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i -~ . -. • We strongly recommend [hat the finished subbase Bade surface be proofrolled with a heavy piece of construction equipment after it has been adequately moisture treated and compacted, and prior to placing the subbase gavels or geogid. Areas, which deform or pump under the wheel loads of the construction equipment should be removed and/or stabilized prior to the placement of the subbase course gavels or geogid. An engineer from this office should observe the proof roll as it is completed. We recommend that the subbase sands and gravels meet the requirements for Class I base course aggregates in accordance with the Colorado Department of Transportation (CDOT) Specifications, 1999. However, the upper end of the gradation requirement should be modified to allow 6-inch minus materials. The base course gavels should meet the requirements for Class V or VI base course aggega[es in accordance with the CDOT specifications. The base course gravels placed over the geogrid materials should be Class V base course aggregates. We recommend that the subbase gavels and base course gavels be tested for compaction and that [he thickness of the completed lifts be measured to verify that the required gravel sections have been constructed. • Surface Drainaee Recommendations: For the adequate performance of any roadway, positive surface drainage must be provided and maintained. This includes periodic cleaning and regading of [he drainage ditches along the edges of the roadway. In addition, the roadway surface should be gaded on a periodic basis to ensure that sufficient crown or super elevations is maintained so that the roadway surface adequately drains to the ditches. We recommend that the subject roadway be constructed with a minimum crown or super elevation of 2 percent. As noted above, the collection and diversion of surface drainage away from the roadway area is extremely important for satisfactory performance of the roadway. The design of surface drainage features should be carefully considered to remove all water from the roadway surface and embankment areas. In addition, the maintenance of all drainage structures and roadway surface should be conducted periodically to ensure proper performance. Limitations: This report has been prepared in accordance with generally accepted soils and pavement engineering practices in this area for use by the client for design purposes. The conclusions and recommendations submitted in this report aze based upon the assumed subsurface conditions and given traffic loadings. If during construction, the subsurface conditions appeaz to be different from those assumed and described herein, this office should be advised at once so that reevaluation of [he recommendations may be made. We recommend the on-site observation of the subgrade proof rolling, gavel placement and fill compaction by an engineer from this office. If you have any service, please c Sincerely, NORTHWEST b~ • -_ ~~'.. 2Vj Brian D. €e~n„P. = A ~ "s -OrCS Job Number: 01-i02 concerning this report or our recommendations, or if we may be of any further office. INC., NWCC, Inc. Page 2