Sources of Nitrate in Groundwater Near Roadway Rock Blasting Sites

Explosives used in blasting operations, natural and anthropogenic sources of nitrate such as septic systems, fertilizers, and decomposing vegetation can potentially contaminate groundwater with nitrate in the vicinity of construction sites and make identification of blasting impacts difficult. Blasting operations for a private construction project in Windham, NH were indicated as the source of water quality impacts to private drinking water wells prompting the New Hampshire Department of Transportation (NHDOT) to implementing a proactive approach to limit the potential for impacts from blasting for ongoing NHDOT projects. NHDOT has developed a baseline drinking water monitoring program designed to detect potential impacts and to ensure alternative drinking water is provided throughout the construction phase of projects. In 2013, the U.S. Geological Survey and NHDOT began a study to determine the source and fate of nitrogen compounds near blasting sites using a combination of time series, isotopic, geochemical, hydrologic, and geologic data. Approximately 1.75 million cubic yards of rock were removed by blasting in several locations for roadway construction at a major highway construction site in southern New Hampshire. Isotope ratios of nitrogen and oxygen in nitrate were used to identify sources of nitrate concentrations in groundwater from wells near the blasting sites. Wells near a rock excavation site where blasting was used shortly after the start of this study and wells with existing persistent nitrate contamination suspected to be the result of septic and past blasting were targeted for temporal sampling and analysis in an attempt to characterize nitrate sources. In general results show a low δ15N signature from synthetic nitrate sources (including explosives) and a high δ15N signature from septic waste sources. Results also indicate that nitrate pulses in wells following blasting events can be distinguished isotopically from other local sources, and that reducing conditions in this geologic setting locally cause denitrification, resulting in lower nitrate concentrations. Transport and persistence of nitrate due to blasting operations and other nitrogen sources in fractured rock environments will be presented.

• Record URL:
  http://www.highwaygeologysymposium.org/wp-content/uploads/66_HGS-OPT.pdf
• 
• Supplemental Notes:
  • Copyright © 2015 Highway Geology Symposium (HGS). Abstract reprinted with permission of the HGS.
• Corporate Authors:

  Highway Geology Symposium

  ,   United States 
• Authors:
  • Pelham, Krystle
  • Langlais, David M
• Conference:
  • 66th Highway Geology Symposium
  • Location: Sturbridge Massachusetts, United States
  • Date: 2015-9-14 to 2015-9-17
• Publication Date: 2015

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: pp 198-208
• Monograph Title: Proceedings of the 66th Highway Geology Symposium (HGS 2015)

Subject/Index Terms

• TRT Terms: Groundwater; Nitrates; Nitrogen; Presplitting (Blasting); Road construction; Rock excavation; Water quality
• Geographic Terms: New Hampshire
• Subject Areas: Construction; Environment; Highways;

Filing Info

• Accession Number: 01638304
• Record Type: Publication
• Files: TRIS
• Created Date: Jun 21 2017 5:16PM