Designing soil contamination monitoring network in petroleum refineries by XGBoost weighting and geostatistical facility allocation methods.

Petroleum refineries are deemed strategic industrial sectors that can release toxic materials to the environment and cause potential hazards. In this regard, designing and installation of soil contamination monitoring networks at petroleum refineries is a necessity. In this research, we designed an optimal monitoring network with maximum coverage and minimum number of monitoring boreholes. The main regarded parameters are the groundwater contamination history, the location of effective structures, the location of flare stacks and the soil texture. In addition, the soil contamination was calculated based on previous contamination of the soil at the sampling points by the Entropy Weighting Model. It was employed with other parameters to estimate the soil contamination across the site. The Machine Learning method of XGBoost was implemented for estimating and assigning priority for every point of the site. To achieve the optimal network in the optimization program, four parameters were regarded including (a) the optimal value of the optimization program's objective function, (b) the number of Advance Zero-half cuts of the Cut Generation algorithm, (c) the consumed time, and (d) the optimal boreholes number of the network corresponding with different effective contamination detection radius. The network was designed by generalized Maximal Covering Location Problem and for optimizing it, the advantages of Mixed-Integer Linear Programming method were used. To evaluate the applicability of the method, it has been developed and implemented in a refinery in the south of Iran. 92.84% of XGBoost estimation accuracy, the optimal number of 113 and the effective contamination detection radius of 160 m were obtained for boreholes of the network. To investigate the efficiency of the model, a new Regret function has been defined. Furthermore, sensitivity analysis of the parameters and feature importance analysis of XGBoost both showed that the main parameter of the model was the location of effective structures.

Investigation of long-term hazards of chemical weapon agents in the environment of Sardasht area, Iran.

The present study aimed to investigate the persistence and existence of chemical warfare agents (CWAs) and related dissipation products in the environment of Sardasht area, Iran. Three types of environmental samples including water, soil, and native local plant materials were collected and analyzed. Gas chromatography-mass spectrometry in the electron impact ionization mode has been developed for the separation, screening, identification, and qualification of chemicals after the sample preparation methods. The initial results revealed that no trace of related compounds or CWAs was detected in the soil and water samples. However, trace amounts of some degradation products of blistering agents like mustard gas (HD) and lewisite were found in a tree wood from a house subjected to chemical attack as well as in barley samples (a mixture of leaves and root) collected from an agricultural field in the area indicating chronic low exposure to the environment and people. In order to validate the applied extraction procedures, ethylene glycol was spiked to some of the samples including groundwater, surface soil, grape, and alfalfa plants. All the recoveries were in the range of 83.6-107.4% with the relative standard deviations varying from 4.9% to 12.4% (n = 3) successfully.

Combination of zeolite barrier and bio sparging techniques to enhance efficiency of organic hydrocarbon remediation in a model of shallow groundwater.

Adsorption and bioremediation are effective processes for remediation of benzene, toluene, and ethylbenzene (BTE) through Permeable Reactive Barriers (PRBs). A few researches focus on adsorption of natural zeolite because of its hydrophilic property. On the other hand, PRBs need to be replaced by fresh materials after a while when all the possible absorption positions were filled up. We tried to find a way to increase the efficiency of PRB, elongation of its replacement period and of course decreasing the cost of remediation. Equipping of PRB with microbial degradation system was the idea. The present study describes the performances of natural Clinoptilolite-Heulandite Zeolite (CH-Z) and three new strains (safe and low-cost media) utilized in a PRB for removing BTE from contaminated shallow groundwater. First, batch tests were conducted to recognize the optimal removal conditions for utilization of C-HZ and strains to remediate BTE compounds. Then, an aerobic PRB system filled with a natural zeolite was designed and investigated in a continuous flow sand-tank model to assess the efficiency of combined PRBs (zeolite + biosparging), for BTE-contaminated groundwater. Batch experiments showed that the BTE removal of zeolite was 89%, as well as, a consortium of three bacterial strains, Variovorax sp. OT16, Pseudomonas balearica OT17, and Ornithinibacillus sp. OT18 efficiently removed the BTE mixture. The process of BTE removal in the PRB under continuous-flow condition was divided into three phases: Phase I, in which the barrier was made of the only zeolite, and in Phases II and III the reactor was fed by microorganisms. This experiment revealed that in Phases I, the concentrations of BTE decrease (92%) due to zeolite adsorption. In Phase II and III, the degradation process became the principal removal mechanism (68% and 81%, respectively). Consequently, this research showed high ability of C-HZ in the BTE treatment, and a combination of Natural Zeolite, with a biological degradation system (CH-Z -PRB) improves the efficiency of BTE remediation. However, the slow biodegradation rates and the continuous injection of BTE in the model confirmed that longer time was needed for the PRB to function optimally. Finally, the combined method of CH-Z- BIO PRB showed the great potential in the restriction of the BTE migration that can be used at the field-scale after up-scaling.

Remediation of BTEX plume in a continuous flow model using zeolite-PRB.

Adsorption is a well-known phenomenon that causes the remediation of BTEX (Benzene, Toluene, Ethylbenzene, and Xylene). Zeolite is typically useful for the removal of BTEX from groundwater. In this study, the migration of the BTEX plume was investigated in a bench-scale tank model as a shallow aquifer. The objective of this research was to analyze the performance of a natural zeolite in-situ PRB remediation technique. Natural zeolite was applied as a physical permeable reactive barrier. In the first part of the experiment, 40 ml of BTEX as a contaminant was injected at the injection point (BI) into the sand tank. Samples were taken periodically via 14 boreholes for BTEX test for 23 days and analyzed using a GC-FID instrument. The results indicated high removal rates of BTEX by passing through the zeolite barrier. Zeolite barrier reduced the BTEX concentration up to 90% of the initial value. However, the barrier efficiency started to decrease after 132 h since pollution injection reached a minimum amount (%53 of the initial value) due to occupying the free space and grain pore where BTEX was adsorbed onto the surface of zeolite, thereby decreasing the barrier efficiency.

Hydrogeological Studies to Identify the Trend of Concealed Section of the North Tabriz Fault (Iran).

The North Tabriz Fault (NTF) is the predominant regional-scale tectonic structure in the northwest of Iran. In the east side of the city of Tabriz, a portion of the fault trend has been completely concealed by recent sediments and urbanization. In this paper, some hydrogeological methods are used to locate the concealed sector. As is clear from the pumping tests results, despite the fact that the northern observation wells were closer to the pumping wells than the southern ones, they have not been affected by pumping. Conversely, all southern wells were affected by pumping and displayed decline of the water table. In addition, obvious differences in groundwater levels combined with clear differences in groundwater quality within a short distance across the probable fault trend are sufficient reasons for the presence of the fault that behaves as a barrier to groundwater lateral flows. Significant change in the elevation of the bedrock base of the aquifer over less than 200 m suggests that the fault has near vertical dip. These results indicate that the inferred trend of the NTF closely conforms to its actual trend. Therefore, the hydrogeological studies can be complementary tools to determine the position and trend of concealed faults.