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HomeMy WebLinkAbout990900016 Geotech Assessment (2007)Ph.253-896-1011 Fx.253-896-2633 GeoResources, LLC 5007 Pacific Hwy. E, Suite 20 Fife, Washington 98424-2649 May 8, 2007 Olympic Ridge, Inc. 15940 Lindsay Lane Poulsbo, Washington 98370 Attn: Mr. Joe Klinker Geotechnical Consultation Report Addendum Response to County Comments stormwater Disposal 50 Montgomery Drive Jefferson County, Washington Job:OlyRdg.Montgomery.L This report addendum addresses comments provided by Jefferson County (Item No. 27) and related to surface water runoff at the site. The proposal is to collect runoff from impervious surfaces at the site and pipe it to the shoreline area via an HDPE pipe. The pipe system would include anchors at the top and bottom of the shoreline bluff, as well as intermittent anchors installed with sleeves in the slope area. This is a common method of conveying stormwater runoff over steep slope areas with minimal impact. Based on our experience and the height of the shoreline bluff at the site, we estimate that the cost for the pipe installation (construction only) will be on the order of $8,000 to $10,000. A contractor can provide a more detailed and accurate cost estimate (proposal). This does not include permitting preparation costs or fees. We do not recommend dispersing or infiltrating the stormwater runoff on the upland area of the site as this will adversely impact slope stability of the upper bluff area. Typically the residential use of septic systems with the removal of stormwater runoff results in a slight reduction in the amount of water infiltrated, and a net increase in slope stability. The removal of stormwater runoff from the site by conveyance to the roadside ditch is not practical at this site. The roadside ditch is upslope of the subject residential site and would require pumping of the storm runoff water. This typically involves a storage tank to collect the runoff and a pump system to send it to the ditch. This assumes that the ditch and down stream area have capacity to handle the additional water. We do not recommend this type of system unless no other options are available. This is based on power being required to the pump system and the risk of power loss during a significant rainfall event. Although backup power systems can be utilized, they are expensive and not without the risk of failure. When they fail, the result is a large amount of water flowing to and over the bluff slope, potentially causing erosion and landslides. • •• Olympic Ridge - Hinkie Montgomery ~ May 8, 2007 Page 2 We have appreciated the opportunity to be of service to you on this project. Please do not hesitate to call with any comments or questions at your convenience. Respectfully submitted, GeoResources, LLC Brad P. Biggerstaff, LEG Principal ~f~~~~N COU ~C BPB:KWG:bpb DocID:OlyRdg.Montgomery. L ~RA~L~Y P. ~I~~g~~YAFF Kurt W. Groesch, PE Principal