SITE STATUS UPDATE TOP 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.)  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

Indoor Air Monitoring Data (Full tables available in handout)

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/m 3 Benzene residential/commercial) Conservative slab attenuation factor of 0.1 to establish target sub-surface concentrations (3.9 & 4.9 ug/m 3 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

Stay up to date… The latest submittals and reports available online: