Benefits of Combining In Situ Chemical Oxidation with In Situ Stabilization: Synergies and Solutions for Complex Sites
Background/Objective.
In situ solidification/stabilization (ISS) has been used at many manufactured gas plant (MGP), brownfield, and Superfund sites. ISS mixes cementitious reagents with contaminated soils reducing the bioavailability and leachability of contaminants. ISS can also be optimized to control certain ll soil characteristics, such as compressive soil strength and reduce hydraulic conductivity. Various reagents are used to promote ISS including Portland cement, blast furnace slag, lime kiln dust, etc. Several of these reagents contain calcium oxide (CaO), also known as quick lime. For example, Portland cement (PC) consists of 60% to 68% CaO by weight.
ISS is often applied at highly contaminated petroleum hydrocarbon sites decreasing the leachability of BTEX, naphthalene (NAP) and other organic contaminant in soil. Cementation reactions also decrease hydraulic conductivity (K), which diverts groundwater flow away from the solidified/stabilized soil. ISS treatment also increases unconfined compressive strength (UCS), often critical for redevelopment.
However, high concentrations of organic contaminant can interfere with cementation reactions requiring excessive application of amendments increasing both amendment and disposal costs of the displaced soil. This ISS limitation can be minimized by utilizing a combined remedy approach like In Situ Chemical Oxidation to degrade some of the organic contaminants present. ISCO combined with ISS has been found to be able to achieve the same or better leachability and compressive soil strength values with less overall reagent addition and displaced soils. Combining one or more remediation technology generates synergies by exploiting the strengths and minimizing the weak- nesses inherent in individual technologies. When successful, combining remedies enhances performance and/or reduces costs compared to each technology used alone.
Approach/Activities.
This presentation will review the advantages and limitations of using the combined ISCO/ISS remedy on a contaminated soil from different petroleum hydrocarbon sites.. The presentation will review current literature and explore both bench and field data demonstrating the successes of ISCO-ISS as a combined remedy.
The objectives of this study generated by Srivastava et al. were to quantify
(1) the ability of a wide range of doses of ISS-activated SP to degrade BTEX and PAH
(2) the impact of BTEX and PAH removal from chemical oxidation during ISCO/ISS treatment on synthetic precipitation leaching procedure (SPLP) measurements, compared with a wide range of ISS doses alone
(3) the effect of activated PS on other ISS performance parameters, such as hydraulic conductivity and unconfined compressive strength
Results/Lessons Learned. Activated SP chemically oxidized a significant portion of the COCs for all the ISCO/ISS treatments, and the mass of COCs oxidized increased with increasing SP dose. The lowest molecular weight contaminants were preferentially oxidized. For the same PC dose, combined ISCO/ISS treatment was more far effective in reducing contaminant leachability than ISS treatment alone, because of the COC removal achieved by the ISCO (activated SP) component.