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March 2006 1 053-2442 1.0 INTRODUCTION Golder Associates (Golder) prepared this Second Supplemental Phase Il Investigation Work Plan � (Work Plan) on behalf of the Mounds View Public School District (District). The purpose of the Work Plan is to direct field efforts to further delineate the vertical and horizontal extent of Volatile Organic Compounds (VOCs) in soil and groundwater previously discovered at the District's Service � Center located at 2959 Hamline Avenue, Roseville, Minnesota. The District recently enrolled the site in the Minnesota Pollution Control Agency's (MPCA) Voluntary Investigation and Cleanup (VIC} Program (VIC No. 21420). This work plan was prepared 'm general accordance with Guidance �,.,., Document #11 of Iv��CA's VIC Program and 'm response to comments provided by MPCA in their memorandum to Golder dated March 2,2006. This introductory section is followed by a statement of objectives of completing work described herein, a description of the site, and a brief history of � previous environmental investigations completed at the site. We then present proposed field activities designed to meet objectives of the investigation, followed by a description of inethods that will be used to conductthe field work and prepare a project report. � 1.1 Obj ectives Objectives of this Phase II Investigation Work Plan are to direct field efforts to: ■ * Further delineate the source(s} of VOCs that have been measured in groundwater underlying the site; � . Further delineate the vertical and horizontal extent of VOC-affected soil and groundwater at the District's Service Center; + Determine the direction of groundwater flow at the site, including vertical and horizontal � hydraulic gradients; . Assess potential affects on localized groundwater flow attributableto a utility corridor along the west side of Hamline Avenue; � • Evaluate temporal trends of VOC concentrations in groundwater; * Preliminarily determine if there are immediate health and/or safety risks to human health or the environment as a result of the VOC-affected soil andlor groundwater; and * Provide site specific information to determine if cleanup of the site is necessary based on the � anticipated future use of the site. � Our proposed scope of work describing investigative techniques that will be employed to help meet these objectives is presented in Section 2.0 of this work plan. � � � 1.2 Site Location and Description The Mounds View Public Schools District Service Center is located at 2959 Ha�nline Avenue North, in the City of Roseville, Minnesota (Figure 1), at an elevation of approximately 890 feet above mean sea level. The original building at the site consisted of a multi-story barz� with a partial basement that was operated as a dairy during the early 1900s. The surrounding area was primarily agricultural until it was developed as residential during the 1950s. From the 1950s to the 1970s the property was owned by the Catholic Diocese and was leased for use as a printing facility. Mounds View Public School District purchased the property in 1970, and it has been used since as office space, storage, and as a maintenance facility for District-owned equipment. � Based on review of historical aerial photographs, an addition, consisting of concrete slab on grade construction, was erected to the southwest of the original buildings sometime between 1957 and � 1966. For purposes of clarity, this addition is referred to as the "First Addition." A"Second �