The Village of Roberts wastewater treatment plant (WWTP) has been in operation since 1962. How can it be responsible for the flooding of Twin Lakes?

In 1962, the population of Roberts was about 343.  Assuming a discharge rate of about 60 gal/day per person and a lake size of 210 acres, the WWTP added about 1.2 in/yr to the level of Twin Lakes.  In 2016, the population of Roberts was about 1682 and the WWTP added about 6.4 in/yr to the level of Twin Lakes.  The level of Twin Lakes has been rising since about 1990, when the population of Roberts reached 1000 and the WWTP added about 4 in/yr to the level of Twin Lakes.  In sum, the output of the Roberts WWTP is now adding about 6.4 in/yr to the level of Twin Lakes, or five times the amount that it was adding in 1962.