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Lvvi <br /> A <br /> ss <br /> O C I A T E S I N C <br /> Average concentration of TPHg in goundwatersample <br /> = (27.000+19,000+20,000)13 ug TPHg x 1 ka x 378 L x 7,950 -gal1 L Water 1,000,000,000 ug 1 gal 1 day <br /> = 0 66 kq TPHg x 22 Ib = 1 45 pounds of TPHg removed per day <br />' day 1 kg <br /> Average concentration of benzene in groundwater sample <br /> t = (38+36+39)/3 ua benzene x 1 k x 3 78 L x 7,950 pal <br /> 1 L Water 1,000,000,000 ug 1 gal 1 day <br />' = 0 0011 ka benzene x 2 2 Ib = 0 0025 pounds of benzene removed per day <br /> day 1 kg <br /> ' 4.0 DISCUSSION <br /> The groundwater extraction pilot test yielded a pumping rate of approximately 5 55 gpm and a <br /> ROI of approximately 85 feet As shown in Section 3 5, approximately 2 90 pounds of TPHg and <br /> 0 005 pounds of benzene were removed during the 48-hour groundwater pumping pilot test <br /> Assuming that a permanent groundwater extraction pump would be Installed in MW-3, the ROI <br /> would extend beyond the eastern edge of the site beneath Stockton Street and the northern edge <br /> ' beneath West Second Street Installation of a groundwater extraction and treatment system would <br /> reduce the potential for impacted groundwater in the vicinity of MW-3 to migrate off-site <br /> ' 5.0 RECOMMENDATIONS <br /> As indicated in Section 4 0, Installation of a groundwater extraction and treatment system would <br /> 1 reduce the potential for impacted groundwater in the vicinity of MW-3 to migrate off-site <br /> However, based on quarterly groundwater monitoring data collected subsequent to completion of <br /> the pumping pilot test conducted in August 2002, ATC is of the opinion that Installation of a <br /> ' groundwater extraction and treatment system is not warranted Laboratory analytical results of <br /> groundwater samples collected from MW-3 indicate a decreasing trend in petroleum hydrocarbon <br /> concentrations Concentrations of petroleum hydrocarbon constituents decreased in the <br /> groundwater sample collected from MW-3 during the third quarter 2003 below levels detected <br /> during recent quarterly monitoring events The concentrations of petroleum hydrocarbon <br /> constituents detected in the groundwater sample collected from MW-3 during the third quarter <br /> ' 2003 represent historically low concentrations for groundwater samples collected from this well <br /> Refer to Table 4 for a summary of historical groundwater monitoring data <br /> ' ATC recommends the site be considered for closure Please refer to ATC's Monitoring Report— <br /> Thrrd Quarter 2003, dated December 2, 3003, for recent groundwater quality data and additional <br /> rational supporting the request for site closure consideration <br /> S 1Environmenta1162605Veportslpump tckdoc 5 <br /> i <br />