Anaerobic Soil Impairs Sprayfield in Ellensburg, WA

Written by E. Philip Small on July 26, 2009.

Twin City Foods will be building pretreatment facilities to mitigate for the effects of hydraulic overloading in the sprayfield it operates in Ellensburg, WA.

According to John Akers, City of Ellensburg, public works director, the company's spray fields are unable to take up nutrients because too much water is being put into the soil.

Located south of the city, Ellensburg's municipal wastewater treatment facility is surrounded by Twin City Foods industrial wastewater sprayfield. The municipal treatment facility lacks aeration capacity to accommodate Twin City Foods' peak wastewater flows. The news article mentions water and dirt loading and implies nutrient loading. But the overriding need for treatment, and the reason this wastewater can't be accomodated by the City's wastewater treatment plant, is the high level of oxygen demanding constituents, as measured by COD and especially BOD. This results from the sugary juice of the fresh corn being processed. Sent to the plant, it requires more aeration that the treatment plant is capable of delivering, equipment too expensive to install and operate for the short time period it is needed. This makes land application the more economical choice for wastewater treatment. Elevated manganese and iron in the monitoring wells corroborates that oxygen demanding constituents in the wastewater are having undesirable effects on the soil.

A Department inspection during November 1991 documented the presence of alternating layers of anaerobic and aerobic soil in augered boreholes. Anaerobic conditions were found to extend down into shallow groundwater. In areas where groundwater was observed to be seeping into surface water (Tjossem Ditch, Blossum Pond, and a backwater of the Yakima River), orange staining of iron bacteria and insoluble iron oxide converted from soluble ferrous iron in the groundwater was observed at several locations. Shallow groundwater concentrations of ferrous iron and manganese exceed State groundwater standards beneath the sprayfield during at least part of each year. [added 2009-07-30]

Anaerobic soil reduces sprayfield nutrient treatment capacity and it results in plumes of anaerobic groundwater laden with reduced constituents. This condition can harbor and nurture common disease organisms that would otherwise do poorly in aerobic groundwater. Anaerobic sprayfields are generally not permitted by Washington Department of Ecology due to public health and safety concerns. On the other hand inducing anaerobic soil and discharging anaerobic groundwater are not specifically prohibited by law, necessitating a pragmatic regulatory response. This can allow anaerobic problems to persist year after year, as they have at this location. Consider the pattern of hydraulic "blinding" visible in the aerial photo below. Similar to the cheese plant sprayfield situation posted here, application uniformity and soil moisture effects on BOD treatment capacity appear to have played a more important role than could be accommodated in the sprayfield design. Not mentioned in the news article is that a change in ownership has cut off Twin City Foods from a portion of the sprayfield area. This reduction in land area has precipitated the need for a treatment lagoon, hopefully ending a decades long history of anaerobic soil failure.

Originally published at http://www.nscss.org/content/anaerobic-soil-impairs-sprayfield-ellensburg-wa