Preliminary Investigation of Perchloroethylene (PCE) Groundwater Plume Using a Passive Soil Gas Survey

James N. Clarke, R.G. (MACTEC Engineering and Consulting, Phoenix, Arizona USA), Deborah Goodwin (Arizona Dept. of Environmental Quality, Phoenix, Arizona USA), Harry O’Neill (Beacon Environmental Service, Inc., Bel Air, Maryland, USA), Joseph E. Odencrantz, Ph.D., P.E. (Beacon Environmental Service, Inc., Newport Beach, California, USA)

ABSTRACT:

In situations where groundwater supplies have been impacted by volatile organic compounds, such as PCE, and the source has not been identified, the costs to identify the source and plume migration patterns may be extremely high. The costs for an investigation increase with the number and depth of borings and the number of samples that are collected and analyzed. MACTEC and the Arizona Department of Environmental Quality (ADEQ) have successfully utilized passive soil gas (PSG) surveys in Arizona to cost effectively investigate VOC impacts to groundwater and identify potential sources of impact. PSG surveys are minimally intrusive and more samples can be collected for the same cost when compared to active soil gas surveys and conventional soil and groundwater sampling programs. The result is a surficial representation of the contaminant plume and the location of “hot spots,” which are the potential sources. This provides a better understanding of the nature and extent of the impact and allows for a focused subsurface investigation, which subsequently reduces drilling and sampling costs.

 

INTRODUCTION

The subject site is known as the Miller Valley Road and Hillside Avenue Water Quality Assurance Revolving Fund (WQARF) Preliminary Investigation (PI) site in Prescott, Arizona (see Figure 1). PCE was detected above the groundwater cleanup level of 5.0 micrograms per liter (μg/L) in a monitoring well at a former gas station at the southeast corner of Miller Valley Road and Hillside Avenue. ADEQ subsequently authorized a PI to identify the source of the PCE. A dry cleaning facility is located approximately 0.25 mi (0.40 km) to the west of the FIGURE 1. Site location. WALNUTSTREET MILLERVALLEYROAD DIVISIONSTREET VALLEYSTREET FRY'S EXISTING BUILDING, TYP. OLD VILLAGE CLEANERS NEW VILLAGE CLEANERS THE OTHER STORE THE OTHER STORE MARKETPLACE MILLER CREEK MILLER CREEK MILLER CREEK MILLERVALLEYROAD HILLSIDEAVENUE FAIRSTREET DIVISIONSTREET PASSIVESOILGASSAMPLE LOCATIONPLANSOUTHSECTION FIGURE 2. Site plan. monitoring well and was a suspected source of the PCE detected in the monitoring well. MACTEC reviewed building plans for the dry cleaning facility and found that the current facility was constructed in 1988. However, the facility had moved from its previous location that was across Hillside Avenue to the north, where it had operated since the 1960s (see Figure 2). There were also other potential sources of PCE in the area.

 

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