{"id":1162,"date":"2026-05-12T21:46:28","date_gmt":"2026-05-12T21:46:28","guid":{"rendered":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/background-information-on-wells\/"},"modified":"2026-05-13T16:26:58","modified_gmt":"2026-05-13T16:26:58","slug":"background-information-on-wells","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/background-information-on-wells\/","title":{"raw":"7.2 Background Information on Wells","rendered":"7.2 Background Information on Wells"},"content":{"raw":"<div id=\"background-information-on-wells\" class=\"level1\">\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nA <em>well<\/em> is a general, all\u2011encompassing term for a hole drilled into the ground for the purpose of accessing fluids in the subsurface. Wells can be constructed to remove fluids (oil wells, water supply wells), to add fluids (waste and brine injection), or to sample and monitor the naturally occurring fluids (monitoring wells). Wells have also been used to recover mineral resources in the subsurface; for example, subsurface sulfur deposits can be accessed by injecting extremely hot water, dissolving the sulfur, and pumping the concentrated sulfur solution up to the surface for recovery. Wells can also be used to access energy resources directly; for example, geothermal energy can be collected by injecting water into thermally active zones and recovering the heated water.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nA well that is designed and installed for the sole purpose of measuring water levels in an aquifer is called a <em>piezometer<\/em>. Piezometers can be much smaller in diameter than water wells and are generally 1.25 to 2\u00a0inches (3 to 5\u00a0cm, i.e., 0.03 to 0.05 m) in diameter. Piezometers can also be called <em>monitoring wells<\/em>. Monitoring wells are usually at least 2\u00a0inches (0.05\u00a0m) in diameter and are generally constructed for the purpose of periodic sampling of water to determine water quality; for example, in contaminated aquifers that require monitoring through time.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nWells are an important aspect of applied hydrogeology, both from a practical standpoint (e.g., water supply wells, dewatering wells) as well as for protection of humans and ecosystems and for scientific study (e.g., water levels, water sampling). Wells are the way we look into the subsurface and gather bits of information that we can use to understand the groundwater and the aquifer through which it flows.\r\n\r\n<\/div>\r\n<div id=\"basic-well-construction\" class=\"level3\">\r\n<h3>Basic Well Construction<\/h3>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nHistorically, wells were dug by hand and the walls were lined with rocks to keep the well clear and open. These days, there are several safer and more efficient ways to drill a hole in the ground and install a well. Basic drilling methods include the following.\r\n\r\n<\/div>\r\n<ul>\r\n \t<li>Cable tool: Uses a weighted drill bit that is repeatedly raised and dropped by a cable, like a pile driver. It may seem archaic, but it is an effective method and results in minimal disturbance in the subsurface.<\/li>\r\n \t<li>Water or mud rotary: The drilling rig turns a drill bit and circulates a drilling fluid (either water or <em>drilling mud<\/em><sup>3<\/sup><em>)<\/em> into the subsurface through the borehole. The drilling fluid lubricates and cools the bit and carries drill cuttings to the surface.<\/li>\r\n \t<li>Air rotary: Like the fluid rotary methods, except air is used, and the bit (called a <em>down\u2011hole hammer<\/em>) acts like a jackhammer run on compressed air. The air carries the cuttings to the subsurface.<\/li>\r\n \t<li>Auger: The drilling rig rotates either a hollow\u2011stem or solid\u2011stem continuous flight auger without drilling fluids. Good for installation of shallow monitoring wells and piezometers.<\/li>\r\n \t<li>Direct push: Uses the weight of the drill rig and hydraulic power to push the bit into the subsurface without rotation.<\/li>\r\n \t<li>Jet drilling: Water is pumped under pressure down a small diameter pipe with a special bit; the pressurized water loosens sediments and rock that are carried out by the circulating water. The bit can also be lifted and dropped (like a cable tool rig) during drilling to help the bit advance.<\/li>\r\n \t<li>Sonic drilling: Uses high\u2011frequency vibrations to advance the drill bit into the formation. The advantage to this method is that no fluids are needed and there is minimal damage to the formation along the sides of the borehole.<\/li>\r\n<\/ul>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nEach one of these methods has advantages and disadvantages and is appropriate for certain applications. Auger, direct push, and jet drilling methods are generally only used in unconsolidated deposits (i.e., loose sediments) rather than solid rock.