Data Series 258
U.S. GEOLOGICAL SURVEY
Data Series 258
Field blanks were taken for the VOCs, gasoline additives, pesticides, pesticide degradates, nutrients, dissolved organic carbon, major and minor ions, trace elements, microbial indicators, and iron, arsenic and chromium speciation samples. Universal blank water is not available for the following constituents: isotopic composition of oxygen and hydrogen, carbon-14, tritium, noble gases, or radioactivity; as a result, field blanks were not collected for these constituents.
In the MS study unit, replicates were collected for all constituents in order to check to reproducibility (precision) of analytical results. Matrix spikes were only added to the VOCs, gasoline additives, pesticides, pesticide degradates, and constituents of special interest samples because these samples were analyzed by chromatographic techniques, which are more susceptible to matrix interferences. The microbial indicator samples were spiked to confirm that the collection and handling procedures adequately preserved these samples.
Surrogate compounds also were only added to VOCs and gasoline additives, pesticides, pesticide degradates, and constituents of special interest samples in order to verify the analytical techniques.
In the MS study unit, field blanks were collected at approximately 12 percent of the sites sampled. Table 6 presents a summary of compound detections in field blanks. The VOCs observed in field blanks, with their maximum detected concentration in parentheses, include 1,2,4-trimethylbenzene (0.56 µg/L), 2-butanone (ethyl methyl ketone) (30.8 µg/L), acetone (12 µg/L), carbon disulfide (E0.09 µg/L), chloroform (trichloromethane) (0.10 µg/L), ethylbenzene (E0.03 µg/L), m-xylene plus p-xylene (E0.12 µg/L), o-xylene (E0.05 µg/L), tetrachloroethene (PCE) (E0.03 µg/L), toluene (0.19 µg/L), and trichlorofluoromethane (0.11 µg/L). All of the environmental samples collected prior to and following these field blanks were free from these constituents (except toluene), hence no ground-water sample detections were censored (besides toluene) as a result of these blank detections. As a result of the high detection frequency for toluene in blanks, all four environmental toluene detections were censored, and will not be considered in the statistical results. Toluene concentrations observed in the environmental samples had a maximum concentration of 0.05 µg/L, which is 3,000 times less than the California regulatory MCL of 150 µg/L.
No detections of pesticide compound were detected in the corresponding blank samples.
Four common ions were detected in field blanks, with their maximum concentrations in parentheses: Ca (0.24 mg/L), Mg (E0.007 mg/L), Na (0.70 mg/L), and Si (3.9 mg/L). All of the environmental samples analyzed had detections of Ca, Mg, Na, or Si at concentrations 6 to 90 times greater than these values, hence no ground-water detections were censored. Fourteen trace elements were detected in field blanks, with maximum concentrations in parentheses: Al (45 µg/L), As (0.52 µg/L), Ba (0.20 µg/L), Cr (0.09 µg/L), Co (0.04 µg/L), Cu (3.1 µg/L), Fe (21 µg/L), Pb (0.14 µg/L), Mn (E0.20 µg/L), Ni (0.36 µg/L), Sr (0.58 µg/L), W (0.36 µg/L), V (0.42 µg/L), and Zn (3.70 µg/L) (table 6). As a result of the blank detections, 12 ground-water detections were censored: one aluminum, arsenic, chromium, manganese; three lead; and five copper. Dissolved organic carbon (DOC) was detected in five out of five blanks, with a maximum concentration of 40 mg/L. As a result, six ground-water detections for DOC were censored. Censored values were all below regulatory thresholds.
The majority of replicate sample pairs collected during the MS study had relative standard deviations (RSDs) of less than 20 percent (table 7). Thirteen replicate sample pairs representing 7 chemical constituents, 3 replicate sample pairs of radionuclides, and 2 replicate sample pairs for radioactivity had RSDs greater than 20 percent (table 7). However, many of the replicate sample pairs with high RSDs had measured concentrations near the LRL for these constituents, and at these low concentrations, small deviations in measured values may account for the large RSDs. Because the variability in measurements occurred at low concentrations, close to the method detection levels and well below regulatory thresholds, this variability was not of QC concern, and no detections were censored as a result of variability in replicate sample samples.
