper layer of a rivereaquifer interface, it is often assumed to have a lower hydraulic conductivity and greater filtering capacity than do the underlying sediments (Velickovic, 2005). The majority of particulate material is removed in the first two feet of the riverbed (Wang et al, 2002;Gollnitz et al, 2003). Loss of the colmation layer resulting from scour could potentially allow contaminants to reach production wells (Schubert, 2000).…”