Ground Water Monitoring Activities Arkansas River Valley Alluvial Aquifer 94-95

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0299 QUALITY ASSURANCE /QUALITY CONTROL SAMPLE COLLECTION METHODS All samples were collected in accordance with the Non -Point Source Task Force protocol for sampling of ground water. Samples were collected from existing wells via outside hydrants or whatever means available prior to any type of treatment (i.e. water softener). As a rule of thumb, three times the volume of water in the well casing plus any volume contained within the associated piping was purged prior to sampling. Rather than attempt to calculate these volumes, a determination of when fresh formation water has reached the point of sampling was verified by measuring pH, conductivity and temperature. A field portable instrument for measuring pH, conductivity and temperature was used for this purpose at each well site. For each well, the pH, conductivity and temperature were measured at periodic intervals (approximately every 5 minutes) while the well was being purged. Water samples were collected when solution chemistry of the ground water had stabilized such that three consecutive readings were within 5 %. It can be reasonably assumed that a stabilization in the values of these parameters indicates that the casing and piping have been purged and fresh formation water had reached the sampling point. Negative bias (loss of constituent) is of significant concern in sampling for volatile compounds. Therefore, great care was taken in sample collection to minimize degassing by operating the sampling port at a low volume. Samples for volatile constituents and those samples which require field filtration were collected first. Samples for nitrate and inorganic analysis were collected next. Samples collected for dissolved metals analysis were filtered in the field with a 0.45 micron size filter. In addition, the sampling team collected quality assurance samples consisting of field blanks, periodic duplicate samples, and spiked samples. Field blanks were utilized for field QA/QC performance and subjected to all conditions to which the samples were exposed. Duplicate and spiked samples were prepared for lab calibration checks. The following types of samples were provided for quality assurance: 1. Field Blank A blank ground water sample was periodically collected to check field decontamination procedures. The blank was prepared by pouring laboratory supplied deionized water through decontaminated sampling equipment following the collection of possible contaminated samples. 2. Duplicates Random duplicate groundwater samples were collected to compare laboratory analysis procedures as well as sample collection procedure.