MPCA Design Guidance for Large Subsurface Wastewater ...

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Step 7 Reduction of fecal organisms by a clogging mat Mat Formation Log Reduction No clogging mat 0 With clogging mat 2.0 Reduction = _______________ (7) Step 8 Determine the fecal organism reduction (in logs) from the charts on the following chart (use information from Steps 1, 4, and 6) Log reduction/inch = _________________ (8) Step 9 Calculate the minimum necessary unsaturated thickness needed for pathogen treatment: - / + = inches (3) (7) (8) (5) Some of the variables can be adjusted if the calculated unsaturated thickness is undesirable. Since the calculated thickness is needed during system operation for pathogen treatment, the anticipated ground water mound as determined by the Hydrogeologic Evaluation (Section 9), must not infringe on this thickness. Therefore, the designed system depth/height of the bottom of the distribution medium can be calculated as shown below: Depth to limiting layer (in.) - - = Needed unsaturated Ground-water mounding thickness (in.) (in.) Depth/height of system (A negative number is an elevated system.) Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 45
Attachment 5 (continued) — Removal of fecal organisms (logs/inch of soil) Sandy Soil Treatment area Loading Rate (gal/ft. 2 /day) 0.24 0.48 0.72 0.96 1.2 1.4 1.9 2.4 2.9 3.4 3.8 D o s i n g F r e q u e n c y D o s e s / d a y 1 2 0.152 0.141 0.130 4 0.163 0.150 0.137 0.117 6 0.173 0.159 0.144 0.123 0.113 0.171 8 0.184 0.168 0.152 0.130 0.118 0.107 0.084 10 0.194 0.177 0.159 0.136 0.124 0.112 0.088 0.070 12 0.205 0.186 0.166 0.142 0.130 0.117 0.092 0.074 0.056 14 0.215 0.194 0.173 0.149 0.136 0.123 0.096 0.078 0.060 0.043 16 0.226 0.203 0.181 0.155 0.142 0.128 0.100 0.082 0.065 0.047 0.031 18 0.236 0.212 0.188 0.161 0.148 0.133 0.104 0.086 0.069 0.052 0.036 20 0.247 0.221 0.195 0.168 0.153 0.138 0.108 0.090 0.073 0.056 0.040 22 0.257 0.230 0.203 0.174 0.159 0.143 0.112 0.095 0.078 0.061 0.044 24 0.278 0.248 0.217 0.187 0.171 0.154 0.119 0.103 0.086 0.070 0.053 Loamy soil treatment area Loading Rate (gal/ft 2 /day) 0.24 0.48 0.72 0.96 1.2 1.4 1.9 2.4 2.9 1 2 0.183 4 0.195 0.180 6 0.208 0.191 0.173 8 0.221 0.201 0.182 0.156 10 0.233 0.212 0.191 0.163 0.149 12 0.246 0.223 0.199 0.171 0.156 0.141 14 0.258 0.233 0.208 0.178 0.163 0.147 16 0.271 0.244 0.217 0.186 0.170 0.153 1.20 18 0.284 0.255 0.226 0.194 0.177 0.160 0.124 20 0.296 0.265 0.235 0.201 0.184 0.166 0.129 0.109 22 0.309 0.276 0.243 0.209 0.191 0.172 0.134 0.114 24 0.334 0.297 0.261 0.224 0.205 0.184 0.143 0.123 0.104 Clayey soil treatment area Loading Rate (gal/ft 2 /day) 0.24 0.48 0.72 0.96 1.2 1.4 1 2 4 0.212 6 0.225 8 0.239 0.218 10 0.253 0.230 12 0.266 0.241 0.216 14 0.280 0.253 0.226 16 0.294 0.264 0.235 0.202 18 0.307 0.276 0.245 0.210 20 0.321 0.288 0.254 0.218 0.199 22 0.335 0.299 0.264 0.226 0.207 0.199 24 0.362 0.322 0.283 0.243 0.222 0.200 Design Guidance for Large Subsurface Minnesota Pollution Control Agency Wastewater Treatment Systems April 2010 46
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 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: Attachment 5 — Pathogen treatment
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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