Innovative applications of subgrade biogeochemical reactors: Three case studies

Subgrade biogeochemical reactors (SBGRs) are an in situ remediation technology shown to be effective in treating contaminant source areas and groundwater hot spots, while being sustainable and economical. This technology has been applied for over a decade to treat chlorinated volatile organic compound source areas where groundwater is shallow (e.g., less than approximately 30 feet below ground surface [ft bgs]). However, this article provides three case studies describing innovative SBGR configurations recently developed and tested that are outside of this norm, which enable use of this technology under more challenging site conditions or for treatment of alternative contaminant classes. The first SBGR case study addresses a site with groundwater deeper than 30 ft bgs and limited space for construction, where an SBGR column configuration reduced the maximum trichloroethene (TCE) groundwater concentration from 9,900 micrograms per liter (μg/L) to <1 μg/L (nondetect) within approximately 15 months. The second SBGR is a recirculating trench configuration that is supporting remediation of a 5.7‐acre TCE plume, which has significant surface footprint constraints due to the presence of endangered species habitat. The third SBGR was constructed with a new amendment mixture and reduced groundwater contaminant concentrations in a petroleum hydrocarbon source area by over 97% within approximately 1 year. Additionally, a summary is provided for new SBGR configurations that are planned for treatment of additional classes of contaminants (e.g., hexavalent chromium, 1,4‐dioxane, dissolved explosives constituents, etc.). A discussion is also provided describing research being conducted to further understand and optimize treatment mechanisms within SBGRs, including a recently developed sampling approach called the aquifer matrix probe.     

An improvement selection methodology for key performance indicators

Key performance indicators (KPIs) are critical measures for determining the health of a manufacturing plant in relationship to the plant’s goals. In today’s competitive environment, manufacturers cannot be careless about their business; in fact, they must ensure that their KPIs are effective and use them to make improvements when necessary. This paper describes a method for suggesting improvements to a manufacturer’s KPIs, based on the results achieved from a workshop to score the KPI on a number of predefined criteria. The approach uses a prospect theory approach to weight the scoring. Different problem formulations were derived that allow for both recommendations for improvements and the recommendations for disinvestments to over-performing KPIs. The authors applied the developed approach to two workshop outputs, each from independent manufacturers, and the results highlighted the significant difference between the two manufacturers in terms of improvement priorities and KPI assessment. The optimal improvement suggestions were compared to those found through a fast heuristic. It was determined that given the underlying assumptions of the approach that the heuristic solutions were just as adequate as the optimal ones.     

The rationales behind the unit-segment theory and its analysis methodology for modeling vehicular movement networks

The theory of space accessibility analysis, space syntax, has been considered for capturing trip-makers’ route-choice decisions with an understanding that, while selecting routes, trip-makers tend to follow forward-facing fields traditionally represented by axial lines. But the idea of treating axial lines as a set of roadway segments representing an urban texture has remained under scrutiny when distinct procedures have been tested without much success. Nor has the axial-line theory seemed to gain much popularity within the orthodox transportation planning community. Studies show that a long axial line is found gaining configurational centrality, in general, for being well connected to its incident lines. Fragmenting a long axial line results in weakening it (in centrality terms), but also in generating a locally oriented model. Recent investigations, dealing with this problem, have resulted in the emergence of the unit-segment theory, which has turned out to be more sensitive to the local structures located within a large urban texture than the axial counterpart for the purpose of modeling vehicular movement networks without using origin–destination trip-counts. Essentially, the question now is: Is the unit-segment analysis also capable of generating syntax configurations that are equally sensitive to large and complex urban textures? What should be the methodology of such an analysis? This paper throws deeper insights into these questions by producing theoretical and empirical research findings and seeks to develop a common ground for both transportation planning and space syntax communities to work together for gaining a better understanding of how urban configurations relate to urban vehicular movement networks.     

Recent Changes in Stream Flashiness and Flooding,and Effects of Flood Management in North Carolina and Virginia

The southeastern United States has undergone anthropogenic changes in landscape structure, with the potential to increase (e.g., urbanization) and decrease (e.g., reservoir construction) stream flashiness and flooding. Assessment of the outcome of such change can provide insight into the efficacy of current strategies and policies to manage water resources. We (1) examined trends in precipitation, floods, and stream flashiness and (2) assessed the relative influence of land cover and flow‐regulating features (e.g., best management practices and artificial water bodies) on stream flashiness from 1991 to 2013. We found mean annual precipitation decreased, which coincided with decreasing trends in floods. In contrast, stream flashiness, overall, showed an increasing trend during the period of study. However, upon closer examination, 20 watersheds showed stable stream flashiness, whereas 5 increased and 6 decreased in flashiness. Urban watersheds were among those that increased or decreased in flashiness. Watersheds that increased in stream flashiness gained more urban cover, lost more forested cover and had fewer best management practices installed than urban watersheds that decreased in stream flashiness. We found best management practices are more effective than artificial water bodies in regulating flashy floods. Flashiness index is a valuable and straightforward metric to characterize changes in streamflow and help to assess the efficacy of management interventions.     

