During Webinar 2 of COLUMBIA’s HRSC Webinar Series, learn about the successful techniques for cost-effective implementation in developing an LNAPL management strategy. Petroleum subsurface investigation and risk evaluation have long presented a difficult challenge, so join our webinar for further discussion on evaluating LNAPL distribution and soil hydraulic permeability. Case studies discussed during this session will include retail stations, pipelines, terminals, railyards, refineries, complex UST sites, military installations, and trucking refueling facilities.
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- LNAPL saturation level (thickness is one indicator) - Groundwater conditions (now and then; perched, unconfined, confined) - Soil grain size & structure - Pore pressure and pore space availability - Condition of the monitoring wells and their adjacent formation, filter pack, and seals - What elevation (depth) intervals are we working with? - What tools do we have that can provide useful data regarding these conditions?
LNAPL Site Conceptual Model Some Factors to be Considered -LNAPL Saturation - In-well thickness (and condition of well) - Saturated vs. unsaturated zones - Pore sharing (water, air, other fluids) - Water level response (current and historical) - Heterogeneous conditions (soil and water) - Head and gradient (both LNAPL and groundwater) - Hydraulic conductivity & transmissivity - Mobile vs. migrating
Quick Notes: - LNAPL share pore space with other fluids including air - The head pressure of the LNAPL must overcome the pore entry pressure for LNAPL migration
- FOUR different frequency bands - Fluorescent light received from the down hole window - Lighter, shorter chain hydrocarbons blue-green - Heavier, longer chain hydrocarbons orange-red - Matrix effects - Reference Emitter (RE) source test required
Quick Notes: - Used to profile hydraulic pore pressure and permeability “effective K” - Integrated EC - Positive pressure flow of water supplied from surface - Determine migration pathways, remediation injection regions, and placements for monitoring wells
Situation: - Historical release - Multiple MWs installed - New or recurring free product thickness (1.5-ft) in one or more wells - Investigate for unidentified source
Fact: - Recurring presence of LNAPL in a monitoring well OR continued elevated groundwater concentrations of hydrocarbons are clear evidence of a remaining source…it just may not be mobile or moving
Quick Notes: - Performance test is GOOD - Background check is GOOD - Material in the formation is different than performance test standard and repeatable - Material is at 17 and 19 feet below grade
Quick Notes: - Performance test is GOOD - Background check is GOOD - Material in the well is lighter (more fresh, less degraded) than product in the formation - Material in the well is different than the performance test standard - Response is repeatable
Options and Next Steps: Is the problem the LNAPL concentration, the Well
performance, the formation, or GW levels? • Are we at Csat, Residual, Mobile, or Moving? • What are the historical records for groundwater levels? • Are the hydrocarbons competing for pore space with the groundwater? • Has a lowering groundwater level in the past opened pore space that enabled LNAPL to move into the well? • What is the relative elevation relationship between the formation response, the monitoring well screen, the filter pack, the seal, and the groundwater level (now and historically) • Do we have a confined LNAPL situation beneath a clay with tight pore space? • Is the MW performing as expected?
Quick Notes: - Used to measure hydraulic conductivity “K” - Portable, manual tool kit - Pressurizes formation and then monitors formation recovery after releasing the pressure - Test performed in existing monitoring well or via direct push drive point - Development and condition of the well or drive point screen critical to the quality of the test
Important Final Thoughts • LOE – Use a (Multiple) Lines of Evidence Approach (no one
tool, sampling methodology, or analytical method works in every soil and every situation)
• Measure the heterogeneity - Local lithologic changes and local hydraulics control your outcome
• LNAPL thickness can be an important contributor to head, the pressure, of the LNAPL and therefore an indictor of mobility – however, make sure you measure true thickness in both the formation on the well
• Equally important are the competing hydraulic conductivity and pore pressure