1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

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SECTION 3: ANALYSIS easily identify the curve break point. In the latter case, the < 0.22 mg/Kg dw value represents the 86th percentile level. Both cumulative percent plots are provided for comparison (see Figures 3-6a and 3-6b). A slightly lower background level (< 0.19 mg/Kg dw) was estimated from the surface sediment data set (97th percentile value). Because there were only 2 samples out of 264 samples that were actually detects in the subsurface sample group, the background level was not assessed for this limited data set. The all sample data set had a large number of nondetect values with 539 samples out of the total 581 samples that were flagged as nondetects. The cumulative percent plot for silver (Appendix E, Figures E-34a) shows a stepped curve. The cumulative percent plots for the all sediment group with only the detected values (Figure E-34b) shows a relatively smooth curve to the break point, where the curve becomes discontinuous and rises more steeply. The break point on the cumulative percent plot for the surface sediments (Figure E-35) was found to occur at the end of the first continuous string of actual detected values, where the curve starts to rise more steeply. Due to the large number of nondetect values in the subsurface sediments, a break point was not assessed (Figure E-36). Thallium The background level for thallium in Bolsa Chica sediments is estimated to be < 0.61 mg/Kg dw. This value represents the 81st percentile value for the all sample group and the 99th percentile when the nondetect values are removed from the data set. Slightly lower values were estimated from the surface (< 0.52 mg/Kg dw) and subsurface (< 0.44 mg/Kg dw) sediment data sets. This data set had an elevated number of nondetect values with 159 samples out of the total 581 samples that were flagged as nondetects. All three cumulative percent plots for thallium rise in a relatively smooth line to the break points, where the curves begin to rise more sharply (Appendix E, Figures E-37 through E-39). Vanadium The background levels for vanadium in Bolsa Chica sediments are estimated to be < 75 mg/Kg dw. This value represents the 91st percentile value for the all sample data set. A slightly lower value (< 72 mg/Kg dw) was estimated from the surface sediment sample group that represents the 84th percentile value. A lower level (< 60 mg/Kg dw) was estimated from the subsurface sample group that represents the 93rd percentile value. All three cumulative percent plots for vanadium rise in a relatively smooth line to the break points, where the curves begin to rise more steeply (Appendix E, Figures E-40 through E-42). Zinc The background level for zinc in Bolsa Chica Lowland sediments is estimated to be < 103 mg/Kg dw. This value represents the 91st percentile value for the all sample data set. Lower levels were estimated from the surface (< 92 mg/Kg dw) and the subsurface sample group (< 89.7 mg/Kg dw) that represent the 81st and 97th percentile values, respectively. All three cumulative percent plots for zinc rise in a relatively smooth line to the break points, where the curves become less continuous and begin to rise more steeply (Appendix E, Figures E-43 through E-45). SAC/143368(003.DOC) 3-17 ERA REPORT 7/31/02
SECTION 3: ANALYSIS 3.1.4 Exposure Analysis The exposure analysis establishes a relationship between stressors at the site (e.g., concentrations of COPECs) and the potential ecological receptors. Information used to establish this link includes site information on sources of stressors, and the spatial distribution of COPECs across the site, estimates of exposure point concentrations, and calculations of reasonable maximum daily dosages from chemical accumulation in the food chain for terrestrial and semi-aquatic birds and terrestrial mammals. 3.1.4.1 Potential Sources and Spatial Distribution of Chemical Stressors The sources of chemical stressors in the Bolsa Chica Lowlands were described in Section 2.1.3, and Section 2.1.4, and will only be summarized here. The Bolsa Chica Lowlands consist of approximately 1,211 acres of terrestrial, wetland, and marine/estuarine habitats. The watersheds that drain into the site are extensive and highly urbanized. Historic use of the site and surrounding areas has included livestock grazing, crop farming, oil and gas production, and recreational. The primary use of the site since the 1940s has been for oil and gas exploration, production, and processing. Potential sources of COPECs include agricultural activities, hunting using lead shot, oil and gas production, and nonpoint source pollution. Farming activities and agricultural runoff could contain metals, fertilizers, and pesticides. Numerous activities associated with oil and gas production result in releases of metals, PAHs, and PCBs; stormwater/urban drainage could contain various chemicals, including metals, pesticides, herbicides, and PAHs. The Bolsa Chica Lowlands have little surface topography other than a network of roads and levees that divide the site into approximately 60 Cells. Groups of these Cells, based on habitat and planned restoration, were considered evaluation areas for estimating potential risks to less mobile ecological receptors during the Risk Characterization. The GIS database was queried, based on randomly located samples, to determine which Cells had sample analytical values that exceeded preliminary screening values. These queries were completed for five different chemical groups including metals, petroleum hydrocarbons, chlorinated pesticides, PCBs, and phthalates. The preliminary screening level was based on conservative effect measures including the LC 20 or the ER-L. In addition, metals were also screened against the estimated background levels. A secondary screening was also conducted that used a less conservative effect measure (LC 50 or ER-M). The results of the screening are presented graphically in Figures 3-7 through 3-16. The GIS database queries showed that random samples from seven Cells did not exceed any screening level for any analyte. These Cells are the same on each of the Figures 3-7 through 3-16 and include Cell 5, Cell 8, Cell 14, Cell 16, Cell 17, Cell 18, and Cell 59. Random samples from several of those Cells were taken in the depth interval of 0 to 2 feet below expected dredge depth. The figures also show that there were no random samples from Cell 23 and Cell 24 (comprising the location of the former waste handling facility) since this entire area was considered only for focused sampling. The results of the preliminary screening generally indicated a large number of Cells where at least one screening level was exceeded for metals, petroleum hydrocarbons, chlorinated pesticides, and phthalates. Exceedances of PCBs were far less widespread based on ERA REPORT 3-18 SAC/143368(003.DOC) 7/31/02
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REVISED FINAL VOLUME I Ecological R
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CONTENTS 3. Analysis...............
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CONTENTS 3-21 Summary of EC 50 s an
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Executive Summary The Bolsa Chica L
Page 9 and 10: EXECUTIVE SUMMARY The ERA report ev
Page 11 and 12: EXECUTIVE SUMMARY “focused sampli
Page 13 and 14: EXECUTIVE SUMMARY Exposure point co
Page 15 and 16: EXECUTIVE SUMMARY sample. However,
Page 17 and 18: EXECUTIVE SUMMARY The chemicals in
Page 19 and 20: SECTION 1: INTRODUCTION • Sedimen
Page 21 and 22: SECTION 1: INTRODUCTION Assessment
Page 23 and 24: SECTION 1: INTRODUCTION Based on th
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Page 41 and 42: SECTION 2:PROBLEM FORMULATION Benth
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CHAPTER 5: SUMMARY, CONCLUSIONS, AN
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SECTION 6 References Abbasi, S. A.
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SECTION 6: REFERENCES Dunteman, G.
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SECTION 6: REFERENCES Kauss, P. B.
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SECTION 6: REFERENCES RareFind. 199
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SECTION 6: REFERENCES U.S. EPA. 199
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SECTION 6: REFERENCES Wentsel, R. S
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