Interpreting Analytical Results
Beyond Guidelines and Exceedances
Frans Hettinga
Tetra Tech EBA Inc.
Calgary, Alberta
Contents
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Focus on groundwater chemistry
Some basics and tricks
What is the value?
A few case studies
Multiple choice
Interpreting analytical results..
a. is boring
b. just tabulate it and compare to Tier 1
c. is always straightforward, an exact science
d. is disconnected from other assessment info
e. all of the above
f. none of the above
Skills needed
Compare to Rubik’s cube
- My record: poor, never finished one, frustrated
- My son’s (12 yr old) record: 2 minutes, 16 seconds
The difference: he figured out the tricks and practiced
Basics
Why are we sampling?
• Compliance with an Approval, site assessment
or monitored natural attenuation
• Tailored suite of parameters or prescribed (e.g.
AER Directive 058: pH, EC, major ions,
dissolved metals, DOC, phenols, BTEX and
PHC fractions)
• Keep it simple, best bang for the buck
Garbage in, Garbage out
• Adhere to sampling protocols, holding times,
preservatives, etc.
• If filtration is required do it in the field
• Check COC’s and use preprinted forms if possible
• Check data upon receipt (e.g. ion balance)
• Upload electronically
The bigger picture – a decaying leaf..
.. or chemical processes and redox
Redox
Who needs it…
• Ties much together (e.g. hints at releases or
natural conditions)
• Indicates degradation environment (oxic/anoxic)
and therefore degradation rate
• Valuable for monitored natural attenuation
• Not rocket science…
Redox Levels – the Simplified Ladder
Redox Sensitive Parameter
Comments
Dissolved Oxygen (DO)
Questionable value; hard to measure the low
levels that matter
Nitrate
>0.5 mg/L often indicates oxic conditions
Dissolved manganese
Becomes mobile after nitrate and oxygen are
consumed
>0.1 mg/L indicates suboxic conditions
Dissolved iron
Next in line to mobilize
>0.1 mg/L indicates anoxic conditions
Sulphate
Sulphate reduction (relative to background)
indicates anoxic conditions
Methane
If present, deep anoxic conditions exists
Keep it simple, but..
• Know the value and limitations of gross indicator
parameters (e.g. DOC, TKN, COD)
• Always request a chromatogram for PHCs
• Identify chemicals of potential concern (CoPC)
beforehand (e.g. MSDS sheets, Phase 1 ESA)
• Link chemistry results to soil, stratigraphy,
hydrogeology, historical info
• Do not blindly use statistics or geochem
programs; follow the rules, stick to the basics
What is the value, what is the reward
Looking beyond exceedances can help:
- make monitoring programs more efficient
- prevent forming “data grave yards”
- use existing data smarter and more effective
A few examples…
Example: Natural Gas Processing Plant
Compliance monitoring identified nitrate as
CoPC
Assumption was made that nitrate was related
to facility activities based on:
- Downgradient monitoring wells had nitrate
> 20 mg-N/L
- One upgradient well (MW05) had no nitrate
NO3-N (mg/L)
2013 data
Setting
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Relatively small facility
East-central Alberta
Surrounded by agricultural land
Semi-arid
Clay till overlying sand
Water table at variable depth (> 2 m)
High TDS groundwater
2013 Groundwater Quality
mg/L
Average
Downgradient
MW05
TDS
2,307
3,930
Sulphate
986
1,660
Nitrate-N
23.2
Non-detect
Non detect
Non detect
BTEX + PHCs
Interpretation hampered by:
• Limited historical data (just 2010 – 2013)
• Basic analytical program without redox sensitive metals (Fe/Mn)
Zoom in on MW05
mg/L
First data (2010)
2013 data
Nitrate-N
1.0
< 0.5
DOC
530
168
0.0114 (just benzene)
All non detect
All non detect
All non detect
BTEX + PHCs
glycols
Interpretation:
• Suspected previous impact at MW05 (dehydrator)
• Caused anoxic conditions at MW05 and denitrification
• Nitrate at other wells likely related to previous agricultural land use
• Based on glycol, BTEX and PHC results no further work
recommended
Example: Staining at a compressor station
Also bubbling gas and liquids
Initial soil analyses:
Parameter
Results
pH
10.5
EC
41.1 dS/m
Na
4,170 mg/kg
Cl
175 mg/kg
BTEX
Non-detect
PHC fractions
Non-detect
A clean Chromatogram?
