IRIS ENVIRONMENTAL 1438 Webster, Suite 302, Oakland CA (510)

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1 Background dlevels of fpahs in California Soils Adrienne LaPierre 1438 Webster, Suite 302, Oakland CA (510)

2 Practical Problems Encountered when Addressing PAHs at former MGP Sites in California Many natural and anthropogenic sources of PAHs PAHs found in surface soils, in both urban and rural environments Risk-Based Levels of PAHs typically below background Remediation to risk-based level not practical In 1998, realized the need to understand background PAH concentrations

3 Overview of Discussion Initial Experiences at former MGP sites Methods used to develop statistically robust background PAH dataset-southern California Site management decisions supported by Background PAH dataset Parallel work in Northern California Hurdles encountered in using background PAH datasets in risk-management decision making

4 Initial Experiences at Former MGP Sites-circa 1995 Risk Based Concentrations (RBCs) of C-PAHs 0.02 mg/kg Local background concentrations from one site were around 0.12 mg/kg Remediating to RBCs not practical Use of a bright-line from local background- Cleaning up entire town

5 Development of a Southern- California Background PAH Dataset Had background PAH data for 22 former MGP sites in southern California (n = 185) Question: appropriateness of pooling all data to develop one statistically robust background dataset? Use of one larger background dataset would provide significant added statistical power in identifying a background-based cleanup goal

6 Development of a Southern- California Background PAH Dataset (cont) Statistical Evaluations of Background PAH data Roughly 4-7 samples collected for most of the 22 sites (2 exceptions- sites with 29 and 47 samples) Samples representative of one population, or is data better described as being composed of many subpopulations?

7 Development of a Southern- California Background PAH Dataset (cont) Question: could observed site-to-site differences be attributable to certain systematic variables? Central valley versus Los Angeles Basin (meteorological effects?) Rural versus urban areas (related to traffic differences?) Analysis suggests that t observed variability not adequately described by these categorical variables.

8 B( (a)p Equivalents (mg/kg)

9 case B(a)P Equivalents (mg/kg)

10 Consistency with a Common Distribution Quantile Plot of Southern California Background Data, Lognormal Distribution Assumption

11 Summary Statistics: Southern California Background PAH Dataset Descriptive Statistic Value Sample size (n) 185 Mean Median 0.16 mg/kg mg/kg Standard Deviation 0.41 Minimum Maximum mg/kg 4.05 mg/kg 95% UCL 0.24 mg/kg UTL 95% coverage, 95% confidence 0.90 mg/kg 95 th percentile 0.64 mg/kg

12 Use of Southern California Background PAH Dataset Characterizing the need for remediation at PAH-impacted sites Use of point estimates (95% UTL) Use of box plots/graphical plots Distributional comparison tests Evaluating Attainment of Remedial Goal Have successfully closed more than a dozen sites in southern Cal using this background PAH dataset

13 Parallel Northern California Background PAH Study Comparable Study for N California area conducted in 2002 Question: how different would the background PAH levels be??? Could the study support one California background PAH dataset???

14 Development of a Northern California Background PAH Dataset Background PAH data from 21 sites in Northern California (n = 156) Similar il statistical i evaluations conducted d Statistical outlier test: 2 outliers identified and removed Removal of samples from 2 sites with disproportionate number of samples Final background dataset: n = 85

15 Development of a Northern California i Background PAH Dataset (cont) Statistical comparisons Between sites Region (Northern, Central, South) Coastal versus Inland

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19 Consistency with a Common Distribution Probability Plot of Lognormal Fit to Data 86 Samples Probability plot of Lognormal Fit to Data - 86 Samples

20 Summary Statistics: Northern Calif. PAH dataset Descriptive i Statistic i Vl Value Sample size (n) 86 Mean Median 0.21 mg/kg mg/kg Standard Deviation 0.41 Minimum i mg/kg Maximum 2.8 mg/kg 95% UCL 0.40 mg/kg UTL 95% coverage, 95% confidence 1.5 mg/kg 95 th percentile 0.92 mg/kg g

21 Combined Northern and Southern California i Datasets Data lognormal ivalents (mg/kg) Ln B(a)P Equi N. California i S. California i

22 Ln B(a)P Equivalents (mg/ /kg)

23 Summary Statistics: combined Northern and Southern Calif. PAH datasets Descriptive Statistic Northern CA Dataset South CA Dataset Sample size (n) Combined Mean 0.21 mg/kg 0.16 mg/kg mg/kg Median mg/kg mg/kg mg/kg Standard Deviation Minimum mg/kg mg/kg mg/kg Maximum 2.8 mg/kg 4.05 mg/kg 4.05 mg/kg 95% UCL 0.40 mg/kg 0.24 mg/kg 0.25 mg/kg UTL 1.5 mg/kg g 0.90 mg/kg g 0.96 mg/kg g 95% coverage, 95% confidence 95 th percentile 0.92 mg/kg 0.64 mg/kg 0.74 mg/kg

24 Conclusions Background PAH data collected from sites in northern and southern California appear to be representative of one background population. Variability observed between sites appears to be random Can use the background dataset developed for either southern or northern California to provide a statistically robust description of background PAH concentrations. Have been using both datasets to support risk management decisions with oversight/guidance/approval from DTSC Background PAH data collected from sites in northern and southern California are not materially different. Both suggest that a reasonable initial remedial target for cleaning up to background is 0.9 mg/kg (B(a)P)-equivalents.

25 Common Hurdles Encountered during Use of Background studies If site wasn t in either of the background studies, shouldn t be able to use the larger background study. Not clear why applicability of background database should be limited to sites in the study. Bright line application of initial remediation target Series of statistical tests always needed to determine whether concentrations at a site are different from background Philosophical belief that there are/could be regional differences in background PAH concentration Such positions raise interesting environmental justice questions