Holstad, Mark

Mark Holstad, started his career in 1976 as an entry-level engineer in the collection section he now manages. He was trained in the practical aspects of the sewer system by Superintendents and Foremen that had cleaned sewers by hand in the mid-1950s. In 1976, based on his Superintendents insights, he investigated and resolved his first repeat SSO. He spent 26 years in the private sector, during which he was responsible for the design of the major components of the Collection System. Since 2007, he has been the Chief Engineer responsible for managing the Water Authority's Collection System.

Titles from this speaker

A Tale of Three Projects: Vortex Manholes Design, Operation and Improvement

Abstract

Vortex manholes have proven effective in resolving some of the worst odor problems in the Water Authority system after multiple alternate solutions failed. The Water Authority’s experience indicates that a primary benefit of vortex manholes is the control of air flow rate to prevent the release of fugitive sewer gas. Testing again demonstrates that H2S levels in the vortex exceed acceptable levels for release. Downstream water quality benefits are addressed but are not conclusively determined. Guided by difficulties with its initial vortices, the Water Authority subsequently developed and implemented design features that provide for improved hydraulics, and associated ventilation, exiting the vortex manhole. The Water Authority has developed and implemented practical design consideration for operation and maintenance (O&M). Modifications were successfully made to correct issues with the initial vortices. The Water Authority operates eight vortex manholes on three interceptors. All are performing well.

SpeakerHolstad, Mark

Presentation time

08:30:00

08:50:00

Session time

08:30:00

10:10:00

SessionClearing the Air: Odor Mitigation and Treatment

Session number513

TopicCollection Systems, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Odors and Air Quality

Author(s)

M. Holstad

Author(s)M. Holstad1;

Author affiliation(s)Albuquerque Bernalillo County Water Utility Authority, NM1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157458

