Marian P. Berndt

Vulnerability of a Public Supply Well in a Karstic Aquifer to Contamination

To assess the vulnerability of ground water to contamination in the karstic Upper Floridan aquifer (UFA), age-dating tracers and selected anthropogenic and naturally occurring compounds were analyzed in multiple water samples from a public supply well (PSW) near Tampa, Florida. Samples also were collected from 28 monitoring wells in the UFA and the overlying surficial aquifer system (SAS) and intermediate confining unit located within the contributing recharge area to the PSW. Age tracer and geochemical data from the earlier stage of the study (2003 through 2005) were combined with new data (2006) on concentrations of sulfur hexafluoride (SF(6)), tritium ((3)H), and helium-3, which were consistent with binary mixtures of water for the PSW dominated by young water (less than 7 years). Water samples from the SAS also indicated mostly young water (less than 7 years); however, most water samples from monitoring wells in the UFA had lower SF(6) and (3)H concentrations than the PSW and SAS, indicating mixtures containing high proportions of older water (more than 60 years). Vulnerability of the PSW to contamination was indicated by predominantly young water and elevated nitrate-N and volatile organic compound concentrations that were similar to those in the SAS. Elevated arsenic (As) concentrations (3 to 19 microg/L) and higher As(V)/As(III) ratios in the PSW than in water from UFA monitoring wells indicate that oxic water from the SAS likely mobilizes As from pyrite in the UFA matrix. Young water found in the PSW also was present in UFA monitoring wells that tap a highly transmissive zone (43- to 53-m depth) in the UFA.

Does diazinon pose a threat to a neighborhood stream in Tallahassee, Florida?

Uiazinon is an organophosphorus insecticide used in lawns, homes, gardens, in orchards, and other agricultural settings to control a wide variety of insects including ants, cockroaches, silverfish, and fleas. Diazinon is a contact insecticide, which means it kills insects by inhibiting the action of enzymes in the nervous system. It is classified as slightly to moderately toxic, depending on the formulation (Extension Toxicology Network, 1996). Diazinon is the only active ingredient in some products, but it is commonly combined with other insecticides or with fertilizers. In 1998, more than 150 products containing diazinon were registered in the State of Florida (Robert Moore, Florida Department of Agriculture and Consumer Services, written commun., 1998). Currently, diazinon is the most commonly used pesticide for homes and gardens. Chemicals applied in yards and gardens can pollute nearby streams and lakes when stormwater runoff carries the chemicals into storm drains that ultimately feed into these bodies of water. This is especially true where these chemicals SIGNIFICANT FINDINGS