Regional Wastewater Collection System Ventilation Dynamics Investigation

Ferris, Texas

PECI personnel, serving as a subconsultant to a partnered firm, performed a month-long field investigation of gravity sewer ventilation dynamics in parallel 39 and 54-inch interceptors serving multiple customer cities. Headspace H2S, pressure/vacuum levels, and other parameters were measured both with and without the influence of mechanical ventilation. It was shown that mechanical ventilation can produce a vacuum in a sewer headspace over a mile upstream from the pull point, and for a significant distance downstream as well. Headspace H2S Concentrations were reduced 50 to 75% under continuous ventilation, contributing to corrosion management.

Regional Collection System Odor Evaluation

Garland and Rowlett, Texas

PECI personnel assessed the source and potential solutions for collection system odors in one of the City of Garland’s wholesale customer’s collection systems. Odor complaints were being attributed to Garland’s treatment plant, but dispersion modeling showed that plant odors were unlikely to be perceived in the City of Rowlett’s neighborhoods.   An investigation revealed pressurized headspace situations, particularly upstream of a major inverted siphon. Chemical treatment and evacuation of the headspace were considered. Improvements are under consideration by both Cities. Our personnel recently updated the comprehensive odor dispersion model for Garland’s 24 MGD Rowlett Creek Treatment Plant.

Regional Wastewater System – Corrosion Management Plan

Tarrant and Denton Counties – Multiple Cities

PECI personnel, along with several other firms, completed a system-wide corrosion management plan for this regional wastewater system serving nine cities in northwest Tarrant and Denton counties. Work involved pole camera inspections of approximately 100 underground structures followed by manned entries and detailed inspection of over a dozen structures warranting closer inspection. The plan will ultimately prioritize numerous projects for both capital and O&M funding, and will develop recommendations for systematic future inspection of pipelines, HVAC equipment, metering facilities, manholes, and other facilities.

Collection System Odor Abatement Evaluation

The Woodlands, Texas

Perkins Engineering Consultants, Inc., personnel have performed testing of collection system headspace air quality and pressures to resolve odor complaints in neighborhoods along two major regional system interceptors. Smoke and pressure testing revealed that headspace pressurization is occurring in gravity interceptors due to surcharging over a mile downstream from the points where complaints are occurring. Field testing has been performed to identify mechanical ventilation rates for developing a headspace vacuum upstream in the affected neighborhood using a fan located downstream near the client’s treatment plant.

Odor Abatement Master Plan

Grapevine, Texas

Perkins Engineering Consultants, Inc. served as a subconsultant to Brown and Gay Engineers, playing a lead role in assessing and prioritizing odor sources at the city of Grapevine’s wastewater treatment plant. The city commissioned this evaluation as a proactive step in addressing extensive residential development in areas immediately adjacent to the facility. This evaluation, completed in 2006, identifies the plant’s headworks facilities, sludge holding tanks, and sludge drying beds as the most cost effective process units to target for initial odor control efforts. The evaluation included training of city personnel for off-site odor monitoring and assessments, and included development of a complaint response protocol or used by city personnel.