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CITY OF LATHROP exposed in the borehole,and the ability to obtain reliable representative samples of the formation materials. 2. Material used by the Contractor to prepare the drilling fluid shall be composed of water from an assigned source and drilling additives processed to meet or surpass the specification in the American Petroleum Institute "Std. 13-A for Drilling Fluid Materials". All drilling fluid additives will comply with recognized industry standards and practices,and they shall be used as prescribed by the manufacturer. Toxic and/or dangerous substances shall not be added to the drilling fluid. 3. The drilling fluid for the rotary construction shall be made up of high-grade bentonite clays or organic polymer additives in common drilling usage in the water well industry and shall possess such characteristics as required to condition the walls of the borehole to prevent caving of formations and excessive loss of circulation, facilitate removal of the cuttings, and produce an easily removed thin filter cake. 4. The drilling fluid for the rotary construction shall be made up of high-grade bentonite clays or organic polymer additives in common drilling usage in the water well industry and shall possess such characteristics as required to condition the walls of the borehole to prevent caving of formations and excessive loss of circulation, facilitate removal of the cuttings, and produce an easily removed thin filter cake. The drilling fluid shall be maintained in such a manner as not to exceed the properties specified below for weight,viscosity, and sand content without the approval of the. In addition, the Contractor shall maintain the minimum viscosity of the drilling fluid that will raise cuttings and adequately condition the walls of the holes. At the completion of all drilling operations,the drilling fluid shall be conditioned and meet the following property ranges for well construction. Direct Circulation Property Drilling Method a) Weight: 8.7—9.3 lbs./gal b) Marsh Funnel Viscosity: 28—35 sec/qt c) API Filter Cake Thickness: <3/32 d) Sand Content of Returns: < 1/2% by volume 5. The drilling rig must be provided with equipment to measure the drilling fluid weight, viscosity, API filter cake, and sand content. 6. The Contractor shall maintain a current log describing the condition of the drilling fluid on the site. The log shall include the following: LUHDORFF&SCALMANINI CONSULTING ENGINEERS 7