| 英文摘要 |
Ding-Mei Leather is located at #6-1, 70 alley, Mei-Shan road, Ren-Mei lane, Niaosong district, Kaohsiung (#1749 Da-Jiao-Tui section), with Mei-Shan road at the north, adjacent to Fengshan chun at the south, Xiang Foods and residential buildings at the west, and adjacent to Ren-li Leather at the east. Since 2009, Ding-Mei Leather has been investigated by the Environmental Protection Bureau (EPB), which revealed that the groundwater tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE), vinyl chloride (VC), chlorobenzene, and 1,1,2-trichloroethane have exceeded the control standards. Ding-Mei Leather and its surroundings (“the site” hereafter) are evidently polluted with chlorine in groundwater. However, the pollution boundary and distribution in depth are yet to be confirmed. Therefore, the Kaohsiung EPB (“EPB” hereafter) retained AECOM to conduct the “Kaohsiung Ren-Mei Area Industrial Land Groundwater Chlorinated Organic Pollution Investigation and Verification Project” (“the project” hereafter) to have a better knowledge of the site’s hydrogeological conditions and to delineate the pollution boundary.
To determine the pollution area, and as specified in the contract, techniques such as geophysical exploration, Membrane Interface Probe (MIP), soil sampling, piezometers and monitoring wells were used during the investigation. Also, considering the potential risks of local residents, monitoring of domestic wells were carried out both in the dry and wet seasons. The Project has completed step-by-step including geophysical exploration, geological drilling, MIP, soil sampling, piezometer and monitoring well groundwater investigations, continuous water level observations, domestic well photography, Health and Safety Assessment and Management, piezometer demolishing, soil and groundwater management system updates. All planned work have been carried out in a timely manner with quality.
During the initial stage, we narrowed down 17 suspected factories to conduct surveys. According to EMS classified information and interview results, the targeted factories have not used chlorinated substances or chlorinated reagents in its manufacturing process. The wet process in leather fabrication utilizes mainly dispersants (naphthalene sulfonic acid and formaldehyde condensate), surfactants (anionic, nonionic fatty alcohol surfactants, natural soap base, inorganic salt and water), and Chromium powder (Cr2O3). It is unclear whether the leather manufacturing industry has contributed in chlorinated pollution at the site. The currently closed-down Zhuo-Zhi Electronics and Hui-Mao Enterprise were located at the west of Ding-Mei Leather, which were involved in printing activites and electronic parts manufacturing, respectively, both of which are considered possible chlorine pollution sources to the site.
Geological investigations are the major highlighted tasks for this project. From geological exploration, the site is backfilled with yellowish-brown silty sand mixed with bricks, clay and coarse sand at 0~4.3m below grade; silty clay and fine sand, sandy silt mixed with little rotten wood at 4.3~6.8m below grade; coarse to fine sand mixed with little gravel at 6.8~13.7m below grade; silty clay mixed with fine sand and sandy silt at 13.7~20m below grade. It is estimated that the bottom of the first aquifer is at 12.35~13.70m below grade, which conforms to cross-examination of ground resistance, MIP-EC, and textures of soil samples. In terms of hydrology, from water level observations, it is determined that the groundwater level is approximately 3.30~5.07m below grade, flowing from east to west into C171S. From spectral analysis of observed water level fluctuations, and average day water level and pumping recovery strength, it is determined that monitoring wells MW1 and MW2 have noticeable impacts from pumping. Adjacent to these two wells are a residential apartment and agricultural land, which extract groundwater, as observed from the monitoring wells.
