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Fig. 5. Map of Chico study area. Unsewered Developed Areas (Study Area) ® Sewered Areas • Water Wells Sampled PS . ISI t;:11111111Y1B11/ �IIIIIIIYI'�11 : • • p, IIIIIIIIII © 000 , Fig. 5. Map of Chico study area. 0 1/4 1/2 3/4 1 Mlle 2 Mlles • Water Wells Sampled « Ground -Water Flow Direction Fig. 6. Map of Baywood-Los Osos study area. Unsewered Developed Areas (Study Area) ® Sewered Areas • Water Wells Sampled PS . ISI t;:11111111Y1B11/ �IIIIIIIYI'�11 : • • p, IIIIIIIIII 0 1/4 1/2 3/4 1 Mlle 2 Mlles • Water Wells Sampled « Ground -Water Flow Direction Fig. 6. Map of Baywood-Los Osos study area. Ground -Water Flow Direction 01/2 1 Mlle 2 Mlles I I for land area and dwelling units. The waste -water loading (inches/year) reflects the discharge from all existing waste- water systems, averaged over the entire study area. An assumption of 150 gpd/DU was used for this calculation. The final entry expresses the waste -water loading, I, as a fraction of the annual rainfall recharge, R, for each study area (from Table 1). Ground -Water Quality Data In each of the three study areas, the effects of septic systems on ground -water quality have been a concern of the local health department and the respective California Regional Water Quality Control Board (there are nine such Regional Boards in California). As a result of these con- cerns, water quality sampling programs were conducted (DWR, 1984; CSWRCB,1989; CRWQCB,1983/ 84; Questa, 1987). Representative data compiled from these sampling programs are summarized in Table 3. For the Bolinas Mesa area, some 30 ground -water monitoring wells were installed in the shallow marine terrace aquifer specifically for the purpose of monitoring septic system effects on ground waters. Well locations are shown on Figure 4. Samples were collected during the 1985-86 water year (October -September) and were analyzed for nitrate -nitrogen, ammonia, and total Kjeldahl nitrogen 495 Unsewered Developed Areas (Study Area) ® Sewered Areas • Water Wells Sampled Ground -Water Flow Direction 01/2 1 Mlle 2 Mlles I I for land area and dwelling units. The waste -water loading (inches/year) reflects the discharge from all existing waste- water systems, averaged over the entire study area. An assumption of 150 gpd/DU was used for this calculation. The final entry expresses the waste -water loading, I, as a fraction of the annual rainfall recharge, R, for each study area (from Table 1). Ground -Water Quality Data In each of the three study areas, the effects of septic systems on ground -water quality have been a concern of the local health department and the respective California Regional Water Quality Control Board (there are nine such Regional Boards in California). As a result of these con- cerns, water quality sampling programs were conducted (DWR, 1984; CSWRCB,1989; CRWQCB,1983/ 84; Questa, 1987). Representative data compiled from these sampling programs are summarized in Table 3. For the Bolinas Mesa area, some 30 ground -water monitoring wells were installed in the shallow marine terrace aquifer specifically for the purpose of monitoring septic system effects on ground waters. Well locations are shown on Figure 4. Samples were collected during the 1985-86 water year (October -September) and were analyzed for nitrate -nitrogen, ammonia, and total Kjeldahl nitrogen 495