ACI Bioremediation™

Project Documentation 

County of Alameda
Public Works Agency

Bioremediation of Hydrocarbon Contaminated Soil 
After Underground Tank Removal

Technology Profile

During a tank excavation for the County of Alameda, petroleum contaminated soils were found. The tanks had previously contained gasoline used for fueling the county's vehicles. Leakage or overfilling of the tanks was the likely cause of the soil contamination. Approximately 100 cubic yards of contaminated soil were removed from the excavation and stockpiled on-site. Analysis showed Total Petroleum Hydrocarbon for Gasoline (TPH-G) levels to be 160 parts per million (ppm). The following treatment options were considered:

1. Dispose as Hazardous Waste - no treatment

2. Treatment at a Disposal Facility

3. Treatment at Santa Rita

4. On-Site Incineration

5. On-Site Aeration

6. On-Site Bioremediation

     On-Site bioremediation was selected as the low cost method. The local Environmental Consulting Company provided the work plans, permits and certified lab work. 

County of Alameda, Public Works Agency 
951 Turner Court 
Hayward, California

Technology Description

    The objective of the biodegradation method is to provide an environment for the microorganisms in which they can thrive and use the petroleum hydrocarbons as a food source. The soil was initially checked to determine if it was capable of supporting the microorganisms. The soil pH was adequate, but the other nutrients and moisture were unacceptable. 
     First, water was injected and sprayed onto the excavated soil. This continued until it was moist throughout.
     Second, the microorganisms were added to soil along with nutrients to enhance their rate of growth. Finally, the soil was covered with 6 mil black plastic to increase the temperature to promote the growth of the microorganisms.
     Nutrients were added periodically during the treatment phase. Both surface spray and direct injection were used to add nutrients. It should be noted that the soil was not tilled or turned over during the treatment process. This was done to reduce the labor requirements and to reduce the potential for aeration of the soil. The soil was never saturated with water to the point that free liquid would drain from the pile and potentially wash the hydrocarbons into the surrounding area.

Status

    The results from this project are summarized in the following Table. Before the treatment, a composite sample, S- I was collected and analyzed. Its TPH-G concentration was 160 ppm. After treating the soil for one week a second sample (BC-0707-03) was collected. Analytical results showed that during the first week of treatment the TPH-G concentration had dropped to 1.2 ppm. Additionally, soil sample BC0702-03 was also analyzed for benzene, toluene, ethylybenzene and xylene (BTEX). Both benzene and toluene were less that the detectable levels of 3 parts per billion (ppb). Ethylbenzene and xylene were present at concentrations of 16 and 44 ppb respectively.
     The soil was treated an additional week and a third soil sample (BC-0709-01) was collected and analyzed. The TPH-G concentration after two weeks of treatment was less than the detectable level of I ppm. Benzene, Toluene, and Ethylbenzene were also less than the detectable level of 3 ppb. Xylene was detected at a concentration of 5 ppb.