Agenda - 08-18-1987 - Laserfiche WebLink

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From this analysis, it is clear that the proposed hydraulic and pollutant loading rates are much too high for the proposed 8.2 acre absorption field area. Other public and private parties who design such systems have stated that a much lower loading rate should be utilized in the design of this system. Based on discussions with other parties who design these systems, OWASA recommends that an HLR not exceeding 0.075 gallons per day per square. foot be utilized in designing the proposed system, provided sufficient documentation is provided to support that the design loading rate will not result in contamination problems. • 3. The proposal for a backup soil absorption area to be reserved provides only an "after-the fact" approach to correcting future wastewater disposal problems. Under that approach, if a failure of the primary system occurred it would continue while the replacement system was being installed in the backup field. A greater degree of reliability and operational flexibility should be incorporated into this large community system since a failure will create a major problem. To provide added assurance that the system will have a long, useful life, the primary soil absorption area should be periodically rested. This will allow the absorption field to gradually drain, theneby.exposing_ _ the infiltrative surfaces to the air allowing bacteria to restore the field's infiltration capability. Periodic resting requires that a second absorption field exist to allow continued disposal while the first is in the recuperative phase. The systems can be alternated on a yearly basis (Reference *1) . This approach is required in Fairfax County, Virginia and other areas. OWASA recommends that at a minimum a dual, alternating absorption field system be required to be installed and utilized for this project. Additionally, the need for reserving an undisturbed backup area should be considered in the event either of the dual absorption areas fails. The combination of a lower hydraulic loading rate and redundant absorption facilities, together with a good maintenance and operation program should provide substantially greater reliability of the community waste disposal system functioning adequately and properly. As recommended in the literature, this conservative approach is justified "because (1) it is more difficult to achieve even distribution of effluent in large systems, thus making localized overloading more likely, (2) groundwater mounding may be a problem with these large systems, and (3) surface failures of these systems may present larger environmental and health consequences because of their size." (Reference #4) 4. Two "community septic tanks" and pump stations are proposed to be constructed, one of which is to be located within approximately 250 feet of Morgan Creek. Adequate measures must be taken to prevent the accidental discharge of wastewater from these facilities into surface and groundwaters. It is recommended that: a. Reserve storage tanks be constructed to store the additional volume of wastewater which is equal to that which would be received under a 24-hour peak day period. That would provide backup storage in the event a pump station failure occurred; -3-