Tables 8A and 8B present a summary of matrix spike recoveries for the MS study. Addition of a spike or known concentration of a constituent to an environmental sample enables the analyzing laboratory to determine the effect of the matrix, in this case ground water, on the analytical technique used to measure the constituent. Acceptable spike recovery values range between 70 and 130 percent (Friedman and Erdmann, eds., 1982). Nine environmental samples were spiked with VOCs, and 4 environmental samples were spiked with the 3 constituents of special interest—NDMA, perchlorate, and 1,2,3-TCP—in order to calculate matrix spike recoveries (table 8A). Seventy-two of the 88 VOC spike compounds, plus the 3 constituents of special interest, had recoveries within the acceptable range of 70 and 130 percent. Three VOC spike compounds had at least one matrix spike recovery greater than 130 percent; however, these compounds were not detected in ground-water samples. Dichlorodifluoromethane and styrene were the only VOC spike compounds that had a recovery below 70 percent; however, these compounds were not detected in ground-water samples. [NOTE—low recoveries may indicate that this compound might not have been detected in some samples if it was present at very low concentrations.]
Nine environmental samples were spiked with pesticide or pesticide degradate compounds to calculate matrix-spike recoveries. Acceptable spike recovery values ranged between 70 and 130 percent. Twenty-six of the 64 spike compounds had recoveries between the acceptable range of 70 and 130 percent (table 8B). Zero spike compounds had recoveries greater than 130 percent. Thirty-eight spike compounds had recoveries below 70 percent. Of these 38 spike compounds, none were detected in ground-water samples. [NOTE—low recoveries may indicate that this compound might not have been detected in some samples if it was present at very low concentrations.]
Three microbial indicator samples were spiked with F-specific and somatic coliphage. All three samples tested positive for F-specific coliphage and somatic coliphage.
Surrogate compounds were added to environmental samples in the laboratory and analyzed to evaluate the recovery of similar constituents. Table 9 lists each surrogate; the analytical schedule on which it was applied; the number of analyses for ground-water samples, blank samples, and sample replicates; and the number of surrogate recoveries below 70 percent, between 70 and 130 percent, and above 130 percent for the ground-water samples, blanks, and replicates. Greater than 95 percent of the ground-water samples, blanks, and replicate samples had recoveries of the surrogates between the acceptable limit of 70 and 130 percent (Fishman and Friedman, 1989). No ground-water sample detections were censored as a result of surrogate recovery data.
Results from analyses of raw (untreated) ground water for the MS study unit are presented in tables 10–22. Table 10 includes water-quality indicators measured in the field, while tables 11–22 present the results of ground-water analyses organized by the compound types and classes: VOCs and gasoline additives; pesticides and pesticide degradates; constituents of special interest; nutrients; major and minor ions; trace elements; arsenic and iron; chromium; isotopes and radioactivity; and microbial constituents. The summary tables present only the constituents that were detected, and only samples that had at least one compound detected. In each table, the sites are grouped by study area, and the first column lists the GAMA identification number for each well. The remaining columns list the constituents detected, the USGS parameter code used to identify the compound and store the information in a computerized database [National Water Information System (NWIS)], and units of measurement, the laboratory reporting level (LRL) for which the compound may be detected, and the concentrations at which the constituents were detected.
The tables include the measured concentration of each constituent, the number of wells at which it was detected, the frequency at which it was detected (in relation to the total number of randomized wells sampled), and the total number of constituents detected at each well. Results from the flow-path wells are presented in the tables, but these results were not included in statistical compilations because these wells were not part of the randomized well selection. Detections that have concentrations or activities above the established thresholds, MCL, SMCL, HAL, NL, or DLR, are indicated in the tables by an asterisk in the remarks column before the value.
Analytical results of VOCs and gasoline additives from USGS NWQL schedules 2020 and 4024 are presented in table 11, which reports results from the preferred analytical method where more than one method was used. Ground-water samples for analysis of VOCs and gasoline additives were collected at the 94 public-supply wells and the 3 monitoring wells sampled in the MS study unit. Twenty-eight VOCs and gasoline additives were detected in 39 wells in the MS study unit. Forty percent of the 97 wells sampled had at least one detection of a VOC and gasoline additive, but detected concentrations were one-third to one-sixty-thousandth of their respective regulatory thresholds. Three of the 97 wells sampled were flow-path wells, and 3 were monitoring wells, and these 6 wells were not included in the following calculations of detection frequency.
