The WIPP EM incorporates studies at three reservoirs on the Pecos River, which is the major perennial fresh water system closest to the WIPP that has extensive human usage. The three reservoirs are: Brantley Lake, located approximately 40 miles northwest of the WIPP; Lake Carlsbad, located in Carlsbad and approximately 25 miles northwest of the WIPP; and Red Bluff Reservoir, located approximately 30 miles southwest of the WIPP. Surface and underground drainage from the area of the WIPP is to the southwest, and Red Bluff Lake is downstream of the area where drainage from the WIPP area enters the Pecos River. Brantley Lake and Lake Carlsbad are both upstream of the WIPP area drainage, and thus would be unlikely to receive contaminants via drainage from the vicinity of the WIPP but could be contaminated by atmospheric deposition. In addition to their proximity to the WIPP, these three reservoirs were selected because of the potential exposure of human populations to contaminants through use by the local population for sport fishing and recreation, and through use of Pecos River water for agricultural irrigation in a large region of the river floodplain throughout New Mexico and Texas.

Detailed summaries of the sampling design and analytical procedures for the WIPP EM sediment studies were presented in the CEMRC 1998, 1999 and 2000 reports. Data presented herein are from twelve samples collected during June-July, 2001. Sampling locations were identified using sonar and a combination of triangulation to known shoreline locations and GPS coordinates established during the 1998 and 1999 sampling seasons. The samples were collected using a grab sampler (Eckman-style dredge). A 5-L composite sample of the top 5 to 10 cm of the sediment bed was collected at each sampling site within each reservoir. Each composite consisted of 3 to 4 individual grab samples. Free water was immediately decanted from the composite samples. The sediment samples were then sealed in a 5-L plastic container, stored on ice, and transported to CEMRC. The samples were air-dried and ground to pass through a 2-mm sieve. More detailed summaries are provided in each year’s annual report, which is issued each February, and encompasses results from sampling and analyses completed through September of the previous year.

Summary for radioactive analytes in sediment samples collected during 1998 - 2000.

For sediment samples collected during May and June of 2000, 11 radionuclides measured by gamma spectroscopy were not detected in any of the samples (²⁴¹Am, ²¹³Bi,¹⁴⁴Ce, ²⁴⁹Cf, ⁶⁰Co,¹³⁴Cs, ¹⁵²Eu, ¹⁵⁴Eu, ²³³Pa, ¹⁰⁶Rh, and ¹²⁵Sb). Eight of the radionuclides measured were detected in all of the samples (²²⁸Ac, ²¹²Bi, ²¹⁴Bi, ¹³⁷Cs, ⁴⁰K, ²¹²Pb, ²¹⁴Pb, and ²⁰⁸Tl).

⁷Be was found in 2 of the 4 samples collected from Brantley Lake and 3 of the 4 samples collected from Lake Carlsbad in 1999 but in none of the samples collected in 1998 or 2000. No ⁷Be was detected in the samples collected from Red Bluff Reservoir in any of the years sampled.

^234mPa was detected in at least half of the samples from Brantley Lake in 1998 and 1999, but none in 2000. ^234mPa was detected in two samples from Lake Carlsbad in 1998 and one sample in 2000. ^234mPa was detected in at least half of the samples from Red Bluff Reservoir collected in each of the four sampling periods.

Comparison of activity concentrations of gamma emitting radionuclides determined in sediment samples collected during the monitoring phase to the activity concentrations determined in samples from the baseline phase reflect no significantly higher analyte levels in the monitoring phase samples.

For the 48 sediment samples collected from 1998 through 2000, measurements were made for 9 radionuclides by alpha spectroscopy (²⁴¹Am, ²³⁸Pu, ^239/240Pu, ²²⁸Th, ²³⁰Th, ²³²Th, ²³⁴U, ²³⁵U, and ²³⁸U). Activity concentrations above MDC were determined for all of these radionuclides in all samples with the exception of ²³⁸Pu. Red Bluff Reservoir had the highest number, with ²³⁸Pu detections in 12 of 16 sediment samples. No ²³⁸Pu was detected in any of the sediment samples from Lake Carlsbad. ²³⁸Pu was detected in 3 of 16 samples from Brantley Lake.

Comparison of activity concentrations of alpha emitting radionuclides determined in sediment samples collected during the monitoring phase to the activity concentrations determined in samples from the baseline phase reflect no significantly higher analyte levels in the monitoring phase samples.