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,9 1 <br />RZA <br />"1 `' " I Working To Restore Nature <br />.� <br />r r �.., r t, hh I h <br />t r, J <br />1710 Main Street <br />Escalon, CA 95320 <br />Phone (209) 838-3507 <br />FAX (209) 838-3509 <br />April 1, 1994 <br />Ms Linda Turkatte <br />San Joaquin County Public Health Services <br />Environmental Health Division <br />P O Box 2009 <br />Stockton, CA 95201 <br />Subject Soil Excavation Report Addendum, Corrigan Property, 620 San Juan Avenue, <br />Stockton, CA <br />Dear Ms Turkatte <br />This letter is submitted as an addendum to RESNA's January 21, 1994 Soil Excavation Report <br />40 The addendum is in response to the San Joaquin County Public Health Services, Environmental <br />Health Division (PHS/EHD) February 28, 1994 request for more information regarding the <br />excavation conducted in December 1993 at the subject site (Figure 1) The excavation was <br />performed to remove hydrocarbon impacted soil associated with underground fuel storage tanks <br />formerly located on the property <br />REGIONAL TOPOGRAPHY/GEOLOGY <br />The site is situated on level terrain underlain by flood basin deposits of Pleistocene and Holocene <br />age These sediments are composed of clay, silt, and some sand In the San Joaquin Valley, <br />the Flood Basin Deposits (Holocene) have been estimated to be as much as 100 feet thick (Page, <br />1986) The USDA Soil Conservation Service identifies these soils as "Jacktone Clay" (USDA, <br />1992) with soil organic matter of 2-5% (1 16-2 9% organic carbon) Because of their fine <br />grained nature, these deposits in general do not yield much water to wells and impede the <br />vertical movement of water The majority of groundwater used for irrigation and drinking water <br />supplies is extracted from more permeable zones beneath the flood basin deposits <br />SUBSURFACE LITHOLOGY <br />Subsurface investigations were conducted by RESNA in March 1991 and January 1993 Seven <br />soil borings (SBI - SB7) were drilled and three monitoring wells (MW1 - MW3) were installed <br />(Figure 2) The maxiiriurn depth explored was approximately 27 feet Soil encountered beneath <br />the project site consisted primarily of elastic silt (MH) and lean clay (CL) An apparent sand <br />(SP) lens was noted in boring MW2 from approximately 17 to 21 feet below grade and fat clay <br />15(k1541R AU -444 rNL <br />