7 Del. Admin. Code § 7103-73.0

Current through Register Vol. 28, No. 3, September 1, 2024

Section 7103-73.0 - Determination of Wetted Field Area

73.1 The wetted field area is subdivided into individual spray fields. Effluent should be applied once or twice per week per field. This allows for aeration and drying of the soil profile. It must be demonstrated by the applicant that a zone of aeration suitable for the rooting zone of the vegetation will be reestablished between wastewater applications. The minimum zone of aeration is often selected as 2 feet but must be based on the vegetation grown.

73.2 The wetted field area is sized to adequately treat four volumes of water; the storage volumes discussed in Subsection 71.0 and seven days of the design average daily flow. In equation form, this relationship is represented as:

A(wetted) = A(ADF) + A(OP) + A(WW/E) + A(WB) eq. 311

Where,

A(wetted) = required wetted field area (acres)

A(ADF) = area (acres) necessary to treat seven days' average daily flows

A(OP) = area (acres) necessary to treat the operational storage (see subsect. 71.1)

A(WW/E) = area (acres(c) necessary to treat the inclement weather/emergency storage (see subsect. 71.2), acres

A(WB) = area (acres) necessary to treat the water balance storage (see subsect. 71.3)

73.3 The Department requires that sufficient area be provided so that the stored wastewater can be irrigated within a reasonable period of time such that system operation and future storage needs are not compromised.The necessary areas for treating the storage volumes are determined using the WLR corresponding to [D(allowed) crit].

73.3.1 Area for Average Daily Flow, A(ADF)

73.3.1.1 The area necessary for distributing the average daily flow is calculated using the following formula:

A(ADF) = 7 days/wk x ADF, gal/day x (1 cf/7.48 gal) x (1 acre/43,560 sf) x 12 in/ft x 1/WLR, in/wk eq. 311.1

73.3.2 Area for Operational Storage, A(OP)

73.3.2.1 Spray field area necessary for treating operational storage associated with a plan of operation which calls for spraying less than seven days per week is already provided in A(ADF). Thus, A(OP) should be calculated only for the other elements of operational storage. As mentioned above, the area is based on the critical month WLR and on eliminating the storage volume within a reasonable period of time.

A(OP) = (gal/wk x 7/90) x (1 cf/7.48 gal) x (1 acre/43,560 sf) x 12 in/ft x 1/WLR, in/wk eq. 311.2

73.3.3 Area for Wet Weather and Emergency Storage, A(WW/E)

73.3.3.1 The wet weather and emergency storage volume is also to be eliminated within a 90 day period. Therefore, the equation for calculating A(WW/E) is the same as 72.2 with the wet weather and emergency storage volume substituted for the operational storage volume.

A(WW/E) = (gal/wk x 7/90) x (1 cf/7.48 gal) x (1 acre/43,560 sf) x 12 in/ft x 1/WLR, in/wk eq. 311.3

73.3.4 Area for Water Balance Storage, A(WB)

73.3.5 The equation to calculate the area necessary to eliminate the water balance storage within a 90 day period would be similar to 72.2 with the water balance storage volume substituted for the operational storage volume:

A(WB) = (gal/wk x 7/90) x (1 cf/7.48 gal) x (1 acre/43,560 sf) x 12 in/ft x 1/WLR, in/wk eq. 311.4

Example calculations of the wetted field area requirements are contained in Appendix B.

7 Del. Admin. Code § 7103-73.0