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Additional Soil and Groundwater Investigation and k. f Monitor Well Installation Report ` CSUS Multi-Campus Regional Center January 11,2002 -Page 16 .rose in the borings, suggesting the aquifer is .under confined or semi-confined conditions because'of the :overlying clays_. This sand bed varies slightly in depth and thickness between borings, but is.continuous across the site. The sand was identified in CPT logs for borings CPT1; CPT2, and CPT3 and in all three monitor well borings. Hydrocarbon: contamination. appears to, have moved primarily in a downward Cr, direction from the former tank location with some lateral spreading. Based on the extent of hydrocarbon impacted soil shown in Figure 7, Condor estimates approximately 3,000 cubic yards of hydrocarbon impacted soil remains in place at the site..'. Laboratory analytical results indicate that groundwater to depths of at least 81 feet bgs has been impacted. by petroleum hydrocarbons at .the site. TPH-G; benzene,-toluene, and`�1,2-DCA were detected in the :'groundwater samples from boring SP-1. TPH-GBTEX, kerosene, and 1,2-DCA were detected in the ' ;groundwater samples from boring SP-2. TPH-G, BTEX, TPH-,D, kerosene, motor oil; and, I;2-DCA were detected in the.groundwater samples from boring SP-3. " Toluene Was detected at a very:low concentration in the groundwater-sample from monitor well MW-1. TPH-G, benzene, toluene, and 1;2-DCA were detected.in the.groundwater sample from monitor well MW-2. TPH-G, BTEX, MTBE, tertiary-butanol, and�1,2-DCA were detected in the groundwater sample from monitor well MW-2. i Based on the laboratory.analytical results-of the groundwater samples, there is not enough information to 'define the groundwater plume either -vertically or horizontally. Hydrocarbon and gasoline oxygenate/additive concentrations in groundwater are greatest in�the vicinity of monitor well MW-3. The groundwater gradient is to the east.Monitor well MW-3:is to.the'southeast of the former tank location so 4 it may not be in the area of the plume with the highest hydrocarbon concentrations.. The results of the sensitive receptor survey indicate the presence of-one intact air conditioning well.(Wl in Figure 6, Appendix A) approximately 1,500 feet north of the site, one irrigation well (W2-in Figure 6, Appendix A) approximately 1,900 feet northeast of the site;. and one municipal well (W3 in Figure 6, Appendix A) approximately 1,400 feet south of the site'within the study area. The municipal well was not in use at the time of the survey. The location of two additional wells within the study area could.not be identified. No surface water bodies were identified within the search radius. One school, four child care ' facilities,and two senior care facilities were identified within the search radius. 8.0 RECOMMENDATIONS f Based on the results of the soil and groundwater investigation, Condor recommends the following: • Continued sampling and analysis of groundwaterfrommonitor wells MW-1, MW-2, and MW-3 on a ` quarterly schedule to monitor the impact of hydrocarbons on the groundwater beneath the site. g Y p Y .. - e Additional shallow and deep groundwater investigation in-�the-downgradient direction (east) of the . fsource area to further investigate the lateral and vertical extent of the contaminant pjume. Over-excavation of the.former tank site to the-saturated zone at a depth of approximately 3 8 feet to remove approximately 1,800 cubic yards of hydrocarbon contaminated soil from vadose zone in the source area. Specifically, Condor -recommends preparation of a work plan for the above proposed additional 'groundwater investigation and soil over-excavation. - NA { 'CONDOR '