Twenty-seven of the 88 VOCs analyzed were detected in ground-water samples from randomized wells in the MS study unit. VOCs detected in 10 percent or more of the wells include trichloromethane (chloroform), which was detected in 20 of the 91 randomized wells sampled, and tetrachlorethylene (PCE), which was detected in 9 of the 91 randomized wells sampled. In total, 34 wells (of the 91 randomized wells) had 86 detections, for a VOC detection frequency of 37 percent. None of the VOCs and gasoline additive concentrations measured were greater than their respective thresholds established for regulatory purposes.
Ground-water samples for pesticides and pesticide degradates, using USGS analytical schedules 2003 and 2060, were collected at 97 wells in the MS study unit (table 12). Ten pesticides and pesticide degradates were detected in 28 wells in the total MS study unit; however, detected concentrations were one-thirtieth to one-fourteen-thousandth of their respective regulatory thresholds. Three of the 97 wells sampled were flow-path wells, and 3 were monitoring wells, and these 6 wells were not included in the calculations of detection frequency.
Ten of the 122 pesticides and pesticide degradates investigated were detected in ground-water samples from the 91 randomized wells in the MS study unit. Compounds detected in 10 percent or more of the randomized wells include simazine, an herbicide, which was detected in 16 of the 91 ground-water samples, and deethylatrazine (2-chloro-4-isopropylamino-6-amino-s-triazine), a pesticide degradate, which was detected in 10 of the 91 ground-water samples. In total, 43 detections in 27 randomized wells were observed in the MS study unit. None of the pesticide concentrations measured were greater than threshold concentrations established for regulatory purposes.
Ground-water samples for the constituents of special interest—perchlorate, N-nitrosodimethylamine (NDMA), and 1,2,3-trichloropropane (1,2,3-TCP)—were collected at 34 wells, 31 public-supply wells and 3 monitoring wells (table 13). NDMA was detected in two wells at concentrations above the regulatory threshold of 0.01 µg/L. 1,2,3-TCP was detected in one well above the regulatory threshold of 0.005 µg/L. Perchlorate was not detected in any ground-water samples.
Samples for the analysis of nutrients and dissolved organic carbon (DOC) were collected at 34 wells, 31 public-supply wells and 3 monitoring wells (table 14) sampled only under the slow schedule in the MS study unit. Ammonia was detected in 9 of the 34 samples, at concentrations ranging from 0.04 to 1.60 mg/L (as nitrogen). Nitrate plus nitrite was detected in 24 of the 34 ground-water samples, whereas nitrite was detected in only 3 of the 34 samples. Concentrations of nitrate plus nitrite ranged from (estimated value) E0.04 mg/L to 37.8 mg/L (as nitrogen), with two samples above the regulatory threshold of 10 mg/L (as nitrogen). Nitrite was detected in 3 wells at concentrations that ranged from E0.004 mg/L to 0.008 mg/L— much below the nitrite MCL of 1 mg/L (as nitrogen). Total dissolved nitrogen (nitrate plus nitrite plus ammonia plus organic-N) was measured in 34 wells at concentrations that ranged from 0.09 to 37.5 mg/L (as nitrogen). Dissolved phosphorus (as orthophosphate) was measured in all 34 wells at concentrations that ranged from E0.005 to 0.106 mg/L (as phosphorus). DOC was measured in 34 wells at concentrations that ranged from E0.2 to 4.4 mg/L. Six samples had DOC detections in the preceding blanks greater than the sample values, and hence were censored and these data were not used for summary statistical calculations. Censored values are preceded by a V or VE in table 14.
