{"id":1612,"date":"2026-02-14T04:22:29","date_gmt":"2026-02-14T04:22:29","guid":{"rendered":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/chapter\/ch019-xhtml\/"},"modified":"2026-08-01T02:52:53","modified_gmt":"2026-08-01T02:52:53","slug":"pumping-and-observation-well-design-and-construction-data","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/chapter\/pumping-and-observation-well-design-and-construction-data\/","title":{"raw":"4.3 Pumping and Observation Well Design and Construction Data","rendered":"4.3 Pumping and Observation Well Design and Construction Data"},"content":{"raw":"
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\r\n\r\nPumping tests should include observation wells but can be performed using a single pumping well if necessary. Use of unpumped observation wells produces more reliable results because it is difficult to accurately measure drawdown in the aquifer via the pumping well bore due to wellbore storage issues early in the testing period and head losses that occur when water flows through the screen and along the bore that contains the pump, pipes, and wires. Also, observation wells provide information regarding storage properties of the aquifer and the spatial variation of hydraulic properties.\r\n\r\n<\/div>\r\n
\r\n\r\nOften, pumping and observation wells can be selected from existing wells completed in the target unit, otherwise wells can be specifically installed for the test. Typically, existing wells (including domestic, municipal, industrial and\/or irrigation wells) are used, when possible, as constructing a new pumping well is costly.\r\n\r\n<\/div>\r\n
\r\n

Design of Pumping and Observation Wells<\/h3>\r\n
\r\n\r\nWell construction logs should be reviewed prior to selecting an existing pumping well for the test. In many regions, driller\u2019s logs are filed with regulatory agencies when wells are constructed (Figure 12<\/a>). These provide information on the stratigraphy encountered during drilling, notes on when water bearing units were intersected, a short pumping test (performance test), borehole and casing diameters, location and type of grouting, and the position of perforated intervals in the well casing.\r\n\r\n<\/div>\r\n
\r\n\r\n\"\"\r\n\r\n<\/div>\r\n
\r\n
\r\n
\r\n\r\nFigure 12 -<\/strong> Example of a driller\u2019s well log report for the completion of a well in Miles City, MT, USA. All length units are reported in ft (convert as 1\u00a0ft=0.305\u00a0m). The log provides information on the owner, location, intended use, and drilling method. It also records completion data including borehole depth and diameter, casing material, perforated interval and diameter, and the grouted\/cemented interval. This well was completed by accessing water from the sand that is encountered at a depth interval between 760 and 830\u00a0ft (232\u00a0m and 253\u00a0m) below land surface. The casing was slotted over this interval to allow water to enter the well. The log provides information on the static water level at the time of drilling, performance testing of the well yield (in gallons per minute, gpm), and a geologic log with notes on the yields of zones that produced water during drilling. In the case of this well, the well was pumped at 30\u00a0gpm (164\u00a0m3<\/sup>\/d) for 24 hours and had 315\u00a0ft (interpreted as 580\u00a0ft\u2011265\u00a0ft) (96\u00a0m) of drawdown. From the performance testing, estimates of transmissivity can be made using methods discussed in Section\u00a012. Finally, the company responsible for drilling the well is noted (Montana Groundwater Information Center, Montana Bureau of Mines and Geology; https:\/\/mbmg.mtech.edu\/mapper\/mapper.asp?view=Wells&<\/u><\/a><\/span>\u2197).\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n
\r\n\r\nIf wells need to be installed to perform a pumping test, standard practices described by Sterrett (2007) should be applied (Figure 13<\/a>). The Groundwater Project book Domestic Wells: Introduction and Overview<\/em><\/a>\u2197 (Drage, 2022) provides a good discussion of drilling techniques used to install domestic wells. Ideally, pumping wells should include a screened or perforated interval that fully penetrates the aquifer and be of sufficient diameter to accept a pump that will produce the desired yield for the planned pumping test. Water supply wells are typically screened across the zones observed to yield the highest discharge rates during drilling, and often a filter or gravel pack is placed between the well screen\u2014or perforated casing\u2014and the borehole wall adjacent to this zone (Figure 13<\/a>). A well is generally considered fully penetrating if at least 80 percent of the aquifer thickness is screened because this makes it possible to obtain approximately 90 percent or more of the maximum yield that could be obtained if the entire aquifer was screened (Kruseman & de Ridder, 2000).\r\n\r\n<\/div>\r\n
\"\"\r\n
\r\n
\r\n
\r\n\r\nFigure 13 -<\/strong> Schematics representing ideal designs of production and observation wells with fully penetrating screened intervals, at least 80 percent of the thickness (Kruseman and de Ridder (1992)).<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n
a) Production well with steel casing that is grouted with cement or bentonite to the top of the gravel pack. The well consists of a solid casing and an attached screen interval set in a borehole. A gravel pack surrounds the screen. The annulus around the remainder of the casing is filled with grout.<\/blockquote>\r\n<\/div>\r\n
\r\n
b) A production well where the perforated interval is a slightly smaller diameter than the well casing. The telescoping screen is set in an open hole and not surrounded by a gravel pack. The remainder of the borehole above the screen is grouted.<\/blockquote>\r\n<\/div>\r\n
\r\n
c) Observation well set in a borehole. Typically, the screened interval is attached to a steel or PVC casing and a gravel or sand pack is installed around the screen. The remainder of the borehole is grouted to the surface.<\/blockquote>\r\n<\/div>\r\n
\r\n\r\nIdeally, observation wells also should be installed with screened intervals equal to or greater than 80 percent of the test unit thickness (Kruseman & de Ridder, 2000). However, this is rarely done for cost reasons. The length of the observation well screen is not important when the pumping well screen fully penetrates the tested unit or observation wells are located outside of the zone impacted by partial penetration effects, as discussed in Section\u00a012. Well casing must be of sufficient diameter to accept water\u2011level monitoring devices. Generally, diameters greater than 25 mm will accept transducers and mechanical tapes (Sterrett, 2006).\r\n\r\n<\/div>\r\n
\r\n\r\nObservation wells need to be in good communication with the formation being tested. Newly constructed wells should be developed after they are installed using methods described by Sterrett (2007). Taylor and Alley (2001) recommend that wells should be hydraulically tested before used as observation wells to assure the perforated interval is not damaged or plugged with silt or fouled with bacteria such that it is not optimally responding to head changes. Depending on the well construction: pumping, bailing, or slug testing (Section 2) can be used to assess if wells are in good communication with the geologic material being evaluated by hydraulic testing.\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\n