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nOnce the borehole is drilled, a well can be installed. In certain situations, it may be acceptable to leave the borehole open and start using it\u2014for example, if you drilled a borehole in the middle of competent bedrock directly through the outcrop. In most cases, however, there is a possibility that the walls of the borehole may collapse inward and block the well. Generally, at a minimum, a short pipe called a <em>surface<\/em> <em>casing<\/em> is installed and sealed into the top of the borehole to prevent water, surface materials, and biota entering the hole from the surface. In addition, there may be several <em>hydrostratigraphic<\/em> <em>units<\/em> in one borehole; and it may be preferable to keep the upper ones isolated from the producing zone. Sections of pipe, called <em>casing<\/em>, are then placed in the well to keep the well open and isolate the upper units. If the producing zone is composed of unconsolidated, or poorly consolidated, sediments, or if it has some fraction of fine sediment associated with it, a <em>well screen<\/em> and\/or <em>filter pack<\/em> must be placed in the producing zone to keep fine particles out and let the water in. <a href=\"#X5ef4f406dc246a7b2f1e53a49a6bd4eb490596d\"><span data-custom-style=\"Hyperlink\">Figure\u00a034<\/span><\/a> shows examples of several geologic scenarios and different casing\/screen setups.\r\n\r\n<\/div>\r\n<div class=\"bc-figure figure\" data-custom-style=\"Captioned Figure\">\r\n\r\n<img style=\"display: block; margin-left: auto; margin-right: auto; ;width: 5.83333in; height: 2.69118in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file36-2.png\" alt=\"A diagram of a clay layer Description automatically generated\" \/>\r\n<div class=\"bc-figcaption figcaption\">\r\n<div data-custom-style=\"Image Caption\">\r\n<div class=\"figcaption-text\">\r\n\r\n<span id=\"X5ef4f406dc246a7b2f1e53a49a6bd4eb490596d\" class=\"anchor\"><strong>Figure\u00a034\u00a0\u2011\u00a0<\/strong>Examples of some typical well construction scenarios.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nConstruction of monitoring wells is more rigorous than construction of water wells. In a water supply well, the objective is to produce as much water as possible; therefore, it is advantageous to have a long screen length that covers as much of the saturated thickness of the aquifer as possible. In a monitoring well, however, it is important to design the well to be precisely completed in the hydrostratigraphic unit which needs monitoring. Several decades of shallow groundwater environmental assessments and remediation projects have generated relatively strict state and federally mandated protocols concerning the installation of monitoring wells.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\n<a href=\"#Xda749547d65e814e1d96b66296c9ed37af4625a\"><span data-custom-style=\"Hyperlink\">Figure\u00a035<\/span><\/a> shows typical monitoring well construction. Monitoring wells and piezometers usually consist of 1.25- to 2-inch (0.03 to 0.05\u00a0m) diameter PVC pipe with threaded fittings and a cap at the bottom of the hole. The PVC pipe will have a section in the aquifer that has thin slots cut into it; this section of pipe is called the <em>screened interval<\/em> or <em>slotted interval<\/em>. Screened interval is a general term that we use to describe the length of the well that is open to the aquifer. The open borehole around the screened interval is backfilled with clean, well-sorted sand, called the <em>sand pack<\/em> or <em>filter pack<\/em>. The sand pack should fill the <em>annulus<\/em> (the space between the well casing\/screen and the edge of the borehole) to a point at least a foot above the top of the screen. The sand pack is then covered with a seal, usually a smectite clay called <em>bentonite<\/em>, which is purchased as dry pellets or a granular powder that swell when hydrated. This seals off the well screen from the upper part of the borehole and keeps surface water or water from overlying formations from moving down the borehole into the monitored zone. The remainder of the borehole is then backfilled with either cement, drill cuttings, or some combination of the two. The well must then be capped with a secure access cover.\r\n\r\n<\/div>\r\n<div class=\"bc-figure figure\" data-custom-style=\"Captioned Figure\">\r\n\r\n<img style=\"display: block; margin-left: auto; margin-right: auto; ;width: 3.2626in; height: 4.08369in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file37-2.png\" alt=\"\" \/>\r\n<div class=\"bc-figcaption figcaption\">\r\n<div data-custom-style=\"Image Caption\">\r\n<div class=\"figcaption-text\">\r\n\r\n<span id=\"Xda749547d65e814e1d96b66296c9ed37af4625a\" class=\"anchor\"><strong>Figure\u00a035\u00a0\u2011\u00a0<\/strong>Typical monitoring well construction.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nShallow monitoring wells are usually installed using hollow\u2011stem augers. Once the required depth is reached, the PVS pipe is put together and inserted down the center of the auger. Sand is then poured in around the pipe, and the augers are pulled up a little bit so that the sand falls into the open borehole. This process is repeated until the screen is covered and the sand is in place. Then the bentonite pellets are added, and the augers are pulled out of the ground. If the bentonite seal is emplaced above the water table, water can be poured in to hydrate the bentonite. The rest of the hole is typically backfilled with cement, and the top of the well is secured with a cap and frequently enclosed within a manhole or protective metal vault.