Current Projects - USGS
Purpose
According to the Nebraska Department of Health and Human Services (NHHS), more than 78 public water supply (PWS) systems in Nebraska, most serving less than 3,300 people each, will have As concentrations above the MCL. Data for the 78 PWS with As levels exceeding the MCL, show As concentrations may not change between sampling or vary by more than 10 ug/L. An explanation for these variations has not been presented. To assess potential variation, a six-month reconnaissance sampling of 20 PWS wells, funded by USEPA, is currently under way. The USGS part of the project will address As concentration and speciation variability.
Objectives
- Determine As concentration and speciation variability on a monthly basis for nine months.
- To improve our understanding of As occurrence, we will collect geologic materials from the major groundwater-bearing units in Nebraska.
- Collect fresh rock samples from cores of representative geologic units currently in the possession of the CSD for background arsenic content.
- Field sample (at 25 cm vertical intervals through at least 100 cm vertically or laterally into outcrops) at least two in-situ weathering profiles developed on bedrock in order to assess potential changes in As content related to pedological and geochemical processes.
- Obtain at least two cores (125 feet total) through alluvial soil profiles in at least two higher-arsenic-level areas along the Republican and North Platte rivers.
- To determine arsenic availability, sequential extraction procedures will be used on 22 samples. Thin sections and X-ray diffraction analysis will also be conducted on these samples.
