Connecticut Department of Energy and Environmental Protection and Environmental Professionals Organization of Connecticut, Inc.

Transcription

1 Connecticut Department of Energy and Environmental Protection and Environmental Professionals Organization of Connecticut, Inc. 95% UCL Guidance Guidance workgroup formed out of the Remediation Roundtable Workgroup comprised of environmental professionals and DEEP staff Purpose was to develop guidance that incorporates the specific requirements of the RSRs Page 1

2 95% UCL Guidance remediation_regulations/95ucl_guidance.pdf Agenda 95% UCL Applicability 95% UCL Data Sets 95% UCL and Documentation Will have a Q&A opportunity after each of these sections Please hold questions until then Page 2

3 Applicability Why would you want to calculate a 95% UCL? When can you use a 95% UCL? Which criteria? What restrictions or concerns? Page 3

4 Definition Added to the RSRs in the June 27, 2013 amendment: a value that, when repeatedly calculated for randomly drawn subsets of size n from a population, equals or exceeds the population arithmetic mean ninety-five percent of the time 22a-133k-1(a)(40) Definition (cont d) So, what does that mean? Allows the use of statistics to estimate a conservative average concentration of an unknown population Allows the environmental professional some flexibility in evaluating the risk posed by the release Allowed for most criteria Page 4

5 Potential Scenarios Drum Storage Area Surface Release of Cutting Oils Potential Scenarios UST Excavation (Heating Oil) that is limited by nearby structures Page 5

6 Potential Scenarios Urban Fill Areas When can you use a 95% UCL? Direct Exposure Criteria (DEC) Pollutant Mobility Criteria (PMC) Groundwater Protection Criteria (GWPC) Surface Water Protection Criteria (SWPC) Cannot be used for: Volatilization Criteria (VolC) Page 6

7 Direct Exposure Criteria Provides the option to demonstrate compliance with the applicable DEC if the 95% UCL of all soil sample results from the subject release area is equal to or less than the applicable DEC 22a-133k-2(e)(1) Direct Exposure Criteria Restrictions Implemented by Release Area Only those soil sample results from locations and depths where the DEC apply should be used to calculate the 95% UCL for DEC compliance (Be sure to account for any institutional controls implemented) Page 7

8 Direct Exposure Criteria Release Area Sample Selection for DEC 95% UCL Calculation When Applying the Inaccessible Soil Exception Pollutant Mobility Criteria Provides the option to demonstrate compliance with PMC if the 95% UCL of at least 20 samples collected from the subject release area and above the water table is equal to or less than the applicable PMC 22a-133k-2(e)(2)(A) Page 8

9 Pollutant Mobility Criteria Restrictions Implemented by Release Area Minimum of 20 samples Only those soil sample results from locations and depths where the PMC apply should be used to calculate the 95% UCL for PMC compliance (Be sure to account for any institutional controls implemented) Pollutant Mobility Criteria Release Area Sample Selection for PMC 95% UCL Calculation When Applying the Environmentally Isolated Soil Exception Page 9

10 Groundwater Protection Criteria Provides the option to demonstrate compliance with the GWPC if the 95% UCL of at least twelve consecutive monthly sampling events from each well location within the subject groundwater plume is equal to or less than the GWPC 22a-133k-3(g)(2)(B) Groundwater Protection Criteria Restrictions Implemented by individual well (not averaged over the plume) Requires at least 12 consecutive monthly samples (no variance) All sampling events must be performed within two years prior to the most current sampling event (limited to 24 monthly samples) Page 10

11 Property Boundary GW Plume ND ND GWPC 95% UCL calculations must be performed individually for each well in the plume. In this example, there would be a separate 95% UCL calculation for each of the 5 wells in the plume (minimum of 12 monthly samples each). Not to Scale ND ND Surface Water Criteria Provides the option to demonstrate compliance with the SWPC if the 95% UCL of all sample results representative of the groundwater plume is equal to or less than the SWPC 22a-133k-3(g)(2)(C) Page 11

12 Surface Water Criteria Restrictions Requires minimum of 4 quarterly sampling events representing seasonal variability Sampling events must include all representative wells (cannot selectively pick wells each round) Surface Water Criteria Restrictions (cont d) All sampling events must be performed within two years prior to the most current sampling event Implemented by incorporating all of the concentrations within plume (not based on individual wells) Page 12

13 Property Boundary GW Plume ND ND SWPC 95% UCL calculation is performed using all wells within the plume. ND In this example, there would be a single 95% UCL calculation for the plume (minimum of 4 quarterly samples from each 5 wells results in a minimum of 20 samples). ND Not to Scale Volatilization Criteria Historically, compliance with the VolC could be demonstrated with a 95% UCL Calculation. No longer an option: Not Protective Temporal Concerns (did not account for accumulating vapors) No Institutional Controls Page 13

