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Grologkil Ttekxles I'm Page 14 Site Conceptual Model Report(2006 Revision) Valentine(Castle Motors) Project No 723 2 June 16,2006 _ plume is forming and migrating, non- dissolved petroleum product remains in the pore spaces in the soil due to capillary forces These forces make it difficult to remove the non-aqueous phase liquids (NAPL) trapped in the pore spaces Fresh water moving through the soil can eventually flush a portion of the NAPL out, but this process can take a very long time and can contribute to an extensive groundwater plume It has been 19 years since the last UST was closed at the site in 1987 The groundwater ' gasoline plume has migrated off site to the northeast and appears to attenuate to non- detectable levels in the vicinity of CPT-3 Based on the residual soil contamination the former dispenser island is believed to be the source of the leak Well MW-3 is near the ' dispenser island and has consistently contained the highest levels of contamination The following graph shows the historical TPH-G concentrations in MW-3 ' MW-3;TPH-G& Benzene VS Elevation 3W 000 — _ ___ _ _ _ _ _ _ _ 000 ' 250.000 -500 -1000 V 200,000 .1500 E 150,000 A !f� i -2000 - e!f r A i A. ` � -TPH-G ' CL 100 coo -25 00 i ]► LU _-+--Benzene A -3000 ► GW Elevation 50 000 • -35 00 0.��ti-�+aria" ♦��+may+ wr4W��;;ry-r►y-�,s ' 0 -00 00 0000000 w�� Rate ' Although a slight decreasing trend is noted in well MW-3 the TPH-G in the soil column is continuing to impact groundwater quality If not addressed, the groundwater plume will continue to migrate with natural mechanisms diluting and degrading the leading edge of the ' plume to some non-detect point near CPT-3 Well MW-8 is approximately half way between the dispenser island and the location of CPT-3 The following graph shows the limited historical TPH-G concentrations in relatively new well MW-8 1