Filtration Preservation Study of Groundwater Samples

Introduction: Since 1977, industrial and municipal facilities have been required to monitor groundwater according to their specific Wisconsin Pollutant Discharge Elimination System Permit. Department guidelines for groundwater sampling contain specific recommendations for proper purging of wells, thorough rinsing, and equipment used, etc. (see Groundwater Sampling Procedures Guidance Document, Dave Sauer, et.al.). This guideline recognized that considerable time and expense is required to perform in-field filtering. As a result, the option to filter nonmetal samples in the laboratory has been accepted, provided it is done as soon as possible.

A study was conducted to analyze the validity of this policy during the summer of 1986. The specific purpose of the study was to determine effects on laboratory analytical results of groundwater when sample filtration and/or preservation is done immediately on the site as compared to results obtained when filtering and/or preservation is done 24 hours later. Parameters analyzed in the study were ammonia nitrogen, Kjeldahl nitrogen, nitrate plus nitrite nitrogen, chlorides, total dissolved solids (TDS), and chemical oxygen demand (COD).