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WASTE DISCHARGE RE#IREMENTS ORDER NO. -3- SAN JOAQUIN COUNTY FOR POST-CLOSURE AND CORRECTIVE ACTION MONITORING CORRAL HOLLOW SANITARY LANDFILL SAN JOAQUIN COUNTY 15. Monitoring data of the perched zone indicates shallow background groundwater quality has a specific electrical conductivity(EC) of approximately 1000 micromhos/cm, with total dissolved solids (TDS) of approximately 600 mg/l. Monitoring data of the deeper flow zone indicates background groundwater quality as measured at monitoring well MW-2 has a specific electrical conductivity(EC) of approximately 1,600 micromhos/cm, with total dissolved solids (TDS) of approximately 1,200 mg/l. 16. The direction of groundwater flow in the perched zone indicates that shallow groundwater mounds at SB-1 and flows both northerly and southerly. Occasionally,the direction of groundwater flow is northerly. The groundwater gradient is approximately 0.007 foot per foot. The groundwater velocity in the perched flow zone is approximately 2 feet per year. Groundwater in the deeper flow zone has been southeasterly in the past,though has not been monitored at the landfill since 1990. 17. The designated beneficial uses of the groundwater, as specified in the Basin Plan, are domestic and municipal, agricultural, and industrial supply. GROUNDWATER MONITORING 18. The groundwater monitoring system includes three wells screened in the shallow,perched aquifer on the eastern side of the landfill, wells SB-1, MW-5 and MW-4. Three well are also screened below 250 feet bgs,MW-1, MW-2, and MW-3, however groundwater has not been present in these wells since 1990. Attachment B shows the locations of the groundwater monitoring wells. 19. The Discharger's detection monitoring program for groundwater at this Unit does not satisfy the requirements contained in Title 27. Whereas the shallow groundwater monitoring on the northeastern side of the landfill does monitor the first encountered groundwater,the southwestern half has no monitoring system currently in place. Wells intended to monitor deeper groundwater have been dry since 1990. Appropriate monitoring should be implemented on the southwestern half of the landfill 20. Volatile organic compounds (VOCs) are often detected in a release from a landfill, and are the primary waste constituents detected in groundwater beneath a municipal solid waste landfill (see Finding Nos. 29 and 30). Since volatile or compounds are not naturally occurring and thus have no background value,they are not amenable to the statistical analysis procedures contained in Title 27 for the determination of a release of wastes from a Unit. 21. Sections 20415(e)(8) and (9) of Title 27 provide for the non-statistical evaluation of monitoring data that will provide the best assurance of the earliest possible detection of a release from a Unit in accordance with §20415(b)(1)(B)2.-4. of Title 27. However, Title 27 does not specify a specific method for non-statistical evaluation of monitoring data.