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North County RC&SL Page 14 of 64 Public Works/Solid Waste Joint Technical Document County of San Joaquin – Revised July 14, 2025 4.2.3 Precipitation The facility receives an average of 17.6 inches of precipitation per year (Western Regional Climate Center Lodi Station, data from 1948 to 2007). Monthly precipitation varies from 0.03 inches in September to 3.4 inches in January. Spatial variation of total annual rainfall is shown on the isohyetal map (Plate 9). 4.2.4 Design Storm The drainage facilities of the NCRC&SL are designed to withstand a 100-year 24-hour precipitation event, with a total 3.65 inches of precipitation (California Department of Water Resources, Oakdale Woodward Dam). The requirements for the design storm for the landfill are identified in the waste discharge requirements (Appendix A). 4.2.4.1 Evaporation The mean annual pan evaporation at the NCRC&SL is 64.92 inches (Western Regional Climate Center Lodi Station, data from 1948 through 2005). The mean monthly evaporation varied between 0.06 inches in December and 10.60 inches in July. These values can be adjusted by multiplying by 0.7 or 0.8 to more closely estimate the evaporation from large bodies of water such as ponds and lakes. 4.2.5 Runoff Volume and Pattern The primary path for water entering the landfill property is from a tributary of South Paddy Creek east of the site. Water entering from this source is diverted into the mitigation area on the northern portion of the site (Plate 3). Within the waste management unit area, several facilities control run-on and runoff. A perimeter berm around portions of the waste management unit intercepts run-on to the landfill. This perimeter berm, berms on the landfill, and a series of ditches, controls surface runoff during storm events, and directs surface runoff to an interim sedimentation basin on the east side of the site.