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placed about 10 feet east and south of a tank, which was located at the south and east side of the Property It is conceivable that high zones of MtBE were present but undefined We believe the main conduit is the sand zone located at 50 feet bgs and deeper This zone does not have any identified clay barrier and it is believed that contaminate flow is unobstructed along it's coarse In our cross-section we have noted the tPH and MtBE concentrations from the 641 E Charter Way boring is toward our well MW-11 The tanks were removed from this site in 2000 The ARCO station at 701 East Charter Way is also contaminated with BTEX and oxygenates Contamination records are available, since this is a LUFT site One of our questions is are they the source of the contamination or are they reflecting the contamination from the site at 641 E Charter Way, which is across Stanislaus Street in a westerly direction A review of the Second Quarterly Report, 2003, the MtBE levels at this site are down significantly The were in the 2000 to 8500 ug/L range in 1998 to 2002 and have fallen to 350 ug/L in April 2003 in well MW-1, which Iis the closest well to the site at 641 East Charter Way At the 749 E Charter Way site the levels of MtBE in well BM-3 have been present since January I 1998 and are present at this time When we drilled boring B-3, no MtBE was found at the surface of the groundwater We drilled and sampled the water at 50 and 60 feet below the surface and found that the results were 2 1 and 16 5 ug/L respectively This increase indicated that the contaminated water was coming from another source and it was the same scenano we encountered at HP-2 where the water enters this site at 55 feet The soil units at boring B-3 were silt and silty sand and we obtained water samples to 50 and 60 feet bgs SAs contaminated water flows, the concentration becomes lower, if it does not encounter another contaminated plume It also becomes less contaminated as it flows vertically down the water column The center of any plume remains relatively stable as it flows and can only be diluted if the outer portions of the plume are diluted The oxygenates or at least TAME, TBA, MtBE and EtBE dissolve in the water and when they do this solution of water and oxygenates becomes slightly heavier than the groundwater Therefore, the solution sinks as it travels along the plume path The sinking is about 1 foot for each 20 feet at SG`'• the flow gradient at Charter Way If the plume sinks to a level where it encounters a clay layer, it continues to sink but more slowly than in sand or silty sand s FjiCM� We havere ared two sets of contour maps for October 97 and Jul 98 Each sets includes P p p Y contour maps for Tert-Butanol and MtBE In 1997, the Tert-Butanol map shows the contaminated ' groundwater entering the site from Charter Way in two prongs, one south of wells BM-7 and BM-9 and the other south,of BM-8 At the same time, the MtBE is entering the site south of BM-4 The same soil unit, a silty sand, is present at both BM-7 and BM-4 Perhaps the MtBE is flowing through the water at a faster rate than the TBA In 1998 both the TBA and the MtBE appear to be entering from the west, but we did not sample ' wells BM-7 or BM-9 by EPA 8260 The pattern in 1999 is the same as in 1998 In 2000 the pattern is similar to that of 1997 In 2001 the water was entering from under San Gardens and from the south at 749 E Charter Way In 2002 the pattern is entering from the west under the Sun Gardens What this means, is that water is entering our site from the clay barrier under Sun Gardens and ' from the south at Charter Way, by two plumes in the groundwater Once the water level had risen 6