For most industrial purposes, it is necessary to treat water containing more than 4 grains of sulphates per gallon. 37 The common method is by neutralization with lime, which produces a hard water, and then softening this with 'soda ash. The quantity of chemicals necessary for this purpose remaining in solutions which originally contained sulphates in excess of 12 grains per gallon, causes foaming in boilers 37 and makes it unsatisfactory or impossible to use. On the basis of area of coal mined in Pennsylvania, Maryland, and West Virginia, and the average figure for percolation in these areas, it has been estimated that the headwaters of the Ohio River already contain an excess of 5 grains of sulphates per gallon. This water can be treated, although it is not entirely free from bad effects in boilers after treatment. With water in this condition due to the mining of only about 400 square miles of the 7000 underlain by coal in this district, it is problematical what condition these same waters will be in long before the total area is mined. Worked-out or abandoned mines produce acid waters almost identical in quantity and quality with that from active mines, at least up to 15-years after operations have ceased. 37 No record of these mines is available and no one is responsible for them at present, even should some scheme of purification be devised. The natural alkalinity of streams and rivers has been sufficient until more or less recently to take care of the major portion of mine drainage, but this condition no longer obtains in most mining districts. Present Methods of Disposal of Acid Water. Use of Limestone. 1. Few attempts have been or are being made to prevent acid mine waters from entering streams. A few mines have installed some sort of equipment in which the free acid is neutralized by contact with limestone, lime, or marl. 13 As a rule this equipment consists of large boxes which are partly filled with the neutralizing agent and have vertical baffles alternately joining at the top and bottom of the box so as to give the water an undulating motion as it flows slowly through the box. A filter bed of coke, cinders, or similar material is provided at the outlet, and the effluent is free from acid and, generally speaking, unobjectionable. More elaborate systems have been installed on the same principle, excepting that settling basins have been provided in which most of the solids in the water are removed. 2. At one mine iron oxide is recovered and sold for use in gas purification and in the manufacture of certain kinds of paints. 6 During the World War the price of iron oxide was sufficiently high to guarantee a fair return on the process, while providing the company with a source of supply of good water used in coke quenching at the mine. It is believed that this is the only instance where any attempt is being made at present to recover salable byproducts from mine drainage waters, and while the company states that the sale by no means pays for the cost of operation, it is more than others have attempted. Drainage from this mine comes from three boreholes and thus is rather easily collected for treatment, but at any other point where the drainage could be collected it might be handled in a similar manner. The use of iron oxide for gas purification and in the manufacture of certain paints is standard practice, and while the market could probably not absorb an unlimited amount of this material, the method works successfully and offers possibilities to a number of other mines. Use of Barium Salts. Barium chloride or barium hydrate has been suggested as a precipitating agent, and has been used to some extent where local conditions permitted, but so far the cost is prohibitive. J. W. Ledoux 39 has suggested a scheme whereby the barium sulphate precipitated is recovered and sold as blanc fixe and indicates a profit from the process. Blanc fixe is used in fairly large quantities in different processes in America, but it would seem that a general use of barium compounds for neutralizing the enormous quantities of acid mine waters would create such a demand for them that the cost of raw materials would soar to unprecedented height, and the resultant production of blanc fixe would be far more than could be utilized, so that present market prices for this material would drop to almost nothing. However, it is worthy of mention and consideration. Experience in Other Countries. The experience of foreign countries, which have long ago had to meet pollution problems in some fomor other, offer us no assistance in this particular one. In Europe, for instance, most mines are from 1000 to 4000 feet deep, and, as in Great Britain, they are generally dry, low in pyrite and sulphur, and often in contact with limestone. In France, the chalk deposits overlying most of the coal beds probably prevent the formation of acid waters. 37 G. S. Rice,b states that in France the coal measures are tight and water does not enter the mines. Cost of Purification At first thought it would appear to be fairly simple to treat mine water by some method of neutralization, but in addition to overcoming the difficulty of first collecting the water for treatment, it must be remembered that neutralizing processes generally require large treating and settling tanks, and usually concentrators, evaporators, and filters. When we begin to estimate the enormous quantities of water it would be necessary to handle daily, the problem assumes almost impossible porportions. In addition immense quantities of chemicals, chiefly limestone, would have to be employed, and while these are fairly cheap at present and might always remain so, yet the aggregate cost runs into large figures. Assuming the average figures as previously stated for Pennsylvania alone, it is estimated that with neutralization with lime the cost of chemicals would exceed $225,000 per year. Lime is here mentioned as being even cheaper than limestone for general use, on account of the large amount of inert materials necessary to be handled with