Cheng-Haw Lee’s research while affiliated with National Cheng Kung University and other places

Groundwater is a precious and limited resource [...]

Climate change can directly or indirectly influence groundwater resources. The mechanisms of this influence are complex and not easily quantified. Understanding the effect of climate change on groundwater systems can help governments adopt suitable strategies for water resources. The baseflow concept can be used to relate climate conditions to groundwater systems for assessing the climate change impact on groundwater resources. This study applies the stable baseflow concept to the estimation of the groundwater recharge in ten groundwater regions in Taiwan, under historical and climate scenario conditions. The recharge rates at the main river gauge stations in the groundwater regions were assessed using historical data. Regression equations between rainfall and groundwater recharge quantities were developed for the ten groundwater regions. The assessment results can be used for recharge evaluation in Taiwan. The climate change estimation results show that climate change would increase groundwater recharge by 32.6% or decrease it by 28.9% on average under the climate scenarios, with respect to the baseline quantity in Taiwan. The impact of climate change on groundwater systems may be positive. This study proposes a method for assessing the impact of climate change on groundwater systems. The assessment results provide important information for strategy development in groundwater resources management.

The purpose of this research is to analyze and introduce a new emergency medical service (EMS) transportation scenario, Emergency Medical Regulation Center (EMRC), which is a temporary premise for treating moderate and minor casualties, in the 2015 Formosa Fun Color Dust Party explosion in Taiwan. In this mass casualty incident (MCI), although all emergency medical responses and care can be considered as a golden model in such an MCI, some EMS plans and strategies should be estimated impartially to understand the truth of the successful outcome. Factors like on-scene triage, apparent prehospital time (appPHT), inhospital time (IHT), and diversion rate were evaluated for the appropriateness of the EMS transportation plan in such cases. The patient diversion risk of inadequate EMS transportation to the first-arrival hospital is detected by the odds ratios (ORs). In this case, the effectiveness of the EMRC scenario is estimated by a decrease in appPHT. The average appPHTs (in minutes) of mild, moderate, and severe patients are 223.65, 198.37, and 274.55, while the IHT (in minutes) is 18384.25, 63021.14, and 83345.68, respectively. The ORs are: 0.4016 (95% Cl = 0.1032–1.5631), 0.1608 (95% Cl = 0.0743–0.3483), and 4.1343 (95% Cl = 2.3265–7.3468; P < .001), respectively. The appPHT has a 47.61% reduction by employing an EMRC model. Due to the relatively high appPHT, diversion rate, and OR value in severe patients, the EMS transportation plan is distinct from a prevalent response and develops adaptive weaknesses of MCIs in current disaster management. Application of the EMRC scenario reduces the appPHT and alleviates the surge pressure upon emergency departments in an MCI.

In-situ chemical oxidation (ISCO) can remove pollutants efficiently. However, the most important key to successfully conducting ISCO on site is to place the oxidant in close contact with the contaminant. Therefore, monitoring tools that provide for enhanced tracking of the injectate offer considerable benefit to guide subsequent ISCO injections. In this study, we applied the MagnetoMetric Resistivity (MMR) method to survey the distribution of an injected oxidant. A pilot test was conducted on a 10 m × 10 m site, and the sodium persulfate injection involved four pulse injections from one injection well. A magnetic field survey coupled with conventional monitoring was performed before the initial injection and after each pulse injection. The results of this study showed that groundwater samples from six observation wells and seven direct-push EC loggings did not provide sufficient data to quantify the distribution and flow behavior of the injected oxidant. However, the magnetic field survey visually showed the dynamic distribution of the injected oxidant, and the flow pathways and flow behavior were assessed accordingly. Although the flow behavior of injected solution was changeable in the aquifer, but the magnetic field survey combined with the monitoring of the well samples helped to explain the abnormal changes in the electrical conductivity of the observation wells and supports the use of the magnetic field survey technology as a method of monitoring ISCO injections.

Climate change and anthropogenic activity are the main factors impacting the hydrological environment. For sustainable water utilization, identifying the impact contribution of these two factors on the streamflow variations is an important topic in recent research. In this study, seven river basins in southern Taiwan were selected as the study area to evaluate the annual streamflow from 1980 to 2017. The decomposition and elasticity methods based on the Budyko hypothesis were applied to quantify the contribution of climate and anthropogenic factors to the streamflow variations. In addition, the normalized difference vegetation index (NDVI) was used to represent the actual situation of land cover and verify the parameters in the Budyko equation. The two quantitative methods consistently demonstrated that the streamflow variations from pre- to post-period occurred due to the climate factor. The elasticity coefficient of variables demonstrated that the streamflow change is more sensitive to precipitation and this influence reduces from pre- to post-period as the streamflow increase. In the NDVI variations, except for the Yanshui and the Linbain rivers, the Budyko equation parameters changed consistently with NDVI. The present study provides effective results on the contribution of streamflow variations in southern Taiwan to serve as a reference for future water management.

