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• w 1 meter to sound. This point is usually clearly visible on the probe. If it is not visible it should -located by dipping the probe into a water container where the contact can be clearly seen, then , marked. The total-length of the water Tavel meter should correspond vvitli the jcngtli of the measuring tape_ In addition, the individual marks on the cable shouldcorrespond with the correct footage. If the cable does not match the measuring tape then the difference(f consistent) should be calculated- as a percentage, (i.c.; 100 foot cable measures 102. feet - 98'10)., All measurements with ibc cable should-then be .multiplied by 0.9s to correct for the error. If the individual footage marks are not placed correctly and arc not consistent in their deviation, the instrument should be replaced If the water level indicator is constructed of a cable then cah`braiion wiII be Pezforined once per year. If there is a discrepancy, the conversion factor will be marked directly on .the inst went. 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 instr=ent will.be recorded-and keptia a.binder-at the:office forfuture_ ! reference. The most recent calibration results will also be recorded in the teclMici=field notes. There is no specific form for water level indicator calibration. OH Meter PH is_sPbject to significant variations due to temgcrattuc, buffering capacity of the wager, and instrument drift- For this reason pH meters must be-c�'bcated before and ager sampling on ch.. day and at least once more during the day. To calibrate a pH meter the insUumtent reading is - a4usted to read correctly for solutions with a standard p$, Standard solutions arc mixed fresh, according to package loris,for each sampling event,' Standard solutions or powders for pH 4,7, and 10 are commercially available. These standards are purchased fresh and-discarded after shelf life has axpixzd. Shelf livesvary depending on the brand of standards used. If pre-prepared solution is used,the expiration date of the solution will be noted on the calibration log. Although different brands of pH meters vary, caBration procedures are similar for all of them.- A generalized calibration procedure follows: l. Turn on the instrument,check the battGty,and allow to warts up if necessary:. 23.493849•FO IU31 OR325 A-2 My 14,2M Cox 2M t;kW44a.tan.