Laserfiche WebLink
\/ <br /> TETRA TECH,INC. <br /> Null Hypothesis: Concentrations of COPCs in groundwater and soil within the study area are above the <br /> screening levels and the rate of natural attenuation is insufficient to reduce concentrations below <br /> screening levels in the near future. <br /> False Rejection Error and Consequences: The data incorrectly indicate that the COC concentrations are <br /> naturally attenuating at a rapid rate (false negative result or low bias). Environmental impacts would be <br /> underestimated, resulting in a potential for unacceptable risk to human health. The tolerance for the false <br /> rejection error is extremely low, so any potential for false negatives or low bias would be scrutinized <br /> during data validation and reanalysis may he required. <br /> False Acceptance Error and Consequences: The data incorrectly indicate that the COC concentrations <br /> are not naturally attenuating at a rapid rate (false positive or high bias). Groundwater and soil <br /> remediation may be recommended,and the remediation costs would be higher than necessary. <br /> 3.7 STEP 7: DEVELOP THE PLAN FOR OBTAINING DATA <br /> 3.7.1 Selecting a Sampling Design <br /> Based on the location of samples collected during previous investigations, soil borings will be advanced <br /> in locations in the southern portion of the Site until groundwater is reached (Figure 3-1). The initial <br /> sampling design will entail six direct push technology (DPT) or hollow stem auger soil borings to <br /> groundwater, an expected depth of approximately 10 feet bgs. One groundwater sample, if encountered, <br /> will be collected per boring. One soil sample will be collected per boring. One passive soil gas sample <br /> will be collected in the vicinity of each soil boring. <br /> 3.7.2 Key Assumptions Supporting the Selected Design <br /> Groundwater has reportedly been encountered at depths ranging from 8 to 10 feet bgs. For planning <br /> purposes, a depth of 10 feet bgs is assumed; however, borings will be terminated when groundwater has <br /> been reached or at 50 feet bgs,whichever is encountered first. Actual boring depths may vary. <br /> Samples must be shipped daily for delivery to the off-site laboratory. It is assumed the off-site laboratory <br /> will have the capability to complete sample analyses within 24 hours, if needed. <br /> Sampling Effort Work Plan Page 3-5 <br /> Tracy Mansfield Property <br />