SEWAGE DISPOSAL AT ICE CAP INSTALLATIONS Project 15 by H. Bader and F. A. Small ABSTRACT The sewage disposal pits at Sites 1 and 2 on the Greenland Ice Cap were studied, and the size of the cavity produced by sewage was calculated from the data obtained. It was concluded that no serious collapsing of cavities will occur. Increased settlement of the overlying snow surface may cause the edge of the station nearest the sewage pit to be tipped very slowly, which can be corrected by lengthening the sewage pipe. The present sewage disposal means at Sites 1 and 2 are considered entirely adequate for many years to come. I. INTRODUCTION 1. The Corps of Engineers has realized a need for an effective method of waste disposal on the ice cap. The present system used at Sites 1 and 2 of piping waste to a pit removed from inhabited camps was suspected of creating a health hazard. The scope of the investigation was limited to measurements of the cavities at Sites 1 and 2. II. INVESTIGATION 2. The sewage pit heads at Sites 1 and 2 are identical (see figure), They are described in Section C, pages 13 and 14 of: Preliminary Report N-33 AC&W Site USAF Greenland Operation and Maintenance Manual October 1953 NED-CE-USA Metcalf & Eddy & Alfred Hopkins Engineers and Architects 334 Boylston Street Boston 16, Mass. The pits were examined by lowering lanterns and measuring tapes. At Site 1, an entry to a depth of 23 ft was also made by a man on a bosun's chair. At both sites the sewage melted out a vertical pit with smooth walls, somewhat irregular at Site 1, where the neve contains ice layers 12 to 18 in. thick. Here the horizontal cross section of the hole is oblong (due to mode of sewage discharge from a slightly inclined pipe). The larger diameter is approximately 10 ft, the smaller diameter from 1 to 3 ft. At Site 2, where ice layers are rarely more than 1 in. thick, the cross section of the hole is quite regular, an 8-x 4-ft oval. Both holes at times had water filling a flat bulb of unknown width. SEWAGE DISPOSAL AT ICE CAP INSTALLATIONS 0 ~ HORIZONTAL CROSS SECTION -SNOW SURFACE t:::I+--WOOD LADDER CORRUGATED STEEL RISER ~~~~~~~:::::::~:~~FOL:~~~~~RM TWO 50-GAL DRUMS 15cmo.o. STAVE PIPE HOLE APPROX 4X 8 H MAX DIM. 63' WALLS NEARLY PERPENDICULAR WATER LEVEL t=03 e----r-r~--<:':. 8 _ -----=::-BOTTOM OF WATER t=O.O C t -.:--~FROZENSEOIMENT Site 2 sewer hole, August 7, 1954 Site 1: In July 1953, only 5 days after sewage had begun to flow, the pit was 53 ft deep, without standing water, One month later there was standing water and Mr. R. Peary of Metcalf and Eddy, Architect-Engineer, made the following measurements: Depth below the Snow Surface (ft) Date Hour Top of Water Bottom of Water 22 Aug. 1700 68.3 70.6 2200 68.4 71.8 23 Aug. 0630 68.3 71.2 1100 68.3 71.3 2300 68.7 71.1 24 Aug. 0830 68.6 71.5 1530 68.8 71.1 2200 68.6 71.1 25 Aug. 0630 68.5 71.4 1330 68.7 71.4 2100 68.5 71.4 26 Aug. 0630 68.5 71.3 1430 68.6 71.4 27 Aug. 1530 69.2 71.4 28 Aug. 1700 69.0 71.2 29 Aug. 1430 69.1 71.2 30 Aug. 1430 68.8 71.2 11 Sept 1730 68.0 71.0 30 Sept 1730 66.3 71.1 SEWAGE DISPOSAL AT ICE CAP INSTALLATIONS On 1 September 1954, the Commanding Officer of Site 1 reported the depth of the pit as 90 ft from the platform (105 ft from the snow surface) without indicating whether or not there was standing water. Site 2: On 7 August 1954, the bottom of the pit was 71 ft below the platform (83 ft below the snow surface) and had 8 ft of standing water (see figure), A core was obtained by dropping a section of 3-ft pipe on a line. The core consisted of an inch.of ice topped by 2 to 3 in. of dense, partly frozen solid sewage. The sewage flowing from the discharge pipe had a temperature of 10 C to 13 C. Calculation of