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HomeMy WebLinkAboutLUA-05-089_Icicle Creek Engineers Report.pdfMarch 24, 2006 Terry DeFoor GWC, Inc. 95 Anchor Court Marco Island, Florida 34145 ICICLE CREEK ENGINEERS Geotechnical, Geologic and Environmental Services INTRODUCTION Report Hydrogeological Consultation Stream B Corridor Renton Hill Property Renton, Washington File No. 0584-001 This report presents the results of Icicle Creek Engineers (ICE's) hydrogeologic evaluation of the "Stream B" corridor at the DeFoor property (referred to in this report as the "Renton Hill Property") in Renton, Washington. ICE previously completed a preliminary geotechnical evaluation and coal mine hazard assessment of the Renton Hill Property; the results were presented in ICE's report dated June 10, 2005. ICE also completed an evaluation of Protected and Sensitive Slope areas; the results were presented in ICE's report dated September 30,2005. We understand that a question has been raised by Jason Walker of Talasaea Consultants, LLC (the wetland and stream consultant for the project) as to whether or not Stream B is a naturally-formed stream. ICE has been requested by Terry DeFoor the project owner, to assist in this evaluation of Stream B from a geomorphological (landform genesis) and hydrogeological perspective. The morphology of this stream is important in identifying its proper sensitive area classification and buffer requirements. To accomplish this evaluation, ICE reviewed historic mine maps dating back to 1911 and historic aerial photographs dated 1936, and completed a detailed surface reconnaissance of the Stream B corridor. STREAM B OVERVIEW We understand that Stream B was identified by Talasaea. Stream B is located in the south portion of the Renton Hill Property, and flows from east to west through an undeveloped forested area. A second stream, referred to as "Stream A" exists to the south of Stream B. Stream B is bordered by Renton A venue South and residential development to the east, residential development to the north, and undeveloped forested land to the south and west. The Stream B corridor and surrounding area have a relatively long history of site use, including residential development (Renton Hill is one of the oldest residential neighborhoods in the City of Renton) and underground coal mining. The site is located at the historical location of the Renton Mine that was active from about 1874 through 1933. HISTORICAL MINE MAP REVIEW We reviewed historic mine maps of the Renton Mine dated 1911, 1918, 1919 and 1932. These historic maps show the underground mine workings and, to a limited extent, surface features such as 230 NE Juniper Street, Suite 101 • Issaquah, WA 98027-2519 • www.iclclecreekengineers.com • (425) 427-8187 phone • (425) 427-6629 fax EX t.f-- Terry DeFoor GWC, Inc. March 24, 2006 Page 2 mining-related buildings, ground surface topography (in local areas), primary roads and streams. No stream is indicated on the historic mine maps at the Stream B location. The mine maps indicate that main entries for the Renton Mine are located in the area currently designated as Wetland A. Stream B flows into Wetland A. Based on our previous coal mine hazard assessment of this area, it appeared that the mine entries, including the main mine entry, were covered and regraded which, in our opinion, created the depression where Wetland A is located. HISTORICAL AERIAL PHOTOGRAPH REVIEW We reviewed historic 1936 stereo image (three-dimensional) aerial photographs of the Stream B area. When viewing these photographs in stereo pairs, the vertical dimension is greatly exaggerated, making it easier to observe and identify valleys, swales or ravines. The current development in the surrounding area, including Renton A venue South and the existing residential development, is consistent with the developed area in the 1936 aerial photographs. In the 1936 aerial photograph, the upland area east of Wetland A is forested and ground surface appears to be relatively planar (no defined swale). For the purpose of this report, a "swale" is defined as a low-relief topographic feature where water may concentrate along the longitudinal axis of the flow path. The area currently occupied by Wetland B is partially cleared with scattered trees. No definitive stream path is visible on the aerial photographs through the Wetland B area. However, we observed a subtle indication of a relatively broad swale taking shape about 50 feet east of the south end of Cedar A venue South in the Stream B area. Stream A is visible within a defined swale in the 1936 aerial photographs. SURFACE RECONNAISSANCE Brian Beaman of ICE completed a surface reconnaissance of the Stream B corridor on March 17, 2006. Stream B "originates" at a 12-inch diameter concrete pipe that is buried under Renton A venue South. The area upgradient (east) of this location is fully developed with residential housing and roads. No swale feature was observed upgradient (east) of this stormwater pipe outfall. At the time of our reconnaissance, water was flowing from this pipe at a rate of about two to three gallons per minute. The ground surface downgradient of the 12-inch diameter pipe outfall is nearly level and covered with dense brush and blackberry vines for a distance of about 150 feet to the