DELTA-N-15 OF NITRATE DERIVED FROM EXPLOSIVE SOURCES IN A KARST AQUIFER BENEATH THE AMMUNITION-BURNING-GROUND, CRANE-NAVAL-SURFACE-WARFARE-CENTER, INDIANA, USA

Military institutions involved in the production and demolition of exp losives, propellants, and pyrotechnics have the potential to degrade g roundwater aquifers through the addition of numerous contaminants incl uding nitrate. A nitrate plume has been identified in a karst aquifer beneath the Ammunition Burning Ground (ABG) at the Crane Naval Surface Warfare Center, Indiana, USA. Wells located in the vicinity of surfac e impoundments and bum pans used for treatment of explosive materials show the highest concentrations of nitrate ranging from 11.2 to 19.6 m g l(-1) as NO3-. Little is known about the isotopic composition of nit rates originating from these processes. Eight wells within the ABG wer e sampled and analyzed for nitrogen isotopic composition of nitrate. A n enrichment in the delta(15)N (delta(15)N = +8.9, +12.0, +13.1. and 13.5 parts per thousand) occurred at four wells located near the prima ry areas of disposal activities within the ABG. Four wells located nea r the outer limits of the ABG had delta(15)N values significantly lowe r than those observed in the central area of the ABG (delta(15)N = +4. 0, +4.1, +4.6, and +2.0 parts per thousand). Soil samples and burn-pan ash samples were collected and analyzed for the nitrogen isotopic com position of nitrate. Three soil nitrate samples had low delta(15)N val ues of -1.7, -1.8. and +2.2 parts per thousand. The burn-pan ash sampl e produced nitrate with a delta(15)N value of +2.9 parts per thousand. The observed enrichment in delta(15)N from samples taken from wells l ocated near the ABG has been postulated to be a result of photodegrada tion or biochemical modification of RDX and TNT contaminated sludges a nd volatilization of NH3 in storage lagoons within the ABG. (C) 1998 E lsevier Science B.V. All rights reserved.