ASSESSING PAST USE OF TANNERY WASTE SLUDGE AS FARM FIELD FERTILIZER IN NORTHWEST MISSOURI

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ASSESSING PAST USE OF TANNERY WASTE SLUDGE AS FARM FIELD FERTILIZER IN NORTHWEST MISSOURI. July 20, 2010 ITRC Meeting Seattle, WA. BACKGROUND. Sludge applied 1983-2009 56,000 acres affected 100+ locations across 4 counties Concern about risk posed by hexavalent chromium (Cr VI) in sludge. - PowerPoint PPT Presentation

Transcript of ASSESSING PAST USE OF TANNERY WASTE SLUDGE AS FARM FIELD FERTILIZER IN NORTHWEST MISSOURI

  • ASSESSING PAST USE OF TANNERY WASTE SLUDGE AS FARM FIELD FERTILIZER IN NORTHWEST MISSOURI

    July 20, 2010ITRC MeetingSeattle, WA

  • BACKGROUNDSludge applied 1983-200956,000 acres affected100+ locations across 4 countiesConcern about risk posed by hexavalent chromium (Cr VI) in sludge.

  • CSM JACKPOT: TANNERY KEPT LOTS OF DATA ON SLUDGE APPLICATION

  • STUDY AREA

  • HERE COMES THE SLUDGE

  • CONCEPTUAL SITE MODELApplications uniform except near buffers, corners, access gates.Appl. rates frequencies & mechanism knownRunoff concentrates sludge in low areasHigh fOC, low pH, & high redox all act to reduce Cr VI to Cr III.

  • EXPOSURE PATHWAYSDirect exposure (inh/ingest) to soil by farmer & nearby residents.Interested in particle fraction
  • CrVI SCREENING LEVELSRepresent mean [CrVI] across exposure area that would pose risk to resident child living adjacent.Farm field = 86 ppm. Based on 80-acre field.

  • SAMPLING STRATEGY56,000 acres affected. Cant sample it all: Select 15-20 farm field DUs for sampling.DUs= Exposure Area = 80 acresSU = 1 acre squares w/in DUFields chosen based on CSM (judgemental) appl. Rate, frequency, time, geography, field type (row crop vs. pasture). SUs also chosen based on CSM attempt to select SUs with maximum within-SU and between SU heterogeneity (most conservative).

  • FARM FIELD DU WITH OVERLAY GRID OF SUs

  • DECISION RULEIf 95% UCL on [CrVI] (measured using SUIS) in any farm field DU exceeds the screening level, investigation will be expanded; otherwise conclude that sludge applications do not pose risk - NFA.

  • PILOT STUDY30 Discrete collected in three FF plotsXRF for total Cr few $/sample. CrVI analysis $160/sample.Analyzed for total and hex CrVariograms showed total and hex Cr vary across fields in similar way & var of Cr >CrVI. Used worst case observed ratio of CrVI:Cr (~20%) to convert CrVI SL to Cr SL.

  • Farm Field Design

    SU 80SU 4SU 72SU 45SU 28Start with 3 SUs and 10 discretes (increments)

    Analyze each increment 4x by XRF

    -Provides measure of within bag heterogeneity-Use mean, SD, AL in VSP to determine # incr. needed in SU

    -If >10 increments needed, collect them.

    REPEAT FOR OTHER 2 SUs

  • VISUAL SAMPLE PLAN ANALYSISOur decision error toleranceFrom SU XRF dataCrVI AL converted to total Cr AL (using pilot data)Number of samples needed within the SUFrom discrete sample XRF data

  • XRF ANALYSIS

  • Farm Field Design

    SU 80SU 4SU 72SU 45SU 28DUISIncrements combined in oe bagIncrements combined in one bagIncrements combined in one bag

    -Split SUIS and combine aliquots to form DUIS (2nd Tier). XRF that.-Send SU & DU IS samples for CrVI analysisCombine SU increments together to form SUIS & XRF 4x-Use mean, SD, AL of the 3 SUIS in VSP to determine number of SUs needed for the DU.If >3 SUs needed, collect them

  • INCREMENTS/SU & SUs/DUNone of the 60 SUs required more than 10 increments based on VSP analysis (none even >4).None of the 19 DUs required more than 3 SUs to be sampled.SDs were low, but key factor was the distance between our estimates of mean [CrVI] & the screening level.

  • Sample ProcessingAir dry discretes, disaggregate, sieve 60 meshCreate SUIS from discretesSplit SUIS into 3; one to form DUIS, one to lab, one for archive. Split technique was simple mix & pour from bag.All SUIS and half the DUIS submitted for CrVI analysisLab used 2D Japanese slabcake for subsampling

  • SU IS Replicates*SUIS made up of 10 increments collected in systematic (serpentine) patternHexavalent Cr, mg/kgTotal Cr, mg/kg

  • Analytical Subsampling2D Japanese Slabcake Method Used

  • Comparison of IS TiersTotal Cr, mg/kg (XRF)Hexavalent Cr, mg/kgMicro scale heterogeneity of total Cr in matrix controlled well by sample splitting technique. Less well for CrVI.

  • Analysis of Relative UncertaintiesData Variability Measured by Width of 1 Side of Uncertainty Interval Normalized to the Mean (i.e., interval width/mean)General trends:-Higher variability in CrVI vs. total Cr-Variability incr. with scale from within sample to within SU to between SU. But,-For some DUs, micro-scale variability within sample dominates.*only portion of DU data shown

  • DATA VALIDATES CSM?Selection of DUs based on application data captured worst case fields. Yes, pos. correlation of application rates/frequency to Cr levels.Our selection of SUs maximized within and between SU variability Yes, SUs chosen as high variability in field had highest SD, SUs chosen as low variability had lower SD.Soil redox conditions control ratio of Cr6:Cr in fields. Yes, fOC highly (negatively) correlated with CrVI

  • DECISION

    Accounting for all sources of variability, and making most conservative assumptions, no 95% UCL was within an order of magnitude of the screening level.No further investigation planned