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Home My WebLink AboutRS_Coal Mine Hazard Assessment_v2 Critical Area Report Geotechnical Engineering Services Preliminary Coal Mine Hazard Assessment Nguyen Property King County Parcel No. 162680-0010 10814 SE 173rd Street Renton, Washington August 28, 2019 ICE File No. 1350-001 Critical Area Report Geotechnical Engineering Services Preliminary Coal Mine Hazard Assessment Nguyen Property King County Parcel No. 162680-0010 10814 SE 173rd Street Renton, Washington August 28, 2019 ICE File No. 1350-001 Prepared For: Doan Nguyen Prepared By: Icicle Creek Engineers, Inc. 29335 NE 20th Street, Carnation, Washington 98014-9632  www.iciclecreekengineers.com  w 425.333.0093 August 28, 2019 Doan Nguyen 4064 South 146th Street Tukwila, Washington 98168 Critical Area Report Geotechnical Engineering Services Preliminary Coal Mine Hazard Assessment Nguyen Property King County Parcel No. 162680-0010 10814 SE 173rd Street Renton, Washington ICE File No. 1350-001 1.0 INTRODUCTION This Critical Area Report summarizes Icicle Creek Engineers’ (ICE’s) preliminary coal mine hazard assessment of a property located at 10814 SE 173rd Street in Renton, Washington (King County Parcel No. 162680-0010), referred to as the Nguyen Property in this report. The Nguyen Property is shown relative to nearby physical features on the Vicinity Map and Site Plan, Figures 1 and 2, respectively. Our services were completed in general accordance with our Confirming Agreement dated July 16, 2019 and were authorized in writing by Doan Nguyen, the property owner, on July 22, 2019. 2.0 PROJECT DESCRIPTION We understand that Mr. Nguyen plans to subdivide the parcel into two lots for future construction of single-family residences. We further understand that the City of Renton has identified the Nguyen Property area as an “Unclassified Coal Mine Hazard” (City of Renton Sensitive Areas Coal Mine Hazards map, dated November 12, 2014) and requires a Critical Area Report (Renton Municipal Code (RMC) 4-3- 050F a.v.). 3.0 SCOPE OF SERVICES The purpose of our services was to complete a preliminary assessment of the potential hazards associated with past underground coal mining in the area of, and including, the Nguyen Property. Specifically, our services included the following: • Review available historic coal mine records from the City of Renton, Washington State Department of Natural Resources (DNR) and our in-house technical library to evaluate the location of the mined- out areas, together with the depth of mining, thickness of zone mined and mining methods. • Mine mapping included superimposing the identified mines onto a property base map. We downloaded Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) data from the Washington DNR LiDAR Portal (King County 2016 acquisition) that was processed for topographic contours using Esri ArcGIS 10.6. This map was used to develop a geologic cross-section showing the location and depth of mined-out areas. • Surface reconnaissance mapping to identify mine openings such as adits or air shafts, together with stockpiles of mine rock fill or other areas in which the original ground surface has been altered. Doan Nguyen August 28, 2019 Page 2 I c i c l e C r e e k E n g i n e e r s 1350001/082819 • Classify the mine hazards as Low, Medium or High Coal Mine Hazards, according to RMC 4.3-050G. 5.e., as appropriate. • Evaluate the potential for regional subsidence in Medium and High Coal Mine Hazard areas (vertical ground subsidence, ground tilt and ground strain), if needed. • Develop mitigation for building design and construction, if needed. 