Section 372.420  Storage

a)         Storage Volume

            All land application systems must provide adequate storage, with adequacy being determined using either of the following methods, except that those facilities that do not generate wastewater year round must use Method I:

1)         Method I

            Adequate storage shall be based on a rational design that must include capacity for the wettest year with a 20-year return frequency.  The volume provided shall be sufficient to hold flows received during the following periods:

A)        When the soil is frozen, including subsoil frost layers;

B)        When there is an ice or snow cover on the ground;

C)        When the soil temperature at 4" depth is less than 40ºF or the mean air temperature is less than 35ºF;

D)        When the ground is saturated or there is standing water (as from late winter snowmelt or spring rains);

E)        When the groundwater table is within 4 feet of the surface;

F)         During days when precipitation exceeds 0.1 inch;

G)        During agricultural and horticultural practices;

H)        During days set aside for equipment maintenance;

I)         During days when the design maximum wind velocity is exceeded; and

J)         When the soil is barren, except for seeded areas, areas with growing crops, or areas with a trashy cover to prevent erosion.

2)         Method II

            The minimum storage capacity, by volume, shall be capable of storing at least 150 days production of wastewater, at design average flow, except that in southern Illinois areas (defined as all areas south of Interstate 70) a minimum of 120 days storage capacity shall be provided.

b)         Design and Construction Requirements

            The storage lagoon must be designed and constructed in accordance with 35 Ill. Adm. Code 370, Illinois Recommended Standards for Sewage Works.