Volume / Issue

Content sourceWEFTEC

Word count12

I Smell a New Approach - A Utility's Adoption and Use of a Sewer Process Model

Abstract

Summary--Using a sewer process model to predict extensive collection system parameters related to odor and corrosion, e.g., sulfide and pH, the Albuquerque Bernalillo County Water Utility Authority (WUA) better understands its own system. The WUA has adopted and used the model in-house to address and resolve, quickly, confidently, and with documented, analytical justification, a wide range of operational, design, and planning issues. This model allows chemical feed optimization and assurance that appropriate wastewater is delivered to the Water Resource Recovery Facility (WRRF) to meet performance requirements. The model is complex and a significant undertaking, yet the WUA has been more effective and efficient since its adoption. This paper describes how to integrate these tools into the Utility's operations, including practical issues of structuring staff, growing the team with consultant support, and developing depth of staff. This paper also describes specific studies performed by WUA staff utilizing the model. Introduction The WUA owns and maintains over 2,400 miles of pipes in the collection system to convey approximately 50 MGD wastewater from the service area to the WRRF. The WUA has implemented various methods and technologies for controlling odors and corrosion in the collection system, resulting in significant institutional knowledge and experience in this engineering science. As part of the 2019 Collection System Odor and Corrosion Control Master Plan, Jacobs Engineering (Jacobs) and the WUA implemented a systematic approach to address odor and corrosion issues by developing a sewer process model of the WUA system. The model was created using WUA ArcGIS piping assets, hydraulic data, and wastewater characteristic data. The model used is the Wastewater Aerobic/Anaerobic Transformations in Sewers (WATS). The WATS model simulates sewers' complex chemical, biological, and physical processes through extensive mass balances and differential equations. The WATS software can predict hydrogen sulfide odor generation, concrete asset corrosion, chemical management, analyze wastewater characteristics at inflows to wastewater treatment plants, etc. The WUA's objective in using the model is to respond in real-time to unexpected-immediate, near-term predictable, conceptual design-phase and routine chemical feed considerations. The Collection Section operates and utilizes the model successfully for a wide range of tasks. Methods The framework for developing and running the WATS model in-house is shown in Figure 1. We identified an in-house engineer (Engineer) with strong technical skills but minimal previous experience in sewer odor control and assigned the responsibility of learning and utilizing the model. We provided a learning environment with adequate resources, strong support, and reviews. Technical support was provided by the modeler's direct supervisor and, under a contract established to provide training and related support, the lead process engineer (Consultant) for developing the WATS model of the WUA system. As noted in Figure 1, per typical WUA practice, the Engineer created a Standard Operating Procedure (SOP) that provides specific documentation and procedures for using the WATS model. The Engineer's knowledge is solidified through the process of writing the SOP. It serves as the Engineer's reference document and a training guide for staff assigned to assist or even to learn to operate the WATS model. After the Consultant provided basic training, it was time for the assigned Engineer to learn by performing or 'doing' repeated model use cases. This WUA Learn-by-doing approach is shown in Figure 2. Results Our first use of the model was to develop specific proposed locations, on three interceptors, for ferric chloride and magnesium hydroxide stations proposed by the Master Plan. Specific locations were found based on land availability, truck access, and other criteria. Chemical feeds were simulated with a target of 0.2 mg/L free iron downstream. Reports were developed in-house and provided to WUA Engineering for consultant design of the new facilities. The next use was to develop flow times from each permitted industrial user to the WUA's only significant WRRF. The WUA's WATS network is based on export data from the WUA's InfoSWWM model, including lengths and average velocities. In the typical use of the WATS model, upstream and downstream pipes are connected, establishing the line being evaluated. The model provides the flow time and multiple parameters pertinent to odor and corrosion control. A report was delivered to Pretreatment, providing a total flow time for each user. Pretreatment has used the report data once for a high BOD spill, but there were no obvious spill impacts to the WRRF influent. An ongoing use is managing the WUA's chemical feed program to prevent odors, manage corrosion, and deliver appropriate wastewater to the WRRF. The WUA utilizes six liquid-phase chemicals: ferric chloride, calcium nitrate, calcium hydroxide, magnesium hydroxide, hydrogen peroxide, and residual iron from the surface water treatment plant (SWTP). The WATS model is the tool used to optimize these feeds. In two studies, the model has been used to protect the WRRF. First, a calcium nitrate tank was to be replaced, and the tank had to be quickly emptied. The model indicated the nitrates would be consumed and would not reach the WRRF. Second, a low-pH Fluorosilicic Acid needed to be disposed of at the SWTP. The model indicated the pH impact at the WRRF would be minimal. In both cases, the model matched the actual results and provided confidence for the action taken. Recently, the model network was extended in two locations to study lines in design or under construction. One was a new gravity line subject to very high BOD. The network extended downstream included an existing gravity, a lift station, and a force main. Results indicated H_2 S levels in the gravity lines would be acceptable, but the unexpectedly high force main discharge would be investigated. The other is a proposed lift station and force main discharging to a gravity line unavailable for service connections. Figures 3 and 4 show results indicating the sulfide levels reached minimal levels well before a location where service connections could result in odor issues. We plan to use this 'free treatment' in the gravity line and not include liquid phase odor control but to provide managed airflow in the gravity line and construct corrosion resistance pipes and manholes. The WUA is currently designing a future satellite WRRF. The service area includes a calcium nitrate station that is to be replaced by a ferric chloride station at an upstream location. We are currently utilizing the model to estimate the increase in BOD when calcium nitrate is no longer fed, to optimize the ferric chloride feed and to estimate the resulting decrease in pH and alkalinity. Lessons Learned Modeling proficiency requires regular use. Once the designated Engineer has learned the model basics, the time allocated to the model may average 15% full-time employment. Naturally, some weeks may require nearly full-time efforts. We observed increased task requests as other groups within the WUA became aware of this new in-house capability. The WATS model has proven effective, but the utility investment and commitment must be recognized. The designated Engineer will ideally have a background in process engineering, but many of these subjects can be taught and learned over time. Sustaining depth of staff requires additional employees to be competent in the model. Writing a basic training SOP helps create and maintain the depth of staff. SOPs should be written with new advancements in the model and should be updated regularly. Benefits and Significance A utility benefits from operating a tool such as the WATS model in several ways. First, should anyone understand your system better than the utility itself? We believe a utility should best understand its system due to ownership and continuity. A utility is best served if it is prepared for all eventualities and can respond quickly. The WATS model allows the utility to do so. A utility continuously adds facilities and systems under a consultant-designed contract describing typical responsibilities. This contract structure often cannot direct timely decisions that optimize the utility-operated sewer systems. Finally, the utility benefits in responding quickly and adequately to a wide range of occurrences that all utilities endure.

This paper was presented at the WEF Odors and Air Pollutants Conference, May 16-19, 2023.

