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This study examined thetrihalomethane formation potential (THMFP) from water extracts of organic fractions ofa mineral soil (Scriber Clay Loam) and an organic soil (Rindge Muck) in the Sacramento-San Joaquin Delta. Organic carbon from the Delta soils, especially peat soils, is ofconcern because they have been identified as important sources of trihalomethane (THM)precursors in the Delta drinking water sources. In addition, the effects of Na+ and Ca2+on the partitioning of organic carbon and THM precursors in these soils were evaluated.Water extracts (1:100, soil : water) were sequentially filtered through a series of pore sizefilters: 1.2, 0.45, 0.1 and 0.025 im. Each filtrate was analyzed for total organic carbon,UV absorbance at 254 nm (UV254), and THMFP. The authors defined organic matterwith size fractions of 1.2-0.45 im, 0.45-0.1 im, 0.1-0.025 im and smaller than 0.025 imas particulate (POC), colloidal (COC), fine colloidal (FCOC) and dissolved organiccarbons (DOC), respectively. Results showed that the dominant fraction in all extractswas DOC, followed in a decreasing order by COC, POC and FCOC. The DOC from theorganic soil was 85%, whereas it was 57% from the mineral soil. Filtrates of waterextracts through 0.45 im from the mineral soil contained 36% COC. Such a high contentof colloidal materials in water caused high turbidity and resulted in abnormally highUV254 values. Monovalent sodium had little impact on the distribution of each fraction,but divalent calcium significantly reduced COC. The difference in THMFP among sizefractionations was relatively small. Thus, the authors believe that DOC contains themajority of THM precursors. Ideally, DOC, organic fractions that passed through 0.025im, should be used in characterizing THM precursors in water; however, slow filtrationmakes it impractical for large volumes. The difference in total organic carbon of 0.1 imand 0.025 im filtrates was only about 2%. Thus, a 0.1 im pore-size filter isrecommended for THM characterization. Includes 16 references, tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 15File Size: 1 file , 490 KB