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' 3291 S.Highway 99 Page 7 <br /> Soil Boring Installation <br /> ' GPE Project 471.2 <br /> August 17,2007 <br /> ' 3.0 Conclusions & Recommendations <br /> 3.1 Conclusions <br /> The conclusions presented below are based on an interpreta ion of the data <br /> collected during the completion of this investigation, and of historical <br /> information obtained during a previous Phase I ESA: <br /> 1. None of the organic chemicals tested for were detected in any of the <br /> samples. <br /> 2. Low levels of several metals were reported in all samples. None of the <br /> reported metals concentrations exceed regulatory actin levels except <br /> ' for arsenic in both soil samples. <br /> 3. Arsenic is a naturally occurring trace metal commonly found in rocks <br /> and soils of California. In cases where the regulatory ction levels are <br /> exceeded by a particular chemical, no action is required or warranted <br /> in cases where the chemical in question is due to a natural background <br /> concentration. In this investigation, no samples were collected to <br /> determine the natural background arsenic concentration at this site, <br /> but in 1995, the Lawrence Berkeley National Laboratory conducted a <br /> ' study that showed that background arsenic concentrations in northern <br /> California can reach as high as 40 parts per million, and <br /> concentrations of 10 or more ppm are fairly common. <br /> 4. In this case, the previous remedial investigation identified lead as the <br /> ' only inorganic contaminant. As part of the remedial investigation, a <br /> sample from the septic tank collected on May 6, 1998 contained only 40 <br /> parts per billion of arsenic, which would meet safe drinking water <br /> standards. <br /> 5. Taken as a whole, these facts suggest the arsenic contained in the soil <br /> samples represents the background level of a naturally occurring <br /> chemical and is not suggestive of residual contamination. The <br /> ' remarkable consistence of 11 ppm of arsenic in both soil samples would <br /> also seem to support this conclusion. <br /> 3.2 Recommendations <br /> Based on the conclusions discussed above, Geo-Phase Environmental, Inc. <br /> recommends no additional work to investigate environmental conditions <br /> associated with the release of circuit board rinseate previously documented <br /> and investigated. <br /> 2937 Veneman Avenue, Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 <br /> Modesto, Ca 95356 Fax: (209) 569-0295 <br /> 1 <br />