Observation Well Spacing<\/h3>\r\n
\r\n\r\nThe spacing of pumping and observation wells is driven by the purpose of test. For a successful pumping test, pumping\u2011induced drawdown at observation locations must generally be both measurable and exceed the magnitude of other influences on water levels (e.g., low\u2011permeability boundaries, surface water bodies, other pumping wells, irrigation, precipitation recharge, and barometric pressure changes). Observation well spacing should be based on the estimated radius of influence of the pumping during the test. The radius of influence is estimated using analytical equations (presented in Sections 7\u201110) that forecast drawdown based on the designed pumping rate, hydrogeologic unit type, hydraulic characteristics, and the duration of the test.\r\n\r\n<\/div>\r\n
\r\n\r\nGeneral guidance for placement of monitoring wells is provided by Sterrett (2007). In unconfined aquifers, he suggests observation wells be placed no further than 30 to 90 m from the pumping well. In confined aquifers they should be placed within 90 to 200 m of the pumping well. These general guidelines are based on the concept that the large storage coefficient of unconfined systems corresponds to a smaller zone of influence. However, as mentioned above, pumping rates, transmissivities, storativities, and test duration all affect the extent of the cone of depression.\r\n\r\n<\/div>\r\n
\r\n\r\nThe USEPA Aquifer Test Guidance (Osborne, 1990) suggests when one observation well is used it should be spaced 15 to 90 m from pumping well. Osborne (1990) states that when multiple observation wells are used, they should be placed in a line at varying distances from the well or \u201c\u2026along rays perpendicular to the pumping well.\u201d<\/em> If boundaries are expected to influence the test, then observation wells should be located near the boundaries. Ideally, observation wells should also be located outside of the anticipated zone of influence to monitor natural and anthropogenic induced changes to the water levels. He also notes that if anisotropic conditions are present, monitoring wells should be placed to reflect the likely pattern of anisotropy.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"
\n
\n
\n