Nonaqueous-phase liquids (NAPLs) usually move through the vadose zone not in a homogeneous spread manner but in the form of disconnected blobs, and they remain in the pores of porous media. A major challenge in remediating an NAPL-contaminated site is to detect and delineate the distribution of NAPLs. Geophysical technologies could act as investigating methods for sites with limited resources and time constraints. Based on the principle of magnetometric resistivity (MMR) method, in this study, we applied an electric current flow pattern and its resulting magnetic field to develop a new application for contaminated site investigation. The physical phenomena about the magnetic distribution, the flow pattern of electric current, and the influence of different media in packed sand were observed via sandbox experiments. A field test was performed at a light NAPL (LNAPL)-contaminated site by combining the magnetic field survey and a soil sample analysis. Two potential contaminated zones were determined according to the specific characteristics of the contour image plotted according to the magnetic field intensity collected on the ground. The quantitative results of the total petroleum hydrocarbons (TPHs) of 18 soil samples were used to verify the results of the magnetic field survey. The comparison results revealed that we obtained a high accuracy of 92.9% in the field test, which indicated that this technology could be used to investigate LNAPL-contaminated sites. Moreover, two phenomena, the scale effect led to poor resolution and the behavior of flow pattern disturbance distorted the survey images, were observed in both the sandbox experiment and the field test.

Knowledge of the geologic structure at a field site is a useful piece of information for hydrologic modeling since it can serve as more site-specific prior information about the hydraulic parameter patterns at the site than generic spatial statistics. Widely accepted electrical resistivity tomography (ERT) survey for mapping subsurface anomalies could be a viable tool for acquiring this information. However, their ability to delineate geologic structures has not been thoroughly investigated. In this study, two-dimensional ERT numerical experiments were first conducted to study the effects of boundary conditions on the dipole-dipole and pole-pole array configurations. An ERT setup subsequently was implemented in a sandbox consisting of complex layers of different sands. A continuous copper wire was installed along the sides of the sandbox to impose potential boundaries. Using data collected with the pole-pole array in the sandbox under different degrees of drainage and the Successive Linear Estimator (SLE) algorithm, we show that ERT yields electrical conductivity estimates of complex layer structures with small uncertainties. In addition, using SLE with physically meaningful correlation scales as prior information can lead to an electrical conductivity field that is consistent with visually observed layer structures. The correlation scale concept also was demonstrated to provide guidance to the design of the electrode spacing in the surveys. Moreover, the estimated field was validated by predicting electrical potential fields from two independent ERT surveys using electrodes at different locations. Results of this study suggest that the combination of ERT and SLE is a viable geophysical survey tool for mapping geologic layer structures. Research Significance This study develops a method to implement prescribed potential boundaries for enhancing the pole-pole ERT survey, illustrates the importance of correlation scales and develops an approach for validating ERT results.

Over the past decades, a new aquifer test technology (sequential pumping tests or hydraulic tomography, HT) has been developed and successfully applied to many field sites to delineate the spatial distributions of hydraulic properties (e.g., transmissivity (T) and storage coefficient (S)). Yet, the reproducibility of its estimated T and S fields and the predictive capabilities of the estimates for different flow scenarios at different time periods remain unexplored. That is to say, if the estimated fields based on sequential pumping tests conducted during different years are the same since the geologic formation and processes may have undergone changes. In order to answer this important question, this study first compares the drawdown-time behaviors from the sequential pumping tests (SPTs) conducted in 2010 with those conducted in 2012 at a field site and then finds they are similar but different in detail. It then uses these data to estimate the T and S fields and checks the reproducibility of the estimates. The estimated heterogeneity patterns are found to be generally reproducible in spite of uncertainties. In addition, the estimates from each year are capable of predicting the observed drawdowns, induced by independent pumping tests during the corresponding year (i.e., self-validation). Moreover, the estimated fields are cross-validated. That is, this study uses the estimates obtained from the 2010 pumping tests to predict the observed drawdowns of the independent pumping tests conducted in 2012. Likewise, it uses the estimates from 2012 pumping tests to forecast the drawdowns of the independent pumping tests of 2010. The results of both self-validation and cross-validation indicate that the estimated T and S fields based on the test in one year can be used to predict bulk flow behavior in the other year. Differences in detailed behaviors may be attributed to changes in the processes, omitted in the depth-averaged flow model.