Investors looking for stocks in the Pollution Control sector might want to consider either Heritage-Crystal Clean (HCCI) or Tetra Tech (TTEK). But which of these two stocks offers value investors a better bang for their buck right now? We'll need to take a closer look.The best way to find great value stocks is to pair a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system. The Zacks Rank favors stocks with strong earnings estimate revision trends, and our Style Scores highlight companies with specific traits.Currently, both Heritage-Crystal Clean and Tetra Tech are holding a Zacks Rank of # 2 (Buy). This system places an emphasis on companies that have seen positive earnings estimate revisions, so investors should feel comfortable knowing that these stocks have improving earnings outlooks. But this is just one factor that value investors are interested in.Value investors also try to analyze a wide range of traditional figures and metrics to help determine whether a company is undervalued at its current share price levels.Our Value category grades stocks based on a number of key metrics, including the tried-and-true P/E ratio, the P/S ratio, earnings yield, and cash flow per share, as well as a variety of other fundamentals that value investors frequently use.HCCI currently has a forward P/E ratio of 29.04, while TTEK has a forward P/E of 35.17. We also note that HCCI has a PEG ratio of 1.94. This popular figure is similar to the widely-used P/E ratio, but the PEG ratio also considers a company's expected EPS growth rate. TTEK currently has a PEG ratio of 2.34.Another notable valuation metric for HCCI is its P/B ratio of 2.46. The P/B ratio is used to compare a stock's market value with its book value, which is defined as total assets minus total liabilities. For comparison, TTEK has a P/B of 6.19.Based on these metrics and many more, HCCI holds a Value grade of B, while TTEK has a Value grade of D.Both HCCI and TTEK are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that HCCI is the superior value option right now.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report HeritageCrystal Clean, Inc. (HCCI): Free Stock Analysis Report Tetra Tech, Inc. (TTEK): Free Stock Analysis Report To read this article on Zacks.com click here.