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4.2 QUALITY ASSURANCE/QUALITY CONTROL <br /> As part of the Quality Assurance/Quality Control a blind field duplicate was taken and <br /> submitted for analysis. Laboratory performance is the evaluated through Relative <br /> Percentage Difference (RPD). Acceptable limits are below 15-20%. RPD Results are <br /> listed in Table 4. To calculate the RPD, the following formula was used: <br /> I obsl-obs2 I x 100 <br /> mean <br /> Where: <br /> obsl =result of the original sample; <br /> F <br /> obs2=result of the duplicate sample; <br /> obsl-obs2=absolute value of the difference of the results; <br /> mean=mean of the two results. <br /> RPD results indicate good performance with RPD ranging from 0.0 to 12.99 percent. <br /> Greater variation for organic constituents TKN is observed. <br /> f Table 4 <br /> Relative Percentage Difference Results for Selected Analytes <br /> City of Riverbank WWTP <br /> MW-11 Duplicate RPD <br /> Parameter Result Result (%) <br /> Total Dissolved <br /> Solids (m /L) 600 590 1.68 <br /> Sodium (m ) 140 130 7.41 <br /> Chloride (m /L) 140 140 0.00 <br /> Total Kjeldahl <br /> Nitro en (m /L) 0.82 0.72 12.99 <br /> City of Riverbank Wastewater Treatment Plant Monitoring Well Installation <br /> DE Project No 109-06 May 2006 <br /> 12 Rev.0 <br />