WorldWide Drilling Resource

Plugging and Sealing an Unused Drilled Well Adapted from Information by Agriculture and Agri-Food Canada An open well no longer in use is a potential threat to groundwater quality in an aquifer and a physical risk to peo- ple and animals. Property owners are responsible for making sure unused wells are properly plugged and sealed. Because of the information need- ed and equipment required to plug deep drilled wells, licensed water well con- tractors are normally hired for the job. For those new to the trade or needing a refresher, the following information outl ines best practices for properly plugging and sealing unused drilled wells. The first step is to find out how the well was originally constructed. Key fac- tors include: . Total well depth. . Depth of casing. . Casing diameter and changes in diameter with depth. . Presence of a wel l screen or open hole in bedrock. . Static water level. . Soil type or types the well pass- es through. . Type of aquifer. . Type of original sealing materi- al, if any. If no water well record exists, con- tractors have to rely on measurements or their personal knowledge of local wells and groundwater conditions. Every well is different, so plugging and sealing procedures may be modi- fied for each well. As a contractor, you should do the following: . Remove the pumping equipment. . Remove the entire length of cas- ing from the hole, or, if the casing is old or corroded, leave it in place, puncturing if possible - ideally, the plugging material will seep through the casing to seal between the cas- ing and the side of the hole (the annular space). . Disinfect the well. . Fill the well screen or bedrock fractures with sand or gravel so grout will not penetrate the aquifer and plug fractures or pores. . Pump a carefully prepared plug- ging mixture, such as bentonite slurry and cement grout, from the bottom to the top of the well through a pipe. * As the grout or slurry f i l ls the well, water in the wel l is forced out the top. * If bentonite is used, it should be the type formulated specifically for plugging and seal ing water wells. . If the casing is left in the ground, cut the pipe off below ground level (at least 10 feet if possible), and fill the bottom of the excavation and space around the casing with the plugging mixture. . Ensure the casing is deep enough so future activities do not disturb the plugging mixture over the cas- ing. . Backfill the remaining hole with clean soil which is less permeable than the native soil (that is, con- taining more silt and clay - remem- 71 WorldWide Drilling Resource ® AUGUST 2014 0,2+ 675;,4 -57 5;,7 ',(78 /558, -753 +0--,7,49 35+,28 95 -09 >5:7 4,,+8 "(4.04. -753 36 95 36 4*2:+,8 %,/0*2, :36 #9(7904. (99,7> /(7.04. (4+ (4+ % 95 65<,7 &07,-,,+,78 0. (7708 "5(+ ,74+(2, ,< '571 $,2 (= &,) 809, <<< .,9,* *53 3(02 8(2,8 .,9,* *53 ',(78 5- =6,70,4*, 3(1, 9/08 204, 5- &,2+,78 (4 :43(9*/,+ !:(209> 75+:*9 04 95+(>?8 3(71,9 690548 04*2:+, 49,74(2 7,88:7, 536,48(904. 25< 549752 67,;,4904. (**0+,49(2 5;,786,,+ +(3(., 95 9/, &,2+,7 %,/0*2, :36 #9(7904. %5298 ( ,9,* ,=*2:80;, (99,7> /(7.04. %5298 (4+ % 95 65<,7 >5:7 0. :4 &07,-,,+ 589 536(*9 >+7(:20* &,2+,7 54 (71,9 (049,4(4*, 7,, ,80.4 0./9,89 >+7(:20* &,2+,7 54 (71,9 ber the “last out, first in” principle when excavating and backfilling the hole). . Mound the fill to allow for settle- ment. . Prepare a record showing the exact location of the plugged well and material used. . Keep the record on file and give a copy to any required authorities. Bentonite or Concrete Plug Well Casing Sand and Gravel Well Screen