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<br />The method of construction will be a combination of excavation and berming. Outer <br />side slopes will be 3:1, and inner side slopes will be 2:1. The anticipated berm height is <br />10 feet. <br />D.2.4.2 Parachute Site Ponds <br />A 15-acre evaporation pond will be located where Unocal previously had two ponds, <br />and the area will be regraded and bermed for the new pond. Therefore, construction of <br />the evaporation pond will not constitute new disturbance. The fluid streams that will <br />be discharged to the evaporation pond are reverse osmosis reject, sand filter discharge, <br />and boiler blowdown. <br />A 21-acre storage pond(the MVR purge pond) will be constructed in order to store <br />purged water from the final processing system (soda ash line). Solids accumulation will <br />occur in this pond primarily in the form of sodium carbonate that crystallizes as heat is <br />dissipated. Solids will be periodically dredged and returned to the process system. No <br />other disposal of solids from this pond is anticipated. The total disturbed area will be <br />approximately 33 acres. <br />Both the evaporation and MVR purge ponds will be constructed with a double liner and <br />leak detection system in accordance with the requirements of CDMG. The liner system <br />will consist of two geomembrane liners and a leak detection and collection system. The <br />top liner will be 60-mil HDPE, and the bottom liner will be 40-mil HDPE. A geonet <br />material will be installed between the two liners to collect and transport any water that <br />may leak through the upper liner. The geonet layer will drain into a sump, which will <br />be equipped with a submersible sump pump. The sump pump will be automatically <br />activated by a fluid-level sensor switch. <br />A 1-acre stormwater retention pond will be constructed. It will be located near the <br />southeast comer of the site. The total disturbed area for this pond will be <br />approximately 2 acres. <br />A 2.8-acre water storage pond will be constructed to store make-up water (fresh water) <br />from the water delivery system prior to treatment and use. The pond will have a clay <br />liner. It will be constructed by regrading and berming the site of a previous Unocal <br />pond system. Therefore, its construction will not constitute new disturbance. <br />The berms for each pond will be designed in accordance with Bureau of Reclamation <br />Design of Small Dams criteria. Adequate freeboard will be provided to: 1) <br />accommodate the normal maximum operating level plus the 100-year (24-hour) <br />precipitation event; 2) accommodate wave action on the pond level described in (1) <br />without overtopping; and 3) provide at least 1 foot of freeboard above the level <br />determined in (2). <br />D-7 <br />