PROJECT OVERVIEW 2

Environmental Site Investigation Project
Conducted for Municipality in Southeast MA
MA MCP Phase II Comprehensive Site Assessment

Introduction

Under the Massachusetts Contingency Plan, Atlantic Environmental Technologies (AET) conducted a Phase II Comprehensive Site Investigation and prepared a Phase II Report for a 6.5-acre parcel owned by a municipality in Southeastern Massachusetts. The site is the location of a Department of Public Works (DPW) service facility. The parcel has been used for the storage of road maintenance vehicles and supplies and a maintenance facility for DPW vehicles. This is the only historical use of this property as was applicable for this investigation. The objective of the Phase II ESA was to delineate the nature and extent of contamination at the site and to assess the possible contribution to migrating groundwater contamination by another party.

Site Characteristics

There are five buildings located on the site of which one is used for vehicle servicing and routing maintenance. AET conducted a review of private and town utilities servicing the property. Site characteristics, including geology, topography and hydrogeologic conditions were determined by AET personnel for this site. Hydrogeologic characteristics that were analyzed included hydraulic conductivity, horizontal flow direction and vertical flow direction. This data was gathered during subsurface investigation procedures described below. A release at this site was first documented during a 1998 tank pull operation and MA DEP written notification of the release was made to MA DEP in January, 1999.

AET Subsurface Investigation

AET supervised the completion of geophysical survey activities at the site including ground-penetrating radar (GPR) and electromagnetic (EM) surveying. These technologies are used to find potential locations of buried objects, most importantly, drums and/or underground storage tanks. The GPR survey indicated that no old USTs remained at the site after the 1998 removal. The GPR was also used to document subsurface utility locations for drilling purposes.

AET Boring and Monitoring Well Installation

AET directed the advancement of numerous soil on and off-site borings during 1999. Monitoring wells were installed in most of these borings so that groundwater quality could be determined. Soil samples were screened in the field using ThermoEnvironmental 580B photoionization detector and the jar headspace procedure. Select soil samples with elevated headspace readings were submitted to a Massachusetts-certified laboratory for analysis of RCRA 8 metals plus chromium, MA VPH and EPA Method 8260 VOCs, and MA EPH and EPA Method 8270 SVOCs. Gasoline contaminated soil was found to be located on-site and groundwater contamination was found to have migrated a substantial distance off site. Several additional monitoring wells were installed downgradient of the site in 2001 in depths extending to 75' below the ground surface in an effort to assess the vertical limits of contamination and to assess the potential for an off site source of contamination.

Groundwater Sampling

AET collected groundwater samples from all on-site and off-site monitoring wells on several occasions since 1999. For each sampling event, groundwater samples were submitted to Groundwater Analytical Laboratories in Buzzards Bay, MA for analysis of MA VPH with VOCs, MA EPH with SVOCs, metals and other chemical parameters. During the installation of monitoring wells in 2001, groundwater samples were collected from varying depths at each well so that the vertical component of groundwater flow and contaminant migration could be determined.

Results of Subsurface Investigations

Free-phase petroleum product was observed in monitoring wells near the on-site release location. Dissolved petroleum concentrations were detected as far as ¼ mile downgradient of the site. Concentrations exceeding drinking water standards were observed in private drinking water wells downgradient of the site. As a result of 2001 drilling and sampling operations, AET determined that there was no off site source of groundwater contamination.

AET Recommendations

• AET determined that soil and groundwater remediation on site was required, including the removal of free-phase product gasoline. AET determined that off-site dissolved petroleum contamination in groundwater would also need to be addressed.
• AET recommended that use of downgradient water supply wells contaminated with dissolved gasoline components be discontinued for drinking water purposes.
• AET suggested that the municipality supply these residents with bottled water until town water could be supplied to these residences. These homes were furnished with town water in December, 1999.
• AET determined that there is a vertical component to groundwater flow and contaminant migration in this area.
• AET determined that soil and groundwater quality in this source area had not achieved applicable cleanup criteria and that remediation was required to achieve a permanent solution at the site.