This project is based on the experience of the previous projects including “Evaluation Project of the Network of the Regional Groundwater Monitoring Wells (RGMWs)” and “Project of Maintenance and Information Correction of the Regional Groundwater Monitoring Wells” which executed in year 2004 and 2006 respectively. The objective of this project is to secure the function of the RGMWs through the extension of the well maintenance work and the correction of the basic well information, thus the RGMWs can provide pollution precaution and help to protect groundwater body. According to the contract, the tasks of this project include (1) providing periodical cleaning to the RGMWs; (2) the verification and correction of the basic well information. The project results of the above two major tasks are described as below:
11. Providing periodical cleaning to the RGMWs
In the previous projects, totally 179 wells were selected from overall 431 RGMWs and evaluated within down-hole video inspection and slug test. In the evaluated 179 wells, totally 100 wells were recommended to receive well cleaning and 15 of the 100 wells have been cleaned during year 2004 and 2006. In this project, totally 68 wells has been selected and evaluated from the 252 wells which were not evaluated in the previous projects. According to the results of down-hole video inspection and slug test, the tested wells can be classified into following four categories: (1) the function is normal (27 wells); (2) needs instant well cleaning and maintenance (40 wells); (3) recommends for well reinstallation or ceases groundwater monitoring (1 wells). In addition to the 40 wells recommended for instant cleaning, additional 8 wells were selected and cleaned from the remaining 15 wells which were not cleaned in the previous projects. Thus the total quantity of cleaned wells in this project achieves 48 wells and has been executed between 9/27/2007 and 11/2/2007. According to the work plan proposed previously, the down-hole video inspection and slug test were applied to each well before and after the well cleaning.
According to the results of down-hole video inspection before well cleaning, scaling and biological fouling on well casing and screen prevails in most RGMWs. After well cleaning, the hydraulic conductivities of 28 wells among the 48 cleaned wells, including Zhu-Nan Elementary School, Miao-Li, et al., have recovered or maintained in good condition. At contrast, the hydraulic conductivities of other 20 wells remain in poor condition and the primary reason is due to the geological conditions of the aquifer (7 wells), including silt or clay properties. In addition, the geological records of 8 well among the 20 wells is missing and the geological conditions of 5 well (Wen-Kai Elementary School, Zhang-Hua, et al.) is not consistent to the hydraulic conductivity. The aquifer geological conditions of this well is recommended to be investigated again in the future.
22. Verification and correction of the basic well information
In this project, the altitude and the screen depth and length of the selected 68 wells was examined. Generally, the altitude recorded in the basic well information showed significant error (-57.255m ~ +20.347m) and all were corrected. On the other hand, the screen depth and length of 37% examined wells showed errors in the basic well information and were correct accordingly.