In-Situ Solidification of Sediments – When Strength Matters for Remediation and Redevelopment
In-Situ Solidification of Sediments – When Strength Matters
for Remediation and Redevelopment
Paul Jansen, Dan Kopcow, Mike Sabulis, Chris Pray, and Jim Ash (GEI Consultants, Inc.)
Tanya Alexander (National Fuel Gas)
Jeff Clock (EPRI)
Mr. Jansen has 29 years of experience in construction and project management leading teams through the regulatory, feasibility, design, remediation and closure process for utility, railroad and refining clients on their complex remediation projects. He has focused in the design and management of manufactured gas plant (MGP) remediation sites working on over 60 MGP sites from New York to Florida, including over 15 ISS projects, several sediment remediation projects with 4 of them involving ISS and treatability work.
The combination of solidification and In-Situ Solidification (ISS) of sediments has only been performed at a select number of sites. GEI has designed and overseen the remediation for four of these sites. For each case, ISS was used both as a remediation tool and to provide a beneficial end use. In each case, unconfined compressive strength (UCS) played a different role. UCS, along with leaching performance and hydraulic conductivity (K), are the typical parameters for solidification remedies for which criteria are specified to meet EPA guidance. The focus of our discussion will center on the UCS criteria: when it is important, when it is overly emphasized, and how the resulting ISS monolith can be used for cost effective remediation-redevelopment projects for valuable waterfront property despite not knowing what the redevelopment will look like at the time of remediation.
The four sites to be discussed are: 1) Tonawanda, NY, where dredged sediments were placed in an upland ISS-reinforced MGP gas holder foundation and solidified; 2) Nyack, NY, where ISS was used to remediate intertidal-zone sediments at an MGP site; 3) New Bedford, MA, where ISS of contaminated in-place and dredged sediments was used to create a confined disposal facility (CDF) that added developable land; and 4) Springfield, MA, where a full-scale ISS pilot test demonstration of submerged open water sediments was performed.
Each site had a different approach to solidification of sediments to address environmental impacts. The first three sites will be used to demonstrate how geotechnical design elements were integral to the project remediation, both in terms of providing temporary works and as an ancillary benefit for potential future redevelopment. In these instances, UCS was a critical performance criterion, particularly from the standpoint of ground-improvement for remediation and redevelopment. However, the fourth example of an ISS remedy will be used to demonstrate that future use of a remediated area should dictate the particular performance criteria specified, since using the standard EPA criterion for UCS provided no additional end use value. In fact, incorporating this UCS criterion increased the cost and carbon footprint of the remediation, unnecessarily consuming resources.
In all four case studies, the leaching, hydraulic conductivity, and UCS performance criteria were met for remediating impacted sediments through solidification. For three of the projects, the appropriate, site-specific application of UCS criteria increased the efficiency of construction and preparing the areas for redevelopment. In the fourth case study, setting inappropriate benchmarks for UCS resulted in unnecessarily increasing the environmental footprint without any discernable end use benefit. ISS performance criteria should be tailored to fit each unique site such that ISS can continue to be a cost effective tool to improve the environment without adding unneeded environmental and financial impacts to construction.