Case Study - Site Investigation, GWMP Monitoring, and RAP Implementation
Project Overview
A release of gasoline to the environment was discovered in 1993 when the Town of Londonderry decommissioned two 2,000-gallon Underground Storage Tanks from one of the town’s fire stations. In 2000, EnviroSense was retained by the Town of Londonderry to conduct environmental investigations per the direction of the New Hampshire Department of Environmental Services (NHDES). The investigations included the re-excavation of the UST graves, and subsequent excavation of gasoline-impacted soil from the former tanks location. Investigation efforts consisted of installation of a network of ground water monitoring wells, and sampling and analysis of ground water and drinking water sources. This investigation identified that the gasoline release had migrated a substantial distance from the tank grave, impacts to soil and ground water exceeded the NHDES risk-based standards, and MTBE had impacted the drinking water supply well at neighboring residential properties. Due to MTBE contamination, drinking water supply treatment systems were installed in two nearby residences, and residential properties throughout the area have been placed on a drinking water monitoring program. The site and surrounding properties are currently under a NHDES Groundwater Management Permit program.
In February 2011, the Town of Londonderry fire department completed their relocation from the Mammoth Road station into a new facility on Grenier Field Road. The town then retained a demolition contractor to raze the old station building. Removal of the building offered an opportunity to excavate additional petroleum-impacted soils that were assumed to be under the building footprint. During removal of the former Fire Station concrete slab on April 21, 2011, environmental monitoring was conducted to determine the general location of impacted soils by measuring the total organic vapors under the concrete slab with a photoionization detector (PID). During monitoring activities, it was determined that the impacts were generally located on the northeast to east portions of the former fire department building footprint. The subsequent excavation activities began based on the PID monitoring conducted during the slab removal.
Excavation activities were initiated in the north corner of the former Fire Station building area and adjacent to the former gasoline tank grave and continued eastward inside the former footprint of the building. Excavated soil was PID field-screened on Site to assess the potential for petroleum impacts and to guide the limits of the excavation area. Bedrock was encountered at approximately 12 feet below grade. Seven confirmatory excavation endpoint soil samples were collected for laboratory analysis to assess potential remaining in-place soil contamination levels. Composite soil samples were collected from the extent of the excavation in the field that coincided with the potential limits of the petroleum-impacted area based on PID measurements. A total of 1,523.36 tons of impacted soil was removed from the Site and sent to the recycling facility.
EnviroSense Role
- Completion of an Initial Site Characterization (ISC).
- Re-excavation of the former UST tank grave to remove residually-impacted soil.
- Completion of a Level II Site Investigation (SI).
- Advancement of multiple soil borings.
- Installation of multiple monitoring wells.
- Determination of ground water flow direction.
- Collection of soil and groundwater samples.
- Collection of drinking water well samples to ensure conditions protective of human health have been maintained.
- Installation, operation and maintenance of Point-of-Entry water filtration systems.
- Completion and submission of a Groundwater Management Permit (GMP).
- Completion of on-going ground water monitoring in accordance with GMP requirements.
- Screening of vapors beneath concrete slab foundation and coordinated with NHDES with development of the Remedial Action Plan (RAP).
- Completion of RAP Implementation consisting of soil excavation, screening, sampling and off-Site disposal of impacted soils and building material at an approved landfill and soil recycling center.
