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1.
Predictive nutrient criteria method, combined with expert elicitation and structural equation model (SEM), was proposed in this study for establishing lake nutrient standard in Chinese lakes (Yungui Plateau ecoregion and Eastern Plain ecoregion). Expert elicitation was involved to quantify the probability of attainment of the designated-use (drinking water source) based on monitoring data. The experts scoring results were introduced to SEM to assess predictive relationships between candidate standard variables and the designated-use attainment. In Yungui ecoregion, the standardized effects of chlorophyll-a (Chl-a), chemical oxygen demand and total phosphorus (TP) on designated-use attainment were ?0.41, ?0.14, and ?0.43, respectively. These result demonstrated that the two most predictive indicators for designated-use attainment were TP and Chl-a. In Eastern ecoregion, the standardized effects of TP, total nitrogen (TN), dissolved oxygen and water temperature (T) on designated-use attainment were 0.77, ?0.12, 0.13 and ?0.02, respectively. The most predictive indicator was TP. The model was further used for estimating the designated-use attainment associated with various levels of candidate standards. TP, TN, Chl-a and Secchi depth (SD) were selected as standard indicators in Yungui ecoregion. TP, TN, and Chl-a were selected in Eastern ecoregion. In order to achieve the 85 % designated-use attainment, standard values of TP, TN, Chl-a and SD in Yungui ecoregion would be 0.02 mg/L, 0.2 mg/L, 1.4 μg/L, and 0.581 m; and standards of TP, TN, and Chl-a in Eastern ecoregion would be 0.039 mg/L, 0.95 mg/L, and 1.75 μg/L, respectively. Finally, the differences between standards in these two ecoregions were also analyzed.  相似文献   

2.
Relative density is an important state parameter that influences the soil behavior. Preparation of sand specimens with uniform density is critical during large-scale laboratory testing in geotechnical engineering. In this study, the details of a stationary air pluviation device used to prepare uniform sand specimens in a large-size test chamber with dimensions equal to 900 mm × 900 mm × 1000 mm (in length, width, and depth) are provided. The proposed device is found to be simple to construct due to presence of only two diffuser sieves with an ability to produce uniform sand beds in a reasonably quick time. Prior to construction of full-scale pluviation device, a scaled-down model of the device with plan dimensions equal to 300 mm × 300 mm is fabricated to perform calibration studies. The range of densities of two gradations of Indian Standard sand (IS Grade II and IS Grade III) obtained using this device for various heights of fall of sand particles and passing through different opening sizes are provided. Relative density in the range of 53–99 % and 74–99 % is achieved for IS Grade II and III sands, respectively. The spatial uniformity in densities is also assessed, and the coefficient of variation (COV) in the density is found to be less than about 7 %. In addition to pluviation method, uniform sand beds are also prepared using pneumatically-operated vibratory method. The target relative density of sand bed is achieved by adjusting the pressure of compressed air inside the vibrator, and the maximum relative density of IS Grade II and Grade III sands from vibratory method is found to be higher than that from pluviation method for the range of pressures chosen in the study.  相似文献   

