BANGOR, Maine — The city has sent out more than 1,700 demands for payment on past-due sewer and stormwater fees, threatening liens against property owners who don’t pay within 30 days.

The notices come after the city discontinued efforts to put liens on properties for unpaid sewer and stormwater bills because of a staffing change. According to Finance Director Debby Cyr, a new computer system has enabled the city to resume the program.

In all, the city sent 870 demand notices on April 21 for past-due sewer fees and 849 notices on April 28 for past-due stormwater fees.

The sewer notices caused confusion for some account holders. Tax Collector David Little said some residents called his and other city departments because they did not understand what the bill was for.

On Wednesday, the city published a notice stating that an administrative error caused the notices, delivered via certified mail, not to specifically indicate they were for outstanding sewer charges. Instead, the notices referenced “rate, toll, rent or other charge.”

Asked about the volume of calls from confused account holders, Little said that “it wasn’t an overwhelming issue.”

While both fees appear on the bills of the approximately 10,800 sewer accounts, the notices were sent separately in accordance with state law because they are separate, distinct charges.

Each notice increases the amount owed by the account holder by $9.50, a fee set by state law for the official demand notices.

If liens are applied after the 30-day time period expires, account holders will face another $51 in lien filing fees in accordance with state law.

City officials discussed the effect demand and lien fees would have on the amount owed for stormwater bills, which are typically small.

According to a city memorandum, of about 900 past-due stormwater fees at the time, 15 percent owed less than $10, while 88 percent owed less than $20 and 94 percent owed less than $30.

“We could potentially take a $5 or $11 bill and add $60 worth of fee to lien them,” Little said at the time. “Liening is our best option to protect the city and collect the money.”

Little told the committee the past-due sewer fees were worth about $240,000 to the city and that the past-due stormwater fees were about $21,000 including interest at the time.

Both sets of demand notices reflect outstanding bills accrued between April and October 2014.

The city implemented the stormwater fee in April 2013 to pay for infrastructure in order to comply with U.S. Environmental Protection Agency’s Clean Water Act.

Under the stormwater fee, residents and businesses with 3,000 square feet of impervious surfaces, such as pavement and roofs upon which rain water or melting snow can pick up contaminants before draining into local streams or rivers, pay $22 per year. They pay $11 extra for every 1,000 square feet beyond that.

Follow Evan Belanger on Twitter at @evanbelanger.