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Work Plan—Site Sampling Page 10 West Weber Site -Stockton GPE Project 536.2 SCR-E3-1-2 Screen Point E3, 1 to 2 Feet S-VOCs,TEPH,CAM-17 SCR-E4-0-1 Screen Point E4,Surface-1 Foot S-VOCs,TEPH,CAM-17 SCR-E4-1-2 Screen Point E4, I to 2 Feet S-VOCs,TEPH,CAM-17 SCR-E5-0-1 Screen Point E5,Surface-1 Foot S-VOCs,TEPH,CAM-17 SCR-E5-1-2 Screen Point E5, 1 to 2 Feet S-VOCs,TEPH,CAM-17 Etc.... S-VOC=Semi-Volatile Organic Compounds TEPH=Total Extractable Diesel and Oil Range Hydrocarbons CAM-17=17 Priority Contaminant Heavy Metals 2.1.1.3 Random Shallow Soil Sample Points Fill material spreading field, Stockton Cold Stora The goal of sampling the soil spreading field is to verify that the fill material does not exceed a threshold contaminant level. In this case, the contaminant is assumed to be total petroleum hydrocarbons (TPH). The California LUFT guidelines have set the threshold level at 10 mg/Kg. In the event that soil sample(s) contain concentrations approaching this concentration, and depending on BTEX concentrations, a more thorough investigation and a formal Risk Assessment of the material may be needed. We assume, however, that the material will yield samples that contain non-detectable to trace TPH concentrations, and that the mean value will be much closer to non-detect than to the threshold. To determine the number and placement of sample points, a statistics-based sample planning program was used. The program is known as Visual Sample Plan (VSP), version 5.0. Pacific Northwest National Laboratory developed the software for the Department of Energy with support from the U.S. EPA. The scenario provided to the VSP software (Appendix C) included the following assumptions: • Sample data will be normally distributed, • Sample points are selected on a random basis, • The primary contaminant being measured is TPH-G, and the threshold action level is 10 mg/Kg, • The sample area will be found to be clean, • The probability of a sample producing either a false negative or a false positive reading is 5 percent, • There is a 95 percent chance that the suite of random samples will correctly determine if the area is adversely impacted with petroleum hydrocarbons. Based on this input scenario, the software determined that a suite of 13 random sample points would be needed, and the 13 points were then selected and designated (see Figure 5). 2.1.1.4 Background Sampling In assessing analytic sample results, it is important to distinguish between chemicals that occur naturally and those that have been introduced and may represent site contamination. Gaining an understanding of the naturally occurring background concentrations of the various chemicals that are being tested, facilitates this process. Most of the chemicals that are being tested for at this site (petroleum products, VOCs, S-VOCs and pesticides) are, for the most 2937 Veneman Avenue, Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto, Ca 95356 Fax: (209)569-0295