Monitor-wells construction

Potential problems can result if monitoring well construction is such that the gravel pack and screened interval are not discretely terminated at the confining layer and its grouted annulus. 

Groundwater in the vicinity of an abandoned wood treatment facility was sampled from monitoring wells constructed at depths ranging from 6.1 to 30.5 meters and was analyzed for CDDs in January 1984 (Pereira et al. 1985). Concentrations of HxCDD, HpCDD, and OCDD in groundwater samples taken... 

Barcelona, M.J. Gibb, J.P. Millar, R.A. "A Guide to the Selection of Materials for Monitor Well Construction and Ground Water Sampling " Illinois Water Survey Champaign, Illinois 1983 p. 39. 

Overall, it is not possible to evaluate whether any of these factors have compromised the data included in published studies. More research is required to determine how U-and Th-series nuclides are affected by various well construction methods and sampling procedures, how reliable are data from wells not designed fro trace element monitoring, and if there are any factors that have affected the data collected from past studies. Most importantly, radionuclide studies must incorporate greater awareness of the potential problems, summarize whatever details are available regarding the wells used, and consider potential problems where the relevant information is not available. 

Foster, J.B. and Goolsby, D.A., Construction of Waste-Injection Monitoring Wells near Pensacola, Florida, Florida Bureau of Geology Information Circular 74, 1972. 

Physical and chemical monitoring is carried out through a U-tube downhole installation (Freifeld et al. 2005) that allows the collection of high quality liquid and gas samples from targeted depths. The multi-level U-tube assembly is completed in the Waarre C unit approximately 300 m distant and updip from the injector well (CRC-1). The Naylor-1 monitoring well is perforated from 2028.3 - 2032.2 m RT and 2039 - 2055 m RT. The U-tube assembly is constructed to sample from U1 at 2027 m RT (gas cap), U2 2040 m RT and U3 2045 m RT both initially below the gas-water contact. 

Monitoring wells were installed to a depth of 3-4 m into soft tailings at sites 1 and 2. The wells are constructed of 1.5 inch-OD PVC pipe with the lower 1.2 m perforated for collection of ground water. Water was sampled using a LDPE tubing- foot valve assembly. Ground water and surface waters were sampled monthly from August to November 2008. Temperature, pH, and conductivity were measured in the field and... 

Remediation commenced with the interception of the recoverable gasoline. One 4-in.-diameter vapor extraction well and three 2-in. vapor monitor wells were installed. Each well was constructed with 4 ft of well screen placed and filter packed across the unsaturated portion of the shale. The annulus of the wells was sealed to the surface with bentonite and cement grout according to local standards. The monitor wells were located in a triangular pattern around the vapor extraction well at distances of 5.3, 10.6, and 25.4 ft. 

Monitoring the well for leaks and nearby aquifers for contamination must also be considered. The extent of monitoring will vary based on the applicable environmental regulations and nearby potable aquifers. Monitoring wells can be constructed to monitor shallow or deep aquifers, and the cost of a these wells is determined by the required depth and the geology of the site. Additional costs include ancillary surface equipment and alarm systems (Mickley 2006). 

It is Important to note that much of the monitoring data presented below results from studies which were not designed for statistical treatment of the results. Therefore, it is often difficult or nearly impossible to draw statistically reliable conclusions about the results from these studies. Also, key information such as depth to the water table and well construction are sometimes unavailable. 

It is best to establish specific stabilization parameters and their performance criteria for each well based on such factors as the aquifer properties the well construction detail the nature of contaminants of concern the sampling technique and field instrument specifications. However, this may be achievable only for wells with historical data on a long-term monitoring program. As a general practice, we may use the guidelines for the stabilization parameter criteria presented in Table 3.4. 

Several methods are available for the drilling and installation of monitor wells. The advantages and disadvantages relating to ease of construction, character of formations penetrated, well diameter and depth, risks of contamination, and intended use of the well have been reported by several investigators ( 5, 6, 7). All field personnel should be thoroughly familiar with well specifications, quality assurance/quality control procedures, and safety plans and requirements prior to installation of monitor wells. 

Monitoring Well Design and Construction. EPA 625/6-87/016, U.S. Environmental Protection Agency, CERI, Cincinnati, OH, 1987. 

Material and method of well construction are both critical. Double cased monitoring wells using casing made of Teflon should be used whenever possible, and the intake part of the well should be made depth discrete Other requirements... 

The lack of specific direction from onshore management then apparently leaves work on the rig being done in accordance with company-written standards and other documentation. As the COO said, the [company] system relied upon the personnel involved in well construction following the requirements of the Well Construction Management System. .. it also relied on the expertise of the [rig] operator s supervisory personnel and the [company] drilling supervisors to monitor and check that the... 

Dig monitoring wells in all four directions of the SLF and monitor quality of groundwater before and after construction of the disposal facility. 

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