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RECOMMENDATIONS FOR HEXAVALENT CHROMIUM SAMPLE COLLECTION AND PRESERVATION The method DHS specifies for the determination of Cr(VI) in drinking water is EPA method 218.6 "Determination of.Dissolved Hexavalent Chromium in Drinking Water, Groundwater, and Industrial Wastewater Effluents by Ion Chromatography". As indicated in the title,this method was originally devised to be applicable to a broad range of aqueous samples, including industrial wastewaters, i.e., it was not primarily intended for the analysis of drinking water. As such, the method provides some latitude in terms of sample preservation and pretreatment, stipulating that consideration should be given to the type of data required. Considering the specific situation with drinking water, the Department provides the following guidance with regard to sample filtration,pH adjustment, and sample transportation and storage: (1) Filtration of samples immediately following sample collection is not recommended. Drinking water samples are typically low in particulate matter and performing filtration in the field without the potential of adsorption losses and/or contamination is difficult. Filtration of drinking water samples is also not performed in the determination of other trace metal contaminants. Filtration of samples immediately prior to the ion chromato- graphic determination is recommended in order to protect the analytical instrumentation, v i.e., to avoid premature clogging of the guard column. (2) Immediately following collection, the pH of samples should be adjusted to the range 9.0-9.5 in order to minimize the potential loss of Cr(VI) through chemical reduction. With some water samples it may be difficult to ieve-the- s' pH with the ammonium sulfate/hydroxide buffer prescribed'by.EPA 218.6 (e.g.,--�olorado River water) without adding so much sulfate that the subsequent ion chror{atographic analysis is compromised through analytical column overloading. For water samples exhibiting this problem, the Department suggests the use of a modified pH-adjustment buffer that contains ten times less ammonium sulfate (33 g/L)but the same concentration of ammonium hydroxide as the buffer prescribed in EPA 218.6. It should be noted however, that at the present time the Department does not have sufficient data to determine whether this modified buffer is adequate for all types of drinking water samples. (3) Samples must be cooled to 4 °C during transport and storage and analyzed within 24 hours of collection. SCREENING FOR HEXAVALENT CHROMIUM USING TOTAL CHROMIUM ANALYSIS The Department's present DLR for Cr(VI) is 1 µg/L This value was originally derived from a single-laboratory MDL of 0.2 gg/L using a multiplier of five. In order to be consistent with the DLR for Cr(VI) of 1 gg/L, any analytical technique for measuring total chromium which is to serve as a screening tool for Cr(VI) must be capable of UCMR Guidance,January 30,2001 Page 3