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Mr. Jim Barton RWQCB March 29, 2013 Page 10 a) The system passes if maximum vacuum stays within 10 percent of the pump vacuum or 2.1 in Hg for 1 minute. b) If the system fails the leak test, remove and reattach the sample tubing at the Sample T and retest. If the system fails the leak test. again, all downhole sampling equipment will need to be removed and the sampling process restarted at Step 4 (the aboveground leak test). 15) Once the downhole leak test is passed and while the system is still under vacuum, retract the,probe 2 to 3 inches to detach the tip and expose the screen. Monitor the vacuum gauge to determine whether the formation(lithology)will yield a sample. a) The time it takes for the vacuum gauge needle to return to zero is called "recovery time." The recovery time should be noted for each sample taken, as this information will allow relative comparison of soil permeability. Samples taken when recovery times are greater than 10 minutes should be considered suspect because the effect of any leakage in the sampling system is increased with longer recovery times. After 10 minutes, the operator should consider either changing the sampling depth, location, or length of pullback from the sampling tip. b) There are three possible vacuum gauge responses to pulling on the sample string: i) If the needle on the gauge does not move: (1) It indicates that the sampling train is plugged or the tip did not open. If this problem occurs, check the sampling train, drive- the probe an additional 2 feet bgs, and reattempt sample collection. ii) If the vacuum gauge does register a change (including an increased vacuum reading),but the vacuum stays high: (1) It may indicate that the soil at the sampling depth is saturated or that the pore space is too tight (due to cemented or,fine materials) to yield a sample. It could also indicate that the sampling train is plugged. If this problem occurs,pull the sample string up another 3 inches. (a) If the same amount of vacuum is maintained after 10 minutes,then the formation is too tight to collect a sample. Drive the probe an additional 2 feet bgs, and reattempt sample collection. (b) If the recovery time (the time for the system to return to zero vacuum [zero in Hg]) is more than 10 minutes, then the formation is too tight to collect a XM•S