Laserfiche WebLink
../ <br /> TETRA TECH,INC. <br /> 3.4.3 Scale of Inference <br /> It is anticipated that environmental conditions are not uniform throughout the study area. Hot spots may <br /> exist. <br /> 3.5 STEP 5: DEVELOP THE ANALYTIC APPROACH <br /> 3.5.1 Screening Levels <br /> Concentrations of TPH-D, TPH-G, TPH-O, VOCs, and SVOCs will be compared to SFBRWQCB ESLs <br /> (SFBRWQCB 2013). Screening levels relevant to this sampling effort are provided for each COC in <br /> Table 3-1. <br /> 3.5.2 Decision Rules <br /> Decision rules will not necessarily be applied to data obtained during this sampling effort. Concentrations <br /> of COCs in groundwater, soil, and soil gas will be compared to the data obtained during previous Site <br /> sampling efforts in nearby borings to evaluate the rate of natural attenuation of COCs at the Site and the <br /> potential need for vapor intrusion mitigation measures in new building construction. <br /> 3.6 STEP 6: SPECIFY THE PERFORMANCE OR ACCEPTANCE CRITERIA <br /> 3.6.1 Baseline and Alternative Conditions <br /> The baseline condition at the Site is "releases of COCl at the Site have impacted and groundwater, soil, <br /> and soil gas with fuel constituents, VOCs, and SVOCs at concentrations greater than the respective <br /> screening levels, and the rate of natural attenuation is insignificant." The alternative condition is <br /> "releases of COCs at the Site have impacted and groundwater with fuel constituents, VOCs, and SVOCs <br /> at concentrations greater than the respective screening levels, and the rate of natural attenuation is <br /> sufficient to reduce concentrations below screening levels." Hence,the statistical hypotheses are: <br /> Ho: Concentrations of COCs in groundwater within the study area are above the screening levels and the <br /> rate of natural attenuation is insufficient to reduce concentrations below screening levels in the near <br /> future; and <br /> Ha: Concentrations of COCl in groundwater within the study area are below the screening levels, or are <br /> above the screening levels and the rate of natural attenuation is sufficient to reduce concentrations below <br /> screening levels in the near future. <br /> 3.6.2 Consequences of Decision Errors <br /> The decision errors inherent in selecting sampling locations and analyzing chemicals consist of potential <br /> errors in sample design, location, heterogeneity, and sample analysis. Samples are biased based on <br /> former operations at the Site, observations made and samples collected during previous investigations, <br /> and the expected path of potential migration. The acceptable range of decision errors due to analytical <br /> errors will be evaluated during the data review,evaluation, and validation process. Data found outside of <br /> acceptance criteria during validation will be qualified as estimated or rejected,as appropriate. The nature <br /> of the deficiency and the proximity to the associated comparison criteria level and other quality control <br /> measures, such as field duplicates, will be used to assess the usability of the data. Adherence to quality <br /> control protocols should reduce the probability of decision errors. <br /> Page 3-4 Sampling Effort Work Plan <br /> Tracy Mansfield Property <br />