Best/Worst Practices for Soil VOC Sampling Webinar VOLATILE ORGANIC COMPOUND ANALYSIS

Transcription

1 Best/Worst Practices for Soil VOC Sampling Webinar VOLATILE ORGANIC COMPOUND ANALYSIS

2 Ensuring Good Soil VOC Data Collection of the sample, shipping, analysis-regulated by state and EPA Everything that happens before collection-generally unregulated -Nielsen Field School offers certification program for soil sampling (

3 Handling of Sample when Soil Core Liner is opened Complex situation since stability of VOCs in the core liner depends on: 1. whether the soil is consolidated/unconsolidated, sand, gravel, clay, organic matter, etc. 2. time elapsed before sampling (off gassing), 3. moisture content, 4. disturbance of integrity of the core, 5. ambient temperature

4 VOC Stability-5% Moisture Concentration µg/kg Time in Seconds

5 VOC Stability-10% Moisture µg/ml MeOH Extract Time in Minutes

6 Volatilization losses occur within seconds of exposure Uncontrollable volatilization for samples with a large surface to mass ratio TCE Concentration (%) Exposure Time (min)

7 Best Practice When Using Acrylic liners Cap the acrylic liner to preserve volatiles and do not split until ready to use Split liner as soon as possible. Every minute counts. Keep liner on ice if extended times are required Sample immediately with En Core or methanol upon splitting Screen and select samples for analysis. US EPA SW 846 Method 3815 is the current method for screening although it s use is not mandatory.

8 Things to Avoid: Leave liner exposed while screening Sample from container used for screening Take second boring to take samples after screening initial boring Use bulk sampling

9 Why change methods? Liability Proper apportionment of responsibility Avoiding future problems. Do it right the first time. Best practices Decisions based upon good data

10 Methods for sampling for soil VOCs Bulk sampling method in use in U.S. until 1998 Brass sleeve Packed jar En Core Sampler Methanol field preservation Low level sodium bisulfate preservation

11 Significant bias between sampling methods Concentration (µg/kg) Bulk Method Concentration (µg/kg) Methanol Method Volatile Organic Compounds: Comparison of Two Sample Collection and Preservation Methods, Liikala, T.; Olsen, K.; Teel, S.; and Lanigan, D., November 1996.

12 Biodegradation increase concentration during EPA holding time Percent of Original Value Days of Analysis Degradation of Hydrocarbons in Soil Samples Analyzed Within Acceptable Holding Times, Jackson, J.; Thomey, N, May 1991.

13 Bulk sampling sources of error Type of soil Microbe content Grit on threads Time to sample and ambient temperature Storage time (hold time) Amount of air space in jar Time spent subsampling for 5.0 g in Lab Purge in water RANGE OF ACCURACY: % true value

14 US EPA Method 5035 was promulgated in 1997 Can you afford to implement a project with so much randomness built in? Field preservation with methanol and sodium bisulfate En Core Sampler

15 Adoption of EPA Method 5035 by region

16 Low and High Level Method in 5035 Low level is for MDLs around 0.5 µg/kg using Sodium bisulfate preservation High level is for MDLs above about 25 µg/kg using Methanol preservation

17 Field preservation: sodium bisulfate 5 gram soil: 5 mls of a 20% sodium bisulfate solution, aqueous (Calcareous soil types should be checked for effervescence prior to sampling or vial may explode.) Check tare weight of all vials before adding soil Collect duplicate samples.

18 Low Level Method Semi-quantitative since water is a poor solvent for soil VOCs. The results are biased low. Used for risk analysis where some VOCs require very low detection limits. Can have high concentrations of acetone as an artifact in some organic soils.

19 Field preservation: methanol Add 5, 10 or 25 gm plug of soil in the field to vial containing methanol. 1:1 ratio(or higher) methanol to soil. Operation must be done quickly. Tared methanol jars should be verified before use.

20 Methanol preservation shows no bias at 30 days GRO Concentration (mg/kg) Time In Days Studies of Sampling, Storage and Analysis of Soils Contaminated with Gasoline and Diesel, Turriff, D. and Klopp, C., August 1994.

21 Advantages of Methanol Preservation No further treatment required Lower material cost

22 Disadvantages of field preservation 1% of vials are irregular More experienced field staff required Difficult under adverse weather conditions More risk of error, e.g., spillage, mixing labels, etc. Vehicle exhaust fumes can contaminate methanol. Shipping restrictions may apply for methanol

23 En Core Sampler Both a sampler and a container 5 and 25 g sizes Designed to collect an average weight exact weight is determined in lab Zero headspace design minimal air trapped New disposable version released November 10, 1997

24 En Core Sampler with container

25 Advantages of En Core Sampler Less field personnel required More sample throughput Easy to use minimal training No hazardous chemicals in the field No shipping restrictions Sample later preserved in controlled laboratory setting Long shelf life no expiration

26 Disadvantages of En Core 48 hour hold time to get into methanol-requires coordination Cost of goods is higher though should be compared to any extra labor costs This is especially true for inexperienced samplers

27 Reliability Allowed in every EPA and Federal program where Method 5035 is required Millions sold without one analytical incident. Quality standards are higher than for bottles because we analyze every lot for performance and cleanliness.

28 Testing of En Core Sampler Every lot tested for quality and performance Samples of each lot retained for future reference Tested at temperature extremes Can be stored frozen ASTM Approved (only sampler approved) and only sampler to pass ASTM specified validation method in ASTM Allowed as an alternative to field methanol in every state that has accepted or required 5035 Often used to minimize liability-consistency of sampling despite variations in experience of field staff

29 Stability of VOCs in En Core Sampler Concentration (µg/kg) Days Storage

30 Hold time study 0-7 days Percent recovery, 95% CI Days Storage

31 Percent Recovery Comparison Percent Recovery Comparison of En Core with Competing Non-Methanol Sampler Percent Recovery

32 To watch training videos or for more info:

33 Questions? Dave Turriff En Novative Technologies, Inc. Tel: WEB: