Only 11 of 60 volatile organic compounds (VOCs) analyzed were detected in ground-water samples (p. 25-26). VOCs were not analyzed in all ground-water samples (VOCs were analyzed in 104 samples). The drinking-water standard was exceeded in one sample for methyl chloride and one sample for ethylene dibromide (EDB). The highest VOC concentrations were 23 µg/L for toluene and 20 µg/L for methyl chloride. Concentrations of all other VOCs were equal to or less than 1 µg/L. Generally, one VOC was detected per sample, thus causing the percentage of samples with VOC detections to be higher than in other NAWQA studies (p. 21). Four VOCs were detected in one sample.
VOCs were detected in ground water from all land-use areas.Benzene, methyl bromide, methyl chloride, and toluene were most frequently detected in samples from agricultural areas, whereas chloroform, methyl tert-butyl ether (MTBE), tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-Dichloroethene were most frequently detected in samples from urban areas. The occurrence of some VOCs in more than one land-use area is expected because several of the VOCs have multiple uses. Many VOCs are components of gasoline or are used as solvents (including inert ingredients in pesticides). The detection of VOCs in samples from forested areas was not expected, just as pesticides were not expected. The presence of VOCs in forested areas could be related to the presence of nearby roads, rights-of-way, or agricultural activities upgradient from the sampled wells. |
Eleven volatile organic compounds were detected in 104 ground-water samples. |
Radon concentrations ranged from 50 to 40,000 picocuries per liter (pCi/L) in the study area and were among the highest in the Nation (p. 20, 26). Radon is a naturally occurring daughter product of the decay of uranium-238. Generally, the concentration of radon in ground water is elevated when the ground water is directly in contact with rocks or sediments containing uranium. High concentrations of radon are usually detected in iron-rich and phosphatic materials (Gundersen and Peake, 1992), such as some of the soils and aquifers in the study area. Radon in water may present health problems primarily when radon is inhaled (Gundersen and Szabo, 1995), such as during bathing or showering. Generally, 10,000 pCi/L of radon in household water contributes about 1 pCi/L to the level of radon in indoor air (Otton and others, 1993). There is currently no drinking-water standard for radon.
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Radon concentrations were high in both the surficial aquifer and the Upper Floridian aquifer. |
The median concentration was 1,150 pCi/L for water samples from the surficial aquifer in the Central Florida Ridge. Radon concentrations in this area were higher in areas where phosphate deposits are generally present; the median was 770 pCi/L in the Southern Coastal Plain and 458 pCi/L in the Coastal Flatwoods area. In the limestone and dolomite of the Upper Floridan aquifer, the median radon concentration was 720 pCi/L. Water samples from this aquifer were collected in Ocala and Tampa, Fla. In the Ocala area, the Upper Floridan aquifer is the primary source of drinking water. |
Last modified: April 14, 1998 10:45 am
