ML18085A018
| ML18085A018 | |
| Person / Time | |
|---|---|
| Site: | PROJ0734 |
| Issue date: | 01/11/2005 |
| From: | Office of Nuclear Material Safety and Safeguards |
| To: | |
| HDFelsher NMSS/DUWP/LLWB 415.6559 T5A39 | |
| References | |
| WSRC-TR-04-00633, Rev. 0 | |
| Download: ML18085A018 (9) | |
Text
Z-AREA GROUNDWATER MONITORING REPORT FOR 2004 (U)
WSRC-TR-04-00633 January 11, 2005
WSRC-TR-04-00633 PAGE 2 of 9 2
Introduction In accordance with SRS Z-Area Saltstone Industrial Solid Waste Permit, #025500-1603, wells ZBG-1, ZBG-1A and ZBG-2 are monitored for the parameters listed below:
pH Specific Conductance Water level Arsenic Antimony Barium Cadmium Chromium Lead Mercury Nitrate as Nitrogen Nitrite as Nitrogen Selenium Silver Benzene and Toluene Radium 226 and 228 (sum)
Gross alpha Nonvolatile beta New wells ZBG-3, ZBG-4 and ZBG-5 were also monitored although the permit has not yet been modified to include them. The wells (with the exception of ZGB-1A which was dry) were sampled twice during 2004. The first event was during first quarter and the second was spread over third and fourth quarters of due to sampling difficulties described below.
The well sampling and analyses were conducted in accordance with Procedure Manual 3Q5, Hydrogeologic Data Collection except in the case of fourth quarter sampling at ZBG-3, ZBG-4 and ZBG-5 where Hydrasleeve no-purge samplers were used. These wells are low producers with historically turbid samples that appear to yield anomalously high results for some metals. Confronted with the choice of not sampling at all or obtaining extremely turbid samples with a bailer, SRS opted to try the Hydrasleeve.
This sampler is capable of obtaining representative samples that are relatively clear without wasting any water in a purging procedure. The underlying principal for most no purge samplers (like passive dilution samplers) is the idea that purging is not needed if the sample can be taken directly from the screen zone with no mixing of stagnant water from above or below the screen zone. The hydrasleeve sampler is an elongated plastic bag with a check valve at the top. The collapsed bag is installed with the check valve near the bottom of the screen zone and left in place for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. During that time, any silts and clays stirred up during installation have time to settle. The sampler is then pulled up rapidly through the sample zone. This opens the valve causing the hydrasleeve to fill. The sleeve is full before it reaches any overlying stagnant water. The valve then closes adding extra protection against the collection of stagnant water. At this point, the sampler can be pulled to surface.
The analytical results are attached. The sampling did not reveal any evidence of a release from the Saltstone vaults. Flow directions and velocities were similar to those observed in past years.
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Flow Direction and Rate Potentiometric surface maps for the water table aquifer were constructed using first and third quarter data. Flow rate can be estimated using the following equation:
Flow(ft/day)= Hydraulic Conductivity (ft/day) x dh(ft)
Porosity (unitless) dl(ft)
Where the hydraulic conductivity constant is 1.7 ft/day, the effective porosity value is 30 percent, the change in head is dh, and the horizontal distance is simply the distance between potentiometric contours (figures 1 and 2).
For first quarter of 2004, the calculation is as follows:
1.7 ft/day x 12 ft = 0.050 ft/day or 18.4 ft/year 0.30 1350 ft For third quarter of 2004, the calculation is as follows:
1.7 ft/day x 12 ft = 0.052 ft/day or 19.1 ft/year 0.30 1300 ft Analytical results The nitrate/nitrite results are by far the most important in determining whether or not an unexpected release is occurring. This is because nitrate is the most mobile constituent likely to leach from saltstone. As in past years, nitrate/nitrite was detected in the downgradient wells but higher concentrations were found in background well ZBG-1. Therefore the downgradient detections do not represent evidence of a release from the vaults.
As was the case last year, samples from wells ZBG-4 and ZBG-5 had unusually high levels of chromium. This is believed to be coming from natural clays suspended in the samples.
Interestingly, chromium concentrations in both wells dropped about 68% in fourth quarter.
This is related to the use of the Hydrasleeve samplers which produce less turbid samples (table 1).
Table 1. Chromium results for ZBG-4 and ZBG-5.
WELL QUARTER Cr (ppb)
ZBG-4 1st 23.18 ZBG-4 4th J 7.41 with Hydrasleeve ZBG-5 1st 67.96 ZBG-5 4th 21.1 with Hydrasleeve Estimated concentrations (J qualified) were reported for arsenic in well ZBG-5 and for selenium in ZBG-4 and ZBG-5. Since the results are estimates well below the practical quantitation limits, no conclusions can be drawn about their meaning. However, it should be noted that there is no plausible mechanism for these metals to leach from saltstone and travel to the wells without being preceded by a plume of nitrate.
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Conclusions The ZBG well series was sampled twice during 2004. ZBG-1A was dry. Flow rate and direction were consistent with historical patterns. The sampling did not reveal any evidence of a release from the saltstone vaults. Hydrasleeve no-purge samplers were used at low producing wells with promising results.
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ZBG 2 220.3 ZBG 5 221.7 ZBG 4 221.11 ZBG 3 220.9 ZBG 1 232.6 219 221 233 VAULT 4 200 0
200 400 Feet Figure 1. Water elevation data in Z-Area for first quarter of 2004.
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ZBG 2 220.3 ZBG 5 220.73 ZBG 4 221.11 ZBG 3 ZBG 1 233.2 221 233 VAULT 4 300 0
300 600 Feet Figure 2. Water elevation data in Z-Area for third quarter of 2004.
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Table 2. Monitoring data.
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