AFFF
aqueous film forming foam: mixed with water, then pumped through a special nozzle to create fire fighting foam.
analyte
A particular chemical compound you want to quantify.
bgs
below ground surface
BOD (biological oxygen demand)
A term commonly used in sanitary waste water treatment. It tells how much oxygen is required for bacteria to break down a substance. High BOD wastes tend to create anaerobic conditions in soil and groundwater because bacteria scavenge all of the available oxygen while doing their thing. This happens on a large scale in the Gulf of Mexico where the Mississippi River empties. At a fire fighting training site, a lot of fuel is dumped in order to create a fire to be extinguished. This fuel plus components that make up most of the foam usually do the same thing.
conductivity
You are probably familiar with electrical conductivity - the relative ease with which a material conducts electricity. Here we are referring to the ease with which a soil or rock formation conducts groundwater. This leads to a plethora of other terms like porosity.
cross section
Publishing data produced by a three dimensional model can be a challenge. You will see two common views:
CSM
Conceptual Site Model. This can take several forms. At its most abstract, it can be a simple diagram like this:
***ITRC fire training model (small version, with link to larger version and more detailed explanation)

You might also see terms like "14 compartment model" (or even "21 compartment model" where fractured rock is involved). This looks like a spreadsheet and essentially lists the various areas within and near the site, their characteristics and how they relate to one another.

Most modern site investigations may start with a simple model, but as field data is gathered it is plugged into sophisticated groundwater models that generate intricate three dimensional plots of contaminant plumes. They are examined closely for 'data gaps' - places where the situation is ambiguous and more data needs to be gathered, for example, by adding a new monitoring well.

A great example can be seen in the WI DNR BRRTS page for the Tyco fire training center. Download the 10/27/2021 DNR response to Arcadis models labeled "Technical Assistance Provided" and "SI ACTIONS REQUIRED; INCLUDES REVIEW OF ISOCONCENTRATION MAPS & EVALUATION OF ESIA" which downloads as filename 20211027_98_Tech_Assist_Provide_Isoconcentration.pdf. Scroll the PDF file down to file pages 13 thru 18 and you will see a series of plume cross sections followed by a single aerial view map where portions are circled in red and numbered with an explanation of the referenced data gap.
Fate and Transport
Fate is where it ends up, transport is how it gets there. Since stuff tends to end up where it finds it easy to be transported, the two are hard to separate.
FTS or fluorotelomer sulfonate
Fluorotelomers are a very common type of compound which works around an original patent by inserting a couple of non-fluorinated carbons between the perfluorinated chain and the acid group (carboxylate or sulfonate). This carbon is vulnerable to breakdown. These often show up in EPA methods looking something like 6:2 FTS. 6 is the length of the perfluorinated carbon chain. 2 is the number of non-fluorinated carbons. Unlike older foams, the chain length is always an even number.
heterogeneous
Sites which have large variations in porosity (groundwater conductivity) over short distances, aka, heterogeneous. For example, Truax Field sits over an ancient river gorge which was filled in by sediment left by the river or dumped by glaciers. At the edges of the gorge, some of the sandstone layers have bedding-plane fractures which are even harder to model than transitions between sand and gravel within the glacial till. Technophilics should visit the site characterization page and the groundwater modeling page.
HRSC
High Resolution Site Characterization, aka, the Triad approach
This approach is required for sites which have large variations in porosity (conductivity) over short distances, aka, heterogeneous.
Technophilics should visit my site characterization page.
ITRC
Interstate Technology and Regulatory Council is an organization for environmental professionals mainly led by state regulators. It develops and publishes guidance on many aspects (EG, PFAS) of conducting site investigation and remediation based on the most up-to-date published research.
k-value
Common variable used by geologists to represent groundwater conductivity.
logging
When drilling a monitoring well or using other means to retrieve samples of soil, there is an opportunity to use special instruments to gather data about the nearby soil or rock. ***find some example logs
mass flux
See the discussion in my site characterization page.

