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HomeMy WebLinkAboutADU Geotech Report 2P 0-0, W.77'7, GEORESOURCES earth science & geotechnical engineering 5007 Pacific Hwy E., Suite 16 f Fife, WA 98424 E 253.896.1011 1 www.georesources.rocks Signature Custom Homes 10407 81h Street East Edgewood, Washington 98372 Attn: Mr. Bill Hines (253) 606-3228 November 20, 2017 Addendum Report: Geologic Hazards Assessment Proposed Single -Family Residence 1715 Morris Avenue South Renton, Washington PN: 7222000334 Doc ID: Signature Homes. MorrlsAve.RGA(1) INTRODUCTION This Addendum Report summarizes the results of our geologic hazard assessment for the single family residence to be constructed at 1715 Morris Avenue South in the Renton area of King County, Washington. We previously prepared an Updated Geotechnical Engineering Report: Stormwater Feasibility dated March 31, 2017. Review comments by the City of Renton Indicated that a steep slope and/or coal mine hazard may be present on our within 50 feet of the subject parcel, and requested a critical areas assessment of these potential hazard to satisfy the City of Renton Critical Areas Ordinance (RMC 4-3-050). The general location of the site is shown on the attached Site Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with you; our previous April 12- 13, 2017 site visits; our more recent November 17, 2017 site visit; our experience In the subject area; and our understanding of the City of Renton Critical Area Ordinance and development codes. As stated in or original report, we understand that the proposed development will include the construction a new single family residence with an additional dwelling until. The Purpose of our services is to evaluate the surface and subsurface conditions across the site as a basis for assessing potential geological hazards, The City of Renton is requiring a geotechnical assessment of this potential hazards and the scope of services for this project will Included the following: 1. Reviewing the available geologic and geotechnical data for the site area; 2. Visiting the site and performing a site reconnaissance to confirm site features and to assess the site's soil, groundwater, and slope conditions; 3. Preparing an addendum report per City of Renton RMC 4-3-050, SlgnatureHomes.MorrisAve.RGA(1).docx November 20, 2017 page 12 We were provided a verbal authorization for this scope of work by Mr. Mike Clow of Signature Custom Homes. No subsurface explorations or laboratory testing were completed as part of the scope for this report SITE CONDITIONS Surface Conditions The site is located in an area of existing residential development in the Renton area of King County, Washington. According to the King County Assessor website, the parcel is generally rectangular In shape, measures about 50 feet wide (north to south) by about 160 feet deep (east to west), and encompasses approximately 8,080 square feet, or 0.18 acres. As stated, the site is undeveloped. The parcel is bounded by existing residential development on the west, south, and north. The parcel is also bounded by Morris Avenue South to the east. The site is situated on top of a localized topographic highlands. In general, the site area slopes down to the north at about 8 to 10 percent with onsite slopes of about 4 to 5 percent. The parcel to the northwest of the site has a cut retaining wall near the property corner that is on the order of 6 to 8 feet exposed height. Total topographic relief on the site is on the order of 4 to 5 feet based on King County IMap data and as observed in the field. Existing topography obtained from King County IMap and generally confirmed in the field is shown on Figure 2. No evidence of slope Instability or soil movement was observed on the slope below the proposed home site at the time of our April 12-13,2017 site visits. No evidence of standing water, seeps, or springs was observed on the site. Site Soils As stated in our previous report, the USDA Natural Resource Conservation Service (NRCS) Web Soil Survey maps the site as being underlain by Beausite gravelly sandy loam (BeC) soils. The Beausite soils are derived from till over residuum from sandstone and are Included in hydrologic soils group C/D. These soils have a "Moderate" erosion hazard when exposed and are Included in hydrologic soils group C. Site Geology As stated in our previous report, according to the Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965), the site is in an area underlain by Renton formation jr). No areas of landslides or landslide debris are mapped on or within the vicinity of the site. No evidence of deep seated erosion or other active landslide activity was observed at the time of our site visit. No areas of landslide deposits or mass wasting are noted on the referenced map within the immediate vicinity of the site. CRITICAL AREAS RECOMMENDATIONS Based on the results of our data review, site reconnaissance, and our experience in the area, It is our opinion that neither a landslide