Refer to Initial POLREP.

1.1.2.1 Location

Refer to Initial POLREP.

1.1.2.2 Description of Threat

The Potentially Responsible Party’s (PRP) contractor West Central Environmental Consultants (WCEC) prepared a preliminary mass balance reconciliation for the amount of spilled gasoline, recovered gasoline, and residual gasoline remaining on-site.   The estimated quantity of gasoline spilled during the incident was 1,169 gallons, based on product inventory from before and after the incident.  Of the 1,169 gallons lost, WCEC recovered an estimated 159 gallons in sorbent materials during the emergency response, based on weight of the saturated absorbents less the weight of unsaturated materials.  Additionally, the excavation removed an estimated 150 to 170 gallons based on disposal sample analytical data, residual soil concentration data, and field instrument observations from the disposal samples.  Thus, an estimated 850 gallons of gasoline remains on-site.

An Initial Cleanup Action and Investigation Work Plan was approved on 17 November 2011; however, the removal action was not implemented until the week of 21 November 2011 due to inclement weather.

From 21 November through 22 November 2011, WCEC excavated approximately 184 cubic yards of PCS, including shot rock, road shoulder fill, and unconsolidated alluvium from the upslope ditch of U.S. Highway 12.  Excavation occurred over a distance of about 127 feet, and the width and depth of excavation below ground surface varied from 6 to 12 feet and 4 to 9 feet, respectively.  The excavation was backfilled with clean material.  The width and depth of excavation was limited due to the occurrence of shallow bedrock, close proximity of loose rocks along a steep cliff, and roadway stability concerns.  The PCS was transported to a nearby landfarm facility for treatment.

Fifteen soil samples were collected from the excavation – 10 discrete sidewall samples and 5 discrete bottom samples.  Four composite soil samples were also collected from the excavated material for use in quantifying the contaminant mass removed through excavation.  Soils from the immediate release area exhibited strong gasoline impacts with photoionization detector (PID) readings approaching 2,000 parts per million (ppm).  PID readings from the sidewalls and the bottom of the excavation ranged from 0 to 26 ppm.  An estimate of residual soil concentrations will be made following receipt of laboratory analytical results.

Three surface water samples were collected on 21 November 2011.  Preliminary data shows non-detect for the contaminants of concern.  The absorbent boom was removed from the Lochsa River on 22 November 2011 following the completion of all excavation activities.  The boom did not contain any gasoline constituents, product, staining, or sheen.

The need fpor additional cleanup actions will be based on the soil and surface water analytical resulkts, river bank monitoring, and other practical considerations.