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Title: Sampling and Analysis Plan for Environmental Control Number: Revision Date: page 13 of 30 <br /> Groundwater Monitoring I PUE.EN.D.026.04 2/19/2020 <br /> comparable between labs(as required). QA/QC terms are described below as well as the steps <br /> that GCC will take to ensure these QA/QC practices are met. <br /> GCC achieves QA/QC requirements by ensuring that field meters are properly maintained and <br /> calibrated,accurate measurements and notes are recorded, field QA/QC samples are collected, <br /> proper sample collection and decontamination field procedures are performed,and a complete <br /> data review and validation(as described in Section 5.2)are performed. Analytical laboratories <br /> are expected to follow internal SOPs, perform required QA/QC sample analysis(e.g., method <br /> blanks,control samples,matrix spikes,and associated duplicates)and include the QA/QC data <br /> in the final analytical report. <br /> The following definitions describe terms typically used for data quality. <br /> Accuracy <br /> Accuracy is defined as the closeness of agreement between an observed value and an accepted <br /> reference value as reported by a laboratory. When applied to a set of observed values(such as <br /> field and laboratory QA sample results), accuracy estimates will reflect a combination of <br /> random and systematic (i.e., bias) components. In practice, accuracy estimates rely on a <br /> determination of the percent recovery measured in spiked samples: <br /> Recovery=%R=((Cs-Cu)/Cn)*100 <br /> where: <br /> Cs=Measured concentration of the spiked sample <br /> Cu=Measured concentration of the unspiked sample <br /> Cn = Nominal (theoretical) concentration increase resulting from spiking the <br /> sample, or the nominal concentration of the lab control sample. <br /> The purpose of reviewing accuracy is to ensure that the laboratories used to analyze samples <br /> collected pursuant to this SAP are accurate and meet data quality objectives. <br /> Precision <br /> Precision is defined as the agreement among a set of replicate measurements without <br /> assumption or knowledge of the true value. Precision is determined by taking the difference <br /> between two measured values and dividing by the average of the two samples to get what is <br /> known as the relative percent difference (RPD). The samples used for this assessment should <br /> contain concentrations of analyte above the laboratory's reporting limit, and may involve the <br /> use of matrix spikes. A quantifiable estimate of precision is made based on the RPD: <br /> RPD(%)_((C 1 -C2)/CAvg)*100 <br /> where: <br /> C 1 =Measured concentration of the first sample <br /> C2=Measured concentration of the sample duplicate/replicate <br /> CA,g=Average of the two concentrations. <br /> RPD and comparison criteria are described in Section 5.2.1. <br />