Actual Site Remediation - Assignment Example

?Actual Site Remediation Selected Approach Directly Heated Thermal Desorption (DHTD) is the remediation approach that has been selected as the most effective remediation methodology for the Former Allied Feeds Site, Sydney, Australia. DHTD comply with all the anticipated regulatory requirements related to the emissions and destruction capabilities. It offers an on-site closed loop process that does not need any further destruction of concentrated wastewater and oils. This remediation approach has been proven as a technology that is robust, flexible in range of feed materials, mature, and well supported by the experts all around the world. Thermal desorption system The basic process of DHTD system has been illustrated in the figure 1 given below. The soil is dried through heating it directly with the help of a rotary dryer made up from a high temperature alloy. The rotary dryer comprises of a natural-gas-fired burner that has the capability to heat the feed material up to a temperature of about 550oC or 1,022oF. The rate of heating the feed soil by using the rotary dryer is primarily based upon the moisture present in the soil, the size distribution of the soil particles, and the discharge temperature of the soil. The processed-gas is conveyed to the emission control system from the discharge hood that receives the gas from the rotary dryer. The emission control system consists of the dual cyclones, evaporative cooler, thermal oxidizer, bag house, quench, draft fans with dual induction, supply system of sodium hydroxide, acid gas scrubber, stack, and continuous emissions monitoring system. The natural-gas-fired burner of the rotary dryer is basically fitted with the thermal oxidizer that functions between the temperature ranges of 930oC to 1000oC. The gas is cooled down by spraying an air atomized water stream at the top portion of the evaporative cooler. The bag house conveys the gas to a quench chamber and a packed scrubber through the induced draft fans. Then, in order to remove acid gases from the gas, a pH controlled water stream passes again through the scrubber before the stack discharges the gas to the atmosphere. A double tipping valve, steam hood, pug-mill, steam duct, stacking conveyor and shuttle conveyor are used in the construction of a cooling and handling system for the treated soil. The double tipping valve is used to discharge the soil from the rotary dryer to the pug-mill. The pug-mill also, receives the combined dust streams, through a series of screw conveyors, from the bag house and the dual cyclones. Then the soil is cooled and moisturized through spraying water in to the pug-mill. Subsequently, the shuttle conveyor passes the cooled and moisturized soil discharged from the pug-mill to a stacking conveyor that, in turn, passes it to the stockpile of the treated soil. The steam-duct transfers the stream discharged from the pug-mill in to the evaporative cooler. The stockpiles of 500 ton each hold the treated soil until they are analyzed for complying with the treatment criteria. Figure 1: The Overview of the DHTD System (Troxler et al. 2010)2. Project Schedule The table 1 given below presents the major milestones related to the implementation and licensing of the thermal treatment plant project. Table 1: Project Schedule (Troxler et al. 2010)2. Commissioning Trials The testing sequence proposed for the selected approach at the site included a process comprising of two stages. In the first stage, the plant processes the non-contaminated soil in order to ascertain that all of the electrical, mechanical, and control equipments are working properly. Then, in the second stage, the plant processes the above-average concentration of the contaminated material which takes about 6 to 7 hours. EPA observed, in the preliminary review of the EIS, that the testing sequence should not include a one-step change from ‘0’ to above average concentration of the contaminant material. Demonstrated performance is required by EPA throughout the range of soil contamination. EPA also, suggests that the Orica HCB Geomelt commissioning sequence could act as a model for this approach. Geomelt is defined as a process that applies the electrical current of a very high voltage to the crucibles holding HCB waste so as to vitrify (turning to a glass-like substance) high concentration of the HCB waste. Directly Heated Thermal Desorption has been recognized as the traditional best technology for the remediation of the contaminated soil which, in relation to the former Allied Feeds site in Sydney, Australia, is not being configured or scaled up through any contemporary approach. The contaminant concentrations in the material to be remediated, except TPHs, have lower magnitude orders than the concentration being remediated through the ‘vitrification’ approach at its first remediation commissioning test of the contaminated materials. It has been found that the tradition commissioning of the DHTD plants comprises of runs with non-contaminated material, after which the full-concentration source testing of the contaminated material is performed. Furthermore, the dangerous waste combustors are allowed to carry out their source tests, in the initial 720 hours of their operation, with the help of using a waste stream of elevated concentration. Commencing of Earthworks The efficacy of the DHTD technology should be