7 Del. Admin. Code § 7103-72.0
Current through Register Vol. 28, No. 3, September 1, 2024
Section 7103-72.0 - Storage Volume72.1 Municipal systems may normally require 45 to 60 days storage to provide maximum flexibility in system operation, while industrial systems generally need less storage. For those facilities where it is practical to halt the generation of wastewaters minimal storage volumes can be designed. At a minimum, the Department requires at least 15 days storage unless other measures for controlling flow are demonstrated in the system design. The Department may reduce storage requirements upon a showing that unusual waste characteristics or operating conditions warrant such a reduction without adverse impact to the environment.72.2 A separate off-line system for storage of reject wastewater shall be provided at all limited and unlimited access sites, unless another permitted reuse system or effluent disposal system is capable of receiving the reject wastewater. Reject wastewater storage shall have sufficient capacity to ensure the retention of wastewater of unacceptable quality. At a minimum, this capacity shall be the volume equal to two (2) days flow at the average daily design flowrate of the pretreatment facility. Provisions for recirculating this reject wastewater to other parts of the pretreatment facility for further treatment shall be incorporated into the design of the facility. The total storage volume required for wastewater irrigation systems consists of three (3) separate storage components such that:
Total Storage = Operational Storage
+
Wet Weather and Emergency Storage
+
Water Balance Storage eq. 310.1
72.3 These separate storage components are described in the Sections that follow.72.3.1 Operational Storage72.3.1.1 Operational storage is a design parameter. For example, many wastewater irrigation systems are designed to apply wastewater 5 days per week and store weekend flows. Facilities which harvest cover crops on a frequent basis may stop irrigation to allow drying of the spray fields. Wastewater storage volume is required during these periods. Operational storage requirements are based on system management evaluations by the designer. 72.3.2 Inclement Weather and Emergency Storage72.3.2.1 Inclement weather and emergency storage provides for periods of excess rainfall or snowfall, saturated and frozen soil conditions and equipment failure when wastewater cannot be applied. The Department has minimum requirements for inclement weather and emergency storage. These are necessary to insure reliability of the slow rate land treatment system.72.3.2.2 The volume provided for inclement weather and emergency storage is determined as follows: Delta P x (30.4 days/month) eq. 310.2
D(allowed) crit
Where,
Delta P = 30 year variation from 5-year return monthly design precipitation, reference Table 309-1 (in)
D(allowed) crit = Maximum allowable hydraulic loading in most
critical water balance month, reference eq. 307.2 (in/month).
72.3.2.2.1 Table 310-1 DELTA P VALUES FOR DELAWARE NATIONAL WEATHER SERVICE CLIMATIC DIVISIONS1| Delaware Climatic Division | Delta P(inches) |
| Northern | 2.9 |
| Southern | 2.1 |
72.3.2.2.1 130 year variation from 5-year return monthly precipitation. Derived from National Oceanic and Atmospheric Administration historical rainfall data for Delaware.72.3.3 Water Balance Storage Water balance storage is a function of wastewater flow, wetted field area and the wastewater loading rate. Therefore, before the water balance storage volume can be determined, the actual rather than design wastewater loading rate (WLR), in in/wk, must be calculated. In order to calculate the WLR, the areas necessary to eliminate the operational and the wet weather and emergency storage volumes as well as the area necessary to treat a normal week's flow at the design loading rate must be calculated. Once the WLR has been calculated, the required monthly water balance storage is determined from water balance calculations and the following equation:
72.3.3.1 WBS = D(potential) - D(allowed) eq. 310.3 Where,
WBS = Required water balance storage (in/month)
D (potential) = Potential wastewater loading (in/month); assumes all influent wastewater is applied to the spray fields
D(allowed) = Maximum allowable hydraulic wastewater loading (in/month); reference eq. 307.2
Example calculations of this type are presented in Section 700.
7 Del. Admin. Code § 7103-72.0