- 期刊
永康地下水含氯污染場址精確整治案例介紹
Surgical Remediation of the Chlorinated Hydrocarbons-Contaminated Groundwater: A Case Study of Yong-Kang
摘要
含氯有機物為國內地下水污染場址中常見之污染物，現地生物復育為應用最多之整治工法，也是國內整治業者熟悉之成熟工法，但仍有不少場址因場址污染及水文地質特性，面臨整治成效不如預期之困境。行政院環境保護署首次辦理國內地下水含氯污染場址之改善示範計畫，藉由採取精確整治之策略，應用包含對場址污染分布、水文地質、生物地質化學等特性高解析之智慧型表徵調查，以及採double-packer injection（DPI），將藥劑精確灌注至需改善地層，再由跨孔式地電阻評估藥劑傳輸，回饋至下階段之灌注設計，依多元成效評估結果調整整治作為等方式，於永康地下水污染場址進行污染改善。本文中以其中之B區控制場址地號改善經驗為案例說明，該改善區於3.5年之計畫期程中已達到各項含氯污染物濃度低於管制標準之目標，比國內已解除列管含氯場址之平均5年期程為短，呈現出精確整治之效益。
並列摘要
1. Introduction: Chlorinated organics are common pollutants in domestic groundwater contamination sites, and insitu bioremediation is the most common approach for remediation of these sites. In-situ bioremediation is a well-established remediation technique for domestic contaminated sites. However, in many sites the remediation effect is not as good as expected due to site pollution, hydrogeological characteristics, inadequate site investigation leading to imprecise injection plans, and a lack of appropriate injection methods to deliver remediation agents to the zone requiring remediation. The Environmental Protection Administration (EPA) of the Executive Yuan carried out the first demonstration project for the remediation of domestic groundwater sites contaminated with chlorinated organics. The wide range of applications of surgical remediation (SR) strategies include the high-resolution smart characterization methods (SCM) to investigate the distribution of contamination, hydrogeology, biogeochemistry, and other characteristics of the site; the double-packer injection (DPI) method to accurately deliver the agent into the formation that needs to be improved; and the cross-hole electrical resistivity tomography (CHERT) to evaluate the agent distribution for feedback for the next stage of injection design and adjustment of the remediation measures based on the results of multiple effectiveness evaluations of the Yong-Kang groundwater contamination site. This article presents the results of the SR and SCM that combine the hydrogeological and pollution characteristics and design of the multi-depth precision injection method with DPI, and the evaluation of the effectiveness of the remediation process with the pollutant molar concentration trend of the control site in Area B (Figure 1) of the Yong-Kang site. Furthermore, it explains how to adjust the remediation agent during the process to address the accumulation of degradation products. 2. Material and Methods: 2.1 Site Survey Method. The site characteristics were investigated using SCM that integrates the dynamic, real-time, high-solution soil and groundwater sampling and establishes a three-dimensional site conceptual model with a description of the hydrological stratigraphic, water permeability, and pollution distribution results. The site investigation methods (Figure 4) include sorting the data investigated over the years, rapid pollution detection of existing wells, ground-penetrating radar detection, earth electric resistance detection, simple well setup and sampling analysis, conducting fresh effectiveness evaluation of wells, geophysical well setup, and geophysical and hydrological tests. 2.2 Remediation Method. In-situ bioremediation is used as the main remediation method because the primary contaminant is tetrachloroethylene (PCE), and the 2014 field pilot test planned in the study area has shown that the anaerobic biological remediation method rapidly degrades high-chlorinated pollutants. DPI was used as the remediation agent injection method, which was introduced from the grouting technology for foundation improvement. During the DPI process, the injection pressure was adjusted to maintain the designed stable injection flow and the pressure/flow relationship, and the injection continued until the design dose was completed. 2.3 Remediation Agent Distribution Detection Method. The flow distribution of the remediation agent in the study area was evaluated using the CHERT time series. The logic of the CHERT electrode configuration was divided into three concepts: hole-to-hole, surface-to-hole, and three-dimensional hole-to-hole electrode configurations. The complexity of the data collected complicated the mathematical theories and analysis methods, but the analytical results provided a more representative scan profile that shows the detailed distribution of the two-dimensional or three-dimensional remediation agent at different time points to evaluate the overall injection effect. 3. Results and Discussion: 3.1 High-Solution Site Investigation. The results of the SCM investigation showed that if only eight monitoring wells were used, the area where PCE exceeded the control standard was 364 m^2 (Figure 6). However, when the data of existing wells and simple wells were added, the area where PCE exceeded the control standard was only about 177 m^2 (Figure 7), which is 48.6% of 364 m^2. If only the remediation expenses are considered, 51.4% of the cost can be saved, implying that the cost of high-resolution investigation can be recovered from the reduction in remediation expenses. 3.2 Pollution Remediation. Based on the integrated high-resolution pollution and hydrogeological SCM results, the SR design was selected to carry out multi-depth injection planning and use appropriate injection methods to deliver the remediation agent at the formation of the planned depth (Figure 10). The CHERT results show that according to the injection plan of the DPI design (Figures 13 and 14), the remediation agent was successfully delivered to designed depths (Figures 15 and 17). Moreover, the CHERT detection reflects the relative quantity of the injected remediation agent and the depth change of the formation structure. Therefore, the CHERT detection result can be used as the distribution evaluation of the remediation agent injection and as a reference for the next stage of injection design adjustments. The types of concentration variations in monitoring wells during the remediation varied (Figures 18- 21) with the locations of the wells, which included the hot spots, high concentration regions, or upstream of the contamination plume. Evaluation of the remediation effect on each location can be discussed in more detail based on the type of pollutant concentration variations in each well combined with the pollution nature of the well location and the injection design status, and effective adjustments such as the transfer of anaerobic bioremediation to biogeochemical transformation for the region near well B-MW4 can be made. 3.3 Benefits of SR. Under the concept of SR, the remediation period to reduce the pollutant concentrations below the restriction levels is 3.5 years, which is shorter than the average of 5 years for the chlorinated organics in domestic groundwater contaminated sites. Therefore, this project used SR methods to obtain good results in terms of cost and schedule benefits. 4. Conclusions: Pollution investigation should be regarded as a necessary investment cost of remediation work that is recoverable as it improves the remediation efficiency and reduces remediation expenses. The pollution distribution area should be accurately identified and pollution investigations need to be conducted at multiple depths to establish an accurate three-dimensional site conceptual model that combines pollution and hydrogeological conditions from the survey results for accurate remediation planning. Using DPI injection to deliver remediation agent precisely and CHERT detection to dynamically adjust the injection design can enhance the remediation effect. Therefore, an SR approach shortens the remediation period and reduces overall remediation expenses. The effectiveness evaluation of pollutant molar concentration variations provides more information about the remediation process; however, its use for domestic groundwater contaminated sites needs to be promoted.