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• Harvest-Lathrop Composting Facility - 7 - 7 February 2018 San Joaquin County Board. a. The Discharger stated in its 2018 Revised Final Technical Report that it shall comply with the General Order requirements for its detention ponds used in composting operations including but not limited to designing and constructing its detention ponds using the following pond liner system (from top to bottom- See Attachment D): 1) 40 mil Linear Low-Density Polyethylene (LLDPE) Geosynthetic Geomembrane Liner' 2) Geosynthetic Clay Liner with equivalent or less flow-through rate as 1-foot thick clay having less 1.0 x 10-6 cm/s or less hydraulic conductivity 3) Compacted Subgrade b. The Discharger stated in the 2018 Revised Final Technical Report that they will install a pan lysimeter below the lowest point of the detention pond capable of effectively monitoring the unsaturated zone below the detention pond bottom as shown in Attachment D. c. The Discharger has shown in 2018 Revised Final Technical Report that the proposed detention ponds required to meet the pond sizing specifications of the General Order may require implementation of a contingency plan during a wettest year period (21.14 inches annual rainfall)where excess wastewater may need to be stored in above ground temporary storage tanks or disposed of at a wastewater treatment plant. The excess wastewater is the result of the Discharger having to maintain reserve capacity in its detention ponds due to runoff and precipitation falling on the ponds from the 25-year 24- hour Design Storm of 2.71 inches. The use of above ground temporary storage tanks or disposal of wastewater at a wastewater treatment plant after 1 February to manage excess compost wastewater is necessary in order for the Discharger to maintain sufficient freeboard and reserve storage for the Design Storm to prevent overflow and/or overtopping of the detention ponds. The Discharger's water balance predicts that if the Design Storm occurs after 1 February the Discharger will need to store excess wastewater in above ground temporary storage tanks or dispose of wastewater off-site during the following months if a wet year similar to the wettest year on record were to occur: Month Estimated Contingency Plan Additional Storage Required'(Gallons) February 623,541 March 930,267 April 733,750 'Potential storage or disposal needed to maintain reserve capacity for Design Storm In order to determine when the Discharger must begin implementing its contingency plan to store excess wastewater in additional above-ground portable storage tanks or dispose of excess wastewater at a wastewater treatment plant, two action levels shall be implemented based on wastewater elevations in the detention ponds if the Design Storm has not already occurred by 1 February. If the Design Storm of 2.71 inches occurred in a 24-hour period prior to 1 February the Discharger must notify the Central Valley Water ' The Discharger may add a protective soil cover above the LLDPE geomembrane liner as shown in Attachment D so long as the Discharger's water balance analysis and detention pond capacity calculations account for the loss in associated wastewater storage capacity.The Discharger's 2018 Revised Final Technical Report Appendix B currently does not take into account loss of storage capacity due to the protective soil cover.