Active-distributed temperature sensing dataset beneath a braided river.

Braided rivers play a significant role in replenishing groundwater, but our understanding of how these recharge rates fluctuate over time remains limited. Traditional techniques for gauging groundwater recharge are ineffective for studying complex braided river systems due to their insufficient spatiotemporal resolution. To address this gap, active-distributed temperature sensing (A-DTS) was used. This method combines fiber optic temperature measurements with an active heat source, enabling quantification of groundwater fluxes. In this study, twelve consecutive A-DTS surveys were conducted on a 100 m long hybrid fiber optic cable to a depth of 5 m beneath the Waikirikiri Selwyn River. This experiment was conducted during a period of relatively stable river stage and flow, highlighting the effectiveness of using A-DTS to measure temporal changes in groundwater recharge.

Attenuation of rotavirus, MS2 bacteriophage and biomolecule-modified silica nanoparticles in undisturbed silt loam over gravels dosed with onsite wastewater.

Contamination of potable groundwater by pathogenic viruses from on-site wastewater treatment systems (OWTS) poses a serious health risk. This study investigated the attenuation and transport of rotavirus, bacteriophage MS2 and DNA-labelled-glycoprotein-coated silica nanoparticles (DGSnp) in 2 intact cores of silt loam over gravels dosed with wastewater from an OWTS at 3.53 L/day. To simulate a worst-case scenario, experiments were conducted under saturated conditions. The results from 6 experiments demonstrated that the rotavirus and DGSnp reductions were very similar and markedly greater than the MS2 reduction. This was reflected in the peak concentrations, relative mass recoveries, and temporal and spatial reduction rates. For a given log10 reduction, the estimated soil depth required for MS2 was over twice that required for rotavirus and DGSnp. This is the first study in which DGSnp was used as a rotavirus surrogate in soil under wastewater applications. Consistent with previous studies, DGSnp showed promise at mimicking rotavirus attenuation and transport in porous media. The results suggest DGSnp could be used to assess the attenuation capacity of subsurface media to rotavirus. However, DGSnp is not conservative and will underestimate the setback distances required for rotavirus reductions by 3%. On the other hand, separation distances determined using the rotavirus parameters and criteria but based on MS2 attenuation, can be too conservative in some subsurface media. To determine safe and realistic separation distances, it would be beneficial and complementary to apply both conservative virus surrogate using MS2 bacteriophage and representative but non-conservative new virus surrogates using biomolecule-modified silica nanoparticles.

Application of an Analytical Solution as a Screening Tool for Sea Water Intrusion.

Sea water intrusion into aquifers is problematic in many coastal areas. The physics and chemistry of this issue are complex, and sea water intrusion remains challenging to quantify. Simple assessment tools like analytical models offer advantages of rapid application, but their applicability to field situations is unclear. This study examines the reliability of a popular sharp-interface analytical approach for estimating the extent of sea water in a homogeneous coastal aquifer subjected to pumping and regional flow effects and under steady-state conditions. The analytical model is tested against observations from Canada, the United States, and Australia to assess its utility as an initial approximation of sea water extent for the purposes of rapid groundwater management decision making. The occurrence of sea water intrusion resulting in increased salinity at pumping wells was correctly predicted in approximately 60% of cases. Application of a correction to account for dispersion did not markedly improve the results. Failure of the analytical model to provide correct predictions can be attributed to mismatches between its simplifying assumptions and more complex field settings. The best results occurred where the toe of the salt water wedge is expected to be the closest to the coast under predevelopment conditions. Predictions were the poorest for aquifers where the salt water wedge was expected to extend further inland under predevelopment conditions and was therefore more dispersive prior to pumping. Sharp-interface solutions remain useful tools to screen for the vulnerability of coastal aquifers to sea water intrusion, although the significant sources of uncertainty identified in this study require careful consideration to avoid misinterpreting sharp-interface results.

Vulnerability indicators of sea water intrusion.

In this paper, simple indicators of the propensity for sea water intrusion (SWI) to occur (referred to as "SWI vulnerability indicators") are devised. The analysis is based on an existing analytical solution for the steady-state position of a sharp fresh water-salt water interface. Interface characteristics, that is, the wedge toe location and sea water volume, are used in quantifying SWI in both confined and unconfined aquifers. Rates-of-change (partial derivatives of the analytical solution) in the wedge toe or sea water volume are used to quantify the aquifer vulnerability to various stress situations, including (1) sea-level rise; (2) change in recharge (e.g., due to climate change); and (3) change in seaward discharge. A selection of coastal aquifer cases is used to apply the SWI vulnerability indicators, and the proposed methodology produces interpretations of SWI vulnerability that are broadly consistent with more comprehensive investigations. Several inferences regarding SWI vulnerability arise from the analysis, including: (1) sea-level rise impacts are more extensive in aquifers with head-controlled rather than flux-controlled inland boundaries, whereas the opposite is true for recharge change impacts; (2) sea-level rise does not induce SWI in constant-discharge confined aquifers; (3) SWI vulnerability varies depending on the causal factor, and therefore vulnerability composites are needed that differentiate vulnerability to such threats as sea-level rise, climate change, and changes in seaward groundwater discharge. We contend that the approach is an improvement over existing methods for characterizing SWI vulnerability, because the method has theoretical underpinnings and yet calculations are simple, although the coastal aquifer conceptualization is highly idealized.