Standard Guide for Development of Groundwater Monitoring Wells in Granular Aquifers

Importancia y uso:

4.1 A correctly designed, installed, and developed groundwater monitoring well, constructed in accordance with Practice D5092/D5092M 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 D3740 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 facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.

Subcomité:

D18.21

Referida por:

D5784_D5784M-18R25, D5781_D5781M-18R25, D6771-21, D6452-18R23, D6725_D6725M-16R24E01, D6724_D6724M-16R24E01, D6001_D6001M-20, D5980-16R24, D6034-20, D7929-20, D5978_D5978M-16R24, D5092_D5092M-16R24

Volúmen:

04.08

Número ICS:

13.060.10 (Water of natural resources)

Palabras clave:

aquifer; groundwater; high-velocity; hydraulic jetting; jetting; mechanical surging; monitoring well; over-pumping and backwashing; representative sample; well development;