BIOREMEDIATION

PROJECT PROFILES:

Understanding the Need for Biofeasibility Studies

by Justin Lauterbach

The importance of conducting a bioremediation feasibility (often referred to as biofeasibility) study prior to committing to a bioremediation cleanup plan cannot be overstated. Some property owners have learned the hard way that there are companies that promise to remediate sites to the desired cleanup criteria by means of bioremediation without having adequate (or any) biofeasibility studies to substantiate their claims. The results are crucial losses in time and money for the clients. Only a biofeasibility study can determine whether or not bioremediation can effectively clean up a specific site within such client - or regulatory - determined project parameter as final contaminant concentrations, time frame and cost. A biofeasibility study will also determine the conditions necessary for achieving the project's closure goals.

Often clients hope to avoid unnecessary expenditures by skipping the biofeasibility study, but the cost of a biofeasibility study need not be prohibitively high. Michael Chaparian pointed out in this article "The Biofeasibility Study" (Env. Protection, July 1995) that typically the cost of a biofeasibility study is sufficient for establishing the feasibility of, and basic requirements for, a bioremediation cleanup plan. Such a study can establish the necessary information for either ensuring a project's success or avoiding wasted hours and dollars on the wrong remedial path. There are minimum requirements for an effective study.

The study must include sampling for initial and final concentrations of the contaminants of concern. It is best that the soil selected for the study come from an area of the site where the contaminant concentrations are highest to determine whether bioremediation can remediate the entire site. Only by actually measuring the concentrations can it be ascertained that the contaminants are actually being degraded by the microbes (or referred to as hydrocarbon ulilizers). A microbial colony growth is an insufficient indicator that biodegradation is, in fact occurring (Chaparian, 1995).

It is however, important that hydrocarbon utilizers can thrive and increase in the presence of the contaminants of concern. An adequate biofeasibility study should also detect and enumerate the presence of such bacteria at the beginning and the conclusion of the study. If a microbial population is not present in the soil sample, then the study must add microbes (if any) are capable of degrading the contaminants can be established.

The soil sample for the biofeasibility study must also be analyzed for nutrient availability, specifically the presence of nitrogen and phosphorous. Hydrocarbon utilizers require sufficient nutrients to live and degrade contaminants at an optimal rate. The addition of nutrients may be all that is required to stimulate microbial growth and, hence the biodegradation of the site contaminants.

Finally, a biofeasibility study should analyze the ambient conditions at the site, that is, the soil moisture and pH levels, as well as any site-specific concerns which could impede the effectiveness of the proposed bioremediation plan. Should the initial analysis show one or more of these factors to be inadequate for biodegradation to occur, then the study should strive to establish appropriate levels for these factors.

Many biofeasibility studies call for a comprehensive soil analysis, carbon dioxide sampling (respirometry testing), stoichiometric equation generation and kinetic modeling. Although these additional steps can provide useful information, much of the data they yield is either unnecessary or largely theoretical. In the initial design stages of a bioremediation project, these steps can slow the project development down, add to the feasibility study costs and result in an unwieldy bulk of data. These steps should be taken only if the site proves to be, or becomes, unresponsive to bioremediation efforts despite prior favorable feasibility testing.

The biofeasibility study should yield the following information:

sufficient presence and capability of microbes for degrading the contaminants of concern to the desired concentrations.
appropriate and sufficient nutrient/microbe mix for successful bioremediation, and
approximate time frame to determine the cost of the bioremediation

To underscore the importance of performing a biofeasibility study prior to initiating a bioremediation plan, we offer case studies for two sites similar in soil type and contamination. The study for the first site yielded feasibility results favorable for bioremediation. The study for the second site showed that bioremediation could not fully remediate the site.

Case Study One Soils at this site were contaminated with heating oil. The remedial plan called for excavation of the soils into piles for ex situ bioremediation. The cleanup criteria was to reduce contaminant concentrations to levels at or below those specified by the Pennsylvania Department of Environmental Protection (PA-DEP), which specifies 500 mg/kg total petroleum hydrocarbons for diesel range organics (TPH/DRO).

A 5-gallon sample of soils was taken from an area believed to be representative of the highest levels of contamination for the site. Analysis showed that initial soil concentrations in the test soils were 612 mg/kg. The sample was placed in an 8-inch deep pan and treated with microbes and nutrients. The sample was then covered and left in a dark room at 70sF.

Two weeks after initiating the feasibility study sampling showed that the contaminents had already been degraded to 291 mg/kg. The study concluded, therefore, that bioremediation could achieve the cleanup goals for the site, and that these goals could be achieved in approximately two weeks.

Bioremediation was initiated at the site in late June 1995. Nine confirmatory soil samples taken in early September 1995 demonstrated that the bioremediation system had successfully degraded the contaminents to levels ranging from non-detectable in five of the nine samples to 20.4 mg/kg in one sample, well below PA-DEP requirements.

Case Study Two At this site, significant amount of #6 fuel oil was released from a 10,000 gallon underground storage tank to the soils. Hydrocarbon concentrations in the soil ranged from 20,000 to 30,000 mg/kg. The soil remediation goal for the site was 10,000 mg/kg TPH in accordance with New Jersey Department of Environmental Protection (NJDEP) standards.

The feasibility study was conducted in a manner similar to that described above under Case Study One. Five days after the start of the study the hydrocarbon concentrations had decreased to 15,000 mg/kg. Two weeks from the start of the study, the soil concentrations had decreased to 11,500 mg/kg. The concentrations of hydrocarbons in the soil did not decrease further to meet the established cleanup criteria.

Due to the results of the feasibility study, RT recommended performing an additional soil analysis to determine the composition of the hydrocarbons. The results of that analysis indicated that the remaining hydrocarbons were primarily compromised of paraffins and asphaltine compounds, which are not regulated by the NJDEP. RT therefore recommended bioremediation for the site with a risk based remediation standard, rather than the NJDEP standard. The amended standard could easily be achieved by bioremediation.

For further information on bioremediation and biofeasibility studies, contact Justin Lauterbach at 856-467-2276

RT Environmental Services, Inc. (RT) maintains a qualified staff of engineers fully versed in the application of bioremediation in the field. RT's experience includes, but is not limited to:

In-situ bioremediation of soil and groundwater
Ex-situ soil piles
Ex-situ groundwater treatment with fixed film bioreactors
Bioremediation of gasoline and petroleum products
Bioremediation of chlorinated compounds
Bench scale feasibility studies