LETTERS
approved
Reverse osmosis
total organic carbon volatile organic carbon total carbon THE DOHRMANN@ DC-50 ORGANIC ANALYZER makes all of these measurements accurately and rapidly. Based on proven, EPA approved':'methods, it avoids interferences and undesirable pyrolysis reactions that historically have resulted in significant errors. DIRECT READOUT: Four-digit pres. entation shows carbon content directly ir mg/liter or ppm. No recorder needed! DIRECT MEASUREMENT: A singlc sample injection gives either Organiccar. bon or Total Carbon content directly, not by difference. INDEPENDENT MEASUREMENT Volatile Organics are determined sepa. rately from Total Organics to aid ir source identification. RELIABLE MEASUREMENTS: De. termines important, lightweight volatile! such as low molecular weight alcohol! and ketones, normally lost by acidifica, tion and sparging. FAST: 5 minutes per determination. ACCURATE: Repeatability of f 1 mgl liter or + 2 % . WIDE RANGE: 1 to 2,000 mg/litei (ppm) without dilution. PRICE: $7,875, including start-up as, sistance and operator training. ~
ENVIRONMENTAL PROTECTION AGENCY, WATER P R O G R A M S , Guidelines Establishing Test Procedures for Analysis of Pollutants. FEDERAL REGISTER VOI. 38, NO. 199, Part 11,Oct.16, 1973. For brochures, reprints, or dates and locations of seminars, contact: DOHRMANN DIVISION, 3240 Scott Blvd., Santa Clara, CA 95050. (408) 249-6000. Telex 346 395.
E NVIROTEC H
CIRCLE 16 ON READER SERVICE CARD
876
Environmental Science & Technolog
Dear Sir: The feature authors (ES&T, July 1974, p 614) have presented a good picture of all of the pretreatment considerations necessary to install a reverse osmosis unit. They have further discussed the removal of various pollutants in general terms. The article could have been extremely valuable to engineers involved in pollution control if the data to which they allude had been quantified. Furthermore, the costs for these various pretreatment and reverse osmosis processes are as important and valuable as a judgment of the effectiveness. David H. Furukawa
Fluid Sciences Division, UOP San Diego, Calif. 92123
Radioactive slime ponds
Dear Sir: The report, "Reconnaissance Study of Radiochemical Pollution from Phosphate Rock Mining and Milling," details results of our investigation of the radiochemical pollution resulting from phosphate rock mining and milling. As you will note, the bulk of the report deals with problems resulting from milling. However, sufficient data exist to add to the article on slime ponds (ES&T, April 1974, p 31 2 ) . I t has long been known that phosphate rock, especially Florida rock, contains uranium. What has not been widely recognized is that the rock also contains uranium decay products, one of the most hazardous of which is radium-226. Slimes tend to contain even more radium than the original ore. A common value, based on the literature and on our study, would be 45 picocuries per gram (pCi/g) o f radium-226. On this basis, the 1971 Cities Service slime-pond failure mentioned is calculated to have involved over 16.5 curies of radium-226. The total radium released to the environment from all slime pond spills i s unknown but would probably add up to several hundred curies. One-and-one-half years after the Cities Service spill, the Peace River downstream of the spill contained over two times the USPHS Drinking Water Standard for
radium-226, as a result of leaching of radium from slimes deposited along the stream. The article mentioned use of slimes for lightweight aggregate. The first decay product of the the radium226 contained in the slimes is radon222, a radioactive gas which has received much notoriety as a result of the Grand Junction, Colo., use of uranium-mill tailings in home construction. The use of slimes in building construction must not be permitted. The radiological problems of the phosphate industry do not end with the mining phase; in fact, they have just begun. The acidulation of phosphate rock to phosphoric acid results in a partitioning, during which the uranium remains with the fertilizer and most of the radium precipitates with the by-product gypsum. The gypsum solids contain approximately 25 pCi/g of Ra-226. A great deal of research effort is under way to develop methods to use by-product gypsum for wallboard. This is currently practiced in Germany. Such use unnecessarily exposes the population to hazardous levels of radon decay products, as was the case in Grand Junction. An acid solution, known in the industry as "contaminated water" is used for transport of the gypsum solids. This material contains 90-1 00 pCi/l. of radium-226, which is 30 times the maximum permissible concentration (MPC) for radium, and three times the AEC standard for unrestricted areas. General industry practice is to recycle this water, with no discharge except during periods of high precipitation. However, some mills located along the lower Mississippi River discharge contaminated water and/or gypsum solids directly to the Mississippi River. The general industry practice is to place the acid (pH < 2) gypsumpond decant in a pit, often a minedout area directly in contact with a limestone aquifer. A s a result, radium values as high as 79 pCi/l. have been detected in the shallow ground water around phosphate mills. Jim V . Rouse EPA National Field Investigations Center Denver, Colo. 80225