14 95% UCL Applicability Summary Use of the 95% UCL provides some flexibility in some scenarios Available option for many criteria DEC PMC GWPC SWPC Not an option for VolC Page 14

15 What Goes Into a Data Set? What samples are appropriate to use How to handle NDs Excavation/hot spot removal Data Set DQOs Data Set evaluation Number of samples Page 15

16 Garbage In/Garbage Out Applicability The RSRs regulate by substance and by release area/plume: Compliance is demonstrated for each substance and each release area/plume individually Therefore each release area/plume must be delineated before a 95% UCL calculation can be used as a compliance option Page 16

17 Release Area "Release" means any discharge, spillage, uncontrolled loss, seepage, filtration, leakage, injection, escape, dumping, pumping, pouring, emitting, emptying, or disposal of a substance "Release area" means the land area at and beneath which polluted soil is located as a result of a release 22a-133k-1(a)(55)&(56) Release Area (cont d) "Polluted soil" means soil affected by a release of a substance at a concentration above the analytical detection limit for such substance Therefore, the Release Area is where there are detections of substances and NDs samples are usually outside of the Release Area (NDs delineate) 22a-133k-1(a)(50) Page 17

18 Groundwater Plume "Groundwater plume" means ground water which has been polluted by a release and in which ground water one or more substances from such release is present at a concentration above the analytical detection limit Therefore, the Groundwater Plume is also where there are detections of the subject substance and NDs wells are usually outside of the Plume (again, NDs delineate) 22a-133k-1(a)(28) Release Area/Plume ND Release Area 100mg/kg 10mg/kg GW Monitoring Well Soil Sample ND 10mg/kg 25mg/kg 500 ppb 5mg/kg ND ND UST 5mg/kg 30 ppb 15 ppb ND Groundwater Plume 5 ppb Not to Scale ND Page 18

19 GW flow direction Not to Scale Former UST Soil Sample depths need to be considered when determining whether to include the sample in the 95% UCL Data Set. In this examples, several of the samples are within the areal extent of the Release Area, but are not in the Release Area due to the depth that they were collected. UST GW flow direction Not to Scale Groundwater samples need to be collected from wells screened at appropriate depths to be included in the 95% UCL Data Set (not just wells within the areal extent of the plume) Page 19

20 Metals Release Area / Plume Metals often have a naturally occurring concentration in soil and groundwater This background concentration should be used to delineate the metals Release Area/Plume rather than NDs Therefore, when dealing with metals, not all detections can be assumed to be in the Release Area/Plume NDs in the Data Set When are NDs appropriate to include in a 95% UCL Data Set? Need to be within Release Area/Plume Other Lines of Evidence: Presence of other substances associated with the subject release Understanding of substance fate and transport Supported by CSM Page 20

21 Excavation Release Area should be characterized fully if excavation is performed and a 95% UCL Calculation is used on remaining material If the 95% UCL data set is composed solely of sidewall samples, material might be left behind that poses a risk to human health & the environment (HH&E) Excavation (cont d) Confirmation Sampling: Confirmation Samples can be used in the 95% UCL Data Set as long as they are still from within the Release Area Confirmation Samples collected from outside the Release Area cannot be included in the 95% UCL Data Set An evaluation should be performed as to whether the Confirmation Samples have potential to skew the 95% UCL Data Set Page 21

22 Excavation (cont d) Materials excavated are no longer in the Release Area Data from excavated material cannot be included in the 95% UCL Data Set Data collected from imported backfill material cannot be included in the 95% UCL Data Set The 95% UCL Data Set needs to be representative of remaining material Sampling Plan for Data Set Important to understand that the DQOs for the 95% UCL Data Set are likely different than the characterization DQOs Following characterization, additional data will most likely need to be collected to support use of a 95% UCL Calculation Page 22

23 Evaluation of Data Set Need to assess the potential for the delineation data to skew the Data Set Additional data may need to be collected to fill in any data gaps and to balance the data set Attempt to remove bias Attempt to introduce randomness Release Area Plan View A Aʹ A Aʹ Section View Release Area Soil samples within Release Area, usable for 95% UCL calculation Soil samples outside Release Area, not usable for 95% UCL calculation Page 23

24 Release Area A Plan View Aʹ A Aʹ Section View Release Area Soil samples within Release Area, usable for 95% UCL calculation Soil samples outside Release Area, not usable for 95% UCL calculation Evaluation of Data Set (cont d) Additional data does not serve to delineate the release: It serves to quantify (characterize) the inground concentration distribution so it can be properly assessed using a 95% UCL Calculation It also serves to better emulate what is in the ground; increasing the likelihood that the 95% UCL provides a good estimate Page 24

