TANC is trying to answer the following question:
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?

How will TANC answer this question:
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.

Specific objectives of TANC:

1. 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.
2. Understanding sources--Measure and quantify selected potential sources of contamination to water-supply aquifers.
3. Quantify contaminants and contaminants strengths in water-supply wells
4. 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.
5. Extend and extrapolate results to similar aquifers, settings, and areas.

1. 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.
2. 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.

Results from the TANC studies are all listed and accessible from the NAWQA TANC website at the following URL:

http://oh.water.usgs.gov/tanc/NAWQATANCProducts.htm

All of the specific papers related to work on the San Joaquin study area are listed in the publications.