SITE STATUS UPDATETOP STOP PETROLEUM RELEASE SITE
GUNNISION, UTAH
Morgan Atkinson – Division of Environmental Response and Remediation, Project Manager
Work Completed Since March 2009 Gunnsion City Council Meeting
Indoor Air Monitoring Sub-Surface Soil Vapor Monitoring Continued Abatement/Corrective
Action Additional Monitoring Well Installation Continued Groundwater Monitoring
Indoor Air Monitoring
Monthly indoor air monitoring required in 15 homes and 16 businesses Ensure petroleum vapors from plume are
not impacting indoor air Noticeable odors and complaints Ensure installed abatement systems are
functioning
Indoor Air Monitoring (cont.) 1 - 2 sampling events since March ’09
Most locations have enough data to determine future sampling frequency
Data available indicates most abatement systems are effectively removing vapors
Sub-Surface Soil Vapor Monitoring
Vapor probes installed in 14 homes and 9 businesses Determine if vapors are accumulating
beneath structures Establish a pathway from the plume to
indoor air Delineate sources of petroleum-related
indoor air vapors
“Draft Indoor Air and Sub-Surface Soil Vapor Monitoring Status Report”
Submitted to DERR, August 24, 2009 Details all indoor, outdoor and sub-surface vapor data collected
to date
DRAFT recommendations include – Risk-based screening levels for indoor air
(0.39/0.49 ug/m3 Benzene residential/commercial) Conservative slab attenuation factor of 0.1 to establish target
sub-surface concentrations (3.9 & 4.9 ug/m3 Benzene) Proposed quarterly sub-surface sampling if below target sub-
surface levels Proposed monthly sub-surface sampling if exceeding target sub-
surface levels.
DERR has issued a comment letter to Wind River requesting additional information – nothing has been approved DERR will require continued monthly indoor air sampling where
target sub-slab levels are exceeded
Continued Abatement &
Corrective Action
5 soil vapor extraction (SVE) systems operating Wind River estimates ~13,000 gallons of gasoline removed
by SVE Vapor removal decreased significantly in most systems
The water table increased by ~2 plus feet in several monitoring wells but has since decreased to near 2007 levels
Vapors treated by carbon canisters only
Sub-slab ventilation systems operating in 2 businesses and 9 homes above plume Monthly operation and maintenance conducted
Future Corrective Action Evaluation required by DERR (letter to Wind River dated August 26, 2009)
Continued Groundwater Monitoring&
Updated Plume Maps
Groundwater concentration maps prepared by Wasatch Environmental display Benzene concentrations over time Maps do not include soil contamination
Additional Work Required
Corrective Action Plan evaluation Evaluation of SVE systems to show
radius of influence and effectiveness in remediating groundwater plume
Evaluate alternative technologies to remove contaminants and reduce plume lifetime
Submit updated CAP for approval
Additional Work Required (cont.)
Additional groundwater monitoring wells required near 200 S. 100 W.
Continued quarterly groundwater monitoring
Continued monthly/quarterly indoor air and/or soil vapor monitoring
DERR ACTIONS Require Wind River to actively clean-up
release Have staff available for meetings and
discussions about clean-up activities and progress
Establish remediation goals for the site based on drinking water standards Soil and groundwater samples that meet
remediation goals must be obtained throughout the full extent of the plume area before closure considered