Information Summary for Stony Hill Road TCE Site in Wake County


March 2014 Update

FAQ / Fact Sheet

SEPTEMBER 19, 2012

When was the contamination first discovered on Stony Hill Road?
In August 2005, a property owner at 7305 Stony Hill Road complained to the Wake County Health Department about a petroleum smell associated with water from his residential well. Wake County tested the well and found that the well water had been contaminated by solvents (TCE and PCE). In October 2005, Wake County notified the N.C. Division of Water Quality (DWQ) about the contaminated well water. 

Between October 2005 and March 2006, DWQ sampled six additional drinking water wells on adjacent properties and also took soil samples. None of the other drinking water wells showed contamination. The contaminated well at 7305 Stony Hill Road was closed for use as a drinking water supply and the owner was connected to a source of uncontaminated water.
What is TCE/PCE, and what are their potential health impacts?

Where did the contamination come from?
The soil samples taken by DWQ showed evidence of chlorinated solvents at 7303 Stony Hill Road. This property is the former location of two small circuit board assembly companies and thought to be the likely source of the well water contamination based on the presence of soil contamination. 

What efforts have been made to fix the problem?
Since 2006, the Division of Water Quality, Division of Waste Management (DWM) and the Attorney General’s Office have taken enforcement actions to compel those potentially responsible for the contamination (known as potentially responsible parties or PRPs) to delineate the extent of the contamination through a comprehensive site assessment. These actions have also extended to corporate entities associated with operations at or ownership of the 7303 Stony Hill Road property (under state law/regulations, the state only funds investigations of sites with unknown responsible parties, known as “orphan sites”). Multiple requests for assessment have been sent first by DWQ and then DWM. (DWM became the lead enforcement agency in 2007.) DWM and the Attorney General’s Office have also made a number of requests for information about historic operations at the site in order to establish the origin of and responsibility for the contamination. 

How soon before the contamination is cleaned up and our well water is clean?
Remediation of contaminated groundwater can be a lengthy process. The contaminants that have spread through the fractured bedrock aquifer become trapped in the small spaces between soil particles and in the rock fractures and are difficult and very costly to remove with current technologies. Additionally, the depth of the contamination and size of the contaminant plume may add to the difficulty of groundwater remediation. The current procedure is to identify the extent of the contamination, analyze the particular qualities of the local geology, then assess the most suitable method of containment and remediation.
Who has been notified of the contamination?
When the initial complaint of contamination came to the Division of Water Quality in 2005-2006, DWQ contacted and received permission to sample the wells of six adjacent properties due to the contamination detected in the well at 7305 Stony Hill Road.

In 2008, DWM provided notice of the contamination at 7303 Stony Hill Road to the developer of the Groves subdivision, a development that had been planned for the adjacent property immediately to the west. After the original developer went bankrupt, DWM provided that same notice to SunTrust Bank as the lien holder and then to Toll Brothers as a subsequent purchaser of the property. 

In June 2012, the Division of Waste Management sent letters to 10 property owners who had drinking water wells located within 1,000 feet of the original contaminated well at 7305 Stony Hill Road.

