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i Addendum to Work Plan for Soil and Groundwater Assessment/Excavation 2 Barbara Drake, 26485 North Thornton Rd.,Thornton, CA January 27, 1995 Task 4 - Soil and Groundwater Sampling - Groundwater Technology will contact a SJCPHS-EHD representative at least 48 hours prior to the date the sampling rig will be on site. Sampling equipment will be decontaminated between each sampling run using a tri-sodium phosphate water solution (or similar) and a clean-water rinse. Groundwater and soil samples will be analyzed by a State-certified analytical laboratory for benzene, toluene, ethylbenzene and xylenes (BTEX) by Environmental Protection Agency (EPA) method 8020, and for total petroleum hydrocarbons-as-gasoline (TPH-G) by EPA method modified 8015. Samples will be delivered to the laboratory under chain-of-custody manifest. Task 5 - The report submitted to summarize the scope of work will include a copy of the laboratory analytical results of all samples submitted for analysis which typically includes QA/QC data sheets, and copies of the chain-of-custody manifests. Chromatogram from each sample and the daily standard will be requested and attached with their respective laboratory reports. In addition to the above material, I have attached a copy of the access agreement reached between the current property owner and the responsible party (Attachment 2). 1 Groundwater Technology recommends that the next phase of soil and groundwater sampling precede the excavation of hydrocarbon-impacted soil for two reasons. First, soil and groundwater sampling will provide additional data regarding the extent and magnitude of hydrocarbon-impacted soil and groundwater which could prove vital In determining the correct method of remediation at the site. Second, due to the recent heavy precipitation, groundwater levels are likely to recharge to very shallow depths below surface. Excavation of hydrocarbon-impacted soil would therefore involve significant dewatering and shoring of the excavation cavity causing costs for the excavation remedial alternative to escalate. Groundwater Technology is prepared to begin the next-phase of investigation at the site within two weeks of work plan and permit approval by the SJCPHS-EHD. Surveying is planned for January 25, 1995. Adjustments to the proposed well locations will be made, if needed, to better fit groundwater gradients at the site. Once the field work is complete, the report will be submitted approximately four weeks after the receipt of laboratory analytical results. 0053add:ltr(mist-15) GROUNDWATER ❑D❑ TECHNOLOGY