City of Houston/HPW/Water Line Replacement
The project involved the replacement of approximately 101,000 feet of water line, ranging from 6 inches in diameter to 12 inches in diameter, in the midtown area of Houston. As part of the scope of work, performed Phase I Environmental Site Assessment (ESA) and a combined geotechnical and limited Phase II ESA in accordance with the ASTM International E1527-13 standard, as modified by the City of Houston Department of Public Works and Engineering, Infrastructure Design Manual Chapter 11.
Phase I ESA: Performed project alignment reconnaissance, review of the available federal and state environmental databases, review of available historical aerial photographs, historical city directories, topographic maps, local soil, geology, flood plain information, and other public records, interviews with the present occupants around the project alignment, and our conclusions and recommendations regarding the potential for environmental concerns along the project alignment and the need for further investigation. The purpose of this assessment was to identify the presence or absence of any recognized environmental conditions (RECs) that may pose an environmental risk to the health and well-being of the construction workers and to determine the need for additional investigation and/or testing of soil and groundwater for waste management purposes. The Phase I ESA scope was completed in four (4) separate reports. Each report covered four (4) to five (5) miles of the alignment. A total of 24 RECs were identified along the project alignment. The RECs included former gasoline stations with leaking petroleum storage tanks, and former dry-cleaning and light manufacturing facilities. A limited Phase II ESA was recommended at RECs to determine potential impacts related to the RECs on the soil and groundwater in the areas of the project alignment.
Combined Geotechnical and Phase II ESA: The scope of work included the preparation of a project work plan, with a health and safety plan, subsurface utility clearance, permitting, lane closure and traffic control, field mobilization, concrete coring, drilling, sample classification & collection for geotechnical and environmental purposes, laboratory analysis and report preparation. To optimize the investigation budget, schedule, and resources; a combined geotechnical and environmental investigation was completed for the project. The geotechnical investigation was required to determine the subsurface soil and groundwater conditions present along the project alignment and to guide the water line trench construction activities including, open trench excavation and dewatering.
Based on the RECs, 70 predetermined geotechnical soil boring locations were adjusted to coincide with the environmental sampling locations. The field engineer performed field screening, soil classification and sample identification of potentially contaminated soils for laboratory analysis; evaluated soil properties and chemical data for providing recommendations in the report. TCEQ’s Texas Risk Reduction Program regulations were applied for waste characterization and to determine appropriate action for remediation. The geotechnical report recommendations included excavation protection for shallow trenches and minimum and maximum sloping, shoring, and/or bracing for trenches deeper than 5 feet (up to 20 feet below). Depending on the soil and groundwater conditions, excavation bottom support and dewatering were recommended along the project alignment.