Story

Project: Former Pesticide Manufacturing

Confidential Client Southeast USA

Summary: A pilot study was conducted to determine the applicability of deep in situ DARAMEND® bioremediation* for treatment of soil containing volatile organic compounds (VOCs) and organochlorine pesticides (OCPs). A total of 43,590 lbs of DARAMEND® was injected into four injection points. The injections were conducted using hydraulic fracturing. Sampling conducted 7 months after the injections showed a decrease in Toxaphene and total OCP with over 90%.

Bench-Scale Treatability Study: Adventus conducted bench-scale tests to determine the applicability of deep in situ DARAMEND® bioremediation for treatment of soil containing VOCs and OCPs. A pilot-scale demonstration project is currently proceeding on site.* The bench-scale work evaluated several DARAMEND® treatment scenarios, using a number of DARAMEND® products, and compared straight anoxic conditions to a cycled aerobic/anoxic protocol. The testing was performed in sealed columns to simulate in situ conditions and prevent contact with the atmosphere.

The most effective treatment consisted of the addition of DARAMEND® product D2002/6390Fe20, which contains slow-release organic carbon, nutrients, and micro-scale zero-valent iron. This treatment reduced the total OCPs from 46.9 mg/g to 1.1 mg/g after 117 days of treatment, representing greater than 97% reduction in total OCPs. During this same period, the VOCs, primarily xylene and ethylbenzene, were reduced by over 99%.

Pilot Study Field Injection:Given the success of this treatment technology at bench-scale, a pilot-scale demonstration project was initiated in October of 2003. The goal of the project was to reduce source zone soil concentrations of OCPs and VOCs through the deep in-situ injection of DARAMEND® into the source area. A series of four applications of 1% DARAMEND® by weight with respect to the mass of soil in the treatment area was implemented. The applications were planned for intervals of between 14 and 21 days. Soil in the treatment zone was a highly weathered limestone at depths of 31' to 37'. The injection method consisted of driving rods to these depths using a Geoprobe rig, followed by hydraulic fracturing and injection of DARAMEND®.

Four locations were chosen for injection, with two to three depths per location. At each location a total of approximately 2,800 pounds of DARAMEND® was injected (i.e. 1,400 pounds per injection at locations with 2 depths and 930 pounds per injection at locations with 3 depths). The DARAMEND® product was delivered to the site in 25 kg bags for ease of handling and the material was handled with negligible dust creation. DARAMEND® was placed in a hopper, and mixed in-line with a guar solution for delivery to the subsurface treatment area (Figure 1 right). To enhance groundwater movement through the DARAMEND® fractures, sand was introduced, at ratios of 1:2 and 1:1 sand to DARAMEND® by mass.

The product was successfully injected in each of these scenarios. Sampling of the treatment area to determine the aerial and vertical extend of the DARAMEND® injections was performed using Geoprobe sampling equipment. The DARAMEND® layers were easily visible in the cores, whether the fracture was a hairline fracture near the tip of the fracture, or whether it was a few inches in thickness closer to the injection location (Figure 2 right).

Fig. 1. Creation of DARAMEND and guar mixture.

Fig. 2. DARAMEND® layer injected between clay and weathered limestone.

Results: Soil concentrations of Toxaphene and total OCPs were measured in June of 2004. Given the fact that OCPs bind strongly to the soil, the concentrations vary widely from one location to the next. For samples that were taken from as close to the same location and depth as possible, and for samples that showed a decrease in concentration between November 2003 and June 2004, the results are tabulated in Table 1.

Four out of twelve samples showed an increase between these sampling dates, however the median concentrations of those increases were 9 μg/g and 12 μg/g for Toxaphene and total OCPs respectively. These data show that the soil concentrations of Toxaphene and total OCPs decreased significantly between the dates shown. The decrease in the average concentration of both Toxaphene and total OCPs was 93%.

Table 1. Influence of in-situ DARAMEND on average Toxaphene and total OCP concentrations between November 2003 and June 2004 for selected samples.

Toxaphene (μg/g) Total OCPs (μg/g) Average Nov 2003 Value 127.7 169.1 Average June 2004 Value 8.7 11.8 Decrease in Average Concentration 93.2% 93.0%

*Prior to establishment of EHC®, this product was referred to as Deep In situ DARAMEND®.