Operation of an underground storage tank refurbishment facility resulted in groundwater and soil contamination. The primary contaminants are tetrachloroethylene, also known as perchloroethylene (PCE), and trichloroethylene (TCE). Contaminated groundwater extends approximately one mile south of the site and has impacted residential water wells. Since groundwater should not be used for drinking purposes, as many as 100 properties with contaminated wells were connected to the public water system.
Thermal treatment was applied to onsite PCE-contaminated soils, which were the source of the onsite and offsite groundwater contamination. Onsite and offsite monitoring wells and residential wells are regularly sampled. As part of site investigation activities, a Human Health Risk Assessment (HHRA) was conducted. The HHRA evaluated the potential health risks associated with exposure to PCE and TCE identified in onsite and offsite groundwater.
Site investigation and remedial activities have produced large soil and groundwater datasets from many sampling locations. The site investigation reports are comprehensive and data intensive—hundreds of pages of analytical results and data summary tables. These reports are reviewed and used by numerous professionals, such as the project manager, hydrogeologists and risk assessors, who have varied perspectives and use the data in different ways.
How to easily understand all the data can be challenging. Data selection for risk assessments can be particularly challenging. Since reliable information regarding the construction and/or depths of residential wells is frequently unknown, in accordance with United States Environmental Protection Agency (EPA) Groundwater Exposure Point Concentration (EPC) Guidance, groundwater concentration data from residential wells are not typically included in risk assessments. Therefore, the offsite monitoring well data rather than residential well data were used to develop the offsite groundwater EPC.
The client uses EQuIS™ as their central environmental database system to manage the large dataset for the site. EQuIS Enterprise dashboards provide easy access to site data for the client and its contractors, and are available for presentation or other interactions with interested stakeholders.
The EQuIS Enterprise dashboards provide charts demonstrating concentration trends over time, maps displaying the spatial distribution of concentrations, historical water depths, and other pertinent site information. Knowing residential data results is a priority and being able to communicate the results quickly is imperative. The pre-configured dashboards are an expedient means to visually display data and allow for quick communication with interested parties.
Since the onsite source mass removal activities, PCE and TCE concentrations in onsite and offsite groundwater have continued to decline. The visual display of quarterly monitored wells demonstrates the decline.
A comparison of maximum concentration detections versus most recent detections provides a quick demonstration of aquifer cleanup progress since treatment. Quarterly monitoring results are immediately available on the EQuIS Enterprise dashboards as soon as the data is uploaded to the database, providing the client with easy access to the most recent data and trends.
For the risk assessment, the offsite groundwater EPC was developed for a reasonable maximum exposure condition using the offsite monitoring well data with a PCE concentration of 30 μg/L and a TCE concentration of 30 μg/L. These concentrations are greater than any concentrations measured in the residential wells and are worst-case exposure scenario for a hypothetical offsite current receptor. During the risk assessment process, the client used the EQuIS Enterprise charts to demonstrate concentration trends and actual residential well values to the risk assessor.
The improved understanding of actual site conditions allowed the risk assessor to appropriately draft language that reflected the actual site conditions, and ultimately, the selection of a preferred cleanup remedy for the site that will be protective of human health.