Abstract
Mounitoring of water quality and trihalomethane formation potential (THMFP) of ground waters (30m for No.1 well, 25m for No.2 well) of an agricultural area of humic volcanic soil on Shirasu plateau where livestock wastes have been applied, was carried out with twelve monthly samplings for one year to ascertain the characteristics of water quality and THMFP. For a comparison, water of a mountain stream running out from the neighboring hillside was also analyzed for both water quality and THMFP. 1) Concentration of some inorganic ions, particularly of NO_3^- , suggested that the ground water of both wells was contaminated with inorganic solutes by the agricultural activities, though the origin of the contamination was not clearly ascertained by this study. Furthermore, the seasonal changes in concentration of Cl^- and Na^+ in No.1 well, which were synchronized with that of NO_3^- , suggested that the ground water of No.1 well was more strongly affected by livestock waste application than No.2 well. As a whole, from the ionic composition, particularly from the key-diagram analysis for water quality understanding, it was inferred that the ground water of both wells was affected by agricultural activities on the ground surface. 2) Concentration of the precursor of trihalomethane (THM), i.e. DOC, were 0.59mg L^<-1> as mean value for ground water of the No.1 well, 0.69mg L^<-1> for the No.2 well, and 0.73mg L<-1> for mountain stream water, implying that the ground waters seemed to be not contaminated with organic matter, as contrasted to some contamination with inorganic materials, even though the organic livestock wastes had been applied on the ground surface. 3) The optical density of water at 1cm pass length of 260nm (OD_<260>) for unit weight of DOC(mg) was much smaller for the ground water than for the mountain stream water, suggesting that the organic matter in the ground water was less humificated than that of the mountain stream water. 4) THMFP of ground water was 4.11μg L^<-1> as mean value for well No.1,and 4.76μg L^<-1> for well No.2,and never exceeded the governmental guideline for drinking water of 100μg L^<-1> as the total. The value for mountain stream water was 10.7μg L^<-1>, indicating that the ground water has much smaller formation potential for trihalomethanes. 5) THMFP of unit weight of DOC (mg) was 7.1,6,9 and 14.7μg for well No.1,well No.2 and mountain stream water, respectively, indicating that organic matter of the ground water had much smaller potential than that of the mountain stream water. The difference between the ground water and the surface water was supposed to be the difference in the degree of humification of organic matter as described above. 6) However, the THMFP for these samples, including the mountain stream water, for unit of optical density measured at 260nm (OD_<260>) by 10mm optical path length was quite similar. Moreover, THMFP (Yμg L^<-1>) was well correlated to the OD_<260> (X) as follows : Y=1038.5 X (r=0.916,n=36) 7) The composition of THM produced from the ground water was characterized by a relatively higher proportion of Br containing species, particularly of CHBr_2Cl and CHBr_3 than the mountain stream water. It was reasoned that the ground water had smaller ratio of DOC/ Br^- than the mountain stream water.