Coupling of the Water Cycle with Patterns of Urban Growth in the Baltimore Metropolitan Region,United States

Regional municipal water plans typically do not recognize complex coupling patterns or that increased withdrawals in one location can result in changes in water availability in others. We investigated the interaction between urban growth and water availability in the Baltimore metropolitan region where urban growth has occurred beyond the reaches of municipal water systems into areas that rely on wells in low‐productivity Piedmont aquifers. We used the urban growth model SLEUTH and the hydrologic model ParFlow.CLM to evaluate this interaction with urban growth scenarios in 2007 and 2030. We found decreasing groundwater availability outside of the municipal water service area. Within the municipal service area we found zones of increasing storage resulting from increased urban growth, where reduced vegetation cover dominated the effect of urbanization on the hydrologic cycle. We also found areas of decreasing storage, where expanding impervious surfaces played a larger role. Although the magnitude of urban growth and change in water availability for the simulation period were generally small, there was considerable spatial heterogeneity of changes in subsurface storage. This suggests that there are locally concentrated areas of groundwater sensitivity to urban growth where water shortages could occur or where drying up of headwater streams would be more likely. The simulation approach presented here could be used to identify early warning indicators of future risk.     

Healing the wounds in the landscape—reclaiming gravel roads in conservation areas

Reclaiming abandoned and unmaintained roads, built originally for forestry and mineral extraction, is an important part of ecological restoration, because the roads running through natural habitats cause fragmentation. The roads can be reclaimed in a passive way by blocking access to the road, but successful seedling recruitment may require additional management due to the physical constraints present at the road. We established a full factorial study to compare the effects of three road reclaiming measures, namely ripping, creation of safe sites by adding mulch and pine seed addition, on soil processes, recovery of understorey vegetation and seedling recruitment in three conservation areas in eastern Finland. We surveyed soil organic matter, frequency and cover of plant functional types, litter and mineral soil, and number of tree seedlings. The soil organic matter was, on average, 1.3-fold in the 50-cm-deep ripping treatment relative to unripped and 20-cm-deep ripping treatments. The germination and survival of deciduous seedlings and grass establishment were promoted by adding mulch. The addition of pine seeds counteracted the seed limitation and enhanced the regeneration of trees. The treatment combination consisting of ripping, adding mulch and pine seed addition enhanced the vegetation succession and tree-seedling recruitment most: the cover of grasses, herbs and ericaceous dwarf shrubs was 1.3–7.6-fold and the number of coniferous tree seedlings was 3.4–7.1-fold relative to the other treatment combinations. Differences between short-term (1–3 years) and longer-term (6 years) results indicate the need for a sufficient observation period in road reclamation studies.     

Estuarine circulation in the Taranto Seas

The Taranto basin is a shallow water marine system in the South of Italy characterized by the presence of a lagoon environment together with a semi-enclosed bay connected to the Ionian Sea. This marine system experienced over the last few decades strong biochemical pollution and environmental degradation, and it is considered a hotspot study site for economic, ecological and scientific reasons. The aim of this study was to examine, on an annual temporal scale and with high spatial resolution, the main hydrodynamical processes and transport scales of the system by means of a 3D finite element numerical model application, adopting the most realistic forcing available. The model allowed us to assess the role played by baroclinic terms in the basin circulation, describing its estuarine nature. In particular, the main features of water circulation, salinity and temperature distribution, water renewal time and bottom stress were investigated. Our results allowed us to equate this system dynamic to that of a weakly stratified estuary, identifying the main driving sources of this mechanism. The vertical stratification over the whole year was proved to be stable, leading to a dual circulation flowing out on the surface, mainly through Porta Napoli channel, and inflowing on the bottom mainly through Navigabile channel. This process was responsible also for the renewal time faster on the bottom of the Mar Piccolo basin than the surface. Due to the great importance of the Taranto basin for what concerns sediment pollution, also the effect of currents in terms of bottom stress was investigated, leading to the conclusion that only in the inlets area the values of bottom stress can be high enough to cause erosion.     

In situ immobilization of cadmium in soil by stabilized biochar-supported iron phosphate nanoparticles

The potential for nanoscale phosphate amendments to remediate heavy metal contamination has been widely investigated, but the strong tendency of nanoparticles to form aggregates limits the application of this technique in soil. This study synthesized a composite of biochar-supported iron phosphate nanoparticle (BC@Fe₃(PO₄)₂) stabilized by a sodium carboxymethyl cellulose to improve the stability and mobility of the amendment in soil. The sedimentation test and column test demonstrated that BC@Fe₃(PO₄)₂ exhibited better stability and mobility than iron phosphate nanoparticles. After 28 days of simulated in situ remediation, the immobilization efficiency of Cd was 60.2 %, and the physiological-based extraction test bioaccessibility was reduced by 53.9 %. The results of sequential extraction procedures indicated that the transformation from exchangeable (EX) Cd to organic matter (OM) and residue (RS) was responsible for the decrease in Cd leachability in soil. Accordingly, the pot test indicated that Cd uptake by cabbage mustard was suppressed by 86.8 %. Compared to tests using iron phosphate nanoparticles, the addition of BC@Fe₃(PO₄)₂ to soil could reduce the Fe uptake of cabbage mustard. Overall, this study revealed that BC@Fe₃(PO₄)₂ could provide effective in situ remediation of Cd in soil.     

The application of regenerable sorbents for mercury capture in gas phase

Mercury is a well-known toxic element, and flue gas streams emitted from coal-fired utilities are one of the largest anthropogenic sources of this element. This study briefly reviews the proposed technologies for reducing mercury emissions from coal combustion, focusing on an emerging process which involves the use of regenerable sorbents and especially those loaded with noble metals. Among the mercury species formed during coal combustion, elemental mercury is the most difficult to remove from the flue gases due to its low reactivity and insolubility in water. The widespread interest in using regenerable sorbents with metals is due to their ability to retain elemental mercury. With this technology, not only can efficiencies of 100 % be reached in the retention of elemental mercury but also a way to avoid the generation of new wastes loaded with mercury. This study considers the main aspects that must be taken into account when developing effective regenerable sorbents for mercury capture, with special attention to sorbents containing noble metals. The characteristics of this process are compared with those of other processes in a more advanced state of development.