Drought is a natural hazard which occurs in all climatic zones. The effect from drought can cause a serious problem for agricultural activities, economies and the environment. There is a need to characterize drought events in terms of drought severity, frequency and possibility of drought occurrence for better drought management. An examination of drought characteristics and drought severity using the Standardized Precipitation Index (SPI) and the Vegetation Condition Index (VCI) was carried out for different land cover types. The study examined how data mining techniques such as association rules could be used to elucidate the relationships between VCI and SPI in order to predict the possibility of drought occurrence. Rainfall datasets were collected from the Thai meteorological department for the period 1980–2009 and digitally encoded into a Geographic Information System database. SPI values were derived both temporally and spatially for quantitative measurement of drought events over the 30-year period. Monthly VCI values were calculated from NDVI data collected from year 2001 to 2009 using multi-temporal Terra MODIS Vegetation Indices Product (MOD13Q1). Data mining technique was introduced and applied to generate association rules between VCI and SPI to predict the possibility of drought occurrence. The results from multi-temporal SPI analysis shown drought event occurred more often for the 3- and 6-month SPI in October at the central and the northeastern part of the region. Spatial SPI revealed that high-drought-risk areas were in the southwest and extending to the central part of the region. The statistically significant correlations between monthly VCI and SPI at the multiple timescales were found for mixed deciduous forest in dry period. This result indicated vegetation condition for this forest type was sensitive for precipitation during dry period. Drought events were found to affect the rice crop in the central part of the region more, as observed from the negative correlation between VCI and SPI during growing season. The representative association rules from VCI and SPI revealed drought event also occurred for paddy field in the central part of the region. Drought periods within the growing season for this area are becoming more prevalent even with increase in annual rainfall. Shorter scale of SPI was found to be effective in characterizing drought conditions. This study combined the different level of software and dataset used which are able to predict future occurrence and severity of drought using the current condition. Results can be applied to assess drought severity and drought-affected areas for efficient drought management and planning

In order to study the effectiveness of using colloidal silica, NYACOL DP5110, to stabilize chromium-contaminated soil, the diffusion of chromium in colloidal silica gel was estimated from laboratory experiments. To measure diffusion coefficients of chromium in the colloidal silica gel, a new measurement method based on digital photography was introduced. A series of experiments were designed and conducted to validate this new method and to estimate the diffusion coefficients of chromium in the colloidal silica gel. Accuracy of the proposed method was evaluated by several differentways. It was found that the apparent diffusion coefficient of chromium in colloidal silica gel ranged from 1.76 to 8.48 x 10(-10) m2/s depending mainly on the concentration of silica in the gel with chromium concentration less than 10(-2) M. Higher silica concentrations yielded lower diffusion coefficients due to the obstruction to the free movement of chromium. The adsorption isotherm of chromate to colloidal silica gel was found to be linear at pH 7; the partition coefficient was calculated to be 0.549 L/g. Mass balance calculations were performed to evaluate the accuracy of the proposed method and found that the measuring error was less than 6.5%. Based on the test data, the estimation of diffusion coefficients for chromium in colloidal silica gel using digital photography seems to be accurate and precise. This method is suitable for analyzing colored chemicals inside clear/white gels. From the results, it can be concluded that the gel behaves as a porous material with silica network forming continuous solid phase and its pore space saturated with water. The chromium ions diffuse in porous silica gel on a tortuous path. Therefore, the bulk diffusion dominates. Thus, the silica can be represented as a fix and impenetrable immersion in the solution. The presence of these motionless silica chains leads to an increase in the mean path of the diffusing molecules between two points in the system. On the basis of the test results, it can also be concluded that colloidal silica, NYACOL DP5110, for in-situ treatment of chromium-contaminated soils seems to be ineffective. Further research of more realistic simulation of diffusion and refined gel formulation with the capacity to convert the chromium to an immobile form is recommended.

Investigation of the spatial distribution of metals was conducted for two constructed wetlands used as tertiary treatment in Chia Nan University of Pharmacy and Science (CNU) and Metal Processing Industries (MPI) located in Tainan, Taiwan. These two distinguished sites were selected to compare the distribution of metals for constructed wetlands treating different types of wastewater. Along the distance, samples of water, sediment, and macrophytes were analyzed for metals including Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Additionally, measurements of water quality including temperature, pH, EC, ORP, DO, TSS, BOD, COD, and turbidity were performed. Results show that, at CNU, wastewater contained higher organic consititute (BOD 29.3 +/- 11.7 mg/, COD 46.7 +/- 33.6 mg/L) with low metals content. Wastewater at MPI contained low level of organic consititute (BOD 7.1 +/- 3.3 mg/L, and COD 66.0 +/- 56.5 mg/L) and higher metals content. Metals distribution of both sites showed similar results where metals in the sediments in the inlet zone have greater concentrations than other areas. The constructed wetlands can remove Cd, Cu, Ni, Pb, and Zn. However, there was no removal of Al, Cr, Fe, and Mn. A distance along the constructed wetlands had no effect on metal concentrations in macrophyte and water.

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