MPCA Design Guidance for Large Subsurface Wastewater ...

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Attachment 3 — Preliminary site evaluation The preliminary site evaluation is a desktop assessment of the selected LSTS site. The designer shall collect readily available published information from various documents and sources that describe the soils, geology, hydrology, etc. of the region in which the proposed LSTS is located. From this and other information, the designer can estimate, or make assumptions, regarding the following parameters: A. Location information - Determine the locations of on-site and nearby property lines, easements, floodplains, wetlands, surface waters, buildings, buried pipelines, etc. Above determined? ___ Yes ___ No B. Treated wastewater characteristics: • CBOD: _________ mg/L • TSS: _________ mg/L • Total nitrogen: _________ mg/L • Total phosphorus: _________ mg/L C. Design AWW flow to LSTS: ____________ gpd (See Attachment 2) D. Infiltrative loading rate: _____________ gpd/ft 2 E. Minimum soil absorption area = C / D: ____________ ft 2 F. Length of entire soil absorption site: ____________ ft G. Width of entire soil absorption site: ____________ ft H. Total area of soil absorption site = F x G: ____________ ft 2 (includes the area between trenches, beds, etc.) I. Average site recharge rate = [C ÷ 7.48] / H: ____________ ft/day J. Have the soils been disturbed at the soil absorption site: ___ Yes ___ No K. Soil permeability at drainfield/soil interface: ____________ in/hr L. Soil permeability of most restrictive layer: ____________ in/hr M. Depth to seasonal saturation (redoximorphic features): ____________ ft N. Depth to ground water: ____________ ft O. Direction of ground water flow: ___________ P. Hydraulic conductivity of saturated zone: ____________ ft/day Q. Ground water gradient: ___________ ft/ft R. Thickness of saturated zone: ____________ ft S. Specific yield of saturated zone: ____________ (dimensionless) T. Distance from soil absorption site to downgradient property boundary: _________ ft U. Width of soil absorption site perpendicular to the direction of ground water flow: _________ ft V. Ambient nitrogen concentration of ground water upgradient of soil absorption site: ____________ mg/L Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 37
W. Average daily ground water recharge from precipitation: _________ ft/day X. Distance to nearest surface water that receives ground water discharge: ________ ft Y. For platted subdivisions, will the development be provided with a community water system or will each residential lot have its own private well? ____ Community water ____ Private wells Z. Distance to nearest water-supply well: _____ ft. and/or sensitive water-supply well: _____ ft 1 AA. Indicators of high phosphorus attenuation potential: • Soil with high levels of iron and aluminum oxides: ____ Yes ____ No • Soil with high levels of calcium and magnesium carbonates: ____ Yes ____ No • Soil with high levels of clay minerals: ____ Yes ____ No • Soil with medium to fine texture: ____ Yes ____ No • Soil with high or low pH: ____ Yes ____ No • Large volume of unsaturated soil below soil absorption site: ____ Yes ____ No • Will portions of the soil absorption site be routinely rested for long periods of time (months): ____ Yes ____ No Using the information obtained from the desktop review of available information, please address the following preliminary evaluations: 1. Soil suitability assessment A. Estimate a soil sizing factor for the soil absorption site based on soil information and effluent characteristics. B. Select an effluent distribution method (drainfield, bed, mound, drip, etc). C. Provide your preliminary assessment regarding the soil’s long-term hydraulic acceptance rate for the chosen treatment and distribution method. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 1 Minnesota R. 4725.4450, adopted on August 4, 2008, requires a minimum separation distance of 300 feet from the soil adsorption area of a LSTS to water-supply wells. This separation distance increases to 600 feet for sensitive water-supply wells. A sensitive water-supply well is a water supply well with less than 50 feet of watertight casing where the casing does not penetrate a confining layer or multiple layers of confining materials with an aggregate thickness of ten feet or more. Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 38
Page 1 and 2: Design Guidance for Large Subsurfac
Page 3 and 4: Table of Contents Page Introduction
Page 5 and 6: How to Use This Guidance Document M
Page 7 and 8: 1. Knowing an MPCA permit is needed
Page 9 and 10: Table 1 Average Daily Flow for Four
Page 11 and 12: • depth to seasonally saturated s
Page 13 and 14: From this evaluation, a few tentati
Page 15 and 16: Permitting Option #1 may be mandato
Page 17 and 18: • Even distribution is necessary
Page 19 and 20: orings/wells may be allowed to be p
Page 21 and 22: Infiltration Trenches Plan View Sha
Page 23 and 24: Infiltration Trenches Plan View Sha
Page 25 and 26: The worksheet in Attachment 11 shal
Page 27 and 28: e. Seasonal operational changes —
Page 29 and 30: f. When mowed the drainfield inspec
Page 31 and 32: 5) A summary of any changes made to
Page 33 and 34: f. All soil test results (density,
Page 35 and 36: Attachment 1 — Knowing an MPCA pe
Page 37 and 38: Example 2: Flow for Other Establish
Page 39: Attachment 2 — Design flow consid
Page 43 and 44: 3. Nitrogen impact assessment (for
Page 45 and 46: Attachment 4A — Soils evaluation
Page 47 and 48: Attachment 5 — Pathogen treatment
Page 49 and 50: Attachment 5 (continued) — Remova
Page 51 and 52: Attachment 6 — Nitrate-nitrogen t
Page 53 and 54: Attachment 8 — Phosphorus treatme
Page 55 and 56: K _____ ft/day — saturated hydrau

MPCA Design Guidance for Large Subsurface Wastewater ...

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