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PERCOLATION TESTING PROGRAM PROCEDURES <br /> INTRODUCTION <br /> The most accurate method to determine percolation rates is to <br /> perform percolation tests in holes which have been kept filled with <br /> water for a minimum of four (4) hours and ideally overnight. San <br /> Joaquin County requires a presaturation period of 24 hours. <br /> Tests are performed by an experienced technician under the <br /> direction of a staff engineer. <br /> Percolation rates are determined from the test data obtained <br /> after the soil has had ample opportunity to become saturated and <br /> to swell. <br /> [1] PREPARATION OF THE TEST HOLE <br /> A four (4) to twelve (12) inch diameter hole is bored to the depth <br /> of the proposed absorption trench. Boring is performed using a <br /> four (4) to twelve (12) inch diameter auger. <br /> The bottom and sides of the test hole are carefully scratched <br /> using a knife or sharp instrument in order to remove any smeared <br /> soil surfaces and to provide a natural soil interface into which <br /> water may percolate. Two (2) inches of coarse or fine gravel are <br /> added to the test hole to protect the bottom from souring and <br /> accumulation of sediments. <br /> [2] SATURATION AND SWELLING OF THE SOIL <br /> Soil saturation is achieved by complete displacement of air in <br /> voids between individual soil particles. Under most circumstances <br /> this can be accomplished in a short period of time by the addition <br /> of water to the test hole. Soil swelling is caused by diffusion <br /> of water into individual soil particles. This is a slow process, <br /> w <br /> *ality Vontrol jnspect ori <br />