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Home My WebLink AboutSEP98-0149 Stormwater Report Review - SEP Inspections - 12/31/1998 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 DATE: Dec. 31, 1998 INTER-DEPARTMENTAL COMMUNICATIONS TO: Randy Neff, DCD - Planner FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. DCD Wo#9845 SUBJ: Stormwater Report Review NAME: Rob Biehl Short Plat SEP98-0149 FPM98-0001 Public Works has received and reviewed a copy of the storm drainage analysis &temporary sediment pond sizing report from N.L. Olson &Associates for the Robert Biehl short plat# 1545. The drainage plan offered raises concerns in its investigation of potential offsite impacts and in meeting the minimal standard requested in an IDC to your department by me dated November 17, 1998. The engineer for this project continues to promote the development of the property as though the only concern was for damage that might occur within the plat itself. As the engineer did with the geotechnical report content requests, he has failed to comply with instructions from the County for stormwater control design requirements. The IDC dated 11/17/98 requests a Large Parcel Permanent Water Quality Stormwater Control Plan which addresses anticipated runoff from the fully developed property, and suggests that developed flows from the property should be restricted to pre-development discharge rates. Major criticisms include; (1) Roof runoff infiltration systems are offered for the individual residences, but no indication of how they were sized is given. The engineer has already typified the soils as glacial till with varying depths of soil overlying the till. For the roof infiltration trenches to be effective, they are expected to be able to evacuate themselves within 24 hours. Ecology's manual recommends soil explorations to a minimum depth of 3' below the bottom of an infiltration facility to verify the suitability of a location to effectively infiltrate water. (2) The engineer has deleted stormwater analysis of what he terms Basin#2 because there is less than 5,000 sf of impervious area within the basin. This department views this as a proposal with a total impact from the entire original parcel. If the developed discharge from Basin #2 is directed to an area either not needing protection or capable of receiving runoff without damage, the engineer may make a claim to that effect, but will be expected to substantiate such a claim with a pre & post development runoff calculations and some indication of where the runoff dissipates to, and that areas' File: H:\WP\STRMWTR\REVIEWS\BIEHL-SP.IDC ability to receive heightened runoff peak volumes. (3) The November 171h IDC requested developed flows to be attenuated back to pre- development discharge levels. No attempt has been made to attenuate developed flows at all, unless the roof infiltration systems are expected to offset the imperviousness created as a consequence of development of the property. Permanent stormwater quantity control features should be incorporated into the site's development that provide protection for the downstream receiving properties. In attempting to locate the property in relation to Mill Pond and Sherwood Creek, I would like to note that no listing of Stewart Creek Road can be found, and its not clear whether the project is in proximity to one of the Sherman Hills Roads or some other private roads. The vicinity map does not correlate well with either the Mason County Road Map, or with the Roadrunner map for this area. All indications are that this property contributes either directly or indirectly to Sherwood Creek. The drainage report should be required to address this issue and make a determination whether downstream erosion and sediment control standards are needed. The proximity of the project to Sherwood Creek, and to the recent road instability leads me to the conclusion flow attenuation needs to be incorporated into this projects' development. In summary, the stormwater site plan delivered to Public Works should not be accepted as the final plan for this proposal. The plan as submitted, appears excellent as a temporary erosion and sediment control plan for such a development, but is lacking in the major features needed to protect offsite properties. Approval of this plan, in my opinion, would be the beginning of an endless string of complaints over the next several years from downslope properties subjected to this property's runoff and accompanying instability and erosion problems. This project appears to be ignoring regulatory requirements, starting with the FPA, continuing through the delivery of a geotechnical report, and now providing the minimal information and documentation requested by both of our departments for stormwater planning. As I offered before to you and the project engineer, if you have any questions regarding this review, or development standards applicable to this proposal, please feel free to contact me at County extension 461. Sincerely, UZAA 1 An A. Tahja File: H:\WP\STRMWTR\REVIEWS\BIEHL-SP. IDC GARY YANDO,DIRECTOR �oN.S TA o A°u DEPARTMENT OF COMMUNITY DEVELOPMENT i o T z PLANNING - SOLID WASTE - UTILITIES N Y Y BLDG. I • 411 N. 5TH ST. • P.O. BOX 578 SHELTON, WA 98584 • (360) 427-9670 1864 December 31, 1998 Mr. Rob Biehl 5801 Soundview Dr. , Suite 101 Gig Harbor, WA 98335 RE: Stormwater Report Review Dear Mr. Biehl : The Mason County Department of Community Development would like to inform you that we can not accept the Stormwater Report has submitted. We are attaching to this letter the comments by Mason County Public Works regarding their review of the report submitted. If you have any questions pertaining to this letter, please contact Alan Tahja at 360-427-9670, Ext. 461. Sinc ly, Ran4yvef Subdivision Planner Printed by Randy Neff 12/03/1998 8 :54am --------------------------------------- From: Gary Yando To: Randy Neff, Robert Fink Subject: --------------------------------------- ===NOTE====------=====12/3/1998==8:47=A I would like to further our discussion on the two geo things we were discussing yesterday. Randy - you do not have to go to Chehalis. Mary Jo said she is going. If she changes her mind she will let us know. Randy - what about the issue with Rick L`n�Ll^v` �lGf� Ol/iYYf Moore? andy - why haven't we prepared a p 9;'i/ response to the concerns expressed by the property owners for the cutting above sherwood creek. Bob - I need to see the definitions for type 1,2,3,4,5, streams. I would like them asap and have them sent to PC. I would like to talk to you before they are sent out. Bob - We need to talk to Wayne about the fish and wildlike document and a concern that was brought out by Pat Byrne regarding the bathtub effect. --------------------------------------- Page: 1