3.
Andrej Gosar 《Natural Hazards》2012,62(3):1059-1079
Site effects studies using microtremor free-field measurements were performed recently in five Slovenian towns characterized by increased seismic hazard to determine resonance frequency of soft sediments. In this study, microtremor investigations were extended to the measurements inside buildings to determine their fundamental frequencies and to assess the possible occurrence of soil-structure resonance. Measurements were performed in 66 buildings, and by spectral analysis, it was possible to determine reliably fundamental frequencies (longitudinal and transverse) for 58 buildings. Residential masonry houses with two or three floors prevail, but some buildings of up to six-floor height were also surveyed. Microtremor measurements have proved to be an effective tool for assessment of fundamental frequencies of buildings. Such experimental approach is very valuable, as analytical seismic evaluation of an existing building is usually very difficult. Statistical analysis of the fundamental frequency versus number of floors (height) was performed to generalize identification of potential soil-structure resonance. The difference in average fundamental frequency is very clear between buildings with two and three floors. The average value of both horizontal components for two-floor buildings is 9.11?±?1.94?Hz, and for three-floor buildings, 7.03?±?1.46?Hz. On the other hand, the difference in frequencies between three- and four-floor buildings (average for later is 6.52?±?0.80?Hz) is very small. The average fundamental frequencies for five- and six-floor buildings are lower, 4.62?±?0.64?Hz and 5.30?±?0.70?Hz, respectively, with no statistically significant difference between both types. Most Slovenian towns are located in shallow sedimentary basins where the free-field soft covers frequencies are in the range 2?C20?Hz. On the other hand, houses with two and three floors represent the large majority of the building stock. To assess the possible occurrence of soil-structure resonance in general, an average fundamental frequency?±?one standard deviation interval is obtained for these two building heights, which gives the range 5.6?C11.1?Hz. The free-field data show that this frequency range occupies from 22?% of the surveyed area in the Kobarid basin to up to 59?% in the Bovec basin and is in between for other three basins. This leads to the conclusion that the possible occurrence of soil-structure resonance is a serious issue for typical geological situations, in which towns are located.  相似文献   

4.
Surface subsidence can cause many environmental problems and hazards (including loss of land area and damage to buildings), and such hazards are particularly serious in coal mining districts. Injecting grout into the bed separation in the overburden has been proposed as an effective control measure against surface subsidence during longwall mining. However, no field trials of this technique have been implemented in mines under villages in China, and thus, its ability to control subsidence in such areas has yet to be demonstrated. In this study, field trials using this technique were carried out during longwall mining under villages in the Liudian coal mine, China. The maximum surface subsidence observed after the extraction was only 0.298 m, which accounts for 10 % of the mining height and is 79 % less than the predicted subsidence. Moreover, no damage occurred to the village buildings either during or after extraction and these buildings remain stable. Thus, this study represents the first successful attempt to control surface subsidence under villages in China using grout injection during longwall mining.  相似文献   

5.
In conventional seismic hazard analysis, uniform distribution over area and magnitude range is assumed for the evaluation of source seismicity which is not able to capture peculiar characteristic of near-fault ground motion well. For near-field hazard analysis, two important factors need to be considered: (1) rupture directivity effects and (2) occurrence of scenario characteristic ruptures in the nearby sources. This study proposed a simple framework to consider these two effects by modifying the predictions from the conventional ground motion model based on pulse occurrence probability and adjustment of the magnitude frequency distribution to account for the rupture characteristic of the fault. The results of proposed approach are compared with those of deterministic and probabilistic seismic hazard analyses. The results indicate that characteristic earthquake and directivity consideration both have significant effects on seismic hazard analysis estimates. The implemented approach leads to results close to deterministic seismic hazard analysis in the short period ranges (T < 1.0 s) and follows probabilistic seismic hazard analysis results in the long period ranges (T > 1.0 s). Finally, seismic hazard maps based on the proposed method could be developed and compared with other methods.  相似文献   

6.
Iranian strong motion records as well as detailed conditions of their instrument sites and the characteristics of their causative seismic sources are compiled and processed. The dataset consists of 2286 three-component records from 461 Iranian earthquakes with at least two high-quality records having moment magnitude from 3.9 to 7.3. These records are about 20% of the Iranian database and are suitable for seismic hazard analysis and engineering applications. Perhaps for the first time in the literature, the distance to the surface projection of the fault is reported for a great number of records corresponding to earthquakes with M > 6.0. The raw accelerations are processed using the wavelet de-noising method. Having corrected and filtered these raw data, the pseudospectral accelerations are calculated for each of the three components of time series, separately. In addition to the ground motion parameters, a large and comprehensive list of metadata characterizing the recording conditions of each record is also developed. Moreover, careful revision of the characteristics of the earthquakes such as location, magnitude, style of faulting and fault rupture plane geometry, if available, is carried out using the best available information in a scientifically sound manner. Finally, we also focus on special ground motion records including records with peak ground acceleration (PGA) >300 cm/s2 and distances less than 30 km. These are “exceptional” records in the Iranian dataset and include less than 2% of the selected dataset.  相似文献   

