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} <br /> Portola Geophysics <br /> 21 Santa Maria Avenue (415) 851-8751 <br /> Portola Valley, Ca. 94025 May 22 , 1987 <br /> 1017 <br /> Mr . Leonardo Alvarez, <br /> EMCON Associates <br /> 1921 Ringwood Avenue <br /> San Jose , California 95131 <br /> SUBJECT : Seismic Refraction Survey , Harney Lane Sanitary Landfill <br /> is <br /> Replacement Site <br /> l° San Joaquin County , California <br /> Dear Mr . Alvarez : <br /> With this letter report , we are presenting the results of <br /> our seismic refraction survey of the Harney Lane Sanitary <br /> Landfill Replacement Site in San Joaquin County , California . <br /> Summary <br /> A total of six ( 6) individual seismic refraction lines <br /> with a combined spread length of 1800 lineal feet were recorded <br /> at a proposed landfill site in San Joaquin County , California . <br /> This work was performed in -accordance with our Proposal for <br /> Geophysical Services dated April 28 , 1987 . The purpose of this <br /> survey was to evaluate the rippability and characteristics of <br /> subsurface materials as well as the presence of groundwater <br /> beneath the project site . <br /> Interpreted Results <br /> I>' <br /> i;. Seismic refraction lines S- 1 through S-6 , with spread <br /> lengths of 300 feet each , were recorded in the locations <br /> indicated on Figure 1 . These locations Cand line numbers ) <br /> correlate with the locations ( and boring numbers ) of exploratory <br /> borings performed by J . H . Kleinfelder and Associates in 1986 . <br /> Data and interpreted results are presented on Figures 2 through <br /> 4 . <br /> In general , the gently sloping to relatively flat alluvial <br /> plain comprising the project site is underlain by one ( 1 ) or two <br /> ( 2 ) velocity zones ( refractors ) to the depths surveyed . The zone <br /> closest to the ground surface is characterized by low velocity <br /> ( 1250 to 1560 ft / sec ) materials to depths from 0 to 7 feet , and <br /> typically only a few feet . The underlying zone is characterized <br /> by medium velocity ( 2920 to 3850 ft /sec ) materials which extend <br /> from depths of 0 to 7 feet to greater than 96 feet . <br /> In the vicinity of line S-5 , three ( 3 ) velocity zones were <br /> encountered . Below a low velocity ( 1560 ft /sec ) zone , low to <br /> * For the purposes of this report , a seismic refraction line <br /> consists of 12 geophones spaced at equal intervals of 25 feet <br /> along a straight line and monitored simultaneously while a sledge <br /> hammer was impacted off each end and /or at the center of each <br /> line . <br />