plume maturity: https://idss-2.itrcweb.org/2-conceptual-framework/
The transmissive zones of early stage plumes contain the highest VOC concentrations in their sources, particularity near the DNAPL phase. Over time the early-stage DNAPL phase, based on aqueous-phase equivalent concentration, is diminished by advection, biotic and abiotic degradation, and mass transfer into lower-permeability regions and other chemical phases within the source as well as the plume. In a middle stage, the aqueous-phase equivalent concentrations across affected phases and zones are relatively equal. In late-stage plumes, contaminant concentrations have attenuated in the more permeable (transmissive) zones, and the larger remaining concentrations remain in the lower-permeability zones within both the source and the plume. These concepts are a useful part of site-specific CSM development because plume maturity has a large effect on the response to treatment of a source and plume and therefore the potential efficacy of possible remediation efforts.
MW
Monitoring Well. ***more on screening in https://idss-2.itrcweb.org/2-conceptual-framework/ Fig 2.7
Mt Simon formation
A sandstone layer which is a primary aquifer (water source ) for municipal wells in Madison and several other areas in and near Wisconsin.
perfluoroalkyl (see PFAS)
PFAS
Per- or Poly- Fluorinated Alkyl Substance. Alkyl means a chain of carbon atoms. Octane is an 8-carbon alkyl in which the carbons have 2 (middle) or 3 (end of chain) hydrogens attached. Fluorination replaces some of the hydrogens (Poly-) or all of them (Per-). The carbon-fluorine bond is one of the strongest in nature which makes it very hard to break. Fluorine is much less plentiful in nature than chlorine, so few or no bacteria have evolved to take up the challenge. This is unlike chlorinated hydrocarbons where the molecules can often be destroyed by injecting bacteria into the ground.
PFOA, PFOS
Eight carbon chains with all of the hydrogen replaced by fluorine. In both there is one less fluorine on the end of the chain, replaced by an acid group. PFOA  has a carboxyl group, as in vinegar. PFOS has a sulfonate group, which is common in detergents, explaining why it became the basis for fire fighting foams.
PFHxA, PFHxS
Analogous 6-carbon chains. Lots of PFHxS is an earmark of film forming foam.
7-carbon chains replace Hx with Hp, 5-carbon chains with Pe.
PFBA, PFBS
Analogous 4-carbon chains. These tend to bioaccumulate less than the 8-chain PFAS but recent research suggests that PFBA accumulates in lung tissue and degrades immune response even at very low plasma levels.
ppt
Parts per trillion. It is very challenging to analyze samples at this level.
precursor
Modern PFAS fire fighting foams do not use much of the perfluorinated compounds analyzed by the EPA methods. Some of them use very complex molecules. This is done in order to improve their effectiveness and/or to get around a competitor's patents. Most are easily oxidized by bacteria under the right conditions, which can happen in soil near the surface but often do not occur in groundwater close to the source zone. But after the precursors travel to a place where oxygen becomes available, they eventually break down into the compounds analyzed by EPA methods. The breakdown usually occurs in stages, and the compounds at the middle stages are referred to as intermediates. Some can be relatively stable so they show up in some analytical results.
PrecursorPlumeNEWMOA_Arcadis.jpg from http://www.newmoa.org/events/docs/239/PFAS_FateTransportWebinarNov2016.pdf
PRL
Possible Release Location. Examples: the Tyco fire training facility in Marinette - sometimes referred to as a burn pit, one of the nozzle test areas adjacent to an airport fire station or an air crash site.
quadrupole time of flight (QTOF)
Mostly a research tool. It detects all of the PFAS compounds instead of a reduced set of 30 to 70. It's a mass spectrometer, so the compounds are broken up into fragments. For unknown compounds, knowing what fragments are produced gives some clues as to what the original molecule looked like. It's not a quantitative instrument because many of the compounds to not have an analytical standard available for comparison. Prominent users include Jennifer Field of Oregon State University.
receptor
A quaint toxicology term for people and wildlife who injest a poison.
RI
Remedial Investigation

SERDP/ESTCP
These agencies are jointly run by DOD, EPA and DOE. They fund basic research and field demonstration, resp, for new techniques in environmental investigation and remediation. The top PFAS researchers are often supported with these funds. Their reports and webinars are a wealth of information.
SL
Screening Level. There are established health levels for a contaminant in groundwater, EG, 70 ppt for PFOS in drinking water proposed by the EPA in 2016.
Screening levels are set somewhat lower, EG 40 ppt for the Truax WIANG investigation. This helps to ensure the investigation doesn't stop before establishing a downward trend at the end of a plume.
TOP assay
Total Oxidizable Precursor assay. A PFAS sample is exposed to strong oxidizing conditions breaking down complex polyfluorinated compounds into the set of 30-some perfluorinated compounds commonly quantified by EPA methods. The method has a couple of limitations. It does not preserve the original chain length - some chains are broken down to shorter lengths. It produces only carboxylates. So the end products are not the same as what would be produced under natural conditions. But it provides an idea of how much precursor mass is present but not reflected in the EPA method results. This is valuable at the source site where the PFAS may be mixed with fuel and other material that create anaerobic conditions. Developed by Erika Houtz PhD,  advised by Professor David Sedlak at UC Berkeley.
transect
See the site characterization page.
Transport
I am familiar with this term from chemical engineering. It envelops fluid dynamics (aka momentum transfer) and various ways that molecules move (or get stuck) in space:

Modeling all of this is hideously complex and nearly impossible if the soil/rock varies dramatically over short distances (heterogeneous).

VOC/CVOC
Volatile organic compound, usually a chlorinated volatile organic compound. Most common ones are TCE (trichloroethylene) and PCE (perchloroethylene), best known as dry cleaning fluids but also used as degreasers. In many cases CVOCs were detected and remediated decades before anyone looked for PFAS. They were often dumped into burn pits along with fuel for fire training purposes. The La Crosse airport VOC plume map was an excellent indicator of where the burn pit PFAS plume would be.