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Analyte n Percentile in mg]L Detection Median Method Number Number 50th I 95th 99th Detection Limit Wells AF Bases umnum 1548 0.16 1 567- 0.07 508 11 Antimony 1285 ND 0.15 0.2 9% 0.026 556 11 Arsenic 1278 ND 0.05 0.15 30% 0.005 498 12 Barium 1619 0.1 0.63 2.1 95% 0.006 482 12 Beryllium 1303 D 0.01 0.01 9% 0.002 570 11 k 212 0.07 2.5 86% 0.03 106 5 1359 NO 0.01 12% 0.004 592 12 1099 120 747 2370 99% 0.500 171 10 1729 0.01 0.62 5 47% 0.005 578 12 134 ND 0.03 0.06 12% 0.010 1211 ND 0.03 0.12 19% 0.011 521 11 1438 ND 0.07 0.24 27% 0.012 558 12 Cyanide 229 NO ND N 3% 0.01 157 7 Fluoride 606 0.34 1.1 1.89 90% 0.10 335 9 Iron 1762 0.45 48.6 252 80% 0.02 559 11 Lead 1737 ND 0.1 0.4 24% 0.004 653 12 Magnesium 11712 24 102 197 99% 0.036 557 12 Manganese 0.06 2 7.35 86% 0.003 544 11 Mercury ND NO 0.01 9% 0.0002 468 12 Molybdenum 0.01 0.1 0.11 32% 0.006 487 10 Nickel NO 0.43 1.13 44% 0.022 551 12 Selenium NO 0.03 0.1 13% 0.005 506 12 Siker NO 0.02 0.03 3% 0.006 588 12 Sodium 82 406 1080 99% 0.24 562 12 Thallium 12571 ND 1 0.2 0.5 4% 0.10 526 11 Vanadium 15201 0.021 0.12 0.44 77% 0.007 482 11 ncVul GROUND WATER BACKGROUND BASED ON CALIFORNIA AIR FORCE BASES BACKGROUND LEVELS FOR SOIL The analysis for California soils is based on approximately 8500 distinct borcholes,sampled for both inorganic and organic chemicals, and over 133,000 analytical records. The number of background borcholes analyzed varied from 105(boron)to 2777(lead);sample sizes varied from 271(fluoride)to 7429(lead);number of AFBs varied from (chloride)to I I(iron and lead). Background levels for soil are biased,with about 50%of the data from Vandenberg,March and Beale AFBs. Detection rates in soil generally exceed those in ground water. This is expected,given the poor solubility of most inorganic chemicals in water. Detection rates in soil vary,with aluminum, barium, iron, magnesium, manganese and vanadium detected in 99% of samples, while antimony, cyanide, mercury, selenium,silver, and thallium had detection frequencies of less than 10%. Antimony, cadmium, chromium-6, cyanide, mercury, molybdenum, selenium, silver, and thallium had median concentrations below MDLs. Except for molybdenum, these same constituents had median concentrations below MDLs for ground water. None of the 95'h percentiles for soil fell below MDLs,unlike ground water. Infrequently,background concentrations(arsenic,beryllium,iron)exceed important environmental thresholds(using residential criteria)such as U.S. EPA Region IX's Preliminary Remediation Goals(PRGs). Chromium-6 was detected at about the same frequency in soil and ground water,though the soil sample size was far greater. SOIL BACKGROUND LEVELS BASED ON CALIFORNIA AIR FORCE BASES Analyte n Pereentlle k Detection Median Method Number Number 50th 95th 991h Detection Limit Boreholes AF Bases Alu,-m 5032 7980 23000 31300 99% 11.0 2009 10 Antimony 6422 ND 12.5 23 9% 6.5 2453 10 Arsenic 6128 2.1 11.1 22.5 60% 0.6 2196 10 Barium 5713 80 357 610 99% 1.0 2148 10 Beryllium 6097 0.3 1.1 10.300001 53% 0.2 2283 9 Boron 327 31 140 190 91% 3.1 105 3 Cadmium 6664 ND 2.2 5.6 20% 0.5 2616 10 Chloride 436 8.91 480.0 1600 92% 0.2 206 2 Chromium 7318 11 50.5 99.3 94% 1.0 2721 10 Chrorniumf6 1770 ND 2.5 7.5 12% 0.2 525 8 Cobalt 5188 6.1 22.9 36.9 87% 1.0 1991 10 Copper 6775 10 56.7 153 95% 2.0 2563 10 Cyanide 1005 ND 0.6 1.3999997 2% 0.5 441 7 Fluoride 271 1.1 8.9 25 81% 0.5 109 3 Iron 5599 13100 37000 52000 99% 5.5 2120 11 Lead 7429 2.91 31.1 153 65% 1.8 2777 11 Magnesium 5182 3490 9870 16900 99 20.0 2008 10 Manganese 5530 234 880 1700 9950 1.0 2096 10 Mercury 5167 NO 0.2 0.3 9% 0.1 1788 10 Molybdenum 4918 NO 20 26 15% 2.1 1876 10 Nickel 6628 6.5 39.3 69 66% 4.0 2507 10 Selenium 5972 ND 11.5 26 6% 0.6 2129 10 Siker 6770 NO 2.2 6.2 8% 1.0 2595 10 Sodium 42571 2281 1720 4220 84% 85.0 1730 10 allium6259 ND 25 176 8% 5.5 2415 10 Vanadium 5508 29.7 93 128 99% 1.0 2105 10 Zinc 7125 34 117 356 98% 0 2708 10