In many countries, lead has accumulated in soil at and around shooting ranges from years of lead shot and bullets being fired into fixed ‘stopbutt’ mounds or at moving clay targets. The US Department of Defence, for example, oversees 3000 small-arms firing ranges around United States, and accounts for 1000 tonnes of lead used annually in live-fire military training. In addition the US has up to 9000 non-military outdoor shooting ranges. The US EPA estimates that nearly 3000 tonnes of lead produced annually in the United States during the late 1990s was used in bullets and pellets.1
As a result, soil lead concentrations above 10,000 mg per kg of soil are commonly reported at shooting ranges in New Zealand, the US, England, Germany and Scandinavia.2 One site assessment in the US revealed lead concentrations ranged from 27,000 mg/kg to 233,142 mg/kg.1 The ANZECC guideline limit, for Australia and New Zealand, is 300 mg/kg, with higher levels requiring further investigation.
Contaminants at shooting ranges may also include antimony, copper, zinc, arsenic, and polycyclic aromatic hydrocarbons (PAHs). However, lead is normally the main concern due to its range of severe toxic effects and the vulnerability of children. Lead is commonly absorbed through drinking lead-contaminated groundwater, eating contaminated foods, or breathing the dust from lead-contaminated soils.
Typical health concerns include:
At Muchea Air Weapons Range, WA, CRC CARE has been leading a project to remediate soil contaminated with lead, copper and antimony. Again, lead is the main concern. Firstly, the most heavily impacted soil is mechanically sieved to extract the larger metal fragments using equipment originally developed for gold mining in South Africa. Over 90% of the lead is recovered in this way. If the resulting slurry is low enough in lead, it is returned to the environment. If not, it is ponded for further treatment.
One traditional slurry treatment involves ‘physical encapsulation’ of lead particles in which they are essentially immobilised in a matrix. However, the effectiveness of this technique is dependent on the matrix never degrading, which cannot be guaranteed. As soon as the lead is re-exposed, the chemistry of the soil environment allows substantial conversion to a soluble form, notably lead carbonate.
CRC CARE has avoided this risk in the WA project by refining a chemical stabilisation process that creates an insoluble skin of lead phosphate around lead particles of all sizes. Recent tests at two sites in NSW3 showed that this approach reduced leachable lead by more than 99%, bringing the final residues well within acceptable limits.
As of late mid-2013, work at the Muchea site had seen 3.5 tonnes of lead remediated from more than 3000 tonnes of contaminated soil, and saved $1.5 million in treatment costs compared with other strategies – such as ‘dig and dump’ – that had been considered by the Department of Defence.
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