\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"well-development\" class=\"level3\">\r\n<h3>Well Development<\/h3>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nOne of the big concerns with well construction is the amount of disturbance to the subsurface caused by drilling. Regardless of the method, the aquifer formation is always affected in some way. Problems related to disturbance include the following.\r\n\r\n<\/div>\r\n<ul>\r\n \t<li>Lots of fine material may get into well screen and filter pack, which can clog or fill (known as silting up) the well.<\/li>\r\n \t<li>Drilling fluids (especially muds) flow into the formation and may clog pores.<\/li>\r\n \t<li>The drill bit can smear the walls of the borehole, closing off pores.<\/li>\r\n \t<li>A large volume of water and drilling fluids must be removed from the formation before samples representative of the formation can be obtained.<\/li>\r\n<\/ul>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nFollowing drilling and installation of the well, the effects of this disturbance must be corrected as best as possible. This process is called <em>development<\/em> of the well. Well development in water supply wells with relatively high yields generally entails pumping water from the well for an extended period, until the water runs clear. In low\u2011yield monitoring wells, if there is not enough water to sustain pumping then it may not be an option. Plungers can be put into wells to force water in and out of the screen for a period. Compressed air can also be forced down into the well to lift water and fine material out of the well screen. Usually, with monitoring wells, any water that was introduced during drilling must be removed so that groundwater samples accurately represent the formation.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\n<em>US Geological Survey Water\u2011Resources Investigations Report 96\u20114233<\/em> (Lapham et al., 1996) is a good general source of information concerning well construction and development. This report is available as a free download from the USGS.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"footnotes footnotes-end-of-document\">\r\n\r\n<hr \/>\r\n\r\n<div class=\"bc-aside aside\" role=\"doc-footnote\">\r\n<div data-custom-style=\"Footnote Text\">\r\n\r\n<span data-custom-style=\"Footnote Reference\"><sup>3<\/sup> Drilling mud is a thick, heavy, and viscous fluid that is circulated through boreholes during drilling to cool and lubricate the drill bit, bring drill cuttings to the surface, and keep the open borehole from collapsing.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div id=\"background-information-on-wells\" class=\"level1\">\n<div data-custom-style=\"First Paragraph\">\n<p>A <em>well<\/em> is a general, all\u2011encompassing term for a hole drilled into the ground for the purpose of accessing fluids in the subsurface. Wells can be constructed to remove fluids (oil wells, water supply wells), to add fluids (waste and brine injection), or to sample and monitor the naturally occurring fluids (monitoring wells). Wells have also been used to recover mineral resources in the subsurface; for example, subsurface sulfur deposits can be accessed by injecting extremely hot water, dissolving the sulfur, and pumping the concentrated sulfur solution up to the surface for recovery. Wells can also be used to access energy resources directly; for example, geothermal energy can be collected by injecting water into thermally active zones and recovering the heated water.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>A well that is designed and installed for the sole purpose of measuring water levels in an aquifer is called a <em>piezometer<\/em>. Piezometers can be much smaller in diameter than water wells and are generally 1.25 to 2\u00a0inches (3 to 5\u00a0cm, i.e., 0.03 to 0.05 m) in diameter. Piezometers can also be called <em>monitoring wells<\/em>. Monitoring wells are usually at least 2\u00a0inches (0.05\u00a0m) in diameter and are generally constructed for the purpose of periodic sampling of water to determine water quality; for example, in contaminated aquifers that require monitoring through time.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>Wells are an important aspect of applied hydrogeology, both from a practical standpoint (e.g., water supply wells, dewatering wells) as well as for protection of humans and ecosystems and for scientific study (e.g., water levels, water sampling). Wells are the way we look into the subsurface and gather bits of information that we can use to understand the groundwater and the aquifer through which it flows.<\/p>\n<\/div>\n<div id=\"basic-well-construction\" class=\"level3\">\n<h3>Basic Well Construction<\/h3>\n<div data-custom-style=\"First Paragraph\">\n<p>Historically, wells were dug by hand and the walls were lined with rocks to keep the well clear and open. These days, there are several safer and more efficient ways to drill a hole in the ground and install a well. Basic drilling methods include the following.<\/p>\n<\/div>\n<ul>\n<li>Cable tool: Uses a weighted drill bit that is repeatedly raised and dropped by a cable, like a pile driver. It may seem archaic, but it is an effective method and results in minimal disturbance in the subsurface.<\/li>\n<li>Water or mud rotary: The drilling rig turns a drill bit and circulates a drilling fluid (either water or <em>drilling mud<\/em><sup>3<\/sup><em>)<\/em> into the subsurface through the borehole. The drilling fluid lubricates and cools the bit and carries drill cuttings to the surface.