The remediation of contaminated ground water is a multibillion-dollar global industry. Permeable reactive barriers (PRBs) are one of the leading technologies being developed in the search for alternatives to the pump-and-treat method. Improving the hydraulic performance of these PRBs is an important part of maximizing their potential to the industry. Optimization of the hydraulic performance of a PRB can be defined in terms of finding the balance between capture, residence time, and PRB longevity that produces a minimum-cost acceptable design. Three-dimensional particle tracking was used to estimate capture zone and residence time distributions. Volumetric flow analysis was used for estimation of flow distribution across a PRB and in the identification of flow regimes that may affect the permeability or reactivity of portions of the PRB over time. Capture zone measurements extended below the base of partially penetrating PRBs and were measured upgradient from the portion of aquifer influenced by PRB emplacement. Hydraulic performance analysis of standard PRB designs confirmed previously presented research that identified the potential for significant variation in residence time and capture zone. These variations can result in the need to oversize the PRB to ensure that downgradient contaminant concentrations do not exceed imposed standards. The most useful PRB design enhancements for controlling residence time and capture variation were found to be customized downgradient gate faces, velocity equalization walls, deeper emplacement of the funnel than the gate, and careful manipulation of the hydraulic conductivity ratio between the gate and the aquifer.
The Canterbury Regional Council, which manages 70 percent of New Zealand's irrigated land, has struggled to control the burgeoning demand for water resources as more land is converted to highly profitable, water intensive dairy farms relying on groundwater. At the center of Canterbury's struggle over water resources and its effective management are two competing groundwater science models. The different approaches and their implications for water management have led to a situation commonly described as a "science impasse" with scientists, policymakers, and stakeholders increasingly focused on "how to break the gridlock over science," particularly in one of the region's major watersheds, the Selwyn. In keeping with the traditional logical positivist, linear approach to science the expectation is that if the scientists can get the science right, then the ultimate goal of water sustainability will be made more likely since the "facts" will guide policymakers toward proper decisions. Yet our research found that while stakeholders do focus tightly on the dominant role of science and scientists when discussing solutions to the impasse, the underlying reality is a societal impasse grounded in the overarching adversarial setting, the logic of the wicked problem set, and the ultimate goal of sustainability. Seeing the "impasse problem" from this new perspective means that getting only the physical science right addresses the symptoms, not the underlying causes of the impasse. The article develops why the traditional instrumental, linear approach to science is unlikely to work in this case and why an alternative approach to science-civic science-offers promise as a way forward. A final section turns to the kind of steps most likely required to transition the Selwyn watershed's "societal impasse" dynamic from an adversarial setting to an effective collaborative governance arrangement conducive to the civic science enterprise. Regional Council-Environment Canterbury (ECan)-which manages 70 percent of NZ's irrigated land using 60% of all water allocated for consumptive use in NZ, is no exception. In the Selwyn watershed of Central Canterbury, ECan has struggled to control the burgeoning demand for water as more dryland farms (mainly sheep) and plantation forests are converted to more profitable water intensive dairy farms relying on irrigation from groundwater. These trends coincide with a period of lower than average rainfall. The result is that lowland streams now experience low or no flows for significant portions of the year.At the center of Canterbury's struggle over water resource management is the science that maps the hydrogeological characteristics of the region. Most dairy farmers, irrigators, and developers prefer a physical processes computer modeling approach--the "Aqualinc" groundwater model. The idea of an impasse runs contrary to the traditional logical positivist, linear approach to science in the policy process that is based on a rational planning model. Implicit to this line of reasoning is the bel...
As we enter the next phase of international policy commitments to halt biodiversity loss (e.g. Post-2020 Biodiversity Framework), biodiversity indicators will play an important role forming the robust basis upon which targeted, and time sensitive conservation actions are developed. Population trend indicators are perhaps the most powerful tool in biodiversity monitoring due to their responsiveness to changes over short timescales and their ability to aggregate species trends from global down to at a sub-national or even local scale. We consider how the project behind the foremost population level indicator - the Living Planet Index - has evolved over the last 25 years, its value to the field of biodiversity monitoring, and how its components have portrayed a compelling account of the changing status of global biodiversity through its application at policy, research and practice levels. We explore ways the project can develop to enhance our understanding of the state of biodiversity and share lessons learned to inform indicator development and mobilise action.
In a previous study, a denitrification wall was constructed in a sand aquifer using sawdust as the carbon substrate. Ground water bypassed around this sawdust wall due to reduced hydraulic conductivity. We investigated potential reasons for this by testing two new walls and conducting laboratory studies. The first wall was constructed by mixing aquifer material in situ without substrate addition to investigate the effects of the construction technique (mixed wall). A second, biochip wall, was constructed using coarse wood chips to determine the effect of size of the particles in the amendment on hydraulic conductivity. The aquifer hydraulic conductivity was 35.4 m/d, while in the mixed wall it was 2.8 m/d and in the biochip wall 3.4 m/d. This indicated that the mixing of the aquifer sands below the water table allowed the particles to re‐sort themselves into a matrix with a significantly lower hydraulic conductivity than the process that originally formed the aquifer. The addition of a coarser substrate in the biochip wall significantly increased total porosity and decreased bulk density, but hydraulic conductivity remained low compared to the aquifer. Laboratory cores of aquifer sand mixed under dry and wet conditions mimicked the reduction in hydraulic conductivity observed in the field within the mixed wall. The addition of sawdust to the laboratory cores resulted in a significantly higher hydraulic conductivity when mixed dry compared to cores mixed wet. This reduction in the hydraulic conductivity of the sand/sawdust cores mixed under saturated conditions repeated what occurred in the field in the original sawdust wall. This indicated that laboratory investigations can be a useful tool to highlight potential reductions in field hydraulic conductivities that may occur when differing materials are mixed under field conditions.
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