Presented by Shannon H. McDonald, P.G.August 4, 2010
Soil sampling approach designed to obtain contaminant concentrations more representative of your exposure unit/domain
Collected discrete samplesInfluenced by sampler biasNot scientifically reproducible or, therefore,
defensibleExpensive to collect sufficient samples to
adequately represent a siteMay miss ‘hot spots’Often biased upward or downward
For Risk Assessments, commonly used either maximum concentration or 95% UCL concentration as representative concentration in exposure domain
Theory of particulate sampling originally developed by geologist Pierre Gy for mining industryDesigned to address “Seven Sampling Errors”
FUNDAMENTAL ERRORAddress by collecting and analyzing sufficient sample
mass
SEGREGATION ERRORAddress by collecting sample increments randomlyCollect samples in sufficient locations to capture spatial
variability
Formally developed:◦By EPA◦November 2006◦Method 8330B◦ For nitroaromatics (energetics and explosives)◦Military munitions sites
Commonly “Multi-Increment™ Sampling” “Multi-Increment” is trademarked by
Envirostat, Inc. Incremental Sampling Methodology? Began to be applied to other types of
contaminantsSemi-volatile organic compoundsMetalsPesticidesPCBs
1. Identify Decision Unit (DU)• Generally not the entire site; subdivide site
into several Decision Units• Size will depend on goal of investigation• Important not to bias or dilute
• Useless to draw around small source area• Should not include large areas known to be
uncontaminated (“dilution effect”)
2. Grid Decision Unit• Need sufficient increments to not “miss”
contaminationo Typically 30 to 50 increments (guidance and
theory)• Addresses distributional heterogeneity• “Systematic random” approach reduces bias
2. Grid Decision Unit (cont.)• Collect one sample increment per grid cell• Collect increments from same relative location
within each grid cell• Start at random point in first grid cell
• Skipped increments?• Because “systematic random”, SKIP (don’t
move) inaccessible increments (due to buildings, pavement, standing water, etc.)
• Otherwise, introduce bias• For example:
3. Collect same volume of soil at each increment• Work backward to calculate how much soil
you will need at the end• Depends on analyses to be performed and
how many replicate samples you plan to collect (discussed later)
• For a site with lead and PAH contamination, TTL collected about 120 grams (4 ounces) of soil per increment
3. Collect same volume of soil at each increment (cont.)• Can use soil probe, hand auger, geoprobe,
etc.• Collect from specified depth at each
increment location• Place each increment in intermediate
container together• For example:
4. Sieve entire sample• Typically use #10 sieve (200-mesh)• Remove fraction of sample >2 mm in diameter
(trash, gravel, etc.)• Sieve resultant “soil” into decontaminated 2nd
container (bucket?)• May require air-drying (no elevated temps!)
first• TTL used large stainless steel trays to air-dry no
more than 2 hours (SVOCs, metals, etc.)
4. Sieve sample (cont.)
4. Grind sample?• Some guidance suggests grinding sample
• Obtains uniform small particle size• Can further reduce Fundamental Sampling Error
• Depends on analytes• ADEM does not use grinding step
5. Subdivide sample• Spread sample out in thin layer (1/4-inch) on
decontaminated surface
5. Subdivide sample (cont.)• Grid into between 30 and 50 sections
5. Subdivide sample (cont.)• Collect equal amounts of soil from each
gridded section• Scale• Stainless steel scoop – FLAT (to scoop to
bottom of sample; collect all particle sizes)
5. Subdivide sample (cont.)• Place one scoop from each grid section into
sample container• Number of containers to fill varies by state
• Alaska and Hawaii recommend triplicate samples• Alabama recommends minimum of TEN ultimate
samples for each analyte
5. Subdivide sample (cont.)• After filling all sample containers:
Relative standard deviation?◦Some guidance suggests calculating the RSD of
analytical results Quality control measure Ideally <30% Indicates data distribution
Calculate 95% Upper Confidence Limit• Ideally requires 10 to 15 concentration measurements• Ensures representative concentration
Ongoing investigation/remediation projectHigh concentrations of PAHs and metalsApproximate 85-acre parcelDivided into 17 decision unitsUsing ISM on each unit, have been able to
receive CLOCs without further remediation on 12 zonesTwo zones pending CLOCsThree zones require more remediation
Need careful planning before going out into the field
Coordinate with regulators before beginning to understand expectations
Alaska – Draft Guidance – March 2009 - http://www.dec.state.ak.us/spar/csp/guidance/multi_increment.pdf
ITRC Methodology Resources and Links – http://www.itrcweb.org/teamresources_79.asp
Hawaii Technical Guidance Manual - Nov. 2009 - http://www.hawaiidoh.org/tgm.aspx?p=0402a.aspx
USACE Interim Guidance – July 2009 - http://www.hnd.usace.army.mil/oew/policy/IntGuidRegs/IGD%209-02v2.pdf
Questions / Discussion???
Shannon H. McDonald, P.G.
TTL, Inc.
4154 Lomac Street
Montgomery, Alabama 36106
(334)244-0766