Science Inventory

Virus Transport from Drywells Under Constant Head Conditions: A Modeling Study

Citation:

Sasidharan, S., S. Bradford, J. Simunek, AND S. Kraemer. Virus Transport from Drywells Under Constant Head Conditions: A Modeling Study. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 197:117040, (2021). https://doi.org/10.1016/j.watres.2021.117040

Impact/Purpose:

The paper describes the evaluation of the transport of viruses contained in storm water runoff and infiltrated through a modern drywell (unsaturated one infiltration well). The computer simulations using HYDRUS 2D/3D assume a idealized axi-symmetric vertical cross section of the drywell and vadose zone down to the water table. The computer runs vary the hydraulic conductivity of the sediments from homogeneous to stochastic heterogeneous. Variation of virus transport properties are considered regarding attachment and inactivation. The simulations explore virus spreading in the horizontal and virus arrival times and concentrations at the water table. The results suggest further investigations of the protective separation distance from the drywell bottom release point to the water table.

Description:

Many arid and semi-arid regions of the world face challenges in maintaining water quantity and quality needs of growing populations. A drywell is an engineered vadose zone infiltration device widely used for stormwater capture and managed aquifer recharge. To our knowledge, no prior studies have quantitatively examined virus transport from a drywell, especially in the presence of subsurface heterogeneity. Axisymmetric numerical experiments were conducted to systematically study virus fate from a drywell for various virus removal and subsurface heterogeneity scenarios under steady-state water constant head flow conditions. Subsurface domains considered were homogeneous or had stochastic heterogeneity with selected standard deviation (σ) of log10(αK) and horizontal (X) and vertical (Z) correlation lengths. Low levels of virus concentration tailing can occur even at a separation distance of 22 m from the bottom of the drywell, and 6-log10 virus removal was not achieved when a small detachment rate ( k_d1=1×10¿ ¿ min¿ ¹) is present in a homogeneous domain. Improved virus removal was achieved at a depth of 22 m in the presence of horizontal lenses (e.g., X=10 m, Z=0.1 m, σ=1) that enhanced the lateral movement and distribution of the virus. In contrast, the presence of highly permeable vertical anisotropy (X =1 m, Z =1, σ=1 ) enhanced the faster downward movement of the virus with an early arrival time at the groundwater table. Therefore, the general assumption of a 1.5-12 m separation distance may not be adequate in most instances, and site specific microbial risk assessment is essential to minimize risk. The transient operation of the drywell minimizes virus migration due to increased residence times, and by pre-treatment using introduced in-situ soil iron oxide to increase the irreversible attachment and solid-phase inactivation.