The water wells in the immediate vicinity of the WIPP site provide water primarily for livestock, industrial usage by oil and gas production operations and monitoring studies conducted by various groups. In July 1999, water samples were collected for CEMRC environmental monitoring studies from six sources in the region of the WIPP (Table 19).

Aquifers in the region surrounding the WIPP include Dewey Lake, Culebra-Magenta, Ogalalla, Dockum, Pecos River alluvium and Capitan Reef. The main Carlsbad water supply is the Sheep Draw well field whose primary source is the Capitan Reef aquifer. The Hobbs and WIPP-Double Eagle water supplies are drawn from the Ogalalla aquifer, while the Loving/Malaga and Otis supply wells draw from deposits that are hydraulically linked to the flow of the Pecos River. The source for the sampling site designated as Private Well #2 is a well seven miles southwest of the WIPP; this water is drawn from the Culebra aquifer.

The 1999 water samples were collected after WIPP started receiving radioactive waste. As of the date of this report, WIPP had not received any mixed waste. Therefore, this summary begins the CEMRC monitoring phase for radionuclides in drinking water but continues the baseline phase for non-radiological constituents. The baseline evaluation began in 1997, and results were reported in the CEMRC 1997 and 1998 reports. As in all of the other WIPP EM studies, the priorities of this work were to (1) continue establishing baseline concentrations for non-radiological constituents of environmental concern as a result of operations at the WIPP facility, (2) begin routine monitoring for radionuclides of concern, (3) continue providing data useful for exposure modeling and (4) refine analytical techniques to improve data quality.

In 1997, drinking water samples were collected for radioanalytical and related studies from the sources described above (the 1997 sample from the Double Eagle well field was collected at a private tap). In 1998, a 200-L sample for radiological analyses and a 9-L sample for non-radiological analyses were collected from each of the six sites sampled in 1999.

Actinide analyses on ~100-L drinking water samples were conducted by CEMRC in 1997 using chemical separation and alpha spectroscopy methods. The results indicated that ^239,240Pu and ²⁴¹Am were not present at levels greater than the MDCs of 5.3 µBq L^-1 and 8.8 µBq L^-1, respectively. Even though Pu and Am would present no significant health hazard at levels less than these MDCs, it was desirable to quantify the levels in order to provide better identification of any changes after the WIPP began receiving waste. For these ultra-low level studies, the 200-L samples collected in 1998 and four additional 200-L samples collected in 1999 were sent to Los Alamos National Laboratory for thermal ionization mass spectrometry (TIMS) analyses for ²³⁹Pu. Three liters of each 1998 drinking water sample were also saved in Marinelli beakers for additional radionuclide analyses by CEMRC.

The NMSU SWAT laboratory analyzed drinking water samples collected in 1997 and 1998 for non-radiological constituents. CEMRC also analyzed 1998 samples and the results indicated a good agreement between the two laboratories. Drinking water from the Carlsbad region has a high mineral content, but the overwhelming majority of inorganic analytes were at concentrations well below Safe Drinking Water Act (SDWA) reference levels. Some metals of concern, due to their expected occurrence in WIPP mixed waste, (notably Be, Hg and Ag) were not detected by SWAT in the 1997 nor the 1998 samples. These elements, however, were detected in a few of the 1998 samples analyzed by CEMRC using a newly acquired ICP-MS. Five other metals, (Sr, Bi, Co, Mn, Mo and V) were also quantified by CEMRC in 1998 samples, but they were not detected by SWAT. SWAT detected organic analytes in a few of the 1998 samples, (dibromochloromethane and bromoform) but at levels below SDWA limits.

In summary, the CEMRC analyses of drinking water samples collected in 1998 were consistent with the results of the previous year's analyses based on SWAT data. Few organic contaminants were detected and those inorganic substances that were quantified were, with a few exceptions, below SDWA reference levels. With the exception of Se analyses and variations possibly associated with sample preservation, the CEMRC data appear to be comparable with results from the SWAT laboratory.

All 1999 samples were collected according to EPA protocols for the collection, handling and preservation of drinking water as follows: (1) 4 L for radiological analyses, (2) 1 L for metals analyses and (3) 1 L for anion tests. None of the samples were filtered before analysis, but a portion of the 4-L sample was transferred to a 3-L Marinelli beaker for gamma spectroscopy analyses. The 1999 samples were collected at the same six locations as the 1998 samples.

CEMRC performed the non-radiological analyses using IC, ICP-MS and AAS. Instrumentation, general methods and quality assurance (QA) work are presented in Appendix K. CEMRC did not test the 1999 drinking water samples for organic constituents because of low and consistent results in prior studies.

Radiological analyses were carried out at CEMRC by first counting the samples in Marinelli beakers using a coaxial, HPGe detector system to determine gamma-emitting radionuclide concentrations. The water was then transferred to the radiochemistry laboratory where actinides were separated and purified using multiple precipitation, co-precipitation and ion-exchange and/or extraction chromatography. Once the actinides were separated elementally, they were co-precipitated with La and deposited onto filters, which were then counted on an alpha spectroscopy system. Radioanalytical QA/QC data are presented in Appendix L.

TIMS analyses were applied to 200-L samples of water from each source that were collected separately from samples analyzed at CEMRC. TIMS analyses also used multiple precipitation, co-precipitation and ion-exchange and/or extraction chromatography techniques, but the purified Pu was co-plated with Pt onto a Re thermal ionization mass spectrometry filament. A thin layer of Pt was deposited over the Pu-Re layer to form a surface ionization diffusion controlled source for mass spectrometric analyses.