SpeakerHolstad, Mark

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionDispersion and Ventilation Modeling

Session number6

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicCollection System Odor Control

Author(s)

M. Holstad

Author(s)M. Holstad 1; A. Romero Flores 3; B. De Flon 5

Author affiliation(s)Albuquerque Bernalillo County Water Utility Authority1;Jacobs Engineering2;Austin Water3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158748

Volume / Issue

Content sourceOdors and Air Pollutants

Word count17

The Great Area-Wide Debate: O&M Cleaning Optimization using SSO Rates

Abstract

Summary Per its mission statement, the Water Environment Federation (WEF) is to 'provide a platform for water sector innovation.' Seemingly mundane, cleaning of wastewater collection systems is extremely costly and requires innovation. Area-wide cleaning, the focus of this paper, is estimated at $1.1B per year based on the currently accepted frequency of five years. This criterion has not been subjected to quantitative analysis now possible with the vast data generated by computerized maintenance management systems (CMMS) routinely utilized by modern utilities. The Sanitary Sewer Overflow (SSO) rate provides an accepted criterion on which to base quantitative comparisons. Simply stated, per the Pareto Principle, determine SSO rates for identifiable portions of the collection system and move cleaning efforts from portions with low SSO rates to high SSO rates. Initial analyses, discussed in this abstract, indicate that portions of the collection system can be identified with significantly different SSO rates. These differences, based on pipe attributes, location in the system, and time since cleaning, provide the opportunity for significant savings. Introduction Core Attributes of Effectively Managed Wastewater Collection Systems recommends proactive system-wide (area-wide) cleaning to regularly clean lines not known to suffer recurring blockages. Problem lines are recommended to be addressed in a separate preventative maintenance (hot-spot) cleaning program. A utility, believing more frequent is better, may select a five-year cycle to demonstrate a commitment to decreasing SSOs. US collection systems include 740,000 miles of public mains (WEF, 2011). The annual cost to properly clean the small diameter portion of the public sewer systems is $1.1B assuming 90% of the public mains are small diameter, and 20% are cleaned each year at a rate of $1.50/LF. This is a staggering societal cost that has not been subjected to rigorous efficiency analysis. Methodology Objective and Goal The objective of this study is to examine the proactive area-wide cleaning program for opportunities to improve the effectiveness of the overall program. This will also result in changes to preventive maintenance hot-spot cleaning programs by identifying cleaning resources that can be reallocated. The long-term goal is to reduce dry weather SSOs with equal or less resources. Metric The SSO rate provides a metric to identify poorly performing portions of the system. Figure 1 provides the definition of the SSO rate. Utility Systems Studied This study includes data from two utilities: The Albuquerque Bernalillo County Water Utility Authority (ABCWUA) and Yarra Valley Water (YVW). See Table 1 for a system comparison. YVW has not implemented O&M cleaning. The YVW system can serve as a 'control' sample to observe how a system functions without intervention by cleaning. Therefore, the SLN study was completed for both systems while the remaining studies utilized only WUA data. Segment Loading Number (SLN) The WUA and YVW evaluated SSO rates at different locations, i.e., SLN, in the collection system. Figure 2 shows the counting method and Figure 3 shows the SSO rates for both systems. Note the significant trend for increasing SSO rates as flow progresses downstream. Time Since Cleaning The purpose of this analysis is to determine the need to clean lines that are not in the hot-spot program. In this analysis, the SSO rate is determined for each year after cleaning and prior to cleaning the cohort of lines subject to area-wide cleaning in a particular year. Lines in the hot-spot cleaning program are not included in this analysis. Figure 4 displays the SSO Rate, by years of cleaning, for each cleaning cohort from FY14 through FY21. The rates are aligned by years before or since cleaning. The average rate is provided for each year before and after cleaning. Area-Wide vs. Hot-Spot Cleaning The purpose of this study is to compare the SSO rate in the hot-spot program versus the rest of the system. Figure 5 provides the rates and trendlines. Results The results of these analyses highlight the importance of evaluating the SSO rates for a gravity system before restructuring a cleaning program. First, the SLN analysis shows a difference in SSO rate upstream in the system versus downstream in the system. The SLN analysis shows a clear increase in SSO rates for the lower portion of the two collection systems. Lines with a higher SLN in the WUA and YVW systems are more likely to have a blockage and cause an overflow. The time since cleaning analysis does not indicate a significant change in the SSO rate for the lines not in the hot-spot program. Rather than increasing, as expected, in successive years after cleaning, the rate is consistent possibly decreasing. The SSO rate comparison of hot-spot and non-hot-spot programs demonstrates a long-term success. Even with hot-spot cleaning rates up to 30 times the remainder of the system, the hot-spot lines have historically suffered a higher SSO Rate. The WUA has focused cleaning on the hot-spot lines and has thereby lowered SSOs. Discussion While the WUA is already moving forward with changes to the area-wide cleaning program, meaningful change must be on the industry level. It is our belief that other utilities also have a desire to reduce SSOs with equal or less resources. 'Clean smarter, not harder' should be the new catchphrase amongst utilities. The analyses identified that SSO rates are not identical across the system. Instead, clear differences are identified, and lessons are being learned about how and when to clean based on SSO rates. The same process can be used to evaluate additional inspections. E.g., shifting a crew from cleaning to inspection will result in less footage cleaned, but result in a lower SSO Rate due to significantly more effective cleaning, i.e., cleaning the right lines. If so, should this not be the preferred program? This also allows utilities to focus on the quality of their cleaning in hot-spot lines rather than meeting a specific goal each year. The analyses performed are just some of the possible studies for reallocating cleaning resources based on SSO rates. Other studies that could be considered include, pipe material and age, groundwater level, and pipe slope. Artificial intelligence and machine learning methods are likely to provide valuable insights. Ultimately, these analyses for effectiveness could become a standard process conducted periodically by utilities utilizing in-house staff or through contracting. WEF is the platform to rigorously compare O&M data to existing O&M criteria. The O&M Technical Project Group (TPG) of the Collection Systems Committee has identified supporting industry evaluation of cleaning criteria as consistent with its focus. This is included in the recent fact sheet developed by the TPG with the hope of sponsoring a workshop at WEFTEC 2024. This presentation is a critical first step. We request your support.

