should give advance verbal notice to the survey party. Information obtained from yard foremen and other employees as to subsurface conditions, as recommended in subparagraph (c) above, will be found to conflict in many instances, but is, nevertheless, frequently a guide to subsurface structures that otherwise might be entirely unknown.

14-55. Key plans. Data under each of the following subdivisions shall be shown on a separate sheet of suitable size and scale, for use as a key or guide to the sectional maps:

(a) Traverse and triangulation, with base lines, station points, and location of monuments; also adjusted distances, angles, bearings, and pluses of base lines. Monuments shall be indicated by a double circle with a number in the inner circle.

(b) Location of bench marks, indicated by a single circle circumscribing an identifying number, with the elevation adjacent to the circle.

(c) A division of the reservation into numbered sections for identifying the various sectional sheets. The divisions should be so arranged that the sectional maps will have one side running parallel with streets and the other side perpendicular thereto. Sectional maps of the standard size (see par. 1463) embrace approximately 3 acres, and the number of sectional maps required will depend on the area of the yard.

14-56. Maps of distributing systems are desirable and necessary; each system should be shown on a separate map unless a combination of related systems can be plainly shown on the same map without confusion. Such maps should be prepared on tracings or reproductions of the general yard map, the distributing systems being shown in heavy ink lines, with buildings, curbs, and other features in light lines. The following are the distribution systems contemplated:

(a) Fresh-water distribution system, including valves, hydrants, and services to buildings.

(b) Salt-water system, including valves, hydrants, and services to buildings. (c) Electric light, power, and telephone distribution systems, including substations, transformers, manholes, and street lamps. Manholes shall be consecutively numbered for identification.

(d) Compressed-air distribution system, including manholes, equalizing tanks, valves, and outlets.

(e) Gas distribution systems, including acetylene, oxygen, and hydrogen lines. (f) Pneumatic tubes and manholes, including central stations, substations, and outlets.

(g) Fire-alarm circuits, boxes, and recording devices.

(h) Sewerage and storm-water drainage systems, including manholes, catch basins, and building drains.

(i) Municipal gas service lines, drips, valves, and meters.

(j) Heating and steam power distribution systems, including conduits, manholes, expansion joints, and valves.

(k) Fuel oil and gasoline distribution systems, including valves and manholes. 14–57. Base lines and coordinates. The survey shall be based entirely upon the rectangular coordinate system. Lines, which in connection with subsurface surveys are denominated base lines, shall be run through the various streets, paralleling the curb or building line, and on concrete or stone sidewalks; the station points shall be indicated by means of a punch and 2 diametrical slashes, and every fifth station shall have its number cut in Roman numerals. Base lines shall be further fixed by permanent monuments of the type later described herein. In measuring base lines, it is preferable to use a tape of invar or other metal of negligible temperature coefficient, graduated throughout, and mounted on two portable tape holders adjustable for height and alignment, the rear holder being provided with a frictionless wheel and a weight to afford the required tension. A New York City standard steel tape with spring balance and thermometer attachment is also suitable for this work. Any tape, before use, should be checked for a given pull and temperature by comparing it with a standardized tape or a standard 100-foot base. The chaining should be carried along on tables about 8 inches in diameter and supported on a tripod about 18 inches high, thus avoiding the use of plumb bobs. All base lines should be shown graphically on the traverse and triangulation sheet, key plan (a). with each intersection numbered.

14-58. Traverse and triangulation. A complete traverse and triangulation of the reservation shall be made, this to be tied into existing United States Coast and Geodetic or other Government survey points in the vicinity; if a tie can not be made to such points, or to reliable State or local survey points, the survey shall be fixed geographically by basing it upon the true meridian through the reservation. In the latter case, the initial coordinates may be assumed, care being taken to avoid negative coordinates. Base lines should be joined to form closed polygons, random lines being avoided as far as possible. The maximum allowable error of closure of the bounding polygon or primary traverse should be 1 in 100,000, and for the secondary traverse 1 in 30,000. All triangulation angles should be be turned in series of 12 repetitions each. A repeating transit should be used for all traverse and base-line work, reading as closely

as 5 seconds. The maximum allowable error of closure on the horizon should not exceed 24 seconds. All references, notes, and other data pertaining to monuments and transit points shall be placed on loose-leaf cards and numbered according to key numbers.

14-59. Field notes. All field notes shall be recorded on looseleaf sheets especially prepared for the purpose. Notes on topography shall be taken by the right-angle station and offset method. All points located must be shown in fractional form, the numerator indicating the station, the denominator the offset, and the bar the right angle. These fractions should be written near the point and at right angles to the base line to which they refer. After the topography is taken, check measurements should be run between manholes and other important points located.

14–60. A folder shall be provided for each sectional sheet, and all field data, including both subsurface and topographic notes, must be filed in the folder assigned to the area involved. All looseleaf records, after being plotted, shall be kept in suitable filing cases.

