KINGMAN The city is pursuing a low-cost fix to upgrade the Hilltop sewage treatment plant, originally estimated to be a $16 million project.
With the assistance of a civil engineering consultant, the Public Works Department has identified a cost-effective solution to producing high quality effluent, or discharge, coming out of the city's maintenance facilities, Wastewater Superintendent Jeff Corwin said.
The city previously received a violation notice by the state for exceeding the nitrate level in samples taken from monitoring wells located near the containment ponds and the point of discharge, prompting the upgrade proposal.
The Clean Water Act of 1974 established the nitrate level as 10 milligrams per liter of water.
The monitoring well sites last produced samples measured at 9-10 mg at one site, while the other measured 14-20 mg.
Corwin said the samples are not an accurate indication of nitrate levels in drinking water, since the drinking water wells are miles from the discharge site and are 700 to 800 feet deep, compared to the 400-foot level of the monitoring wells, adding that ground seepage is a natural part of the de-nitrification process.
"The water we're drinking is 10,000 years old," Corwin said, adding that nitrate measurements near well sites for drinking water measure about 2 to 3 mg per liter.
The city's objective is to "upgrade on the front end" to remove inert material and grit, allowing organic material to oxidize more effectively rather than in the wetland area where currently much of the amoniafication-nitrification- de-nitrification process occurs, Corwin said.
Grit inhibits treatment of inorganic material in the collection system, he added.
The proposal, estimated to cost between $3.5 to 5 million, entails updating aeration equipment and updating or installing new head works to remove inert material.
Corwin said the city additionally plans on lining the lagoon ponds to prevent groundwater seepage.
The $16 million estimate was based on the assumption that the city and a development company were going to use effluent for watering a golf course, entailing a water re-use system, Corwin said. However, the developer has since sold the property.
Inert material currently is being removed from the lagoons after draining, Corwin said. Removal of the material from the head works conversely filters discharge before entering the lagoons, increasing sludge space and providing more time for aeration and amoebic breakdown occurring in the de-nitrification process.
Corwin said the city has also identified areas that contribute inert material during storm-water events, namely collection areas from Fairgrounds Boulevard and Main Street storm flow and manholes on Bank Street, of which manhole liners are designated. Bank Street currently has watertight manholes, he said.
Corwin said he feels confident these measures should result in a 50-percent reduction in the levels taken at monitoring wells.
Currently, the head works at the Hilltop facility is capable of treating two million gallons of sewage a day, with the city now producing an average of 1.6 million, Corwin said.
The facility servicing the downtown area handles about 250,000 gallons, he added, noting that the proposed upgrades would apply to both plants.
Corwin said he expects a meeting with the state along with the advising consultant to take place within a couple of months for approval of the proposals.