Subsurface Investigations for the Penitencia Water Treatment Plant Sulfuric Acid Extension Project

Subsurface Investigations for the Penitencia Water Treatment Plant Sulfuric Acid Extension Project

Project Purpose: The purpose of this project is to conduct subsurface investigations to locate underground utilities in the project area and develop geotechnical recommendations for design and construction of the project. Project: Valley Water proposes to conduct subsurface investigations directed towards locating underground utilities near the PWTP Sulfuric Acid Extension Project sites to minimize impacts to existing utilities prior to initiating construction, as well as to explore subsurface conditions at the proposed vault location - and associated water line and chemical feed channel as needed - in order to develop geotechnical recommendations for design and construction of the project. The proposed geotechnical investigation would include drilling, sampling, and logging of exploratory borings to depths of up to about 30 feet or refusal (the depth below the ground surface at which the borings could no longer be advanced with the soil drilling technique being used). One boring would be excavated initially with the possibility of additional borings to be excavated as needed. Borings would be drilled using a truck-mounted drill rig equipped with hollow stem auger and rotary wash capabilities. Soil samples would be obtained near the ground surface and at vertical intervals of approximately 2.5 feet to depths of up to about 10 feet and approximately every 5 feet thereafter. Soils would be sampled using a hand auger in the upper 5 feet. Below the hand-auger interval, samples would be collected using either a 2- inch outside diameter, standard penetration test (SPT) split-barrel sampler or a 3-inch outside diameter, split-barrel "California-type" sampler in general accordance with ASTM D3550. The SPT and California-type samples would be obtained by driving the sampler with a 140-pound automatic hammer with a free fall distance of 30 inches, in general accordance with ASTM D1586. Following completion of the borings, the holes would be backfilled with cement grout. Drill cuttings and drill fluids would be contained in 55-gallon steel drums and sampled for analytical testing prior to offsite disposal. The proposed underground utility investigation would involve drilling a series of test holes, or potholes, using a combination of truck-mounted air or water vacuum excavation equipment and hand-digging to expose buried utilities, including all existing pipelines, which are either metallic or non-metallic, telephone/electrical cables, or other utilities crossing through or near the project site. Cable locating techniques, including, but not limited to, Electronic Marker Systems (EMS), metal detection, and radio frequency (RT) receivers, as required, would also be used to accurately locate and identify all known and unknown existing underground utilities. Three potholes would be excavated initially with additional to potholes to be excavated as needed. Typical pothole size would be 12 inches in diameter or 12-inch by 12-inch square. Potholes would be excavated up to 10 feet in depth to collect necessary data required or to verify the presence of absence of utilities. Upon completion, potholes would be backfilled with clean sand to two feet above the found utility then with recyclable excavated material thereafter, to create a highly compacted backfill mix. The backfill will be compacted in 8-inch lifts. The asphalt concrete paving will be restored to match the existing roadway thickness. Excavated materials would be sampled and tested in accordance with local, state and federal and landfill acceptance criteria prior to disposal at an appropriate landfill.

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