ASSESSING PAST USE OF TANNERY WASTE SLUDGE AS FARM FIELD FERTILIZER IN NORTHWEST MISSOURI July 20, 2010 ITRC Meeting Seattle, WA

BACKGROUND  Sludge applied  56,000 acres affected  100+ locations across 4 counties  Concern 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 MODEL  Applications uniform except near buffers, corners, access gates.  Appl. rates frequencies & mechanism known  Runoff concentrates sludge in low areas  High fOC, low pH, & high redox all act to reduce Cr VI to Cr III.

EXPOSURE PATHWAYS  Direct exposure (inh/ingest) to soil by farmer & nearby residents.  Interested in particle fraction <0.25mm  Leaching to groundwater & GW ingestion  Surface water, ecological risk (not assessed)

CrVI SCREENING LEVELS  Represent mean [CrVI] across exposure area that would pose risk to resident child living adjacent.  Farm field = 86 ppm. Based on 80-acre field.

SAMPLING STRATEGY  56,000 acres affected. Can’t sample it all: Select farm field DUs for sampling.  DUs = Exposure Area = 80 acres  SU = 1 acre squares w/in DU  Fields 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 RULE  If 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 STUDY  30 Discrete collected in three FF plots  XRF for total Cr few $/sample. CrVI analysis $160/sample.  Analyzed for total and hex Cr  Variograms 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 = Farm Field DU area = 1-acre SU area = SU increment sample location SU 80 SU 4 SU 72 SU 45 SU 28 Start 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 ANALYSIS Our decision error tolerance From SU XRF data CrVI AL converted to total Cr AL (using pilot data) Number of samples needed within the SU From discrete sample XRF data

XRF ANALYSIS

Farm Field Design = Farm Field DU area = 1-acre SU area = SU increment sample location SU 80 SU 4 SU 72 SU 45 SU 28 DUIS Increments combined in oe bag Increments combined in one bag Increments combined in one bag -Split SUIS and combine aliquots to form DUIS (2 nd Tier). XRF that. -Send SU & DU IS samples for CrVI analysis Combine 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/DU  None 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 Processing  Air dry discretes, disaggregate, sieve 60 mesh  Create SUIS from discretes  Split 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 analysis  Lab used 2D Japanese slabcake for subsampling

SU IS Replicates SURepl1Repl2Repl3RSD *SUIS made up of 10 increments collected in systematic (serpentine) pattern Hexavalent Cr, mg/kg SURepl1Repl2Repl3RSD Total Cr, mg/kg

Analytical Subsampling DU-SUCrVI Cr VI Lab dupRPD D Japanese Slabcake Method Used

Comparison of IS Tiers IDAve of SUISDU-IS Result%RPD DU DU DU DU DU DU DU DU DU DU DU DU DU DU DU DU DU DU DU IDAve of SUIS DU-IS Result%RPD DU DU DU DU DU DU DU Total Cr, mg/kg (XRF) Hexavalent Cr, mg/kg Micro scale heterogeneity of total Cr in matrix controlled well by sample splitting technique. Less well for CrVI.

Analysis of Relative Uncertainties Data 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