7.
Community-scale estimates of building damage and economic loss are modeled for Seaside, Oregon, for Cascadia subduction zone events ranging from 8.7 to 9.3 MW with corresponding slip distances of 3–25 m considering only the effects of the tsunami. Numerical simulations are obtained from the National Oceanic and Atmospheric Administration’s method of splitting tsunami model which includes a source model, subsidence, and calculations of the propagation and inundation flow characteristics. The damage estimates are based on fragility curves from the literature which relate flow depth with probability of damage for two different structural materials of buildings. Calculations are performed at the parcel level for the inundation hazard without including damage caused by the earthquake itself. Calculations show that the severity of building damage in Seaside is sensitive to the magnitude of the event or degree of slip because the majority of the city is located on low-lying coastal land within the estimated inundation zone. For the events modeled, the percentage of building within the inundation zone ranges from 9 to 88 %, with average direct economic losses ranging from $2 million to $1.2 billion.  相似文献   

8.
Qi  Wenhua  Su  Guiwu  Sun  Lei  Yang  Fan  Wu  Yang 《Natural Hazards》2016,86(1):107-139

This paper presents the development of an “Internet+” approach to mapping exposure and seismic vulnerability of buildings in a context of rapid socioeconomic growth. This approach is a combination of the following interdependent components: (1) extraction of footprint areas of a large number of buildings from high-resolution Google Earth images; (2) estimation of floor numbers of these buildings with an integrated use of high-resolution Google Earth images, Tencent/Baidu Street Views, crowdsourcing data, and associated building-relevant local knowledge; and (3) identification of structural types of these buildings by a combined use of crowdsourcing data and associated building-relevant local knowledge. The efficacy of this “Internet+” approach was demonstrated through an application in Tangshan, China. Field-based verification indicated that the overall mean absolute percentage error of the proposed “Internet+” approach in assessing the total floor area of the addressed buildings was 4.64 %. The verification also showed that the overall consistency between the estimated structural types using the proposed approach and the actual structural types of the buildings with structural type uncertainties could reach 97.54 %, with a kappa coefficient of 0.94. Because of its good accuracy, noteworthy speed, substantial labor savings, negligible cost and distinctive capability in covering large areas in near real time, this “Internet+” approach might have promising prospects in actual seismic loss risk reduction challenges.

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9.
In this study, a novel method that integrates C4.5 decision tree, weights-of-evidence and m-branch smoothing techniques was proposed for mineral prospectivity mapping. First, a weights-of-evidence model was used to rank the importance of each evidential map and determine the optimal buffer distance. Second, a classification technique that uses a C4.5 decision tree in data mining was used to construct a decision tree classifier for the grid dataset. Finally, an m-branch smoothing technique was used as a predictor, which transformed the decision tree into a probability evaluation tree. The method makes no conditional independence assumption and can be applied for class imbalanced datasets like those collected during mineral exploration for prospectivity mapping of an area. The traits of comprehensibility, accuracy and efficiency were derived from the C4.5 decision tree. In addition, a case study for iron prospectivity mapping was performed in the eastern Kunlun Mountains, China. Sixty-two Skarn iron deposits and eight evidential maps related to iron mineralization were studied. On the final map, areas of low, moderate and high potential for iron deposit occurrence covered areas of 71,491, 14,298, and 9,532 km2, respectively. For the goodness-of-fit test, 91.94 % of the total 62 iron deposits were within a high-potential area, 8.06 % were within a moderate-potential area and 0 % were within a low-potential area. For ten-fold cross-validation, 82.26 % were within a high-potential area, 14.52 % were within a moderate-potential area and 3.22 % were within a low-potential area. To evaluate the predictive accuracy, Receiver Operating Characteristic (ROC) curves and Area Under ROC Curve (AUC) were employed. The accuracy of the goodness-of-fit test reached 97.07 %, and the accuracy of the ten-fold cross-validation was 95.10 %. The majority of the iron deposits were within high-potential and moderate-potential areas, which covered a small proportion of the study area.  相似文献   

