Case study – benzene contamination pilot study - retail gasoline site, Northglenn, Colorado

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Courtesy of Remediation Products Incorporated (RPI)

Introduction

LTE was contracted by Shell Oil Products US (Shell) to conduct a pilot test program at a petroleum hydrocarbon impacted retail facility north of Denver, Colorado. The goals of the pilot program were to: 1) Determine the viability of using a carbon-based injectate (RPI’s BOS 200®) to remove hydrocarbons from soil and groundwater, 2) Assess transient hydraulic conditions resulting from the injection and 3) Demonstrate that biological breakdown of hydrocarbons was occurring.

Impacted groundwater was found in a very dense clay zone. Benzene concentrations at the pilot well (MW-10) varied between 1.0 and 7.0 milligrams per liter (mg/L) since 2005. The pilot injection program was deliberatively under-dosed to determine if the injectate would be effective and to allow for a more precise measurement of the full scale requirements.

Evaluation

A limited site assessment was performed to determine the vertical profile of impacted soils and groundwater, and quantify the amount of petroleum hydrocarbons present. Three piezometers were installed within 20 to 50 feet of MW-10 to determine the radius of influence of the injection and to understand the hydraulic effects that result when an injectate is placed into the subsurface. In addition, LTE obtained and evaluated a variety of parameters including oxidation reduction potential (ORP), pH, and dissolved oxygen, nitrate and sulfate concentrations following the actual injection event.

Design/Installation

The injection program was developed based on targeted hydrocarbon concentration reduction of 75% with the quantity of injectate and placement of injection locations targeted toward the more highly impacted soil horizons. The treatment injectate consisted of 3,000 pounds of a carbon-based product (BOS 200®) injected into 10 locations on a 10-foot triangular grid pattern surrounding MW-10.

Prior to completing the injection program, LTE obtained a Rule Authorization (RA) from EPA Region VIII to inject BOS 200® into the subsurface.

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