25 Example Data Distributions Data distribution Environmental data is commonly Lognormal Normal vs. Lognormal data distribution 95% UCL 95% UCL Number of Samples The greater the number of samples collected, the more confidence that the 95% UCL will not underestimate the true mean of the data set (and the closer the 95% UCL will be to the true mean) More data is better Page 25

26 Number of Samples (cont d) EPA Guidance (1992) <10 samples per area of concern provide poor estimates of mean samples per area of concern provide somewhat better estimates of the mean 20+ samples per area of concern provide fairly consistent estimates of mean Number of Samples (cont d) Guidance Document recommends at least 10 samples before considering using a 95% UCL Calculation Minimum value required for statistical method should not be seen as the target needed to emulate the in-ground distribution of contaminants Should consider the strength of the data set number of samples, standard deviation (SD), number of NDs, skewness, randomness, etc. Page 26

27 Data Set Summary The decision made based upon a 95% UCL result is only as good as the data set represents the conditions in the ground Samples that delineate the Release Area / Plume are not to be included in the 95% UCL Data Set 95% UCL Data Sets need to be developed for individual Release Areas/Plumes Data Set Summary (cont d) Important to consider the representativeness of the data set does the sampled distribution match the distribution in the ground? Assessment should be made to determine if the sampling program had the potential to be biased and skew the sampled data set A well-developed Conceptual Site Model (CSM) should be in place before calculating the 95% UCL release area conditions should be well known Page 27

28 Revisiting Potential Scenarios Drum Storage Area Surface Release of Cutting Oils Revisiting Potential Scenarios UST Excavation (Heating Oil) that is limited by nearby structures Page 28

29 Revisiting Potential Scenarios Urban Fill Areas (DEC Compliance Using RSR exemption for PMC) Page 29

30 Calculating the 95% UCL Guidance documents for calculating the 95% UCL Guidance for Calculating the 95% Upper Confidence Level for Demonstrating Compliance with the Remediation Standard Regulations _0622_concentrationterm.pdf - Supplemental Guidance to RAGS: Calculating the Concentration Term Page 30

31 Calculating the 95% UCL (cont d) Recommend the use of EPA or other software to calculate the UCL - ProUCL (current version 5.0) Option exists to use other software as desired, however should be able to appropriately handle: Different data distributions (ProUCL tests for Normal, Lognormal, and Gamma Distributions) Non-Detects Calculating the 95% UCL (cont d) Use different 95% UCL calculation methods for different distributions: Normal, Lognormal, and Gamma distributions have different calculation methods Non-parametric (no known distribution) methods available for data sets that don t exhibit a particular distribution Less assumptions are made in the calculation method Often will lead to higher results than a method for a known distribution Page 31

32 95% UCL Handling NDs Use proper estimation method given the distribution of the data set Normal, Lognormal, and Gamma Distributions Regression on Order Statistics (ROS Methods) Non-parametric Distributions Kaplan-Meier (KM Method) ½ Detection Limit no longer recommended ProUCL Output Recommended Results All recommended results are valid to use Sometimes ProUCL will recommend multiple calculation methods From the Guidance Document - In these cases, the environmental professional should evaluate the data set and select the most appropriate 95% UCL Page 32

33 ProUCL Output (cont d) Some items to consider when evaluating the most appropriate 95% UCL result: Distribution of data set Sample locations Distribution of concentrations throughout the Release Area Comparison of recommended 95% UCL estimates to criteria Number of samples collected ProUCL Output (cont d) Example Output - Benzo(a)pyrene Criteria is 1000 µg/kg Two results are below criteria One result is above criteria Page 33

34 95% UCL Documentation Recommended documentation to include in the Verification Report: Discussion CSM for release area release mechanism, contaminant fate & transport, and how the use of the 95% UCL is protective of HH&E If NDs are used in data set, should include the rationale for the inclusion of the NDs 95% UCL Documentation (cont d) Discussion (cont d) Evaluation of the overall data set If multiple 95% UCL methods are recommended by ProUCL, should include an evaluation of the appropriateness of the method used Table All sample results used in the data set Depths at which the samples were collected Other potentially useful information Page 34

35 95% UCL Documentation (cont d) Map Illustrate all sample locations Document the 3D limits of the subject Release Area Show locations (also in 3D) of other Release Areas at the site Include the limits of excavation, if applicable Include any other information that may help the reader Method/Documentation Summary Guidance Document ProUCL recommended Properly handle NDs Assess appropriateness of multiple recommended methods Documentation Provide discussion of rationale don t leave it up to the reader to infer rationale Page 35

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