CWEA and WWOA Technical Sessions

Lisbon Community Sewerage, Capital Project No. S6259
by Timothy Wolfe, PE, Guihua Wang, PhD, PE, Ben Lapa, AP, Jordan Wolfe, KCI Technologies Inc.

This paper discusses innovative sewerage management and treatment solutions to a cluster wastewater system. With EPA’s recognition of decentralized wastewater as an important component of the country’s infrastructure, the cluster system has become an emerging issue in many localities.

The Lisbon community, located in western Howard County, is a historic town consisting of residences, schools, small businesses, and farms. The study area, which encompasses approximately 58 acres, has been highly sought after by developers and is expected to have the growth potential similar to what Ellicott City is today.

Most of the buildings in the study area were built in the 1700’s. During that period, the construction was typically on small lots (approximately 0.2 acre) with associated small septic systems including dry wells, septic tanks, and disposal trenches. The small size of the lots and the underlying geology has made subsurface sewage disposal in this area difficult. Existing records at the Howard County Health Department indicated that the Department initiated numerous repairs due to the deteriorating conditions of the septic systems. The presence of total coliforms and even fecal coliforms in well water supply has been documented by the Health Department.

In order to aid in understanding the condition of the septic systems in the study area, KCI developed a sanitary survey protocol for well water sampling. Seventeen out of the twenty-nine sampled properties showed positive total coliforms in well water. Four out of these properties showed positive E. Coli. The presence of fecal coliforms and E. Coli suggests that the water is contaminated with human or animal wastes. In addition, five of the sampled properties showed nitrates over 10 mg/L.

It is unlikely that the study area will be included in Howard County’s Water and Sewer Master Plan in a foreseeable planning year. Therefore, various on-site sewage treatment systems were examined based on the future build-out condition.

Planned Implementation of Grease and Root Control Programs by Carlos A. Espinosa, PE, KCI Technologies Inc.

Grease and roots typically bring about the majority of back-ups and overflows in collection systems. In the case of grease, municipalities are faced with outdated plumbing codes and sewer regulations that were not intended to control the discharge of grease into the sanitary sewer. Furthermore, enforcement of existing regulations is impaired by the lack of staff and resources. Roots present a different challenge to collection system operators. Often, root infested sewers are located in isolated, heavily wooded right of ways, with limited access. Roots can cause pipes and manholes to collapse, requiring expensive repairs under emergency conditions. The paper will identify the challenges faced by collection system owners and present alternatives to overcome these challenges. It will present a planned approach to implementing effective Root and Grease Control Programs, utilizing a work order system and GIS tools. The paper will discuss available technologies and chemicals designed to combat grease and roots. It will provide standard specifications for outsourcing the work, and will demonstrate how to implement an in-house program including developing Grease/Root Control Field Books.

Development of the Baltimore City Wastewater Collection and Transmission Model by Jeffrey S. Pelletier, PE, Camp, Dresser & McKee Inc. and Robert Jacobsen, PE, KCI Technologies Inc.

The City of Baltimore entered into a Consent Decree with the United States Environmental Protection Agency (USEPA) and the Maryland Department of the Environment (MDE) in September 2002, requiring the elimination of sanitary sewer overflows (SSOs) and the control of combined sewer overflows (CSOs) within a 14-year period, at an estimated cost of nearly one (1) billion dollars.

The primary tool used to assess the hydraulic capacity of the Collection and Transmission System is a computer model developed utilizing InfoWorks CS® by Wallingford Software. The model was developed utilizing a macro-/micro-modeling approach. The macro-model is a highly skeletonized representation of the system, including only the interceptors and larger diameter trunk sewers. The macro-modeling was performed by the Technical Wet-Weather Program Managers. Subsequently, micro-models (detailed sewershed-level models) were developed for each of the City’s eight sewersheds by eight separate consultant teams.

There were a number of benefits realized using the macro-/micro-modeling approach. First, the macro-model provided boundary conditions to the micro-models at each point of connection. Next, the early development of the macro-model provided for the characterization of the interceptor/trunk sewer system prior to the completion of the micro-models, allowing for the identification of larger diameter sewers with capacity-related issues, as well as those sewers with surplus capacity during extreme design storm events. This early knowledge enabled the Program Managers to provide the Sewershed Consultants with guidance as to the most appropriate wet weather control technologies to evaluate in their respective sewersheds. Additionally, as each micro-model is completed, it will be integrated into the macro-model and the hydraulic impact of the recommended wet weather controls will be evaluated downstream to the WWTP, thus ensuring that all eight individual Sewershed Plans dovetail into an appropriate and cost-effective wet-weather solution for the residents of the City of Baltimore and users of the surface waters of the Chesapeake region.

Incorporating Two-Stage Equalization into a Sequencing Batch Reactor ENR Process by G. Raymond Schulte, PE, John M. Slusser, Guihua Wang, PhD, PE, Steven E. Anderson, PE, David B. Woolard

This paper addresses a unique two stage flow equalization system. The existing Warsaw, VA Wastewater Treatment Plant is an aerated lagoon facility, designed for secondary treatment, and is near the end of its useful service life. In response to the Chesapeake Bay improvement initiative, a new VPDES permit was issued for the plant, with ENR nutrient limits.

An existing lagoon is incorporated into the replacement plant, for side-line wet weather flow attenuation. The two tank SBR process is operated automatically, based on time sequencing and tank liquid levels. Typical SBR systems incorporate control logic that allows for wet weather mode operation, by reducing the treatment cycle time. The Warsaw plant SBR controller retains this logic, but allows adjustment of the minimum process cycle time. With the minimum cycle time set near the normal peak design flow time, both SBR tanks will fill and shift to treatment mode during high flows. When this occurs, a valve diverts influent flow to the lagoon. Following the wet weather event, the accumulated wastewater in the lagoon is pumped to the plant when influent flow is lower than a pre-set threshold. Elimination of high peak flows optimizes the treatment process and helps to insure permit compliance during wet weather.

An effluent filter and UV disinfection system follow the SBR process. A second in-line flow equalization tank is located on the discharge side of the SBR, to limit the peak flow to downstream processes. The attenuation of the flow allows for rapid decanting of the SBR tanks, reducing their size, and also reduces the size of the filter and UV disinfection system. Flow out of the equalization tank is regulated, to limit the maximum outlet flow, by means of a modulating pinch valve, with a feedback flow meter signal.