The process for undertaking a life cycle costing analysis for ponds and sediment basins is the same as described in Life-Cycle Costing - Constructed Wetlands and Life-Cycle Costing - Bioretention Systems.

The origin of all of the ‘expected’ values and algorithms in MUSIC’s costing module, as well as the statistical operations used to generate ‘upper’ and ‘lower’ estimates for ponds and sediment basins are explained in Table 1.

## Tip BoxWorked Example - To Manually Adjust the Estimate of One of the alternative algorithms in Table 7-4. allows users to estimate the typical annual maintenance cost using the size attribute A worked example is given below showing how to manually calculate an estimate of Consider an urban catchment in Melbourne 20 ha in size with 50% impervious area that generates stormwater that is to be treated by a 194 m The load of trapped TSS is calculated by right-clicking on the basin’s treatment node icon and examining the Statistics » Mean Annual Loads section of MUSIC. In this example, the inflow load is 11,700 (kg/year) and the outflow load is 2,340 kg/year, so the trapped load is 9,360 kg/year. Using a mass to volume conversion factor of 1,800 kg/m Using the same procedure for gross pollutants, the inflow load is 2,550 kg/year and the outflow load is 0 kg/year (as MUSIC assumes 100% is captured). Using a mass to volume conversion factor of 260 kg/m For coarse sediment, it is known that in gross pollutant traps that capture nearly all coarse sediment and gross pollutants, approximately 29% of the volume is sediment (on average). So the load of coarse sediment (m3/year) = the volume of trapped gross pollutants (i.e. 9.81 m Now the three elements of the total trapped volume are known, the user can choose which of these should be added to estimate V. |

Table 1 Summary of cost-related relationships for ponds and sediment basins.

Element of Life Cycle Costing Model | Default Option for Estimation in MUSIC | Alternative(s) | Notes |
---|---|---|---|

Life cycle | 50 years (From collected survey data, | No alternative in music. | One could convincingly argue the life cycle is infinite for well-maintained ponds / basins, but we need to set the LC to a finite number to calculate a life cycle cost. Upper and lower estimates derived using a 84th and 16th percentile, respectively. |

Total acquisition cost (TAC) | TAC ($2004) = 685.1•(A)0.7893 R Where: A = surface area of treatment zone in m | No alternative size / cost relationships in MUSIC. For literature values, see Taylor (2005b) – included in Appendix H. | Upper and lower estimates derived using a 68% (or 1 standard deviation) prediction interval for the regression. Note that a linear equation (TAC = 96.15•(A) + 16,200) produced a slightly higher R |

Typical annual maintenance (TAM) cost | TAM ($2004) = 6.831•(A) R Where: A = surface area of treatment zone in m
| No alternative size / cost relationships in MUSIC. For literature values, see Taylor (2005b) | Upper and lower estimates derived using a 68% (or 1 standard deviation) prediction interval for the regression. |

Annualised renewal / adaptation cost (RC) | RC ($2004) = 0.52% of TAC p.a.
| No alternative size / cost relationships in MUSIC. For literature values, see Taylor (2005b) | Upper and lower estimates derived using a 84th and 16th percentile, respectively. |

Renewal period | 20 years
| No alternative in music. For literature values, see Taylor (2005b). | Period estimated after reviewing the CRCCH data set. There is great uncertainty surrounding this period (and the associated RC), given the lack of experience in ‘resetting’ the macrophyte zone of constructed wetlands in Australia. Range of data = 10 - 50 years (10 - 20 = most common range). Note that Fletcher et al. (2005) suggested 20 – 50 years. |

Decommissioning cost (DC) | DC ($2004) = 42% of TAC
| No alternative size / cost relationships in MUSIC. | Upper and lower estimates derived using a 84th and 16th percentile, respectively. |

General caveats / notes for this type of device | For the purposes of costing “wetlands”, the treatment device includes an inlet zone sediment basin / pond and macrophyte zone, but no gross pollutant trap pre-treatment device. Retrofitted wetlands were excluded from the data set that was used to generate these relationships, due to limited data and unusually high total acquisition costs. |