Interpreting Analytical Results

Transcription

1 Interpreting Analytical Results Beyond Guidelines and Exceedances Frans Hettinga Tetra Tech EBA Inc. Calgary, Alberta

2 Contents Focus on groundwater chemistry Some basics and tricks What is the value? A few case studies

3 Multiple choice Interpreting analytical results: a. is boring b. just tabulate it and compare to Guidelines c. is always straightforward, an exact science d. is disconnected from other assessment info e. all of the above f. none of the above

4 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: motivated to learn the trick & practice

5 Why are we sampling? Compliance with a regulatory Approval Part of site assessment activities, due diligence Assess monitored natural attenuation

6 What are we sampling for? Tailored suite of parameters Example: as per a groundwater monitoring program proposal in an EPEA Approval Prescribed suite Example: AER Directive ph, EC, major ions, dissolved metals, DOC, phenols, BTEX and PHC fractions Specific contaminants of concern Example: solvents, hydrocarbons, metals

7 Garbage in, Garbage out Adhere to sampling protocols, holding times, preservation, QA/QC, etc. If filtration is required do it in the field Check COCs and use preprinted forms if possible Check data upon receipt (e.g. ion balance, ph- Aluminum) Upload electronically

8 Interpreting results: keep it simple, but.. Know the value and limitation of gross indicator parameters (e.g. DOC, TKN, COD) Always request a chromatogram for PHCs Identify chemicals of potential concern 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

9 Data Interpretation Tools - Redox Who needs it Redox ties much together (e.g. hints at releases or natural conditions) Indicates degrading environment (oxic/anoxic) and therefore degradation rate Valuable for monitored natural attenuation Not rocket science

10 Look at the bigger picture a decaying leaf..

11 .. or chemical processes and redox

12 Redox Levels the Simplified Ladder Redox-Sensitive Parameter Dissolved Oxygen (DO) Nitrate Dissolved manganese Dissolved iron Sulphate Methane Comments Questionable value; hard to measure the low levels that matter >0.5 mg/l often indicates oxic conditions Becomes mobile after nitrate and oxygen are consumed >0.1 mg/l indicates suboxic conditions Next in line to mobilize >0.1 mg/l indicates anoxic conditions Sulphate reduction (relative to background) indicates anoxic conditions If present, deep anoxic conditions exists

13 What is the value, what is the reward Looking at the bigger picture, beyond exceedances can help to: - make monitoring programs more efficient - prevent forming data grave yards - use existing data smarter and more effective A few examples

14 Example 1: Natural Gas Processing Plant Compliance monitoring identified high nitrate concentrations. Assumption was made that nitrate was related to facility activities. Rationale: - Down-gradient monitoring wells had nitrate > 20 mg-n/l - Up-gradient well (MW05) had no nitrate

15 NO3-N (mg/l) 2013 data

16 Setting Relatively small facility East-central Alberta Surrounded by agricultural land Semi-arid Clay till overlying sand Water table at variable depth (but > 2 m) High-TDS groundwater

17 2013 Groundwater Quality Average Down-gradient MW05 TDS 2,307 mg/l 3,930 mg/l Sulphate 986 mg/l 1,660 mg/l Nitrate-N 23.2 mg/l Non-detect BTEX + PHCs Non-detect Non-detect Interpretation hampered by: Limited historical data (just ) Basic analytical program without redox sensitive metals (Fe/Mn)

18 Zoom in on MW05 First data (2010) 2013 data Nitrate-N 1.0 mg/l < 0.5 mg/l DOC 530 mg/l 168 mg/l BTEX + PHCs mg/l (just benzene) All non-detect glycols All non-detect All non-detect Interpretation: Suspected previous impact at MW05 (dehydrator) Caused anoxic conditions at MW05 and denitrification C 6 H NO 3 6 HCO N 2 Nitrate at other wells likely related to previous agricultural land use Based on non-detect glycol, BTEX and PHC results, no further work was recommended

19 Example 2: Staining at a compressor station

20 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 Also bubbling gas and liquids

21 A clean chromatogram?

22 Requested: - Routine water chemistry - TOC - Total metals Subsequent Water Analyses Select Results ph 13.5 TOC 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

23 Summarized chemistry: Highly alkaline and saline Elevated metals Not a hydrocarbon product No methane, but trace hydrogen gas Gas analyses (Tedlar bag)

24 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 DOC) Presence of hydrogen gas is key

25 The Cause Cathodic Protection Client interviews suggested anode bed near facility fence was to blame. Petroleum coke surrounding the sacrificial anodes was the source of metals; sodium and silica are also present in the coke ( alkaline battery ). Produced gas (including hydrogen) pushed impacted water outwards along underground lines. Targeted and cost-effective analyses solved problem in less than two weeks. Operational changes were implemented to prevent further impact.

26 Example 3: Redevelopment issues due to benzene Benzene concentrations in groundwater up to 4 mg/l, exceeding applicable guidelines No other BTEX compounds present Also no PHC fraction F1 or F2 Deep groundwater table within sand layer Groundwater was highly mineralized, nonpotable

27 Previous Building

28 Potential Sources and Further Work Service station ~100 m upgradient? Adjacent asphalt lab? Confusion due to absence of toluene, ethylbenzene, xylenes, F1 and F2 Added VOC scan (EPA 8260) Other than benzene, VOC results only showed 1,2-dichloroethane (up to mg/l) 1,2-DCA is lead-scavenger formerly added to leaded gasoline

29 Outcome Concluded that plume was old and only benzene remained due to attenuation The presence of lead-scavenger pointed to the service station as the source Re-development proceeded with risk management measures Service station owner contributed to costs

30 Example 4: MTBE plume Injection well site Initially AER regulated (Directive 058) Compliance monitoring program required semiannual groundwater sampling for basic program including routine water chemistry, dissolved metals, phenols, BTEX, PHCs, DOC

31 DOC results for one monitoring well Date June 2002 October 2002 March 2003 June 2003 October 2003 DOC 9.2 mg/l 827 mg/l 42.6 mg/l 14.8 mg/l 1,710 mg/l Based on DOC spikes the analytical program was expanded by adding a VOC scan (EPA 8260) No clear indication at first what caused high DOC but lab flagged unknown peak Eventually identified as MTBE (230 mg/l in 2004)

32 MTBE was formerly produced in the Edmonton area for used as fuel additive (mainly exported) Persistent and highly mobile Highest concentration on-site was 960 mg/l vs. guideline value of mg/l Finding triggered immediate remedial action (dig-anddump and recovery trench) Concentrations have decreased considerably Current status

33 In Conclusion Look beyond exceedances to get the most out of analytical data Connect the dots ; (groundwater) chemistry data is not stand-alone info; always consider stratigraphy, hydrogeology, historical info

34 Questions?