This paper was presented at the WEF Collection Systems Conference, June 27-30, 2023.

SpeakerHolstad, Mark

Presentation time

09:30:00

10:00:00

Session time

08:30:00

11:45:00

SessionSession 15: Optimization & Modelling

Session number15

Session locationKansas City Convention Center

TopicPressurized Systems, Integrated Planning, Intelligent/Smart Sewer Systems, Asset Management and CMOM, Wet Weather Management & Control (CSOs/SSOs)

Author(s)

Holstad, Mark

Author(s)M. Holstad1; J. Malouff1; A. Flores-Garcia1;

Author affiliation(s)Albuquerque Bernalillo County Water Utility Authority1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2023

DOI10.2175/193864718825158887

Volume / Issue

Content sourceCollections

Word count11

Two Sides of the World One Surprising Collection System Truth

Abstract

INTRODUCTION The Albuquerque Bernalillo County Water Utility Authority (ABCWUA) in Albuquerque, New Mexico, has vast experience designing, installing, operating, and maintaining small-diameter gravity sewers. To create an extensive study on how the design criterion of slope affects Sanitary Sewer failure performance, the ABCWUA collaborated with the Yarra Valley Water (YVW) Utility in Melbourne, Victoria. Collectively, this research compiled 30-years of SSO data relative to each system's slope, age, and piping material. Shown in Table 1 is the systematic comparison and contrast between ABCWUA and YVW. The purpose of this research is to analyze the performance of small-diameter gravity sewers in Collection Systems. The current criterion for Sanitary Sewer design is steep slopes (>1%) are required for gravity sewers to be adequately functional in self-cleansing. However, this design criterion applied worldwide yield deeper and steeper sewers. When designing for situations where this steep slope criterion is not met, pumping systems are a more expensive alternative but often provide unsatisfactory performance. Sanitary Sewer failure performance is measured by Sanitary Sewer Overflows (SSOs). This research supports the following, steep sewers do not provide compensatory benefits in terms of odors, asset management of existing assets is suboptimal, and tractive force should be the method used for small-diameter pipes. METHODOLOGY The SSO Rates, denoted per equation 1, measure the relative Sanitary Sewer performance. SSO Rate = (Number of SSOs)/(([(Sewer Length (Kilometers))/100])/Years) (1) The number of SSOs is the respective count of failures for a given year. The sewer length is the total linear sewer distance in km, and the years are the total number of time periods in the study. Table 2 presents the selected ABCWUA and the YVW Sanitary Sewer system piping diameters, describing the pipe material and slopes used for the analysis. Table 3 explains the definitions for the flat, middle, and steep slopes. Inspections of ABCWUA pipes validated and complemented the theoretical results with observations from the field. Traditionally, low velocities, resulting from flat slopes and low flows, are understood to result in solids deposition and odors. The presence of solid sediments at the bottom of a pipe is attributed to a situation where the line can not self-cleanse. A set of field observations were performed to monitor actual lines. This study selected four flat and steep line pairings with the same construction age and material type (e.g., 1965, vitrified clay pipe (VCP)). In Table 6, two lines were studied for each selected flat or steep location in the ABCWUA Collection System, one with a segment loading number (SLN) of 1 (i.e., dead-end) and the other SLN of 7. A previous study by Holstad (2019) showed SSO frequency increases on piping segments with larger SLN values. RESULTS See Table 5 for the summary of the two systems rolled up over the decades built. Sewers from 1960 to 1989 were selected because older sewers did not have design slopes available, and 1989 was old enough to experience some deterioration. Both systems showed lower SSO Rates in flat slopes than steep. The difference in