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meter to sound. This point is usually clearly visible on the probe. 'if it is tot visible it should e 1 .located by dipping the probe into, a water container where the contact-can be cl e4Y seen, n, marked. The total length of the water level meter should correspond with the length of-the measuring tape. In addition, the individual marks on the cable should correspond with the correct footage. If the cable does not match the measuring tape then the difference Cif consistent) should be calculated. as a .percentage, (Le, 100 foot cele measures 102. feet 989/0).. All meastirements with the cable should-then be multiplied by 0.98 to correct for the error. If the individual footage mirks are not placed correctly and are not consistent in their deviation, the irLitrument should be replaced. If the water level indicator is constructed ®f:a cable then cahibration will be peifortned once per year. If there is a discrepancy, the conversion factor will be marked directly on the instrument Water level indicators constructed of tape are more subject to stretching and should be calibrated every 6 months and marked with the appropriate conversion.. Calibration data for each instrument will be.recorded.and keptin a.binder•at,the:office for-f rture_-. - reference. The most recent calibration results will also be recorded in the technicians field notes. Therc is no specific form for water level indicator calibration. H Meter k pH is subject to significant variations due to temperatltte, bufferingcapacity of the water, and instniment drift-For this reason pH meters must be-cali'bza#ed before and after sampling on each.. day and at least once more during the day_ To c ah-trate a pH meter the .instrument reading is 4usted to read correctly for solutions with a standard pK Standard solutions are mixed fresh, according to package instructions,-for each sampling-event. Standard solutions or powders for pH 4, 1, and 10 are commercially available. These standards .are purdwed fresh and-discarded after shelf life has Shelf lives vary depending on the brand of standards used,If pre-prepared solution is used; the expiration datte of the solution will be noted on the calibration log. Although different brands of pH meters vary, calibration pr=xIures are similar for all of them.- A generalized calibration procedure follows: 1. Turn on the instriunent, check the barter., and allow to warm up if necessary.. 23-483849-FO 1t2310R325 A-2 July 14,2004 2000�:kta!etdet,tar.