HDR Engineering Inc. 10/6/2022 - Laserfiche WebLink

Exhibit A 7. Conduct eight (8) geotechnical borings with a truck/trailer-mounted drill rig equipped with a hollow-stem auger. Two borings for the new drainage pipes will be drilled to a depth of 20 feet below ground surface (bgs). Six borings for the proposed stormwater treatment facility, proposed casing under BNSF railroad, and outfall structure will be drilled to depths ranging from 40 to 50 feet bgs. 8. Install one groundwater monitoring well in one of the borings. Install a data logging transducer in the monitoring well to record seasonal water levels and monitor groundwater fluctuations over time. The transducer will be set to take groundwater elevation readings every half hour to hour and will be conducted for one year to include at least one wet season per the requirements of Director's Rule 21-2015, DWW-200. As part of this scope, HWA will conduct two site visits to download groundwater data from the transducer. The water level information collected will be used during the second phase of the project to assist in developing recommendations for possible dewatering and construction impacts. 9. Standard Penetration Test (SPT) samples will be taken at 2.5-to 5-foot intervals throughout each boring. If suspect soils or groundwater are encountered in the boring where the permanent groundwater monitoring is installed, the drillers will develop the well after construction of the well has been completed. All borings will be monitored and logged under full-time observation of a representative of the geotechnical engineer. The borings will be drilled by a licensed geotechnical/well driller under subcontract to the geotechnical engineer. 10. Generate boring logs and perform laboratory testing of select samples from the borings. Testing may include moisture content, grain-size distribution, direct shear, consolidation, and Atterberg limits. Soil and laboratory test information will be presented in summary boring logs that will be generated upon completion of our exploration program. 11. During drilling of the geotechnical borings, screen soils for organic vapors by headspace analysis using a photoionization detector (PID) a water sheen test, and visual and olfactory methods (i.e., stained or discolored soils and/or adverse odors). If field indications of contamination are detected, collect at least one soil sample from each suspect contaminated boring location. Groundwater samples would also be collected from suspect contaminated boring locations via temporary wells installed during drilling activities. Soil and groundwater samples will be collected following HWA and regulatory agency standard operating procedures. 12. If suspect contaminated soil and groundwater samples are collected, the samples collected will be submitted to a Washington State Department of Ecology (Ecology)-accredited, third- party analytical laboratory (OnSite Environmental of Redmond, Washington). For each suspect boring, the soil samples with the highest level of organic vapors and/or most discernible visual/olfactory contamination will be selected for chemical analysis. Field staff will deliver samples to the analytical laboratory within 48 hours of sampling. We will employ full chain-of-custody procedures to allow tracking and handling of the samples. HWA will select one soil sample and one groundwater sample (if encountered) per suspect boring (maximum of six soil samples and six groundwater samples) for chemical laboratory analysis of the following: • Petroleum hydrocarbons—gasoline via Ecology test method NWTPH-Gx, • Petroleum hydrocarbons—diesel, oil via Ecology test method NWTPH-Dx, • Benzene, toluene, ethylbenzene, and xylenes (BTEX) via Environmental Protection Agency (EPA) test method EPA 8260D, • Carcinogenic polycyclic aromatic hydrocarbons (cPAHs) via EPA test method EPA 8270E/SI M Lexington Avenue Storm Drainage Improvements Preliminary Design Scope of Services 8