Aerobic Bioremediation via Concentrated Oxygen Injection
Project Name: Former Gasoline Retail/Service Station
Client: Government Agency
Impact Characterization: Mixed fuels, primarily gasoline, resulting from activities associated with the operation of a former retail gasoline storage/sales facility. Contaminate impact was documented to both the subsurface soil and groundwater regimes. Contamination was documented beneath the site proper as well as in the subsurface of an adjacent neighborhood due to prolonged groundwater transport.
In situ Technical Overview: The subject project is one of several sites being addressed by a 1999 EPA Brownfield. The area of remediation extends to multiple commercial and residential properties including County owned properties. Precision was contracted in 2004 to provide expert technical evaluation of a remedial corrective action plan (CAP) designed by others under the Brownfield Grant. Evaluation efforts focused on the effectiveness and applicability of the remedial action proposed by others. To accomplish the evaluation objectives, Precision implemented the recommended remedial CAP at the subject site via a small-scale pilot test.
The Team of PES and Aquifer Drilling and Testing, Inc. (ADT) initiated the bench-scale testing procedures by installing a network of pilot remedial test points including: piezometers, groundwater extraction and monitoring wells to various depths within the overburden at the site.
The installed pilot test points were used to test applicability of the proposed remedial method under site-specific conditions. The proposed high vacuum – total fluid extraction (multi-phase recovery) was pilot tested using a vacuum truck. PES technical staff collected data from surrounding monitoring points to assess effectiveness of the remedial method.
Once the pilot test study was completed PES presented the results in a comprehensive site investigation report. Pilot test results indicated the need to augment the proposed corrective action plan. PES therefore recommended the Department seek a remedial alternative for the site. In conjunction with feedback from the Department, PES proceeded to implement aerobic bioremediation via concentrated oxygen injection. The methodology consists of the injection of oxygen below the water table to stimulate and enhance aerobic biodegradation of petroleum hydrocarbons.
To implement the remedy, PES technical staff fabricated and installed 43, pre-pack, ¾-inch diameter, injection well points in a 15ft by 15ft grid pattern at the site. Injection well points were installed utilizing direct push methods ten-feet into the adversely impacted water-bearing zone. The oxygen delivery system was then connected to a remedial trailer utilizing individual ½-inch diameter HDPE piping. To complete the integrated system PES utilized remedial equipment that had previously been purchased by the Department, which resulted in a significant cost savings for the client.
Precision is currently performing periodic monitoring and maintenance of the system to gauge site advancement towards closure. Monitoring efforts consist of routine assessment and remedial point sampling for various physical and chemical parameters within the groundwater as well as system operation, maintenance and optimization. Data is collected and reviewed by PES and disseminated to the Department in groundwater monitoring/remedial progress reports.
Vapor Intrusion Assessment and Engineered Controls: In response to the existence of both commercial and residential structures within the footprint of the documented contaminant plume, PES was asked to perform a vapor intrusion study of several buildings. The study involved a building assessment and collection of sub slab, indoor and outdoor air samples using six-liter, stainless steel, summa canisters. All aspects of the comprehensive study were performed in accordance with recently published New York State Department of Health (NYSDOH) Guidelines. The results of the vapor intrusion assessment indicated the need to install structure-specific soil vapor extraction system(s) to reduce subsurface/sub slab contaminant levels as well as provide a mechanism to reduce/prevent adverse impacts to indoor air quality.
During the response action, the PES/ADT Team installed nine, four-inch diameter, vapor extraction wells and several additional groundwater monitoring wells at the former Gillette and Millington properties. Limited special access required utilization of ADTs limited access hollow stem auger rig. Standard hollow stem auger methods – coupled with continuous split spoon sampling were used during the installation of each soil vapor extraction well. PES geologic staff oversaw all drilling activities to ensure the wells were installed in accordance with the design principles of the SVE system.
Following install of the extraction wells, PES construction staff installed a network of trenches to allow for pipe installation to connect the remedial system to the extraction wells. PES procured an equipment shed to house the remedial equipment, provided for the installation of primary and secondary electrical services and installed the completed system in July 2007.
Site Progression Specifics: PES and ADT performed the work, including soil boring and well installations, sampling and technical review, vapor intrusion study work, remedial system installation, operation and maintenance utilizing properly trained and skilled PES/ADT personnel and equipment.
PES began work at this spill site in 2004 with the review of the ROD as produced by others. The initial remedial system (oxygen injection) was installed in the Fall of 2004. Vapor intrusion work was completed in Winter 2007 and the soil vapor extraction system was designed, installed and completed in the Spring/Summer of 2007. PES continues to perform ongoing site monitoring and remedial system operation, maintenance and evaluation for the Department.
Work completed at this spill site has been done on a time and materials basis with budgets established for large portions of the work. The work has been performed within the time and budget framework for the site to the satisfaction of the client.