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Portola Geophysics <br />21 Santa Maria Avenue (415) 851-8751 <br />Portola Valley, Ca 94025 M a y 22, 1987 <br />0 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 />Replacement Site <br />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 />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 (and 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 />