The various subsurface lines are differentiated by colors as follows: _A_—Sewers, vermilion. _B_—Water mains, blue. _C_—Potomac Electric Power Co., carmine. _D_—Washington Railway and Electric Co., carmine. _E_—Capital Traction Co., violet. _F_—Chesapeake and Potomac Telephone Co., green. _G_—Washington Gas Light Co., green. _H_—Western Union Telegraph Co., orange. _I_—Postal Telegraph Co., orange. _K_—Private vaults, black. _L_—City Electric Co., yellow. ] [Illustration: FIG. 4. Punch Drill. ] Underground pipes and structures are located by excavations, which may be quite extensive in some cases. Their position is fixed by measurements referred to manholes and other underground structures which are somewhat permanent in position. A city engineer should grasp every opportunity to record underground structures when excavations are made in the streets. The character of the material through which the sewer is to pass is determined by borings. =16. Borings.=—Methods used for the investigation of subsurface conditions preliminary to sewer construction are: punch drilling, boring with earth auger, jet boring, wash boring, percussion drilling, abrasive drilling, and hydraulic drilling. The last three methods named are used only for unusually deep borings or in rock. Punch drills are of two sorts. The simplest punch drill consists of an iron rod ⅞ of an inch to 1 inch in diameter, in sections about 4 feet long. One section is sharpened at one end and threaded at the other so that the next section can be screwed into it without increasing the diameter of the rod, as shown in Fig. 4. The drill is driven by a sledge striking upon a piece of wood held at the top of the drill to prevent injury to the threads. The drill should be turned as it is driven to prevent sticking. It is pulled out by a hook and lever as shown in Fig. 5. It is useful in soft ground for soundings up to 8 to 12 feet in depth. Another form of punch drill described by A. C. Veatch[16] consists of a cylinder of steel or iron, one to two feet long split along one side and slightly spread. The lower portion is very slightly expanded and tempered into a cutting edge. In use it is attached to a rope or wooden poles and lifted and dropped in the hole by means of a rope given a few turns about a windlass or drum. By this process the material is forced up into the bit, slightly springs it, and so is held. When the bit is filled it is raised to the surface and emptied. Much deeper holes can be made with this than with the sharpened solid rod. [Illustration: FIG. 5.—Lever for Pulling Punch Drill. ] [Illustration: FIG. 6.—Earth Augers. ]