PROJECT OVERVIEW 3

Source Area Removal Action
Conducted for the Air Force Center for Environmental Excellence (AFCEE)
Air Sparge /Soil Vapor Extraction System
Massachusetts Military Reservation
Cape Cod, MA

Introduction

Atlantic Environmental Technologies, Inc (AET) was the environmental engineer and Licensed Site Professional (LSP) for an historical release of aviation gasoline and JP-4 jet fuel from an underground pipeline. According to available records, the pipeline was used to carry both jet fuel and aviation gasoline from 1965 until 1973. The release was reported to have occurred in 1972 and free-phase product was first discovered in the area in 1992.

From 1992 to 1993, numerous subsurface investigations were conducted at the release site by other environmental consultants. It had been determined that the source area covered 11 acres and contained contaminated vadose zone soil, contaminated groundwater and floating product. The vertical extent of contamination was determined to be a ten to twenty foot layer in the vicinity of the groundwater surface. Groundwater modeling and soil properties were used to estimate the quantity of recoverable hydrocarbons attributable to this release at 395,000 lbs.

Treatment System Design and Installation

AET acted as the engineer and LSP for the site remediation and management of state regulatory issues. An Air Sparging/Soil Vapor Extraction (AS/SVE) system was designed to operate utilizing 23 AS wells and 23 SVE wells. It was also anticipated that AS/SVE would stimulate biodegradation of hydrocarbons. This was later verified by monitoring Carbon Dioxide levels, an indicator of microbial activity. The SVE wells and AS wells were installed in 1995.

The SVE system was designed to operate at a maximum flow rate of 3,500 Standard Cubic Feet per Minute (SCFM). Petroleum derived contaminants in the air stream would be destroyed via catalytic oxidation. Effluent from the catalytic oxidation unit would be treated via vapor phase Granular Activated Carbon (GAC) as secondary treatment.

AET oversaw the installation of the treatment equipment and piping in 1995. Start-up of the AS/SVE system was conducted in October, 1995. Start-up monitoring indicated that the actual operating flow rate of the SVE system was 2,791 SCFM or 80% of system capacity.

AS/SVE Monitoring
SVE Influent/Effluent

AET monitored operation of the AS/SVE system for a 29-month period ending in February, 1998. Emissions of volatile organic compounds (VOCs) to ambient air, resulting from remedial actions, are regulated by the MA DEP's Bureau of Waste Prevention. The destruction efficiency requirement in accordance with MA DEP is 95%. AET conducted monthly influent and effluent air sampling for the SVE system using the NIOSH Methods 1501 and 1008. Results from this testing indicated that the destruction efficiency was greater than 95% for the entire operating period of the system. Due to decreasing influent VOC concentrations, on June 13, 1997, the catalytic oxidation unit was removed and SVE treatment was via GAC only.

Groundwater

AET conducted groundwater monitoring during the operation of the remediation system to assess the effectiveness of the AS/SVE system. Groundwater samples were collected from select monitoring wells at the site on a quarterly basis and analyzed via MA VPH w/ BTEX, MA EPH and EDB. Consistent reductions in dissolved VOC concentrations were achieved across most of the site during the operation period. Closure sampling for groundwater was conducted on March 17, 1998 with exceedences of MA DEP GW-1 and GW-3 Cleanup Standards being detected in only four of the monitoring wells sampled at the downgradient edge of the 11 acre source area.

Carbon Dioxide and Oxygen Monitoring

On May 17, 1996, after a 45-day shutdown period, CO2 and O2 concentrations were measured in each SVE well using field instrumentation. In all of the SVE wells, lower O2 percentages were directly proportional to higher CO2 percentages. These results indicated increased microbial activity and, therefore, increased degradation of petroleum hydrocarbon contaminants.

Soil Sampling Closure Sampling

In accordance with prior agreements, closure soil sampling was conducted in 1998 to determine final soil conditions. Ten soil borings were advanced in the source area with split spoon sampling being conducted at five-foot intervals from ten feet above the water table to ten feet below the water table. A total of four soil samples from each boring were submitted for laboratory analysis via MA VPH w/ BTEX and MA EPH w/ 4 PAHs. MA DEP soils averaging was used and the entire vadose zone within the source area was considered one exposure point. Various individual sample results exceeded applicable MA DEP Method 1 Soil Cleanup Standards, however, for all parameters, the soils average was below the MA DEP Method 1 Soil Cleanup Standards.

AET Conclusions and Recommendations

Soil contaminant concentrations were reduced to acceptable levels in accordance with MA DEP, whereby the average concentration of each contaminant was below the applicable MA DEP Method 1 Cleanup Standards. Groundwater contamination remained above the applicable GW-1 and GW-3 MA DEP Method 1 Cleanup Standards in March 1998 in four wells at the downgradient edge of the 11-acre source area. For a majority of source area, MA DEP drinking water standards (GW-1) were achieved during the 2-½ year remediation period.

Operation of the AS/SVE system provided for the removal of approximately 45,000 lbs. of petroleum hydrocarbons from the subsurface. Removal of this material from the vadose and saturated zones constituted removal of the source of future dissolved groundwater contamination. Completion of these actions has allowed for the process of natural attenuation to begin to reduce residual dissolved groundwater contamination in the downgradient plume.