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Hydrogeologic Report 2GEOENGINEER~ EMAIL TRANSMITTAL www.geoengineers.com 1550 Woodridge Drive Southeast. Port Orchard. Washington 98366 TELEPHONE. (360) 769-8400. FAX: (360) 769-8700 To: Jack Long Date: 5/10/2007 Pacific Frontier. LLC 1 1 1 nth Street NE File: 15854-001-01 Auburn. Washineton 9800? Email Address: jacklong pacificfrontierllc.com Regarding: Crystal Springs Project in Yelm, Washineton Date Description 09 ?007 Letter Remarks: Please call if you have questions. Copy To: Jeff McInnis Petra EnQineerino jeff~~petraene.net Grant Beck, Community Development Director Citti of Yelm erantb~ci.yelm.wa.us '~/~~ Signed: j Joel ~V Purdy ~~ j purdy~eeoeneineers.com DISCLAIMER: This document and any attachments are confidential and intended solely for the use of the individual or entity to whom they are addressed. Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. GEOENGINEERS~ May 9, 2007 Pacific Frontier, LLC 111 5th Street Northeast Auburn, Washington 98002 Attention: Jack Long Subject: Letter Response to Mitigated Determination of Non Significance Comments Crystal Springs Project Yelm, Washington File No. 15854-001-01 INTRODUCTION ~~ ~~ F /// This letter presents our response to a City of Yelm comment in the Mitigated Determination of Non Significance (MDNS) dated March 27, 2007 regarding the hydrogeologic assessment conducted by GeoEngineers, Inc. (GeoEngineers) related to the subject project in Yelm, Washington. In the hydrogeologic assessment, dated February 19, 2007, we evaluated the hydrogeologic characteristics of the site. Our evaluation was in response to a January 18, 2007 letter from the City of Yelm to Petra Engineering, LLC requesting a hydrogeologic report pertaining to potential high groundwater flood hazard areas (City of Yelm Code Chapter 14.08.120.G) on or near the site. Crystal Springs is a Planned Residential Development (PRD) of 4.15 acres located within a portion of Section 19, Township 17 North, Range 2 East, W. M. in Thurston County. The proposed development will include approximately 29 new single-family residential lots. The development will also include paved roadways, water and sanitary sewer mains, miscellaneous utilities, stormwater conveyance and detention systems. No infiltration facilities are proposed for the site. Stormwater will be collected and routed to a detention pond located in the eastern portion of the site. Septic effluent will be piped to the City of Yelm's sewer system. A significant amount of fill will be placed to level the site and raise the overall elevation of the ground surface. SCOPE OF SERVICES The intent of our letter is to provide a response to a City of Yelm comment. Specifically, we are responding to the MDNS Mitigation Measures comment #3: 3. The applicant shall provide illustration in the form of a written report demonstrating that the requested modifications proposed in the Hydrogeological Assessment addressing the high ground water flood hazard areas will not direct the high ground water in a way which could potentially have an adverse affect (sic) to neighboring properties. Earth Science+Technotogy 1550 Woodridge Or SE telephone 360.769.8400 Port Orchard, WA 98366 racsimiie 360.769.8700 website www.geoengineers.com Pacific Frontier, LLC May 9, 2007 Page 2 RESPONSE The stormwater captured within the Crystal Springs project will be routed to a detention pond on the eastern portion of the site with a discharge at Elevation 330 feet (100-year floodplain elevation). The groundwater flow gradient beneath the pond is from southwest to northeast toward Yelm Creek. If infiltration occurs, our evaluation indicates the groundwater gradient will direct the flow toward Yelm Creek. The stormwater infiltration, should any occur, could result in a localized mounding of groundwater beneath the pond which is within the 100-year floodplain. Because our evaluation indicates that the existing structures on the adjacent properties to the southeast, south and west are upgradient from the detention pond, it is our opinion the mounding will not be adversely affected by potential groundwater mounding from stormwater infiltration. Discharge from the detention pond and groundwater infiltration, if it occurs, would be to Yelm Creek and not toward adjacent properties. CONCLUSION It is our opinion that the stormwater facilities at the site will not direct groundwater in a way that will have an adverse effect to neighboring properties because of two main reasons: 1) our evaluation indicates the stormwater pond is located downgradient of the neighboring properties, and 2) the natural groundwater flow gradient will therefore direct any infiltrated stormwater toward Yelm Creek. LIMITATIONS We have prepared this letter for the exclusive use of the Pacific Frontier, LLC and their authorized agents for the Hydrogeologic Assessment for the Crystal Springs project in Yelm, Washington. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood. File No. 15854-001-01 ~iE~EN'GINEERS~ Pacific Frontier, LLC May 9, 2007 Page 3 Thank you for providing this opportunity for GeoEngineers to be of service. If you have any questions regarding this letter, please contact our office at (360) 769-8400. Sincerely, GeoEngineers, Inc. `'`-' i.~-'4- oel W. Purdy, LG, LH Senior Hydrogeologist ©~ W as~y~~ ~'~~~ fo ~ ~ HydrngeDtagi~S V ~~` r'~ _ r~ 588 , ~~ ; ~I/JI I f C ~ - ~ r --•, ~~ Garry .Squires, , LG, LEG - J EL PU DY Principal JWP:GHS:jI ORCH\ 15\ 15854001\01\Finals\ 1585400101 L2.doc Two copies submitted cc: Jeff McInnis, P.E. Petra Engineering, LLC 535 Dock Street, Suite 213 Tacoma, Washington Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, teat, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. File No. 15854-001-01 ~iEDENGINEERS~