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. • Page 2 of 2 <br /> Inspection <br /> Land Development Transportation Infrastructure Institutional Brownfields/Redevelopment Natural Resources <br /> From: Nuel Henderson [EH] [mailto:nhenderson@sjcehd.com] <br /> Sent: Tuesday, December 01, 2015 3:52 PM <br /> To: Rick Day <br /> Subject: Manteca Firing Range Question <br /> Rick, <br /> As you can tell I haven't quite finished my review and evaluation of the report of findings, mostly due to the work <br /> plow in my office. I am anxious to get my comment letter out, but at this point I do have a question on the <br /> statistical analysis and resultant mapping. I do not anticipate there to be any problem, but I want to understand <br /> how the data and analysis were applied. My question regards use of XRF data to infer the total lead content <br /> based on the correlation between measured values. <br /> Total lead concentrations exceeding 50 mg/kg were found to correlate to STLC concentrations exceeding 5 mg/I <br /> (California Hazardous) and total lead concentrations exceeding 135 mg/kg correlated with TCLP concentrations <br /> exceeding 5 mg/I (RCRA Hazardous). The correlation between the XRF data and total lead concentrations was <br /> found to be y = 15.764(x)0"'e. What I didn't see was the XRF concentration values that would be expected to <br /> correlate to the total lead concentrations of 50 mg/kg and 135 mg/kg, but it appears that the XRF data was <br /> directly utilized as total lead concentrations on the map. I've never really learned how to use fractional exponents, <br /> so I have no intuitive feel for the conversion of XRF to total lead data, but this implies to me a 1:1 correlation <br /> between XRF and total lead data. Is that correct or close? Can the XRF data be used directly for total lead, or am <br /> I missing something. Admittedly, statistics are not an area of strength for me. <br /> Nuel <br /> 12/16/2015 <br />