Table 5.

Summary of predicted dissolved phosphate concentrations at the River Nar from individual septic tank assessment

Unsaturated zone travel time (years)Predicted concentration of effluent upon entry to the River Nar (mg P l−1) after:
40 years70 years
Distance from property to River Nar (m)Modelled depth to water table (m)Kd = 4.0 l kg−1Kd = 7.1 l kg−1Kd = 4.0 l kg−1Kd = 7.1 l kg−1Kd = 4.0 l kg−1Kd = 7.1 l kg−1
310.50.61.14.884.554.894.88
807.29160.920.311.240.92
897.29160.670.181.000.67
1603.1475.33E−022.81E−030.215.46E−02
2441.7242.98E−031.56E−053.71E−023.10E−03
2491.7242.52E−031.18E−053.35E−022.62E−02
2551.9242.06E−038.51E−062.96E−022.15E−03
3904.46101.56E−056.22E−092.01E−032.73E−05
4544.46102.04E−06Negligible5.87E−042.20E−06
4916.08136.38E−07Negligible2.90E−046.94E−07
5014.46104.67E−07Negligible2.40E−045.09E−07
5082.9463.76E−07Negligible2.11E−044.10E−07
53710.213231.53E−07Negligible1.22E−041.68E−07
7452.8462.79E−10Negligible1.63E−063.17E−10
8486.9915NegligibleNegligible2.55E−07Negligible
8669.61221NegligibleNegligible1.85E−07Negligible
90213.4173NegligibleNegligible9.76E−08Negligible
9182.946NegligibleNegligible7.35E−08Negligible
9242.946NegligibleNegligible6.61E−08Negligible
9566.0813NegligibleNegligible3.76E−08Negligible
9586.0813NegligibleNegligible3.63E−08Negligible
9676.0813NegligibleNegligible3.10E−08Negligible
9789.61221NegligibleNegligible2.55E−08Negligible
102616.62137NegligibleNegligible1.10E−08Negligible
11544.159NegligibleNegligible1.19E−09Negligible
16195.9713NegligibleNegligibleNegligibleNegligible
20134.259NegligibleNegligibleNegligibleNegligible
20481.223NegligibleNegligibleNegligibleNegligible
20531.223NegligibleNegligibleNegligibleNegligible
20711.223NegligibleNegligibleNegligibleNegligible
239424.83155NegligibleNegligibleNegligibleNegligible
243326.03358NegligibleNegligibleNegligibleNegligible
245126.03358NegligibleNegligibleNegligibleNegligible
244526.03358NegligibleNegligibleNegligibleNegligible

Italic values are concentrations higher than the 0.06 mg P l−1 SSSI SRP standard. ‘Negligible’ (1.20E−98) indicates that the effluent OP from these locations has not reached the watercourse.