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Ilk 17 March 2015 AGE Project No. 06- 1457 Page 2 of 3 ?, J detections of hydrocarbon constituents , but is likely the result of shallower, impacted soils being transported down-hole during drilling and sampling . �l Contaminants migrating through the vadose zone adhered to soils as liquid I hydrocarbons dispersed in nearly all directions surrounding the former tank pit, product piping areas and dispenser area. Contaminants migrated through soils until reaching first-encountered ground water. Although the actual dates of the UST system releases are unknown , it is likely that first encountered groundwater during the period of the initial release was significantly lower than contemporary groundwater is -Gurrently at the site , �tl. ll allowing contaminants to migrate to deeper soils and at a higher adsorbed (i _ I concentration . This is evidenced by samples collected at borings MW-9 and EW-2 , _ where petroleum concentrations were significantly elevated in soil samples. Once contaminants eventually reached groundwater, they began to disperse in the flow `- direction of groundwater, which has generally been to the east, northeast to southeast. f Based on data collected to date, it appears that at least two different flow units are the primary route for contaminant migration in relation to UST at the site : the current water table is the upper most zone or first zone encoufftered , as illustrated in historical boring logs and CPT logs , and generally ranges from 35 to 50 (Appenix08) , while a second LJ distinct coarse-grained zone (likely a "smear zone") ranges at depths from 70 to 80 _ (Appendix C) . Based on an evaluation the historic boring logs , combined with CPT L sounding/soil behavior data, AGE believes that these two units are the primary zones LJ that require additional lateral assessment at this time and present a data gap for an accurate site conceptual model (e. g . "deep" lateral definition) . However, grab I groundwater samples collected off-site , from the upper water table were non-detected for dissolved petroleum (boring B7-36' , B8-35' and CPT4-42') Furthermore , based on _ analytical data collected during periodic monitoring events at well MW-5 and 2014 CPT borings CPT-5 t trough CPT-8 , additional lateral assessment is warranted in the 70- to 80- foot flow unit Tables 1 through 3) . (07c ' bo EHD Comment #2 : Sample soil and groundwater through the shallower zone to J assess for contamination ; especially in the shallower sandy unit. For each of the proposed drilling locations (Figure 3) , soil samples will be collected at five-foot intervals beginning at 5 feet bsg and ending at the total proposed depth of 80 [ feet bsg . If field evidence of hydrocarbon impact is noted in sandy intervals within the shallow zone (i . e. A to 50 feet bsg) , a grab groundwater sample will be collected prior fI to continuing advancing of augers . If significant soil impact is noted in field soil samples I_J in the shallow zone , the initial boring will be terminated and a shallow monitoring well will be constructed . However, a soil sample collected off-site from the upper water table depth was non-detected for petroleum (CPT445') . Shallow wells will only be installed at J the direction of EHD staff and after EHD staff and a California Professional Geologist has reviewed field data . Should shallow wells be installed at the initial proposed boring U _ 16417r" i ; ' / _s, i kI`' lf 1 � Advanced GeoEnviranmental, Inc. �3d