LAKESIDE — The Helix Water District board of directors has agreed to supply water over the next 20 years for a controversial sand-mining project in the El Monte Valley in Lakeside. The board will now send a letter to county planners confirming they can meet the needs of the project should it win approval. Two of the five board members last week voted to withhold the information — Joel Scalzitti and Mark Gracyk. Horizon Hill El Monte Investors, LLC, is the latest company with plans to bring a sand mining project to the picturesque spot in Lakeside, rich in the kind of aggregate that is favored by home builders. The area north of Lake Jennings between El Monte Road and Willow Road is zoned for sand mining and the extracting of product has been in the plans of different developers for more than 20 years.