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INTRODUCTION 1.01 Purpose This report presents the results of subsurface investigations conducted for the construction of a vertical groundwater barrier wall (slurry wall) at the 25'" Avenue Grave! Pits owned by the City of Greeley (the City). Haley & Aldrich, Inc. (Haley & Aldrich) conducted a subsurface investigation program in order to analyze the soil, groundwater, and bedrock conditions along the proposed slurry wall alignment. Laboratory testing was also performed to verify soil classifications and to determine engineering properties of the bedrock. This report presents the data obtained from the exploration and testing program. 1.02 Background Information The 25'" Avenue property is located directly east of North 35th Avenue and directly south of the Cache La Poudre River, within the northwest quarter of Section 36, Township 6 North, Range 66 West of the 6th Principle Meridian. The project location is shown on Figure 1. The total area of the property is 89.2 acres. Two adjoining gravel pit ponds exist within the property boundaries and have a combined water surface area of 59.2 acres. Flatiron Companies performed gravel mining on-site to depths of approximately 25 to 30 feet (ft). The pits were dewatered during mining. Mining operations did not remove all of the sand and gravel deposit, which extends to a maximum depth of approximately 60 ft. The pits were reportedly mined to a vertical face, then reclaimed to a 3;1 slope. Reclaimed slope material is reported by Flatiron Companies to consist of overburden and material obtained from the bottom of the pit, which was pushed into place with a bulldozer. The City is considering resuming mining operations at the site to the full depth of the gravel deposit after the slurry wall is installed. The details of future mining, including whether or not the previously placed reclamation fill would be removed and how close temporary or permanent mine slopes may come to the slurry wall, have not been determined at this time. The preliminary alignment for the slurry wall as determined by Haley & Aldrich is approximately 8,450 fr long with depths ranging from approximately 42 to 65 fr. This alignment encloses a combined tand and water surface area of approximately 74.4 acres. The proposed slurry wall would be installed in the overburden and coarse alluvial deposits and keyed into underlying sedimentary bedrock. Inlet/Outlet stmctures are proposed to serve as water transfer mechanisms between the reservoir and the adjacent 35th Avenue Stormwater Ditch. The ditch, in turn, outlets directly into the Cache La Poudre River. 1.03 Objectives The primary objective of the geotechnical subsurface investigations performed by Haley & Aldrich was to provide detailed information about subsurface conditions along the alignment of the groundwater barrier wall for use during the final design and as information for the prospective contractors. The specific goals were as follows: