Formatted Title
Paradigm Shift in Liability Management
Background/Objectives
An underground refined petroleum products pipeline developed a leak that resulted in pooled petroleum at the surface. Upon discovery, the leak was repaired and affected soil was excavated down to 12 feet. Released petroleum percolated through complex stratigraphy consisting of alternating sand, silt, clay, and sandstone lenses before reaching groundwater at approximately 60 feet. The groundwater plume was delineated, and the following remedial goals were established: 1) permanently remove all measurable phase separate hydrocarbons (PSHs) and 2) reduce benzene and TPH groundwater concentrations to ≤0.050 mg/L and ≤25.0 mg/L, respectively. Remedial design was developed solely using data produced during delineation. Five remedial technologies (soil vapor extraction, dual phase extraction, skimmer pumps, absorbent socks and in situ chemical oxidation [ISCO]) were applied over a 13-year period. A significant rebound occurred at the conclusion of each remedial technology. None of the remediation goals were achieved.
Approach/Activities
A new conceptual site model (CSM) was developed incorporating high resolution site characterization (HRSC) and 3-D contaminant modeling. This study revealed laterally discontinuous pooled hydrocarbons, which occurred at multiple vertical intervals. These hydrocarbon pockets were serving as secondary sources leaching to groundwater resulting in chronic post-remedial rebound. A revised remediation plan was created to focus on eliminating all secondary sources in the vadose zone before remediating the dissolved phase contaminants. A patented non-ionic surfactant blend was designed based on site-specific chemistry to desorb, mobilize, and remove sequestered hydrocarbons in the vadose zone. HRSC data allowed targeted injection that abated the secondary source with precision. After secondary source abatement was believed to be complete, the dissolved phase contamination was remediated by incorporating ISCO.
Results/Lessons Learned
By eliminating the ongoing secondary sources prior to dissolved phase remediation, contaminant reduction efficiencies were drastically improved. Within 45 days of surfactant treatment, the secondary source abatement was complete, and all measurable PSH (<0.01 ft) was eliminated from all monitoring wells without rebound. Approximately 30 days after initiating ISCO, benzene and TPH groundwater concentrations were reduced below their regulatory goals. To produce a buffer margin to allow for minor potential rebound, a 15-day final polish stage of ISCO additionally reduced benzene and TPH groundwater concentrations ≥99.99% from the release baseline concentrations. Reductions were sustained in post-remedial groundwater monitoring. The regulating agency concurred with the remedial results and recommended No Further Action status be granted by the court. In a subsequent hearing for the Agreed Order, the presiding Judge agreed with the regulator’s recommendation and issued No Further Action status.
During the first 13 years of active remediation, effort and money was split between progress towards site closure, managing annual cash flow, and avoiding enforcement. This resulted in considerable time, cost and effort spent trying different technologies with little progress. A revised CSM prompted a change in remediation tactics and an aggressive, more thoughtful treatment strategy was employed. Development, permitting, implementation and validation was achieved in under two years. Although annual allocated expenditure increased, overall project costs were substantially reduced from the projected budget (on a net present value basis). More importantly, a significant liability was quickly mitigated, rather than perpetuated for another decade. This success resulted in a paradigm shift for the responsible party regarding future liability management by minimizing the time to No Further Action status using a precise and aggressive remedial strategy.