10.1021/acs.est.5b03671.s006
James R. Degnan
James R.
Degnan
J. K. Böhlke
J. K.
Böhlke
Krystle Pelham
Krystle
Pelham
David M. Langlais
David M.
Langlais
Gregory J. Walsh
Gregory J.
Walsh
Identification
of Groundwater Nitrate Contamination
from Explosives Used in Road Construction: Isotopic, Chemical, and
Hydrologic Evidence
American Chemical Society
2016
source
highway construction site
breakthrough
δ15 N
identification
groundwater
contamination
mass balance calculations
unexploded NH 4NO
denitrification
biogenic
concentration
Groundwater Nitrate Contamination
data
δ18
2016-01-19 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Identification_of_Groundwater_Nitrate_Contamination_from_Explosives_Used_in_Road_Construction_Isotopic_Chemical_and_Hydrologic_Evidence/2086201
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.