4.0 COAL MINE HAZARD DESCRIPTION AND REGULATORY CONSIDERATIONS The principal physical hazards associated with abandoned coal mines include the following: • Sinkholes (High Coal Mine Hazards) • Regional ground subsidence (Medium Coal Mine Hazards) • Non-affected areas (Low Coal Mine Hazards) Coal Mine Hazards are defined by RMC 4-3-050G.5.e as follows: High Coal Mine Hazards – High Coal Mine Hazards are 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 for workings for gently dipping seams. These areas may be affected by collapse or other subsidence. Medium Coal Mine Hazards – Medium Coal Mine Hazards are 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. Low Coal Mine Hazards – Low Coal Mine Hazards are 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. In addition, RMC 4-3-050G.5.i provides the following regulatory considerations related to coal mine hazards: i. Mitigation – Additional Engineering Design and Remediation Specifications: After approval of the mitigation approach proposed as a result of RMC 4-3-050D, and prior to construction, the applicant shall complete engineering design drawings and specifications for remediation. Upon approval of the plans and specifications, the applicant shall complete the remediation. Hazard mitigation shall be performed by or under the direction of a licensed geotechnical engineer or engineering geologist. The applicant shall document the hazard mitigation by submitting as-builts and a remediation construction report. ii. Hazards Found during Construction: Any hazards found during any development activities shall be immediately reported to the Development Services Division. Any coal mine hazards shall be mitigated prior to recommencing construction based upon supplemental recommendations or reports by the applicant’s geotechnical professional. iii. Construction in Areas with Combustion: Construction shall not be permitted where surface or subsurface investigations indicate the possible presence of combustion in the underlying seam or seams, unless the impact is adequately mitigated in accordance with the recommendations of the applicant’s geotechnical professional. Other considerations include the possible presence of Mine Rock Fill and undocumented mining. Mine Rock Fill includes stockpiles of mining by-products consisting of broken rock and coal. Undocumented mining, typically as shallow prospects, are sometimes encountered in the vicinity of large-scale documented underground coal mining areas. Doan Nguyen August 28, 2019 Page 3 I c i c l e C r e e k E n g i n e e r s 1350001/082819 5.0 ABANDONED UNDERGROUND COAL MINE DESCRIPTION 5.1 GENERAL Past underground coal mining in the Nguyen Property area was evaluated by reviewing the following documents: • Morrison Knudsen, January 1985, “Engineering Investigation for the Renton, Washington Area,” U.S. Department of the Interior Office of Surface Mining, Abandoned Mine Lands Program. • DNR, undated, Table 11 – Summary of Coal Production in King County, Washington, by Mine and Year from 1888 through 1967. • DNR, Geologic Information Portal (https://www.dnr.wa.gov/geologyportal), Coal Mine Maps, Map K36_E (Mine Map, Springbrook Coal Mine, Renton, Wash., 1940). • US Geological Survey (USGS), Mullineaux, D.R., 1965, Geologic Map of the Renton Quadrangle, King County, Washington, Map GQ-405, scale 1:24,000. 5.2 ABANDONED UNDERGROUND COAL MINES The abandoned coal mine that underlies the Nguyen Property area is referred to as the “Springbrook Mine No. 3.” The Springbrook Mine No. 3 was operated in the 1930s through the 1950s and produced an estimated 286,000 tons of coal. Coal was extracted on an incline of about 57 degrees down to the south. Based on our review of the above-referenced historic mine documents and maps, the 1st and 2nd Levels of the Springbrook Mine No. 3 underlie the Nguyen Property as shown on the Abandoned Underground Coal Mine Map and Geologic Cross-Section A-A’, Figures 3 and 4, respectively. The mined-out workings of the 1st and 2nd Levels of the Springbrook Mine No. 3 are estimated at depths ranging from about 150 to 335 feet below the ground surface within the Nguyen Property as shown on Figure 4. Based on our review the Morrison Knudsen 1985 study, no surface features associated with the Springbrook Mine No. 3 were observed within 500 feet of the Nguyen Property. The original surface entries (main slope and air shaft) to the Springbrook Mine No. 3 are located about 900 feet east of the Nguyen Property. 