hazard, nor coal mine area exists on or within the vicinity of the site. SignatureHomes.MorrisAve.RGA(1).docx November 20, 2017 page 13 Geologically Hazardous Areas per City of Renton Municipal Code (RMC 4-3.050) Lands to Which These Regulations Apply and Non-regulated Lands: The following critical areas are regulated by this Section. Multiple development standards may applyto a site feature based upon overlapping critical area(s) and/or critical area classifications: a. Flood hazard areas. b. Steep slopes (must have a minimum vertical rise of fifteen feet (15)), landslide hazards, erosion hazards, seismic hazards, and/or coal mine hazards or on sites within fifty feet (50') of steep slopes, landslide hazards, erosion hazards, seismic hazards, and/or coal mine hazards classified under RMC 4-3-050G5a which are located on abutting or adjacent sites. The review comments by the City of Renton on our previous Stormwater Feasibility Letter dated January 15, 2016 and revised on March 31, 2017, indicate that the site is mapped to be within 50 feet of a steep slope and coal mine hazard areas. Based on our previous April 12 and 13 site visits, and our more recent November 17, 2017 site visit, and review of published geological literature, we offer the following comments relating to steep slopes and coal mine hazards. The City classifies steep slopes per RMC 4.3.050.G,5.a as either a sensitive slope or a protected slope per the following definitions: Sensitive Slopes: A hillside, or portion thereof, characterized by; (a) an average slope of twenty five percent (25%) to less than forty percent (40%) as Identified in the City of Renton Steep Slope Atlas or in a method approved by the City; or (b) an average slope of forty percent (40%) or greater with a vertical rise of less than fifteen feet (15') as identified In the City of Renton Steep Slope Atlas or in a method approved by the City; (c) abutting an average slope of twenty five percent (25%) to forty percent (40%) as identified in the City of Renton Steep Slope Atlas or In a method approved by the City. This definition excludes engineered retaining walls. Protected Slopes: A hillside, or portion thereof, characterized by an average slope of forty percent (40%) or greater grade and having a minimum vertical rise of fifteen feet (151) as Identified In the City of Renton Steep Slope Atlas or in a method approved by the City. The subject site is located on top of the south Renton glacial upland area, with the regional topography generally sloping down to the north, west, and south. Slopes around the subject site generally range from about 4 to 5 percent. According to King County IMap, there is a slope of about 30 to 33 percent that is to the northwest of the site, but this slope is actually a retaining wall on the adjacent parcel that has an exposed height of about 6 to 8 feet. We have assumed this wall was permitted and properly engineered and Is therefore stable. Slopes between 25 to 30 percent with about 10 feet of relief occur along Davies Avenue South, more than 250 feet west of the subject site. The steep slope down to the Green River valley is more than 500 feet from the site. In our opinion, there are some Isolated sensitive slopes west of the subject property, but these slopes have apparently been stabilized by retaining walls. Given the mapped soil types and developed nature of the area, the impacts to and from these slopes will be minimal. GEORESOURCES SlgnatureHomes.MorrisAve.RGA(1).docx November 20, 2017 page 14 The City classifies coal mine hazard areas per RMC 4-3.050.G,5.e as either a low, medium, or high hazard per the following definitions: • Low Coal Mine Hazards (CL): Areas with no known mine workings and no predicted subsidence. While no mines are known in these areas, undocumented mining is known to have occurred. • Medium Coal Mine Hazards (CM): Areas where mine workings are deeper than two hundred feet (200') for steeply dipping seams, or deeper than fifteen (15) times the thickness of the seam or workings for gently dipping seams. These areas may be affected by subsidence. • High Coal Mine Hazard (CH): Areas with abandoned and improperly sealed mine openings and areas underlain by mine workings shallower than two hundred feet (200') in depth for steeply dipping seams, or shallower than fifteen (15) times the thickness of the seam or workings for gently dipping seams. These areas may be affected by collapse or other subsidence. According to the Washington State DNR OFR 94-7, the site Is located north of the Sunbeam and Patton coal mines as shown on Plate K-33. The site is also located west of the Renton coal mine as shown on Plate K-32. A map showing the location and approximate lateral extent of the mines created from the Washington State Department of Natural Resources Geological information Portal is attached as Figure 3. Copies of the K-32 and K33 coal mine maps are attached as Figures 4 and 5. It appears that the Patton coal mine workings are located within the NE