2016-01-21 thiessen polygons presentation
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Transcript of 2016-01-21 thiessen polygons presentation
Attainment of Remediation Standards and Site-Specific Criteria
Attainment of Remediation Standardsand Site-Specific CriteriaKassidy KlinkJanuary 21, 2016Compliance Averaging Options: Spatially Weighted Average
Technical Guidance for the Attainment of Remediation Standardsand Site-Specific Criteria (September 24, 2012; Version 1.0)
Spatially Weight Average (A3.0 A9)ApplicabilityRI and RA phasesAll exposure pathwaysSingle point, horizontal and vertical delineation compliance necessaryDefinitionSampling results are weighted according to the area they representThe corresponding area defined by Thiessen Polygonspolygons whose boundaries define the area that is closest to each point relative to all other pointsthey are mathematically defined by the perpendicular bisectors of the lines between all points
Finished example with polygons
Step 1: Plot your data points
Step 2: Define Functional Areas (A2.1)Horizontal Limitations (A2.1.1)0.25/0.5 acres (residential Inhalation/Ingestion-Dermal) and 2 acres (commercial/industrial)Inhalation & Ingestion-Dermal: May be increased by up to 50% if > 1 functional area & contamination cannot be divided evenlyIGW must be 100 parallel to ground water flow direction. Unlimited perpendicular to flowCan combine multiple AOCs (including gaps) if 100: either must use multiple functional areas (default DAF), or use entire delineated AOC as area (site-specific DAF and IGW standard must be calculated)Bias towards worst case fit
Step 2: Functional Areas ContinuedShape Limitations (A2.1.2)Inhalation & Ingestion-DermalSquare = preferred shape
Length of shape can be no more than 4X width
IGWMust be 100 in length parallel to ground water flowUnlimited size perpendicular to ground water flow
Step 2: Functional Areas ContinuedVertical limitations (A2.1.3)Inhalation & Ingestion-Dermal
IGW
Note: Only analyze zones that have concentrations > standard
Functional area example
Step 3: Calculate initial area weighted mean (A3.0)
Note: If area weighted mean < standard, then no further action is necessary.
Step 4: Polygon replacement (A3.0)Replace your most contaminated polygon with fill or background concentration until area weighted mean < standard.Unrestricted use = remediate removed polygons to fill/background. Restricted use = subject to institutional/engineering controls + RAP.
ConclusionsEasy way to determine area weighted meanPotential to reduce the area to be remediatedProvides a clear path forward for a clientApplicable to all pathways