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Groundwater Sampling an Analysis Plan Former Texaco Service Station Chevron Site ID 309075 January 14, 2011 3.0 PROPOSED SCOPE OF WORK `J ARCADIS reviewed chromatograms for the groundwater samples collected from MW-1, MW-2, MW-3, MW-4, MW-5, MW-6, and MW-6D during the first semiannual groundwater monitoring and sampling event, conducted on June 15, 2010. TPH-DRO and TPH-MO sample chromatograms were reviewed and compared to the standard TPH-DRO and TPH-MO chromatograms (Attachment E). Most of the chromatograms reviewed are uncharacteristic compared to the respective standards. ARCADIS recommends further evaluation of the petroleum hydrocarbons being detected onsite through a laboratory library search. The library search will be conducted on the groundwater samples collected during the first semi-annual 2011 monitoring and sampling event. The first semiannual event is typically scheduled for June; however ARCADIS proposes moving the sampling event to April and the subsequent second semiannual monitoring and sampling event to October. 3.1 EVALUATION OF TPH-DRO AND TPH-MO DETECTIONS u Further evaluation of the nature of the organics being measured and reported as TPH-DRO and TPH-MO (as described in Section 3.1.1 below) will be limited to monitoring wells with detections of TPH-DRO and TPH-MO exceeding 100 micrograms per liter (pg/L). A minimum organics ,J mass of 100 pg/L should provide adequate resolvable peaks for this evaluation and is consistent with the Water Quality Objectives (WQO) for TPH-DRO and TPH-MO. .� 3.1.1 Methodology Following a three volume well purge, split samples consisting of three 1 liter (L) amber bottles will be collected from each well. The samples will be sent to an appropriate laboratory and the laboratory will solvent extract each of the three 1 L bottles, resulting in three aliquots of sample extract per well. One aliquot of sample will be analyzed by USEPA Method 8015 for TPH-DRO and TPH-MO. If the TPH-DRO/TPH-MO results are greater than 100 pg/L, the remaining two aliquots will be further analyzed. One of the remaining two aliquots of extract will be passed through 10 grams of silica gel to remove polar compounds (in general accordance with USEPA Method 3630C) and the cleaned up extract will be analyzed by USEPA Method 8015 for TPH-DRO and TPH-MO. The silica gel sample and the non-silica gel sample TPH-DRO and TPH-MO results will be evaluated as follows: • Comparison of the TPH-DRO and TPH-MO concentrations to evaluate the proportion of polar versus non-polar compounds present o The silica gel sample and non-silica gel sample TPH-DRO and TPH-MO chromatograms will be compared to one another and to the laboratory diesel and motor oil standard chromatograms. The comparison will include an evaluation of peak retention times and distribution patterns, or any other distinguishing characteristics. Among other things, the lJ \\CA5FP\Data\Aproject\ENV\CHEVRON\309075\6 Deliverables\Work Plan\SAP\309075_SAP_6671110950.doc 3 U