In the recent years, there were many sediment sites found contaminated in Taiwan. Whether removal or not does involve in the huge amount of cost and the uncertainty of environmental and health issues that need to be clarified. In order to make clear of sediment quality in Taiwan and further establish the quality guidelines, management strategy, and treatment technology evaluation, the Environmental Protection Administration (EPA) of the Executive Yuan offered the opportunity of the this project study. The results of this project include the establishments of the related regulation, sediment quality analysis and evaluation mechanism, health and ecological risk assessment, and contamination investigation mechanism. Under the framework of the current “Soil and Groundwater Protection Act” regarding sediments, the workgroup of this project has assisted EPA in the following: 1. Classification Management and Use Limitation Regulation of Sediment Quality Indicator, 2. Regulation in Sediment Quality Reporting Issued from Industry Competent Authorities of Sediment, 3. Assessment Method and Report Composition Guideline of Environmental Impact, Health Risk, and Technology and Economical Evaluation of Sediment, 4. Feasibility Evaluation and Approval Principle of Sediment Remediation, and 5. Composition Guideline of Sediment Remediation Proposal. Besides, it is necessary to have a guiding project in the early stage of the sediment regulation establishment served as a management basis; thus, a workforce allocation among different governmental departments regarding sediment quality assurance and control in the near, middle, and long run was studied to make sure a better use of administrative resources before the sediment quality control mechanism is up and running.
The sediment quality evaluation is the trigger of a series of the later-on management in sediment. The waters of the regulated sediments include rivers, lakes, reservoirs, and irrigation ditches. In order to know the current status of the sediment quality in the most important waters, this project took the chance to investigate the sediments in the Er-jen River, Da-du River, Chengcing Lake Reservoir, and Bao-shan Reservoir. Overall, a total 125 grab samples in the 2 investigations were analyzed. Among the 125 samples, only small amount of lake sediment samples were found concentrations over the lower limit of the nickel quality guideline and others were found normal in quality. With respect to river sediments, most samples from the San-ye River (tributary of the Er-jen River) were found high in heavy metals and over the respective upper limits. The downstream of the Er-jen River at the Sampling Station 11, 13, and 49 was found that some constituents were over the upper limits, possibly due to the convergence of San-ye River into the Er-jen River. Dioxins concentrations found in the San-ye River near the Yun-ning Bridge in the second sampling were over the upper limit. The San-ye River and the Er-jen River watershed were found illegal release of wastewater by the Tainan Environmental Protection Bureau. It is recommended to enhance the patrol so that the pollution source can be controlled. With respect to the tributary (Han River) of the upstream of the Da-du River, heavy metals of mercury and nickel were found over the upper limits in both samplings.
For the toxicity tests of some samples from the Er-jen River, the results showed that 14 samples (56%) were found Tier I (possibly harmful to aquatic life and human health). In the San-ye River, all results of toxicity tests showed Tier I level, indicating the most polluted region. Thus, sediment ecological risk and health risk assessments in the Er-jen River and the downstream of the San-ye River were conducted. Biological investigation targets were Arius maculates in the Er-jen River, although its economic values is not high but it serves as food. Sediment quality guideline constituents, such as copper, zinc, lead, chromium, cadmium, PCBs, and PAHs, were tested on the fish samples. Lead concentration was found high in Elops hawaiensis (0.968 mg/kg) in the first sampling attempt, with 4 samples found high in lead over the aquatic livestock limit (edible portion: 0.3 mg/kg). In the second sampling attempt, the dioxins concentration of Liza macrolepis was found 3.087 ng-TEQ/kg, close to the food consumption limit. The same sample also showed high concentration of PCBs of 245.5 µg/kg, the highest concentration of all fish samples (food consumption limit is 1,000 µg/kg wet weight). The reason why the fish in the second sampling attempt were found high in contaminant concentration could be that the fish had more fat (about 4 times as usual) in February (winter).
The contaminated sediments can be categorized into organic matters (PCBs and dioxins) and heavy metals (copper, zinc, cadmium, and lead). Because the real environments are of complexity, it is not easy to remove organic and inorganic contaminants of high affinity at the same time. With respect to choose the right methods for removing contaminated sediments in Taiwan, such as environmental dredging, which will help avoiding contaminants resuspended into aquatic environments before treatments. This project summarized the timing and the principles of using remediation actions, including in situ remediation, off-site remediation, environmental dredging and storage, physical, chemical, and biological treatments. A few international examples of sediment remediation were introduced, as well as the most current update of technology development regarding sediment remediation and investigation.