Subsequent Water Analyses
Requested:
- Routine water chemistry
- TOC
- Total metals
Select Results
pH
13.5
DOC
2,150 mg/L
Sodium
12,000 mg/L
Sulphate
100 mg/L
Arsenic
1.64 mg/L
Nickel
1.55 mg/L
Silica
1,510 mg/L
Vanadium
1.59 mg/L
Gas analyses (Tedlar bag)
Summarized chemistry:
Highly alkaline and saline, elevated metals, not a
hydrocarbon product, not methanogenic
Putting one and one together
• Site is flat so natural groundwater discharge
unlikely
• Water table > 1 m deep
• Not a “normal” groundwater type (too alkaline,
too many “exotic” metals, high silica, high TOC)
• Presence of hydrogen gas is key
The Cause – Cathodic Protection
• Client interviews suggested anode bed near
facility fence is to blame.
• Consists of sacrificial iron anodes embedded in
petroleum coke.
• Coke is source of metals, sodium and silica are
also added.
• Targeted and cost effective analyses solved
problem in less than 2 weeks.
• Discussed operational changes to prevent
further impact.
Example: Benzene plume
The issue:
Assessments prior to redevelopment identified
benzene in groundwater greater than applicable
guidelines
Potential sources:
Adjacent service station(s) and laboratory
Previous Building
Assessment Data
• Stratigraphy: alternating sand, clay and silt
layers
• Groundwater table around 6 – 7 m below grade
within sand
• Highly mineralized, non-potable groundwater
• BTEX compounds non-detect except benzene
• Benzene concentrations up to 4 mg/L
• Fraction F1-BTEX non-detect, no F2 either
Potential Sources and Further Work
• Service station ~100 m upgradient?
• Adjacent asphalt lab?
• Confusion due to absence of toluene,
ethylbenzene, xylenes, F1-BTEX and F2
• Suggested plume was old (only benzene
persisted) and added VOC scan (EPA 8260)
• Other than benzene, VOC results only showed
1,2-dichloroethane (up to 0.141 mg/L)
• 1,2-DCA is “lead-scavenger” formerly added to
leaded gasoline
Outcome
• Discussions with consultant for service station
owner
• VOC results supported that 1,2-DCA and
benzene were linked
• Re-development proceeded with risk
management measures
• Service station owner contributed to costs
Example: MTBE plume
• Injection well site
• ERCB regulated (Directive 058)
• Compliance monitoring program required semiannual groundwater sampling for:
- Routine water chemistry
- Dissolved metals
- Phenols
- BTEX and PHCs
- Dissolved organic carbon (DOC)
DOC results for one monitoring well
Date
DOC
June 2002
9.2 mg/L
October 2002
827 mg/L
March 2003
42.6 mg/L
June 2003
14.8 mg/L
October 2003
1,710 mg/L
• Analytical program expanded based on DOC trends
• VOC scan (EPA 8260) added
• No clear indication at first what caused high DOC but lab
flagged “unknown peak”
• Eventually identified as MTBE (230 mg/L in 2004)
Current status
• MTBE was formerly
produced in the Edmonton
area for used as fuel
additive (mainly export)
• Persistent and mobile
• Highest concentration onsite was 960 mg/L vs.
guideline value of 0.015
mg/L
• Finding triggered
immediate remedial action
and concentrations have
decreased
In Conclusion
• Look beyond exceedances and to get the most
out of analytical data
• Connect the “dots”; (groundwater) chemistry
results and assessment data are always related
• The lab can help; not just with providing the data
but also with expert advise
Questions?