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Evaluation of Natural Attenuation: 7500 West Eleventh Street, Tracy, CA Page 12 <br /> 1=� 3.0 MONITORING OF FLOATING PRODUCT <br /> k On February 24, 2005, Monitoring Wells MWFP-1 through MWFP-5 and groundwater- <br /> quality Monitoring Wells MW-7, MW-13 and MW-14 were checked for the presence of <br /> LNAPL floating on the groundwater by slowly lowering a hydrocarbon/water interface <br /> i probe into each well. As is recorded in Table 3, no floating product was detected in any <br /> of those wells except for Well MW-7, in which 0.02 ft. of floating product was measured. <br /> No floating product had previously been detected iTi Monitoring Well MW-7 since a <br /> thickness of less than 0.02 ft. was measured in that ?vel1 in April 2004. The 0.02 ft. of <br /> product in the well on February 24, 2005 had accumulated since the well was last purged <br /> on October 27, 2004. We note that 117 days had as since that date, while the span of <br /> time between October 27 and the previous monitoring round on July 26, 2004 was only <br /> 92 days. That difference in the elapsed time between purgings may, in part, account for <br /> the appearance of the small quantity of LNAPL in MW-7 on February 24, 2005. <br /> r=: However, we also note the generally-increasing trend in the concentrations of total <br /> petroleum hydrocarbons in that well since that well was subject to weekly purging of <br /> floating product in November 2003 (see Table 2). That data is consistent with SJC's <br /> previously-stated assessment (The San Joaquin Company Inc. 2004c, d, e) that the <br /> LNAPL that is present on the groundwater in the area of the plume in the region of <br /> Monitoring Well MW-7 is not likely to be efficiently abated by simple periodic <br /> i { <br /> extraction from a 2-in. diameter well. <br /> --I <br /> 4 <br /> >i <br /> i <br /> sic <br />