View our full 4 part Metals Stabilization webinar series.
Part 1: Treatability Studies (reagents, leach test)
Part 2: Design (goals, investigation, remedy testing)
Part 3: Implementation (mixing, injection, PRBs)
Part 4: Performance Monitoring (testing, evaluation, optimization)
The USEPA is making a significant change in how leaching tests are used in decisions regarding waste disposal, beneficial reuse of materials in construction applications, and in assessing treatment effectiveness as presented in a 2010 background document1. Two of the test methods presented in this document are now part of USEPA SW-846 as:
Continue Reading | August 2013 Remediation Trends
Batch versus Column Testing Treatability studies for stabilization of metals have traditionally focused on batch testing where soil/waste is combined with a leaching solution and allowed to react for a specified period of time. Liquid to solid (L/S) ratios, stirring methods, and reaction times are specified for a given set of tests. This approach is required for hazardous waste characterization (e.g., TCLP) and can provide approximations for the conditions of in situ stabilization remedies with the Synthetic Precipitation Leaching Procedure (SPLP) or comparable groundwater leaching procedures. Batch procedures use relatively small volumes of soil/waste and leaching solutions and can be completed within days.
Column studies can address a number of issues that cannot be addressed with batch tests, or are better controlled within a column, such as:
Bench-Scale Treatability Testing
Treatability studies provide a low cost evaluation for the development of site- specific chemistries for remediation of heavy metals and organics. Well-designed treatability studies can identify better reagent choices at lower doses that result in cost savings and reduced risk of treatment failure. With a treatability study, chemistries are designed for specific site conditions, and allow for evaluating alternate treatment scenarios and land use options.
Treatability Study Approach
In-Field Confirmation Testing
Testing services comparable to treatability tests can also be used during the full-scale implementation of a remedy in order to provide “real time” confirmation of success:
Bench and Field Laboratory Services
The ReSolution Partners treatability study laboratory can provide batch and column studies for metals stabilization, total oxidant demand determination, and organics oxidation. Our experienced staff develop innovative, site-specific test protocols and chemistries designed to meet project goals. Screening indicators are often determined during bench-scale studies that can be measured during full-scale implementation to evaluate treatment performance.
Testing Capabilities-Leaching extraction screenings including:
-Total Oxidant Demand (TOD) determination on solid and aqueous samples for:
-Colorimetry analysis for:
-Total persulfate analysis on solid and aqueous samples by titration.
-Organics oxidation destruction efficiency in soil (total and leachable) and in groundwater.
-Selected total ion analyses on aqueous samples by Ion Specific Electrode (ISE) methods.
-Alkalinity Neutralization Capacity / Calcium Carbonate Equivalent (ANC/CCE) determination for solid and aqueous samples.
-Total moisture in solids determination
-pH determination for solid and aqueous samples
Stabilization of soil and waste by chemical addition is used to reduce the leachability of metals in unsaturated settings and in groundwater. The point of application is usually the source area where spills have occurred or waste has been disposed. In some settings, however reagent application in these areas is not feasible or appropriate.
Such settings include:
An alternative approach in these settings is to manage the leached constituents in the groundwater leaving the site such that acceptable concentrations are achieved before a point of compliance or point of exposure is reached. Permeable reactive barriers (PRBs) can be installed that allow the metal- bearing groundwater to pass through a saturated zone where emplaced reagents cause the metals to be removed from the groundwater. PRBs can be installed across the entire width of the affected groundwater if the PRBs can be installed as gates in below-ground impermeable barriers that direct the groundwater to the gates. Two examples of such gates are described in this newsletter.
A former industrial site had been redeveloped into an apartment complex. Surficial soil remediation was completed to meet the new land use, but groundwater remediation was deferred until after the site was redeveloped. Zinc concentrations as high as 30 mg/L below the site flowed toward a nearby creek where the discharging groundwater resulted in surface water zinc concentrations in excess of the Surface Water Quality Criteria of 2 mg/L for protection of aquatic life.
The development covered the likely zinc source areas, making source remediation infeasible. The proposed remedy was therefore to install a PRB on the downgradient side of the site to remove the zinc before the groundwater discharges to the creek.
ReSolution Partners completed a treatability study to identify reagents that would remove the zinc from the groundwater as well as be suitable for injection by direct-push technologies in the limited space available in the apartment complex. An injectable slurry was identified that lowered zinc concentrations in bench trials to ≤ 0.010 mg/L. Additional bench trials were completed in response to regulatory agency concerns regarding the longevity of the PRB. Multiple extraction procedures using site groundwater were combined with site hydrogeologic conditions to show that aqueous zinc concentrations were 0.088 mg/L after an equivalent of more than 400 years of groundwater flow through the PRB. This was considered adequate by the State regulatory agency, and ReSolution Partners completed pilot scale trials to evaluate the physical injection (e.g., reagent distribution, radius of influence).
The pilot test confirmed reagent distribution and in situ zinc concentration reductions. The full-scale PRB application included a total of 45,000 gallons of slurry injected at 63 locations over 4 weeks. Within two years the zinc concentrations in the creek met the 2 mg/L remediation goal, and the site achieved regulatory closure.
