Landfills are the final depositories for a wide range of solid waste from both residential and commercial sources, and therefore have the potential to produce leachate containing many organic compounds found in consumer products such as pharmaceuticals, plasticizers, disinfectants, cleaning agents, fire retardants, flavorings, and preservatives, known as emerging contaminants (ECs). Landfill leachate was sampled from landfill cells of three different age ranges from two landfills in Central Oklahoma. Samples were collected from an old cell containing solid waste greater than 25 years old, an intermediate age cell with solid waste between 16 and 3 years old, and operating cell with solid waste less than 5 years old to investigate the chemical variability and persistence of selected ECs in landfill leachate of differing age sources. Twenty‐eight of 69 analyzed ECs were detected in one or more samples from the three leachate sources. Detected ECs ranged in concentration from 0.11 to 114 μg/L and included 4 fecal and plant sterols, 13 household\industrial, 7 hydrocarbon, and 4 pesticide compounds. Four ECs were solely detected in the oldest leachate sample, two ECs were solely detected in the intermediate leachate sample, and no ECs were solely detected in the youngest leachate sample. Eleven ECs were commonly detected in all three leachate samples and are an indication of the contents of solid waste deposited over several decades and the relative resistance of some ECs to natural attenuation processes in and near landfills.

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In late 1988, parallel studies of Lake Five-O (pH 5.14) in the Florida panhandle and Lake Barco (pH 4.50) in north central Florida were initiated to develop hydrologic and major ion budgets of these lakes as part of an overall effort to improve understanding of the hydrologic, depositional, and biogeochemical factors that control acid-neutralizing capacity (ANC) in seepage lakes. Preliminary findings from these studies indicate that earlier perceptions of lake hydrology and mechanisms of ANC regulation in Florida seepage lakes may have to be revised. The traditional perspective of seepage lakes in the Florida panhandle views these systems as dominated by precipitation inputs and that ANC regulation is due largely to in-lake processes. Our results for Lake Five-O show modest to steep hydraulic gradients almost entirely around the lake. In addition, the horizontal hydraulic conductivity of the surficial aquifer is high (8-74 m day-l), indicating that large quantities of groundwater flow into Lake Five-O. Calculations of net groundwater flow from hydrologic budgets also indicate that groundwater may comprise at least 38 to 46% of the total inflow. For Lake Barco, net flow estimates of the minimum groundwater inflow range from 5 to 14% of total inflow. Enrichment factor and ion flux calculations for Lake Five-O and Lake Barco indicate that terrestrial as well as in-lake processes contribute significantly to ANC regulation. The extent that terrestrial processes contribute to ANC generation is directly related to the magnitude of groundwater inflow as well as the degree of ion enrichment or depletion that occurs in the surficial aquifer. Net ANC generation in both study lakes was dominated by artion retention (NO•-and SO•-). Where previous studies concluded that in-lake reduction was the primary sink for SO,•-, our preliminary calculations show that adsorption of SO•-within the watershed is perhaps twice as important as in-lake reduction as a source of ANC. Net base cation enrichment in both lakes was negligible. Agency's (EPA) Eastern Lakes Survey (ELS) indicate that •early 60% of the acidic lakes in the easternUnited States ldefined as lakes with acid-neutralizing capacity or ANC -<0 ./aeq I. -l) are seepage lakes [Brakke et al., 1987]. In Florida, •here more acidic lakes are found than in any other region in the country [Linthurst et al., 1986], 84% of the acidic lakes are seepage lakes [Pollman and Canfield, 1991]. Nealy half of these acidic lakes are clearwater lakes where the acidity is 'attributable to strong acids, notably H2SO 4 [Pollman and Canfield, 1991]. Paleolimnological evidence indicates that •me seepage lakes in Florida have become more acidic sime about 1950, although the mechanisms accounting for s•:h change (hydrologic and/or atmospheric) are unclear [Sweets eta!., 1990]. Moreover, although the factors that . 12opyn•t 1•I by the American Geophysical Union. hl•er aUmMr 91WR01435. •:•.143.1397/91 t91WR-01435505.00 regulate ANC are fairly well known, the quantitative importance of individual factors is...

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