7301 HARDESON RD 2019-01-11 - Laserfiche WebLink

f • Cadman,Inc. : August 31,2018 Page 2 During the winter of 2017-2018, the Hardeson Pond was partially constructed and used as a temporary stormwater runoff storage pond during construction of the Fed Ex Distribution Facility. As part of permit requirements, prior to final approval of the constructed infiltration pond,the City of Everett required that the infiltration rate be verified by a full-scale infiltration test,a minimum of two representative PIT tests,or another test method acceptable to the City. In addition, a minimum of one sieve analysis was required on the eastern portion of the pond to verify soil conditions. In accordance with the City permit requirements, we completed two PITs and obtained samples for sieve analyses within the Hardeson Pond on August 16, 2018. VERIFICATION PITS The verification pilot infiltration tests, PIT-2 and PIT-3 were completed on August 16, 2018. PIT-2 was excavated to a final depth of 4 feet and PIT-3 was excavated to a final depth of 6 feet.The locations of PIT-2 and PIT-3 are shown on Figure 2. Logs of the test pits are included in Attachment A. The test pits were excavated to perform small-scale PITs to verify the design infiltration rate for the Hardeson Pond. LAB TESTING Soil samples were collected from test pits PIT-2 and PIT-3,taken to our laboratory,and reviewed to confirm or modify field classifications, as well as to evaluate engineering properties of the soil. Representative samples were selected for sieve analyses.The results of these tests are summarized on the test pit logs at the depths at which the samples were obtained. Laboratory test results are presented in Attachment A. SUBSURFACE CONDITIONS General subsurface conditions at the site were evaluated with explorations completed as part of our August 10, 2017 geotechnical report.The soils observed in the previous explorations(PIT-1 and boring H-B-1) generally consisted of fill and advance outwash.The locations of PIT-1 and H-B-1 are shown on Figures 1 and 2 and the exploration logs are included in Attachment A for reference. Fill was encountered within the Hardeson Pond to a depth of 10 feet as observed in H-B-1.Several feet of fill had been stripped from the site at the time PIT-1 was excavated,therefore the fill was only about 31/2 feet thick in PIT-1. The fill is typically in a loose condition and generally consists of gray and brown silty fine to medium sand with trace amounts of gravel and organic matter. Soils encountered below the fill consist of native Advance Outwash composed of dense to very dense fine to medium sand with silt grading to clean fine to medium sand. The soils encountered in test pits PIT-2 and PIT-3 were consistent with the soils observed in our previous explorations, however, fill was not encountered in PIT-2 and the advance outwash was more granular than observed at PIT-1 and PIT-3(i.e.,contained primarily fine to coarse gravel with sand). GROUNDWATER Groundwater data collected from monitoring well H-B-1 between May 2014 and July 2017 indicates that the groundwater level varied between Elevations 357.1 and 358.6 feet during the 40-month monitoring period. We understand the base of the proposed Hardeson Pond infiltration facility will be Elevation 427.0 feet,which provides a vertical separation of about 69 feet above the seasonal-high water level measured in H-B-1. GEOENGINEERSI File No.7087-026-02