west. A network of eroded gullies, some containing water and some not (the dry gullies are referred to as "orphaned gullies"), cross this area in a braided manner. The gullies are consistently 1-to 3-feet deep (near-vertically sided) and I- to 2-feet across. Bedrock (sandstone) is exposed in the walls and base ofthese gullies. At a distance of about 150 feet downgradient (west) of the 12-inch diameter pipe outfall, the ground surface steepens and the network of braided gullies join to form a single gully for a distance of about 100 feet. The single gully crosses a smooth-surfaced area, with a slight definition of a swale beginning to form, much like several other subtle swale features across the Renton Hill Property. The gully through this area averages about 6-to 8-feet deep (near vertically sided) and 3-to 5-feet across. Bedrock (sandstone) is exposed in the walls and base ofthis gully. The ground surface continues to steepen until it reaches a wide swale feature (at least 100-feet wide). A gully, 2-to 6-feet deep and is 3-to 5-feet wide is incised within the swale feature. This wide swale appears to be the same feature noted on the 1936 aerial photographs. The base of this wide swale is roughly coincident with the south end of Cedar Avenue South. At this location, Stream B flow across a gently sloping to nearly level area and bends slightly to the Icicle Creek Engineers 0584001/032406 Terry DeFoor GWC, Inc. March 24, 2006 Page 3 southwest where it enters the Wetland A area. Stream B is deeply incised into this gently sloping area in a gully that is 4-to 6-feet deep and 2-to 4-feet wide. A second deeply incised gully, referred to as Stream C, with similar physical characteristics, flows toward Stream B from the northeast, but does not connect with Stream B. Stream C originates from a 12-inch diameter stormwater pipe outfall at the south end of Cedar Avenue South. CONCLUSIONS AND RECOMMENDATIONS Based on our information review and site reconnaissance, it is our opinion that Stream B is not a naturally-occurring stream. The geomorphological and hydrogeological characteristics of Stream B indicate that the "stream" was created by stormwater discharge from the 12-inch diameter pipe that flows from the downhill (west) side of Renton Avenue South. Our opinion is based on the following observations: • No evidence of an existing stream channel was observed on the historic mine maps. • It is unlikely that the mine operators would have maintained a mine entry area in-line with a stream discharge. • No evidence of a defined swale or stream channel was observed in the 1936 aerial photographs. • No visible "watershed" (a natural topographic basin of water flow) exists in the area upgradient (east) of the 12-inch diameter pipe discharge point at Renton Avenue South. • The braided gullies in the area below the discharge point are more consistent with unmanaged stormwater runoff being released from the 12-inch diameter stormwater pipe in Renton Avenue South. • The depth of incisement of the Stream B gullies throughout its reach indicates unmanaged storm water runoff; again originating at the 12-inch diameter storm water pipe in Renton Avenue South. The physical characteristics of Stream B more resemble an adversely eroding "ditch" rather than a stream. As noted above, the best physical description is "gully" rather than using a more common term for streams such as channel. During our reconnaissance, we observed a broad swale-like feature in the lower portion of the Stream B corridor. This feature is less pronounced than other depression or swale-like features across the Renton Hill Property that are fully vegetated with no stream incisement, and do not receive storm water discharge. In our opinion, the Stream B corridor would be forested with no defined stream channel if the 12- inch diameter stormwater pipe discharge originating at Renton Avenue South was not present. In our opinion, the gullying of Stream B has created a safety hazard. The City of Renton should be notified of these safety hazard conditions along with appropriate corrective measures to reduce this hazard. USE OF THIS REPORT We have prepared this report for use by GWC, Inc. and their associates and engineers for their use in planning development of the Renton Hill Property. The data and report should be provided to permitting agencies for their information, but our report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. Icicle Creek Engineers 0584001/032406 Terry DeFoor GWC, Inc. March 24. 2006 Page 4 Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No warranty or other conditions, express or implied, should be understood. ******************** We trust this infonnation meets your present needs. If you have any questions or if we can be of further assistance, please call. Document ID: 058400 l.Report4 Three copies submitted cc: Jason Walker (one copy) / Talasaea Consultants. LLC 15020 Bear Creek Road NE Woodinville. Washington 98072 Rob Stevens (one copy) Core Design 14711 NE 29th Place. Suite 10] Belluvue. Washington 98007 Ricci Grube AlTA, PLLC (two copies) 1080 Broadacres Building 160 I Second Avenue Seattle, Washington 98101 Icicle Creek Engineers Yours very truly, Icicle Creek Engineers, Inc. Brian R. Beaman, P.E., L.H.G. Principal EngineeriHydrogeologist 0584001/032406