Evaluating the Applicability of Regulatory Leaching Tests for Assessing Lead Leachability in Contaminated Shooting Range Soils

Abstract

The toxicity characteristic leaching procedure (TCLP) is the current US-EPA standard protocol to evaluate metal leachability in wastes and contaminated soils. However, application of TCLP to assess lead (Pb) leachability from contaminated shooting range soils may be questionable. This study determined Pb leachability in the range soils using TCLP and another US-EPA regulatory leaching method, synthetic precipitation leaching procedure (SPLP). Possible mechanisms that are responsible for Pb leaching in each leaching protocol were elucidated via X-ray diffraction (XRD). Soil samples were collected from the backstop berms at four shooting ranges, with Pb concentrations ranging from 5,000 to 60,600 mg kg(-1) soil. Lead concentrations in the TCLP leachates were from 3 to 350 mg l(-1), with all but one soil exceeding the USEPA non-hazardous waste disposal limit of 5 mg l(-1). However, continued dissolution of metallic Pb particles from spent Pb bullets and its re-precipitation as cerussite (PbCO(3)) prevented the TCLP extraction from reaching equilibrium at the end of the standard leaching period (18 h). Thus, the standard one-point TCLP test would either over- or under-estimate Pb leachability in shooting range soils. Lead concentration in the SPLP leachates ranged from 0.021 to 2.6 mg l(-1), with all soils above the USEPA regulatory limit of 0.015 mg l(-1). In contrast to TCLP, SPLP leaching had reached equilibrium, with regard to both pH and Pb concentrations, within the standard 18 h leaching period, and the analytical SPLP results were in good agreement with those derived from modeling. Thus, we concluded that SPLP is a more appropriate alternative than TCLP for assessing lead leachability in range soils.

Toxicity characteristic leaching procedure over- or under-estimates leachability of lead in phosphate-amended contaminated soils

“…Similar results were observed by Cao et al (2008), who reported that the average Pb dissolution rate from the soil during the first 1 h was several times higher than at the next sampling time at pH = 3. Although Pb dissolution was slightly slower after 18 h, the Pb concentrations continued to increase with time, especially for Pb(NO 3 ) 2 -soil and PbCO 3 -soil.…”

“…Similar results were reported by Halim et al (2004) and Ghosh et al (2004), who argued that the TCLP did not simulate the pH-Eh conditions in landfills and demonstrated that the test underestimated As leaching from bearing solids and that equilibrium was not achieved within 18 h of standard exposure time. Cao and Dermatas (2008) investigated the leachability of Pb in shooting range soils using the TCLP and showed that Pb concentrations and solution pH values were not at equilibrium after the standard extraction time of 18 h due to continued dissolution of metallic Pb particles and the re-precipitation of Pb as cerussite. Rubinos and Barral (2013) reported that the standard TCLP largely underestimated the release of trace metals from bauxite red mud because of its high capacity for neutralizing acidity.…”

Immobilization of Heavy Metals by Co-pyrolysis of Contaminated Soil with Woody Biomass

“…Previously, the SPLP test was regarded as an applicable test to evaluate metal leaching from inorganic wastes such as contaminated soils (Cao and Dermatas 2008). Our SPLP data show that the success of metal encapsulation with biochar is dependent on several contributing factors including the type of metal, heating temperature and biomass addition.…”

The Distribution of Metals in Soils and Pore Water at Three U.S. Military Training Facilities

“…Lead concentrations as high as 60,600 mg/kg from a backstop berm have been reported (Cao et al, 2005). Military and sport ranges can be similar with respect to lead loading, but there are significant differences-the foremost being the size of the projectiles.…”