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0 <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES <br /> July 2,2009 Reference No.241729 <br /> -2- <br /> expected to have analyte concentrations exceeding this value. This type of background value is suitable <br /> for individual point-comparisons;in this case the monitoring well results. <br /> During calculation of the background values(95/95 UTLs), the considerations listed under <br /> Title 27 S. 20415(e)(9)will be appropriately assessed.essed. Specifically,the following items will be addressed <br /> to assess the data: <br /> i) Data Distribution:Each parameter will be tested to determine if a normal,gamma,or lognormal <br /> distribution describes the background data set(for discussion of distributional fit tests refer to <br /> USEPA's ProUCL 4.00.04 Draft Technical Guide,2009,and USEPA's QA-G9S Data Quality <br /> Assessment:Statistical Methods for Practioners,2006,documents). The method for calculating an <br /> appropriate UTL will be based on the observed data distribution. If no suitable distribution is <br /> identified,then a non-parametric(rank-based)statistical UTL will be used; <br /> ii) Censored data:If monitored parameter concentrations are below the appropriate practical quantitation <br /> limits under CCR guidance(Appendix IX to Chapter 14 of Division 4.5 of Title 22),resulting in <br /> censored(non-detect)results,the presence of these non-detect data will be accommodated <br /> appropriately per methods recommended in USEPA's ProUCL 4.00.04 Draft Technical Guide(2009). <br /> In particular,the Kaplan-Meier(KM)method will be used in the calculation of sample means and <br /> standard deviations required for UTL calculations;and <br /> iii) Outliers: The background data sets will be assessed for outliers(using the methods presented in <br /> USEPA's QA-G9s,2006,guidance)prior to UTL calculations. Outliers will be interpreted on a <br /> case-by-case basis,and may be excluded from background value calculations if they are not <br /> concluded to represent a shift in background conditions(e.g.,trend)unrelated to any site effects. <br /> 2.0 CONSTITUENTS FOR CALCULATION OF BACKGROUND CONDITIONS <br /> As indicated in the RWQCB review of June 10,2009,the background and intraplume concentrations of <br /> constituents of concern (COCs),such as petroleum hydrocarbons,do not require a calculation of <br /> background conditions.The following constituents(non-COC and dissolved lead)will be used to <br /> calculate background conditions for the Site,using the indicated analytical methods and frequency of <br /> sampling. <br /> Frequency of <br /> FChd <br /> ent Anal ticaIMethod Sampling <br /> ivi Field measurement Quarterly <br /> Field measurement Quarterly <br /> ,Nitrate,Sulfate EPA Method 300 series Quarterly <br /> solved solids S EPA Mthod 160.1 Quarterlminerals:calcium,copper,totalum,manganese, otassium,sodium and zinc Method 200.7/200.8/6020 Quarters <br /> Dissolved lead EPA Method 200.8/6020 Quarterly <br /> Worldwide Engineering, Environmental, Construction, and nr Services <br />