demonstrated by the Earthworks to the satisfaction of the community and the regulators and specifically, to show the ability of the plant to meet the Clean Air Regulations of the plants and the equipments. Since the EPA requested to increase the commissioning sequence, in view of the provided comparatively low overall concentrations of contaminants to be remediated, therefore, an extra step has been included to the previously proposed commissioning sequence. According to the EIS, all the contaminant concentrations found on the site were detected as averages and maximums. The material to be treated by means of the DHTD, during the conduct of the project, will be dried, blended and screened in order to acquire the concentrations of the contaminant which will cause air emissions that meet the regulations and the conditions of the license, after being treated through the DHTD. Due to homogenization and preconditioning and stockpile sampling, there is no chance that a quantity of the contaminated material would ever pass through the DHTD at even the present average concentrations found in the discrete sample points. Proof of Performance Testing The soil was preconditioned by Earth Tech to maximum twenty percent moisture content and fifty parts per billion (ng/g) dioxin content (Earth Tech, 2002)1. The thermal contractor guarantees that the DHTD employed at the former Allied Feeds site meets the Clean Air Regulations requirement, in relation to Plant and Equipment, which limits the dioxin emission to 0.1 ng/Nm3. Soil Remediation Validation The Remediation Action Plan (RAP) provided by the EIS describes that how the low resolution immunoassay could be utilized for the pre-remediation validation dioxin analysis of the contaminated soil. EPA has observed that the results acquired by applying immunoassay methods for showing dioxin concentrations in soil would not be acceptable to the agency without the verification of the efficacy of the approach. Thus, it was proposed by the Earth Tech that immunoassay or bioassay methods should be employed as a tool for decision making, field screening, and management of the materials1. However, initially these methods were not proposed to be used for the purpose of verifying that whether or not the material complies with certain criteria. Nevertheless, immunoassay and bioassay have been found to provide rapid screening results of remediated soil stockpiles, as for instance, in order to enable their disintegration or co-location that can be, otherwise, determined through NATA-accredited analytical results requiring several weeks for processing. Provided that considerable number of analyses will be executed over the on-site materials through the life of the project, there will be an opportunity to develop a database of analytical results from which the relationship may or may not be established between the low resolution laboratory methods and the high resolution laboratory methods. If good relationship among these methods has been determined then the Earth Tech Agency, EPA, and Site Auditor would emphasize over the potential to modify the analytical program in order to include the immunoassay or bioassay methods for validating the materials and for reducing the frequency of the high resolution analyses. Soil Validation and Thermal Treatment Standards The table 2 given below presents the final criteria for validation and thermal treatment of the project. Table 2: Final Criteria for Soil Validation and Thermal Treatment (Troxler et al. 2010)2. Description The technology of immunoassay is used to identify and quantify organic and inorganic compounds. Antibodies are used by the immunoassay, which have been created for binding with the target compound or group of compounds. The immunoassay technology has been extensively employed in the environmental field for field analysis since the immunoassay kits are comparatively faster and simpler to use and the antibodies can be greatly explicit to the target compound or class of compounds. Concentrations of analytical compounds are detected by employing a sensitive colorimetric reaction. The investigation of the presence of the target analytical compound is done by comparing the color formed from a sample of unknown concentration with the color developed from the sample that contains the analytical compound at a certain concentration. The intensity of color in the sample of the analytical compound determines the concentration of that analytical compound. The naked eye can also roughly determine the concentration whereas the photometer or spectrophotometer can be used as well for determining the concentration more accurately. Performance Testing Results The state Department of Environment, Climate Change and Water issued the license for this project to ensure that a PoP test is executed at the start of the project to illustrate that the soil treatment standards and stack emission standards are fully met. According to the initial preliminary stack testing, all stack emission results were found to fulfill the regulatory criteria. The soil stacks were approved on the basis of these preliminary tests and then the interim thermal treatment operations were performed whereas the numerous operating issues of the plant were being fixed. During the performance test period of the plant, the following key modifications were made to it: 1. The insulation was fitted to the cyclones in