Microbial Removal Rates in Subsurface Media Estimated From Published Studies of Field Experiments and Large Intact Soil Cores

Abstract

Information about the microbial removal efficiencies of subsurface media is essential for assessing the risk of water contamination, estimating setback distances between disposal fields and receiving waters, and selecting suitable sites for wastewater reclamation. By analyzing published data from field experiments and large intact soil cores, an extensive database of microbial removal rates was established for a wide range of subsurface media. High microbial removal rates were found in volcanic soils, pumice sand, fine sand, and highly weathered aquifer rocks. Low removal rates were found in structured clayey soils, stony soils, coarse gravel aquifers, fractured rocks, and karst limestones. Removal rates were lower for enteroviruses than for other human viruses; for MS2 phage than for other phage species; for waste-associated microbes than for those cultivated in the laboratory; and for contaminated media than for uncontaminated media. Microbial removal rates are inversely correlated with infiltration rates and transport velocity. The assumption of first-order law, or a constant removal rate (when the transport scale reaches a representative elementary volume), is appropriate for most of field data analyzed. However 30% of the datasets (26 out of 87 pairs) are better described with the power law, implying reduced removal rates with transport distance. The latter is most prominent for organically contaminated media, especially in relatively fine aquifer media. The presence of organic matter, heterogeneity in microbial properties, change in solution chemistry, detachment, and physical straining, may have caused the discrepancies from the first-order law traditionally used in transport models for describing microbial removal.

EPA Method 1615. Measurement of Enterovirus and Norovirus Occurrence in Water by Culture and RT-qPCR. I. Collection of Virus Samples

“…Most of the facilities using groundwater in these studies obtained water from aquifers located in karst regions. These, along with those located in limestone and crystalline (fractured bedrock) settings are likely to have higher virus concentrations than in other settings 8,15,16 . USEPA virus methods specify sampling volumes of 200 L (ICR) to 300 L (Method 1615) of surface water and 1,000 L (ICR) to 1,500 L (Method 1615) of groundwater 17,18 .…”

Applying spatial regression to evaluate risk factors for microbiological contamination of urban groundwater sources in Juba, South Sudan

“…Hynds et al (2012) estimated that the approximate zone of impact of septic tanks extended up to 110 m up-gradient of the wellhead, if high 120-h prior precipitation rates were considered. Conversely, in a review, Pang (2009) reported that the maximum observed E. coli transport distance was as great as 920 m, for sewage polluted groundwater in gravel aquifers in Burnham, New Zealand, at velocities as high as 56-153 m/ day (Sinton 1980). Future studies might investigate the cut-off distance for spatial autocorrelation as related to microbial transport in different hydrogeological environments.…”

Bacteria transport and retention in intact calcareous soil columns under saturated flow conditions

“…Many factors affect bacterial removal rates in soil under saturated conditions. These include physical-chemical properties of soil, properties of bacteria, solution chemistry, inactivation, physical straining, heterogeneity and preferential flow paths (Pang, 2009). …”