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meter to sound. This point is usually clearly visible on the probe, If it is not visible it should k� located by dipping the probe into a water container where the contact'can be cl early seem, then- 1. 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 cnf consistent) should be calculated. as a percentage, (Le 100 foot cable measures IO2 feet = 98"/a}. A11 measurements with the cable should-then be multiplied by 0.98 to eorr-ect for the error. if the individual footage marksarc not placed correctly and arc not consistent their deviation, the instrument should be replaced. If the water level indicator is constructed of a cable then calibration willbeperfotzned 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.. Calxibration data for each instrument will be-recorded-and keptia a.binder at the:office forfeiture_ - reference, 'Ihe most recent call-bration results will also be recorded in the technicians field notesThcrc . is no specific form for water level indicator calibration. —HH Meter PH is subject to significant variations due to temperature, buffering capacity of the water, and instrument drift For this reason pH metersmust be-calibratedbefore and after sampling on each.. day:and at least once more during the day. To calibrate a pH meter the instrurnent reading is adjusted to read correctly for solutions with a standard pH. - Standard solutions are mined fresh, according to package kens,for each sampling event. Standard solutions or powders for pH 4, 7, and I0 are commercially Available- 1hese standards .arc FMchased fresh and'discarded after shelf life has cid. Shelf lives vary depending on the brand of standards used. if pre--prepared solution is used,the expiration daze of the solution will be noted on the calibration log. Although different brands of pH meters vary, calibration proccdum are similar for all of them.. A generalized calibration procedure follows: l. Turn on the instrument,check the battery,and allow to wam up if accessary;. _- .23.4838451-FO I%23l0R'325 A-2 July 14,2404 2000 xkwtWa,tae.