MPCA Design Guidance for Large Subsurface Wastewater ...

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Infiltration Trenches Plan View Shaded area = system size for ground water mounding and phosphorus Length Width GW Flow Direction 3) Nitrogen Dilution – System Area The area to calculate nitrogen dilution from precipitation recharge would be the same as for ground-water mounding and phosphorus, plus the downgradient area inside the property boundary that infiltrates precipitation (“green space”). The calculation for the above example is: ((19 x 8′) + 3′) x ((3 x 10′) + (4 x 100′)) + (175′ x ((3 x 10′) + (4 x 100′)) = 141,900 ft 2 [ width ] [ length ] [ downgradient area ] Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 19
Infiltration Trenches Plan View Shaded area = system size for nitrogen dilution Length Property Line Width GW Flow Direction D. Final Sizing The most restrictive total land area from items C 1), C 2), or C 3) above will be multiplied by 1.25 with the additional 25 percent area set aside for future use if needed. This can be accomplished in a variety of ways. The first way is to design enough area in between the trenches for additional trenches (this will not be the solution if phosphorus or nitrogen breakthrough is the failure) or additional area set aside elsewhere. If area is set aside elsewhere, then adequate downgradient green space must also be added. The different sizing considerations are interrelated. For example, lowering the waste strength would allow a greater hydraulic loading rate (Attachment 4B), which would impact the soil’s ability to remove fecal organisms (Attachment 5). Therefore, arriving at a final sizing/loading rate can be very complicated. Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 20
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: 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 and 40: Attachment 2 — Design flow consid
Page 41 and 42: W. Average daily ground water recha
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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