PROJECT OVERVIEW 5

Subsurface Remediation
Conducted for the Rockland Trust Company
Enhanced Bioremediation Project
228 Union Street
Rockland, MA

Introduction

Atlantic Environmental Technologies, Inc (AET) acted as the environmental engineer and Licensed Site Professional (LSP) for release of #2 heating oil for a bank (Rockland Trust) in Rockland, MA. During the removal of a 3,000 gallon #2 fuel oil tank in March of 1998, it was evident that a petroleum release had occurred. The tank was noted to have two visible holes and elevated PID readings were obtained during field screening of soil samples. PID readings greater than 100 PPM due to a UST release constitute a 72-hour reporting condition in Massachusetts. MA DEP was notified of the release at 11:00 AM on March 5, 1998.

Due to the presence of grossly contaminated soil in the immediate vicinity of the UST, the decision was made to conduct excavating and stockpiling of contaminated soils. Removal of highly contaminated soils usually helps to curtail the additional contamination of groundwater and shorten the remediation time required for the site. During excavation, it was also noted that contamination extended beneath the building and that in-situ remediation would be required after excavation. In total, 118 tons of #2 fuel oil contaminated soil was excavated and transported to a nearby soil recycling facility.

Residual Petroleum Contamination

Confirmatory soil sampling from the excavation and data gathered during subsequent boring and monitoring well installation and sampling indicated that residual petroleum contamination remained at the site. Free-phase product was noted to have entered the open UST excavation on the surface of the groundwater. Four monitoring wells were installed within the building to assess the soil and groundwater contamination concentrations beneath the building. Exceedances of applicable MA DEP cleanup standards were obtained from both groundwater and soil analyses. An assessment of indoor air quality was also conducted with no adverse impacts being noted.

Twelve additional borings/monitoring wells were installed at the site as follow up investigation work with little additional petroleum contamination being observed. In March 1999, only one monitoring well at the site continued to exhibit groundwater contamination concentrations exceeding the applicable GW-2 cleanup standards.

Remedial Design and Implementation

Because #2 fuel oil is not highly volatile and because much of the residual contamination existed along the foundation of and beneath the building, AET recommended that a bioremediation program be implemented at the site. The use of bioremediation techniques is not disruptive to normal site activities and is known to be effective for fuel oil remediation. Because natural attenuation of fuel oil contamination appeared to be occurring rapidly prior to any remedial activities, it was known that there was a robust population of petroleum consuming bacteria in the subsurface already. AET anticipated that by stimulating this already ongoing process, site closure could be achieved quickly and efficiently.

Bioremedial Activities

On December 19, 1998, AET personnel supervised the first injection of bioremediation additives to the subsurface. Injections were made to microwells dedicated for bioremediation purposes referred to as Bio-injection Points (BIPS). Application of bioremediation additives was made to seven BIPS on December 19, 1998. For each BIP, additives were applied in this order: Microbac Bacteria, Nutrient Mixture and lastly, Oxygen Releasing Compounds (ORCs). Applications were made to the subsurface at depths ranging from ten to twelve feet, the approximate depth to groundwater at the site.

AET observed the second injection of bioremediation additives on May 15, 1999. On this occasion, applications were made to four BIPS in the same manner as the previous injection event of December 19, 1998.

Bioremedial Activities

AET conducted groundwater sampling after the bioremediation procedures to assess the effectiveness of the process and to monitor for remedial additives. In Massachusetts, when groundwater additives are used for a remediation process, the environmental consultant must demonstrate that concentrations of these additives are not in excess of background concentrations more than fifty feet downgradient of the release area. In this circumstance, no downgradient detections of remedial additives were observed. In addition, petroleum concentrations were observed to be at their lowest point since the project began for the final groundwater sampling event of November 8, 2000. There remained only one cleanup standard exceedence for this final groundwater-sampling event.

AET Conclusions and Recommendations

The ongoing source of groundwater contamination was eliminated with the UST removal and the excavation of grossly contaminated soil. The implementation of the bioremediation process greatly increased the rate of naturally occurring biodegradation at the site for residual petroleum contamination. By November 2000, only one groundwater exceedance remained at the site. AET conducted a cost comparison of continued groundwater remediation in the area of the exceedance versus conducting a Risk Analysis as allowed by MA DEP to determine if the remaining contamination could be left behind. As a result of the cost comparison, AET conducted a Method 2 Risk Assessment for the site whereby the need further remediation of groundwater and soil at the site was negated.

AET submitted a Class A-2 RAO for the site on January 24, 2001, which constitutes a permanent solution for the release in accordance with the Massachusetts Contingency Plan (MCP). Submission of this report completed the environmental requirements of Rockland Trust Company for this release and a condition of No Significant Risk was achieved.