Southeast Hamilton Sewer Study Preliminary Engineering Report - PowerPoint PPT Presentation

Southeast Hamilton Sewer Study Preliminary Engineering Report Overview City of Hamilton July 14, 2020

Preparation Team WGM Group City of Hamilton

Goals and Objectives • Identify existing nutrient loads from on site wastewater disposal in SE Hamilton Area – aquifer and Bitterroot River • Consider population projections and future wastewater generation • Evaluate alternative for wastewater treatment that will protect future water quality – public health & environmental • Provide document for future wastewater planning within the SE Hamilton Area

Project Process • Follow Standard Preliminary Engineering Report Outline • Provide notice to state and federal agencies for comments • Complete an Uniform Environmental Checklist • Evaluate various alternatives • Prepare cost estimates • Identify Preferred Alternative

Study Area • Within the 2006 WWFP Planning Area • 1,200 Total Acres • 1,002 Current Parcels • Current Population = 2,505 • 13 Different Subbasin Collection Areas • 2 Outlying Subbasin Areas • Golf Course Road • Grantsdale

Existing Conditions • No Regional Public Sewer or Water Infrastructure • Individual Wells (+1,000) • Individual Septic Systems – Some of Unknown Condition (+1,000)  Seepage Pits, Septic Tanks, Drainfields, Others  Upgradient of City of Hamilton Drinking Water Wells

Need for Project • Public Health – Nitrates in Aquifer  Health Effects - Methemoglobeinemia (Blue Baby Syndrome)  Sensitive Populations – Infants, Pregnant Women, Dialysis Patients  MCL = 10 mg/L (US EPA) • Environmental Health – Bitterroot River Nutrient Loading  Increased Algae Growth  Decreased Oxygen  Fish Fatalities

Nutrient Loading Model • ArcNLET – GIS based model • Uses topography, soils, septic system locations • Septic System Ground Water Bitterroot River • Benefits:  Relatively quick and inexpensive model to run  Easy identification of locations with high nutrient loading  Planning level nutrient estimation tool

Existing Conditions Septic Plume

Projected Conditions Septic Plume Continued Onsite Septic Daly Ave Area Systems Well No. 2 Well No. 5 Well No. 1 Shady Ave Area Westana Mobile Home Park

Nutrient Loading Model Results • High density housing on septic systems results in significant nutrient loads to groundwater wells and Bitterroot River • Aquifer Nitrogen Loading: 16,700 lbs/year 21,000 lbs/year • Bitterroot River Nitrogen Loading: 11,000 lbs/year 13,600 lbs/year • Daly Area: High groundwater impact, greater distance to river • Shady Area: High groundwater and river impact • Grantsdale Rd/Westana mobile park: remote location

Population Trends • Parcels ≥ 5 acres – high potential density development • Parcels ≤ 1 acre – low potential density development • Parcel Size ~ Projected % Development • % Development = Total Future Lots • Future Population = 2.5 People/Unit

Population Trends

Population Projections

Wastewater Forecasting • 85 gallons/capita/day (2006 Hamilton Wastewater Facility Master Plan) • Peaking Factor for Conservative Estimate • Peak Flows Sensitivity – Storm and Sewer Analysis Application (SSA)

Future Scenarios Bitterroot River Nutrient Loading

Sewer Master Plan • Interceptor Mains (Backbone) – SSA for Pipe Sizing • Collections Mains for Side Streets • Potential for Phased Development – Decentralized Treatment • Considerations for Development Outside of Sewer Study Area

Cost Estimate Example Daly Interceptor – Detailed Cost Breakdown

Cost Estimate Example Focus Areas for Immediate Improvements

Benefits of the Preferred Alternative • Improves public health by reducing sewage-related pollutants discharged to aquifer providing safe and reliable drinking water. • Provides protection to the Bitterroot River by reducing nutrient loading that reach surface water. • Provides improved opportunity for economic development. • Provides a resource for future wastewater planning in the SE Hamilton Area.

THANK YOU!