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Wongdeff From: John Lane <jlane@condorearth.com> Sent: Wednesday, April 15, 2020 1:00 PM To: Wong,Jeff Cc: Micheline Kipf;Zach Solow; kstroing@aol.com Subject: Following up on Pressure Grouting 3/4-inch Sparge Wells at Ranch Market Attachments: Grout Comparison Diagram.pdf Hi Jeff, Following up on your voice mail regarding using a tremie pipe to place grout in the 3/-inch sparge wells prior to pressure grouting them. I maintain that trying to use a tremie pipe/tube (1/2-diameter maybe?) in a 3/-inch casing that will be pressure grouted immediately after placing the grout hinders rather than helps the process. 1. There is approximately 10 feet of standing water column in each of the sparge wells (DTW= 32/33' in December 2019; DTB =42/43'); 2. There will still be 10 feet of standing water column within the tremie tube/pipe once it is placed; 3. The mixed grout is denser than the groundwater, so when it is placed in the tremie pipe/well,the grout displaces the standing groundwater, which is primarily forced into the formation in sandy soils like we have at the Site, although some GW may be forced to the surface; 4. The typical tremie pipe that is used by driller is 3/-inch PVC, because smaller diameters necessitate thinner grout, which makes the seal (the goal of well destructions) less effective; 5. Since the sparge wells are%-inch in diameter,they are effectively a tremie pipe; 6. Once the cement is placed (with or without tremie)the well will be pressurized to force grout into the formation and additional grout added as needed to create an effective seal; 7. The reason tremie pipe is effective when placing an annular grout seal is because it limits the possibility of bridging, cavitating the bore hole wall, and thinning the grout by preventing mixing with groundwater.This is accomplished through 3/-inch tremie pipe typically,the same diameter as the sparge wells. We don't have this same issue in a cased, 3/-inch well; 8. If we use a tremie, it would have to be about%2-inch diameter,which would actually promote bridging in the tremie using a typical grout mix/thickness. So, we would have to use thinner grout in a smaller than reasonable diameter tremie pipe; 9. The tremie pipe/tube itself will displace much of the volume of the 3/-inch sparge well so the process will be more incremental as the sections of pipe are removed (my guess is the tremie pipe will displace about half of the volume per foot). All of the above underscore the fact that using a tremie in these wells is not technically sound because 1)the %-inch casing is the same as a typical tremie pipe, 2) the grout will displace the standing GW because it is more dense,typically forcing the GW back into the sandy(SW) formation, 3) there is no opportunity for "splashing" of the grout in a %-inch pipe (effectively a tremie) as there might be in a 2-inch well (why we use a 3/-tremie), 4) the use of a very small diameter tremie (less than the typical %-inch diameter) would necessitate using a thinner grout mix, 5) the sparge well will be immediately pressurized to force the GW (now beneath the grout) and grout into the formation and additional grout will be added as needed. All that being said, if EHD requires that V&W Drilling use a tremie pipe against my recommendations as stated above, V&W Drilling would fashion a tremie from %-inch plastic tubing or PVC pipe (if the small diameter pipe can be located)to place the neat cement(thin mix) prior to pressurizing the well. Thank you,