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Limited Groundwater Investigation 8 4.3 Quality Assurance/Quality Control (QA/QC) 4.3.1 Laboratory QA/QC. This section presents the data quality criteria that were met as part of the overall project objectives. Laboratory analyses were performed by APCL using accepted laboratory procedures in accordance with specified analytical protocols. APCL is a State certified Environmental Laboratory Accreditation Program (ELAP) testing laboratory for the analysis of Cr VI (EPA Test Method 7196) and metals (EPA Test Method 6010). The final approval for their ELAP certification for the EPA Test Methods Test Method 7199 is pending final approval. As such, EPA Test Method 7196 was conducted as a backup for the EPA Test Method 7199. The groundwater samples were reported to the method detection limit (MDLs) for each test method, achieving the lowest possible detection limits. Concentrations reported between the MDLs and Practical Quantitation limits (PQLs) are considered estimated concentrations and have a "J" qualifier associated with the sample result. Laboratory quality control acceptance criteria that were applied to samples analyzed during this project meet USEPA SW-846 requirements. Quality control results attributed to sample matrix effects were documented and noted in the laboratory reports.All laboratory QA/QC results were within acceptable control limits for the analysis conducted. These included continuing calibration, laboratory control spikes, and matrix spike/matrix spike duplicates samples. No analytes were found in the method blanks,with the exception of Cr (0.7 J µg/L) under EPA Test Method 6010 for the samples analyzed for the Lathrop facility. The concentration of Cr detected in the method blank was lower then the concentrations of Cr (total and dissolved) reported in the investigation samples, but at similar a concentration to equipment blank sample EQB-050701-2. 4.3.2 Field QA/QC Samples. Two duplicate groundwater samples LP-G1-Water/LP-G6-Water and FC-G3-Water/FC-G6-Water were collected as part of the groundwater sampling activities and are included in Table 1. The calculated relative percent differences (RPDs) for these samples are between zero to 104 percent for dissolved Cr VI, 57 to 84 percent for total Cr, and 14 to 118 percent for dissolved Cr. The Lathrop facility equipment blank sample associated with the groundwater sampling rods (EQB- 050701-3) contained detectable concentrations of total Cr (7.4 µg/L) and dissolved Cr (0.97 µg/L) (Table 1). Both concentrations were several orders of magnitude lower than the associated groundwater sample results, indicating that the detection of Cr in these samples had no impact on the environmental samples. Additionally, total and dissolved Cr was also detected in the soil sampling equipment blanks at concentration less than the groundwater samples. Dissolved Cr VI was not detected in the equipment blank samples. The French Camp equipment blank sample (EQB-050801-6) associated with the groundwater sampling rods also contained detectable concentrations of total Cr (4.5 J µg/L) and dissolved Cr (2.3 J µg/L) (Table 1). Total Cr concentrations in three of the five groundwater samples (FC-G1, FC-G4 and FC-G5) were higher than the total Cr concentration detected in the equipment blank. However, dissolved Cr concentrations in groundwater from sampling locations FC-G2 (3.5 J µg/L) and FC- G3 (5.2 µg/L) were close to the equipment blank concentration. Groundwater collected from sample location FC-G1 had a lower concentration of dissolved Cr (1.8 J µg/L) than the associated equipment blank (2.3 J µg/L). For the remaining groundwater samples (FC-G2 through FC-G5), dissolved Cr concentrations were higher than the equipment blank sample. Dissolved Cr VI was not detected in the equipment blank samples. PAwp\jobs\20587\LP—FCG\T'.doc—DCN 102300 June 2001