Publication Summary

The Washington State Department of Ecology conducted a Class II groundwater inspection of the city of Moses Lake Dunes Wastewater Treatment Plant (WWTP) on April 27-29, 1998.

The Washington State Department of Ecology (Ecology) conducted a Class II groundwater inspection of the city of Moses Lake Dunes Wastewater Treatment Plant (WWTP) on April 27-29, 1998. The inspection consisted of:

1. An evaluation of the WWTP groundwater monitoring network, 2. An audit of the WWTP sampling procedures, 3. A comparison of Ecology and Moses Lake split sample results, and 4. An evaluation of Moses Lake′s compliance with permitted effluent limits.

Four of the facility′s five monitoring wells were sampled during the inspection for general and physical chemistry parameters and total metals. The fifth well was not sampled because it was dry.

The facility is complying with permitted effluent discharge limits for annual and monthly discharge volumes (Ecology, 1997a). However, facility wastewater has degraded groundwater quality to the extent that secondary drinking water standards for total dissolved solids, manganese, and iron are not met in the facility down-gradient wells. Significant down-gradient increases are also apparent in other constituents including nitrate, ammonia, total Kjeldahl nitrogen, sodium, fluoride, chloride and sulfate.

Groundwater metals analyses results were all less than applicable groundwater quality standards, although several parameters (barium, calcium, cobalt, magnesium, potassium, sodium, and strontium) were elevated in one or more of the down-gradient wells, relative to concentrations noted in the up-gradient well.

Differences between Ecology and Moses Lake split sample results were generally within acceptable limits.

The monitoring well network at the Dunes WWTP does not adequately characterize groundwater gradients or facility impacts to groundwater beneath and immediately down-gradient of the WWTP. Additional down-gradient and cross-gradient wells are needed to differentiate the facility wastewater effects from those originating on down-gradient property owned or managed by the Basic American Foods vegetable processing facility.

The groundwater sampling procedures employed at the Dunes WWTP (1) are not consistent with current industry protocols, and (2) do not meet the monitoring requirements specified in the facility discharge permit. The Dunes WWTP should develop a formal written monitoring plan in accordance with the implementation guidance for the groundwater quality standards (Kimsey, 1996).

Link to EIM data for User Study ID KSIN0003