10.
Smectite clay has been proposed for embedding canisters with highly radioactive waste in deep repositories because of its isolating capacity. Montmorillonite-rich bentonite is a premier buffer candidate for many national organizations that are responsible for disposal of such waste. Experience from the use of drilling mud at large depths indicates that other smectite clay minerals are more stable chemically and saponite is one of them. The physical properties of smectitic mixed-layer minerals like Friedland clay are known to be less sensitive to high salt contents and such clay may also be a buffer candidate. Montmorillonite-rich MX-80 clay, Greek saponite with a minor amount of palygorskite, and Friedland clay were investigated in hydrothermal tests with dense samples confined in oedometers with 95 °C temperature at one end, which was made of copper, and 35 °C at the other, for 8 weeks. A 1 % CaCl2 solution was circulated through a filter at the cold end. At the end of the tests, the samples were sliced into three parts, which were tested with respect to expandability, hydraulic conductivity, and chemical composition. The tests showed that while the saponite was hardly changed at all and did not take up any copper, MX-80 underwent substantial changes in physical performance and adsorbed significant amounts of copper. The Friedland clay sample was intermediate in both respects.  相似文献   

11.
Impact of debris flow consists of two distinctive phases due to its physical composition. One is the dynamic impact from fluid phase, and the other is collision from the solid phase. At present, there is no effective way to differentiate these two phases of impact. An empirical mode decomposition (EMD)-based signal process method was proposed in this paper to extract fluid and solid impact force of debris flow from the mixed signal. Miniaturized flume tests have been carried out with 14 work conditions, and the impact signals were captured by a digital logger. From the experiment, frequencies of fluid phase and solid phase impact signals were identified in the range of 0.05–2 Hz and 300–600 Hz, respectively. The impact signals from solid and liquid phases were reconstructed using the proposed method. In addition, the impact force of fluid phase that measured directly from the flume tests and calculated from isolated signals showed good agreement and the average difference was about 10%. However, large deviation of solid phase impact was observed especially when this method was applied to the full-scale debris flow events and the difference ranged from 26.33 to 61.47%. This proposed method provided an alternative approach to study the debris flow impact force in terms of slurry and large particles separately.  相似文献   

12.

Large-scale impacts from natural disasters suffered by society encourage researchers and public agencies to develop methods to evaluate, mitigate, respond, and recover from these events. A key aspect for the calculation of the potential earthquake losses is to properly describe the characteristics and value of assets exposed to seismic hazard. This article describes a methodology to develop an exposure model at a census-block resolution for residential structures in Chile using statistical data. The methodology is based on three steps: (1) obtaining dwelling count, construction material and location from census data, (2) defining classification rules for dwellings associated with houses and apartment buildings, and (3) assigning structural typologies and replacement cost. The resulting exposure model consists of a database with the number of residential structures classified into 18 structural typologies at each census block and the associated replacement cost. A total of 4,259,804 residential structures were identified in the national exposure model. Overall, clay brick and concrete block masonry account for 53.5 % of the structures of the country followed by timber (33.7 %), reinforced concrete (8.1 %), and adobe (4.6 %). Also, a methodology using remote digital survey techniques is proposed and used to obtain local exposure models for the cities of Iquique, Rancagua, and Osorno. The results of the national exposure model are compared with the local exposure models. An important feature of the proposed methodologies is that the building stock is classified into structural typologies, which is a key aspect for conducting seismic risk assessment. The methodologies used to construct the national and local exposure models may be extrapolated to other countries by adjusting the classification rules. The exposure models that were constructed represent an important input for risk calculations, by improving the technical capabilities for seismic risk management of the country.

