ANALYTICAL METHODS FOR MULTI-ISOTOPIC BASELINE STUDY OF GROUND AND SURFACE WATERS

Three case studies in NH and MA, incorporating multi-isotopic analyses (Sr, Pb, and U), have provided insightful baseline water quality information to community water providers regarding waterflow, water source determinations, and changes in resources over time. To insure the validity of multi-isotopic analyses, initial sampling, laboratory handling protocols, and data analysis methods must be given careful attention. At the typical concentration levels of Pb and U in these waters (< 5 ppb), contamination during sampling can invalidate analytical results. Sampling equipment, such as commercially available filters and filter systems, have Pb blanks sufficient to contaminate water samples, thus the filters need to be acid-cleaned prior to use. Sampling of stratified water bodies, at different depths, requires careful planning and specially cleaned sampling vessels. The affinity of organic matter for both Pb and U can make laboratory analysis of surface waters for these elements difficult. In surface waters, Pb isotopic compositions are sensitive to atmospheric deposition and can be variable; therefore short-term response (storm event sampling) data can be skewed. The overall low Pb content in ground and surface waters makes low-blank (< 10 pg total procedure blank for sample volumes up to 30 mL) laboratory procedures essential. Sr, Pb, and U isotopic data from our case studies show clear patterns that relate to local geology, abundance of organic matter, seawater mixing, and seasonal variations of flow, on local and regional scales. Multi-isotopic analyses are a complement to broader chemical fingerprinting of water sources. We will present details of studies in Hampton, NH, Littleton, MA, and Billerica, MA, to illustrate applications of multi-isotopic baseline monitoring.