3313 OAKES AVE 2020-07-14 - Laserfiche WebLink

GeoTest Services, Inc. December 9,2016 3313 Oakes Avenue, Everett,WA Job No. 16-0659 Stormwater Pollutant Treatment If LID facilities will be considered for this development, the infiltration facilities on-site may require some form of pollutant pre-treatment or treatment with an amended soil prior to onsite infiltration or offsite discharge. Cation exchange capacities and organic contents of site topsoil and shallow subsurface soils were determined to establish their pollutant treatment suitability. Cation Exchange Capacity and Organic Content Testing Two composite samples were collected during our subsurface explorations for pollutant treatment purposes. Cation exchange capacity (CEC) and organic content (LOI) tests were performed by Northwest Agricultural Consultants. Laboratory test results are presented in Table 2. TABLE 2 CEC& Organic Content Laboratory Test Results Test Pit Sample Cation Exchange Capacity Number Depth (ft) (meq/100 grams) Organic Content (%) TP-2 0.5 12.0 3.6 TP-5 1.0 3.7 1.5 Based on the results listed in Table 2, the fine-grained, near-surface topsoil encountered in TP-2 appears to be suitable for onsite pollutant treatment purposes based on Section 9.3, "Soil Requirements for Infiltration Treatment Facilities", stated in Chapter 3 of the 2010 Everett Stormwater Management Manual. This section also states that cation exchange capacity must be greater than or equal to 5.0 meq/100 grams for treatment purposes. Thus, the fine-grained, near-surface soils would also appear to be suitable for this purpose. It should be noted, however, that the fine grained topsoil is likely to have low infiltration rates due to the elevated fines contents. As such, it is our opinion that native soils are suitable for providing treatment, but are unlikely to provide adequate infiltration of stormwater. GTS recommends that an off-site, imported treatment soil be utilized for this project. Geotechnical Consultation and Construction Monitoring GeoTest Services recommends that we be involved in the project design review process. The purpose of the review is to verify that the recommendations presented in this report have been properly interpreted and incorporated in the design and specifications. We recommend that geotechnical construction monitoring services be provided. These services should include observation by GeoTest personnel during fill placement/compaction activities and subgrade preparation operations to verify that design subgrade conditions are obtained beneath the proposed building(s). We also recommend that periodic field density testing be performed to verify that the appropriate degree of compaction is obtained. The purpose of these services would be to observe compliance with the design concepts, specifications, and recommendations of this Page 15 of 17