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13.
Groundwater is being used for drinking and irrigation purposes in the agricultural dominated Indian state of Punjab. Fifty-six groundwater samples were collected from Bathinda, a south-western district of Punjab, during the pre-monsoon (March 2010) and post-monsoon (October 2011) seasons. These samples were tested for major cations, anions and contaminants. Various classification systems were used to study the groundwater quality with respect to drinking as well as irrigation purposes. Total dissolved solids (TDS) and total hardness (TH) are generally used to determine the suitability of groundwater for drinking purpose. Considering TDS as a parameter, 54 and 57 % groundwater samples were found to be unsuitable for use during the pre- and post-monsoon seasons. A wide range of TH values were observed in the pre-monsoon and post-monsoon waters samples (mean 250 and 270 mgL?1). About 75 % of pre-monsoon and 79 % of post-monsoon samples exceeded the maximum permissible limit (MPL) of TH (150 mg L?1) proposed by WHO. In terms of contaminant ions, 40 % and 55 % of the pre- and post-monsoon water samples were unfit for drinking purposes w.r.t. fluoride (MPL 1.5 mg F L?1), 29 and 36 % were unfit w.r.t arsenic (MPL 10 μg L?1) and 33 and 45 % were unfit w.r.t nitrate (MPL 45 mg NO3 ? L?1), respectively. To determine the suitability of groundwater of Bathinda for irrigation purpose, three classification systems proposed by different research workers were used. The parameters electrical conductivity (EC), sodium adsorption ratio, and residual sodium carbonate (RSC) were calculated on the basis of chemical data. Considering EC and RSC together, 32 % samples collected during pre-monsoon season were fit, 19 % were marginal and 49 % were unfit for use. However, during post-monsoon, samples fit for irrigation decreased to 17 % and samples unfit for irrigation increased to 70 %. Increases in the percentage of unfit samples for irrigation after monsoon indicates addition of salts along with the rain water percolated into the groundwater. The other two classification systems, i.e. US Salinity diagram and Wilcox diagram also showed the similar results.  相似文献   

14.
Radon and its progenies have been ranked second of being responsible for lung cancer in humans. Hong Kong has four major groups of uranium-rich plutonic and volcanic rocks and is suffering from radon emanated therefrom. However, there is a lack of radon potential maps in Hong Kong to resolve the spatial distribution of radon-prone areas. A ten-point radon potential system was developed in Germany (2005) to predict radon potential using both the in situ geogenic and geographic parameters under hierarchical ranking. Primarily, the ten-point system requires the desk study of the geological environment of sampling sites, which has an advantage of saving resources and manpower in extensive radon potential mapping over the traditional soil radon concentration sampling method. This paper presents a trial of radon potential mapping in Hong Kong to further verify the system. Despite some slight departures, the system demonstrates an acceptable correlation with soil radon concentrations (R 2 = 0.62–0.66) from 768 samples of mainly intermediate radon potential. Hong Kong has a mean soil radon concentrations of 58.9 kBqm?3, while the radon potential from the ten-point system achieves an average of 4.93 out of 10 over the territory. The vicinity of fault zone showed high soil radon concentrations and potentials, which were conducive to uranium enrichment and rapid soil-gas diffusion near faults. High uranium-238 content in soil was found to cause high soil radon concentration with a large R 2, 0.84. The Jurassic granite and volcanic crystal tuff cover more than 85 % of the whole Hong Kong area, and they show relatively high radon concentrations (Geometric mean 83 and 49 kBqm?3, respectively) which are associated with their high uranium contents (Geometric mean 234 and 197 Bqkg?1, respectively). While indoor radon concentration is an important factor for radon risk assessment, this study has not considered the correlation between indoor radon concentration and radon potential. The reason is that almost all buildings in Hong Kong are high-rise buildings where indoor radon concentrations are governed only by the radium content in the building materials and the ventilation conditions.  相似文献   

