Significance and Use
4.1 A correctly designed, installed, and developed groundwater monitoring well, constructed in accordance with Practice should provide the following: representative samples of groundwater that can be analyzed to determine physical properties and water quality parameters of the sample or potentiometric levels that are representative of the total hydraulic head of that portion of the aquifer screened by the well, or both. The well may also be utilized for conducting aquifer performance tests used for the purpose of determining the hydrogeologic properties of the targeted hydrostratigraphic unit in which the well has been completed.
Note 1: An extensive research program on annular sealants was conducted from 2001 through 2009 and in subsequent years by the Nebraska Grout Task Force (Lackey et al., 2009 and State of California, 2015). This research included cement and bentonite grouts and the use of pellets and chips. The general finding of the study indicates all sealing methods suffer from some shrinkage in the portion of the well in the unsaturated zone. The best grouts were cement-sand, bentonite chips, neat cements, and bentonite slurries with more than 20 percent solids. Especially problematic is the use of low solids content bentonite slurries in the unsaturated zone leading to a prohibition on their use in California (State of California, 2015). It is also highly recommended that State and Federal codes/regulations regarding seals within the unsaturated zone be evaluated prior to design to ensure codes are met.
4.2 Well development is an important component of monitoring well completions. Monitoring wells installed in aquifers should be sufficiently developed to such that they serve their intended objectives. Well development methods vary with the physical characteristics of the targeted hydrostratigraphic unit in which the monitoring well is screened, the construction details of the well, the drilling method utilized during the construction of the borehole prior to well installation, and the quality of the groundwater. The development method for each individual monitoring well should be selected from among the several methods described in this guide and should be employed by the well construction contractor or the qualified personnel in responsible charge of the monitoring well completion.
4.3 The importance of well development in monitoring wells cannot be overestimated. If a monitoring well is inherited with a project, it is best for the well construction contractor or the qualified personnel to consider the possibility that well development was not performed or was carried out inadequately, which may influence both previous and future sampling results if the wells were not redeveloped and/or appropriate documentation of well development cannot be obtained. Proper and careful well development will improve the ability of most monitoring wells to provide representative, unbiased chemical and hydraulic data. The additional time and money spent performing this important step in monitoring well completion or maintenance will reduce the potential for damaging pumping equipment and in situ sensors, and increase the probability that groundwater samples are representative of the targeted formation water monitored. Practice provides evaluation factors for the activities in this guide.
Note 2: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice are generally considered capable of competent and objective testing/sampling/evaluation/and the like. Users of this standard are cautioned that compliance with Practice does not in itself assure reliable results. Reliable results depend on many factors. Practice provides a means of evaluating some of those factors.
1.1 This guide covers the development of screened wells installed for the purpose of obtaining representative groundwater information and water quality samples from granular aquifers, though the methods described herein could also be applied to wells used for other purposes. Other well-development methods that are used exclusively in open-borehole bedrock wells are not described in this guide.
1.2 The applications and limitations of the methods described in this guide are based on the assumption that the primary objective of the monitoring wells to which the methods are applied is to obtain representative water quality samples from aquifers. Screened monitoring wells developed using the methods described in this guide should yield relatively sediment-free samples from granular aquifer materials, ranging from gravels to silty sands. While many monitoring wells are considered “small-diameter” wells (that is, less than 10 cm [4 in.] inside diameter), some of the techniques described in this guide will be more easily applied to large-diameter wells (that is, 10 cm [4 in.] or greater inside diameter).
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service needs to be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.