Study of Natural Bioremediation Projects Using Time-Release Oxygen Compounds.

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Courtesy of REGENESIS

ABSTRACT: Enhanced natural bioremediation studies are being conducted on a series of sites throughout the midwest United States. Each site exhibits a unique geologic condition, contaminant concentration, enhancement application, and remediation goal. Based on a review of 14 sites, the usage and effectiveness of enhanced bioremediation has been categorized to provide general guidelines for applications and monitoring. The enhancement application reduced petroleum hydrocarbons in 65% of the sites; however a rebound in petroleum hydrocarbons was observed in 41% of the sites. The most significant factor affecting the bio-remediation effectiveness is the presence of free product and source material.

INTRODUCTION

In the early 1990s, BE&K/Terranext ground water BTEX data from gasoline underground storage tank (UST) sites indicated natural bioremediation was occurring downgradient of source areas. At finite distances downgradient of the source, an equilibrium was reached between the BTEX mass and the ability of natural organisms to bioremediate the mass. Ground water data indicated the dissolved oxygen levels in source areas were generally zero, whereas the dissolved oxygen levels downgradient were higher. BE&K/Terranext approached state regulators about conducting site trials to test a time-release oxygen compound to enhance this bioremediation process at sites which could not be aggressively remediated.

In 1995 and 1996, BE&K/Terranext used the Regenesis oxygen release compound (ORC®) at five sites to evaluate the effectiveness of enhanced natural bioremediation. Varying ORC application methods were utilized at sites with different geology and contamination levels. During that time, it became apparent that several factors affected the outcome of these projects. In an effort to improve the performance of future bioremediation projects, BE&K/Terranext collected data from 14 sites to identify factors which lead to successful, as well unsuccessful projects.

Site Characteristics. In addition to five BE&K/Terranext sites, data were collected from nine project files at state regulatory agencies. Each site is located within a 450 kilometer radius of Kansas City, Missouri. The site names and locations have been omitted at the request of the state agencies. Details regarding the site status, maximum BTEX concentrations, geology, ground water depths, and plume descriptions are summarized in Table 1.

The geology of 82% of the sites generally consists of fine grained soils overlying coarse grained sands. At the remaining 18% of the sites, clay overlies a silty clay, a shale, or fractured limestone. Ground water depths ranged from 1 to 6 meters, but was less than 4 meters at 78% of the sites. All of the sites are believed to fall within a ground water velocity category of less than 0.08 meters per day. At six sites, the maximum BTEX concentration was less than 5,000 micrograms per liter (mg/l) and at eight sites the maximum BTEX concentration was greater than 5,000 mg/l. Plume sizes range from 0.04 to 4.5 hectares, with an average of 1 hectare. Free product was identified at three sites. The first treatment occurred in 1995, but the majority occurred in 1996 and 1997. Regenesis’ ORC product was used at each site.

TABLE 1 - SITE INFORMATION TABLE

Site Number and Current Status

Maximum Site VOCs Levels Before ORC Treatments, mg/l

General Geology and

Depth to Ground Water (DTW)

Contamination and Plume Description

Plume Area

(m2)

 

Site 1

Active Station

Benzene:

Total BTEX:

15,500

42,400

1.2m of clay over coarse sand

DTW: 2.5m

Significant soil source material. Ground water impacted 90m downgradient. Possible upgradient source.

350

Site 2

Active Station

Benzene:

Total BTEX:

6,300

9,000

2m of clay over coarse sand

DTW: 2.7

Significant soil source material. Ground water impacted 90m downgradient. Possible upgradient source.

580

Site 3

Former Station

Benzene:

Total BTEX:

2,600

9,300

1 to 2m of clay over coarse sand DTW: 2.7m Minor soil impacts limited to source area. Ground water impacted 60m downgradient. Upgradient sources.

1,400

Site 4

Active Station

Benzene:

Total BTEX:

2,400

51,000

.6 to 1.3m of clay over coarse sand and gravels

DTW: 2.4m

Minor soil impacts limited to source area. Ground water impacted 75m downgradient. Plume defined by 4 monitoring wells.

2,300

Site 5

Active Coop and 2 Active Stations

Benzene:

Total BTEX:

19,800

65,000

2.4 to 3m of clay over coarse sand and gravels

DTW: 3.3 to 4m

Extent of soil impacts unknown. Ground water impacted 300m down-gradient. Known additional sources cross-gradient.

46,500

Site 6

Active Station

Benzene:

Total BTEX:

10,000

44,000

1.5 to 2.m of clay over sandy, silty clay DTW: 6 to 9m Minor soil impacts limited to source area. Ground water impacts limited to on-site areas, 30 x 60m.

1,860

Site 7

Former Station

Benzene:

Total BTEX:

5,500

7,000

0.9m of clay over coarse sand and gravels

DTW: 1.8 to 2.1m

Minor soil impacts, portion of impacted soil removed. Ground water impacts approximately 90 x 90m. Known upgradient ground water source.

8,400

Site 8

Active Station

Benzene:

Total BTEX:

Free Product

1.5 to 2.4m of silts and clays over sand DTW: 4.6m Significant soil impacts limited to source areas. Ground water impacts approximately 90 x 90m.

8,300

Site 9

2 Active and 2 Former Stations

Benzene:

Total BTEX:

Free Product

9m feet of clay over sands and gravels

DTW: 5.5 to 6.1m

Extent of soil impacts unknown. Ground water impacts extend 900m downgradient. Free product exists over entire site.

FP plume:

1,860

Site 10

2 Active Stations

Benzene:

Total BTEX:

15,000

45,000

1 to 1.5m of clay over shale

DTW: 2 to 2.7m

Extent of soil impacts unknown, but extend into shale. Ground water impacts approximately 120 x 120m.

15,000

Site 11

Active Station

Benzene:

Total BTEX:

1,500

7,200

2.4 to 3m of clay over sand (approximately 30m thick)

DTW: 4 to 4.5m

Significant soil impacts limited to source areas. Ground water impacts extend approximately 30m downgradient.

1,600

Site 12

2 Active Stations

Benzene:

Total BTEX:

Free Product

6.1 to 6.7m of clay over sand with shale at 11.3m.

DTW: 6.1m

Limited soil impacts at two source areas. Ground water plume extends 45 and 37m downgradient. Free product present in both source areas.

1,500

1,500

Site 13

Former UST site

Benzene:

Total BTEX:

3,800

28,500

1.2 to 2.7m of clay over sand

DTW: 2.1m

Excavate soil impacts during UST removal. Ground water impacts 45 x 15m

675

Site 14

3 Former Stations

Benzene:

Total BTEX:

800

13,000

2.5 to 3.7m of clay over fractured limestone

DTW: 1 to 4.3m

Soil impacts extend into limestone and are limited to source areas. Ground water impacted by migration through limestone fractures.

11,000

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