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Environ Sci Technol. 2016 Jan 19;50(2):593-603. doi: 10.1021/acs.est.5b03671. Epub 2015 Dec 28.

Identification of Groundwater Nitrate Contamination from Explosives Used in Road Construction: Isotopic, Chemical, and Hydrologic Evidence.

Author information

1
U.S. Geological Survey, New England Water Science Center , 331 Commerce Way, Suite 2, Pembroke, New Hampshire 03275, United States .
2
U.S. Geological Survey , 12201 Sunrise Valley Drive, 431 National Center, Reston, Virginia 20192 United States.
3
New Hampshire Dept. of Transportation, Bureau of Materials and Research , 5 Hazen Drive, Concord, New Hampshire 03301, United States.
4
Hoyle, Tanner & Associates, Inc., I-93 Exit 3 Project Field Office , 77 Indian Rock Road, Windham, New Hampshire 03087, United States.
5
U.S. Geological Survey , Box 628, Montpelier, Vermont 05602, United States.

Abstract

Explosives used in construction have been implicated as sources of NO3(-) contamination in groundwater, but direct forensic evidence is limited. Identification of blasting-related NO3(-) can be complicated by other NO3(-) sources, including agriculture and wastewater disposal, and by hydrogeologic factors affecting NO3(-) transport and stability. Here we describe a study that used hydrogeology, chemistry, stable isotopes, and mass balance calculations to evaluate groundwater NO3(-) sources and transport in areas surrounding a highway construction site with documented blasting in New Hampshire. Results indicate various groundwater responses to contamination: (1) rapid breakthrough and flushing of synthetic NO3(-) (low δ(15)N, high δ(18)O) from dissolution of unexploded NH4NO3 blasting agents in oxic groundwater; (2) delayed and reduced breakthrough of synthetic NO3(-) subjected to partial denitrification (high δ(15)N, high δ(18)O); (3) relatively persistent concentrations of blasting-related biogenic NO3(-) derived from nitrification of NH4(+) (low δ(15)N, low δ(18)O); and (4) stable but spatially variable biogenic NO3(-) concentrations, consistent with recharge from septic systems (high δ(15)N, low δ(18)O), variably affected by denitrification. Source characteristics of denitrified samples were reconstructed from dissolved-gas data (Ar, N2) and isotopic fractionation trends associated with denitrification (Δδ(15)N/Δδ(18)O ≈ 1.31). Methods and data from this study are expected to be applicable in studies of other aquifers affected by explosives used in construction.

PMID:
26709616
DOI:
10.1021/acs.est.5b03671
[Indexed for MEDLINE]

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