Base material” means hard, durable particles or fragments of stone or gravel, free of muck, organics or other deleterious material, four-inch maximum size, 20 percent to 55 percent passing No. 4 screen, and no more than 10 percent passing the 200 sieve. Materials that break up when alternately frozen and thawed or wetted and dried may not be used. All materials shall have a degradation value, as measured by Alaska Test Method 313, of 25 or greater for local roads and pioneer roads and of 35 or greater for collector roads. Base materials of less than a degradation of 25 or 35 (depending on road classification) may be approved by the borough engineer when supported by a design prepared, signed and sealed by a registered professional. Upon completion of the required road construction, the registered professional shall provide a letter with the final plat stating the roads appear to meet the intent of the design. The design must address at a minimum but not be limited to methods for obtaining degradation testing samples, mining of materials that met degradation values, stockpiling materials prior to placement on roads, placing materials on roads to eliminate silt pockets, and roadside drainage and road crown that adequately keeps roadway drained.