Challenge

This property was historically impacted by releases of large quantities of waste oil.  The waste oil was brought to the site to, ostensibly, heat on-site greenhouses and to be processed and resold.  Remediation of the impacted upland portion of the site has been largely completed under the Massachusetts Contingency Plan.  GZA is finalizing the design and permitting for remediation of a three-acre portion of the wetland area and pond containing visible oil from the surface down to as deep as 14 feet below the surface.  Soil within the wetland consists of a 30-foot deep deposit of peat with very low weight-bearing capacity which poses significant challenges for earthmoving equipment access to remediate the wetland by excavation.  Furthermore, stormwater flow through the wetland increases rapidly with any substantial rain event.  This presents difficult challenges for containing oil sheens and floating separate phase oil that would result from disturbance of the wetland root mat.


Solution

GZA developed a “pre-load remediation strategy” for the two acres of vegetated wetland that provides access to the work area as an intrinsic aspect of the proposed method, and avoids disturbing the root mat and minimizes the generation of sheens and floating oil.  The primary goal of the remediation is to eliminate visible oil and other waste oil related contaminants from the biotic zones of the wetland soil and sediment. The pre-load remediation of the vegetated wetland involves placement of an organoclay oil migration barrier, overlain by two to three feet of mineral fill.  The pre-load fill will consolidate the underlying peat and cause the wetland soil surface and pre-load fill to subside. Once sufficient subsidence has been achieved (approximately 1.9 feet) the upper portion of the fill will be removed, and a vegetated wetland will be restored over the residual fill. The one-acre pond will be remediated by hydraulic dredging of approximately 7,000 cubic yards of soft, oily surficial sediment. The dredged sediment slurry will be actively dewatered using filter presses because upland area for equipment staging and material management is very limited. An organoclay barrier will be installed on the dredged subgrade, and sand will be used as replacement benthic habitat.


Benefit

The mineral load fill will provide a work platform for operation of earthmoving equipment. The organoclay barrier and load fill will be placed directly on the root mat, thus avoiding physical disturbance that would generate relatively large quantities of sheen and floating oil. GZA has had pre-application meetings with multiple regulatory agencies and discussions have been favorable toward the proposed remediation.  GZA is currently preparing an Environmental Impact Report (EIR) under the Massachusetts Environmental Policy Act (MEPA)  which is expected to be submitted in October 2019.

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