Leachate reduction and pollution control strategies for landfills in hilly areas based on site condition analysis and numerical simulation.

Landfill is an important means of municipal solid waste treatment. Previous studies have shown that the combination of "cut-off wall and pumping well" technology is an effective measure to deal with the leachate emission reduction and pollution control of landfill, and has been widely used in plain areas. However, for landfills in hilly areas with complex terrain and geological conditions, there is still a lack of clear and referable ideas and operational strategies for leachate emission reduction and pollution control. In this study, we proposed strategies for determining the position and depth of cut-off walls and pumping wells and reasonable combinations of the cut-off wall depth and pumping quantity for leachate reduction and pollution prevention of landfills in hilly areas. The determination of leachate reduction and pollution control strategy need to be achieved in two stages, qualitative and quantitative: (1) In the qualitative stage, the natural conditions (Weathering degree, groundwater flow characteristics, topography condition, hydrometeor condition, and aquifer thickness) and engineering conditions (Operation status, landfill location, and excavation status) of the study area are analysed in detail, and then the depth range and location of the cut-off wall and pumping well are determined. (2) In the quantitative stage, we need to quantify the combination of the cut-off wall depth and pumping quantity by using profile particle tracing and pollutant transport modelling. A reasonable cut-off wall depth needs to control the leakage of pollutants inside the wall, and a reasonable pumping quantity needs to ensure that the depth of the pollutant distribution is equivalent to the depth of the separation line, which separates the water flow towards the pumping well and the water flow downstream. (3) The effectiveness of the leachate reduction and prevention strategies proposed in this study was verified through an example of a landfill in Northeast China. This study provides a reference and operation method for leachate emission reduction and pollution control of landfills in hilly areas.

Potential risk assessment of groundwater to address the agricultural and domestic challenges in Ordos Basin.

The safety of groundwater has been a great concern for irrigation and drinking purposes in recent decades due to the increasing impacts of anthropogenic activities. There are several standards to evaluate the groundwater quality for different utilization purposes. In this paper, 804 samples covering the entire Ordos Basin across five provinces were used to evaluate the irrigation suitability and human health risks. The results showed that the sequence of cationic concentration was Na+ > Ca2+ > Mg2+ > K+ > NH4 +, and the anion concentration was HCO3 - > SO4 2- > Cl- > NO3 - > F- > NO2 -. For drinking purposes, TDS, Na+, SO4 2-, F-, TH and NO3 - exceed seriously the regulated standard in the study area. For irrigating purposes, 80% of the water in the study area belongs to "good water" according to the evaluation of salinity and alkalinity. Saline water which is not suitable for irrigation accounts for about 9%. High health risks of fluoride ions are mainly observed to the samples representing the western part of the study area, while the health risks of nitrates spread throughout the study area. Health risk is not only related to location, but also varies with age, and it is found that children suffer more threats than adults.