Samples for the analysis of major and minor ions and dissolved solids (DS) were collected at 31 public-supply wells and 3 monitoring wells (table 15) in the MS study unit. The following results are for the public-supply wells only. Calcium concentrations ranged from 15.4 to 171 mg/L, with a median value of 56 mg/L. Magnesium concentrations ranged from 0.64 to 73.1 mg/L, with a median value of 21 mg/L. Potassium concentrations ranged from 1.46 to 16.9 mg/L, with a median value of 3.05 mg/L. Sodium concentrations ranged from 20.3 to 209 mg/L, with a median value of 65.2 mg/L. Bromide concentrations ranged from 0.04 mg/L to 0.92 mg/L, with a median value of 0.27 mg/L. Chloride concentrations ranged from 11.2 to 241 mg/L, with a median value of 72.5 mg/L. Fluoride concentrations ranged from 0.10 to 0.50 mg/L, with a median value of 0.30 mg/L. Iodide concentrations ranged from E0.001 mg/L to 0.205 mg/L, with a median value of 0.006 mg/L. Silica concentrations ranged from 24.4 to 71.2 mg/L, with a median value of 39.7 mg/L. Sulfate concentrations ranged from 6.8 to 563 mg/L, with a median value of 138 mg/L. Five samples had sulfate concentrations above the recommended SMCL threshold of 250 mg/L, and one sample had sulfate concentrations greater than the upper SMCL of 500 mg/L. TDS concentrations, measured as residue on evaporation at 180°C, ranged between 281 and 1,330 mg/L, with a median value of 467 mg/L. Sixteen samples had TDS concentrations above the recommended SMCL threshold of 500 mg/L, and 4 samples had concentrations greater than the upper SMCL of 1,000 mg/L.
Samples for the analysis of trace elements were collected at 31 public-supply wells and 3 monitoring wells (table 16) in the MS study unit. Censored values were not considered as detections for this study. Aluminum was detected in 10 ground-water samples with concentrations ranging from E0.8 to 20 µg/L; one aluminum detection was censored due to the presence of aluminum in the preceding blank. Antimony was detected in 9 ground-water samples, with concentrations ranging from E0.11 to 0.39 µg/L. Arsenic was detected in 29 ground-water samples, with concentrations ranging from 0.2 to 7.3 µg/L; one arsenic detection was censored due to the presence of arsenic in the preceding blank. Barium was detected in 34 ground-water samples, with concentrations ranging from 4.0 to 191 µg/L. Beryllium was detected in 2 ground-water samples, with concentrations ranging from 0.06 to 1.28 µg/L. Boron was detected in 34 ground-water samples, with concentrations ranging from 30 to 753 µg/L. Cadmium was detected in 23 ground-water samples, with concentrations ranging from E0.02 to 0.37 µg/L. Chromium was detected in 24 ground-water samples, with concentrations ranging from E0.04 to 14.2 µg/L; one chromium detection was censored due to the presence of chromium in the preceding blank. Cobalt was detected in 33 ground-water samples, with concentrations ranging from E0.03 to 1.2 µg/L. Copper was detected in 28 ground-water samples, with concentrations ranging from E0.3 to 5.4 µg/L; five copper detections were censored due to the presence of copper in the preceding blank.
Iron was detected in 23 ground-water samples, with concentrations ranging from E4.0 to 2,830 µg/L; three samples had iron concentrations above the non-health-based SMCL threshold of 300 µg/L. Three iron detections were censored due to the presence of iron in the preceding blank. Lead was detected in 27 ground-water samples, with concentrations ranging from E0.06 to 6.62 µg/L. Lithium was detected in 34 ground-water samples, with concentrations ranging from 3.4 to 110 µg/L. Manganese was detected in 31 ground-water samples, with concentrations ranging from E0.1 to 2,410 µg/L; eight of the samples had concentrations of manganese above the non-health-based SMCL threshold of 50 µg/L. One manganese detection was censored owing to the presence of manganese in the preceding blank. Mercury was detected in 3 of the samples, ranging in concentration from E0.01 to 0.05 µg/L.
