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C GEO-PHASE ENVIRONMENTAL WORK PLAN Groundwater Monitoring Well Construction Former Nelson Ready Mix 2059 Navy Drive j Stockton, California January 167 2006 GPE Project No. 518.2 I i 1.0 INTRODUCTION 4 A diesel release at the subject site has impacted the groundwater with elevated j concentrations of gasoline. The lateral and vertical extent of the contamination remains . unknown and the direction of groundwater flow is uncertain, although it is believed to f flow toward the southwest. A suite of three monitoring wells is proposed to help define the extent of the contamination and to determine the direction of groundwater flow. 2.0 SITE HISTORY j The subject Property is the site of an idle ready mix plant that formerly was operated as Nelson Ready Mix. In 1995 a former 4,000-gallon diesel tank was removed under County permit. Confirmation soil samples collected from beneath the tank pit and the dispenser contained diesel-range petroleum hydrocarbons. On February 20, 2004, the pit was over-excavated and approximately 300 cubic yards of soil were removed and stockpiled on the site. Diesel-impacted groundwater entered the pit and the water was pumped out and properly disposed of The pit was subsequent backfilled. The report that documented the excavation recommended site closure, but closure was denied due to insufficient site characterization. On January 31, 2005, San Joaquin County EHD issued a letter directing that additional work be completed to define the extent of the diesel contamination. On November 21, 2005, Arcadis installed 3. soil borings at points through and near the backfilled tank pit. Groundwater samples were collected and tested for the presence of 2937 Veneman Ave.,#13240 Geo-Phase Environmental Inc. Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295