With respect to the pollution investigation, since the site is associated with Dense Non-aqueous Phase Liquid (DNAPL) typed pollution, denser than water and insoluble in water, with a tendency to migrate with gravity, hence screening methods such as geophysical techniques and MIP were applied during the initial stage to screen the suspected areas. Then according to the MIP results, the abnormal reaction distribution were indicated (from 45m to about 60m farthest southwest of Ding-Mei, and 50m to about 145m farthest southeast of Ding-Mei, the abnormal depths are concentrated at 6~12m below grade). The next step was soil and monitoring well sampling. The results from 17 soil samples revealed that soil sample S10 had a PCE concentration of 13mg/kg, exceeding the control standards at 10 mg/kg, with a depth of 7.5~8m, below the groundwater surface (4~5m below grade). Additional investigation indicates that the sampling point S16 (nearby well C171S) has been discovered at a deeper depth (8.5~9m below grade) containing PCE and 1,2-cDCE at 1.09 mg/kg and 0.27 mg/kg, respectively, both below the control standards; sampling point S17 (nearby well C172S) has been discovered at shallow depth (4~4.5m) containing PCE 0.26 mg/kg, and at a deeper depth (11.5~12m below grade) PCE at 0.99 mg/kg, both below the control standards. Besides the 3 aforementioned sampling points, all other sampling points were not identified with cVOCs. During the 3 groundwater investigations from monitoring wells conducted in 2014 March (dry), July and September (wet), and November (dry), the general items exceeding monitoring standards include ammonia nitrogen, iron, manganese, and total organic carbon. VOCs exceeding monitoring standards include wells C171S, C172S, MW7 and MW1 with PCE and TCE exceeding the control standards, which have also migrated to the bottom of the first aquifer. Among them, C171S located downstream has been identified with the highest in PCE and TCE concentration, with maximum values at 2.59 mg/L and 0.291 mg/L, respectively. Through analysis with comparison involving past groundwater records, Radon-222 concentration ratio, mole fraction, radar distribution, Stiff diagram, and additional soil investigations, C172S should be very close to the pollution source.
From photographs taken in domestic wells, it is determined that the well depth should be 21.4~74.3m below grade, with a screen starting at no less than 25m below grade. According to drilling results, the bottom of the first aquifer is approximately at 12.35~13.70m, which suggest that local domestic wells mainly extract water from the second aquifer. The monitoring results of domestic wells during the wet and dry seasons indicate that the general items exceeding the Drinking Water Quality Standards include total dissolved solids, nitrite nitrogen, ammonia nitrogen, total hardness, iron and manganese. Items exceeding monitoring standards include ammonia nitrogen, iron and manganese. Most VOCs were not identified, only Xiang-Long stainless steel (W22) was identified with TCE (0.0013 mg/L) and PCE (0.0014 mg/L), and Ti-Hsin Enterprise (W4) identified with a slight VC (0.00287 mg/L), all of which are below the groundwater monitoring standards.
In summary, current investigation results contribute to the development of a preliminary contaminated site conceptual model. Only soil sample S10 was identified with PCE exceeding the control standard at 13 mg/kg. The depth of pollution distribution is around 7.5~8m below grade; in terms of groundwater, it is estimated from the PCE pollution range in July and September in 2014 that the impacted groundwater depth is from 3.30~12.85m below grade, with a maximum pollution zone of 170m in length and 60m in width, with an approximate impacted area and volume of 8,275m2 and 27,658m3, respectively. Furthermore, the Health and Safety Risk Assessment results showed that the current domestic well water quality (relatively consistent with current conditions) scored an average of 3.28x10-8, compared to the total non-carcinogenic risk of 2.28x10-3, which is lower than the acceptable upper limit.
Judging from previous and current project results, and considering the great fluctuation in groundwater data, it is recommended to continue periodic monitoring, targeting the neighbouring areas of the monitoring wells that exceeded the control standards (C171S, C172S, MW7, MW1) for further understanding the pollution conditions. In addition, it is suggested to monitor at different depths to have a better understanding of the vertical phase pollution profile. Also, due to the pollution having reached the bottom of the first aquifer, PCE can possibly exist as pure phase, hence; it is advised that the second aquifer be investigated in the future. Since tracking down the pollution source can be a great challenge, from the polluter’s point of view for potential fines, we would still advise tracing the pollution source in the future to an appropriate extent for verification purposes. Starting from the factories within the nearby pollution sources, such as Ren-Li, a GC-MS overall scanning of wastewater influent and effluents may be conducted to confirm the presence of chlorinated organic substances, and also the soil and groundwater on site should be investigated.
From a follow-up management aspect, due to the fact that domestic wells used by local residents have scored lower than the acceptable upper limit in both the total carcinogenic and total non-carcinogenic risk values, future work should be focused on continuous monitoring of domestic wells and monitoring wells. When the domestic wells have exceeded concentrations in TCE or VC for Drinking Water Quality Standards, PCE or 1,2-cDCE exceeding the Type II groundwater monitoring standard (no Drinking Water Quality Standards available), it is recommended to conduct administrative controls to inform the residents of unsafe drinking water quality, to urge residents to discontinue drinking usage or emphasize that pre-treatment is required. If domestic wells continue to rise in contaminant concentrations, it is recommended that the EPB proactively take improvement actions for risk mitigations.
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