6.0 SITE DESCRIPTION 6.1 GEOLOGIC SETTING The surficial geology in the area of the Nguyen Property has been mapped by the USGS (1965) as Glacial Till. Glacial Till (commonly referred to in this area as “hardpan”) consists of an unsorted mixture of silt, sand, gravel, cobbles and boulders. Glacial Till is generally dense to very dense as a result of being overridden by glacial ice. Based on our review of the geologic map and historic mine maps, the Glacial Till is underlain by Renton Formation bedrock. Renton Formation bedrock consists of non-marine sandstone and shale with coal seams with sedimentary bedding dipping about 57 degrees down to the south beneath the Nguyen Property and surrounding area. Based on nearby ICE projects where test borings were completed, the Glacial Till ranges from about 20- to 30-feet thick in the area of the Nguyen Property. Doan Nguyen August 28, 2019 Page 4 I c i c l e C r e e k E n g i n e e r s 1350001/082819 6.2 SURFACE CONDITIONS Our surface reconnaissance of the Nguyen Property was completed on August 1, 2019 by Jeff Schwartz, a Licensed Engineering Geologist/Hydrogeologist from ICE. The weather at the time of our site visit was clear with temperatures in the 80s. Based on our review of King County Tax Assessor records, the Nguyen Property Is rectangular in shape, occupies about 0.25 acres and is currently undeveloped. A single-family residence was demolished in 2009 within the Nguyen Property. The Nguyen Property is bordered to the south by SE 173rd Street, and to the north, east and west by developed residential properties. The Nguyen Property and surrounding area occupies a level to gently sloping area. The ground surface within the Nguyen Property gently slopes down to the south from about Elevation 416 feet at the north end of the property to about 412 feet at the south end of the property with a 3-foot-deep stormwater ditch bordering the south end of the property adjacent to SE 173rd Street. We observed the Nguyen Property to be vegetated predominately with very dense blackberry bushes, brush and young deciduous trees up to about 4 inches in diameter, with scattered mature deciduous trees along the perimeter of the property. We did not observe topographic depressions or other ground surface irregularities that may be associated with past mining activities. We did not observe any evidence of Mine Rock Fill, such as broken rock or coal fines, on the surface of the Nguyen Property. We reviewed the LiDAR hillshade image (King County iMap, https://gismaps.kingcounty.gov/iMap/ and the Washington DNR LiDAR Portal, http://lidarportal.dnr.wa.gov/) of the Nguyen Property area. No unusual surface features, such as sinkholes, were observed on the LiDAR images within or around the Nguyen Property. 7.0 ANALYSIS OF COAL MINE HAZARDS 7.1 HIGH COAL MINE HAZARDS High Coal Mine Hazard areas are underlain by abandoned underground coal mines at a depth of less than 200 feet and are associated with the risk of sinkhole formation. Based on our review of the historic mine maps, the mined-out workings of the 1st and 2nd Levels of the Springbrook Mine No. 3 underlie the property at depths ranging from about 150 feet to 335 feet as shown on Figure 4. As previously described, Glacial Till, which has the strength characteristics of unreinforced concrete, is expected to underlie the Nguyen Property area at a depth of about 20 to 30 feet. The presence of Glacial Till provides additional protection from sinkhole development. Also, on steeply inclined underground mines/coal seams (inclination of more than 35 degrees), roof caving is reduced because of lessor overburden pressure. When sinkholes do form over steeply inclined seams, the location is almost always over the upper limit of the mined-out area, which occurs to the north of the Nguyen Property. Based on our knowledge of the Nguyen Property and soil overburden/bedrock conditions in the area (likely 20 to 30 feet of Glacial Till underlies the property; Glacial Till is not susceptible to sinkhole formation), a 150-foot minimum depth should be used at this site rather than 200 feet because of the mitigating reasons described in the previous paragraph. Doan Nguyen August 28, 2019 Page 5 I c i c l e C r e e k E n g i n e e r s 1350001/082819 Based on our evaluation, no High Coal Mine Hazards occur within the Nguyen Property. 