 If the site is in a high ground water area, the present level of the ground water table should be determined using these holes. Most counties or states have a certain required distance separating the disposal field from both bedrock and ground water. 18 ONSITE WASTEWATER DISPOSAL More detailed techniques for determining ground water depth will be described later. As the soil from the test hole is brought to the surface, it should be inspected to determine its structure and texture, and even its colora- tion. Under some conditions, such as when shallow ground water fluctuates considerably from season to season, or where the soil structure is such that it might provide relatively direct channels from an absorption trench to ground water or bedrock, it is wise to dig (with a backhoe) an inspection trench large enough to climb into. Orient the trench SO that there will be sunlight on the sidewall surface, and be sure that the sidewalls are stable before you enter the trench. Keep in mind the following Occupational Safety and Health Administration (OSHA) standards: Banks more than 5 ft high shall be shored, laid back to a stable slope, or some other equivalent means of protection shall be provided where employees may be exposed to moving ground or cave-ins. Trenches less than 5 ft in depth shall also be effectively protected when examination of the ground indicates hazardous ground movement may be expected. The following sections describe some of what can be learned by observing soils. Soil Type Typically, soil is about one-half solid material and one-half pore space. About one-half of the pore space contains water and one-half contains air. Organic material in typical soil ranges from none to about 6%. Soils are usually classified according to particle size. Anything over 10 in. in diameter is considered a stone; cobbles range from 3 to 10 in., and gravel ranges from 2 mm to 3 in. Table 3.1 shows the U.S. Department of Agriculture size classification for soils. It is the relative proportion of sand, silt, and clay t