Groundwater and NAPL Monitoring

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

2010 McCormick & Baxter Annual Report

Outline Monitoring Objectives NAPL Thicknesses and Recovery Groundwater levels and flow patterns 2010 Groundwater Quality Assessment Conclusions

Monitoring Objectives Groundwater & NAPL monitoring at the Site is

used to: Evaluate functional performance of the barrier wall

and associated RCRA-soil cap Meet the ROD RA groundwater objectives: to

prevent human exposure to or ingestion of groundwater, remove mobile NAPL to the extent practicable, minimize NAPL discharges to the Willamette River, and minimize vertical migration of NAPL to the deep aquifers.

Activities to Accomplish Objectives Track groundwater and river elevations and

gradients Document NAPL thicknesses, removal, and

recovery Assess COC concentrations in groundwater (2006

and 2010)

NAPL Monitoring Tasks - 2010 Weekly gauging at eight monitoring wells

outside the barrier wall and one well (EW-1s) inside the wall to determine recovery potential

Weekly recovery from wells outside barrier wall that have sufficient NAPL MW-Ds, MW-Gs, MW-20i (DNAPL only) EW-1s (inside barrier wall)

Semiannual gauging for NAPL in remaining wells Quarterly NAPL gauging was performed between 2006

and 2009 Semiannual NAPL gauging starting in 2010 (June and

October)

Total NAPL Recovery1989-2010 ~6500 gallons

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

MW-Ds (outside, FWDA)

MW-20i (outside, FWDA)

MW-56 (inside, FWDA)

EW-1s (inside, TFA)

EW-8s (inside, TFA)

2010 NAPL Recovery Summary

LNAPL Not recovered from any wells at the Site in 2010 LNAPL was only observed in EW-10s, which is

consistent with historical data, show no LNAPL accumulation in any other monitoring wells outside the barrier wall.

DNAPL ~146 gallons extracted in 2010

~54 gallons were from interior well EW-1s ~92 gallons from wells outside the barrier wall (primarily MW-

20i) The extraction rate of approximately ~7.7

gallons/month from wells outside the barrier wall is consistent with measurements from recent years.

NAPL thicknesses remain stable

Groundwater Level Monitoring Tasks

Semiannual groundwater level monitoring at site wells and MW-7 in Willamette Cove Shallow Zone Contour Maps (June 2010, October 2010,

and June 2011)

Continuous (30-minute basis) transducer data at select barrier wall wells and 2 interior wells Historic and 2010 (through June 2011) Hydrographs

June 2010

October 2010

June 2011

MW-36s/MW-37sinside/outside

2010-2011 Data MW36/MW37

MW44s/MW45sinside/outside

2010-2011 Data MW44/MW45

MW-52s/MW53sinside/outside

Historically, MW-52s groundwater elevation was ~18.5 NAVD88 (May 2003). The level has gradually dropped since installation of the barrier wall. Rate of decline increased with installation of the impermeable soil cap. Approaching equilibrium with the River

MW15s/EW1sinside

Groundwater Level Observations 2010 groundwater elevations and gradients are generally

consistent with previously observed conditions. Shallow groundwater flow is diverted around the barrier

wall to the northwest and south. Horizontal gradients outside the barrier wall are the greatest during periods of high precipitation and decrease during periods of low precipitation.

Groundwater gradients inside the barrier wall remain flat and generally to the west, except when peak river stage causes a reversal in gradient.

While most of the monitoring wells mimic the stage variations in the river, the oscillations in the shallow interior walls are delayed and muted and likely due to changes in pressure at depth rather than a hydraulic connection to the river.

Under typical river conditions, vertical groundwater gradients are low and typically downwards.

Groundwater Quality Assessment Comprehensive Baseline Assessment in 2006 Focused Groundwater Assessment for wells of interest in

2010

Total PAHs

Spring 2010

Spring 2006

PCP

Spring 2010

Spring 2006

Benzo(a)pyrene

Spring 2010

Spring 2006

Groundwater Quality AssessmentFindings

In general the Spring 2010 sample results are either less than or similar to the Spring 2006 results.

Of the wells sampled in 2010, only two shallow wells (EW-19s and MW-37s) contained elevated levels of PAHs. Both of these wells are located in the outside the northwestern corner of the barrier wall in an area known to contain residual NAPL.

These results are consistent with historical data and support the current understanding of contaminant occurrence at the Site.

Groundwater and NAPL MonitoringConclusions

Shallow groundwater within Barrier Wall has basically equilibrated with the River

Shallow groundwater outside and inside the barrier wall are not hydraulically connected (i.e., barrier wall is performing as expected)

GW inside barrier wall is hydraulically connected to the river from the “drain” in corner at base of wall

Intermediate and deep zones inside and outside the barrier wall continue to mimic river with very low vertical gradients (primarily downward)

Barrier wall is performing as designed to prevent NAPL (from within the wall) from migrating to the River; also, significantly reduces the flux of contaminated groundwater to river