On Covering Segments with Unit Intervals

We study the problem of covering a set of segments on a line with the minimum number of unit-length intervals, where an interval covers a segment if at least one of the two endpoints of the segment falls in the unit interval. We also study several variants of this problem. We show that the restrictions of the aforementioned problems to the set of instances in which all the segments have the same length are NP-hard. This result implies several NP-hardness results in the literature for variants and generalizations of the problems under consideration. We then study the parameterized complexity of the aforementioned problems. We provide tight results for most of them by showing that they are fixed-parameter tractable for the restrictions in which all the segments have the same length, and are W[1]-complete otherwise

The Updated version of SF Box: A method for soil quality classification as a basis for applicable site-specific environmental risk assessment of contaminated soils

This technical note summarises major changes in the updated version of SF Box, which is part of the SCORE – the Multi-Criteria Decision Analysis method for decision support in soil remediation projects. SCORE stands for the Sustainable Choice Of REmediation and SF Box stands for Soil Function toolBox. The SF Box tool has been developed for soil function assessment to complement environmental risk assessments, in order to increase awareness of decision-makers for inherent soil qualities other than concentration of contaminants and their availability/mobility, which are critical for proper soil functioning, e.g. availability of water and nutrients for soil organisms, but often ignored in remediation projects (driven by protection of the soil environment with ambition to recover ecosystem functions) in Sweden. The tool is based on a scoring method using soil quality indicators (SQIs) for assessing (I) the soil’s capacity to perform its functions in its own reference state of being ‘clean’, i.e. “what can this soil do and can it perform its functions well, assuming that it is free of contaminants?”, and (II) the effects of the remedial actions themselves on soil functions, i.e. “can the remediated soil continue to perform these functions well?”. The earlier version of SF Box addresses the soil functions associated with Primary Production. By (i) taking into consideration the perspectives of soil microbiology, soil fauna and vegetation, (ii) slightly modifying the set of SQIs (consisting of soil texture, content of coarse material, organic carbon/matter, available water, C/N ratio, pH and available phosphorus), and (iii) revisiting the curves for scoring of soil performances on each SQI, the SF Box tool has been updated to assess the soils’ capacity to function as a basis for Life and Habitat of flora and fauna. This updated version is therefore aimed to provide an improved basis for site-specific environmental risk assessment by means of (1) differentiating between the effects of contamination on soil biota and the effects of soil capability to function as a host to these species in its own reference state free from contaminants, and (2) classification of the soils (usually characterized by heterogeneity at contaminated sites) in accordance with their overall performance on the selected SQIs for further analysis of ecotoxicological risks in each soil class

Stabilization of PFAS in groundwater with sorbents : Can the spreading of per-and polyfluoroalkyl substances (PFAS) from contaminated sites be stopped with sorbents?

Spridning med grundvattnet från kraftigt förorenade hotspots utgör en viktig källa till per- och polyfluorerade alkylsubstanser (PFAS) i miljön och vattenresurser. Inom projektet StopPFAS undersöktes fastläggning av PFAS till sorbenter som en metod att begränsa PFAS-spridning med grundvattnet och elektrokinetisk sanering (EKR) undersöktes som ett komplement samt för regenerering av fastläggningszoner. Dynamiska kolonnstudier visade att kolloidalt aktivt kol (CAC) effektivt kan fastlägga PFAS när god kontakt mellan PFAS i grundvattnet och CAC uppnås. Fastläggningen ökade med ökande längd på den fluorerade kolkedjan. Skakförsök visade vidare att fastläggningen för kortkedjiga PFAS minskade när de förekom i en blandning tillsammans med andra PFAS till följd av konkurrens. Fältförsök i pilotskala med injektering av CAC som en permeabel barriär reducerade särskilt initialt PFAS-halten nedströms barriären, men en betydande andel PFAS tog sig ändå förbi. Låg genomsläpplighet och heterogenitet försvårade installationen. Noggrann hydrogeologisk karakterisering och att lyckas distribuera CAC där den huvudsakliga föroreningstransporten sker bedömdes avgörande för att metoden ska bli framgångsrik. I labförsök med jord utan sorbenter gav EKR höga extraktionshastigheter för kortkedjiga PFAS, men för långkedjiga PFAS var effektiviteten låg. EKR bedömdes potentiellt användbart för PFAS-sanering i kombination andra metoder för långkedjiga PFAS. EKR var inte framgångsrikt för regenering av aktivt kol.Spreading with groundwater from heavily polluted hotspots is an important source of per- and polyfluoroalkyl substances (PFAS) in the environment. Within the StopPFAS project, application of sorbents was investigated as a method to limit PFAS transport with groundwater, and electrokinetic remediation (EKR) was investigated as a complementary method and for regeneration of sorption zones. Dynamic column studies showed that colloidal activated carbon (CAC) can effectively immobilize PFAS when good contact between PFAS in the groundwater and CAC is achieved. The sorption increased with increasing fluorinated carbon chain-length. Batch tests further showed that the sorption of short-chain PFAS decreased when they were present in a mixture with other PFAS due to competition. Pilot-scale field trials with injection of CAC as a permeable barrier reduced PFAS concentrations downstream of the barrier, but a significant proportion of PFAS still escaped. Low permeability and heterogeneity made installation difficult. Accurate hydrogeological characterization and succeeding in distributing CAC where the main contaminant transport takes place were deemed crucial for the method to be successful. In lab experiments with soil without sorbents, EKR gave high extraction rates for short-chain PFAS, but for long-chain PFAS the efficiency was low. EKR was deemed potentially useful for PFAS remediation in combination with other methods for long-chain PFAS. EKR was not successful for regeneration of activated carbon.Tuffo 2023-2</p

