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Alum Treatment Information


Aluminum is used extensively by water treatment facilities -- including Kennebec Water District -- to create potable drinking water through a process known as phosphorus inactivation. 

There are three ways to inactivate phosphorus: treating incoming water high in phosphorus (KWD), stripping phosphorus from the water column in a lake, or binding phosphorus in surficial (lakebed) sediments.

In the case of China Lake, each way is applicable, with the most advantageous being the latter: binding phosphorus in (lakebed) sediments. The track record for such treatments is favorable, including past efforts in Maine: 

  • East Pond: 2018

  • Lake Auburn: 2019 (but sounds like they're nearing "assimilative capacity" i.e. development/external loading )

  • Annabessacook Lake: 1978 (FIRST LAKE to be treated in Maine, water quality steadily improving due to treatment and management of external load)

Other Lakes around the US have also experienced success: 

Additionally, the empirical evidence that higher Al:Fe ratios in the sediment prevents phosphorus release also favors this approach.


Previous assessments of China Lake’s water quality concluded that an aluminum treatment would be an effective strategy (MDEP, 2001; Kleinschmidt, 2012). Successful phosphorus inactivation of sediment under water greater than 7 m deep could reduce the average phosphorus concentration in the east basin by about 40% in each basin (Table 13) and result in a reduction of at least 90% of the internal load.

If only the east basin was treated, the P concentration in the west basin would be reduced by about 20%. 

The cost of an alum treatment in the west basin is estimated at $2.1 million and is not a recommendation for the 2022 WBMP.

For the east basin with a 90% reduction in internal P load, the probability of algae blooms would decrease from 26.7 to 2.2%, equivalent to a decline in the period with poor conditions from over 3 months to about a week. For the west basin with only P inactivation in the east basin, the bloom probability decreases from 12.7 to 6.1%. With a 90% reduction in the west basin internal load, the bloom probability further declines to 0.1%.


The cost of phosphorus inactivation is a function of the necessary dose and area to be treated. Ten composite samples, seven of which were tested, is a good start toward estimating inactivation needs, but is hardly adequate for a lake of this size. Working with available data, however, sediment assays with aluminum addition were conducted at Colby College and had generally favorable results. Using these results and applying the most applicable ones to the areas for which sediment samples were not tested, estimates of dosing needs and related costs were developed (Appendix K). Dose determination is approximate, given the limited amount of data available, but a suggested dose is offered based on best professional judgement based on available data. 

After analysis, the project’s technical advisory committee (TAC) recommended an aluminum treatment in the east basin at depths > 7 m to significantly reduce the internal P load and improve water quality positive in the west basin.

When applied in a lake, the alum is buffered to remain pH neutral and will not harm fish when applied properly. Fish and aquatic life surveys will be conducted before, during and after the treatment, as well as in-plume monitoring of pH, and floc evaluation during treatment to ensure that pH remains neutral. Watershed management by itself will not achieve desired water quality conditions in China Lake but will provide protection for the future and increase the efficacy of an in-lake treatment which is necessary to meet the objective of minimizing algal blooms in China Lake.

and A large barge is used to add alum to lakes with chronic internal P loading make reserves less susceptible to release under anoxia.

Suggested doses range from 30 to 70 g/m2 and the cost to treat the east basin is about $1.4 million, while the cost to treat the west basin is about $2.1 million, based on the best available information, but more sample collection and analysis is strongly advised before planning a P inactivation treatment. At the cost envisioned, the cost to better define dosing needs is minor by comparison and getting a better feel for how much to apply where to achieve target conditions is strongly advised. Following review of the results of the sediment analysis and P inactivation summary by the project’s technical advisory committee, a treatment for the east basin was recommended for this Plan. A preliminary treatment areas and aluminum dose map is presented in Appendix K which will be refined following additional sediment sampling and analysis expected to occur within the first year of plan implementation.

aluminum treatment, east basin only to reduce phosphorus by 656 kg/yr

Cost of Treatment

B5: Conduct aluminum treatment(s) in the east basin

Years 4 - 5

CLA, Colby, consultants CLA, Town of China & Vassalboro, grants or low interest loans, Maine DEP, Donors, Landowners


B6: Implement an aluminum treatment monitoring plan before and during treatment(s)

Years 4 - 5

CLA, LSM, Colby, KWD, consultants CLA, KWD, Private Donors


B7: Continue fall drawdown and revisit timing and volume following downstream dam removal to maximize P removal Years 1 - 10

Town of Vassalboro Town of Vassalboro


B8: Assess the need for an aluminum treatment in the west basin following treatment of the east basin. If needed, collect additional sediment samples and develop a treatment plan.

Years 6 - 7

CLA, DEP, Colby, KWD CLA, KWD, Private Donors


TOTAL: $1,441,500


After the Treatment

Baseline monitoring, detailed above, will provide an accurate assessment of the pre-treatment conditions in China Lake and measure changes in the long-term water quality trends. Additional monitoring performed during and after the aluminum treatment(s) will be required (a condition of the Maine DEP permit to apply the aluminum) to ensure water quality criteria are met for the protection of fish and aquatic life from aluminum toxicity and will allow for evaluation of short and long-term effects of the treatment(s). Short-term objectives include maintaining appropriate pH, alkalinity, and aluminum levels during the aluminum treatment, and long-term objectives include documenting reduced in-lake TP concentrations and the elimination of harmful algal blooms in China Lake. Pre (at least one week prior to treatment) and post aluminum treatment monitoring (within a week after treatment) and monitoring during the aluminum treatment, and monthly thereafter will be required as part of the permitting process.

A detailed aluminum treatment monitoring plan including monitoring schedule, frequency, and parameters before, during, and after the proposed aluminum treatment(s) will need to be developed prior to an aluminum treatment. The plan will include all parameters measured during baseline plus:


Alkalinity samples will be collected from the epilimnion (epilimnetic core) as determined by the dissolved oxygen and temperature profile as well as a bottom grab sample.

Aluminum samples (total and dissolved) will be collected monthly from an epilimnetic core and bottom grab following an aluminum treatment until concentrations return to pre-treatment levels.

Sediment samples (composited) will be collected and analyzed using a modified Psenner Al/Fe/P speciation technique at 5-year intervals.

Fish and aquatic life surveys will be ongoing during and after the aluminum treatment (see below). The plan will also outline requirements for monitoring throughout the day during the aluminum treatment at specific monitoring locations including the treatment area, a control point, in plume monitoring and floc evaluation, and daily fish and aquatic life surveys of the shoreline during the aluminum treatment, and monthly thereafter. Surveyors will also observe shoreline areas for fish, shellfish, snail, amphibian, and bird fatalities, insect hatches and other signs of potential aluminum or pH toxicity.

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