Preliminary assessment of radionuclide transport via storm-water runoff in Los Alamos Canyon, New Mexico
— Michael R. Dale

Observations on streamflow, suspended-sediment concentration and radionuclide activity during a 7-8 September 1995 flow event provide insight into contaminant transport in Los Alamos Canyon. Measurable discharge data from two gaging stations, one above and one below the mouth of DP Canyon, show that flow persisted for 8.8 hrs and at the downstream gage ranged from 651 to 0.28 L/sec. Four storm-water samples, taken at 30-min intervals during the peak flow where NM-4 crosses Los Alamos Canyon below the mouth of DP Canyon, showed suspended-sediment concentration ranged from 40.3 to 4.4 g/L. Mean activity concentrations for the suspended sediments (pCi/g) include 15.4 for gross beta, 2.44 for ⁹⁰Sr, 1.54 for ^239/240Pu, 0.15 for ²³⁸Pu, 1.36 for ²⁴¹Am and 6.63 for ¹³⁷Cs. Mean activity concentrations for dissolved radionuclides (pCi/L) include 17.9 for gross beta and 5.05 for ⁹⁰Sr; ²³⁸Pu, ²⁴¹Am and ¹³⁷ Cs were not detected in the dissolved phase. The radionuclide ^239/240Pu was detected at or near the method or instrument detection limit (0.05 to 0.04 pCi/L). Preliminary estimates of total radionuclide transport during the first 90 min of flow include 41.5 uCi of ⁹⁰Sr, 26.2 uCi of ^239/240Pu, 2.5 uCi of ²³⁸Pu, 23.1 uCi of ²⁴¹Am and 112.8 uCi of ¹³⁷ Cs. Historical data indicate transport of radionuclides with suspended sediments in Los Alamos Canyon varies from year to year. This variability may be linked to the fluctuation in discharge contributed by DP Canyon. Additional monitoring of flow and transport processes in canyons that contain contaminants is warranted.