First, each of the seven causes above are considered for all equipment in the capture acidity, including rare or abnormal occurrences. This process produces a list of equipment that is considered to have potential for overpressure along with the cause(s) for that equipment. Next, the relief needs for each cause for an equipment are evaluated to determine the case with the highest flow rate required to relieve pressure. Then a PSV will be sized and incorporated into the system to prevent a hazardous situation where necessary. Finally, the original list is reviewed to make sure the PSV's added to the system can safely relieve all of the potential causes identified in the first step.

Civil Engineering

Geologic and Soil Load Assessment

Geotechnical Investigation

Hanson Engineering Group Inc. (Hanson) performed geotechnical investigation of the site. The results of the investigation are contained in the final geotechnical report dated June 2021. Hanson’s geotechnical investigation included drilling 26 exploratory borings and installing three groundwater level monitoring wells. Bedrock was cored at selected boring locations. In addition, data from previous geotechnical investigations performed by MACTEC, Inc at the facility were reviewed.

Subsurface Conditions

Soil – Three general soil types were encountered at the boring locations: specifically, from ground surface downward, topsoil, loess, and glacial till. Topsoil was generally one foot thick. The loess encountered extends to depths of 10 to 15 feet below ground surface and is typically composed stiff silty clay. Glacial till present beneath loess is typically composed of very stiff silty clay and continues to bedrock encountered at depths ranging between 38 and 48 feet at the boring locations.

Bedrock – Bedrock encountered at the boring locations consists of silty and clayey shale. The water content of shale was typically less than 10 percent. Reported unconfined compressive strengths of the shale were low but we believe this is due to poor sample quality.

Groundwater – Groundwater levels reported in the borings ranged between 5 and 35 feet below ground surface. Groundwater levels in the three groundwater level monitoring wells were measured approximately

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monthly from April 16 to June 16, 2021, and ranged between 3 and 10 feet below ground surface (elevation 456.7 to 460.6). The Hanson report recommends that a groundwater level of three feet below existing ground surface be used for final design.

The Hanson report contains capacity versus depth plots for pipe pile, H-pile, auger cast-in-place pile (ACIPs) and drilled shafts, and states that rigid inclusions are a technically viable ground improvement technique for the project. Rigid inclusions can be considered where the combination of the sustained pressure on the foundation and friction coefficient along the base of the foundation are adequate to resist lateral forces. Rigid inclusions can be designed using the Hanson charts for ACIPs.

Frost Protection

The geotechnical report states the minimum foundation embedment for frost protection is 30 inches. Use of a non-frost susceptible fill (a granular material having six percent or less fines) is acceptable if the material can be drained either through granular backfill placed for utilities or in drains specifically constructed to drain the non-frost fill. A two-inch-thick layer of insulation is an acceptable alternative to non-frost fill. The insulation layer must be underlain by a six-inch-thick (min.) layer of non-frost fill that drains. A mud mat can be poured on top of the non-frost fill or insulation at the contractor’s discretion.

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