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<br />is 150 mm or larger as the filtration rate is quite slow. <br />• Polyethylene back up discs will improve the filtration rate <br />and reduce the frequency of paper ruptures. When the sample <br />contains a large quantity of suspended solids, prefiltering <br />the sample through a medium fast paper such as Whatman No. 7 <br />will improve the efficiency of the procedure. Because of the <br />slaw vacuum filtration rate, the lab should be equipped to <br />filter six samples simultaneously. <br />For pH adjustment, the preservative should be added in just <br />less than the quantity that e::perience dictates will be <br />required. The bottle should 6e shaken and the pH measured <br />using wide range pH paper. The final quantity of <br />preservative is then added a few drops at a time. A 50 ml <br />graduated cylinder and dropper pipette should be used to add <br />the preservatve. The pH paper should be calibrated against <br />the field pH meter on the same sample from time to time. <br />All field apparatus should be rinsed with distilled water <br />between samples. A supply of distilled water, some 500-600 <br />ml beakers and 500 ml wash bottles should be on hand at the <br />sample site. All this should be available at the mill <br />analytical lab. <br />Quality control consists of replicating samples and <br />• submitting blanle samples of distilled water. This should be <br />done on a frequency of 1:20 or less if so indicated. <br />"Spiked" samples should be submitted on the same <br />frequencies. This is particularly so with respect to <br />mercury. In addition samples of the preservatives should be <br />analyzed far mercury. Standard mercury solutions, 12.5 mg/1 <br />concentration, are available from Hach chemical Co. The <br />spike is prepared by dilution of the standard to <br />concentrations in the range of 0.005-D.O1D mg/1. Standard <br />solutions are available for preparation of spiked samples <br />for other parameters. <br />Test kits are available for monitoring waste waters; <br />however, many of these I:its employ calorimetric and similar <br />methods which are not EPA approved. Therefore they are <br />suitable only for screening purposes. <br />• -28- <br /> <br />