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The basic symbol G is used if the estimated percentage of gravel is greater than that for sand. In contrast, the symbol S is used when the estimated percentage of sand is greater than the percentage of gravel. Gravels range in size from 3-inch to 0.25-inch (No. 4 sieve). Sands range in size from No. 4 sieve to No. 200 sieve. Use the grain size scale used by engineers (ASTM Standards D422-63 and D643-78) to further classify grain size as specified by the USCS. Note: This grain size scale differs from the Modified Wentworth Scale used in teaching most geologists. Also, it introduces a distinction between sorting and grading. The modifying symbol W indicates good representation of all particle sizes. The modifying symbol P indicates that there is a predominant excess or absence of particle sizes. The symbol W or P is only used when there is less than 15 percent fines in a sample. Modifying symbol M is used if fines have little or no plasticity (silty). Modifying symbol C is used if fines have low to high plasticity (clayey). The following rules apply for the written description of the soil group name: Types of Soil Rule Sands and gravels (clean) Less than 5 percent fines Sands (or gravels) with fines 5 to 15 percent fines Silty (or clayey) sands or gravels Greater than 15 percent fines Other descriptive information includes: Color Maximum grain size Composition of grains Approximate percentage of gravel, sand, and fines (use a percentage estimation chart) Modifiers Description Trace Less than 5 percent Few 5 to 10 percent Little 15 to 25 percent Some 30 to 45 percent Mostly 50 to 100 percent Mineralogy Grain shape (round, subround, angular, subangular) Moisture (dry, moist, wet) Structure Organic material Odor Additional Soil and Groundwater Sample Work Plan, Page 3 BNSF Mormon Yard, Stockton, California 11twybost21bost,Np \wp12018 \ 1899020 00_mormon_yard1work_plan_dappb_sogboreholeloggIng acpt chng_wp.doc