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Table 2. Development Characteristics of the Case Study Areas *Based on estimated apportionment of total area. Sources: See text. (Questa, 1987). The monitoring wells representing condi- tions in the North and South study sites were sampled three times, and the others were sampled once. Table 3 shows the total nitrogen expressed as NO3-N, assuming that the other forms of nitrogen, which occur in small quantities, will in time convert to nitrate within the ground water. These values were obtained by summing the nitrate -nitrogen and total Kjeldahl nitrogen data. Nitrate -nitrogen data for the Chico area were obtained from the sampling of existing water -supply wells located within the defined study area, and drawing from the shallow ground -water zones. Well locations are shown on Figure 5. These data were obtained and reported by the California Department of Water Resources, Department of Health Services and Regional Water Quality Control Board during the period of 1984-1989 (DWR, 1984; CSWRCB, 1989). The data shown for Baywood-Los Osos were obtained from a special monitoring study conducted by the California Regional Water Quality Control Board during 1983-1984 water year (CRWQCB, 1983/84). Samples were obtained quarterly from a network of wells completed in the upper aquifer; these included active water -supply wells and moni- toring wells. The wells were distributed relatively uniformly 496 over the Baywood-Los Osos area, as shown on Figure 6. In comparison with the other two study areas, in the Baywood- Los Osos area a significantly larger fraction of the monitor- ing wells (6 out of 14) is upgradient of the major concentra- tion of development; these wells are shown in the southeast quadrant of Figure 6. Therefore, the data are shown separately for the upgradient and downgradient group of wells. The downgradient wells would be expected to show the full effect of nitrate -nitrogen additions from the entire developed area. Comparison with Predicted Values The mean values for nitrate -nitrogen shown in Table 3 represent, for each of the study areas and subareas, the resultant concentration that may be compared with pre- dicted values obtained from equation (1). A graphical plot of the mean nitrate -nitrogen data for the various areas is pro- vided in Figure 7; for comparison with predicted values, the curves of Figure 1 are included. As indicated, the observed values for all areas, except the upgradient wells for Baywood-Los Osos, fall within the envelope defined by the curves of predicted values. This Bolinas Mesa area Characteristic North study site South study site Area wide Chico area Baywood/Los Osos Land area (acres) 2.75 1.72 240 4,550 2,350 No. of dwelling units 8 9 320 13,650 5,170 (DU) Density (DU/gross 2.9 5.2 1.3 3.0 2.2 acre) Gross average acreage 0.34 0.19 0.69 0.33 0.45 per lot, A (acres) Average waste -water 5.8 10.5 2.6 6.0 4.4 loading over gross area, I (in./yr) Relative waste -water 0.40 0.73 0.18 0.35 0.37 loading, I/R Sources: see text. Table 3. Ground -Water Nitrate -Nitrogen Data Summary Range of NO3-N concentrations Density of wells sampled No. of wells Total (Mg 11) Study area (wells per acre) sampled samples Minimum Mean Maximum Bolinas Mesa • North study site 2.55 7 21 1.5 11.7 64.9 • South study site 4.07 7 21 1.5 13.9 51.0 • Total area 0.125 30 58 0.7 5.3 64.9 Chico area 0.0286 130 289 0.0 9.6 40.6 Baywood-Los Osos • Upgradient wells 0.00511 * 6 21 0.0 4.5 13.4 • Downgradient wells 0.00681 * 8 32 0.0 10.4 40.0 *Based on estimated apportionment of total area. Sources: See text. (Questa, 1987). The monitoring wells representing condi- tions in the North and South study sites were sampled three times, and the others were sampled once. Table 3 shows the total nitrogen expressed as NO3-N, assuming that the other forms of nitrogen, which occur in small quantities, will in time convert to nitrate within the ground water. These values were obtained by summing the nitrate -nitrogen and total Kjeldahl nitrogen data. Nitrate -nitrogen data for the Chico area were obtained from the sampling of existing water -supply wells located within the defined study area, and drawing from the shallow ground -water zones. Well locations are shown on Figure 5. These data were obtained and reported by the California Department of Water Resources, Department of Health Services and Regional Water Quality Control Board during the period of 1984-1989 (DWR, 1984; CSWRCB, 1989). The data shown for Baywood-Los Osos were obtained from a special monitoring study conducted by the California Regional Water Quality Control Board during 1983-1984 water year (CRWQCB, 1983/84). Samples were obtained quarterly from a network of wells completed in the upper aquifer; these included active water -supply wells and moni- toring wells. The wells were distributed relatively uniformly 496 over the Baywood-Los Osos area, as shown on Figure 6. In comparison with the other two study areas, in the Baywood- Los Osos area a significantly larger fraction of the monitor- ing wells (6 out of 14) is upgradient of the major concentra- tion of development; these wells are shown in the southeast quadrant of Figure 6. Therefore, the data are shown separately for the upgradient and downgradient group of wells. The downgradient wells would be expected to show the full effect of nitrate -nitrogen additions from the entire developed area. Comparison with Predicted Values The mean values for nitrate -nitrogen shown in Table 3 represent, for each of the study areas and subareas, the resultant concentration that may be compared with pre- dicted values obtained from equation (1). A graphical plot of the mean nitrate -nitrogen data for the various areas is pro- vided in Figure 7; for comparison with predicted values, the curves of Figure 1 are included. As indicated, the observed values for all areas, except the upgradient wells for Baywood-Los Osos, fall within the envelope defined by the curves of predicted values. This