7.2 MEDIUM COAL MINE HAZARDS Medium Coal Mine Hazard Areas are areas where mine workings are deeper than 200 feet for steeply dipping seams and may be affected by subsidence. Regional ground subsidence occurs when the ground surface subsides over a large area and the underground mine workings collapse. Surface deflection is caused by plastic deformation of the strata overlying the mine as the roof sags into the mine. To evaluate regional ground subsidence, we used methods described in the Subsidence Engineers Handbook (1975) which provides for the estimation of vertical ground displacement, ground strain and ground tilt. Our analysis suggests that the vertical ground subsidence from the collapse of The Springbrook Mine No. 3 is about 0.5 to 2 inches for the Nguyen Property with ground tilt up to about 1:350 (damage threshold is 1:350) and a ground strain of about 0.0004 inches per inch (in/in - damage threshold is 0.003 in/in). Based on our evaluation and analysis the entire Nguyen Property is within a Medium Coal Mine Hazard area as shown on the Coal Mine Hazards Map, Figure 5. 7.3 LOW COAL MINE HAZARDS Low Coal Mine Hazards are areas with no known mine workings and no predicted subsidence. Based on our evaluation, no Low Coal Mine Hazards occur within the Nguyen Property. 7.4 MINE ROCK FILL We did not observe any evidence of Mine Rock Fill on the ground surface of the Nguyen Property. 7.5 UNDOCUMENTED MINING It is not likely that undocumented mining-related prospects and surface features exist within the Nguyen Property based on our review of available information and our site observations. 8.0 CONCLUSIONS Based on the results of this preliminary coal mine hazard assessment, our conclusions and recommendations regarding coal mine hazards at the Nguyen Property are as follows: • Based on our review of the historic mine maps, the mined-out workings of the 1st and 2nd Levels of the Springbrook Mine No. 3 are estimated at depths ranging from about 150 to 335 feet below the ground surface within the Nguyen Property. • Based on our mine mapping, the mined-out workings of the 1st and 2nd Levels of the Springbrook Mine No. 3 are deeper than 150 feet below the ground surface at the Nguyen Property. For this reason, no High Coal Mine Hazard areas exist within the Nguyen Property (as described in section 7.1 of this report). • Based on our mine mapping and analysis, the Nguyen Property is within a Medium Coal Mine Hazard area with regional ground subsidence ranging from about 0.5 to 2 inches across the property. Buildings and utilities should be allowed in these areas, but mitigation is required (as described in section 9.0 of this report) for the potential of regional ground subsidence. • No Low Coal Mine Hazard areas exist within the Nguyen Property. Doan Nguyen August 28, 2019 Page 6 I c i c l e C r e e k E n g i n e e r s 1350001/082819 • Undocumented mining is unlikely to have occurred within the Nguyen Property based on our information review and observations. However, if mining-related features such as excavated bedrock, coal spoils or a prospect opening or void are encountered during site development, ICE should be contacted immediately for further evaluation. • It is possible that an abandoned dry well, septic tank or dug water well, and/or Mine Rock Fill, may be encountered. We recommend that ICE be contacted immediately if unusual subsurface conditions (such as a void) or evidence of Mine Rock Fill are encountered. 9.0 MITIGATION Residential use within the Medium Coal Mine Hazard area should be allowed provided that the following mitigations for design and construction are implemented. • Use of rigid foundations (conventional reinforced concrete spread footings) supporting a flexible superstructure (wood-frame). • Small, square or nearly square-shaped building pads should be favored over large, irregularly-shaped building pads. • No brick or basement construction should be allowed. 10.0 USE OF THIS REPORT We have prepared this report for Doan Nguyen for use in the preliminary evaluation of coal mine hazards at the property subject to this study. Our report, conclusions and interpretations should not be construed as a warranty of subsurface conditions at this time. A contingency for unexpected conditions should be included in the budget and schedule. 