Wawona Soil Investigation for Suitable Effluent Disposal Field
In 2013, the California Regional Water Quality Control Board initiated a renewal review of the Wawona discharge permit, and issued a Time Schedule Order which established new effluent limitations for dichlorobromomethane when discharging into the South Fork of the Merced River. Chlorination is part of the Wawona Wastewater Treatment Plant tertiary treatment process and dichlorobromomethane is a byproduct of chlorination.
Park staff is strongly considering abandoning the secondary discharge option of discharge into the South Fork of the Merced River to remove any possibility of dichlorobromomethane from entering the river. Preliminary estimates indicate that the cost of additional treatment to remove dichlorobromomethane will be cost prohibitive. As an alternative, park engineers and operators are considering removing all discharge into the South Fork by investigating the feasibility of constructing a land-based disposal system that would act as a new secondary discharge; all discharge into the South Fork would then cease.
The area around the Wawona Wastewater Treatment Plant has been assessed to have potential for a new land-based effluent disposal field. Soil condition assessments will validate and confirm the viability of four areas around the Wawona Wastewater Treatment Plant (see attached maps). Eight 6-inch piezometer borings will be made 12 ft below ground and eight 6-inch percolation borings will be made 5 ft below ground for each of the locations.