Management of the groundwater contaminated by military explosives
Permanent address of the item is
Räjähdeainekontaminaation hallinta pohjavedessä
Residual concentrations of the most commonly used explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been identified in soil and groundwater at military training ranges in Finland. Military training areas are often located at groundwater areas classified as important drinking water resources. The aim of this thesis is to examine degradation, migration, toxicity and environmental fate of TNT, RDX and HMX and to evaluate remediation and treatment methods for explosives contaminated groundwater. TNT, RDX and HMX are degraded by biological, chemical and abiotic processes. Dissolution and adsorption are important in determination of migration but are largely site-specific characteristics. Despite of different properties, TNT, RDX and HMX are all found in groundwater. Possible treatment methods for groundwater are pump-and-treat, permeable reactive barriers and in situ chemical oxidation, but soil remediation has to be coupled with water treatment. The experimental part of this work contained two water treatment experiments and monitoring abiotic degradation of TNT and RDX. Efficiency of UV irradiation in degradation was tested with 407 J/m2 and 550 J/m2 UV doses. UV irradiation was chosen as it is used at some water work stations to ensure delivery of pathogen-free water. The aim was to evaluate feasibility of UV irradiation in degradation of explosives during standard water treatment practices. As a result, 29.6% of TNT and 36.9% of RDX was removed under 407 J/m2 dose and 29.6% (TNT) and 46.7% (RDX) with 550 J/m2. Hence, UV irradiation is not efficient enough for explosives degradation as sole method. Removal of explosives from TNT/RDX containing water by reverse osmosis (RO) was tested using Kärcher water purification system. The equipment can be used for production of drinking water at crisis management sites for military forces and civil population. As a result, TNT, RDX and intermediates present were removed below detection limit and safe drinking water can be produced by RO from explosives contaminated water. Due to quantity of reject water (60% of intake), method is not suitable for treatment at water works. Abiotic degradation was evaluated by monitoring removal of TNT and RDX from water exposed to natural light and in dark conditions. Under exposure to natural light, TNT and intermediates were removed within first week, while only 3.7% (7 d) and 33.3% (14 d) of TNT was degraded in dark. In contrast, only 16.0% and 28.6% of RDX was degraded during first and second week. RDX was not degraded under dark conditions.