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�,. 40 General Engineering and Environmental Management Services Because SPSA is located in a coastal plain with a shallow depth to the groundwater table, the intra- gradient design allowed excavation through the uppermost aquifer into the second. This required HDR to work closely with regulatory agencies and prove the integrity of the system. For example, detailed fate and transport modeling was necessary to illustrate that the proposed liner system was as effective, or more so, than the EPA - mandated system. In response to Virginia's regulations that prohibit the dewatering of aquifers, HDR went through an additional process to receive a special exception for SPSA's Cell V. An innovative approach is Cell V's use of a double- composite liner system installed below the local groundwater table to facilitate an inward gradient (below the normal groundwater level). This greatly improves the landfill economics by gaining additional airspace through significant excavation prior to liner placement, while at the same time affording a higher level of environmental protection. The inward gradient design of Cell V nearly doubled the waste capacity of the original, aboveground design, and increased space at almost no additional capital costs. The result for SPSA is a lower per ton cost for material put in the landfill, and a higher level of environmental protection. Another way in which the intra - gradient design has relieved the Authority's economic burdens is through the soil yielded by the excavation. Prior to this resource being made available, SPSA had exhausted its soil surplus years ago and had been transporting soil to the landfill site at a cost of $6 to $7 per cubic yard. At over 1.5 million cubic yards, the excavation of soil will offset nearly $10 million dollars in cost of importing off -site soil for use as cover material. The SPSA Landfill is an "inward gradient" design, with the liner system placed as much as 30 feet below the local groundwater table. The Cell V design saved SPSA over $17 million in 1999. The 44 -acre Cell VI contiguous expansion was recently permitted and designed, and construction of the first phase was completed in April 2006. In part due to the design innovations of Cell V, the SPSA recently received the highest award presented in Landfill Management by SWANA. HDR has provided landfill design and construction administration service to SPSA since 1984. The permitting process, established in Virginia, includes rigorous documentation of the engineering design. The permitting included extensive leachate modeling to demonstrate that the existing pretreatment facility was adequate to accept the addition of the expansion's flow. Also, a formal regulatory variance was obtained to allow for an alternate liner system. Obtaining this variance has saved SPSA several million dollars by nearly doubling the cell capacity, as well as avoiding bringing in off -site material for landfill cover. The double- composite liner system, installed below the local groundwater table to facilitate an inward gradient, includes a groundwater collection system, soil liner component, and geosynthetic clay liner, as well as dual geomembrane liners. Post - closure care groundwater monitoring is performed by Carolinas and Virginia staff for the closed landfills in Isle of Wight County, Virginia, and the city of Franklin, Virginia. Services included the evaluation and statistical analysis of detection and assessment monitoring data, groundwater flow determination, plume delineation studies, and monitoring well design and installation oversight. Page 25 1 al