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1605 School Street,#4 <br /> Moraga CA 94556 <br /> GEOLOGICAL 925(808-8965) <br /> s®nncts <br /> September 16,2013 RECEIVED <br /> Ms. Rebecca Silva JAN 0 2 2014 <br /> Senior Environmental Scientist <br /> GEOCON Consultants, Inc. ENVIRONMENTAL <br /> 3160 Gold Valley Drive, Suite 800 HEALTH DEPARTMENT <br /> Rancho Cordova, California 95744 <br /> Subject: Geophysical Investigation Results <br /> Underground Storage Tank(UST) Search <br /> SR 26 and North Market Street <br /> Linden, California <br /> Mr. Silva- <br /> 1.0 INTRODUCTION <br /> This letter presents the findings of Advanced Geological <br /> Services, Inc. (AGS) geophysical investigation <br /> conducted at the southwest corner of SR-26 and North <br /> `.i Market Street in the town of Linden, California (Figure <br /> 1). AGS understands that an underground storage tank <br /> (UST)was encountered during some recent construction <br /> work in that area and the purpose of the geophysical <br /> investigation is to determine UST dimensions and to <br /> locate any nearby underground utilities. <br /> The field work was performed on September 6,2013 by <br /> AGS geophysicist Roark Smith. The utility locating <br /> work was performed using a RadioDetection RD-8000 <br /> pipe and cable locating system. To look for the UST, Figure 1—Site Location in Linden,California <br /> Mr. Smith used a Fisher M-Scope metal detector, a <br /> Geonics EM61 electromagnetic(EM)metal-detector with digital recording capabilities,and a GSSI SIR- <br /> 3000 ground penetrating radar(GPR)system. Briefly,the M-Scope and EM61 instruments were used to <br /> look for buried metal areas representing the possible UST location, and GPR was used to obtain <br /> graphical profiles of the subsurface to help identify buried metal objects detected by the EM61 survey <br /> and to look specifically for USTs, which produce a distinctive, readily-identifiable image on a GPR <br /> record. In general, EM61 surveying is an important part of a UST investigation because it provides a <br /> deeper investigation depth than GPR,which can be as shallow as two feet at some sites. Depending on <br /> their size,the EM61can detect objects as deep as 10 feet; however,the EM61 can detect only metallic <br /> objects and is subject to interference from vehicles,buildings,and other metal-containing above-ground <br /> objects. <br /> ADVANCED GEOLOGICAL SERVICES <br />