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d` �-' � 'rV' ,r. :,s;: - � "A'�.,f'"".u.^. .�.�s'sc�9� .'a�::'u`tl _._.� ;.1.. ...L^«.saxbei.w��`�„-•e._,_......:i....vy, ,Ym.,,r...,.r:..>.�- -.� �.k aye Mr. Glenn R. Dembroff L3ltramar Inc. April 9, 1991 Page 2 Fieldwork conducted at the site by Delta, including the activities outlined above, were performed in accordance with the field methods and procedures described in Enclosure A. Sitegite Information The site is currently operated as a retail Ultramar gasoline station. Ultramar purr:iased the site from Conoco Inc. in )uly 1990. The site is located in a rural agricultural area that is currently undergoing residential and commercial development. The flat-lying topography surrounding the site is between 30 _ and 35 feet above mean sea level. previous investigative activities have been performed at the site by the previous owner(Conoco Inc.) since 1985 resulting in the drilling and installation of a total off 33 vadose and/or ground water monitoring wells. All but one of the 33 well;(MW 20)is current] dry. The regional drought conditions that exist are partially responsible for lowering the ground water table below the monitoring well screens. Site Soils The soil borings for monitoring wells were advanced at the site on Three bruary 7 and 8,1991,to a depth F of re feet (MW-35 and MW 36)and 70 feet(MW-34)below the surface. The location of these borings is shown in Figure 2 and the soil boring logs are presented in Enclosure B. Sediments underlying the site consist predominantly of an interbedded sequence of sand,silty and clayey sand,and silty and sandy clay straturr.to a depth o€approximately 60 feet below the surface. In the Loring for monitoring well MW-34,a moist,unsaturated sandy clay and clayey sand layer was present between approximately 59 and 68 feet below the surface. These strata were underlain by a saturated sand stratum that was sampled at a maximum depth of 70 feet below the surface. Soil 5am'3ie Anal ses soil samples were obtained at 5-foot intervals and were screened for the presence of organic vapors using a photoionization detector(PID) as described in Enclosure A. PIIS results are recorded on the soil boring logs contained in Enclosure B. vapor ing Soil samples were selected for s made in the field, Onenso les sample was selectee!for altal s from position and physical observat on each boring. These samples were collected from a depth of approximately 45 feet 1-clow the surface. The samples were submitted to a California-certified laboratory and analyzed for tlae presence of total petroleum hydrocarbons (TPH)as gasoline,and benzene,toluene,etbylbenzene and xylenes(BTEX). A summary of the analytical results for soil samples collected in February 1991 is presented in Table 1. Copies of the sail sample laboratory reports are presented in Enclosure C. TPH as gasoline was not detected in the soil sample collected form boring MW-34 or boring MW-36. A TPH conccntrat-ton of 390 parts per million (ppm)was detected in the soil sample collected from boring MW-35.