Use of Sequential Filtration for Determining Transportable Lead in Ground Water

Abstract

This study examines the effects of sequential filtration on the particle abundance and lead concentrations in ground water from four monitoring wells in New Jersey with a history of high turbidity, elevated metal concentrations, or where differences in metal concentrations exist between filtered and unfiltered samples. In these monitoring wells, both transportable suspended particles, such as colloidal particles that are suspended in solution, and nontransportable particles that are disturbed during sample collection but not considered mobile transportable species may be present in solution with potential overlap in particle size distribution. Filtration, particularly the operational pore size (25 to 0.45 μm) of the filter, was evaluated as a method to obtain a representative sample of the transportable metal, as defined by the dissolved phase and particles that are persistently suspended in solution. Two monitoring wells at the Denzer‐Schaefer site, a silty/clay aquifer with high particle concentrations (>8900 mg/L) from samples taken with bailers and a low‐flow purge (LFP) pump, showed that a filter of pore size 25 μm could remove 60% to 90% of soil‐derived particles, with minimal loss of suspended particles from solution. The two monitoring wells within the highly conductive Picatinny Arsenal sand aquifer provided higher particle abundance with the samples collected with bailers (4300 to 6500 mg/L) than with the LFP pump (4 to 11 mg/L), indicating greater artificial particle disruption with a bailer. At Picatinny Arsenal, the major portion of nontransportable particles in the ground water samples could be removed by filtration through a 25–μm pore size filter, with a minimal loss in suspended particles. Filtration of ground water through a 25–μm pore size filter followed by acidification at the sampling site would provide investigators a tool to examine particle transport in aquifers where there exists the potential for artificial particle disruption during sampling.

A Downhole Passive Sampling System To Avoid Bias and Error from Groundwater Sample Handling

“…Unfortunately, filtration also removes the mobile colloidal fraction, and some regulatory jurisdictions prohibit this procedure. Multiple filtration methods have been employed to delineate the mobile fraction from artifact (30) but are rarely employed in the field. The closure action of the ISS sampler does not mobilize normally immobile formation particulates because no pumping is involved and therefore allows collection of naturally mobile colloidal contaminant load closer to that of ambient groundwater flow.…”

Demonstration/Validation of the Snap Sampler Passive Ground Water Sampling Device for Sampling Inorganic Analytes at the Former Pease Air Force Base

“…In contrast, even low-flow sampling has been shown to artificially elevate particle levels in some wells (Bailey et al 2005), and most diffusion samplers cannot collect colloidal particles because of the small pore sizes of the membranes.…”

Demonstration/Validation of the Snap Sampler

“…Because the Snap Sampler is deployed prior to sampling to allow the well to recover from any disturbance associated with placing it in the well and because this device collects a whole-water sample instantaneously, presumably samples should not have elevated turbidity (i.e., soil-derived, non-transportable particles) and thus should reflect the true, naturally mobile, colloid-borne contaminants flowing through the well. In contrast, even low-flow sampling has been shown to artificially elevate particle levels in some wells (Bailey et al 2005), and most diffusion samplers cannot collect colloidal particles because of the small pore sizes of the membranes.…”