Pumping tests should include observation wells but can be performed using a single pumping well if necessary. Use of unpumped observation wells produces more reliable results because it is difficult to accurately measure drawdown in the aquifer via the pumping well bore due to wellbore storage issues early in the testing period and head losses that occur when water flows through the screen and along the bore that contains the pump, pipes, and wires. Also, observation wells provide information regarding storage properties of the aquifer and the spatial variation of hydraulic properties.<\/p>\n<\/div>\n

\n

Often, pumping and observation wells can be selected from existing wells completed in the target unit, otherwise wells can be specifically installed for the test. Typically, existing wells (including domestic, municipal, industrial and\/or irrigation wells) are used, when possible, as constructing a new pumping well is costly.<\/p>\n<\/div>\n

\n

Design of Pumping and Observation Wells<\/h3>\n
\n

Well construction logs should be reviewed prior to selecting an existing pumping well for the test. In many regions, driller\u2019s logs are filed with regulatory agencies when wells are constructed (Figure 12<\/a>). These provide information on the stratigraphy encountered during drilling, notes on when water bearing units were intersected, a short pumping test (performance test), borehole and casing diameters, location and type of grouting, and the position of perforated intervals in the well casing.<\/p>\n<\/div>\n

\n

\"\"<\/p>\n<\/div>\n

\n
\n
\n

Figure 12 –<\/strong> Example of a driller\u2019s well log report for the completion of a well in Miles City, MT, USA. All length units are reported in ft (convert as 1\u00a0ft=0.305\u00a0m). The log provides information on the owner, location, intended use, and drilling method. It also records completion data including borehole depth and diameter, casing material, perforated interval and diameter, and the grouted\/cemented interval. This well was completed by accessing water from the sand that is encountered at a depth interval between 760 and 830\u00a0ft (232\u00a0m and 253\u00a0m) below land surface. The casing was slotted over this interval to allow water to enter the well. The log provides information on the static water level at the time of drilling, performance testing of the well yield (in gallons per minute, gpm), and a geologic log with notes on the yields of zones that produced water during drilling. In the case of this well, the well was pumped at 30\u00a0gpm (164\u00a0m3<\/sup>\/d) for 24 hours and had 315\u00a0ft (interpreted as 580\u00a0ft\u2011265\u00a0ft) (96\u00a0m) of drawdown. From the performance testing, estimates of transmissivity can be made using methods discussed in Section\u00a012. Finally, the company responsible for drilling the well is noted (Montana Groundwater Information Center, Montana Bureau of Mines and Geology; https:\/\/mbmg.mtech.edu\/mapper\/mapper.asp?view=Wells&<\/u><\/a><\/span>\u2197).<\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n

\n

If wells need to be installed to perform a pumping test, standard practices described by Sterrett (2007) should be applied (Figure 13<\/a>). The Groundwater Project book Domestic Wells: Introduction and Overview<\/em><\/a>\u2197 (Drage, 2022) provides a good discussion of drilling techniques used to install domestic wells. Ideally, pumping wells should include a screened or perforated interval that fully penetrates the aquifer and be of sufficient diameter to accept a pump that will produce the desired yield for the planned pumping test. Water supply wells are typically screened across the zones observed to yield the highest discharge rates during drilling, and often a filter or gravel pack is placed between the well screen\u2014or perforated casing\u2014and the borehole wall adjacent to this zone (Figure 13<\/a>). A well is generally considered fully penetrating if at least 80 percent of the aquifer thickness is screened because this makes it possible to obtain approximately 90 percent or more of the maximum yield that could be obtained if the entire aquifer was screened (Kruseman & de Ridder, 2000).<\/p>\n<\/div>\n

\"\"<\/p>\n
\n
\n
\n

Figure 13 –<\/strong> Schematics representing ideal designs of production and observation wells with fully penetrating screened intervals, at least 80 percent of the thickness (Kruseman and de Ridder (1992)).<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

