You are here:
ENHANCED RECOVERY METHODS FOR 85KR AGE-DATING GROUNDWATER: ROYAL WATERSHED, MAINE
Citation:
SIDLE, W. C. ENHANCED RECOVERY METHODS FOR 85KR AGE-DATING GROUNDWATER: ROYAL WATERSHED, MAINE. Presented at American Geophysical Union Meeting, Royal Watershed, ME, December 01, 2005.
Impact/Purpose:
To inform the public.
Description:
Potential widespread use of 85Kr, having a constant input function in the northern hemisphere, for groundwater age-dating would advance watershed investigations. The current input function of tritium is not sufficient to estimate young modern recharge waters. While tritogenic helium has promise for some modern recharge waters, its analytical accessibility is poor and is not cost effective for projects with numerous samples. Past practical limitations of water sample quantity near 500 L for 85Kr analysis have been corrected by our portable in-situ gas stripping equipment in conjunction with micro-purging of the well, with subsequent extraction of a minimum of 20 μL Kr for analyses. Further a prototype recirculating extraction technique has lowered the water sample quantity to ≤300 ml where high 85Kr precision is not necessary and removal of the well pump is not practical. Our field sampling innovations have been coupled with a 34% increase in gas counting efficiency by cavitation pretreatment resulting in minimum detection for 85Kr at 4 mBq mL-1 at 95% significance levels. Cross validation with Pulse Burst Spectroscopy and γ-spectroscopy yield comparable 85Kr statistics for 81% of our sample inventory. Currently, 85Kr ages of flows are being investigated in the Royal Watershed, Maine, in order to determine the residence times of elevated drinking water Pb concentrations.