Engineering Report Guidance for Collection Systems With a Design Flow of 22,500 Gpd or Greater - PUB2415

This document provides engineering consultants a comprehensive guide of the Missouri Department of Natural Resources’ recommendations and requirements for an approvable engineering report.

A facility plan is required for wastewater treatment facility projects and projects receiving funding from the department under 10 CSR 20-4. Facility plans are more extensive and detailed documents compared to engineering reports. For more information concerning department funding and requirements visit the Financial Assistance Center.

Engineering reports shall be submitted prior to the submittal of a construction permit application for projects involving collection systems (e.g., gravity sewers, pressure sewers, pumping stations and force mains). See 10 CSR 20-8.110(2)(B) and 10 CSR 20-6.010(4). Engineering reports are not required for:

• Collection projects permitted under the general construction permit.
• Collection projects limited to only 8-inch gravity.
• Collection projects that submit a Missouri registered professional engineer’s Sewer Extension Design Certification with the permit application.
• Collection projects not required to obtain a construction permit from the department.

The following is a sample format for the required engineering report content:

Cover Page

Include the following:

• Project name.
• System owner.
• Continuing authority.
• Contact information.
• Submittal date.
• Missouri registered professional engineer seal, signature and date.

Problem Defined

State the project’s purpose. Describe the existing system, including an evaluation of the existing conditions and problems needing correction. Include any schedules of compliance, enforcement administrative orders or agreements.

Hydraulic Capacity and Organic Waste Load

Existing Systems

Flow and organic loading projections for the design life of the system shall be made using actual data that accurately represents the average and peak flows. Evaluate the probable degree of accuracy of data and flow projections. Include impacts of industrial sources and all critical data and methodology.

New Systems

Estimates for organic loading, design average flow and design peak hourly flow must include the origin of the flow estimate and any assumptions. Also, consider contributions from industrial facilities and major institutional and commercial facilities.

For consistency, use the following flow definitions:

• Design average flow – The average of the daily volumes to be received for a continuous 12-month period expressed as a volume per unit time. However, the design average flow for facilities having critical seasonal high hydraulic loading periods (e.g., recreational areas, campuses and industrial facilities) shall be based on the daily average flow during the seasonal period.
• Design maximum daily flow – The largest volume of flow to be received during a continuous 24-hour period expressed as a volume per unit time.
• Design peak hourly flow – The largest volume of flow to be received during a one-hour period expressed as a volume per unit time.
• Five-day Biochemical Oxygen Demand (BOD5) – The amount of oxygen required to stabilize biodegradable organic matter under aerobic conditions within a five-day period.
• Design average BOD5– Generally the average of the organic load received for a continuous 12-month period for the design year expressed as weight per day. However, the design average BOD5 for facilities having critical seasonal high loading periods (e.g., recreational areas, campuses and industrial facilities) shall be based on the daily average BOD5 during the seasonal period.
• Peaking factor – Accounts for normal infiltration for collection systems built with modern construction techniques. The average design flow value shall be used in conjunction with a peaking factor from the following equation:

Peaking Factor = Q Peak Hourly / Q Design Avg = (18 + √P) / (4 + √P)
Where:
Q Peak Hourly = design peak hourly flow
Q Design Avg = design average flow
P = Population in thousands

Impact on Existing Wastewater Facilities

If the new collection system is to serve an existing development, the likelihood of I/I contributions from existing service lines and non-wastewater connections to those service lines shall be evaluated.

Location Drawings

Provide a system map (report size) and include drawings or sketches identifying the site of the project, anticipated location and alignment of the proposed facilities.

Site Evaluation

Provide the following project site information: topography, soils, geologic conditions, depth of bedrock, groundwater level, floodway or floodplain considerations, distance to water supply structures, roads, residences and other pertinent site information.

Engineering Criteria

Provide the design criteria and calculations used to determine design flow, velocity, pipe size and all pumping station calculations, including energy requirements. Indicate whether special accessories and stream crossings are incorporated in the proposed project. Identify any unusual specifications, construction materials and construction methods used in the proposed project. Include any maps, photographs, diagrams and other supporting data needed to describe the system.

Include a discussion of emergency operation, flood protection, alarm system, and access road requirements for pumping stations in accordance with 10 CSR 20-8.130.

Cost Estimate

Cost estimates for capital and operation and maintenance should be included.