Identification
of Groundwater Nitrate Contamination
from Explosives Used in Road Construction: Isotopic, Chemical, and
Hydrologic Evidence
James R. Degnan
J. K. Böhlke
Krystle Pelham
David M. Langlais
Gregory J. Walsh
10.1021/acs.est.5b03671.s005
https://acs.figshare.com/articles/dataset/Identification_of_Groundwater_Nitrate_Contamination_from_Explosives_Used_in_Road_Construction_Isotopic_Chemical_and_Hydrologic_Evidence/2086213
Explosives
used in construction have been implicated as sources
of NO<sub>3</sub><sup>–</sup> contamination in groundwater,
but direct forensic evidence is limited. Identification of blasting-related
NO<sub>3</sub><sup>–</sup> can be complicated by other NO<sub>3</sub><sup>–</sup> sources, including agriculture and wastewater
disposal, and by hydrogeologic factors affecting NO<sub>3</sub><sup>–</sup> transport and stability. Here we describe a study
that used hydrogeology, chemistry, stable isotopes, and mass balance
calculations to evaluate groundwater NO<sub>3</sub><sup>–</sup> 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 NO<sub>3</sub><sup>–</sup> (low δ<sup>15</sup>N, high δ<sup>18</sup>O) from dissolution of unexploded
NH<sub>4</sub>NO<sub>3</sub> blasting agents in oxic groundwater;
(2) delayed and reduced breakthrough of synthetic NO<sub>3</sub><sup>–</sup> subjected to partial denitrification (high δ<sup>15</sup>N, high δ<sup>18</sup>O); (3) relatively persistent
concentrations of blasting-related biogenic NO<sub>3</sub><sup>–</sup> derived from nitrification of NH<sub>4</sub><sup>+</sup> (low δ<sup>15</sup>N, low δ<sup>18</sup>O); and (4) stable but spatially
variable biogenic NO<sub>3</sub><sup>–</sup> concentrations,
consistent with recharge from septic systems (high δ<sup>15</sup>N, low δ<sup>18</sup>O), variably affected by denitrification.
Source characteristics of denitrified samples were reconstructed from
dissolved-gas data (Ar, N<sub>2</sub>) and isotopic fractionation
trends associated with denitrification (Δδ<sup>15</sup>N/Δδ<sup>18</sup>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.
2016-01-19 00:00:00
source
highway construction site
breakthrough
δ15 N
identification
groundwater
contamination
mass balance calculations
unexploded NH 4NO
denitrification
biogenic
concentration
Groundwater Nitrate Contamination
data
δ18