SITE
Confidential Federal Site in US
OBJECTIVE
To field-validate the use of the horizontal multi-port (nested) VertebraeTM Well System (Vertebrae) for characterization and monitoring contaminant mass flux in groundwater systems, namely Per- and polyfluoroalkyl substances (PFASs), and the certification of the well systems as PFASs free.
BACKGROUND
The subject site has had numerous high-definition studies and its characterization is well defined. Vertebrae were chosen to provide comparable data sets, allowing high resolution transect analytical data for PFASs. In addition, other studies are being completed to determine K values (hydraulic conductivity), gather other comparative data and determine any anisotropic effects.
Vertebrae is a multipurpose nested well installed by Horizontal Directional Drilling (HDD). When installed and sampled thewell system generally provides a clearer and more accurate representation of the plume, thus allowing a surgicalremediation treatment plan, or at this site the information is being used to determine flux and risk-based monitoringapproaches. The provided data generally has spacing that is more dense than traditional groundwater samplecollection and thus similar to High Resolution Site Characterization (HRSC) tools.
Well Certification Data
- The well system components are pre-sampled for PFAS sites to test for PFASs.
- The well systems are made with HDPE, geotextile, and tracer wire. Tie wraps are also used to bundle the risers where necessary. All these components are analyzed to ensure quality.
- The supplied geotextile contains trace amounts of PFASs, which are methanol washed prior to testing and used to meet the low-level requirements of PFASs sampling. Below are the abbreviated sample results from the well geotextile post washing.
- Well testing reveals if any PFASs are present. No PFASs were evident in the well product or installation process.
VERTEBRAE ACTIVITIES
- Three HDD bores were advanced to install a total of 24 well segments at various depths in both transect and parallel (or, “longsect”) configurations.
- The wells were installed at depths where appreciable contamination is known to exist to allow comparison to current data.
- In addition, data is being collected using high resolution methods to further compare data sets.
- The well segments were sampled along with adjacent vertical monitoring wells using peristaltic pumps and standard operating procedures.
- Groundwater flux is being measured using the washout tracing method.
- Data is also being compared to fiber optic Distributed Temperature Sensor (DTS) flux measurements.
VERTEBRAE COMPARISON
- Since this is an ongoing study, the data shown here serves as a preview of the information to be published later.
- The data indicates representative groundwater samples collected from similar aquifer locations and indicates the positive correlation and excellent capability for groundwater sampling using horizontal wells for PFASs.
- The data below represents a monitoring well, with two Vertebrae segments on each side of the vertical well. The data accurately portrays the fate and transport of the distal end of the plume.
- There is no evidence that the horizontal nature of the well system affected PFAS concentrations.
VERTEBRAE Benefits
- Unlike most HRSC tools, these well systems can be sampled repeatedly, for instance, quarterly. This allows monitoring of the site conditions instead of having to recomplete a HRSC event. This is especially significant for sites with long term goals such as PFASs sites where attenuation and monitoring are a likely course of action.
- The installation occurs congruent to the lithology and plume shape. It can be installed in transects or longsects and the well vault or riser can terminate in one point making it an aesthetically suitable option given the long life for the wells. This also keeps sampling technicians out of the way of site traffic or operations.
- The wells are certified to be PFAS free and are suitable for sampling all current known Contaminants of Concerns (CoCs).
Vertebrae, which was first just a great injection tool, is now advancing cutting edge characterization.
This is changing the way the industry thinks about sampling.