15.
Effective evaluation, management and abstraction of groundwater resources of any aquifer require accurate and reliable estimates of its hydraulic parameters. This study, therefore, looks at the determination of hydraulic parameters of an unconfined aquifer using both analytical and numerical approaches. A long-duration pumping test data obtained from an unconfined aquifer system within the Tailan River basin in Xinjiang Autonomous Region in the northwest of China is used, in this study, to investigate the best method for estimating the parameters of the aquifer. The pumping test was conducted by pumping from a radial collector well and measuring the response in nine observation wells; all the wells used in the test were partially penetrating. Using two well-known tools, namely AquiferTest and MODFLOW, as an aid for the analytical and numerical approaches, respectively, the parameters of the aquifer were determined and their outputs compared. The estimated horizontal hydraulic conductivity, vertical hydraulic conductivity, and specific yield for the analytical approach are 38.1–50.30 m/day, 3.02–9.05 m/day and 0.204–0.339, respectively, while the corresponding numerical estimates are 20.50–35.24 m/day, 0.10–3.40 m/day, and 0.27–0.31, respectively. Comparing the two, the numerical estimates were found to be more representative of the aquifer in the study area since it simulated the groundwater flow conditions of the pumping test in the aquifer system better than the analytical solution.  相似文献   

16.
Employing the histogram matching approach, the sediment regime alteration of the upper Yangtze River was assessed and its possible causes and environmental influences were discussed. Daily sediment load and flow data from 1950 to 2008 were collected from Yichang hydrometric station. The annual sediment load series was segmented by heuristic segmentation algorithm in 1986 and 2003, and the multi-year mean values of the three phases were 5.28 × 108, 3.89 × 108 and 0.57 × 108 t, respectively. One change point was found by cross wavelet transform in 2003 when the cross wavelet power became insignificant, which indicates the interruption of the common annual cycle of the sediment load and flow series. The sediment regime from 1986 to 2002 was altered by a total of 41 % compared with the regime from 1950 to 1985. It may be mainly attributed to numerous dams constructed in the tributaries, the Gezhouba Dam constructed in the mainstream, and land use and land cover change, e.g., the increased grassland with a coverage density larger than 50 %. The sediment regime alteration after 2003, assessed to be a total of 83 %, may be mainly attributed to the Three Gorges Reservoir. It breaks the natural process of sediment transport, reduces sediment concentration and releases clear water to the downstream which may result in some environmental problems, e.g., limited nutrients availability, river bed erosion, benthic habitat destruction, etc. The assessment of sediment regime alteration may provide some references for the environmental management and conservation of the Yangtze River.  相似文献   

17.
Within the framework of the performance based earthquake engineering, site specific earthquake spectra for Van province has been obtained. It is noteworthy that, in probabilistic seismic hazard assessment, as a first stage data from geological studies and records from the instrumental period were compiled to make a seismic source characterization for the study region. The probabilistic seismic hazard curves were developed based on selected appropriate attenuation relationships, at rock sites, with a probability of exceedance 2, 10 and 50% in 50 yrs period. The obtained results are compared with the spectral responses proposed for seismic evaluation and retrofit of building structure in Turkish Earthquake Code (2007), section 7. The acceleration response spectrums obtained from probabilistic seismic hazard analysis are matched to adjust earthquake accelerograms recorded during the 2011 Van earthquakes by using SeismoMatch v2.0 software. The aim of this procedure is to obtain a set of reasonable earthquake input motions for the seismic evaluation of existing buildings.  相似文献   

