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20 <br /> 604 <br /> TE <br /> from the subsurface The percent CO2 wasRrangingAbetween7111^and3 <br /> 1 . 25 percent from February 23 , 1993 (7831 hours of operation) to <br /> May 14, 1993 (9721 hours of operation) . The latest sampling, <br /> June 18, 1993 (10562 hours of operation) show a decrease in the <br /> CO2 to 0 7516 or a 40°s reduction Indicating significant removal <br /> of the amount of hydrocarbons available for oxidation (both <br /> biological and chemical) . <br /> Concerning pulsing the system, presently the system pulses <br /> itself. When the blowers reach too high of a temperature, they <br /> will automatically shut off. This automatic shut off occurs <br /> during the late morning until the early evening hours . The two <br /> blower system will operate for one half hour, then one of the <br /> blowers will shut off for its cool down, which last approximately <br /> 20 minutes The lone operating blower will then shut off <br /> approximately 5 minutes later for its 20 minute cool down This <br /> continues through out the day, until ambient temperatures cool to <br /> allow continue operation of the blowers during evening to early <br /> morning hours (8 00 PM - 10 . 00 AM) <br /> A typical vacuum run (pulsing) during daytime hours is as <br /> follows . Both blowers are running until approximately 10 00 AM, <br /> blower ##1 shuts off for 20 minute cool down At 10 05 AM, blower <br /> #2 shuts down for 20 minute cool down At 10 20 AM, blower #1 <br /> starts and at 10 .25 AM, blower #2 starts . Both blowers operate <br /> until 10 50 AM, when blower #1 again shuts off for 20 minute cool <br /> down In a two and one half hour period, the vacuum system <br /> operates at full capacity - 2 blowers (78-89 cfm) 50°s, with one <br /> blower (35-40 cfm) 20%s and is off 3001 . This indicates that, in a <br /> 24 hour period, the system operates 19 hours under full vacuum, 2 <br /> i� hours under 1/2 vacuum and is off for 3 hours <br /> CONFIRMATION SAMPLING <br /> Three areas of residual contamination have been designated, Area <br /> A (encompasses the western pump island - pump island #1) , Area B, <br /> (encompasses the eastern tank field area) and Area C <br /> (encompassess the eastern tank field - pump island #3) , see <br /> Figure 3A. <br /> Area A, confirmation soil sampling by soil boring VSB5 indicated <br /> that .in July, 1992 contamination was still present. PHS/RHD <br /> requests a m.zn.imum of one confirmation soil borings in Area A. <br /> Area B, confirmation soil sampling by soil borings VSB3, VSB9, <br /> and VSB11 .indicated that an July, 1992 contamination was stall <br /> present an an area of lateral extent approximately 40 feet by 20 <br /> feet PHS/EHD requests a minimum o two confirmation soal borings <br /> an Area B. <br /> Area C, confirmation soil sampling by soil boring SB4 and <br /> sampling for destruction of vapor extraction well P1 indicated <br /> minor amounts of TPH-gasoline at the 35 foot depth of SB4 of 6 <br /> PPm and 60 ppb xylenes. PHS/EHD considers this area remediated. <br /> COMMENTS: An evaluations of the number and placement for <br /> confirmation sample borings will be made after results from <br /> page 2 <br />