<\/li>\n<li>Air rotary: Like the fluid rotary methods, except air is used, and the bit (called a <em>down\u2011hole hammer<\/em>) acts like a jackhammer run on compressed air. The air carries the cuttings to the subsurface.<\/li>\n<li>Auger: The drilling rig rotates either a hollow\u2011stem or solid\u2011stem continuous flight auger without drilling fluids. Good for installation of shallow monitoring wells and piezometers.<\/li>\n<li>Direct push: Uses the weight of the drill rig and hydraulic power to push the bit into the subsurface without rotation.<\/li>\n<li>Jet drilling: Water is pumped under pressure down a small diameter pipe with a special bit; the pressurized water loosens sediments and rock that are carried out by the circulating water. The bit can also be lifted and dropped (like a cable tool rig) during drilling to help the bit advance.<\/li>\n<li>Sonic drilling: Uses high\u2011frequency vibrations to advance the drill bit into the formation. The advantage to this method is that no fluids are needed and there is minimal damage to the formation along the sides of the borehole.<\/li>\n<\/ul>\n<div data-custom-style=\"First Paragraph\">\n<p>Each one of these methods has advantages and disadvantages and is appropriate for certain applications. Auger, direct push, and jet drilling methods are generally only used in unconsolidated deposits (i.e., loose sediments) rather than solid rock.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>Once the borehole is drilled, a well can be installed. In certain situations, it may be acceptable to leave the borehole open and start using it\u2014for example, if you drilled a borehole in the middle of competent bedrock directly through the outcrop. In most cases, however, there is a possibility that the walls of the borehole may collapse inward and block the well. Generally, at a minimum, a short pipe called a <em>surface<\/em> <em>casing<\/em> is installed and sealed into the top of the borehole to prevent water, surface materials, and biota entering the hole from the surface. In addition, there may be several <em>hydrostratigraphic<\/em> <em>units<\/em> in one borehole; and it may be preferable to keep the upper ones isolated from the producing zone. Sections of pipe, called <em>casing<\/em>, are then placed in the well to keep the well open and isolate the upper units. If the producing zone is composed of unconsolidated, or poorly consolidated, sediments, or if it has some fraction of fine sediment associated with it, a <em>well screen<\/em> and\/or <em>filter pack<\/em> must be placed in the producing zone to keep fine particles out and let the water in. <a href=\"#X5ef4f406dc246a7b2f1e53a49a6bd4eb490596d\"><span data-custom-style=\"Hyperlink\">Figure\u00a034<\/span><\/a> shows examples of several geologic scenarios and different casing\/screen setups.<\/p>\n<\/div>\n<div class=\"bc-figure figure\" data-custom-style=\"Captioned Figure\">\n<p><img decoding=\"async\" style=\"display: block; margin-left: auto; margin-right: auto; ;width: 5.83333in; height: 2.69118in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file36-2.png\" alt=\"A diagram of a clay layer Description automatically generated\" \/><\/p>\n<div class=\"bc-figcaption figcaption\">\n<div data-custom-style=\"Image Caption\">\n<div class=\"figcaption-text\">\n<p><span id=\"X5ef4f406dc246a7b2f1e53a49a6bd4eb490596d\" class=\"anchor\"><strong>Figure\u00a034\u00a0\u2011\u00a0<\/strong>Examples of some typical well construction scenarios.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>Construction of monitoring wells is more rigorous than construction of water wells. In a water supply well, the objective is to produce as much water as possible; therefore, it is advantageous to have a long screen length that covers as much of the saturated thickness of the aquifer as possible. In a monitoring well, however, it is important to design the well to be precisely completed in the hydrostratigraphic unit which needs monitoring. Several decades of shallow groundwater environmental assessments and remediation projects have generated relatively strict state and federally mandated protocols concerning the installation of monitoring wells.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p><a href=\"#Xda749547d65e814e1d96b66296c9ed37af4625a\"><span data-custom-style=\"Hyperlink\">Figure\u00a035<\/span><\/a> shows typical monitoring well construction. Monitoring wells and piezometers usually consist of 1.25- to 2-inch (0.03 to 0.05\u00a0m) diameter PVC pipe with threaded fittings and a cap at the bottom of the hole. The PVC pipe will have a section in the aquifer that has thin slots cut into it; this section of pipe is called the <em>screened interval<\/em> or <em>slotted interval<\/em>. Screened interval is a general term that we use to describe the length of the well that is open to the aquifer. The open borehole around the screened interval is backfilled with clean, well-sorted sand, called the <em>sand pack<\/em> or <em>filter pack<\/em>. The sand pack should fill the <em>annulus<\/em> (the space between the well casing\/screen and the edge of the borehole) to a point at least a foot above the top of the screen. The sand pack is then covered with a seal, usually a smectite clay called <em>bentonite<\/em>, which is purchased as dry pellets or a granular powder that swell when hydrated. This seals off the well screen from the upper part of the borehole and keeps surface water or water from overlying formations from moving down the borehole into the monitored zone. The remainder of the borehole is then backfilled with either cement, drill cuttings, or some combination of the two. The well must then be capped with a secure access cover.