A seven-year study was conducted to assess the effectiveness of hybrid poplar trees to remediate polycyclic aromatic hydrocarbon (PAH) compounds in soil and groundwater at a creosote-contaminated site. A reduction in the areal extent of the PAH plume was observed in the upper half of the 2-m-thick saturated zone, and PAH concentration levels in the groundwater declined throughout the plume. PAH concentrations began to decline during the period between the third and fourth growing seasons, which coincided with the propagation of the tree roots to the water table region. Remediation was limited to naphthalene and several three-ring PAHs (acenaphthylene and acenaphthene). PAH concentrations in soil and aquifer sediment samples also declined over time; however, levels of four-ring PAHs persisted at the lower depths during the study period. The naphthalene to total PAH concentration ratio in the most contaminated groundwater decreased from >0.90 at the beginning of the second growing season to approximately 0.70 at the end the study. Remediation in the lower region of the saturated zone was limited bythe presence of a 0.3-m-thick layer of creosote present as a dense nonaqueous phase liquid (DNAPL). The nearly steady-state condition of the PAH concentrations observed during the last three years of the study suggests that the effectiveness of the phytoremediation system is limited by the rate of PAH dissolution from the DNAPL source.

A field study is currently being concluded at Grand Junction and Durango, Colorado, and at Monticello and Salt Lake City, Utah, to evaluate the public health aspects of atmospheric 222Rn in the vicinity of uranium tailings piles. Air is collected continuously for 48 hr periods from each station in order to average out diurnal fluctuations. The integrated sample is then analyzed for 222Rn. A total of 57 stations is in operation. Each station is re-sampled every three weeks for one calendar year to include seasonal fluctuations and to permit a more realistic estimate of the yearly dose to people in the immediate vicinity. This paper presents data and conclusions from the 1 yr study. Of the 13 stations directly over tailings, average radon concentrations ranged from 3.5 pCi/l. to 16 pCi/l. Of the 44 stations not over tailings, only two averaged greater than 1 pCi/l. The results indicate negligible radiation exposure of the surrounding population from this source.

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The U.S. Public Health Service (USPHS) has recently completed comprehensive studies of radioactive pollution of the Animas River, an interstate stream, under requirements stated in the Federal Water Pollution Control Act. The studies were conducted as a result of the interstate pollution abatement enforcement action instituted by USPHS at the request of New Mexico. They illustrate several of the basic principles that are important to the rational, successful control of radioactive water pollutants, and provide a practical case study that may be useful as a guide for solving future problems of radioactive liquid waste control. The Animas receives wastes from a uranium ore refinery in Durango, Colorado, and flows south into New Mexico. It is the main source of water for the area and is used for domestic water supply, irrigation of croplands, recreation, and waste disposal. Study results indicated that the total internal radiation exposure of downstream populations was greater than the limits recommended for general population exposure. Studies of the fate of Ra220, the primary pollutant, in the stream environment and in local water plants, led to the development of rational, efficient pollution abatement measures. These measures were installed quickly, and subsequent surveys showed that they resulted in a much higher standard of radiation protection than would have been achieved by enforcement of preset, arbitrary effluent or stream standards.