the magnitudes of the reported SSO Rates is partially due to ABCWUA having a proactive cleaning program, whereas YVW has a reactive response to spills. The primary exposure of interest in this study was slope, the secondary exposures were material and age, and the outcome was SSO Rate. The Bayesian network analyses confirmed slope, material, and age impact SSO Rate. Figure 1 provides the identical directed acyclic graph (DAG) representation of both systems. The DAGs were identical but not the calculated strengths for the directed edges representing the individual dependencies between the variable nodes in each network. Per Table 6, for ABCWUA, material primarily drove SSO Rates (i.e., VCP lines had higher SSO Rates than polyvinyl chloride (PVC)). While for YVW, the decade was the main variable impacting SSO Rates (i.e., older lines built in the 1960s had higher SSO Rates than the 1970s and 1980s). However, for both utilities, the main exposure of interest, slope, was second in strength percentage (i.e., steep lines had higher SSO Rates than flat). Lastly, the directed edge from decade to material explained the transition from VCP to PVC over time. ABCWUA closed-circuit television (CCTV) inspections revealed flat lines had more debris depositions than steep. However, none of these steep lines had deposits significant enough to cause an SSO. Figure 2 shows the top segment in a typical flat line has approximately 1-inch debris, and the downstream segment has a channel cut in the debris layer. Figure 3 reinforces this finding with YVW fault collection data showcasing that most blockages were attributed to tree roots and fat build-up. The hydrogen sulfide (H2S) data is provided in Table 7, the results found flat lines did not experience significant odors. While we placed OdaLogs on flat lines, the customers, who talked with us, were adamant there existed no odor issues in their neighborhood. â€ƒ DISCUSSION How can flat lines have lower SSO Rates? The answer may be in what an SSO is, a blockage where the sewage upstream is greater than the available storage volume. The storage volume is simply the space occupied by the pipes and manholes upstream of the blockage and below the spilling manhole. As shown in Figures 4 and 5, the flat (0.3%) and steep (3.0%) systems have approximately 1200 cubic feet (cf) and 300 cf of storage for the same pipe and manhole configurations. For a typical flow rate of 10,500 gallons per day (gpd), and recognizing that blockages are seldom complete, a steep line will overflow in approximately 7 hours while a flat line will attenuate storage and not overflow. The CCTV observations match well with previous computational and model analyses (Littlewood et al. 2003), which found that under intermittent flow, solids moved differently but adequately to avoid SSO-causing deposits. The low H2S is due to the availability of oxygen to exposed deposits (ASCE 1989). CONCLUSION The above findings challenge a fundamental understanding of Collection Systems, that flat sewers provide inferior service and should be avoided (EPA 1974, ASCE 2007). Instead, flat sewers should be preferred over alternatives such as lift stations, low-pressure grinder pump systems, etc. These alternative systems are more expensive, are not SSO-free, and are prone to odors. Asset management is based on risk assessment. Once flat sewers are recognized as less likely to spill, resources can be focused on the steeper lines more likely to spill. For instance, YVW is trialing a proactive cleaning program and developing a manhole-level monitoring program to prevent SSOs and will focus on the lines more likely to spill. See Figure 6 for their modified asset management approach.

This paper was presented at the WEF Collection Systems Conference in Detroit, Michigan, April 19-22.

SpeakerHolstad, Mark

Presentation time

14:00:00

15:00:00

Session time

13:30:00

16:45:00

Session number2

Session locationHuntington Place, Detroit, Michigan

TopicAsset Management, Collection Systems, Sanitary Sewer Overflow

Author(s)