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Harvest-Lathrop Composting Facility - 3 - 7 February 2018 San Joaquin County Due to shallow groundwater (first encountered groundwater) at the Facility the Discharger has stated in its 2018 Revised Final Technical Report that it will maintain a minimum separation of 2 feet between the base of the ponds (lowest point of waste in the containment system i.e., base of waste) and groundwater level. The Discharger will install piezometers around the detention ponds to establish a potentiometric surface map of groundwater elevation below the detention ponds. The approximate piezometric locations are shown on Attachment B. The Discharger shall provide additional monitoring and reporting as described in Section 10 of this staff memorandum to ensure that minimum 2 feet separation is maintained between base of waste and highest groundwater level. The subsurface soils underneath the site consists of fine grained Silty Sand (SM) and Silt (ML). Upper 10 feet bgs consists of dry to moist, fine-grained, Silty Sand (SM), which is underlain by Silt (SM) in medium dense condition. Fines content, i.e. particles passing #200 sieve (0.074 mm opening size) range from 15 to 53 percent. Laboratory test results of in-situ soils indicated that the soils underneath the working surface are not uniformly compacted and hydraulic conductivities are both above and below 1.0 x10-5 cm/sec. Annual rainfall average is approximately 9.85 inches. The historic maximum and minimum annual rainfall is 21.14 inches and 4.11 inches respectively, for the period of record spanning from 1949 to 2010. Precipitation measurements were recorded at the Tracy- Carbona weather station. The weather station is located approximately 13 miles from the Facility. The mean annual evaporation for the site is 97.48 inches per year, for the period of record spanning 1955 to 2010. Evaporation measurements were recorded at the Tracy Pumping Plant, approximately 15 miles from the Facility. The National Oceanic and Atmospheric Administration (NOAA) Atlas 14, Vol. 6, Version 2, rainfall frequency map provided the rainfall data used in the hydrology analysis of the site. The NOAA rainfall frequency map indicated that the peak 25-year, 24-hour storm event was determined to be 2.71 inches. According to Federal Emergency Management Agency (FEMA) map number 06077C0610F the Facility is protected by a levee from the 1% annual chance (100-year)flood and in an area determined to be outside the 0.2% annual chance (500-year) floodplain. However, the site is within a dam inundation zone for the Lake McClure, San Luis, and/or New Melones dams in the headwaters of the San Joaquin River tributaries. At the Facility there is one on-site agricultural water supply well that supplies water for the composting operation and one on-site domestic water supply well which supplies water to the Facility office building. The nearest off-site water supply well is located approximately 0.36 miles east of the north-east Facility boundary. 3. PROPOSED COMPOSTING OPERATIONS The proposed composting operation will be divided into three distinct operational areas: (1) a Receiving Area of 1.7 acres, (2) Active Composting and Curing Areas totaling 6.8 acres, and (3) a Finished Product Storage Area of 2.6 acres. The composting operation will also include two wastewater detention ponds (Pond 1 and Pond 2) with surface areas of approximately 0.7 and 1.7 acres respectively (See Attachment B). Ancillary facilities that are not subject to the requirements of the General Order include various buildings, truck and employee parking, fuel storage area, and a truck scale. ScANNE©