No radionuclides were measured above MDC in 1998 or 1999 samples as measured by gamma spectroscopy targeting 11 naturally occuring and 12 anthropogenic gamma-emitters. This was expected due to the small sample size used for this screening effort. Naturally occurring actinides were detected in all of the samples from each location in each of the two years. The greatest concentrations of ²³⁸U, ²³⁵U, ²³⁴U and ²²⁸Th were detected in Private Well #2. The sum of measured actinide concentrations for the 1999 sample from this well was 743 mBq L^-1. It was followed by Otis (207  mBq L^-1), Hobbs (128  mBq L^-1), Loving (113  mBq L^-1), Double Eagle (87  mBq L^-1) and Carlsbad (42  mBq L^-1).

The uranium isotope concentrations in 1999 water samples were quite similar (± 16%) to the 1998 samples. ²³⁴U concentrations were 2.6-3.2 times greater than ²³⁸U concentrations as was expected. Progeny radionuclides, (²³⁴Th, ^234mPa, ²³⁴U and ²³⁰Th) are believed to recoil into the water from the alpha decay of the parent, ²³⁸U. There they may be suspended or dissolved and transported with the water within the aquifer. ²²⁸Th (a progeny of ²³²Th, which was not detected) varied considerably between the two years, especially at Otis (350% higher in the 1999 sample). Th is somewhat less soluble in water than U and thus may be less susceptible to transport. This helps to explain why U concentrations were always greater than Th concentrations, most of which were not detected even though the parent isotopes (²³⁸U and ²³²Th) are expected to be in equal radiological abundance (Taylor, S. R. and S. M. McLennan, 1995, Rev. of Geophys 33,241).

Pu was not detected in 1999 or 1998 drinking water samples processed by actinide separation chemistry and alpha spectroscopy. A few individual results initially indicated that ²³⁹Pu might be present, but these results were determined to be due to laboratory artifacts, and no Pu was observed in a second set of samples. Again, TIMS analyses on drinking water samples did not indicate ²³⁹Pu was present above the maximum MDC of ~3 µBq L^-1 (Table 19) which is approximately ten times lower than minimum MDCs of CEMRC analyses using 3-L samples. One may summarize, therefore, that Pu has still not been detected in drinking water from the local area. Finally, the radioanalytical results for U agreed quite favorably with the results obtained by ICP-MS collected in both 1998 and 1999. In contrast, the Th results were quite variable, possibly as a result of differences in solubility of U and Th.

To evaluate trends in concentrations ver time, the concentration data for drinking water samples collected in 1998 and 1999 were compared. The concentrations of almost all analytes in the sample pairs were in close agreement (Table 20). Of the 264 pairs of values compared, there were only two cases in which the differences between years were a factor of 5 or greater.

There were no particularly noteworthy differences in the Loving or Otis samples for 1997 as compared with 1998 and 1999 samples, except for a higher Sb level in the sample from Loving. As in 1998, several inorganic, non-radiological substances exceeded reference levels (secondary maximum contaminant levels) in the 1999 samples from the Otis and Private Well #2 sources. Specifically, these were chloride (by autoanalyzer), and sulfate. The fact that the 1997, 1998 and 1999 data showed essentially identical patterns for these two analytes indicates that the high concentrations were not spurious results but rather a true indication of elevated levels.

With respect to heavy metals, the Cr level in the 1999 Carlsbad sample was 793% greater than in the 1998 sample with an observed concentration of 2.7 µg L^-1. For the Hobbs samples, the Pb concentration was a factor of 44 lower in the August 1998 sample compared with the July 1997 sample (0.2 vs. 8.7 µg L^-1), and even lower in the 1999 sample (0.09 µg L^-1). In contrast, the Tl concentration was more than four-fold higher in the 1998 Hobbs sample compared to the 1997 sample (0.26 vs. 0.05 µg L^-1), but was non-detectable in the 1999 sample. The greatest Pb levels were observed in samples from Loving (1.7 µBq L^-1), Carlsbad (1.4 µg L^-1) and Private Well #2 (1.4 µg L^-1). The Cu and Pb concentrations were well below SDWA reference levels in all samples. As was the case in 1997, the highest concentrations of Ni and Tl were found in drinking water from Private Well #2, and as before, those concentrations were well below reference levels. In fact, the concentrations of Ni, Mg, Co, As and Al were lower at all sites in 1999, and Se levels were below the MDC of 0.12 µg L^-1.

It is important to emphasize that these results are not appropriate for use in assessing of regulatory compliance. However, it is noteworthy that the CEMRC results for Carlsbad drinking water collected in 1999 agreed very well with the measurements published by the City of Carlsbad Water Department (1998 Annual Consumer Report on the Quality of Tap Water). All of the CEMRC values were within the range of concentrations reported by the City of Carlsbad except for nitrate. CEMRC reported levels of 4.9-5.9 mg L^-1 of nitrate in 1998 and 1999 samples, while Carlsbad reported 0.81 mg L^-1 for a single sample collected in November of 1998. City of Carlsbad samples were collected at wellheads, while CEMRC samples were collected at a downstream point where water from individual wells has been combined, which may have contributed to the differences in nitrate measurements. However, the ~5 mg L^-1 is still less than half of the EPA maximum contaminant level of 10 ppm. Tables presenting drinking water data summarized herein are available on the CEMRC web site at http://www.cemrc.org.