Technical Report No. 16
Kenneth Ishizaki, Nathan C. Burbank, Jr., L. Stephen Lau
The source of most of Oahu’s domestic water supply is from ground water occurring in the permeable materials of volcanic rock. Movement of the ground water is intrinsically through thin cracks in basaltic lava. This project studied passage of an organic-rich liquid through cracks in basalt. Permeability of “blue rock” portions of a basalt was determined as 2.6 x 10-4 gallons/day/ft2 of water, classing the rock as impervious. A range of 7.7 to 10.4 per cent in porosity values was obtained from the “Blue rock” portion; the clinker portion yielded a value of 50 per cent. Difficulties in experimental verification of the Hagen-Poiseuille’s derivation of radial flow through thin cracks were encountered in measuring flow at low gradients and aligning crack surfaces absolutely parallel. These discrepancies caused some variation in the determination. The flow rate is proportional to the 0.9 power of the head. Flow rates are less than theorized by Hagen-Poiseuille’s derivation with the flow rate of clarified sewage being less than tap water under identical conditions. The greatest retardation in flow of non-biodegradable liquids through thin cracks occurred in the initial hours followed by a systematic reduction of flow to a terminal and nearly constant flow of 718 to 1/100 of the initial flow rate. Flow rates through a basalt decrease faster than through a simulated thin crack made of lucite plastic. Flow of organic-rich liquids through such cracks, similar to non-biodegradable liquids, exhibits a decrease in flow initially and continues this trend for as long as 220 hours. The terminal flow velocity of tap water is much greater than that of sewage which appears to proceed to a no-flow condition. The clogging phenomenon was dependent upon microbial activity and food supply in sewage. Retardation of flow of organic-rich liquid is attributed to presence of microbial cells and their biochemically synthesized products in the cracks. The products are primarily polysaccharides and slimes along with ferrous sulfide, a common material found in septic sewage in contact with soil or rock.