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Corral Hollow Sanitary Landfill Page 2 of 2 21 December 2012 San Joaquin County the current proposed design to move the discharge point a proposed concrete lined v-ditch (Shaw Report)will convey the culvert's discharge to a point closer to GMW SB-1. A second culvert was discovered (See Attachment 1 and Photo#2 in Attachment 3)that drains a triangular area sandwiched between Interstate (1) 580 and the 1580 onramp from Corral Hollow Road. The second culvert drains into an area adjacent SB-1. Furthermore, it was observed from this discharge point looking southward towards Corral Hollow Creek that the drainage slope was minimal to non-existent in some areas. The lack of proper slope as depicted in the area shown in Attachment 1 is cause of concern since it allows storm water.ponding contributing to shallow groundwater mounding in areas adjacent to refuse. Thirdly, a drainage feature on the 1580 onramp (See Photo#3 of Attachment 3)was seen that drains storm water from the onramp into an area where ponding may occur. This drainage area has a very shallow slope with vegetation that could encourage ponding adjacent to refuse. Finally, an unlined v-ditch along the CHSL perimeter road was observed that in the past has been a source of moisture in underlying refuse that may be the cause of landfill gas production and VOCs observed in shallow groundwater. Though the proposed corrective action to cover the underlying refuse with a geomembrane material will be completed in 2013 the current design is to continue to leave the perimeter road v-ditch unlined. 6. Discussion: Board Staff believes that implementation of best management practices (BMPs) regarding collection, conveyance, and discharge of storm water away from underlying refuse may improve shallow groundwater quality currently impacted by Volatile Organic Compounds (VOCs). Though approximately 1.6 acres of uncovered underlying refuse will be covered per Title 27 requirements in 2013 the deposition of storm water in areas adjacent to refuse is not recommended.A more desirable scenario is recommended in Attachment 2. 5. Recommendations/Conclusion: Board Staff recommends that BMPs regarding the collection, conveyance, and discharge of storm water around the northeast comer of CHSL be implemented to reduce groundwater mounding at GMW SB-1. Attachment 2 suggests some BMPs that could reduce percolation of storm water in the northeast comer of CHSL. These BMPs collect storm water from the two culverts that drain storm water around Interstate 580 and convey it either to Corral Hollow Creek or the southern storm water retention pond. Furthermore, by regrading the area between 1580 and CHSL to provide adequate slope to encourage runoff towards Corral Hollow Creek and to prevent ponding the BMPs will minimize percolation and reduce chances of moisture contacting adjacent areas where refuse is buried. The reduction of moisture in a closed landfill results in reduction of landfill gas production and leachate production which in turn reduces the chances of discharges of waste to receiving waters (groundwater and surface water). Vinoo Jaip(/P.E. V Water Resources Control Engineer Title 27 Permitting and Mines Unit 3 Attachments Attachment 1. Topographic Map Showing Current Storm Water Drainage Attachment 2. Recommended Drainage Improvements Attachment 3. Site Inspection Photos