Since receipt of sampling results indicating the presence of a groundwater contaminant plume, DWM and EPA have contacted local residents by phone, email and through a public meeting held Aug. 14, 2012, at a local church.
Why are more contaminated wells being discovered at the present time? 
Although the Stony Hill Road site would have ranked as lower risk based on the 2005 well testing results (and removal from service of the one known contaminated well), DWM decided to perform additional well testing in 2012  to support  enforcement action and to get an update on site conditions. DWM sent letters in June 2012 to 10 property owners who had drinking water wells located within 1,000 feet of the original contaminated well at 7305 Stony Hill Road.  Only three property owners gave permission for testing – the owners of the wells at 7305 and 7303 Stony Hill Road (the original contaminated well and the source site respectively) and the owners of a residence located at 7333 Stony Hill Road. Results of the June 20 sampling event showed TCE/PCE contamination above drinking water standards  in the well at 7333 Stony Hill Road. Based on that new information, DWM contacted EPA the day the results were received and asked for assistance in testing additional wells. Since that time, EPA has tested several dozen wells in the area; that testing has identified additional drinking water wells with solvent contamination – some with levels below the drinking water standards threshold and others with levels exceeding a safe concentration for drinking water.
In performing the additional well testing, EPA and DWM discovered a potential second source of contamination that had been previously unknown. That site – about 1/2 mile from 7303 Stony Hill Road – is located on property that was once owned by a previous owner of the original source site. Some of the highest TCE concentrations have been found in the well on that property and on properties nearby. Hydrogeologists at DWM believe that the groundwater contamination from this site seems to be following fractures in the bedrock along a line that is entirely different from the movement of contamination from the original site at 7303 Stony Hill Road. The nature of the contamination is also different. Test results from properties closer to 7303 Stony Hill Road show both TCE and PCE; wells near the second site only show high levels of TCE.

In December 2012 and again in April and December of 2013, DWM and EPA sampled all of the contaminated wells and a number of the surrounding wells for TCE and PCE.  These sampling events have shown that the levels in the contaminated wells have been relatively constant.  Two new wells have had low levels of TCE detected in them, with one of those wells returning to a no detection status.  We believe that this demonstrates that the contaminated groundwater plume is stable.
Where has the contaminated groundwater been found? 
A map showing the location of the contaminated wells is available at:  Stony Hill Road, Wake County
This map illustrates the difficulty in predicting the movement of contamination through fractured bedrock. For example, even when accounting for the existence of the possibility of two distinct contamination sources, the homes showing contamination levels above the safe drinking water standard are not necessarily contiguous.  
What are the next steps?
EPA Emergency Response and Removal Branch (ERRB) has connected all contaminated wells to community well systems run by AQUA America.  The wells supplying these systems are being sampled on a quarterly basis.  In addition, fifty-eight meter boxes have been installed by ERRB for private residences with clean wells in close proximity to the contaminated wells. Hooking up to the community well system is a homeowner decision.

Is Vapor Intrusion a concern for this site?  
Due to a concern over the possibility of vapor intrusion from contaminated groundwater  into structures, the Division of Waste Management's Inactive Hazardous Sites Branch contracted with S&ME, Inc. to conduct soil gas, sub-slab and crawlspace sampling at all of the highly contaminated well locations.  Fourteen residences with the highest groundwater contamination levels had soil gas samples collected outside their building footprint at approximately 10 foot depth.  Seven of those residences had detections of TCE and/or PCE in the soil gas samples.  Six of these residences plus 13 additional residences had air samples collected from their crawlspaces.  None of the crawlspace samples had any detections of PCE or TCE.  In addition, the one remaining impacted residence plus four additional residences had sub-slab samples collected.  Only one sub-slab sample had a detection of PCE at 43 micro grams per cubic meter (ug/m3).  This is below the IHSB Soil Gas Screening Level of 278 ug/m3.  All other sub-slab samples had no detections of PCE or TCE.  

10/12/12 Press Release: DENR to conduct below-ground vapor testing in Wake Forest neighborhood

Map of Stony Hill Road Sample Results as of 9/14/2012

Individual residential well levels for TCE and PCE are indicated on this map. EPA and DENR have established that the following levels are safe for public drinking water supplies:

  • TCE: 5 ppb
  • PCE: 5 ppb

EPA Documents for Stony Hill Road site:

DENR PowerPoint presentation from 9/19/12 Stony Hill Road area homeowners meeting

Agency Contacts for the Stony Hill Road TCE Site:

Ken Rhame, 919-707-5911

Technical Inquiries:
Jim Bateson, 919-707-8329
Media Inquiries:
Cathy Akroyd, Public Information Officer, 919-707-8234

Dr. Kenneth Rudo, 919-707-5911
Dr. Richard Langley, 919-707-5913