Environmental Project

Sustainable Solution for Arsenic Remediation

Red Barn Cattle Dip Vat Site Brighton, FL

Solution Overview

Client:

The Seminole Tribe of Florida, a federally recognized sovereign nation which employs 2,000+ personnel with $24M in purchasing power.

Business Challenge:

Remediate groundwater contaminated with arsenic from historic cattle dip vat operations.

Solution:

Apex professionals with comprehensive understanding of aquifer biogeochemistry used in-situ chemical oxidation (ISCO) to stimulate naturally occurring bacteria as part of the remedial process.

We used non-toxic, sustainable materials to accelerate in-situ remediation.

Results:

  • 95% reduction in arsenic concentrations.
  • Savings up to $1M over expensive pump and treat (P&T) system.
  • Green, sustainable technology.
  • Use of common, local materials.

Challenge

Apex was retained to conduct a pilot study for an in-situ chemical oxidation (ISCO) of arsenic in groundwater associated with a former cattle dip vat in Brighton, FL.

Solution

Apex helped the tribe remove the arsenic from the groundwater. The remedial design stimulated naturally occurring and ubiquitous sulfate reducing bacteria (SRB) to generate hydrogen sulfide through natural respiration processes. This technique reduces iron and forms a stable precipitate with dissolved arsenic. The primary mechanism for arsenic removal from groundwater entailed physical precipitation of the arsenic with iron and other inorganic compounds, especially those associated with the reduction of sulfate to form arsenopyrite. Sodium lactate was injected into four injection wells followed by 1,000 gallons (per well) of magnesium sulfate solution. We conducted post‑remediation groundwater monitoring using select pilot test area wells.

This process used non-hazardous amendments such as locally grown sugar cane and/or orange processing byproducts.

Results

SRB testing and DNA analysis reported sulfate reduction was estimated to be approximately 20-fold higher in one of the injection wells. This evidence confirmed that the introduction of sulfate and lactate to the aquifer successfully stimulated the SRB population to grow and thrive. Further post injection evidence of SRB activity was observed in black staining in soil cores near injection wells and the black discoloration of sampled groundwater from the injection wells, indicated the generation of iron sulfide from SRB respiration processes and binding to dissolve elemental iron.

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