\n

a) Production well with steel casing that is grouted with cement or bentonite to the top of the gravel pack. The well consists of a solid casing and an attached screen interval set in a borehole. A gravel pack surrounds the screen. The annulus around the remainder of the casing is filled with grout.<\/p><\/blockquote>\n<\/div>\n

\n

b) A production well where the perforated interval is a slightly smaller diameter than the well casing. The telescoping screen is set in an open hole and not surrounded by a gravel pack. The remainder of the borehole above the screen is grouted.<\/p><\/blockquote>\n<\/div>\n

\n

c) Observation well set in a borehole. Typically, the screened interval is attached to a steel or PVC casing and a gravel or sand pack is installed around the screen. The remainder of the borehole is grouted to the surface.<\/p><\/blockquote>\n<\/div>\n

\n

Ideally, observation wells also should be installed with screened intervals equal to or greater than 80 percent of the test unit thickness (Kruseman & de Ridder, 2000). However, this is rarely done for cost reasons. The length of the observation well screen is not important when the pumping well screen fully penetrates the tested unit or observation wells are located outside of the zone impacted by partial penetration effects, as discussed in Section\u00a012. Well casing must be of sufficient diameter to accept water\u2011level monitoring devices. Generally, diameters greater than 25 mm will accept transducers and mechanical tapes (Sterrett, 2006).<\/p>\n<\/div>\n

\n

Observation wells need to be in good communication with the formation being tested. Newly constructed wells should be developed after they are installed using methods described by Sterrett (2007). Taylor and Alley (2001) recommend that wells should be hydraulically tested before used as observation wells to assure the perforated interval is not damaged or plugged with silt or fouled with bacteria such that it is not optimally responding to head changes. Depending on the well construction: pumping, bailing, or slug testing (Section 2) can be used to assess if wells are in good communication with the geologic material being evaluated by hydraulic testing.<\/p>\n<\/div>\n<\/div>\n

\n

Observation Well Spacing<\/h3>\n
\n

The spacing of pumping and observation wells is driven by the purpose of test. For a successful pumping test, pumping\u2011induced drawdown at observation locations must generally be both measurable and exceed the magnitude of other influences on water levels (e.g., low\u2011permeability boundaries, surface water bodies, other pumping wells, irrigation, precipitation recharge, and barometric pressure changes). Observation well spacing should be based on the estimated radius of influence of the pumping during the test. The radius of influence is estimated using analytical equations (presented in Sections 7\u201110) that forecast drawdown based on the designed pumping rate, hydrogeologic unit type, hydraulic characteristics, and the duration of the test.<\/p>\n<\/div>\n

\n

General guidance for placement of monitoring wells is provided by Sterrett (2007). In unconfined aquifers, he suggests observation wells be placed no further than 30 to 90 m from the pumping well. In confined aquifers they should be placed within 90 to 200 m of the pumping well. These general guidelines are based on the concept that the large storage coefficient of unconfined systems corresponds to a smaller zone of influence. However, as mentioned above, pumping rates, transmissivities, storativities, and test duration all affect the extent of the cone of depression.<\/p>\n<\/div>\n

\n

The USEPA Aquifer Test Guidance (Osborne, 1990) suggests when one observation well is used it should be spaced 15 to 90 m from pumping well. Osborne (1990) states that when multiple observation wells are used, they should be placed in a line at varying distances from the well or \u201c\u2026along rays perpendicular to the pumping well.\u201d<\/em> If boundaries are expected to influence the test, then observation wells should be located near the boundaries. Ideally, observation wells should also be located outside of the anticipated zone of influence to monitor natural and anthropogenic induced changes to the water levels. He also notes that if anisotropic conditions are present, monitoring wells should be placed to reflect the likely pattern of anisotropy.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":8,"menu_order":12,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1612","chapter","type-chapter","status-publish","hentry"],"part":515,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapters\/1612","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/wp\/v2\/users\/8"}],"version-history":[{"count":4,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapters\/1612\/revisions"}],"predecessor-version":[{"id":2547,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapters\/1612\/revisions\/2547"}],"part":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/parts\/515"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapters\/1612\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/wp\/v2\/media?parent=1612"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/pressbooks\/v2\/chapter-type?post=1612"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/wp\/v2\/contributor?post=1612"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/wp-json\/wp\/v2\/license?post=1612"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}