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1 <br /> G�alagaalTecluilcslnc rel Page 11 <br /> Site Conceptual Model Report <br /> Marci Property <br /> Project No 7012 <br /> August 23,2004 s /•' a s <br /> ' • Rollin Leasing Co 82 50 Loorru Rd E Stockton CA 95205 Chemical used — <br /> g g rP , -5- <br /> Diesel Aquifer affected;eanfNm leak 5/24/99 MTBE detected LUST site <br /> ' • Conti Trucking Inc , 2660 Loomis Rd , Stockton, CA 95205 Lust site, the case has <br /> been closed Chemical used Diesel <br /> ' Of these sites reviewed in the EDR Report and selected ones listed above, we have not found <br /> any that we suspect as bung realistic off-site sources for diesel that may be contributing to <br /> the contaminations found on this site However, as this project proceeds, we will keep an eye <br /> open for other possible sources of diesel that may be found through other means <br /> ' 4.0 DISCUSSION AND CONCLUSIONS <br /> ' 4.1 Discussion <br /> The data indicate that diesel contamination exist in both soil and water at the site The <br /> ' plumes are limited in lateral and vertical extent but data gaps exist It is not known why <br /> diesel contamination is present in greater concentrations in the location of well MW-5 <br /> located 40 feet from the former UST excavation Groundwater monitoring indicates that <br /> although former gradients were highly vaned, the groundwater direction has been <br /> predominantly to the southeast since additional data was obtained from the new wells <br /> installed in 2002 This places well MW-5 in an up gradient position from the former USTs <br /> It is possible that subsurface lithology contributes to migration in a northwest direction but <br /> this has not been confirmed Additional site investigation is needed to define the lithology <br /> with continuous logging rather than five foot intervals As discussed in Section 2 8, the <br /> ' groundwater velocity is faster than the predominant clayey matrix would indicate Therefore <br /> it is probable that sand layers are present that are not intercepted or are underestimated when <br /> using the historical 5 foot sampling interval <br /> The locations that should be investigated further include <br /> • North and southwest of MW-5 <br /> ' • Adjacent to MW-7 <br /> • North of MW-7 <br /> - - . Southeast of MW-104 - <br /> ' • South of the shop/office <br /> Continuous core sampling and/or Cone Penetrometer Testing in conjunction with discrete <br /> ' soil and groundwater sampling would allow the subsurface hydrogeology parameters to be <br /> determined with greater accuracy Obtaining soil and groundwater samples in these areas <br /> would also allow for further plume definition <br /> Once the plumes are further defined alternative cleanup technologies can be considered The <br /> P P g <br /> RWCQB-CVR developed the Water Quality Control Plan for the San Joaquin River Basin <br />