cavity produced by sewage, assumed to be water: tw =temperature of sewage water, degrees C t =temperature of neve, degrees c (negative) s y = average density of neve, grams per cubic centimeter n = average porosity of neve V = volume of sewage, liters vw = volume of neve melted, liters vsm = volume of neve saturated with water at 0 c, liters 55 H = heat content of sewage, calories w 0.917-y !1 = v t w n = ' w 0.917 w Heat necessary to warm V liters of neve from t to 0 C = -1/2 t V y • s s s s Heat necessary to melt V s liters of neve at 0 C = 80 VsY • v w t w = v sm y(80 -1/2 t s) • Volume of cavity producted in the neve: v t v w w sm y (80 -1/2 t) The total volume of water at 0 C is now: v + v = v l + w l w sm w t [ y (80-1/2 t) This water permeates into surrounding neve saturating a volume of neve: v + v 0.917 v w sm w 1+ w v ss t ] n 0.917 -y ~ y (80-1/2 t) A small portion of this water freezes, releasing latent heat to warm up the volume of saturated neve to 0 C. Some of the saturated snow will freeze owing to heat conduction into the surrounding neve. Example: Site 2: Sewage (12 months at 850 gal per day)= 1.2 x 106 liters t = 10 c. w t = -24 c. s y = 0.6. V = 2.2 x 105 liters, sm Vss = 4.1 x 107 liters. SEWAGE DISPOSAL AT ICE CAP INSTALLATIONS III. DISCUSSION 3. As the visible cavity (pit) has a volume of only 50,000 liters, there must be a hidden cavity volume of 170 m3 to the side and below water level and some 40,000 m3 of saturated neve. If the saturated mass is spherical, its diameter would be 42 m. The effects of sewage flowing into neve can now be visualized. It begins by rapidly melting out a vertical pit until solids accumulate to form an impermeable bottom. Melting then spreads sideways, with spillover producing new vertical holes. It appears likely that the repeated processes of vertical and horizontal penetration take place in a conical volume, with the cone axis inclined in the direction of inclination of the neve layers, Depth of penetration is limited by the permeability of the neve, which at Site 2 approaches zero at a depth of some 200 ft. The apex of the cone lies at a depth of 70 ft at both sites. A state of near equilibrium will be reached after many years, when the surface area of the cone becomes large enough to permit escape of all the heat input of the sewage, which then freezes, In the meantime a rather large volume of neve is honeycombed by cavities, saturated with water, and made more plastic than its surroundings by higher temperature, The increased plasticity of the neve will be counteracted by less plastic masses of ice. It is considered certain that no serious collapsing of cavities will occur; the only possible consequence is increased settlement of the overlying snow surface, If the installation is too close to the sewage outlet, it may be tipped, Tipping would be very slow, and, as soon as detected, could be remedied by excavating a tunnel to extend the sewage pipe away from the station, IV. CONCLUSION 4. The present sewage disposal means at Sites 1 and 2 are considered entirely adequate for many years to come, If increased settling of the edge of the station nearest to the sewage pit is observed, the sewage pipe should be lengthened. SIPRE Report 21 SEWAGE DISPOSAL AT ICE CAP INSTALLATIONS by H. Bader and F. A. Small The research work reported here was accomplished by Dr. Bader, physicist and Chief, Snow and Ice Basic Research Branch, and Mr. Small, geologist, Snow and Ice Applied Research Branch, as part of SIPRE Project 22.2-6, S11ow and 1ce engi11eering in Northern Greenland, and Corps of Engineers Greenland Project 15, Waste disposal. SNOW ICE AND PERMAFROST RESEARCH ESTABLISHMENT Corps of Engineers, U. S. Army Wilmette, Illinois