Risk assessment is an effective scientific tool which enables to quantify the human health impacts due to exposure to contaminated water. This paper aims at presenting an integrated approach for the health risk assessment of subsurface contamination by benzene leached from a landfill in the Netherlands and at demonstrating the effect of hydrogeological conditions such as the hydraulic conductivity distribution, the recharge rate and the first-order degradation rate constant on the outcomes of health risk analysis linked with particle tracking random walk approach under some contamination scenarios. The results demonstrate that hydrogeological conditions, especially the degradation rate, affect the cumulative mass of benzene in a certain plane or at an exposure point in the field of concern. The 50th fractiles are utilized as a measure of the carcinogenic risk evolution under the transient condition of the exposure duration. It is revealed that the probability distributions of the health risk vary with the corresponding hydrogeological condition and exposure duration because of the relation between the discharge rates of groundwater and the total mass of particles flowing into the exposure point, leading to the difference of a time series of the health risk variation. Moreover, the exceedance probability of the acceptable risk of 10^<-6> are estimated in the range of 0% to approximately 71% for all available cases, whereas most cases slightly exceed the acceptable risk in the exposure duration of 50 or 70 years. In the current design scenarios, there may be low health risks exposed to a benzene-contaminated water to a hypothetical population living in the neighborhood of the landfill.
A cell-based distributed hydro-environmental model is developed which enables to analyze groundwater nitrate-nitrogen (N-N) contamination in rural areas, with well-coordinated incorporation of the water quality tank submodel for surface zone and the nitrate-nitrogen transport submodel for unconfined groundwater aquifer into the previously developed hydrologic model (Takeuchi et al., 2010). Cell-based building of all component submodels allows us to mesh the problem domain with unstructured cells of triangular shape, and therefore renders it possible to reflect in a refined fashion a variety of land-use practices in an analysis of the problem. The solutions based on reality, associated with groundwater flow and quality, can thus be obtained at a high (or field-plot-scale) resolution. It is also of great advantage that quantities of the hydro-environmental components of interest, such as surface water discharge, ground-water recharge, surface nitrogen discharge, and N-N leaching, can be obtained cell by cell or land-use by land-use. Application of the model to a real rural area having diverse terrains testifies to its satisfactory performance in a global sense. The simulated N-N concentrations of the groundwater vary in the ranges of the observed concentrations. The model also well reproduces the observed realities that the N-N concentration is high in upland areas such as alluvial fan and river terrace, while low in the lowland areas such as delta and valley floor, and is lowered in the irrigation season. It is thus considered that the model presently developed is useful for simulating and assessing the process and geographic distribution of groundwater N-N contamination in rural areas where fertilizing-induced groundwater contamination is a special concern.
Maize, a staple food crop in Malawi in sub-Sahara region has been grown under rainfed conditions for many years but many factors affect its production. Changing rainfall pattern has been a main factor which is believed to have come about due to the changing climate in recent years. A case study of over 60 years of rainfall data in Malawi's central region was analyzed where rainfall data over time was compared with maize production yields. Other non-climatic factors were also studied to explain their impact on production. Both observed monthly and daily rainfall data were used. Thiessen polygon method was used to calculate daily areal rainfall from the available 4 gauging stations. Since the gauging network was not adequate a regression analysis of the areal rainfall against the recorded time series from the stations was carried out. A regression equation created from the station with highest correlation was used to predict the daily rainfall data which was analyzed in detail to identify daily pattern changes. It was found that rainfall distribution characteristics have changed over time becoming more unpredictable and, hence, reducing production. In general, everytime there was an erratic rainfall pattern, maize production was affected. The paper recommends building more sustainable irrigation systems so that agricultural production can be under control during droughts. It also recommends removing policy that depends on rainfed food production and economic activities to control the problems associated with the changing rainfall pattern.
The purpose of this paper is to evaluate the feasibility of financial supports of the red soil erosion prevention policy through local taxation in Okinawa Prefecture. The double-bounded dichotomous choice method was employed to evaluate the local willingness-to-pay for the prevention of red soil erosions. Through the survey, we evaluated the median willingness-to-pay (medianWTP) for the local taxation to compensate prevention cost at as much as 1,621 yen a year per household. Total willingness-to-pay (TWTP) can be obtained by aggregating individual WTPs. The estimated TWTP was 806 million yen per year. This paper also estimates the red soil erosion prevention cost as follows, 1) 523 million yen per year for the buffer area method, 2) 470 million yen per year for the straw rolls method, and 3) 1,200 million yen per year for the mulching method. As a result, both the buffer area and the straw rolls methods were evaluated to be within TWTP while mulching method beyond TWTP.
This paper describes experimental results and discussions regarding pipeline flow control using constant flow valve installed at midway of the pipeline. Two types of direct acting constant flow valve (fixed flow rate and variable flow rate) were tested using a test-pipeline located in Ohno Mountain of Kagoshima. The result indicated that both types of valve controlled the flow rates of pipeline, and the performance in terms of flow control was similar. A considerable issue of the flow control approach was the cavitation continuously generated when pressure was negative at the downstream side of the constant flow valve, because it damages the valves. The approach should be taken with any kind of devise on pipeline system design, such as by slope design at downstream side of the valve. Throughout the experiment, self-induced vibration, by setting up automatic pressure reducing valve and constant flow valve in series, was not confirmed.
In this study, in order to examine a wind-induced mixing phenomenon in a closed water area with floating-leaved plant, we conducted experiments on wind flow characteristics, entrainment phenomenon and turbulent structure by using a test tank with wind tunnel and artificial plants. From the experimental results of wind flow characteristics, we quantified the impact of occupancy rate of plant on resistance characteristics. From the experimental results of entrainment phenomena, we defined the parameter that can explain a mixing magnitude between the density stratifications, and quantified the impact of the rate on vertical mixing. From the experimental results of turbulent structure of the upper layer, we clarified a difference of turbulent structure at each occupancy rate and quantified the impact of the rate on turbulent characteristics.
Soil infiltration process greatly contributes to the hydrological process in watershed, thus, soil infiltration water and runoff water were collected to characterize pollutant load from two planted forests. Especially, this study focused on the heavy rain which is reported to be increasing because of climate change. Glass fiber wick samplers were used to collect soil infiltration water samples, while runoff water was collected at the weir. Results showed that the wick sampler successfully collected the soil infiltration water without accumulating excess water above the device. The amounts of pollutant loads in soil infiltration water (total organic carbon; TOC, total nitrogen; TN) were positively correlated with pollutant loads in runoff water, which directly showed the contribution of soil water to runoff water. During the research period, environmental pollution load density in soil infiltration water was negatively correlated with sampled soil water volume. This could be a dilution effect caused by rainfall infiltration. However, after the heavy rainfall, soil infiltration water quality showed higher concentration than other rainfall events. The trend was clear in the long lasting strong rainfall, especially for well conductive forest slope. Because of the high permeable properties, pollutant loads from the soil surface easily reached to the depth of glass fiber wick (50cm depth), without filtering process through the soil body.