Shallow permeable overburden soil with underlying fractured bedrock. Water is supplied to residents at the site from two bedrock wells approximately 150 meters downgradient from the source area.
Targeted Environmental Media:
 Fractured Bedrock
More than 800 liters of stove oil fuel were released from above ground storage tanks. Downgradient of the spill, a dissolved contaminant plume developed measuring approximately 1,300 square meters with an estimated plume front migration rate of 0.2 meters/day. Within the fracture rock, the free phase of the contaminant measured up to 3 centimeters thick.
Major Contaminants and Maximum Concentrations:
- Benzene (280 µg/L)
- Toluene (630 µg/L)
- Ethylbenzene (230 µg/L)
- Xylenes (780 µg/L)
- Pumping Tests
Comments:
Horizontal gradients ranged from 0.001 0.031. Vertical gradients ranged from 0.003 0.23. Pump testing estimated hydraulic conductivity at 0.00002 cm/sec. Pore water velocity measured 0.5 m/day. The water table fluctuates seasonally between 2 to 3 meters. Based on seepage velocity, potential travel time to the downgradient communal well system was approximately 244 days; however, travel time was measured at 750 days based on the observed plume migration.
- Chemical Oxidation (In Situ)
- Bioremediation (In Situ)
Comments:
Initial cleanup actions included the removal of approximately 190 tonnes of impacted soil and fractured rock which were disposed of off-site.
In-situ chemical oxidation (ISCO) using sodium percarbonate with enhanced bioremediation was the selected remedy. RegenOX was the sodium percarbonate used and oxygen release compound (ORC) was the final step in the process.
A pilot-scale test was performed in July 2007 to evaluate subsurface hydraulic and geochemical response to the injection under various pressures. 375 liters of sodium percarbonate were injected when the water table was low. Based on test results, the radius of influence was on the order of 5 meters. Due to the favorable results, a full-scale program was implemented.
In August 2007, the first full-scale injection took place with 13,100 liters of sodium percarbonate injected into 23 wells when the water table was low. Monitoring of adjacent monitoring wells reflected good distribution of the oxidant. Contaminant concentration was reduced between 50 to 80% within the source zone.
In October 2007, a second injection took place with 12,100 liters of sodium percarbonate injected into a rising water table. A third injection of 12,500 liters of sodium percarbonate took place in November 2007 into a higher water table than the October injection. Further monitoring was planned.
A polishing injection of oxygen release compound (ORC) was planned for the spring of 2008 into a high water table with monitoring to take place after the injection.
NOTE: In addition to the specific contaminant concentration for BTEX, Petroleum Hydrocarbon (PHC) F1 fraction was observed in the hot zone shortly following fuel release at 50,000 ug/L; PHC F2 Fraction and PHC F3 Fractions were observed north of the hot zone shortly following fuel release at 8,400 ug/L and 1,300 ug/L (respectively); and PHC F4 Fraction had a maximum groundwater concentration less than 100 ug/L.
Benzene 5.0 ug/L
Toluene 24.0 ug/L
Ethylbenzene 2.4 ug/L
Xylene 300 ug/L
Sum of Petroleum Hydrocarbon (PHC) fractions 1 (F1) (C6 C10) and F2 (C>10 C16) less than or equal to 1000 ug/L
Sum of PHC F3 (C>16 C34) and F4 (C>34) less than or equal to 1000 ug/L
Over 5,400 kg of RegenOx was mixed on site with potable water to create a solution between 2.5 and 5% RegenOx. Over 66,700 L of oxidant solution was delivered. All free product was treated and the groundwater was treated to drinking water quality standards.
Use of ISCO can be used to remediate impacts in fractured bedrock;
ISCO can work within a reasonable timeframe and can meet stringent drinking water quality criteria;
source removal is required to increase effectiveness;
well delivery system must ensure good delivery of product can be achieved;
the Natural Oxidant Demand (NOD) of the subsurface materials needs to be considered;
water table seasonal fluctuations can create a significant smear zone;
plan injection times to correspond to high water table levels.
References:
Application of In-Situ Chemical Oxidation to Remediate a Fractured Bedrock Dissolved Heating Oil Plume, Eastern, Ontario. Reported in Technology Innovation News Survey (TINS) August 1 - 31, 2008. http:www.clu-in.orgproductstins.
Roy, S.K. (Jacques Whitford Ltd.); R. McGregor (Vertex Environmental Solutions Inc.); J. Sauriol (Jacques Whitford Ltd.)
2008 RPIC Federal Contaminated Sites National Workshop, 28 April - May 1, Vancouver, BC. Real Property Institute of Canada, 2008.
Case Study PHCs. Vertex Environmental Inc. http:www.vertexenvironmental.cadocumentsPHCs-6.pdf
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