<\/p>\n<\/div>\n<div class=\"bc-figure figure\" data-custom-style=\"Captioned Figure\">\n<p><img decoding=\"async\" style=\"display: block; margin-left: auto; margin-right: auto; ;width: 3.2626in; height: 4.08369in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file37-2.png\" alt=\"\" \/><\/p>\n<div class=\"bc-figcaption figcaption\">\n<div data-custom-style=\"Image Caption\">\n<div class=\"figcaption-text\">\n<p><span id=\"Xda749547d65e814e1d96b66296c9ed37af4625a\" class=\"anchor\"><strong>Figure\u00a035\u00a0\u2011\u00a0<\/strong>Typical monitoring well construction.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>Shallow monitoring wells are usually installed using hollow\u2011stem augers. Once the required depth is reached, the PVS pipe is put together and inserted down the center of the auger. Sand is then poured in around the pipe, and the augers are pulled up a little bit so that the sand falls into the open borehole. This process is repeated until the screen is covered and the sand is in place. Then the bentonite pellets are added, and the augers are pulled out of the ground. If the bentonite seal is emplaced above the water table, water can be poured in to hydrate the bentonite. The rest of the hole is typically backfilled with cement, and the top of the well is secured with a cap and frequently enclosed within a manhole or protective metal vault.<\/p>\n<\/div>\n<\/div>\n<div id=\"well-development\" class=\"level3\">\n<h3>Well Development<\/h3>\n<div data-custom-style=\"First Paragraph\">\n<p>One of the big concerns with well construction is the amount of disturbance to the subsurface caused by drilling. Regardless of the method, the aquifer formation is always affected in some way. Problems related to disturbance include the following.<\/p>\n<\/div>\n<ul>\n<li>Lots of fine material may get into well screen and filter pack, which can clog or fill (known as silting up) the well.<\/li>\n<li>Drilling fluids (especially muds) flow into the formation and may clog pores.<\/li>\n<li>The drill bit can smear the walls of the borehole, closing off pores.<\/li>\n<li>A large volume of water and drilling fluids must be removed from the formation before samples representative of the formation can be obtained.<\/li>\n<\/ul>\n<div data-custom-style=\"First Paragraph\">\n<p>Following drilling and installation of the well, the effects of this disturbance must be corrected as best as possible. This process is called <em>development<\/em> of the well. Well development in water supply wells with relatively high yields generally entails pumping water from the well for an extended period, until the water runs clear. In low\u2011yield monitoring wells, if there is not enough water to sustain pumping then it may not be an option. Plungers can be put into wells to force water in and out of the screen for a period. Compressed air can also be forced down into the well to lift water and fine material out of the well screen. Usually, with monitoring wells, any water that was introduced during drilling must be removed so that groundwater samples accurately represent the formation.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p><em>US Geological Survey Water\u2011Resources Investigations Report 96\u20114233<\/em> (Lapham et al., 1996) is a good general source of information concerning well construction and development. This report is available as a free download from the USGS.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"footnotes footnotes-end-of-document\">\n<hr \/>\n<div class=\"bc-aside aside\" role=\"doc-footnote\">\n<div data-custom-style=\"Footnote Text\">\n<p><span data-custom-style=\"Footnote Reference\"><sup>3<\/sup> Drilling mud is a thick, heavy, and viscous fluid that is circulated through boreholes during drilling to cool and lubricate the drill bit, bring drill cuttings to the surface, and keep the open borehole from collapsing.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":8,"menu_order":21,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1162","chapter","type-chapter","status-publish","hentry"],"part":1486,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1162","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/users\/8"}],"version-history":[{"count":3,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1162\/revisions"}],"predecessor-version":[{"id":1857,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1162\/revisions\/1857"}],"part":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/parts\/1486"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1162\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/media?parent=1162"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapter-type?post=1162"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/contributor?post=1162"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/license?post=1162"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}