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July 2 l, 2014 <br /> Two Single-Family residences <br /> L&A Job No. 14-065 <br /> Page 22 <br /> USDA TEXTiJRE TRIANGLE CLASSIFICATION OP SOIL SAMI'LES <br /> Sample Percentage Percentage Percentage USDA Texture <br /> No. Clay Silt Sand/Gravel 'Triangle Classification <br /> 1 3.7 8.8 87.� Sand <br /> 2 1.2 4.6 94.2 Sand <br /> The Stormwater Mana�ement Manual for Western Washington, 2005 Edition, published <br /> by Washington State Department of Ecology, is used to determine estimated design <br /> infiltration rates of the target soil layers from which soil samples were obtained. <br /> According to the table of Recommended Infiltratian Rates Based on USDA Soil Textural <br /> Classification shown on Plate A-4, the estimated short-term and long-term infiltration <br /> rates would be 8 iph (inches per hour) and 2.0 iph, respectively, for "sand". The long- <br /> tenn rate is derived from the short-term rate with a correction factor of 4. The infiltration <br /> rates thus determined for the soil samples are presented on the table below. <br /> a ESTIMATED INFILTRATION RATES <br /> Sample Test Pit Estimated Infiltration Rate, Iiich./Hour <br /> No. No. Short Term Correction Factor Long Term <br /> 1 2 8.0 4 2.0 <br /> 2 3 8.0 4 2.0 <br /> a Based on tISDA Texture Triangle Classification <br /> The D�o sizes of the soil samples determined from their particle size distribution tests are <br /> shown on Plate A-2. The Dio size is the size of soil particles of 10% passing by weight. <br /> According to the table of Alternative Recommended Infiltration Rates Based On ASTM <br /> Gradation Testin� presented on Plate A-5, the Alternative Estimated Infiltration Rates of <br /> LIU & ASSOCIATES, INC. <br />