Sludge Utilization for Hydrocarbon Remediation
To evaluate the efficacy of sludge for remediating oil contaminated soils on a wellsite.
Site preparation of an oil contaminated wellsite southwest of Robb, Alberta began in June 2006. Activities on the site included:
- Baseline soil sampling to identify and delineate hydrocarbon concentrations.
- Non-contaminated surface soils were removed from the lease and stored in berms around the perimeter.
- Hydrocarbon contaminated soils were excavated and redistributed over the lease .
- The site was leveled and ripped prior to sludge application and samples were obtained to characterize the site following material movement.
- 82 BDT of sludge was applied (145 t/ha application rate) and incorporated to a depth of 30 cm with a Rotoclear in June 2006 and again in 2007.
- Plots were established along the northwestern edge of the study site to assess oil degradation rates
- Post incorporation samples were obtained following soil mixing and in spring summer and fall, 2007, 2008 and 2009 at the primary sampling locations 1, 2, 2a, 3 and 4.
- Surface water samples were obtained on and off the treatment area.
- The soil berms were seeded in June 2006; the west side of the lease was seeded in May 2008; east side of the lease was planted with lodgepole pine in June 2008.
- A climate monitoring station was installed to measure: air temperature, rainfall, wind speed and direction, soil temperature and soil moisture.
- Soil collars were installed at the primary sampling locations to measure soil respiration with a Li-Cor LI-8100 Automated Soil CO2 Flux System.
- saturated paste extract properties: electrical conductivity (EC), sodium adsorption ratio (SAR), Ca, Mg, Na, K, Cl, NO3, PO4)
- petroleum hydrocarbon fractions F1, F2, F3, and F4 (PHC F1-F4)
- benzene, toluene, ethyl benzene and xylene (BTEX) and polyaromatic hydrocarbons (PAH).
- total elemental content including hot water extractable boron, hexavalent chromium, and extractable barium.
Results and Conclusions
- Sampling conducted by ARC staff on May 25, 2005 indicated that the oil contaminated soil occurred primarily in the 30 to 75 cm depth interval with maximum oil contents of 3 to 4%.
- Soils at the site were classified as fine (AB Tier 1).
- Soil EC in 2009 <1.5 dS/m and SAR was <1
- Ba, Sn, and Zn exceeded AB Tier 1 guidelines in some samples analsyzed
- Total hydrocarbons in the surface layer declined from 72% to 85% over the entire measurement period from June 2006 to August 2009.
- Primary sampling locations met AB Tier 1 criteria for F1 and F4 petroleum hydrocarbons (PHC).
- Significant reductions occurred in the F2 and F3 PHC fractions however AB Tier 1 criteria were still exceeded.
- The F2 PHC fraction decreased by 53% to 73% of the initial levels in the surface soil layer over the measurement period.
- PAHs naphthalene, phenanthrene, pyrene, fluoranthene and fluorine exceeded the AB Tier 1 criteria at several depth intervals at the primary sampling locations.
- There was no evidence that the surface water moving downslope adjacent to the treatment area had been impacted
- The surface water (snowmelt) within the treatment area exhibited slightly higher EC and SAR compared to offsite samples.
- Soil respiration measurements completed indicated that sludge amended treatments had consistently higher respiration values indicating enhanced microbial activity.
- Density of grass and legume cover varied primarily as a function of the surface characteristics of the site.
- Surface crusting impacted grass establishment.
- Tree seedlings showed excellent survival and establishment (86%) in the first year.
- The sludge had good sustainability and longevity as an amendment.
- Sludge incorporation using a Rotoclear unit was effective to achieve an incorporation depth of 25 to 35 cm. Subsequent mixing to enhance aeration and degradation should be considered.
- Although mechanical pulp sludge is beneficial as an enhancement for remediating oil contaminated soils, which is supported by the observed decreases in Total Hydrocarbon concentrations and F1 to F4 PHC fractions, remediation to AB Tier 1 criteria is limited by the F2 and F3 fractions.