quarter of the SE quarter of Section 19, and the Sunbeam Mine is located within the SW quarter of the SE quarter of Section 19. Based on the DNR GIS maps, it appears that the actual project Is more than 200 feet north of mine area. Furthermore, based on the coal mine maps, it appears that workings were likely more than 200 feet below grades. It is our opinion that the risk from coal mine related subsidence is minimal, and the site should be classified as CL. The risk for subsidence at the subject site is no greater than the adjacent properties, which are currently developed. LIMITATIONS We have prepared this report for use by Signature Custom Homes and other members of the design team, for use in the design of a portion of this project. The data used in preparing this report and this report should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on our observations of subsurface conditions, data from others and limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions. GEORESOURCES SlgnatureHomes.MorrisAVe.RGA(1).docx November 20, 2017 page 15 We have appreciated the opportunity to be of service to you on this project. If you have any questions or comments, please do not hesitate to call at your earliest convenience. Respectfully submitted, GeoResources, LLC Kyle E. Billingsley, EIT Engineering Staff /I I KEITH SCOTT SCHEMB91 Keith S. Schembs, LEG Principal KEB:KSS:DCB/kss/ Doc to: SlgnatureHomes.MorrisAve.RGA(1) Attachments: Figure 1: Site Location Map Figure 2: Site Vicinity Map Figure 3: USGS Geologic Map Figure 4: K-32 Coal Mine Map Figure 5: K-33 Coal Mine Map Dana C. Biggerstaff, PE Senior Engineer GEORESOURCES .3. [1 0 �1•gL� w 1r.T w r- _ rY � c �a 0. S 17th It a "� 9 4 v. it II V. rc �� ti. 5:@( 191.; ti: .`• 19ni 91 0 26th °t Cs:r + 2CAI Approximate Site Locations (Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/) i s Not to Scale GeoResources, LLC Site Location Map 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 1715 Morris Ave S Phone: 253.896-1011 Renton, Washington Fax: 253-896-2633 Doc ID: SignalureCustomHomes.MOniSAVe.F November 2017 Figure 1 6 —T— N JJJ i a, r � 61419 61621 � b � T C 6 1418 �•1 61615 61614, 61615 61416 41625 61624 b 61425 I b i ' bI41 i i 611011 , 1421 Q) 61)03 4 N Z 1)05 l i i S k�( 6 ]04 1 VOS 6506 1x1111 v 6170Y� , 6 06 } n1e -n 6 6712 b17ll 1 i 1714 yi 33 Y WSl) 0/ yv66071 661i� 6619 - 1 —02 0� 61715 �� — ?23 P 171i� ) '17221�7t0 61)16 '� { d1719I 1 �iF 111 6Ins 61 , [ \ t l.'S I v 6gssi iii d2 1726 ,( 716' bvz7 �1= 6sxo 1 ll t b61 i [_ i 2fIna! ITJS i i t'_4iea ` i paot, '\1nii i 'i 6isosi �� 6rs`47 a Sismi , 805 1808. �4 4 �so3 ,� • X 1Ri, , �l OS 603 0Si) 5'-- 6 0 60 1 1� i%1 4 1 61811 f i 6160 �61E12 1�i 61413 isle I lan� _ 819 � 1 11 v'„ 1-- V-� e b l)} {'� t,�f', r ��6ie24 eisni �en� ( t 652 19 61 �i '�I1Cn St I t- i[ 001�f 013 .3� 6325 ( 901 61?04 1 6419 ,i 6425 65°I1 1 soJ b 1. �u —i Approximate Site Locations (Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/) ncl�v: Not to Scale GeoResources, LLC Site Vicinity Map 5007 Pacific Highway East, Suite 16 Proposed Single Family Residence Fife, Washington 98424 1715 Morris Ave S Phone: 253-896-1011 Renton, Washington Fax: 253.896-2633 Doc ID:SignalureCustomHomes.MorrisAVe.F November 2017 Figure 2 I� ■ c Q Jtk LI TMPo +� SI i - J Approximate Site Location Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965) K33 Sunbeam Mine Patton Mine Renton Coal Co. 577tl,St S Sah t Renton Coal Co. K31 Renton Mine Seattle Elec. Co. all,st 1 (1 t rp\45' 4v�� r 9t i`t 5VI iC 1I !.\iAPi - pritllb5\ _. st!»vi�sv A r. syst sti 151h I L vii t. ii t �S 7811 ft, C Sf t� 5W 19N t t � 1 ±E 21 ISt SL :)n:f PI I� ■ c Q Jtk LI TMPo +� SI i - J Approximate Site Location Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965) GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253.896-1011 Fax: 253-896-2633 to USGS Geologic Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington Doc ID: SignatureCuslomHomes.MorrisAVe.F November 2017 Figure 3 1 K33 Sunbeam Mine Patton Mine Renton Coal Co. Renton Mine K32 Renton Coal Co. K31 Renton Mine Seattle Elec. Co. GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253.896-1011 Fax: 253-896-2633 to USGS Geologic Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington Doc ID: SignatureCuslomHomes.MorrisAVe.F November 2017 Figure 3 1 is Approximate Site Location (Map From Washington state department of natural resources geologic Information portal -coal mine hazard maps https://geologyportal.dnr.wa.gov/#coag GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 K-32 Coal Mine Map Proposed Residential Development 1715 Morris Ave S Renton, WA i Approximate Site Location (Map From Washington state department of natural resources geologic information portal -coal mine hazard maps https://geologyportal.dnr.wa.gov/#coag GeoResources, LLC 5007 Pacific Highway East, Suite 16 .Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 K-33 Coal Mine Map Proposed Residential Development 1715 Morris Ave S Renton, WA