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 warranties or other conditions, express or implied, should be understood. ******************** Doan Nguyen August 28, 2019 Page 7 I c i c l e C r e e k E n g i n e e r s 1350001/082819 We trust this report meets your present needs. Please call if you have any questions. Yours very truly, Icicle Creek Engineers, Inc. Jeffrey M. Schwartz, LEG, LHG Project Engineering Geologist/Hydrogeologist Brian R. Beaman, PE, LEG, LHG Principal Engineer/Geologist/Hydrogeologist Document ID: 1350001.REP Attachments: Vicinity Map – Figure 1 Site Plan – Figure 2 Abandoned Underground Coal Mine Map – Figure 3 Geologic Cross-Section A-A’ – Figure 4 Coal Mine Hazards Map – Figure 5 Submitted via email (pdf) and surface mail (one original copy) cc: Han Phan, PE, PBG (email) I c i c l e C r e e k E n g i n e e r s 1350001/082819 FIGURES ICE FILE NO. FigureCHECKED: BRB DRAWN: JMS DESIGNED: --- SCALE: As Shown 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 1350-001 1DATE: 08/28/19 VICINITY MAP Approximate Scale in Miles 0 ⁄1 Base map obtained from King County iMap ()https://gismaps.kingcounty.gov/iMap/ King County Parcel No. 162680-0010 PRELIMINARY COAL MINE HAZARD ASSESSMENT KING COUNTY PARCEL NO. 162680-0010, RENTON, WASHINGTON Lake Washington RENTON ICE FILE NO. FigureCHECKED: BRB DRAWN: JMS DESIGNED: --- DATE: 08/28/19 SCALE: As Shown 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 1350-001 PRELIMINARY COAL MINE HAZARD ASSESSMENT KING COUNTY PARCEL NO. 162680-0010, RENTON, WASHINGTON SITE PLAN 2 Nguyen Property King County Parcel No. 162680-0010 Approximate Scale in Feet 0 50 100 Base map prepared using Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) data (King County 2016 acquisition) obtained from the Washington State Department of Natural Resources (DNR) LiDAR Portal () http://lidarportal.dnr.wa.gov and processed for 2-foot topographic contours using Esri ArcGIS Desktop 10.6 SE 173rd Street 108th Avenue SE ICE FILE NO. FigureCHECKED: BRB DRAWN: JMS DESIGNED: --- DATE: 08/28/19 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 1350-001 PRELIMINARY COAL MINE HAZARD ASSESSMENT KING COUNTY PARCEL NO. 162680-0010, RENTON, WASHINGTON SCALE: As Shown Approximate Scale in Feet 0 50 100 EXPLANATION Location of Geologic Cross-Section (see Figure 4) A A’ ABANDONED UNDERGROUND COAL MINE MAP Nguyen Property (King County Parcel No. 162680-0010) NOTES: 1) Base map prepared using Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) data (King County 2016 acquisition) obtained from the Washington State Department of Natural Resources (DNR) LiDAR Portal (http://lidarportal.dnr.wa.gov) and processed by ICE for 2-foot topographic contours using Esri ArcGIS Desktop 10.6. 2) Historic underground coal mine map from ICE in-house map collection. Springbrook Mine No. 3 3 A’ A nd2 L e vel of the Sprin g b r o o k M i n e N o . 3 (mined out) st1 Level of th e S p r i n g b r ook Mine N o . 3(mined out ) ICE FILE NO. FigureCHECKED: BRB DRAWN: JMS DESIGNED: --- SCALE: As Shown 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 1350-001GEOLOGIC CROSS-SECTION A-A’ 4 PRELIMINARY COAL MINE HAZARD ASSESSMENT KING COUNTY PARCEL NO. 162680-0010, RENTON, WASHINGTON DATE: 08/28/19 A (north) A' (south) 500 500 0 100Elevation in Feet400 300 200 100 Elevation in Feet0 400 300 200 100 0 200 ~335 feet ~150 feet Nguyen Property (King County Parcel No. 162680-0010) Medium Coal Mine Hazard -100 Glacial Till Renton Formation Bedrock Renton Formation Bedrock Note: See Figure 3 for the location of Geologic Cross-Section A=A’ Approximate Scale in Feet Horizontal Scale = Vertical Scale Sp r in gb roo k M in e No . 3 s t1 Le v el, m ined -ou t nd2 L e ve l , m in ed -ou tunmin ed co a l unmin ed co a l unmin ed co a l -100 ?? ICE FILE NO. FigureCHECKED: BRB DRAWN: JMS DESIGNED: --- DATE: 08/28/19 SCALE: As Shown 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 1350-001 PRELIMINARY COAL MINE HAZARD ASSESSMENT KING COUNTY PARCEL NO. 162680-0010, RENTON, WASHINGTON EXPLANATION COAL MINE HAZARDS MAP 5 Nguyen Property (King County Parcel No. 162680-0010) Approximate Scale in Feet 0 50 100 Base map prepared using Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) data (King County 2016 acquisition) obtained from the Washington State Department of Natural Resources (DNR) LiDAR Portal () and processed for 2-foot contours http://lidarportal.dnr.wa.gov using Esri ArcGIS Desktop 10.6 SE 173rd Street 108th Avenue SEMedium Coal Mine Hazard Area (see report text for details)