ECOLOGICAL MANIFESTATION OF A STRONTIUM-NINETY GROUNDWATER PLUME

To quantify the pathway of strontium from a groundwater plume to biota living near the Ottawa River shoreline, we used mini-piezometers, seepage meters, a portable gamma spectrometer, shoreline vegetation and tree-swallow nest boxes. In heterogeneous terrain (K = 10^-2 to 10^-7 cm/s), conventional methods such as vertical drilling can be prohibitively expensive. Using a variety of inexpensive and rapid methods in this study, we obtained detailed and broad coverage of seepage and contaminant flux, hydraulic gradient, radiation and biotic uptake. Although radionuclide discharge did not pose a risk to biota, including humans, the levels of ⁹⁰Sr⁺² in the groundwater plume allowed us to trace the transport of Sr⁺² from discharge areas to local plants and animals. Gross beta counting (in Bequerels) was used to measure ⁹⁰Sr⁺². In a relatively small (115 m²), but interesting area of the discharge zone, seepage measurements (> 33 L/m²·day) and gross beta analysis of artesian groundwater from < 0.6 m beneath the riverbed showed that the average annual seepage flux of ⁹⁰Sr to the river was 7.0E+05 Bq/m². In this area, river water, under late winter ice, contained elevated levels of gross beta and electrical conductivity. Twelve-day-old tree swallow nestlings from nest boxes that were located within 150 m of the groundwater discharge area contained from 0.14 to 0.51 Bq/g (fresh wgt.) gross beta as opposed to 0.10 to 0.13 Bq/g in nestlings from control areas. Maximum gross beta values from groundwater to biota were as follows: groundwater discharge (590 Bq/L), phreatophytes (60 Bq/g dry wgt), surface water beneath the ice sheet (49 Bq/L), sediments (9 Bq/g) and tree swallows (0.51 Bq/g). The source of elevated gross beta radiation in the swallows was ⁹⁰Sr⁺², transported by groundwater to littoral sediments and to insects, which, when they emerged, were eaten by swallows.