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Assessing Ground Water Vulnerability with the Type Transfer Function Model in the San Joaquin Valley, California

^a Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0224
^b Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94035-2115

View larger version (75K): [in a new window]   Fig. 1. The location of the San Joaquin Valley within California. The borders of the eight counties in the San Joaquin Valley are shown.

View larger version (48K): [in a new window]   Fig. 2. The areas from the five counties in the San Joaquin Valley that were used to assess potential atrazine leaching. The location of the study area is shown in Fig. 1.

View larger version (51K): [in a new window]   Fig. 3. (a) Soil texture in the San Joaquin Valley study area. (b) Type transfer function (TTF)-simulated peak atrazine concentrations for a compliance depth d = 3 m in the San Joaquin Valley study area. (c) TTF-simulated arrival time of the peak concentration at depth d = 3 m in the San Joaquin Valley study area.

View larger version (61K): [in a new window]   Fig. 4. Type transfer function (TTF) concentration estimates at d for Day 200 (upper panels) and Day 700 (lower panels) of the simulation period in response to a single, label-recommended application of atrazine for eastern Fresno County. All estimates were made under consideration of spatially uniform annual recharge and for a compliance depth of d = 3 m. (a) TTF Set III (one TTF for each texture). (b) TTF Set IVa (two TTFs for each texture, lower estimate). (c) TTF Set IVb (two TTFs for each texture, higher estimate). (I) Simulation Day 200. (II) Simulation Day 700.

View larger version (57K): [in a new window]   Fig. 5. The distribution of organic carbon content foc in the upper soil profile throughout the San Joaquin Valley study area (after Blanke, 1999).

View larger version (19K): [in a new window]   Fig. 6. Correlation of (a) peak concentrations above a threshold of 1 x 10–3 mg L–1 with (b) surface organic carbon and (c) soil texture. In (c), 1 = sand, 2 = loamy sand, 3 = sandy loam, 4 = loam, 5 = silt, 6 = silt loam, 7 = sandy clay loam, 8 = clay loam, 9 = silty clay loam, 10 = sandy clay, 11 = silty clay, and 12 = clay.

View larger version (55K): [in a new window]   Fig. 7. Results from the type transfer function (TTF) pesticide leaching assessment for eastern Fresno County at a compliance depth of d = 3 m using spatially distributed recharge. (a) The spatially distributed annual average recharge for the Fresno study area. (b) Peak atrazine concentrations. (c) Arrival time of the peak concentrations at d.

View larger version (66K): [in a new window]   Fig. 8. Type transfer function (TTF) concentration estimates for Day 200 (a–c) and Day 700 (d–f) of the simulation period in response to a single, label-recommended application of atrazine for eastern Fresno County. All estimates were made under consideration of spatially distributed annual recharge and for a compliance depth of d = 3 m. (a) TTF Set III (one TTF for each texture). (b) TTF Set IVa (two TTFs for each texture, lower estimate). (c) TTF Set IVb (two TTFs for each texture, higher estimate). (d) TTF Set III (one TTF for each texture). (e) TTF Set IVa (two TTFs for each texture, lower estimate). (f) TTF Set IVb (two TTFs for each texture, higher estimate).

View larger version (45K): [in a new window]   Fig. 9. Comparison of areas with type transfer function (TTF) predictions exceeding the maximum contaminant level (MCL) for TTF Set III in eastern Fresno County. (a) Spatially uniform recharge values. (b) Spatially distributed recharge values.