Formatted Title:

EPA LEAF Testing of Ultra-Lightweight Foamed Glass Aggregate (UL-FGA)

Background/Objectives:

Ultra-lightweight foamed glass aggregate (UL-FGA) is an innovative, one hundred percent recycled content material manufactured using curbside collected glass. When said glass is milled to a powder and combined with a foaming agent and passed through a temperature-controlled kiln, a nominal 1 to 1.5 inch thick, vesicular, inert and durable aggregate product is produced weighing on the order of 15 lb/ft³, almost 4 times less dense than water. The traditional uses of aero-aggregate include as a lightweight geotechnical fill on soft and/or coastal soils, over pipes, green roofs with the most celebrated use being the emergency repair of Interstate 95 in Philadelphia as a mechanically stabilized earth wall after the bridge collapsed due to a truck fire. Environmental applications are growing and has involved its use in trickling filters due to its high surface area. It has also been used as a fire suppression barrier around storage tanks at refineries and odor suppression in the European Union on the surface of manure ponds. These have served as motivation for its use on various ponds and lagoons at industrial sites where the release of odors and/or volatiles may be required. This necessitates an understanding of its impacts to water quality under a wide range of pH conditions.

Approach/Activities:

The UL-FGA was submitted for leaching by EPA Methods 1311 (TCLP), 1312 (SPLP), 1313 and 1316 for the target analyte list (TAL) metals. EPA 1313 was conducted with nitric acid (per method) and independently with sulfuric acid to simulate a variety of industrial processes and residuals including acid mine drainage and/or acid tar lagoons. The liquid to solid (L/S) ratios varied from L/S 10 (EPA 1313), 20 (EPA 1311, 1312) and 0.5 to 10 (1316) with added L/S of 20, 50 and 100 to simulate more dilute pond/lagoon type conditions where the UL-FGA could be in direct contact with high quality surface waters. Because of its cubic shape when manufactured, the asperities of the UL-FGA tend to self-abrade when tumbled generating fines as an artifact of the procedure. Therefore, to better simulate field conditions of a vapor barrier on a pond/lagoon, the EPA 1313 self pH and pH 2 (SO4 only) target replicates were also performed with the 1 to 1.5 inch nominal material in an extractor with a magnetic stirrer to mitigate against self-abrasion and with an extended extraction time of 7 days for L/S of 10 and 100.

Results/Lessons Learned:

While curbside collected glass as a source material is exceptionally clean, heavy metals are associated with colored bottles (green, brown, blue) and the pigments used on beer (e.g. corona) and wine bottles which tend to contain arsenic (As), cadmium (Cd), chromium (Cr) and lead (Pb) including crystal (Pb). That said, the total TAL metals results pass the most stringent Pennsylvania and New Jersey fill requirements which explains why the UL-FGA manufactured in the metro Philadelphia flagship plant enjoys widespread use by both state DOTs.

Because glass bottles are primary amorphous silica, milled glass and UL-FGA tend to titrate around the pK_a1 of salicic acid at pH~9.5. As such, the 1-1.5 inch nominal UL-FGA has a self pH (pH_o) of 9.9 and 7.9 at L/S 10 and 100. The pH of the 3/8-inch minus material can be up to 10.5 similar to natural limestone. The water quality associated with both gradations satisfies USEPA primary drinking water standards for heavy metals. The 1-1.5 inch UL-FGA also satisfies the primary drinking water criteria when exposed to strongly acid conditions (pH~1) except for Pb (<0.5 mg/L) which was still 10x below the TCLP standard. An actual TCLP performed on 3/8-inch minus material was similarly valued at pH 5.4 due to the alkalinity released associated with the smaller UL-FGA media when tumbled for 18 hours per the method. Based on these leaching results, the use of UL-FGA as a vapor barrier on a variety of ponds and lagoons to limit volatilization of hydrocarbons, odors or other noxious gases appears safe.

Archibald Filshill

Affiliation

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(Group 2, Poster Board #68) EPA LEAF Testing of Ultra-Lightweight Foamed Glass Aggregate (UL-FGA)