> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str.md). # septic.str This file contains the septic system parameters. Data contained in the septic.str data file are: type of septic system, geometry of biozone, characteristics of biomass, and bio-physical reaction coefficients occurring in the biozone (adapted from Siegrist et al. (2005)). | Field | Description | Type | Unit | Default | Range | | ------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------- | ------- | ------------ | ------- | -------- | | [name](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/name_sepdb.md) | Name of septic system record | string | n/a | n/a | n/a | | [typ](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/typ.md) | Septic system type | integer | n/a | 0 | | | [yr](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/yr.md) | ​Year the septic system became operational | integer | n/a | 0 | | | [operation](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/operation.md) | ​Septic system operation flag | integer | n/a | 0 | 0-2 | | [residents](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/residents.md) | ​Number of permanent residents in the house | real | n/a | 1 | 1.0-12.0 | | [area](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/area.md) | ​Average area of drainfield of individual septic systems | real | m^2 | 1 | | | [t\_fail](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/t_fail.md) | Time until failing systems gets fixed | integer | days | 0 | 0-150 | | [dp\_bioz](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/dp_bioz.md) | Depth to the top of the biozone layer from the ground surface | real | mm | 1 | | | [thk\_bioz](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/thk_bioz.md) | Thickness of biozone layer | real | mm | 1 | | | [cha\_dist](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/cha_dist.md) | Distance from septic system to the stream | real | km | 2 | | | [sep\_dens](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/sep_dens.md) | Number of septic systems per square kilometer | real | n/a | 2 | | | [bm\_dens](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/bm_dens.md) | Density of biomass | real | kg/m^3 | 1 | | | [bod\_decay](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/bod_decay.md) | BOD decay rate coefficient | real | m^3/day | 2 | | | [bod\_conv](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/bod_conv.md) | Conversion factor representing the proportion of mass bacterial growth and mass BOD degraded in the septic | real | n/a | 2 | | | [fc\_lin](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/fc_lin.md) | Linear coefficient for calculation of field capacity in the biozone | real | n/a | 1 | | | [fc\_exp](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/fc_exp.md) | Exponential coefficient for calculation of field capacity in the biozone | real | n/a | 2 | | | [fecal\_delay](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/fecal_decay.md) | Fecal coliform bacteria decay rate coefficient | real | m^3/day | 2 | | | [tds\_conv](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/tds_conv.md) | Conversion factor for plaque from TDS | real | n/a | 2 | | | [mort](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/mort.md) | Mortality rate coefficient | real | n/a | 2 | | | [resp](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/resp.md) | Respiration rate coefficient | real | n/a | 3 | | | [slough1](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/slough1.md) | Linear coefficient for calculating the rate of biomass sloughing | real | n/a | 2 | | | [slough2](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/slough2.md) | Exponential coefficient for calculating the rate of biomass sloughing | real | n/a | 2 | | | [nit](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/nit.md) | Nitrification rate coefficient | real | n/a | 2 | | | [denit](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/denit.md) | Denitrification rate coefficient | real | n/a | 3 | | | [p\_sorp](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/p_sorp.md) | Linear P sorption distribution coefficient | real | L/kg | 1 | | | [p\_sorp\_max](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/p_sorp_max.md) | Maximum P sorption capacity | real | mg P/kg soil | 1 | | | [solp\_slp](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/solp_slp.md) | Slope of the linear effluent soluble P equation | real | n/a | 3 | | | [solp\_int](/io-docs/~/changes/GiVD5ID0WVyRIAumaMy2/introduction/structural-practices/septic.str/solp_init.md) | Intercept of the linear effluent soluble P equation | real | n/a | 3 | | #### References > Siegrist, R.L., J. McCray, L. Weintraub, C. Chen, J. Bagdol, P. Lemonds, S. Van Cuyk, K. Lowe, R. Goldstein, and J. Rada (2005): Quantifying Site-Scale Processes and Watershed-Scale Cumulative Effects of Decentralized Wastewater Systems. Project No. WU-HT-00-27. Prepared for the National Decentralized Water Resources Capacity Development Project, Washington University, St. Louis, MO, by the Colorado School of Mines.