Molybdenum was detected in 34 ground-water samples, with concentrations ranging from 0.9 to 42.6 µg/L; one of the public-supply wells had concentrations of molybdenum above the HAL threshold of 40 µg/L. Nickel was detected in 34 ground-water samples, with concentrations ranging from 0.42 to 7.24 µg/L. Selenium was detected in 29 ground-water samples, with concentrations ranging from E0.06 to 17.6 µg/L. Silver was not detected in any ground-water samples. Strontium was detected in 34 ground-water samples, with concentrations ranging from 226 to 1,790 µg/L. Thallium was detected in 3 ground-water samples, with concentrations ranging from E0.02 µg/L to 0.05 µg/L. Tungsten was detected in 4 ground-water samples, with concentrations ranging from 0.15 to 0.90 µg/L. Uranium was detected in 31 ground-water samples, with concentrations ranging from E0.03 to 28.9 µg/L. Vanadium was detected in 31 ground-water samples, with concentrations ranging from E0.1 to 20.5 µg/L. Zinc was detected in 33 ground-water samples, with concentrations ranging from E0.38 to 1,470 µg/L.>
Table 17 presents the results from the USGS NRP Boulder lab for 38 samples collected for total dissolved inorganic arsenic and iron, as well as for the individual species arsenic (III) and iron (II). Total arsenic and iron results agree well with samples from the same wells identified in table 16, which were analyzed at the USGS NWQL in Denver.
Table 18 presents chromium speciation analyses from the USGS NRP Boulder lab for total dissolved chromium and hexavalent chromium (VI) in all 97 ground-water samples. Values ranged from <1.0 to 36.0 µg/L. None of the total chromium concentrations were above the regulatory threshold of 50 µg/L; however, 86 ground-water samples had chromium (VI) values above 1 µg/L, the DLR threshold. Detection limits for the purposes of reporting (DLR) are set by CADHS for the purposes of tracking unregulated chemicals for which monitoring is required.
Gross alpha and beta radioactivity and isotope activities were measured in selected ground-water samples collected for the MS study unit (table 19). Alpha radioactivity (72-hour and 30-day count) and beta radioactivity (72-hour and 30-day count) samples for analysis were collected at 34 wells; samples for radium-226, radium-228, and radon-222 were collected at 31 wells; and samples for carbon isotope samples were collected at 33 wells. Alpha radioactivity in the 34 samples (table 19) ranged from below quantification limits to 17.4 picocuries per liter (pCi/L) for 72-hour counts, and from below quantification limits to 16.3 pCi/L for 30-day counts. One alpha radioactivity sample exceeded the MCL threshold of 15 pCi/L for both the 72-hour and 30-day counts with values of 17.4 and 16.3, respectively. Beta radioactivity in the 34 samples ranged from below quantification limits to 21.2 pCi/L for 72-hour counts, and from below quantification limits to 21.4 pCi/L in 30-day counts. Radium-226 was detected in 30 out of the 31 samples, with a maximum concentration of 0.58 pCi/L. Radium-228 was detected in 15 out of 31 samples, with a maximum concentration of 0.96 pCi/L. Radon-222 was detected in all 31 samples collected, and had activities ranging from 170 to 1,610 pCi/L. Twenty-three samples for radon-222 activities were above the proposed MCL of 300 pCi/L. Ground-water samples for carbon-14, as percent modern carbon (pmc), and delta carbon-13, as per mil, were collected at 33 wells, and results ranged from 5.68 to 100.1 pmc, and from -20.4 to -10.5 per mil, respectively. The isotopic composition of carbon is reported, in delta notation, as per mil (parts per thousand).
Ground-water samples for the isotopic composition of oxygen and hydrogen, analyzed at the USGS Stable Isotope Laboratory, were collected at all 97 wells (table 20). Tritium was detected in 61 out of 97 samples, with activities that ranged from less than 1 to 14 pCi/L.
Tritium and noble gas samples, analyzed at the LLNL, were collected at 97 wells (table 21). Tritium activities, measured by the helium in-growth method, ranged from below 1 to 17 pCi/L. Noble gas concentrations and the helium isotope ratios (helium-3/helium-4) measured in each sample are presented in table 21.
Ground-water samples from 30 wells in the MS study unit were analyzed for microbial constituents (table 22). The following microbial constituents were determined: total coliform bacteria and Escherichia coliform, and the viruses F-specific coliphage and somatic coliphage. Coliform bacteria was detected in four wells. Counts ranged from an estimated 1 colony/100 mL to 110 colonies/100 mL. MCLs for microbial constituents are based on recurring detection, and counts will be monitored during future sampling.
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