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On-Site Wastewater Treatment and Disposal Systems - Forced ...

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Table 7-6 can be used to determine the necessary seepage pit sidewall<br />

area for various effective depths below the seepage pit inlet.<br />

TABLE 7-6<br />

SIDEWALL AREAS OF CIRCULAR SEEPAGE PITS (ft2ja<br />

Seepageb<br />

Pit Thickness of Effective Layers Below Inlet (ft)<br />

Diameter 1 2 3 4 5 6 I 8 9 10<br />

T-----------<br />

1<br />

2<br />

3<br />

4<br />

5<br />

6<br />

7<br />

8<br />

1:<br />

11<br />

12<br />

3.1<br />

6.3<br />

129.:<br />

15:7<br />

18.8<br />

22.0<br />

25.1<br />

28.3<br />

31.4<br />

34.6<br />

37.7<br />

136 1; :z :F! :; 4242 50 25 :; 63 31<br />

19<br />

25<br />

31<br />

::<br />

47<br />

5”:<br />

63<br />

47<br />

63<br />

79<br />

7”:<br />

94<br />

868” 10’:<br />

110 126<br />

$35<br />

141<br />

94<br />

126<br />

157<br />

38<br />

44<br />

50<br />

57<br />

66<br />

75<br />

ii<br />

101<br />

94<br />

110<br />

126<br />

113<br />

132<br />

151<br />

132<br />

154<br />

176<br />

151<br />

176<br />

201<br />

170<br />

198<br />

226<br />

188<br />

220<br />

251<br />

57<br />

63<br />

69<br />

85<br />

94<br />

104<br />

113<br />

126<br />

138<br />

141<br />

157<br />

173<br />

170<br />

188<br />

207<br />

198<br />

220<br />

242<br />

226<br />

251<br />

276<br />

254<br />

283<br />

311<br />

283<br />

314<br />

346<br />

75 113 151 188 226 264 302 339 377<br />

a Areas for greater depths can be found by adding columns. For<br />

example, the area of a 5 ft diameter pit, 15 ft deep is equal to<br />

157 + 79, or 236 ft.<br />

b Diameter of excavation.<br />

b. System Layout<br />

Seepage pits may be any diameter or depth provided they are structurally<br />

sound <strong>and</strong> can be constructed without seriously damaging the soil. Typi-<br />

cally, seepage pits are 6 to 12 ft (1.8 to 3.6 m) in diameter <strong>and</strong> 10 to<br />

20 ft (3 to 6 m) deep but pits 18 in. (0.5 m) in diameter <strong>and</strong> 40 ft (12<br />

m) deep have been constructed (22). When more than one pit is required,<br />

experience has shown that a separation distance from sidewall to side-<br />

wall equal to 3 times the diameter of the largest pit should be main-<br />

tained (3).<br />

237

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