18.
Leh and surrounding region of the Ladakh mountain range in the trans-Himalaya experienced multiple cloudbursts and associated flash floods during August 4–6, 2010. However, 12.8 mm/day rainfall recorded at the nearest meteorological station at Leh did not corroborate with the flood severity. For better understanding of this event, hydrological analysis and atmospheric modeling are carried out in tandem. Two small catchments (<3 km2) were studied along the stream continuum to assess the flood characteristics to identify the cloudburst impact zones. Peak flood discharges were estimated close to the head wall region and at the catchment outlet of the Leh town and the Sabu eastern tributary catchments. Storm runoff depth is estimated by developing a triangular hydrograph by using the known time base of the flood hydrograph. This triangular hydrographs have been transformed further into storm hydrographs to gain a better understanding of the storm duration by using the dimensionless hydrograph method at selected cross sections. Storm duration is estimated by using the relationship between time to peak and time of concentration of the catchment. The peak flood estimates ranged from 122(±35 %) m3/s for Leh town catchment (2.393 km2), 545(±35 %) m3/s for Sabu eastern tributary catchment (2.831 km2) to 1,070(±35 %) m3/sec for Sabu catchment (64.95 km2). To assess the atmospheric processes associated with this event, a triple nest simulation (27, 9 and 3 km) is performed using Advanced Research Weather Research and Forecasting (WRF) modeling system. The simulation does show the evolution of the event from August 4 to 6, 2010. Observation constraints, orographic responses, etc. make such analysis complex at such scale. Independent estimate by the atmospheric process model and the hydrological method shows the storm depth of 70 mm and 91.8(±35 %) mm, respectively, in catchment scale. Hydrological evaluation further refined the spatial and temporal extents of the cloudbursts in the respective catchments with an estimated storm depth of 209(±35 %) mm in 11.9 min and 320(±35 %) in 8.8 min occurring in an area of 0.842–1.601 km2, respectively. This study shows that the insight developed on the cloudburst phenomena by the atmospheric and the hydrological modeling is hugely constrained by the spatial and temporal scales of data used for the analysis. Apart from this, study also highlighted the regular occurrence of cloudburst events over this region in the recent past. Most of such events go unreported due to lack of monitoring mechanisms in the region and weaken our ability to understand these events in complete perspective.  相似文献   

19.
Three years after the oil spillage and pipeline explosion that claimed about 100 human lives at Ijegun Community of Lagos–Nigeria, a combination of carefully designed 2D Electrical Resistivity Profilling and Vertical Electrical Sounding methods was deployed to map and characterise the subsurface around the contaminated site. Data acquired were processed, forward modelled and tomographically inverted to obtain the multi-dimensional resistivity distribution of subsurface. The results of the study revealed high resistivity structures that indocate the presence of contaminant (oil plumes) of different sizes and shapes around the oil leakage site. These high resistivity structures are absent in the tomograms and resistivity-depth slices computed for Iyana—a linear settlement not affected by oil spillage. The five geo-electric layers and the resistivities delineated in the area are the top soil layer, 220–670 Ωm; clayey sand layer, 300–1072 Ωm; top sand layer, 120–328 Ωm; mudstone/shale layer, 25–116 Ωm and the bottom sand layer, 15–69 Ωm. The base of the first four geo-electric layers corresponds to 3.9, 8.4, 27.2 and 34.6 m respectively. The two groundwater aquifers delineated correspond to the third and fifth geo-electric layers. The top aquifer has been infiltrated by oil plumes. The depth penetrated by the oil plume decreases from 32 m to about 24 m across the survey profiles from the two ends. It was concluded that the contaminant plumes from the oil spillage are yet to be completely degraded as at the time of the study. It is recommended that the contaminated site be remediated to remove or reduce the contaminant oil in the subsurface.  相似文献   

20.
Animal skin, a proteinaceous material containing about 60–65 % moisture, is an ideal substrate for the growth of microorganisms, if not preserved properly. Conventionally, large quantities of sodium chloride are used for skin preservation. De-salting and soaking carried out during processing of the skin generates serious environmental constraints. In view of this, low-salt skin preservation with de-oiled neem cake is attempted. To ensure the antimicrobial properties of de-oiled neem cake, aqueous and solvent extracts of the cake were studied against bacteria and fungi which were isolated from raw skin. The antimicrobial assay was performed using the well diffusion method for aqueous, methanol and hexane extract of de-oiled neem cake, which showed maximum zone of clearance for aqueous and methanolic extract against the isolated bacteria and fungi, respectively, present in raw skin. The percentage of inhibition study reveals that the methanolic extract showed 100 % inhibition against many organisms and the water extract against some organisms. The raw skin was cured using de-oiled neem cake with reduced amount of salt and left for a period of 21 days. The skins were checked periodically for microbial growth as per the conventional methods. Finally, the low-salt preserved skins were processed into chrome-tanned leathers and their strength properties were compared with leathers which were preserved by the conventional method. The results suggest that de-oiled neem cake along with minimal salt has adequate curing efficiency on raw skin and if this system is implemented, pollution caused due to sodium chloride would be significantly minimized.  相似文献   

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