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1.0 INTRODUCTION ERM-Rocky Mountain, Inc. (ERM) performed a subsurface investigation of the aboveground storage tanl: (AST) system at the Southwestern Portland Cement Company (SWPC) in Lyons, Co]orado. The purpose of the investigation is to characterize soil and groundwater conditions to facilitate closure of the AST system in accordance with all applicable environmental regulatory requirements, and in a timely and cost effective manner. SWPC anticipates construction of a replacement AST system. The registration and closure of ASTs are regulated under Colorado regulations 7 CCR 1101 Part 1101 through Part 1114 and corresponding site characterization and remediation guidelines are provided by the Colorado Department of Labor and Employment, Oil Inspection Section (Storage Tank Facility Owner/Operator Guidance Documents, July 1, 1995). The regulations exclude mining facilities including gravel pits, quames, and borrow pits from the AST regulations provided that the AST system is under tight control by the owner or contractor, and isolated from other structures. Although the AST system appears to meet the regulatory exclusion, as a best management practice, SWPC has elected to follow a site characterization and remediation program guided by AST regulations and guidance. The subsurface investigation was conducted to satisfy Colorado's initial site characterization requirements for storage tank systems. The investigation objectives include characterizing site conditions to determine the lateral and vertical extent of soil and groundwater affected by operation of the AST system. The investigation included advancing of seven soil boreholes, converting six of the boreholes into temporary groundwater motutoring wells, and advancing two hand-auger sample holes. A total of eight soil and seven groundwater samples were collected for laboratory analysis from the boreholes, nronitoring wells, and hand-auger sample holes installed at the site. This report presents site investigation field activities, analytical results, findings, conclusions, and recommendations. 1.1 SITL• DESCRIPTION The SWPC plant is located in Lyons, Colorado approximately 1 mile southeast of the junction between U.S. Highway 36 and State Highway 66. The SWPC AST system is located in the southwestern portion of the plant site, adjacent to the northeast of the plant vehicle maintenance shop. Saint Vrain Creek is located approximately 0.7 mile north of the SWPC AST system. The location of the SWPC pant site is shown on the attached Figure 1, a USGS topographic map. The plant site slopes gently to the east and lies within the Saint Vrain Creek floodplain. Alluvial deposits underlying the site contain soils ranging from clay, silt, and sand to gravel, cobbles, and boulders. Groundwater beneath the site flows to the east-northeast toward Saint Vrain Creek. ERM-ROCKY MOUNTAIN, [NC. P'..\IOOOISWPC1961019\REPORT.DOC Printed on Recycled Paper 1