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Limited Subsurface Investigation Report— City of Ripon / Madsen Sunrise Dairy, Ripon, California <br />September 30, 2010 <br />Based on the results of this investigation, additional subsurface investigation is warranted at the site. <br />Additional groundwater samples should be collected to further define and evaluate the nature of the <br />hydrocarbon impact to groundwater at the site. These samples should be analyzed using silica gel, cleanup to <br />potentially eliminate the contribution non -petroleum hydrocarbon compounds to future analytical results. <br />GR proposes the installation of three Cone -Penetrometer Test probes at the locations shown on Figure 4. <br />These probes will be fitted with groundwater sampling tools that are driven directly to the target depth in one <br />continuous motion. In addition, GR recommends the collection of one hydropunch groundwater sample also <br />shown on Figure 4. The proposed hydropunch boring will be drilled using hollow -stem augers which will <br />serve as a casing through which to advance the hydropunch tool thereby minimizing the potential for vertical <br />cross contamination from hydrocarbon impacted fill identified during the current investigation. A work plan <br />detailing our proposed scope of work and methods will be forthcoming. <br />In addition, GR recommends that additional excavation and sampling be conducted in the vicinity of soil <br />sample TW -13, collected at 13 feet bgs beneath the west end of the former, diesel UST. This scope of work <br />was previously proposed in GR's report number 25-948223.1, Limited Subsurface Assessment Work Plan, <br />dated April 15, 2010. The purpose of this work is provide vertical and lateral definition diesel impacted soil in <br />the vicinity of TW -13 (2000 ppm diesel) and to remove potentially diesel impacted soil which could be a future <br />source of groundwater contamination beneath the site. After the additional excavation and sampling, the <br />existing UST pit can be backfilled. It is GR's understanding that the SJCEHD has approved using the existing <br />pea gravel stockpile (currently temporarily stored in the UST pit) as backfill based on the composite samples <br />collected from the pea gravel during the UST removal. <br />25-948223.1-3 <br />