REP42389 - Laserfiche WebLink

Home Browse Search

E W u z f w !wane !al Q Ce•,w Dm••I Q R: lioo-Uao y // ~~ LCOFRD bbnN !bb fwt••IM ® Ftl•nq 7•••I,•la ®GYN•Inw. ,• pe0 -I ]20 4/n. f0 SNALE-TO- SNALE-TO- SO cm 60 cm 90 cm CAPILLARY SURFACE SURFACE aMR1ER UNLEACNED LEACNED flg. 1. Pronle mnngulltlon! of the ]cloned FhAle dLsposAl 1KAImenUl. Mno_ d a~r~;ti;,depth'.~lectnca~condncnvttles.el$oaQ- ,.~{,~,t5 jq,~e.S,tQ; J,pcm immediatetyabove`the~ha(erin, dic~ting~t thi; fisthedepthlatwhich.solublesalts-begia~ to,,aocttmulate4 Other processes such az capillary rise and diffusion may also be occurring at the soil-shale inter- faces to produce the disvibutions shown here. Of the vace elements. considered in this study, F presents perhaps the greatest hazard [o groundwater con- tamination because of its high mobility. Runnells et al. (1979) found that F concenvations in Paraho retorted shale leachates contained two to five times the USEPA standards for drinking water. Figure 3 shows that there has been considerable movement and redistribution of F within the seven soil-retorted shale profiles. This move- ment is most obvious in the 30-cm topsoil treatment. Fluorine has accumulated at both upper and lower soil- shaleinterfaces and has decreazed in the middle portion of the shale layer. The same effect is noticeable in the 60-cm topsoil treatment although it is no[ nearly az well developed. This redistribution pattern can be explained in terms oC the two processes mentioned earlier, leaching and capillary rise. When precipitation exceeds evapotranspiration, the net downward movement of walcr through the shale undoubtedly leaches F (and other soluble constituents) deeper in the profile, resulting in a greater concentration of F at the lower shale-soil inter- face. When evapotranspiration increases, evaporation and plant roots (which were observed to extend 18-22 crrt into the shale) remove moisture from the topsoil and up- per shale layers. This may result in movement of water from the moist middle shale layers to the dry upper layers by capillary action, depositing additional F near the up- per soil-shale interface. The difference in distribution bet- ween Fand SAR could simply be a result oC differences in solubilities between the fluorine and Na compounds present. Molybdenum showed only slight redistribution within the profiles (Fig. 3). Although Mo concentrations in the 8 to 28 cm of soil immediately adjacent to the shale in- creased approximately 0.6 µg/g, the majority of the Mo CONTROL remained within the shale layer itself. The limited mobility of Mo shown here is surprising considering the observa- tions made by Runnells et al. (1979). In laboratory studies, these researchers found concentrations of 2 to 5 g/mL in leachates from Paraho retorted shale, sug- gestingthat Mo would be much more mobile under field conditions than it actually is. ]t is also interesting to note that the leached shale treatment had no greater movement oC Mo than any other veatments. Apparently leaching haz G[tle effect on reducing Mo concentrations under field conditions. Boron has been reported to be present in high concen- trations in retorted shale and thus represents a potential hazard to plant growth (Schmehl, 1971; Kilkelly and Lindsay, 1979) and groundwater contamination (Runnells et al., 1979) because of its high mobility. All of the B concentrations found in the soil-shale profiles in this study, however, were relatively low (Fig. 4). In Cact, the highest concentration of B was in the disturbed control treatment (2.2 µg/nrL). The exposed shale treatments did have slightly higher B concentrations than the control in the upper 60 cm, but the concentrations are low enough that they probably do not represent much of a hazard to plant growth. Arsenic was one of the least mobile of the dace elements studied. In spite of the observation made by KJein et al. (1981) and Hazsler et al. (1984) that volatiliza- tion of As and subsequent movement of gaseous As represents a potential pathway for movement within [he profile, and the findings oC Runnells et al. (1979) that small amounts of As occur in leachates from Paraho retorted shale, there haz been no observable movement of As out of the shale layer and into the adjacent soil after 6 yr in the Feld. A number of other trace elements showed distribution patterns similar to As. Cadmium, Cu, Fe, Mn, Ni, Pb, Se, and Zn also showed no movement out of the shale layer into the soil. Table 1 lists the average concentra- tions of these elements in the topsoil and retorted shale material. J. EDClron. Qoal., VoI. 15, no. S, 19g6 2g3