limestone, although of course limestone is cheaper weight for weight. As such neutralization would make a very hard water, in most cases unfit for industrial use without softening, the additional cost for softening purposes would be about $750,000 annually. It is difficult to arrive at any significant figures for original cost of installation, upkeep and operation, because no data are available, but installation alone would certainly be not less than $10,000,000 even if duplicate sets need not be built to take care of drainage difficult to collect at one central place. is conceivable that the increased demand for lime and soda ash would result in a considerably higher price than is quoted at present, in which case the annual cost for chemicals alone is problematical. b Chief mining engineer, Bureau of Mines, Department of Commerce. It G. S. Rice has suggested that the use of limestone for rock-dusting to prevent coal-dust explosions will also have considerable effect in neutralizing acid waters within the mine, and this seems to be a very logical conclusion. Neutralization of acid mine waters will require an expenditure of large sums of money, but it does not seem to be prohibitive in most cases to treat these wastes to overcome in a large measure present objections to their entranc into streams. Whether this will be an economically sound policy or not will depend upon the collection of more definite data than is available at present. Other than satisfying aesthetic demands, there is no reason for spending more money and effort annually to purify natural waters than the damage amounts to in money and difficulties experienced by users of waters so polluted. The question is, or should be, to decide how much pure waters are worth from all possible viewpoints, and then determine the cost of purification in the same manner. If the one is cheaper than the other, common sense will demand the more favorable. Some such idea is the basis of the organization of the Sanitary Water Board of Pennsylvania, and that State seems to have taken a long step in the proper direction by classifying all streams within the State into three general groups: (1) Those so grossly polluted that their cleaning up is impractical or impossible, in which case no restrictions will be placed on wastes dumped into them other than those demanded by common decency or the public health. (2) Those streams that are polluted, but may be gradually restored, in which cases the character of trade wastes is investigated and passed on as individual cases, and those considered hariful must be satisfactorily purified before permission can be obtained to dispose of them by running into this class of stream. (3) Those streams as yet unpolluted and which are to be kept so by keeping out all industrial or municipal wastes in the future. Properly armed with judicious authority, accurate information and conscientious attention to duty, such a body may solve the problem for. the best interest of all. It will take time and money in large amounts, but from the magnitude of the problem at present and its increasing seriousness for the future, even a partial solution will be well worth the cost. Good judgment will have to be used in not burdening industries within one State with large expenditures for purification until other States have established similar regulations, as otherwise, in keen competition with others in industrial markets, the first would be unfairly hampered. While the problem seems to be one for the individual States to solve, no real results may be expected until all affected are working in unison along the same lines and under similar regulations. some means. 2. Conclusions. For mine drainage wastes the only solution is neutralization by With present-day practice the question of waste disposal resolves itself simply into one of two things; whether it is more economical, everything considered, to treat these wastes at their source, or to bear with the damage done by them later, if untreated. Before a decision can be made, it seems advisable to investigate suggested methods further with the idea of obtaining more accurate data on costs and practicability in general. It is evident that the cost of neutralization of mine waters would necessarily be added to the cost of the coal to be paid by the consumer. 3. The problem is not one that can be easily solved, and regulations governing disposal are too important and far-reaching in effect to permit of hasty or ill-considered action. Undoubtedly further work should be done as there are no data available except for more or less limited or local condi- 4. Methods now suggested should be tried if possible at some place where most difficult conditions are likely to be encountered, in order to Thanks are due Dr. R. R. Sayers, chief surgeon of the US. 'Bureau of Eng. News-Record, vol. 91, Sept. 6, 1923. 7. Eng. News-Record, vol. 91, Oct. 18, 1923, p. 638. 9. 17. Jour. Franklin Inst., vol. 191, June 1921, p. 807, C. A. Emerson, Jr. Mining and Metallurgy, vol. 1, May 1920, p. 29, L. D. Tracy, also Trans. Am. Inst. Min. and Met. Eng., vol. 66, 1921, p. 609. New York State Conservation Comm. Report, 1923. New York State Conservation Comm. Report, 1919. U. S. Geol. Survey Water Supply Papers No. 103, 113, 121, 151, 152, 161, 18. U. S. Geol. Survey Bull. 11: 34, Coal in 1919, 1920 and 1921. 33rd. Annual Report of City Council of McKeesport, Pa. Trans. Am. Soc. Civil Eng., vol. 85, 1922, p. 475. Science, Sept. 24, 1920, William Firth Wells. Mining and Metallurgy, vol. 2, January 1921, p. 30, H. N. Eavenson. Hearings on the Subject of the Pallution of Navigable Waters held before the Committee on Rivers and Harbors, House of Representatives, 67th 35. 36. 37. 38. 39. 40. 59th Proceedings of Conference held in Washington, D. C., May 13, 1923. Mining and Metallurgy, vol. 4, March 1923, p. 147, A. B. Crichton. Engineers and Engineering, March 1924, p. 94. The Powers, Tuties and Regulations of the Sanitary Waters Board, Reports of Investigations, Bureau of Mines, Department of Commerce. |