Designing and building a sewer system for a 140-unit RV park connected to a city mainline involves careful planning, compliance with regulations, smart engineering design, and quality construction practices.

A properly designed system ensures smooth operations, minimizes maintenance costs, and provides guests with a clean, safe environment.

In this guide, we’ll explain the key steps, considerations, and best practices for successfully completing such a project.

Steps to Design and Build Sewer System for 140 Unit RV Park With City Mainline

1. Initial Planning and Feasibility Study

Before anything else, you need to conduct a feasibility study. This includes:

• Site Survey: Hire a professional surveyor to map out the land, including elevations, slopes, existing utilities, and geographical features.
• Capacity Check with City Utilities: Contact your local city or county public works department to verify that the city’s sewer mainline can handle the additional flow from 140 RV units. If not, upgrades may be required.
• Local Codes and Permits: Every jurisdiction has specific rules for wastewater systems. You’ll need:
  • Site plan approval
  • Wastewater discharge permits
  • Environmental review (if needed)
  • Connection permit to the city mainline

Tip: Meet early with city engineers—they can help you avoid costly design mistakes later.

2. Understanding Flow Requirements

You must size the system properly based on the expected wastewater flow. Here’s how to estimate:

• Average Flow per RV: Typically, 75–100 gallons per day per RV unit.
• Total Flow:
  • 140 units × 100 gallons = 14,000 gallons/day maximum expected flow.

Add a safety margin (~15%) for seasonal fluctuations or special events:

• 14,000 × 1.15 = 16,100 gallons/day.

This flow volume determines the pipe sizes, lift station needs, and city mainline connection points.

3. System Design Overview

An RV park sewer system typically consists of:

• Lateral Lines (individual connections from each RV pad)
• Collection Mains (group laterals together and carry wastewater)
• Manholes and Cleanouts (for maintenance access)
• Lift Stations (only if gravity flow is insufficient)
• Force Mains (pressurized sewer pipes if a lift station is used)
• Connection to City Mainline (approved by the city)

The goal is to design a gravity-fed system as much as possible. Gravity systems are cheaper to maintain and operate.

4. Detailed Steps to Design
5. Lay out the RV Sites and Sewer Laterals

Each RV space should have a sewer hookup (3–4 inch diameter PVC pipe), typically positioned at the rear third of the parking space.

Design considerations:

• Slope laterals at 2% (1/4 inch per foot).
• Include a backwater valve to prevent reverse flow during surges.

a. Main Sewer Line Design

The collection mains collect flows from laterals. Design the system with:

• Minimum Slope:
  • 4-inch main: 2% slope
  • 6-inch main: 1% slope
• Minimum Velocity: Aim for at least 2 feet per second to avoid solids settling.
• Manholes: Install at:
  • Every change in direction over 45°
  • Every 300–400 feet on straight runs
• Pipe Material: Schedule 40 PVC is common, but some cities require SDR-35 or even ductile iron.

b. Lift Station Design (If Needed)

If the land is flat or the sewer main is higher than the park, a lift station is required. Key components:

• Wet Well: Where sewage collects.
• Pumps: Usually dual pumps (one backup) rated for the peak flow.
• Control Panel: For automatic operation.
• Alarm System: For pump failure alerts.

Design to handle peak flow plus a margin, and ensure the wet well is big enough to prevent rapid pump cycling.

c. Force Main Design

If a lift station is required, sewage must be pumped through a force main:

• Typically 2–4 inches in diameter
• Must resist pressure (use pressure-rated PVC or HDPE)
• Must tie into the city gravity main at an approved drop structure or manhole

5. Construction Phases

Once the design is approved, construction begins in stages:

Phase 1: Site Preparation

• Clear and grade the land.
• Install temporary erosion controls.
• Locate and mark existing utilities.

Phase 2: Installation of Sewer Lines

• Trench according to pipe sizes and slopes.
• Install bedding material (sand or gravel) under pipes.
• Lay pipes carefully to maintain the designed slope.
• Backfill carefully to avoid pipe deflection.

Phase 3: Manholes and Cleanouts

• Pour concrete bases for manholes.
• Install manhole sections with gaskets.
• Install cleanouts at required intervals.

Phase 4: Lift Station (if required)

• Excavate and pour base pad.
• Set wet well and pumps.
• Install electrical systems and backup generators if needed.

Phase 5: Connection to City Mainline

• Coordinate with city inspectors.
• Tie into the main under supervision.
• Conduct pressure and leakage testing as required.

6. Testing and Inspections

Testing is crucial to ensure long-term performance:

• Low-Pressure Air Testing: To detect leaks in pipes.
• Mandrel Testing: To check if pipes are deformed during installation.
• Deflection Testing: Pipes must not deflect more than 5% of their diameter.
• Visual Inspections: Manholes, joints, and slopes are visually checked.
• Pump Station Testing: Pumps must operate automatically under simulated conditions.

City inspectors will witness and sign off on all tests before you can operate.

7. Operation and Maintenance Plan

Once the system is operational, establish a maintenance plan:

• Regular Inspections: Inspect cleanouts, manholes, and lift stations monthly.
• Pump Maintenance: Service pumps per manufacturer’s guidelines.
• Jet Cleaning: Use jet trucks to flush mains every 1–2 years.
• Grease Management: RVs can discharge fats—grease traps may be needed for communal kitchen areas.

Maintain detailed logs of all inspections and maintenance activities.

8. Costs to Expect

The cost of designing and building the sewer system can vary widely:

• Survey and Engineering – $30,000 – $60,000
• Permits and Fees – $10,000 – $25,000
• Materials (pipes, manholes) – $100,000 – $250,000
• Labor and Installation – $150,000 – $350,000
• Lift Station (if needed): $75,000 – $150,000
• Contingency (10–15%) – Variable

Total Estimated Budget: $350,000–$800,000, depending on site conditions.

9. Common Challenges and How to Avoid Them

• Flat Sites: Carefully grade to maximize gravity flow or plan for a lift station.
• Rocky Soil: Trenching becomes expensive—budget extra.
• Flood Zones: Design sealed manholes and elevated lift stations.
• Permit Delays: Start the permitting process early and maintain good communication with city officials.
• Seasonal RV Use: Install winterization options if operating in cold climates.

Conclusion

Designing and building a sewer system for a 140-unit RV park connected to a city mainline is a major project that demands expertise, coordination, and attention to detail.

By investing time in thorough planning, accurate design, quality construction, and proactive maintenance, you can create a reliable system that serves your park for decades.

Partner with qualified civil engineers, experienced contractors, and your local public works department.

Always prioritize quality materials, proper slopes, and solid construction practices to avoid costly repairs and environmental issues later.

With the right approach, your RV park’s sewer system will be a strong foundation for a successful, well-loved destination!