Occurrences of arsenic (As) are sporadic in drinking water from many wells in mid-coastal Maine. This is particularly the case where water supplies are pumped from fractured igneous and metamorphic bedrock. Although health risk-based As contamination levels are lowered, it is likely that the provenance of trace As concentrations will need to be scrutinized. Approximately 33% of wells sampled in the Goose River ground-watershed had at least one occurrence of 10 lg l ±1 As. Geologic mapping in combination with the rock petrology and mineral chemistry were important in deciphering probable local source areas for arsenic. Median whole rock As is greater than 39 mg kg ±1 in the Bucksport Formation and anatectic granitoids of the Waldoboro Pluton Complex. 34 S isotopic composition of arsenian pyrites indicate that local areas of anomalous arsenic-bearing, transported soils are not the source of trace As in groundwater, but, instead, the As is derived from oxidation processes in the fractured bedrock along the western margin of the ground-watershed. In groundwater, the As 3+ /As 5+ ratios ranged from 0.01 to 4.45 and were inconsistent spatially and temporally. Although it is probable that the stability ®eld in most groundwater supplies is HAsO 4 2± , arsenic speciation is not necessarily an aid to predicting transport. Instead an isotopic evaluation of associated groundwater SO 4 2± clearly indicates a consistent correlation of elevated As with enriched d 34 S SO4 . The d 34 S SO4 ranges of +4.05 to +4.61& may be characteristic of local oxidation in the fractured groundwater¯ow systems. Potential areas of geogenic As transport may be predictable.

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Measurements of naturally occurring deuterium isotope (3D) assist in tracing water components during wet weather flows in an urban watershed. A transect of installations in the vadose and saturated zones was completed in the vicinity of a small stream and storm sewer. High-resolution deuterium mass spectrometry discriminated between storm sewer leaks and other water sources such as direct runoff, bank seepage, and groundwater flow to a stream channel. Isotope hydrograph separation indicates that groundwater or vadose water predominantly contributed to the volume of stream water compared to direct surface runoff during a storm event. Significant differences in SD in the subsurface suggest that multiple flow components exist beyond the time period of a storm event. Deuterium measurements are helpful for modeling leaks and seepage and refining mass balances of flows in urban watersheds. Water Environ. Res., 71, 1251Res., 71, (1999. ObjectivesIsotope tracers offer new diagnostic tools for discrimination of wet weather flow components (Sidle, ] 998), including subsurface characterization of storm sewers. This exploratory work focuses on the distribution of a naturally occurring hydrogen isotope, deuterium (SD), in the vicinity of a small urban stream and storm sewer pipe. The primary objective is to discern whether SD measurements can distinguish storm sewer leakage to subsurface and receiving waters other than overland runoff before its design discharge location. Allied objectives include tracing water sources and flow paths in the vicinity of the sewer during storm events and estimating subsurface flow components during storm runoff. MethodsField. The site includes one known storm sewer paralleling an unnamed first-order stream (longitude N 84°35', latitude E 39°]5') in the urban Mill Creek watershed, Hamilton County, Ohio. From nearby outcrops northwest of Mt. Healthy, Ohio, bedrock consists of calcareous shale interbedded with thin limestone layers ( Figure ]). The shale sequence may behave locally as a semiconfining unit. Clayey-sand glaciofluvial outwash deposits overlie bedrock, and stream channels consist of erosional valley-fill deposits of sand and gravel.Generalized hydrology in the area (Walker, 1986) suggests that bedrock yields are less than 3 LIs but may leak to overlying September/October 1999 unconsolidated deposits. Valley-fill deposits may yield 1.5 to 6.5 LIs. No previous detailed hydrologic studies exist to indicate flow characteristics and components in the local stream-deposit aquifer near the known storm sewer. Presumably, base flow is toward the stream channel because local topographic relief influences shallow groundwater flow paths. Outflow from bedrock may occur with sufficient hydraulic gradients. Overland flow either empties directly to the stream channel or diverts to the subsurface during storm events. The wetted perimeter of the transected stream channel is 23 m with a hydraulic depth of 0.9 m. The storm sewer pipe discharges to the stream channel 434 m downstream from the design t...

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Efforts to sample representative, undisturbed distributions of uranium in ground water beneath the Fernald Environmemal Management Project (FEMP) prompted the application of a novel technique that is less invasive in the monitoring well. Recent studies (Kearl et al. 1992; Barcelona et al. 1994) indicate that representative samples can and should be collected without prior well volume exchange purging or borehole evacuation. Field experiments conducted at the FMMP demonstrate that under specific sampling conditions in a welldefined hydrogeologic system, representative ground water samples for a monitoring program can be obtained without removing the conventional three well volumes from the well. The assumption is made that indicator parameter equilibration may not be necessary to determine when to collect representative samples at the P'liMP. Preliminary results obtained from the field experiment suggest that this may be true. The technique employs low purge rates (< 1 L/min) with dedicated bladder pumps with inlets located in the screened interval of the well, while not disturbing the stagnant water column above the screened interval. If adopted, this technique, termed micro‐purge low‐flow sampling, will produce representative ground water samples, significantly reduce sampling costs, and minimize; waste water over the monitoring life cycle at the FEMP. This technique is well suited for sites that have been fully characterized and are undergoing long‐term monitoring.