Septic systems located near coastal waterways can contribute to nutrients that lead to eutrophication, harmful algal blooms, and high levels of fecal coliforms such as E. coli. This study defines pathways and timescales of nitrogen transport released from septic systems using a groundwater-flow and nitrogen transport model of a coastal subdivision connected to 2,000 septic systems and dissected by a dense network of canals. Lift station effluent data are used as a proxy to quantify average household septic nitrogen and fluid contributions of 11 kg/year and 160 m³/year, respectively. These fluxes are upscaled and applied to five sewer conversion zones, each having a known number of septic systems. Model results provide a basis for assessing nitrogen transport timescales associated with (1) coastal groundwaters for regions with high septic density near the coastline and (2) groundwater–canal interaction. Timescales associated with nitrogen removal by natural groundwater flow in a sandy surficial aquifer, following septic to sewer conversion, are predicted by the model to be on the order of 2–3 years for 50% reduction and 8–10 years for 90% reduction. Both numerical and collected field data indicate that canals significantly influence groundwater flow and have the potential to convey nitrogen to coastal waters at rates several orders of magnitude higher than introduced by submarine discharge along the coast. Pre and post sewer conversion data on nitrate and total nitrogen in shallow groundwater from a nearby field site, obtained post-model development, support the nitrogen concentrations and timescales predicted by the numerical model.

位于沿海水道附近的化粪池系统会产生导致富营养化、有害藻华和高水平粪便大肠菌群（如大肠杆菌）的营养物质。本研究使用连接到 2,000 个化粪池系统并由密集的运河网络解剖的沿海分区的地下水流和氮传输模型，定义了从化粪池系统释放的氮传输的途径和时间尺度。提升站污水数据被用作量化平均家庭化粪池氮和液体贡献的 11 kg/年和 160 m ³/年，分别。这些通量被放大并应用于五个下水道转换区，每个区都有已知数量的化粪池系统。模型结果为评估与 (1) 海岸线附近具有高化粪池密度的地区的沿海地下水和 (2) 地下水-运河相互作用相关的氮迁移时间尺度提供了基础。在化粪池转化为下水道之后，与砂质地表含水层中自然地下水流脱氮相关的时间尺度，模型预测为 2-3 年减少 50%，8-10 年减少 90%。数值和收集的现场数据都表明，运河显着影响地下水流，并有可能以比沿海海底排放引入的速度高几个数量级的速度将氮输送到沿海水域。