Stabilization of PFAS in groundwater with sorbents : Can the spreading of per-and polyfluoroalkyl substances (PFAS) from contaminated sites be stopped with sorbents?

Spridning med grundvattnet från kraftigt förorenade hotspots utgör en viktig källa till per- och polyfluorerade alkylsubstanser (PFAS) i miljön och vattenresurser. Inom projektet StopPFAS undersöktes fastläggning av PFAS till sorbenter som en metod att begränsa PFAS-spridning med grundvattnet och elektrokinetisk sanering (EKR) undersöktes som ett komplement samt för regenerering av fastläggningszoner. Dynamiska kolonnstudier visade att kolloidalt aktivt kol (CAC) effektivt kan fastlägga PFAS när god kontakt mellan PFAS i grundvattnet och CAC uppnås. Fastläggningen ökade med ökande längd på den fluorerade kolkedjan. Skakförsök visade vidare att fastläggningen för kortkedjiga PFAS minskade när de förekom i en blandning tillsammans med andra PFAS till följd av konkurrens. Fältförsök i pilotskala med injektering av CAC som en permeabel barriär reducerade särskilt initialt PFAS-halten nedströms barriären, men en betydande andel PFAS tog sig ändå förbi. Låg genomsläpplighet och heterogenitet försvårade installationen. Noggrann hydrogeologisk karakterisering och att lyckas distribuera CAC där den huvudsakliga föroreningstransporten sker bedömdes avgörande för att metoden ska bli framgångsrik. I labförsök med jord utan sorbenter gav EKR höga extraktionshastigheter för kortkedjiga PFAS, men för långkedjiga PFAS var effektiviteten låg. EKR bedömdes potentiellt användbart för PFAS-sanering i kombination andra metoder för långkedjiga PFAS. EKR var inte framgångsrikt för regenering av aktivt kol.Spreading with groundwater from heavily polluted hotspots is an important source of per- and polyfluoroalkyl substances (PFAS) in the environment. Within the StopPFAS project, application of sorbents was investigated as a method to limit PFAS transport with groundwater, and electrokinetic remediation (EKR) was investigated as a complementary method and for regeneration of sorption zones. Dynamic column studies showed that colloidal activated carbon (CAC) can effectively immobilize PFAS when good contact between PFAS in the groundwater and CAC is achieved. The sorption increased with increasing fluorinated carbon chain-length. Batch tests further showed that the sorption of short-chain PFAS decreased when they were present in a mixture with other PFAS due to competition. Pilot-scale field trials with injection of CAC as a permeable barrier reduced PFAS concentrations downstream of the barrier, but a significant proportion of PFAS still escaped. Low permeability and heterogeneity made installation difficult. Accurate hydrogeological characterization and succeeding in distributing CAC where the main contaminant transport takes place were deemed crucial for the method to be successful. In lab experiments with soil without sorbents, EKR gave high extraction rates for short-chain PFAS, but for long-chain PFAS the efficiency was low. EKR was deemed potentially useful for PFAS remediation in combination with other methods for long-chain PFAS. EKR was not successful for regeneration of activated carbon.Tuffo 2023-2</p