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

Other design features which are frequently incorporated include fencing,
center inlet, specific berm slopes, and buffer zones. Five- or 6-ft
(1.5- to 1.8-m) high fencing is preferred to limit animal and human in-
trusion. Submerged center inlets are recommended to facilitate mixing,
to provide even solids deposition, and to minimize odors. Interior berm
slopes, steep enough to minimize rooted aquatic plant growth in the
lagoon, but resistant to erosion, are desirable. Slopes sufficient to
accomplish this objective have been reported to be between 3:l and 2:1,
depending primarily on height and soil characteristics. Buffer zones
are normally controlled by local regulations, but typically range from
100 to 300 ft (30 to 91 m).
7.3.3.5 Construction Features
To prevent seepage through the berm in unlined lagoons, a good interface
between the berm and the native soil is necessary. In areas where the
use of subsurface disposal systems is restricted due to slowly permeable
soils, B-horizon soils are frequently appropriate for berm construction.
Excavation of the topsoil prior to berm placement (so that the base of
the berm rests on the less permeable subsoils) reduces the incidence of
seepage, as does compaction of the berm material during placement. For
evaporation lagoons, care during construction to insure placement of a
leak-free liner reduces the need for impermeable berm material and asso-
ciated construction precautions.
7.3.3.6 Operation and Maintenance
Start-up of a lagoon system requires filling the lagoon from a conven-
ient freshwater source to a depth of at least 2 ft (0.6 m). This ini-
tial filling helps to prevent rooted plant growth and septic odors.
Solids removal is required periodically for evaporation lagoons. Data
are not available to indicate the exact frequency of solids removal
required, but intervals of several years between pump-outs can be anti-
cipated.
The reported need for chemical addition to control odors, insects,
rooted plants, and microbial growth varies on a case-by-case basis with
climate, lagoon location and configuration, and loading rate. Mainte-
nance of a minimum 2-ft (0.6-m) wastewater depth in the lagoon, and fre-
quent trimming of vegetation on the berm and in the vicinity of the la-
goon, are suggested. No other maintenance is required.
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