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Two years of semi-annual monitoring was considered in evaluating associated <br /> costs Through regression analysis, it was estimated that benzene levels in <br /> groundwater would be significantly reduced by the year 2001 Costs <br /> associated with monitoring include sampling labor, drums and purge water <br /> disposal, laboratory analysis, and reporting Based on these considerations, it <br /> is estimated that two years of monitoring would cost about $16,000 <br /> 6.3 Recommendation <br /> An engineered approach, such as sparge and venting, would address impacted <br /> groundwater on a timelier basis than passive monitoring of its natural <br /> attenuation However, it is projected that benzene levels in groundwater could <br /> naturally degrade significantly within a two year period Certainly, the cost <br /> analysis for the two methods favor passive monitoring at this site If one of <br /> these methods would be required by the PHS/EHD, then Philip would <br /> recommend passive monitoring as the choice <br /> As an alternative, Philip would request that the PHS/EHD considerrantin <br /> g g <br /> case closure for this site Our request for this is based on the following items <br />' • The extent of petroleum Impacted groundwater is largely contained within <br /> Earthgram's property boundaries <br /> O The magnitude of impact is relatively low <br /> compared to historic levels <br /> Benzene concentrations for the last two monitoring events have been <br />' measured to be less than 300 gg/L TPH-G concentrations for the last two <br /> events have been measured to be less than 17 milligrams per liter <br /> • DIPE levels are relatively low, and were in fact, non-detectable during this <br /> Iast monitoring event <br /> • Associated health risks from the impacted groundwater are limited <br /> Potential receptors, public water wells in the vicinity, are located and <br /> constructed such as they would not be affected <br /> • Data indicates that natural petroleum degradation is occurring, and that � <br /> benzene and TPH-G concentrations are projected to be non-detectable by <br />' the years 2001 and 2006 <br /> I <br /> If case closure would be granted, then Earthgrains would mobilize to abandon <br />' all of the site monitoring wells <br /> May 1999 Subsurface Investigation and Groundwater Monitoring Report <br /> The Earthgratns Company Facility <br />' 2651 South Airport Way <br /> Stockton,California <br /> Prepared for THE EARTHG RAINS COMPANY Prepared by Philip Services Corp <br /> E 512t3825121382EGU25997%0599REP DOC June 22, 1999 <br /> 14 <br />