Agenda - 09-21-1999 - 2 - Laserfiche WebLink

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where the bulk of the lateral groundwater flow in Piedmont surficial aquifers is known to occur. Wells screened within this horizon of high fracture density and of high local fracture connectivity will have "fast" near -field responses, resulting in slug test overestimates of bulk hydraulic conductivity. Measurements obtained from core at the Guess Road Site indicate fracture densities at least an order of magnitude greater than those reported by Dr. Kabala for the Duke Gate 11 site. JEI and the NC Solid Waste Section are well aware of the limitations associated with applying porous media concepts to fractured bedrock aquifers. The approximations arrived at on the basis of a porous media approach are justifiable partly on the basis of the high fracture densities in the lower parts of the weathering profile beneath the site, and in the upper parts of bedrock. Use of these approximate methods are also justifiable on the basis of the low environmental risk associated with C &D waste. • Questions about the accuracy of the 1% effective porosity estimate used for our calculations are moot, as the magnitude of this value is critical only for calculations applicable to the porous media approach. • The uppermost parts of regolith referred to on page 18 of the Site Application are composed of completely weathered predominantly silty material, and can indeed be expected to act in an isotropic manner. • The 25 -year storm design criterion for storm water control is not "highly questionable ". This criterion exceeds the 10 -year design storm required by the sedimentation and erosion control rules implemented by the North Carolina Land Quality Section, and is equivalent to the standard used for lined municipal landfills. Design parameters for sedimentation and erosion control devices proposed at the facility are yet to be established. Criteria for these will be established during the detailed design required by the Construction Plan Application process, and could be based on a larger, less frequent storm. The EPA recently published results of extensive research in support of its decision to recommend disposal of lead -based paint debris in C &D landfills rather than lined municipal landfills. In their report, they state: "Thus, at the national level, the modeling results indicate that the impact on groundwater at drinking -water wells down gradient of C &D landfills accepting LBP debris appears to be very low and would only occur after an extremely long period of time. " (Federal RegisterNol. 63, No. 243/Friday, December 18, 1998/ Proposed Rules; Lead; Management and Disposal of Lead - Based Paint Debris). • In making the case for a high risk from dissolved arsenic, Dr. Kabala cited three laboratory studies about the role bacteria play in dissolving arsenic under conditions devoid of oxygen. While correct in stating that landfill waste becomes oxygen - starved, he says nothing about just how quickly these extreme conditions change with distance from waste. He mentions nothing about the acidity of the site subsurface, its high clay content, or its high iron oxide and sulfide contents, all of which tend to adsorb free arsenic or limit its solubility. Nothing was mentioned about the concentrations of arsenic found in the EPA's C &D Leachate Database (May 18, 1995 Draft Report on Construction and Demolition Landfills, prepared for the U.S. Environmental Protection Agency, available online. Response to Comments of Dr. Z.J. Kabala 4 Joyce Engineering, Inc C&D Landfill Siting September 27, 1999 Orange County, North Carolina