order to increase the treatment temperature of the cyclone fines, resulting in to a minimal residence time being spent in the rotary dryer; 2. The bag house was refurbished; 3. The rotary dryer discharge plenum was modified so as to raise fines retention; and 4. The pug-mill was modified as well. Finally, in January 2007, the PoP test was completed that lead to the beginning of commercial scale treatment operations. Besides the PoP test, the license also compelled the execution of monthly stack gas compliance testing. Initially, the monthly stack testing required all emission parameters to be included, however, later the monthly testing only required to include dioxins/furans and particulates whereas quarterly testing was introduced to test all parameters. The table 3 given below presents the summary of the stack test results for PoP test and for monthly compliance tests. Table 3: Compliance Test Stack Emission Results (Troxler et al. 2010)2. Effectiveness of the Actual Site Remediation There are various benefits of employing the immunoassay approach as a management tool in the field, instead of using the formal analysis for this purpose in a fixed laboratory, which involves portability, speed, convenience of use and comparatively, lower cost of each sample. Immunoassay approaches are in the process of being validated or approved from the US EPA to be used for a number of contaminants. Table 4: US EPA Approved Immunoassay Approaches Method Number Method Name 4010 Screening for PCPs by Immunoassay 4015 2, 4-D in Water and Soil by Immunoassay 4020 PCBs in Soil by Immunoassay 4025 Dioxin in Water and Soil by Immunoassay 4030 RPH in Soil by Immunoassay 4035 Soil Screening for PAHs by Immunoassay 4040 Toxaphene in Soil by Immunoassay 4041 Chlordane in Soil by Immunoassay 4042 DDT in Soil by Immunoassay 4060 TCE in Soil by Immunoassay 4670 Triazine Herbicides as Atrazine by Immunoassay 4500 Mercury in Soil by Immunoassay (Earth Tech 2002)1. The time needed for preparing and analyzing the samples varies on the basis of the immunoassay kit being used. First, the soil samples must be exposed to extraction for the purpose of eliminating the target analytical compound into a solution. Approximately 5 minutes are required for each sample for the process of extraction that even includes the time required for weighing the sample, adding the extraction solvent to it, shaking the acquired solution, allowing it to settle, filtering the extract, and diluting the extract. The overall time required for this preparation could vary from some minutes to 2 hours or even more for each batch of 20 samples whereas the time needed for analyzing usually varies from 30 minutes to 2 hours. Since the kits and preparation times vary extensively, therefore, the throughput of the samples can also vary to a great extent. As no extraction is required for water samples, hence their throughput is greater than that for the soil samples. Following factors affect the actual throughput of the given sample (Earth Tech, 2002)1: • Experience and expertise of the operator. • Exact brand of immunoassay test kit. • Size of the batches of samples analyzed together. • Number of quality control samples analyzed with the investigative samples. • Number of dilutions needed, if a quantitative test kit is employed. It is possible to obtain as many as 30 or 50 samples each day for soils. The detection limits for immunoassay approaches can be sometimes compared with the detection limits for traditional analytical methods. The type and measure of quality control required are based on the type of the immunoassay test kit being used and on the data quality goals of the project. As for instance, data employed for directing excavation would need considerable lesser quality control measure as compared to analyses validating that the treatment methods have achieved the established action levels. Table 4: Indicative Hierarchy of Remediation Approaches used for Mixed Organic and Inorganic Contaminated Compounds. Organic Concentration Inorganic Concentration Treatment Methodology Below threshold requiring DHTD treatment Below threshold requiring treatment No action Above threshold requiring DHTD treatment Below threshold requiring treatment DHTD treatment Above threshold requiring DHTD treatment Above threshold requiring treatment, including mercury DHTD treatment and periodic collection and stabilization of loag house dust. Limit feed rate into DHTD to control mercury emission. Above threshold requiring DHTD treatment Above threshold requiring treatment, no mercury DHTD treatment and periodic collection and stabilization of loag house dust. (Earth Tech 2002)1. The table 3 given above summarizes the soil sampling gathered from the former allied feeds site, 4Sydney, Australia by the Earth Tech Engineering. The information presented in this table indicates some areas where there are hot spots that include multiple contaminants. More soil samples are gathered with the progress of validation and excavation operations along the site. References: 1. Earth Tech (2002) Supplementary Report: Remediation of the Former Allied Feeds Site, Rhodes Peninsula. Australia: ERM Pty Ltd. 2. Troxler, L.R., Hunt, W.J., Taylor, J. and Mc Niven, C (2010) ‘Thermal Desorption Treatment of Dioxin-Contaminated Soil at the Former Allied Feeds Site, Sydney, Australia’, Environmental Engineering Science, Volume 27, Number 7. Read More