What are the primary man made and natural contaminant sources, aquifer processes, and well characteristics that control
the transport and transformation of contaminants along flow paths to supply wells in representative water-supply aquifers?
The general approach for work on this topic involves coupling an understanding of processes in principal aquifers that
encompass individual topical study areas (large area investigations) with detailed evaluation of processes at the local
scale (small area investigations). The nesting of this work with other components in the program (land-use studies,
major-aquifer studies and sources-water assessments) is also an important element of this overall effort. TANC will focus
on arsenic as a naturally occurring contaminant and primarily urban contaminants.
- Characterize the geohydrology of study areas, including hydraulic properties, ground-water flow, geochemistry,
sources of contamination, existing water quality, and mechanisms necessary to understand the transport of
contaminants in the study area.
- Understanding sources--Measure and quantify selected potential sources of contamination to water-supply aquifers.
- Quantify contaminants and contaminants strengths in water-supply wells
- Understanding and quantifying transport and transformation processes--Identify and evaluate the primary physical,
chemical, biological, hydrologic, and water-resources engineering processes that have widespread potential to
influence the contaminants movement from source areas to supply wells.
- Extend and extrapolate results to similar aquifers, settings, and areas.
This study requires a multi-scale approach to address contaminant sources, transport, and fate in the context
of the regional ground-water system.
- Large area investigations - A regional model extending from just north of the Stanislaus River to south of
the Merced River, west to the San Joaquin River, and east to the outcropping of consolidated deposits will
characterize the regional flow system and determine the dominant flow paths to the public-supply wells. As
permitted, a database of lithologic information will be compiled to construct the permeability distribution
for the model.
- Small area investigations - These detailed investigations will be done to evaluate the relative importance
of physical and chemical processes affecting the contaminants along dominant flow paths. A transport model,
encompassing a portion of the urban Modesto area, will be used to determine average flow paths to a selected
public-supply well. A network of about 20 monitoring wells will be installed and sampled for a broad range
of constituents, including age dating to provide information on areal distribution of contaminants in the
local study area.
Study area for the topical study of transport of anthropogenic and natural
contaminants to community supply wells, in and around Modesto, California.
TANC project sampling activities are shown on the following video clip. Click on photo to view video (Not enabled yet).
Processing ground water samples for water quality analyses
Results from the TANC studies are all listed and accessible from the NAWQA TANC website at the following URL:
All of the specific papers related to work on the San Joaquin study area are listed in the publications.