Contaminant transfer and hydrodispersiveparameters in basaltic lava flows: artificial tracertest and implications for long-term management

Abstract

Abstract:The aim of this paper is to evaluate the vulnerability after point source contamination and characterize water circulations in volcanic flows located in the Argnat basin volcanic system (Chaîne des Puys, French Massif Central) using a tracer test performed by injecting a iodide solution. The analysis of breakthrough curves allowed the hydrodispersive characteristics of the massive lava flows to be determined. Large Peclet numbers indicated a dominant advective transport. The multimodal feature of breakthrough curves combined with high values of mean velocity and low longitudinal dispersion coefficients indicated that water flows in an environment analogous to a fissure system, and only slightly interacts with a low porosity matrix (ne < 1%). Combining this information with lava flow stratigraphy provided by several drillings allowed a conceptual scheme of potential contaminant behaviour to be designed. Although lava flows are vulnerable to point source pollution due to the rapid transfer of water within fractures, the saturated scoriaceous layers located between massive rocks should suffice to strongly buffer the transit of pollution through dilution and longer transit times. This was consistent with the low recovery rate of the presented tracer test.

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

“…These aquifers can be characterized as dual-porosity systems where fractures within the rocks transmit water quickly and zones with only primary porosity transmit water much more slowly [80,81]. For example, Bertrand et al [82] used an artificial tracer to examine water and contaminant transport in heterogeneous basalt flows that exhibited dual-porosity behavior. They found that while almost all of the water and tracer was quickly advected through fractures, a significant portion of the tracer was lost and was hypothesized to have been captured and stored in slow, primary-porosity zones.…”

MFIT 1.0.0: Multi-Flow Inversion of Tracer breakthrough curves in fractured and karst aquifers

“…Despite the range of possibilities offered by these programs, the fitting and interpretation of tracer BTCs remains a challenging task in some cases, notably for BTCs exhibiting multiple local peaks and extensive backward tailing. Such BTC shapes, which fall in the general category of non-Fickian (or anomalous) transport (Berkowitz et al, 2006;Neuman and Tartakovsky, 2009), are frequently observed in fractured and karst aquifers (Tsang and Neretnieks, 1998;Streetly et al, 2002;Massei et al, 2006;Loefgren et al, 2007;Goldschei-der et al, 2008;Field and Leij, 2012;Bertrand et al, 2015;Yang et al, 2019).…”