Abstract
2016 Project of Contamination Confirmation and Monitoring Plan for Areas of Likely-contaminated Groundwater in Tainan (hereinafter “the project”) had tasks including the investigation into the groundwater contamination of organochlorides and fluoride in Xinshi Industrial Park, the investigation into the groundwater contamination of organochlorides in Baoan Industrial Park, Arsenic groundwater contamination in Baoan Industrial Park, groundwater management at restricted farmlands, and groundwater management at illegal dump-sites.
1. The investigation into the groundwater contamination of organochlorides and fluoride in Xinshi Industrial Park
In the project, before soil sampling and well installation, NGST (NAPL Ground Scanning Technique) and Ground Electrical Resistivity Survey (GERS) were applied to locate the likely-contaminated areas. In this case, MOSPEC Semiconductor (hereinafter MOSPEC) was recognised as one of those areas and subject to Membrane Interface Probe (MIP) following. MIP detected the signal response of residues in soil and groundwater. It was revealed that the MOSPEC subsurface 6.5~8.0 m below ground level (bgl) gave indicative peak signals which led to further soil sampling and well installation.
The investigation adopted the soil sampling at three spots (S01, S02, S03), S02 of which had a sample set containing Cis-1,2-dichloroethylene exceeding the control standard. S01 and S03 sample sets were all below the control standard, but the residual compound was identical. Following the well installation at the same three spots (becoming monitoring wells D00493, D00494, D00495) were groundwater sampling in 2017 dry period and 2018 high flow period. Three monitoring wells were identified that their groundwater was contaminated by organochlorides exceeding the control standards, which were trichloroethylene, Cis-1,2-dichloroethylene, 1,1-dichloroethylene, and chloroethylene. The subsurface plume was believed still not spreading outbound yet, however. In addition, the groundwater samples extracted from D00493 and D00495 in the dry period and high flow period were all contaminated by fluoride exceeding the control standards. The monitoring well D00190 outside MOSPEC was also found fluoride over the control standard. Due to the sole usage and aftermath collection of hydrofluoric acid in MOSPEC which was sitting at the upstream of the regional groundwater, MOSPEC was responsible for the excessive concentration of fluoride at monitoring well D00190. It was recommended that MOSPEC should cover the range from the wastewater treatment facility to the monitoring well D00190 for the complementary investigation and remediation.
It was confirmative that in Xinshi Industrial Park MOSPEC was the source of excessive organochlorides in soil and groundwater and the source of fluoride. Tainan Environmental Protection Bureau (EPB) had announced MOSPEC as the site under restriction on March 28th 2018 (Env-Doc no. 1070345317D). The environmental evaluation score of a contaminated site (usually called TOL) for MOSPEC was 2,346.25 (> 1,200) and thus, Tainan EPB submitted it to Environmental Protection Administration (EPA).
To appraise the risks caused by the plume and the exposure pathway, the project adopted EPA’s “Health Assessment System” to evaluate the condition under Tier 1 and Tier 2 with two scenarios set. The first scenario only considered the exposure to the vapour of the contaminated groundwater, whilst the second scenario considered the exposure due to the excavation or the usage of the contaminated groundwater in which the soil, groundwater and aerial pathway were involved. Under the first scenario, the respective risk values of carcinogen and non-carcinogen of Tier 1 and Tier 2 were all below the tolerance limits and thus, it was recommended to maintain the first scenario for the safer condition. Under the second scenario, the respective risk values of carcinogen and non-carcinogen of Tier 1 and Tier 2 were all higher than the tolerance limits which were results of the exposure to the contaminated groundwater and thus, it was recommended to apply restrictions on the groundwater usage to reduce the risks.
2. The investigation into the groundwater contamination of organochlorides in Baoan Industrial Park
The investigation on Baoan Industrial Park in the project covered part of CHIMEI plant and used one of its present monitoring wells installed by EPA to support the investigation. Screened by the industrial features, NGST, and GERS, spots for MIP were pinned. The results of MIP indicated that factories such as Fangmei, CHIMEI, Fuchia and Haiping (now called Fengming) were detected giving peak signal from subsurface which led to further soil sampling and well installation.
There were four spots for soil sampling (one in each factory mentioned) and the concentrations of relevant organochlorides in all soil samples were far below the control and monitoring standards. In the background survey on the groundwater before the new well installations, monitoring well D00188 was found chloroethylene concentration at 0.0146 mg/L, higher than the monitoring standard but lower than 0.0529 mg/L known in 2016 June.
The groundwater in the industrial park was sampled in 2017 dry period and 2018 high flow period after the new well installations. The results showed that the two concentrations of chloroethylene were below the monitoring standard and the concentrations of other organochlorides such as Cis-1,2-dichloroethylene and Trans-1,2-dichloroethylene also complied with the monitoring standard. The new monitoring wells in Fangmei, CHIMEI, Fuchia and Fengming were named D00498, D00499, D00500, and D00501. The groundwater samples from these four monitoring wells had no organochlorides exceeding the monitoring standard. However, the groundwater samples from D00500 and D00188 had common residual organochlorides. Based on the observation on the regional groundwater, the stream was flowing from the east to west which might cause a correlation between two wells.
Beyond the scope of work of the project was the microbial analysis for soil and groundwater samples to understand the microbial species, amount and activity in Baoan Industrial Park. It was a measure to see if the organochloride plume was subject to anaerobic degradation in the natural environment. Our results showed no existence of Dehalococcoides, tceA gene and vcrA gene in soil and groundwater samples from Baoan Industrial Park. It was an explanation that no significant amount of organochlorides were present in the environment for the microbe to survive, which was in accordance with the results of groundwater sample analysis and MIP.
