Using chemical and microbiological indicators to track the impacts from the land application of treated municipal wastewater and other sources on groundwater quality in a karstic springs basin |
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Authors: | Brian G Katz Dale W Griffin |
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Institution: | (1) U.S. Geological Survey, 2010 Levy Ave., Tallahassee, FL 32310, USA |
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Abstract: | Multiple chemical constituents (nutrients; N, O, H, C stable isotopes; 64 organic wastewater compounds, 16 pharmaceutical
compounds) and microbiological indicators were used to assess the impact on groundwater quality from the land application
of approximately 9.5 million liters per day of treated municipal sewage effluent to a sprayfield in the 960-km2 Ichetucknee Springs basin, northern Florida. Enriched stable isotope signatures (δ18O and δ2H) were found in water from the effluent reservoir and a sprayfield monitoring well (MW-7) due to evaporation; however, groundwater
samples downgradient from the sprayfield have δ18O and δ2H concentrations that represented recharge of meteoric water. Boron and chloride concentrations also were elevated in water
from the sprayfield effluent reservoir and MW-7, but concentrations in groundwater decreased substantially with distance downgradient
to background levels in the springs (about 12 km) and indicated at least a tenfold dilution factor. Nitrate-nitrogen isotope
(δ15N–NO3) values above 10 ‰ in most water samples were indicative of organic nitrogen sources except Blue Hole Spring (δ15N–NO3 = 4.6–4.9 ‰), which indicated an inorganic source of nitrogen (fertilizers). The detection of low concentrations the insect
repellent N,N-diethyl-metatoluamide (DEET), and other organic compounds associated with domestic wastewater in Devil’s Eye Spring indicated
that leakage from a nearby septic tank drainfield likely has occurred. Elevated levels of fecal coliforms and enterococci
were found in Blue Hole Spring during higher flow conditions, which likely resulted from hydraulic connections to upgradient
sinkholes and are consistent with previoius dye-trace studies. Enteroviruses were not detected in the sprayfield effluent
reservoir, but were found in low concentrations in water samples from a downgradient well and Blue Hole Spring during high-flow
conditions indicating a human wastewater source. The Upper Floridan aquifer in the Ichetucknee Springs basin is highly vulnerable
to contamination from multiple anthropogenic sources throughout the springs basin. |
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Keywords: | Pharmaceutical compounds DEET Wastewater Land application Upper Floridan aquifer Florida USA |
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