Patterns of subsidence in the lower Yangtze Delta of China: the case of the Suzhou-Wuxi-Changzhou region.

Investigation indicates that the subsidence pattern in the lower Yangtze Delta area is related to groundwater extraction. Suzhou-Wuxi-Changzhou region ("Su-Xi-Chang") belongs to the hinterland of the lower Yangtze Delta that has a total area of 12,000 km2. From 1979 to 2000, long-term pumping of groundwater at Su-Xi-Chang has caused a rapid decline in groundwater table, resulting in large-scale land subsidence. In this paper, establishment of a GPS-based monitoring system for land subsidence using 30 years of data, is presented. The data were obtained through monitoring of 184 wells. Also analyzed herein is the relationship between the observed lowering of the groundwater table and subsidence. Monitoring data indicate that the depression cone of groundwater table and the occurrence of subsidence are basically identical in time and space. The generation of both features is attributed to excessive extraction of ground water in the region. Finally, countermeasures against subsidence are proposed.

Patterns of VOC and BTEX concentration in ambient air around industrial sources in Daegu, Korea.

Patterns of VOC and BTEX (Benzene, Toluene, Ethylvenzene, and Xylene) distribution at industrial emission sources, proximal residential areas of industrial estates, and ambient air were studied in Daegu, Korea. Daytime and night-time sampling was done at 12 sites and 9 emission sources to provide samples for analyses, using the TO-14 method. Measured BTEX component ratios B/T, T/EB, T/X and EB/X in ambient air were found to be 2.6 g, 11.3 g, 1.0 g and 1.2 g in the residential area; 2.2 g, 11.0 g, 1.0 g and 1.6 g in the commercial area; and 1.0 g, 14.9 g, 1.0 g and 1.3 g in the industrial area. The significant difference observed between the ratios for the residential and commercial areas implies that the two areas have different emission sources. This is also indicated by the significant differences observed between daytime and nighttime BTEX concentrations. Toluene and xylene were detected at very high concentrations, at the sampling sites. This pattern reflects the type of industrial processes and materials that are managed at the emission sources, as well as topographic/climatic factors that impact upon pollutant transport processes in the atmosphere. The BTEX distribution pattern in Daegu is observed to be similar to that of several Asian cities, particularly Hong Kong. These results are useful in the design of emission source control measures for VOCs and BTEX in Daegu.

Clay charge reversal effects on aqueous polymer sorption on lateritic soils.

The effects of charge reversal about the measured point of zero charge (pH(0) approximately 5.2) of untreated and treated Sete Lagoas lateritic soil of Brazil on aqueous polymer sorption was investigated. The polymers are anionic sodium carboxymethyl cellulose (CMCA), nonionic polyethylene oxide (PEO), and cationic polyacrylamide (PAM). They were prepared at aqueous concentrations and pH ranges of 0.1-2.0 g l(-1) and 2-9, respectively. Soil treatment involved the removal of iron oxides by treatment with dithionate-bicarbonate-citrate. Batch sorption test results show that the presence of iron oxides in lateritic soil tends to suppress sorption of CMCA (especially at pH=pH(0)) and PEO (for the whole pH range) but has uncertain effects on cationic PAM sorption. CMCA sorption on the untreated soil improves on either side of pH(0), in direct proportionality to solution concentration, except at pH<4.0, where disassociation of the polymer molecules may decrease sorption energy. Increase in the sorption of non-cationic polymers (CMCA and PEO) at pH>pH(0) is attributable to dispersion of clay, cation bridging and polymer molecular reconfiguration. For cationic PAM, electrostatic bonding to negatively charged soil particle surfaces accounts for the sorption increase. For treated soil samples, polymer sorption pattern is similar to those expected for the montmorillonitic clayey soils of temperate zones. These results indicate that the pH(0) of lateritic soils, within the regime that exists in the field, should be considered in assessing the potential effectiveness of polymer dust suppressants for tropical lateritic soils.

Soil desiccation rate integration into empirical dust emission models for polymer suppressant evaluation.

Dust constitutes an environmental and human health menace in many regions of the world. The rate of soil desiccation is a significant determinant of the availability of fine soil particles for entrainment in air as dust. Dust suppressants such as polymer solutions can reduce soil desiccation rate, thereby reducing dust emission factor. Herein, a dust emission estimation methodology that involves the integration of desiccation time curves to find the average desiccation rate is formulated. This is combined with soil characteristics, stressor (environmental and possibly vehicle) characteristics and liquid content in soil to estimate potential emission factors. Using this methodology, the dust suppression potential of aqueous polyethylene oxide (PEO) solution was investigated experimentally with Na-montmorillonite (Na-mmt) as the model dust-generating material. PEO with a molecular weight of 8 x 10(6) and at aqueous concentrations ranging from 0.5 to 10 g/L, was mixed with 10 g of Na-mmt (surface area=31.82+/-0.22 m2/g) and desiccated for 700 h in a specially designed chamber at 25 degrees C and 30% relative humidity. The results show that generally, aqueous PEO is superior to distilled water as a dust suppressant for Na-mmt at concentrations in the range of 0.5-2.0 g/L. The experimental data obtained are introduced into the formulated estimation methodology, and potential emissions of dust from PEO-admixed Na-mmt are determined.

Polyacrylamide sorption opportunity on interlayer and external pore surfaces of contaminant barrier clays.

Physico-chemical interactions among polymer molecules in aqueous solution and clay mineralogical/textural characteristics influence the sorption of polymer molecules on clay barrier minerals. Amendment of potentially unstable barrier clays with aqueous polymers can improve barrier material resistance to environmental stresses during service. In this research, the ability of molecular coils of polyacrylamide (PAM) to overlap in solution and to enter interlayer space in Na-montmorillonite (specific surface=31.82+/-0.22 m2 g(-1)) and kaolinite (specific surface=18+/-2 m2 g(-1)) were analyzed theoretically and experimentally, using solution viscosity measurements, and X-ray diffractometry. Experimental data on two theoretical indices: relative size ratio (RSR); and molecular availability (Ma) that are formulated to scale polymer molecular sorption on clay interlayer, indicate that the sorption of PAM A (Mw=4000000) and PAM B (Mw=7000000) does not produce any significant change in the d-spacing of both clay minerals. Although the negative Ma values of -3.51 g l(-1) for PAM A and -3.88 g l(-1) for PAM B indicate high levels of entanglement of polymer molecular coils in solution, sorption data confirm that the entangled coils are still able to sorb onto Na-montmorillonite highly and kaolinite to a lesser extent.

A quantitative methodology for indexing environmental sensitivity and pollution potential.

A methodology for rating the suitability of sites for the location of industrial facilities is formulated and applied to the case of a coal-fired power plant location. The methodology comprises two major interlinked components: the environmental plant location indexing component, which involves the identification, scaling and weighting of environmental sensitivity factors; and the impact analysis component, which involves the superimposition of the pollution generation impacts of an industrial facility on spatially gridded zones of various environmental sensitivities. For each rectangular areal unit defined by a square grid, the Unit Pollution Potential Index is determined by the severity and distribution of key environmental sensitivity factors and the coverage of superimposed pollutant effects as determined by contaminant fate and transport models. For any alternative site of a planned facility, the summation of the unit indices over the area of influence of the facility provides the quantitative Pollution Index, which can be used as a basis for comparison of alternative sites for planned facilities. For this paper, this methodology is applied to the hypothetical case of the siting of a coal-fired power plant in the northeastern region of the United States, in which three alternative sites are considered. The three sites: A, B and C yielded indices of 47.83, 47.91 and 47.6, respectively, indicating that site C is the most suitable for siting the power plant.