3. The investigation into Arsenic groundwater contamination in Baoan Industrial Park
As the pending official extent of Arsenic groundwater in Rende District, the project used monitoring wells in Baoan Industrial Park, XRF scanner on rock core of Central Geological Survey (CGS), and rock core sampling beside the monitoring well D00354 which was rich in Arsenic to define the extent.
The groundwater samples from those wells rich in Arsenic (monitoring wells D00186, D00188, and D00354) were analysed in 2018 high flow period and revealed the arsenic concentrations were matching the historical average, i.e. 0.0417~0.499 mg/L, ND~0.417 mg/L, and 0.216~0.69 mg/L. D00354 gave the highest concentration of Arsenic as proof of high arsenic groundwater. The rock core excavated at Wenhsien from CGS was under XRF scanning in the investigation, and the results showed that the minimum Arsenic concentration was 3.5 ppm (at 4.0~4.5 m bgl) and the maximum one was 2,792 ppm (at 18.0~18.5 m bgl), giving the average 49.3 ppm. The Arsenic concentration was tending to increase along the depth. During the rock core sampling, ferric hydroxide sediment and sea shell residues were found among layers as solid proof for historical coastal movement. The confining bed was believed at 8~13 m bgl by physical analysis and geological cross-section graph. The sampled rock core also went through the XRF scanning, and the highest value was 21.5 ppm at 9.5 m bgl. The average was 8.1 ppm and the high Arsenic interval was at 8.5~12 m bgl.
Through XRF twelve relatively high Arsenic samples of the sampled rock core were further analysed for the quantity. The maximum concentration was 25.7 mg/kg at 12 m bgl, and the tendencies along the depth of Arsenic, Iron and Manganese were consistent with each other, indicating a match to EPA’s definition of natural Arsenic source. Additionally, the confining bed and the high Arsenic interval were both at 8~13 m bgl.
The sequential extraction showed Arsenic was mostly from silicate minerals (61.9%) and then crystal ferric hydroxide (19.6%), accounting totally for 80%. It was substantial evidence to support the theory that Arsenic groundwater contamination was nature-caused.
The results of the investigation matched EPA’s definition “Procedure to determine the extent and sources of Arsenic in groundwater”. Thus, it was concluded that the Arsenic groundwater contamination in Baoan Industrial Park was nature-caused through the historical coastal movement and chemical release.
4. Groundwater management at restricted farmlands
Through the project, there were new simple wells installed at restricted farmlands, i.e. XN-465, XN-756, XN-654, XN-665, and TA-75-1 (monitoring wells GW-465, GW-756, GW-654, GW-665, GW-75-1 respectively). The known monitoring wells were D00155, D00156 and D00157.
The first groundwater sampling was in 2017 dry period. The results showed no concentrations of critical heavy metals and volatile organic compounds higher than the monitoring or control standards in the new simple wells and known monitoring wells, whilst each well had different general substances over the monitoring standards. For example GW-756, GW-654, GW-75-1 and D00155 were found Manganese exceeding the monitoring standard. The second groundwater sampling was in 2018 high flow period in which the results were similar to those of the dry period. No critical heavy metals and volatile organic compounds were identified exceeding the monitoring or control standards in the new simple wells and known monitoring wells, whilst each well still had different general substances over the monitoring standards.
Considering the long-term groundwater monitoring and management procedure, those new wells installed by the project should be included for the further groundwater sampling because they were sampled less than 4 times which was inadequate for statistical analysis and trend judgement. The common issue among the known wells was the high concentrations of general substances, and it was recommended to continue collecting samples till 4 times for statistical analysis on general substances, except for heavy metals and volatile organic compounds whose concentrations had been lower than the half of monitoring standards twice in consecutive.
For hazard evaluation on restricted farmlands, farmland XN-424 was rated 96 and 32 in “Remediation Priority” and “Urgent Response”, respectively, and was recommended Tainan EPB offer this farmland the most generous portion of resources. Following in the rank were TA-75-1, XN-665, and XN-756 all rated 72 and 18 in two subjects respectively.
5. Groundwater management at illegal dump-sites
The project used the known monitoring wells at illegal dump-sites SL-331, JS-19 and JJS-26 to collect groundwater samples for analysis. Also, there were new simple wells installed at new illegal dump-sites, i.e. two at SR-328’349, two at SL-331, one at GY-270, two at BF-1555~1559, and two at SS-1134-20~22.
Considering the long-term groundwater monitoring and management procedure, the new wells installed by the project should be included for the further groundwater sampling because they were sampled less than 4 times which was inadequate for statistical analysis and trend judgement. The data collected from the known well R00574 in SL-331 was analysed by a statistical method (Mann-Kendall) indicating the trend of Chromium as Decreasing. It needed groundwater sampling only once a year and could be terminated when the concentration was lower than the half of the monitoring standard. On the other hand, the total phenol at the same well was determined as Increasing, and it was recommended to carry out the groundwater sampling twice a year, typically targeting BTEX and TPH to see if they were the majority of total phenol. The general substances of two wells, S-26-1 and S-26-2, in JJS-26 were determined as Stable without critical heavy metals exceeding the monitoring standards. Thus, the groundwater sampling for S-26-1 and S-26-2 could be carried out once a year without monitoring critical heavy metals and volatile organic compounds. Monitoring wells S-26-A, S-26-B, and S-26-C were sampled less than 4 times and should be included for further analysis.
For hazard evaluation on illegal dump-sites, CLC-807, Expressway 61, HP-444’445, and SJT-1131 were all rated high in “Remediation Priority” and “Urgent Response” although the bias caused by the land area. Tainan EPB was recommended to offer these sites the most generous portion of resources to retrieve more information.
