dnapl investigation in fwda outside the barrier wall oregon deq, hart crowser, inc., and gsi water...

DNAPL Investigation in FWDA Outside the Barrier Wall

Oregon DEQ, Hart Crowser, Inc., and GSI Water Solutions

2011 Data Gap Investigation

Wells with NAPL

Outside Barrier WallMW-Ds MW-Gs MW-20i MW-10s

Inside Barrier WallEW-1s EW-18sEW-8s MW-22i EW-23s MW-10rEW-15s MW-56s

NAPL Thicknesses posted are from June 15, 2010

2011 DNAPL Investigation Purpose – To assess the

nature, extent, source(s), and potential pathway(s) of DNAPL to MW-20i

Conclusion – The source of DNAPL to MW-20i is small and localized. No evidence of a threat to the Willamette River.

DEQ and EPA Recommendation – Terminate NAPL recovery in late April 2011, and conduct four subsequent gauging efforts to assess whether NAPL thicknesses increase

2011 NAPL Investigation Objectives

Determine whether there is potentially mobile DNAPL within the backfill of two City of Portland (COP) high pressure sewer lines in the vicinity of MW-20i;

Determine whether there is a pool of mobile DNAPL overlying the silt that migrates to MW-20i (or elsewhere); and

Investigate the relationship between the DNAPL observed in monitoring wells MW-20i, MW-Gs, and MW-Ds.

DNAPL Investigation Area

DNAPL Investigation Locations

2011 NAPL Investigation Results Pot holing did not reveal

NAPL within the backfill surrounding the high pressure sewer lines near MW-20i.

While limited sheen and staining were observed, exploratory drilling did not reveal a pool of mobile DNAPL in the vicinity of MW-20i.

There is no evidence of a source of mobile NAPL with a continuous pathway to the River.

Fence Diagram showing conceptual NAPL extent before the investigation

Fence Diagram showing refined conceptual NAPL extent

Fence Diagram showing refined conceptual NAPL extent

MW-Ds (outside, FWDA)

NAPL Monitoring:MW-Ds (outside, FWDA)

NAPL Monitoring:MW-Gs (outside, FWDA)

NAPL Monitoring:MW-Gs (outside, FWDA)

NAPL Monitoring:MW-20i (outside, FWDA)

NAPL Monitoring:MW-20i (outside, FWDA)

NAPL Monitoring: EW-1s (inside, TFA)

NAPL Monitoring: EW-1s (inside, TFA)

DNAPL Investigation Conclusions Thin layers of sheen and staining were observed

primarily within the smear zone, overlying finer-grained units and few stringers within the sand with depth

No evidence of mobile NAPL in borings

Source of NAPL to MW-20i was not identified; however, given the numerous investigation boring conducted in the vicinity in 2004-2006, there is clearly no significant pool of NAPL that could threaten the Willamette River

There is no compelling evidence of NAPL migration to the Willamette River, and therefore, no reason to continue to recover NAPL from wells outside the barrier wall