Perc Study Process

The goals of this study are to assess the public health risk from indoor air levels of further define the extent of Perc contamination in soil and soil gases in the study area. Once these assessments have been made, the Task Force will determine:

• how to reduce indoor air levels of Perc where they do not meet the public health safety standard;
• how to prevent the contaminants from spreading through the soil and groundwater; and
• how to clean up the soil and groundwater that is currently contaminated.

It is believed that the concentration of Perc in the air, soil and groundwater will decrease as one moves away from the cleaners. To evaluate the boundaries of the contamination and the risk, the study will be conducted using a tiered approach.  That is, the properties closest to the cleaners will be the first tier.  As the study progresses, the boundaries will be adjusted based on the findings.

Four Perc Study Stages

1. Homeowner Survey

Prior to any sampling, homeowners in the study area will be asked to fill out a survey regarding the use of household cleaners and the frequency of carpet, furniture and garment dry-cleaning. In addition to the survey, homeowners will be asked to sign site access agreements for the soil, water and air sampling, and will be requested to remove certain cleaning products and dry-cleaned garments from their homes a minimum of 48 hours prior to the air sampling. Homeowners will also be asked to refrain from having carpets and furniture cleaned or pesticides applied during the study period. These initial steps must be accomplished prior to the sampling if the air quality testing is to provide a reliable indicator of chronic Perc exposures.

2. Soil vapor monitoring installations with Geoprobes

With the aid of a piece of equipment called a Geoprobe®, the Technicians are able to drill a hole in the ground approximately 2 inches in diameter and advance a Membrane Interface Probe (MIP) to depths up to 50 feet.  The MIP is a tool that produces real-time, continuous chemical and physical logs of this underground environment called the subsurface. Data from these analyses can be used to determine if a pollutant has migrated down through the soil and possibly into the groundwater aquifer and to assist in identifying areas in need of additional study. The purpose of this segment of the study is to evaluate the subsurface for the presence of Perc and other solvents.  Results from these tests will provide the Task Force with real-time data and a 3-dimensional picture of the soil and groundwater characteristics, including the location of contaminants as well as potential and existing pathways for the contaminants to travel.

While the sampling equipment used with the Geoprobe is very small in diameter, about the size of a can of soda, it is a very sensitive piece of equipment and installation requires truck or all-terrain vehicle access at the site. Technicians will repair any damage to lawns or landscaping as a result of this work. 

Shortly after installation of these soil gas monitoring points, a mobile laboratory called TAGA (Trace Atmospheric Gas Analyzer) will be on hand to collect and provide analysis of the soil vapor samples.  The TAGA mobile laboratory is used primarily for analyzing volatile organic compounds in soil vapor and air.  The information generated is screening data that provides analytical results to on-site project managers within hours.  This rapid turn-around-time is invaluable when one of the data quality objectives is to define the levels of pollution at various points at a given site.

As standard procedure, the workers will be wearing special clothing and hoods.  On a daily basis, these workers directly handle contaminants in the soil and groundwater that homeowners never access because they are underground.  The workers are required to wear protective clothing as a precaution against potential risks.  This sampling poses no foreseeable health risk to homeowners, neighbors or pets.

3. Soil gas probes installations in basements

Based upon the information gained from the MIP, the study team will identify houses that have a potential for intrusion of vapors from the ground.  Permission will be sought from selected homeowners for installation of gas probes in basements to allow soil gas samples to be collected from below the floor of their basement or crawl space slab.

These probes will be semi permanent installations allowing ongoing monitoring of the contaminant plume and assessment of soil gas concentrations during remediation efforts if those become necessary.

4. Soil vapor monitoring and indoor air sampling with TAGA unit   

The Trace Atmospheric Gas Analyzer (TAGA) is a self-contained mobile laboratory capable of real-time sampling and analysis from various environmental sources and concerns.  In addition, the TAGA has specialized sampling equipment for measuring indoor air and at remote locations. More information about the TAGA can be found at:

http://www.epa.gov/earth1r6/6lab/taga.htm

Once the house has been screened for VOCs using the TAGA, samples will be collected for fixed laboratory analysis.  Samples will be collected using Summa Canisters, which are about the size of a basketball and are specially designed containers.  Samples will be collected over a 24-hour period from the basement and the main living area.

Follow-up validation of these initial results will occur offsite in the 7-8 weeks following the initial air sampling.

STUDY AREA

HOMEOWNERS ROLE

• Complete an interview and homeowner survey if you live in tier one of the study area.
• Provide site access, as possible.  Click here for PDF file of EPA Access Agreement
• Clear homes of all products with perc and related compounds.
• Do not bring in newly dry-cleaned garments for a period of one week.
• Do not use pest control applications or have professional carpet and furniture cleaning for a period of two-three weeks.
• Stay informed.