• Site Characterization
  • Monitoring Wells/Soil Vapor Wells
  • Vertical Groundwater Delineation
  • Vapor Extraction/Natural Attenuation
  • Pilot Study/VE Remedial System

Gentry County, MO

2010 to present

Site Description

Leaking USTs and impacted soil were removed from a convenience store site in Gentry County, MO. Site characterization activities determined that elevated chemical of concern (COC) concentrations are present in soil and groundwater, and a large groundwater plume is present off-site at residential and non-residential properties. A city well has reported detections of petroleum compounds, and this site has been identified as one of several possible sources.

Site Characterization Summary

A total of 30 soil borings, 6 soil vapor wells, 16 permanent shallow unconsolidated monitoring wells, and 2 deep unconsolidated monitoring wells were installed by Sunbelt crews to delineate the soil and groundwater contamination. Vertical profile sampling in wells installed to depths of 75 feet have indicated detections of COCs in groundwater at approximately 44–46 feet in depth.

Feasibility Study Summary

Remedial alternatives were evaluated at the site due to the historical presence of gasoline, also known as light non-aqueous phase liquid (LNAPL), in groundwater both on and off-site. A short-term vapor extraction (VE) test was conducted at the site on several monitoring wells. The pilot study was conducted to evaluate the potential for utilizing VE to remove source area mass coupled with monitored natural attenuation (MNA).

Vapor Extraction (VE) Testing Results

Four wells were evaluated for VE at the site. Two wells produced approximately 30 pounds of petroleum mass per day. Groundwater levels in the range of 25 to 28 feet would result in more exposed screen and contaminated soil that could result in higher flow rates at lower pressures and potentially more removed mass.

Natural Attenuation (NA) Evaluation

A review and analysis of the NA related data when compared in conjunction with the COC concentration data show that significant concentration reduction is taking place at the site related to biological degradation. The granular nature of the saturated zone, the permeability of the unsaturated zone to allow precipitation to percolate into the saturated zone and replenish the oxygen is amenable to the NA of petroleum hydrocarbons at the site.

Current Status

A vapor extraction (VE) system has been installed at the site. Preliminary test results indicate high rates of petroleum mass removal.