14-61. Bench marks. Numerous bench marks shall be established around the navy yard, especially on all monuments, using, so far as possible, existing bench marks after checking them; all bench marks must be tied into one system and referred to mean sea level, as established by the United States Coast and Geodetic Survey.

14-62. Monuments shall be of 1:2:4 concrete, 4 feet long, 18 inches square at the base, and 8 inches square at the top, with a 1-inch diameter brass plug 4 inches long embedded in the center so that one end is flush with the top of the concrete. Hair cross marks shall be made on the plug to indicate line and distance. For use as a bench mark, a 3-inch diameter bolt, 4 inches long, shall also be embedded in the monument, with its head inch above the concrete and about 2 inches from the edge. Monuments shall be placed before the actual work of chaining and angular measurements is started, in order to insure the greatest accuracy. They shall be placed at ends of base lines and at all base line intersections of primary and secondary traverses. In setting monuments, the top should be 6 inches below grade and protected by a cast-iron cover.

14-63. Sectional record maps: Scale, size, and scope. Sectional record maps shall be plotted preferably on a scale of 10 feet to the inch on heavy cloth-mounted paper, cut to size 33 inches

by 45 inches. These sheets shall be laid out by coordinates and shall have plotted upon them all detail information pertaining to a regular topographical map; in addition, a complete subsurface record shall be placed on these sheets, showing the kind, size, dimensions, and depth of all subsurface structures, such as pipes, sewers, manholes, and conduits. The topographical features shall first be plotted in pencil from the field notes.

14-64. Field plotting: Equipment and personnel required. After the topographical features have been plotted, the sectional maps should be taken into the field for checking and plotting subsurface work, including manhole interiors, service connections, pipes, sewers, conduits, ducts, tunnels, and all similar structures. The sheets should be mounted on a standard drafting board and carried on a hand pushcart having a suitable roof over the board to protect the draftsman from the glare of the sun, as well as to protect the sheet. The roof should be of light waterproof material, attached to the cart approximately 5 feet above ground and extending 9 inches over the sides of the board; the latter should have a half-inch raised edge and two waterproof covers attached at the ends to protect the sheets. The draftsman should work on one end of the sheet and keep the other end covered. The edges of the sheet should be fastened down with clamps. There should be provided a compartment underneath the board for drafting instruments and tools and a holder for carrying a wood rod 1 inch by 11⁄2 inches and 14 feet long. The rod should be graduated into feet and inches; at the zero end a metal strip extending 6 inches at right angles to the rod is required for measuring depths of manholes and sizes of pipes. Personnel required for field plotting will be one subsurface draftsman, two rodmen for chaining, and one laborer to push the cart and open manholes.

(a) In recording and made in all cases for

14-65. General rules for field plotting. plotting electric conduits, allowance should be a 3-inch concrete envelope around the conduit. In noting the dimensions, the width or horizontal measurement shall be indicated first; for example, 36" x 24" indicates a width of 36 inches and a height of 24 inches. (b) Pipes under 4 inches in diameter shall be shown by a single line; of diameter 4 inches and over, in outline. The walls of pipe galleries are to be shown only when the galleries are large; they should be omitted for all branches less than 2 feet in width. The size

of such structures should be indicated on the sectional sheet by the inside measurements, but in plotting allowance must be made for the thickness of walls. All pipes in galleries shall be shown in longdashed lines, and at least one section of each run shall be made to indicate the pipe arrangement in elevations. (c) In showing pipes or conduits passing through the walls of a manhole, or under other obstructions, lines must invariably be broken at the point of passage and carried on continuously beyond the obstructions. Wall thickness of manholes and other similar structures shall be taken as 8 inches, unless otherwise determined by measurement or by authentic construction plans. (d) In plotting, all pencil work should be fairly heavy to insure clearness. Leaders or arrows to the various structures should be drawn only to the edge. Dimensions and notes should not be written on any portion of the sheet that is to be colored. The depth of structures from the street surface shall always be noted by the letter "C"; thus, 24" C indicates a ground cover of 2 feet. Such notes should be placed as close as possible to the point to which the actual measurement refers.

14-66. Symbols, lettering, and coloring. After all subsurface structures have been accurately plotted in pencil, the sheet should be inked in and the various runs shown in color. A high-grade make of water colors shall be used. The various systems shall be indicated by the following colors:

All lettering must be uniform, and shall be in accordance with subsurface standards later illustrated herein on Plate No. 14-9. All symbols on distribution maps shall conform to standards shown on Plates Nos. 14-25 to 14-29, but the standard symbols prescribed for pipes on Plates Nos. 14-25 and 14-26 shall not apply to sectional subsurface sheets where the scale is either 20 feet or 10 feet to the inch.